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  • Springer  (172)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of polymers and the environment 3 (1995), S. 199-203 
    ISSN: 1572-8900
    Keywords: Chemiluminescence ; oxidation ; stability ; acrylonitrile-butadiene-styrene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The thermal oxidative stability of various formulations based on emulsion-grade ABS was studied by the chemiluminescence technique. Emulsion products were found to be essentially less stable than ionic mass polymerization resins. Among the antioxidants studied, Santonox R is clearly more efficient than Irganox 1076 and Irganox 3114, and its superiority is reflected primarily in improved induction period values. The introduction of Tinuvin 770 and Tinuvin 328 UV stabilizers into emulsion resins does not change the durability of the products. In mixtures where both Irganox 1076 and UV stabilizers are present, a certain antagonistic effect was noted at high UV stabilizer concentrations.
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  • 2
    ISSN: 1572-8765
    Keywords: carbonado ; diamond ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of carbonado type synthesized polycrystalline diamonds produced from graphite together with catalytic Ni-Mo alloy doped with TiB2 and BNcub was investigated. It was found that the addition of these boron compounds increases the oxidation resistance of the carbonado type synthesized polycrystalline diamonds. The oxidation mechanism acting on the carbonado type synthesized polycrystalline diamonds and the role of boron compounds in increasing the resistance to the oxygen reaction are discussed.
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  • 3
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    Springer
    Cellulose 5 (1998), S. 153-164 
    ISSN: 1572-882X
    Keywords: cellulose ; TEMPO ; polyglucuronic acid ; degree of polymerization ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Various cellulose samples were oxidized by 2,2,6,6,-tetramethylpipelidine-1-oxyl radical (TEMPO)-NaBr-NaClO systems, and the effects of oxidation conditions on chemical structures and degrees of polymerization of the products obtained were studied. In the case of regenerated and mercerized celluloses, almost all C6 primary alcohol groups were selectively oxidized to carboxyl groups, and water-soluble polyglucuronic acid (cellouronic acid) sodium salts were obtained almost quantitatively; the degrees of polymerization were influenced greatly by the amount of TEMPO added, and the oxidation time and temperatures. Cellouronic acids prepared from mercerized linter and kraft pulps had size exclusion chromatograms with two separate peaks due to higher and lower molecular weight fractions. On the other hand, only small amounts of carboxyl groups were introduced into native cellulose samples. Since polyglucuronic acids prepared from cellulose by the TEMPO–NaBr– NaClO systems regularly consist of the glucuronic acid repeating unit, differing from the conventional water-soluble cellulose derivatives, they may open new fields of cellulose utilization.
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  • 4
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    Electronic Resource
    Springer
    Cellulose 2 (1995), S. 265-272 
    ISSN: 1572-882X
    Keywords: Hydrogen peroxide ; oxycellulose ; bleaching ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Peroxides are important bleaching agents, industrially, for cellulosic products. They are also used in detergents. Peroxides can degrade cellulose as well as decolorize it and remove stains. Both free radicals and perhydroxyl anions have been suggested as the intermediates in the reactions occurring between cellulosic products and hydrogen peroxide. The proposed mechanisms are reviewed with emphasis primarily on cotton cellulose. Further work is required to establish unequivocally the mechanism of degradation and decolorization of cellulose products.
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  • 5
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    European journal of nutrition 36 (1997), S. 336-339 
    ISSN: 1436-6215
    Keywords: Amino acids ; protein ; metabolism ; meal feeding ; oxidation ; breath test ; Aminosäuren ; Protein ; Stoffwechsel ; Fütterung ; Oxidation ; Atemtest
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Medicine
    Description / Table of Contents: Zusammenfassung Die aktuellen Mengen an freien Aminosäuren im Blut reichen nur aus, um die Ganzkörper-Proteinsynthese für einige Minuten aufrecht zu erhalten. Das zeigt, daß die freien Aminosäurenkonzentrationen in der Zirkulation klein und konstant gehalten werden im Vergleich zu den Mengen der Aminosäuren, die täglich aufgenommen und über die Körperproteine umgesetzt werden. Das Verschwinden der Aminosäuren exogenen oder endogenen Ursprungs aus dem freien Aminosäuren-Pool, findet hauptsächlich durch die Proteinsynthese und den Aminosäurenabbau statt. Die Partitionierung der Nahrungs-Aminosäuren zwischen diesen beiden Prozessen im Kurzzeitbereich werden als bedeutsam für die Ökonomie der Ganzkörper-Aminosäuren angesehen. Eine Verbesserung der Aminosäurenökonomie könnte durch solche nutritiven Maßnahmen erreicht werden, welche die Clearance der Nahrungsaminosäuren durch die Proteinsynthese anstelle des Aminosäurenabbaus begünstigen. Diese nutritiven Maßnahmen sollten sich an den „Schwellenwerten“ des Abbaus der individuellen Aminosäuren orientieren.
    Notes: Summary Actual amounts of free amino acids in the blood are sufficient to support whole body protein synthesis for some minutes only. This indicates that the levels of free amino acids in the circulation are kept small and constant relative to the amounts of amino acids supplied by daily intake and turnover of body proteins. The clearance of the amino acids originating from either endogenous or exogenous sources is mainly due to protein synthesis and metabolic degradation. The partitioning of dietary amino acids between these processes, on the short term, is supposed to play an important role in whole body amino acid economy. Therefore whole body amino acid economy could be improved by nutritional measures that favour the clearance of dietary amino acids by protein synthesis instead of by metabolic degradation. These nutritional measures should to be focused on threshold values for metabolic degradation of individual amino acids.
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  • 6
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    Nutrient cycling in agroecosystems 41 (1995), S. 67-75 
    ISSN: 1573-0867
    Keywords: additives ; agronomic efficiency ; P availability ; phosphate rocks ; rice ; (Oryza sativa L.) ; thermally altered rock P
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The P availability in soil and agronomic efficiency of the products of non-premium grade, unreactive Purulia phosphate rock (PPR) heated alone or with Na2CO3 or KCl at different temperatures were investigated in two P deficient soils. The heated products of PPR alone did not improve the P availability in soil or P utilisation by rice over the original PPR. The products of PPR-KCl mixtures heated at 300-900°C were not effective at all. Out of several products of PPR with Na2CO3, the product prepared from PPR and Na2CO3 mixture in the weight ratio 2:1 heated at 900°C was comparable to superphosphate (SP) with respect to P availability in soil, straw and grain yield and P uptake by rice. The effectiveness of the products of PPR-Na2CO3 mixtures heated at 700°C though inferior to SP were superior to that of the original PPR in the highly acidic P deficient soil from Choudwar. However, products of another phosphate rock (PR) from Jordan and NA2CO3 mixtures heated at 900°C were less effective in comparison to SP. The amount of inherent silica present in Jordan PR was inadequate to promote the apatite-NA2CO3-SiO2 reaction towards completion thus leading to an inferior product. On the other hand, similar products of non-premium grade Kasipatnam and Mussoorie PRs which are not suitable for direct application were comparable to SP in their effectiveness when these PRs were fused with Na2CO3 in the weight ratio 2:1 at 900°C. X-ray diffraction studies indicated presence of water and citrate soluble phosphate phases viz., Na3PO4, NaCaPO4 and possibly Ca7 (PO4)2 (S104)2 in these products of PR-Na2CO3 mixture heated at 900°C. The water and citrate soluble phases of these products could release adequate P for absorption by crop.
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  • 7
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    Nutrient cycling in agroecosystems 42 (1995), S. 261-276 
    ISSN: 1573-0867
    Keywords: Azolla ; BNF ; cyanobacteria ; green manure ; heterotrophic bacteria ; legume ; rice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The review summarizes the current status of the utilization of N2-fixing organisms as biofertilizer in rice cultivation. Heterotrophic bacteria, free-living cyanobacteria,Azolla, and legume green manures are considered with regard to their potential for increasing yield, their current use and the prospects for their use with regard to the identified limiting factors. Biological N2 fixation has been the most effective system for sustaining production in low-input traditional rice cultivation. On the other hand, the utilisation of N2-fixing organisms in intensified rice production encounters serious limitations. The utilization of free-living bacteria and cyanobacteria is refrained by their modest potential and the non establishment of inoculated strains.Azolla and legumes used as green manures have a high potential as N source, but their utilization is severely limited by socio-economic factors.
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  • 8
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    Nutrient cycling in agroecosystems 43 (1995), S. 143-148 
    ISSN: 1573-0867
    Keywords: method of nitrogen application ; modified urea ; N-15 recovery ; rice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Rice is a very responsive crop to nitrogen, but the efficiency of the N-fertilizer is low. Greenhouse experiment has been conducted to evaluate several methods to improve fertilizer efficiency and reduce N-losses in rice fields. N-15 labelled urea was applied to 10 kg soils in pots, urea was applied alone, addition of two urease inhibitors N-(n-butyle) thiosphosphoric triamide (NBPT) and hydroquinone (HQ), with addition of nitrification inhibitor Dicyandimide (DCD), or with the combination of both inhibitors. The fertilizer was applied either broadcast on soil surface or at depth of 8 cm below the surface. At maturity, plants were separated into grain and straw, dried and weighted. Soil and plant samples were analyzed for total N and N-15 excess. Both fertilizer placement and inhibitor application significantly increased straw and grain yield, as well as N- uptake. Nitrogen derived from fertilizer (% Ndff) was more than doubled, when urea was applied deep and in combination with inhibitors. Total plant recovery of N-15 labelled urea ranged from 17% to 75% according to treatment. Regardless of inhibitors application, plant recovery was increased from 39% to 65% when urea was applied at depth of 8 cm. Approximately, 2/3 of the applied urea (64%) was lost, when urea was applied alone. Those losses were reduced down to 12% with deep placement and inhibitor application. The two management practices show significant effect on minimizing N-losses and increasing plant recovery.
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  • 9
    ISSN: 1573-0867
    Keywords: long-term experiments ; potassium ; rice ; soil testing ; ion-exchange resin ; potassium-supplying capacity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Based on the analysis of soil K status in 11 long-term fertility experiments in Asia, two approaches for assessing the K-supplying power of lowland paddy soils were evaluated to predict total K uptake by irrigated rice. A regression model combining commonly used static soil test parameters that appeared to integrate measures of K release from nonexchangeable forms as well as chemical factors affecting K activity in soil solution explained 72% of the crop K uptake in NP and NPK treatments. However, this approach would require determination of six soil properties and it does not provide a direct measure of K release dynamics. The second approach used mixed-bed ion exchange resin capsules to measure K release during 2-wk anaerobic incubation. The resin method provided an integrative measure of soil K status and the factors controlling K transformation and diffusion rates, which are embodied in two kinetic parameters describing the dynamics of rapid- and slow-phase K release. The resin method was sensitive to past fertilizer history and the resulting buildup or depletion of soil K reserves and it was a better predictor of total K uptake in the NP and NPK plots (r2=0.82) than static soil tests. The results also indicated that high (Ca+Mg)/K ratios may contribute to K deficiency in rice soils.
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  • 10
    ISSN: 1573-0867
    Keywords: long-term experiments ; phosphorus ; rice ; nutrient balance ; phosphorus uptake ; fertilizer P response ; soil testing ; ion-exchange resin ; phosphorus supplying capacity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Data from long-term experiments at 11 sites in Asia with a wide range of nutrient input treatments and yield levels were used to quantify crop P requirements of rice (Oryza sativa L.) and the P balance in intensive, irrigated rice systems. Uptake of 1.8–4.2 kg P was required to produce one ton of grain yield. Physiological P use efficiency varied between 220 to 900 kg grain kg P-1. Without added P, there was a net loss of 7 to 8 kg P ha-1 per crop; with added P there was a net gain of 4 to 5 kg P ha-1 per crop. Phosphorus adsorption kinetics on mixed-bed ion-exchange resin capsules provided an integrative measure of soil P status, P diffusion, and acid-induced P solubilization. The resin capsule was a sensitive tool to characterize buildup or depletion of soil P as a result of different P balances. Both Olsen-P and the resin capsule were suitable methods to predict P uptake of tropical lowland rice. It is hypothesized that both methods measure a similar soil P pool which is soluble under alkaline, aerobic conditions but transformed into acid-soluble P froms as a result of submergence and reduction. Present recommendations for P fertilizer use on rice of 20–25 kg P ha-1 are adequate to maintain yields of 5–6 t ha-1, but sustaining higher yields of 7–8 t ha-1 will require farm-specific management strategies based on knowledge of the long-term P balance and soil P-supplying capacity.
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  • 11
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    Nutrient cycling in agroecosystems 46 (1996), S. 189-193 
    ISSN: 1573-0867
    Keywords: available P ; green manure ; P source ; P uptake ; residual effect ; rice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract To evaluate residual recoveries of fertilizer phosphorus (P) two field experiments were conducted in Quezon Province, Philippines during 1991 dry season, under irrigated condition. Average grain yield increase was 0.50–0.9 t/ha due to residual effects of inorganic fertilizer P, regardless of source. Residual effects of fertilizer P with Sesbania rostrata or alone increased grain yield by 0.3–1.0 t/ha over control. Significantly higher yields were obtained with S. rostrata fertilized with Morocco phospate Rock (MPR) and S. rostrata + MPR applied on rice than the control. Results revealed that there is a promising effect of residual P from the applied P sources in increasing rice grain yield. Total P uptake increased due to residual P from fertilizer P applied. Results suggest that increased P uptake increased dry matter and grain yield.
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  • 12
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    Nutrient cycling in agroecosystems 46 (1996), S. 195-203 
    ISSN: 1573-0867
    Keywords: available phosphorus ; green manure ; phosphorus source ; phosphorus uptake ; relative effectiveness ; rice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract To evaluate alternative fertilizer phosphorus (P) sources in lowland rice, two field experiments were conducted under irrigated conditions in Quezon Province, Philippines during 1990–1991 crop year. In another field experiment fertilizer P recycling through a green manure crop applied in the succeeding rice, was studied. Addition of fertilizer P increased grain yield by 1.5–2.0 t/ha (46%) in 1990 wet season (WS) and by 1.6–2.1 t/ha (56%) in 1991 dry season (DS). However, fertilizer P source and application level did not effect grain yield significantly. Results indicated that the less water-soluble and less expensive partially acidulated phosphate rock (PAPR), phosphate rock (PR) and less reactive PR were as effective as the more soluble but more expensive triple superphosphate (TSP). The relative effectiveness (RE) of local guano was significantly lower than that of other sources of fertilizer P. Fertilizer P applied to a pre-rice Sesbania rostrata green manure increased rice grain yield by 1.5–1.9 t/ha during 1991 DS. Further, S. rostrata fertilized with Morocco phosphate rock (MPR) gave significantly higher rice grain yield than did rice fertilized with MPR applied alone. In the P source experiments Olsen method and Pi correlated better with growth attributes than Bray 2 P. Phoshours uptake did not differ significantly among P sources and levels. Results suggest that P uptake was improved with green manuring. Correlation analyses revealed a close correlation between P uptake and dry matter yield and P uptake and grain yield.
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  • 13
    ISSN: 1573-0867
    Keywords: long-term experiments ; nutrient balance ; potassium ; rice ; potassium use efficiency ; potassium uptake ; potassium response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Research in many countries indicates a negative K balance in intensive, irrigated rice systems but comparative studies across different environments are few. Using a uniform sampling methodology, we measured K uptake, K use efficiency, and K balance in six different fertilizer treatments of long-term fertility experiments with rice at 11 sites in five Asian countries. Depending on the absolute yield level, K uptake requirements of rice ranged from 17 to 30 kg K per ton of grain. For yields greater than 8 t ha-1, total K uptake exceeded 200 kg ha-1. The K balance at most experimental sites was negative, with an average net removal of 34–63 kg K season-1. There was significant depletion of soil K reserves at many sites. Based on these data, we estimated that the amount of K cycled annually from the soil into rice plants is 7–10 million t in irrigated rice systems of Asia. About 1 million t of this total amount is removed with the harvested grain. Present recommendations for K addition in most intensive irrigated rice domains are insufficient to replace K removal. However, response to K can only be expected on soils with deficient supply capacity and where other nutrients, particularly N and P, are not limiting. Efficient K management for rice must therefore be based on the K input/output balance, the achievable yield target, and the effective K-supplying power of the soil.
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  • 14
    ISSN: 1573-0867
    Keywords: millet ; sorghum ; rice ; maize ; wheat ; nutrient harvest index ; post-anthesis nutrient uptake ; recovery fraction ; simulation modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In land use plans, fertilizer recommendations are indispensable to avoid soil nutrient depletion or soil water pollution. Nutrient relations of five cereals have been evaluated on the basis of a literature review with the aim of arriving at such fertilizer recommendations at regional level. Nutrients considered were nitrogen, phosphorus and potassium for millet, sorghum, maize, rice and wheat. The relevant nutrient relations are fertilizer nutrient application to nutrient uptake, and nutrient uptake to crop yield. In addition, post-anthesis nutrient uptake is considered. Subsequently, obtained results are used in simulation modelling exercises to calculate the time required to attain an equilibrium nutrient balance and to investigate the effect of erosion control and straw recycling. Although fertilizer requirements could be assessed for each of the five cereals, monitoring of nutrient supply from natural sources remains necessary. Moreover, research on fertilizer use should focus on improvement of fertilizer recoveries and multiperiod models for both N and P uptakes by crops to allow quantitative land use planning where the time scale is included.
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  • 15
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    Nutrient cycling in agroecosystems 46 (1996), S. 29-39 
    ISSN: 1573-0867
    Keywords: Côte d'Ivoire ; rice ; fertilizers ; adoption ; gender ; socioeconomic factors ; field factors ; markets ; population pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract This paper analyzed the factors that affect the adoption of chemical fertilizers by rice farmers in Côte d'Ivoire using a Tobit model. The results show that the major factors that positively influence farmers' use of fertilizers in rice fields are cultivation of lowlands, use of mechanization, farm size, land pressure and availability of non-farm income. Factors found to negatively affect the use of fertilizer in rice fields are the distance of the field to the village, distance of the village to the major market, and if the cultivator is a female. The paper concludes with strategies for targeting soil fertility interventions on farmers' rice fields.
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  • 16
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    Nutrient cycling in agroecosystems 51 (1998), S. 269-279 
    ISSN: 1573-0867
    Keywords: denitrification ; gas entrapment ; nitrification inhibitors ; 15N ; rice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Denitrification rates (d) in a flooded alkaline clay were measured following addition of either $$^{15} NO_3^ - or^{15} NH_4^ + $$ to the floodwater, by collecting evolved N2 + N2O in an enclosure in the absence or presence of rice plants. Similar estimates of d were obtained in the $$^{15} NO_3^ - $$ treatment when the isotopic composition of the enclosed atmosphere was determined using arc redistribution or direct mass spectrometric analysis. Approximately 90% of the gaseous products of denitrification were physically trapped in the soil five days after $$^{15} NO_3^ - $$ addition. Mechanical shaking of the soil-water system was an effective method for releasing entrapped gas. Denitrification showed a marked diurnal variation in both $$^{15} NO_3^ - $$ and $$^{15} NH_4^ + $$ treatments planted to rice, with higher rates during the day than at night. Measured rates of denitrification were higher in planted than in unplanted pots for both $$^{15} NO_3^ - $$ and $$^{15} NH_4^ + $$ treatments for normal gas sampling. However, evidence was obtained that this was not a real effect, but was due to release of entrapped gas. Denitrification losses corrected for gas entrapment were estimated at 〈5% of applied $$^{15} NH_4^ + $$ . The 15N mass balance indicated that a much larger amount of applied ammonium (15–25%) was lost by NH3 volatilisation. The rate of denitrification corrected for gas entrapment was similar to the rate of nitrification estimated by inhibition of ammonium oxidation. Although the inhibitors 2-ethynylpyridine and acetylene prevented denitrification by effectively inhibiting nitrification of $$^{15} NH_4^ + $$ , the total recovery of 15N in the soil-plant system did not increase. The total recovery of $$^{15} NH_4^ + $$ was 7–9% higher in the presence than in the absence of rice.
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  • 17
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    Nutrient cycling in agroecosystems 51 (1998), S. 259-267 
    ISSN: 1573-0867
    Keywords: nitrification ; nitrification inhibitors ; 15N-dilution ; rice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Nitrification rates (n) in the floodwater of an alkaline clay were measured in the absence or presence of rice plants by inhibition of ammonium oxidation and 15N-dilution techniques. Floodwater nitrate concentrations in control treatments showed a marked diurnal variation, and were higher than in the inhibitor treatments after the first day. Ammonium concentrations in floodwater declined exponentially in all treatments, being markedly affected by diffusion and NH3 volatilization but little affected by nitrification and plant uptake. Nitrification rates in floodwater estimated by 15N-dilution were generally higher than the rates estimated by the inhibitor method. Estimates of n were generally higher during daylight hours than at night, and did not differ significantly between planted and unplanted pots. Microbial immobilisation of labelled ammonium and gross N immobilisation were not affected by addition of the nitrification inhibitor 2-ethynylpyridine.
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  • 18
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    Nutrient cycling in agroecosystems 53 (1998), S. 71-81 
    ISSN: 1573-0867
    Keywords: fallow ; legumes ; nitrogen fixation ; rice ; weeds ; West Africa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Traditional upland rice-based cropping systems in West Africa rely on periods of fallow to restore soil fertility and prevent the build-up of insect pests and weeds. Demographic growth and increased demand for land is forcing many farmers to intensify their rice production systems. Declining fallow length and increasing number of crops before leaving the land to extended fallow result in a significant yield reduction. Promising cropping system alternatives include the use of site specific, weed-suppressing, multi-purpose cover legumes as short duration fallows. Constraints to rice production related to intensification were determined in 209 farmers' fields in four agro-ecological zones during 1994 and 1995. Nitrogen accumulation and weed suppression were evaluated in 54 legume accessions, grown for six months during the dry season, under a range of hydrological and soil conditions in 1994/95. Their effect on the yield of upland rice was determined in 1995. To increase benefits from improved fallow technology, the timing of legume establishment in relation to rice and the effect on crop and weed growth of removing, burning, mulching, or incorporating fallow residues prior to the rice crop were determined. Intensified land use resulted in a significant plot-level yield reduction that was highest in the derived savanna and the bimodal forest zones where it was associated with a doubling of the weed biomass in rice and a significant reduction in soil N supply. Legume fallows appear to offer the potential to sustain rice yields under intensified cropping. Legume biomass was in most instances significantly greater than in the weedy fallow control and several legume species suppressed weed growth. Nitrogen accumulation by legumes varied between 1–200 kg N ha-1 with 30–90% Ndfa. Rice grain yield following legume fallows increased by an average of 0.2 mg ha-1 or 29% above the weedy fallow control. Relay establishment substantially increased legume biomass. However, seeding of the legume at 28 days or earlier significantly reduced grain yield due to interspecific competition. Incorporating or mulching of fallow residues provided no significant yield advantage as compared to burning. Absolute effects varied as a function of site, legume species, and management practice.
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  • 19
    ISSN: 1573-0867
    Keywords: ammonia volatilization ; green manure ; inhibitor ; NBPT ; rice ; urea hydrolysis ; wheat straw
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Using a forced-draft chamber technique, the suppression of NH3 volatilization losses by applying N-(n-butyl) thiophosphoric triamide (NBPT) was studied in an alkaline sandy loam soil amended with green manure or wheat straw. Applied urea was completely hydrolysed in 12, 8 and 6 days in unamended, green manure and wheat straw amended soil, respectively. By applying 0.5% (w/w of urea) NBPT, complete hydrolysis of urea was delayed up to 16 days in the unamended soil, whereas in wheat straw amended soil urea hydrolysis was completed by the 12th day even when it was treated with 2% NBPT. Applied at 1 or 2% level, NBPT delayed the NH3 volatilization to the 4th day after application of urea in green manure or wheat straw amended soil. Hydrolysis of urea was more effectively retarded by applying NBPT in the unamended soil than in soil amended with green manure or wheat straw. In the unamended soil, 7.1% of the applied urea was lost through NH3 volatilization. The losses were reduced to 1.2 and 0.7% by applying 0.5 and 1% NBPT, respectively. Enhanced NH3 volatilization caused by the green manure or wheat straw was counteracted by applying NBPT.
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  • 20
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    Nutrient cycling in agroecosystems 54 (1999), S. 189-197 
    ISSN: 1573-0867
    Keywords: boron toxicity ; oilseed rape ; rice ; rotation ; soil boron ; seed yield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Yields in intensive rice (Oryza sativa L.) -based rotations in Asia are stagnating or declining because of decreasing nutrient availability and depletion of soil nutrient reserves. In the rape (Brassica napus L.)–rice–rice cropping rotation of southeast China, where boron (B) deficiency is widespread and B fertiliser is needed to correct it, our objective was to evaluate the risks of fertiliser-induced B toxicity in oilseed rape and in rice. Response of oilseed rape to B fertiliser application at rates up to 6.6 kg B ha-1 was studied in seven field experiments on three contrasting soils of Zhejiang province, alluvial, red and blue-purple soils. The effects of up to 3.3 kg B ha-1 in 1 year, 6.6 kg B ha-1 in 2 years or 9.9 kg B ha-1 in 3 years were studied on oilseed rape and the one or two rice crops grown immediately after rape in each annual crop rotation. Soils varied in initial hot CaCl2-extractable B in the 0–15-cm layer from 0.24 to 0.99 mg kg-1. At the stem elongation stage of oilseed rape, 3.3 kg B ha-1 depressed shoot dry matter on soils with low clay and organic matter content. However, the subsequent effects of high fertiliser B on seed yield were minimal even at 6.6 kg B ha-1. Moreover, the application of a total of 6.6 or 9.9 kg B ha-1 as successive annual applications of 3.3 kg B ha-1 to oilseed rape generally had no negative effect on seed yield of oilseed rape. The single exception was on a sandy alluvial soil where a total of 6.6 kg B ha-1 in 2 years slightly depressed seed yield of oilseed rape. Grain yields of rice crops grown in rotation after oilseed rape were unaffected by B applications up to 6.6 kg ha-1. The minimal effects of a total of 6.6 kg B ha-1 applied over 2 years on seed yield were consistent with the modest increase in hot CaCl2-extractable B levels. It is concluded that there is limited risk of B toxicity from the use of borax fertiliser at up to 4–8 times recommended rates in rape–rice cropping rotations in southeast China. The low risk of B toxicity can be attributed to the relatively high B removal in harvested seed, grain and stubble, the redistribution of fertiliser B by leaching in the 0–60 cm layer and to B sorption.
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    Nutrient cycling in agroecosystems 55 (1999), S. 89-94 
    ISSN: 1573-0867
    Keywords: algae ; flooded soils ; N cycling ; nitrogen ; 15N ; rice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Algal N labelled with 15N added to a flooded soil in laboratory columns without plants was studied to determine the changes over time in the fate of N assimilated by algae and to study how its fate is affected by (a) exclusion of light simulating complete closure of the rice canopy, and (b) addition of fertilizer-NH4 *. In the light but with no added fertilizer-N there was little net mineralization of the added algal N during the first 4 weeks, but after 8 weeks 42% had been mineralized, of which 95% was denitrified. Exclusion of light caused net mineralization to proceed more rapidly in the first 4 weeks due to the death of algal cells and lowered reassimilation. After 8 weeks 51% had been mineralized, of which 54% was denitrified, 16% volatilized and 30% was present as KCl exchangeable NH4 +-N. Application of fertilizer-NH4 + apparently caused mineralization of 25% of the algal N within one week but the results were probably affected by pool substitution in which labelled N mineralized to NH4 +-N was diluted with fertilizer – NH+ 4 and then immobilized leaving more labelled NH4–N in the mineral pool. After 8 weeks, 42% of algal N had been mineralized, of which 69% was estimated to have been denitrified, 19% lost through NH3 volatilization and 12% remained as extracted NH4 ++NO- 3. Uptake of N by a rice crop would reduce the gaseous losses. Algal N was mineralized quickly enough to be available during the growing season of a rice crop and, depending on field conditions, algae may have a role in assimilating N and protecting it from loss as well as being a major driving force for NH3 volatilization through diurnal increases in pH.
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    Nutrient cycling in agroecosystems 49 (1997), S. 91-95 
    ISSN: 1573-0867
    Keywords: greenhouse effect ; land use ; methane ; oxidation ; soils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Intact core samples from soils with different textures and land use were tested for their capacity to oxidise methane. The soil cores were taken from arable land, grassland and forest. It was found that coarse textured soils (6.74–16.38 µg CH4 m-2 h-1) showed a higher methane uptake rate than fine textured soils (4.66–5.34 µg CH4 m-2 h-1). Increasing soil tortuosity was thought to reduce the methane oxidation rate in fine textured soils. The oxidation rate of forest soils (16.32–16.38 µg CH4 m-2 h-1), even with a pH below 4.5, was very pronounced and higher than arable land (11.40–14.47 µg CH4 m-2 h-1) and grassland (6.74–9.30 µg CH4 m-2 h-1). Within the same textural class arable land showed a faster methane uptake rate than grassland. In grassland with a fine texture, even methane production was observed. Nitrogen availability and turnover in these land use systems were thought to cause the different oxidation rates. Decreasing the moisture content slowed down the oxidation rate in all soils. This could be caused by an increased N turnover and a starvation of the methanotrophic bacteria.
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    Nutrient cycling in agroecosystems 49 (1997), S. 59-70 
    ISSN: 1573-0867
    Keywords: land use ; methane ; nitrogen fertilizer ; oxidation ; soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Aerobic soils are an important sink for methane (CH4) contributing up to 15% of annual global CH4 destruction. However, the sink strength is significantly affected by land management, nitrogen (N) fertilizers and acidity. We tested these effects on samples taken from the Broadbalk Continuous Wheat, Park Grass permanent grassland and Broadbalk and Geescroft Wilderness experiments at Rothamsted. The rates of uptake from the atmosphere of both enhanced (10 ppmv) and ambient (2 ppmv) concentrations of CH4 were measured in laboratory incubations of soil cores under controlled conditions. The most rapid rates of uptake were measured in soil from deciduous woodland at pH 7 (measured in water); acidic (pH 4) woodland soil showed no net CH4 oxidation. While disturbance of the cores used in the experiments did not affect the rate of CH4 uptake, extended (150 years) cultivation of land for arable crops reduced uptake rate by 85% compared to that in the soil under calcareous woodland. The long-term application of ammonium- (NH4) based fertilizer, but not nitrate- (NO3) based fertilizer, completely inhibited CH4 uptake, but the application for the same period of farmyard manure that contained more N than the fertilizer had no inhibitory effect. Although the effects of agricultural practice on the oxidation of CH4 in soil are significant, the differences in oxidation rates between land use types are even greater. The likely effects of forest clearance, agricultural intensification and anthropogenic emissions of CH4 over the last 2500 years have been estimated for the United Kingdom. The calculations indicate that 54% of the current CH4 uptake by UK soils is the result of increased CH4 mixing ratio. They also indicate that land use change has decreased the potential sink strength by 62% or 37 kt CH4 g-1. In countries with much larger land areas than the UK, such as China, aerobic soil is likely to be a more significant factor in calculating net fluxes of CH4. It is important that the impacts of different agricultural managements and land use systems are understood and quantified so that the best possible estimate of CH4 sinks is calculated for comparison with sources.
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  • 24
    ISSN: 1572-8986
    Keywords: RF SiCl4 discharge ; mass spectrometry ; kinetics ; decomposition ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Time-resolved mass spectrometry was used for analysis of the plasma reactions in radio frequency (RF) SiCl 4 and SiCl 4 −O 2 discharges as functions of starting partial pressure and electrical power. Molecular concentrations of the reactants and products from SiCl 4 alone and with O 2 were obtained from the mass spectra and used for plotting the kinetic curves. The SiCl 4 and O 2 consumption rates were calculated from the kinetic curves and compared with results of theoretical simulation of the reaction. Direct electron impact decomposition was found to be the main pathway for pure SiCl 4 conversion. On the contrary, the consumption of SiCl 4 in the SiCl 4 +O 2 mixtures was largely chemical. The experimental macrokinetics are in agreement with a model in which oxidation is caused by the atomic oxygen.
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    Plasma chemistry and plasma processing 19 (1999), S. 131-151 
    ISSN: 1572-8986
    Keywords: Styrene ; oxidation ; silent discharge ; plasma ; dielectric barrier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A silent discharge plasma reactor has been developed to study the oxidation of styrene vapor in argon/oxygen mixtures. A number of analytical techniques were employed to determine the destruction efficiency and to characterize the intermediate products. The destruction efficiency was measured as a function of initial styrene concentration, temperature, and energy density of the plasma. The formation of solid products was observed in most experiments. At low temperature (100°C), the solid deposit was polymeric in nature, while at high temperature (300°C) the solid appeared to be amorphous carbon. A combination of high temperature and high energy density resulted in high destruction efficiency and minimal production of solid films. The destruction efficiency vs. energy density is shown to be more complex than a simple model predicting exponential behavior. Several reasons for the discrepancy are suggested. The “e-folding” energy density for the destruction of styrene is compared to literature values for other organic compounds, measured using similar types of plasma reactors.
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    Plasma chemistry and plasma processing 19 (1999), S. 383-394 
    ISSN: 1572-8986
    Keywords: Nonthermal plasma ; benzene ; Al2O3 ; BaTiO3 ; oxidation ; absorption ; atmospheric pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The combination of plasma discharge and adsorption was examined for oxidation of dilute benzene in air in a plasma reactor packed with a mixture of BaTiO 3 pellets and porous Al 2 O 3 pellets (i.e., an alumina hybrid reactor). The oxidative decomposition of benzene was enhanced by the benzene concentrating on the Al 2 O 3 pellets. Furthermore, there was a higher selectivity to CO 2 in the products from the hybrid than from a plasma reactor packed with BaTiO 3 pellets alone. The presence of the Al 2 O 3 pellets suppressed the formation of N 2 O.
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    Plasma chemistry and plasma processing 19 (1999), S. 421-443 
    ISSN: 1572-8986
    Keywords: Streamer corona ; NO x removal ; nonthermal plasma ; oxidation ; reduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract In this paper, the NO-to-NO 2 conversion in various gaseous mixtures is experimentally investigated. Streamer coronas are produced with a dc-superimposed high-frequency ac power supply (10–60 kHz). According to NO x removal experiments in N 2 +NO x and N 2 +O 2 +NO x gaseous mixtures, it is supposed that the reverse reaction NO 2 +O→NO+O 2 may not only limit NO 2 production in N 2 +NO x mixtures, but also increase the energy cost for NO removal. Oxygen could significantly suppress reduction reactions and enhance oxidation processes. The reduction reactions, such as N+NO→N 2 +O, induce negligible NO removal provided the O 2 concentration is larger than 3.6%. With adding H 2 O into the reactor, the produced NO 2 per unit removed NO can be significantly reduced due to NO 2 oxidation. NH 3 injection could also significantly decrease the produced NO 2 via NH and NH 2 - related reduction reactions. Almost 100% of NO 2 can be removed in gaseous mixtures of N 2 +O 2 +H 2 O+NO 2 with negligible NO production.
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    Oxidation of metals 8 (1974), S. 393-407 
    ISSN: 1573-4889
    Keywords: cobalt alloys ; oxidation ; manganese
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Earlier studies have suggested that manganese might be attractive as an alternative fcc stabilizer to nickel in cobalt base alloys because of its beneficial effect on the sulfidation resistance. Because it has relatively high oxygen affinity, it seemed possible that it might modify the ability of the alloys to form a protective Cr 2O3 scale. Thus, a range of alloys having compositions close to the critical Co-20 Cr value have been investigated in the temperature range 900–1150° C for times up to 240 hr in air and oxygen. Similar, but less extensive studies, have been conducted on alloys containing iron or nickel. None of these elements has a significant effect on the oxidation behavior, or on the ability of the alloys to develop a protective Cr 2O3 layer. However, manganese has a significant adverse effect on the scale spallation, apparently because of its increasing the brittleness of the oxide, particularly the CoO.
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  • 29
    ISSN: 1573-4889
    Keywords: dilute alloys ; oxidation ; Wagner-Hauffe rule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Concerning the parabolic oxidation of alloys with a low content of a different valence element, we show that the Wagner-Hauffe valence approach contains some inaccuracies. This paper is devoted to the growth of an oxide MO with metal excess or oxygen deficit. The analytical processing consists in solving the differential equation connecting the point defect flux to the oxygen pressure. This equation has been solved analytically in the case where the foreign-element concentration is very high compared to that of the point defects in the pure oxide. On this assumption with a lower-valence dopant, as long as the oxide conductivity remains essentially electronic, the oxidation is limited only by the transport of ionic defects across the scale under the electric-potential gradient. Moreover, an increase of the dopant concentration may lead to an oxide exhibiting partial ionic conductivity. Consequently, the parabolic constant variations as a function of the dopant concentration is not monotonic, contrary to results published before. With a higher-valence dopant, the conductivity always remains electronic, and this result agrees with predictions based on the Wagner Hauffe approach, though the demonstrations are fundamentally different.
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  • 30
    ISSN: 1573-4889
    Keywords: oxidation ; copper ; Li-doped copper ; Cr-doped copper ; short-circuiting ; Mott's parabola ; Wagner's parabola
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The influence of shorting circuitry attachment between metal-oxide and oxideoxygen interfaces on the oxidation kinetics of copper, lithium-doped copper (Li: 400 ppm), and chromium-doped copper (Cr: 12 ppm) have been studied in dry air $$(P_{O_2 } = 21.27kPa)$$ in the temperature range of 523–1073 K. Oxide film or scale growth under short-circuiting as well as under normal oxidation conditions conforms to the parabolic rate law. The oxidation kinetics under short-circuiting resulted in decreased rates for Cu and Li-doped Cu up to a temperature of 773 K, while Cr-doped Cu exhibited an enhancement in rate compared to its normal oxidation in the same temperature range. However, above 873 K, all three systems under shorting circuitry attachment exhibited enhanced rates compared to their normal oxidation rates in conformity to the existing theoretical model. Use of additional resistances in series in the outer short-circuit Pt path have clearly established that below 773 K Mott's fieldinduced migration plays the most important role, while at elevated temperatures Wagner's electrochemical potential-gradient factor acts as the main driving force in the scale-growth process. The results have been interpreted on the basis of average defect concentration, the electrochemical potential gradient, electrical field gradient, and transport coefficient in the Cu2O layer.
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    Oxidation of metals 46 (1996), S. 109-127 
    ISSN: 1573-4889
    Keywords: oxidation ; Ni3Al base alloy ; chromium ; cobalt ; titanium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation behavior of Ni3Al+2.90 wt.% Cr, Ni3Al+3.35 wt% Co, and Ni3Al+2.99 wt.% Ti alloys was studied in 1 atm of air at 1000, 1100, and 1200°C. Isothermal tests revealed parabolic kinetics for all three alloys at all temperatures. Cyclic oxidation for 28 two-hour cycles produced little spallation at 1000°C, but caused partial spallation at 1100°C. Especially, at 1200°C severe spallation in all three alloys was observed. Although additions of Cr, Co, or Ti to Ni3Al alloys slightly increased the isothermal-oxidation resistance, the additions tended to decrease the cyclic-oxidation resistance. The major difference in the oxidation of the three alloys compared with the oxidation of pure Ni3Al alloys was the existence of small α-Al2O3 particles in the middle of the α-Al2O3 scale and the formation of irregularly shaped Kirkendall voids at the alloy-scale interface.
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    Oxidation of metals 47 (1997), S. 381-410 
    ISSN: 1573-4889
    Keywords: Ni-Base superalloys ; Astroloy ; Waspaloy ; Udimet 720 ; oxidation ; chromia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Several commercially available Ni-base superalloys were exposed isothermally in air at temperatures between 750° and 1000°C and also under cyclic conditions at 1000°C. The kinetics of oxidation were determined and the scales were analyzed by electron microscopy and X-ray diffraction. Thin adherent chromia-rich scales formed on the alloys at 750°C after 1000 hr. Although Waspaloy showed the lowest weight gain in this test, it also showed the deepest internal corrosion due to oxidation of the grain-boundary carbides. At temperatures up to 1000°C the external scales were also chromia-rich but there was greater internal corrosion. Titanium in the alloys oxidized, diffusing through the chromia scale to form faceted rutile (TiO2) grains at the surface as well as forming TiO2 and TiN internally. The amount of rutile at the oxide surface increased with temperature and alloy Ti concentration. Alumina formed as discrete internal oxides below the chromia scale, although Astroloy when oxidized isothermally at 1000°C developed a semicontinuous internal layer of alumina due to its higher Al content. Under cyclic conditions Astroloy formed a thicker, less-protective scale of transition oxides probably due to its lower Cr content.
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  • 33
    ISSN: 1573-4889
    Keywords: oxidation ; Incoloy 909 ; superalloy ; scale ; high temperature ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of an Fe-38Ni-13Co-4.7Nb-1.5Ti-0.4Si superalloy (Incoloy 909 type alloy), was investigated at temperatures between 1000 K and 1400 K in Ar-(1, 10%)H20 atmosphere using metallographic, electron probe microanalysis, and X-ray diffraction techniques. The oxide scales consist of an external scale and an internal scale which has an intergranular scale (above 1200 K) and an intergranular scale. The oxide phases in each scale are identified asα-Fe2,O3 (below 1200 K) or FeO (above 1300 K) and CoO · Fe2O3 and FeO · Nb2O5, respectively. The morphologies, the oxide phases and the oxidation rates do not depend on the partial pressure of H2O in the range between one and ten percent in Ar gas. The rate constants for the intergranular-scale formation in this alloy are about one-tenth as large as those in Fe-36%Ni alloy reported previously. At all the temperatures the scales grow according to a parabolic rate law and the apparent activation energies for the processes are estimated.
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  • 34
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    Oxidation of metals 47 (1997), S. 445-464 
    ISSN: 1573-4889
    Keywords: oxidation ; Fe-Cr-Al alloy ; water vapor ; ESCA ; RHEED
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Fe-21.5 wt. %Cr-5.6 wt. %Al oxidation, at 1000°C, in dry or wet oxygen shows that steam has an influence on the oxide-scale growth mechanism. Steam modifies the kinetics of early-stage oxidation. In dry oxygen, an initial fast linear regime is observed during one hour. Under wet conditions, weight-gain curves follow the same parabolic regime over the entire oxidation test. The scale structure strongly depends on the presence of steam in the gaseous environment. With dry oxygen, the scale is composed mainly ofα-Al2O3 after the initial formation ofγ-Al2O3 identified by ESCA and RHEED. The kinetics transient stage corresponds to the necessary time for the internal part of the initialγ-Al2O3 scale to transform into a continuousα-Al2O3 diffusion barrier. Under wet oxygen conditions, transient oxides are identified as (Mg, Fe) (Cr, Al)2O4, MgAl2O4 (orthorhombic), Al2O3 (hexagonal), these oxides transform into MgAl2O4 (cubic), Cr3O4, Fe2O3,α-Al2O3, with time. When water vapor does not change drastically oxidation kinetics, the induced presence of iron and chromium in the oxide scale could be responsible for weakening the protectiveness of alumina scales.
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    Oxidation of metals 47 (1997), S. 507-524 
    ISSN: 1573-4889
    Keywords: alloys ; high temperature ; oxidation ; transient state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The initial transient high-temperature oxidation stage for binary alloys forming the most-stable oxide has been examined by means of a numerical procedure based on the finite-difference method. At variance with previous models, the present treatment takes into account the effect of the rate of the reaction at the scale/gas interface over the corrosion kinetics. The calculations concerning the transient stage are developed either using the general parabolic rate law to represent the overall scaling kinetics or using the rate law of the reaction at the scale/gas interface as a boundary condition without imposing any particular rate law to the overall process. A correct analysis of the oxidation behavior of binary alloys during the transient stage must take into account the kinetics effect of the rate of the surface reaction. The concentration of the most-reactive element at the alloy/scale interface changes regularly with time, decreasing gradually from the initial bulk value to its final steady-state value. The present results are in good agreement with those obtained by means of an approximate analytical model developed previously.
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  • 36
    ISSN: 1573-4889
    Keywords: high temperatures ; oxidation ; transient state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The transient state in the oxidation of solid solutions of a most-noble componentA in a most-reactive componentB (beta phase) for binaryA-B alloys presenting a limited reciprocal solubility of the two metals has been examined assuming that theirB content is sufficient for the exclusive growth of externalBO scales. Above a criticalB content of the alloy theBO scales may grow directly on the surface of the beta phase, while below this limit they can only form over a layer ofB-depleted solid solution ofB inA (alpha phase), which appears after a critical time. An approximate analytical expression for the profile of concentration ofB in the alloy has been adopted to calculate the flux ofB in the metal. Moreover, the effect of the reaction between the gas and the external oxide surface has been taken into account using a procedure developed by Wagner for the oxidation of pure metals. The corrosion kinetics as well as all the parameters involved, such as the concentration ofB at the alloy-scale interface, have been calculated as functions of the corrosion time. The results show that, as time proceeds, the instantaneous parabolic rate constant increases and the concentration ofB at the alloy-scale interface decreases, both tending gradually to their corresponding steady-state values. It is also predicted that if the rate of transformation of the beta phase in the alpha phase after the alloy reaches the composition of equilibrium at the interface with the oxide is lower than the corresponding rate of displacement of the alloy surface due to scale growth, the corrosion of beta phase alloys may eventually lead to the formation of two phase mixtures of alpha phase andBO which are expected to grow at much larger rates than in the presence of a uniform continuous alpha layer.
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    Oxidation of metals 48 (1997), S. 1-39 
    ISSN: 1573-4889
    Keywords: Ni-base ODS superalloys ; oxidation ; initial stages of oxidation ; alumina ; chromia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Mechanically-alloyed Ni-base ODS superalloys currently receive attention for application in future gas turbines because they exhibit outstanding mechanical properties at high temperatures. They also protect themselves against oxidation by forming chromia and/or alumina scales. However, little attention has been given so far to the initial stages of oxidation of Ni-base ODS superalloys, containing Cr as well as Al in considerable amounts. In the current work, oxidation at 1150°C was studied for different holding times up to 200 hr for the commercial materials MA6000 and PM3030 which contain. Al in increasing amounts. MA 754, a chromia former, was investigated as a reference. It was shown that for the potential alumina formers MA6000 and PM3030 the continuity and therefore protectiveness of the secondary Al2O3 at later stages is indeed determined by the initial stages of oxidation.
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    Oxidation of metals 48 (1997), S. 129-141 
    ISSN: 1573-4889
    Keywords: decarburization ; nickel ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A commercial-grade nickel containing small amounts of carbon, manganese, and silicon was exposed to air for periods up to 288 hr at 1050°C to study the effect of oxidation on the formation of oxides of these impurity elements. Exposure of nickel to air led to decarburization. The maximum amount of decarburization occurred during the initial period of air exposure and the loss in carbon was more in the metal with a smaller section size. Decarburization in the metal produced voids in the oxide scale due to the formation of CO2 gas. It has been shown further that CO and/or CO2 gas bubbles, which form in high purity nickel on grain boundaries during exposure to air at elevated temperatures, cannot exist in commercial-grade nickel where manganese is present as an impurity. Instead, oxides of manganese form in the grain boundaries as well as in the matrix. This is because manganese oxide is more stable than CO or CO2 gas.
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  • 39
    ISSN: 1573-4889
    Keywords: oxidation ; kinetics ; iron ; iron-nitride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of α-Fe and ɛ-Fe2N1−z at 573 K and 673 K in O2 at 1 atm was investigated by thermogravimetrical analysis, X-ray diffraction, light-optical microscopy, scanning electron microscopy and electron probe X-ray microanalysis. Upon oxidation at 573 K and 673 K, on α-Fe initially α-Fe2O3 develops, whereas on ɛ-Fe2N1−z initially Fe3O4 develops. In an early stage of oxidation the oxidation rate of ɛ-Fe2N1−z appears to be much larger than of α-Fe. This can be attributed largely to an effective surface area available for oxygen uptake, which is much larger for ɛ-Fe2N1−z than for α-Fe due to the porous structure of ɛ-Fe2N1−z as prepared by gaseous nitriding of iron. The development of a magnetite layer in-between the hematite layer and the α-Fe substrate, at a later stage of oxidation, enhances layer-growth kinetics. After 100 min oxidation at 673 K the (parabolic) oxidation rates for α-Fe and ɛ-Fe2N1−z become about equal, indicating that on both substrates the oxide growth is controlled by the same rate limiting step which is attributed to short-circuit diffusion of iron cations. Oxidizing ɛ-Fe2N1−z increases the nitrogen concentration in the remaining ɛ-iron nitride, because the outward flux of iron cations, necessary for oxide growth, leads to an accumulation of nitrogen atoms left behind.
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    Oxidation of metals 48 (1997), S. 201-214 
    ISSN: 1573-4889
    Keywords: titanium-aluminum alloys ; niobium ; intermetallics ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In a recent study, CO2 has been reported to enhance the oxidation rate of binary titanium-aluminum alloys. The detrimental effect of CO2 was not, however, observed in a ternary alloy containing niobium. In this paper, possible explanations for these observations are examined. First, results from the literature regarding the effects of niobium in improving the resistance of titanium-aluminum alloys are briefly reviewed. Second, a thermodynamic analysis which offers a possible explanation for the beneficial effect of niobium in eliminating the CO2-enhanced oxidation of titanium-aluminum alloys is presented.
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  • 41
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    Oxidation of metals 48 (1997), S. 215-224 
    ISSN: 1573-4889
    Keywords: nanocrystallization ; oxidation ; mechanism
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    Notes: Abstract Many mechanisms for the effect of reactive elements on the selective oxidation and scale adhesion of alloys have been proposed. However, nanocrystallization (or microcrystallization) has recently been found to have almost the same effect as that of reactive elements. This note reviews the effect of nanocrystallization on the selective oxidation and adhesion of Al2O3 scale with particular reference to the author's own results.
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  • 42
    ISSN: 1573-4889
    Keywords: oxidation ; titanium ; rutile ; scale ; high temperature ; kinetics
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    Notes: Abstract The oxidation behavior of pure titanium has been investigated in the temperature range of 1000 K to 1300 K in CO2 or Ar-10%CO2. Optical microscopy, electron probe microanalyses, and X-ray measurements on the oxide scales formed during oxidation indicate that their structures are nearly independent of temperature and the corrosion atmosphere. The scales consisted of two layers, an external one and an internal one, having a rutile (TiO2) structure. The parabolic rate law was confirmed for growth of the external scale and the permeation depth of oxygen in titanium with apparent activation energies of 266 and 226 kJ/mol, respectively. The rate-determining diffusion species in the oxidation processes are discussed.
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  • 43
    ISSN: 1573-4889
    Keywords: zirconium ; X-ray diffraction ; oxidation ; phase analysis ; texture
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    Notes: Abstract The oxidation of zirconium at high temperature (T〉 400°C) leads to reaction products of two allotropic oxide (ZrO2 monoclinic and ZrO2 tetragonal). The distribution and proportion of these two phases were studied as a function of time and space by X-ray diffraction techniques. Quantitative analyses are possible after some corrections, and we demonstrate the presence of a phase gradient in the oxide scale. The interest of this nondestructive method is then discussed.
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  • 44
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    Oxidation of metals 48 (1997), S. 357-380 
    ISSN: 1573-4889
    Keywords: chromium ; copper ; binary alloys ; two-phase alloys ; oxidation ; high temperatures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation in air of three two phase Cu-Cr alloys with nominal Cr contents of 25, 50, and 75 wt. % was studied at 700–900°C. The alloys corroded nearly parabolically, except at 900°C, when the corrosion rates decreased with time more rapidly than predicted by the parabolic rate law. The corrosion rate decreased for higher Cr contents in the alloy under constant temperature and generally increased with temperature for the same alloy composition. The scales were complex and consisted in most cases of an outermost copper oxide layer free from chromium and an inner layer composed of a matrix of copper oxide or of the double oxide Cu2Cr2O4, often containing particles of chromium metal surrounded by chromia and then by the double oxide. Metallic copper was also frequently mixed with chromia. Cr-rich regions tended to form continuous chromia layers at the base of the scale, especially at the highest temperature. No chromium depletion was observed in the alloy.
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  • 45
    ISSN: 1573-4889
    Keywords: iron ; oxidation ; CeO2 coating ; in situ ; growth stress ; residual stress ; texture ; X ray diffraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In situ XRD stress determinations have been performed during oxidation of pure iron (p(O2=2 × 10−3 Pa,T=800°C)). The compressive stress, initially present in the substrate due to surface preparation, is completely released at 400°C. Under the test conditions, the in situ compressive-stress level determined in the FeO scale during oxidation is not strongly dependent upon the presence of a ceria coating. On blank and coated specimens, the compressive stress varies from −400 ± 80 MPa to −150 ± 100 MPa during 30 hr oxidation. The decrease is quicker at the beginning of the test performed on blank specimens. Epitaxial relationships between the wüstite scale and iron (under low-pressure starting conditions) caused thein situ compressive stress in the oxide scale to be two times greater compared to the usual test conditions. This indicates that epitaxial relationships can be a source of stress in an oxide scale that ceria coatings may lower compressive stresses.
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  • 46
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    Oxidation of metals 48 (1997), S. 527-551 
    ISSN: 1573-4889
    Keywords: chloridation ; oxidation ; Fe-Cr alloys ; Ni-Cr alloys
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The chloridation-oxidation behavior of Fe-Cr (0–25 wt. %Cr) and Ni-Cr (0–20 wt.%Cr) alloys was studied at 800°C in three different H2-HCl-H2O(ν) environments. In a low-HCI and low-H2O(ν) environment, where Cr2O3 is thermodynamically stable, the corrosion resistance of the Fe-Cr alloys increased with increasing Cr content in the alloys. In a high-HCl and high-H2O(ν) environment, where FeCr2O4 is stable and CrCl2 is metastable, the corrosion resistance of the Fe-Cr alloys depended similarly on the Cr content. Low-Cr-Fe-Cr alloys exhibited large weight losses, while Fe-Cr alloys with higher than 19 wt. %Cr showed good corrosion resistance. In an environment of high-HCl in the absence of H2O(ν), the evaporative corrosion rate was fast and limited by gas phase diffusion, and independent of the Cr content in the Fe-Cr alloys. Ni and Ni-Cr alloys generally showed good corrosion resistance in the environments of high H2O(ν) because of the low NiCl2 vapor pressure and formation of a protective Cr2O3 scale. However, in the environment of high HCl in the absence of H2O(ν), selective formation and evaporation of CrCl2 occur, which results in Cr depletion and networks of voids for even a high-Cr Ni-Cr alloy.
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  • 47
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    Oxidation of metals 48 (1997), S. 553-596 
    ISSN: 1573-4889
    Keywords: chloridation ; oxidation ; HCl ; high-temperature alloys ; high-temperature corrosion
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Chloridation-oxidation studies of nine commercial high-temperature alloys were carried out at 800°C in three different H2-HCl-H2O(ν) environments: (A) both low HCl and H2O(ν) partial pressures, where either Cr2O3 or FeCr2O4 is stable, (B) both high HCl and H2O(ν) partial pressures, where FeCrO4 is stable and CrCl2 is metastable, and (C) high HCl partial pressure in the absence of H2O(ν), where either CrCl2 or Cr2O3 is stable. Although alloy 600 has the lowest Cr content of these nine alloys, it showed excellent corrosion resistance in all three environments because of its high Ni content. Alloy 304, with the lowest Ni content of the nine alloys, exhibited poor corrosion resistance in the environment C, fair resistance in the environment B and good resistance in the environment A. Alloy 800 showed very good resistance in Environment A, and fair corrosion resistance in Environment B; however, it suffered linear weight-loss kinetics when exposed to Environment C The alloys 617, 214, HR-160, X, 230 and 86 have good corrosion resistance in Environments A and B because of their relatively high contents of oxide-scale-forming elements Cr and/or Al. In Environment C, chlorine dramatically decreased the adhesion of the scale on the surface, and aluminum in alloys 617 and 214 hardly showed its usual beneficial effect in combating corrosion, nor does silicon in alloy HR-160. Different corrosion mechanisms are proposed for the alloys in the different environments.
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  • 48
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    Oxidation of metals 44 (1995), S. 265-308 
    ISSN: 1573-4889
    Keywords: oxidation ; corrosion ; high temperatures ; erosion ; wear
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract There are several engineering systems which require materials of construction to tolerate elevated temperatures, and aggressive environments of one kind or another; and where, furthermore, the performance of the system is limited by the materials capability. This paper reviews a number of these systems, drawn principally from the electric power industry, and describes both the current approaches to improving the materials capability, and potential directions for research and development for the future. Particular emphasis is given to cases where the problems related to oxidation and high-temperature corrosion are of major importance.
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  • 49
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    Oxidation of metals 44 (1995), S. 339-374 
    ISSN: 1573-4889
    Keywords: analytical techniques ; Fe, Cr, Fe−Cr alloys, Ni, Al, β-NiAl ; oxidation ; transport processes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper considers the application of analytical techniques (particularly AES, SIMS, RHEED, laser Raman, Mössbauer, TEM, EELS) to high-temperature oxidation studies. Specific systems reviewed include NiO on Ni, oxides on Fe, Cr and their alloys, and Al2O3 on Al and β-NiAl. The often complementary information provided by the various techniques leads to a better understanding of oxide growth mechanisms on an atomic sale, interfacial segregation phenomena, and the role of reactive elements in modifying transport processes in oxides.
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  • 50
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    Oxidation of metals 44 (1995), S. 239-264 
    ISSN: 1573-4889
    Keywords: oxidation ; carburization ; sulfidation ; scaling ; internal precipitation ; diffusion
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Scaling reactions between pure metals and multiple oxidant gases are reviewed briefly. It is recognized that elemental oxidant activities are usually so low that the actual reactant species are heteronuclear molecules such as SO2, CO2, etc. The formation of duplex, sulfide-oxide scales on iron and manganese, even when sulfide is unstable with respect to oxide, is attributed to direct reaction with SO2. The persistence of the metastable sulfide is due to its preservation by the rapidly growing scale. The reaction of pure chromium with a number of mixed gases is also discussed. The continued formation of carbides and nitrides beneath an external Cr2O3 scale layer indicates that the latter material is permeable to gas species. Interaction among different gas species is observed, and is attributed to selective adsorption on internal surfaces within the chromium oxide. New work on the reaction of alloys with mixed gases is reported. Several austenitic heat-resistant alloys were exposed at 1000°C to gases containing one, two or all of the oxidants carbon, sulfur and oxygen. Gases containing two or more oxidants produced multiple zones of internal precipitation. The precipitates were chromium-rich oxides, sulfides and carbides arranged in order of thermodynamic stability: oxides beneath the external scale, carbides deepest within the alloys and sulfides in an intermediate zone overlapping the oxide zone. Each precipitate zone widened according to parabolic kinetics. This finding confirms the as yet untested prediction made by J. L. Meijering in 1971. However, the rate at which a particular zone grows changes according to presence of other oxidants. Interactions between the oxidants can be large and reaction rates are currently not predictable.
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  • 51
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    Oxidation of metals 45 (1996), S. 153-181 
    ISSN: 1573-4889
    Keywords: oxidation ; 18O diffusion ; nickel ; stress effects on diffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This study deals with the influence of various mechanical loadings (fatigue, creep, creep-fatigue) on oxygen diffusion in a particular system, oxidizing nickel. A distinction between the behavior of the oxide layer and underlying nickel was noted during the first step of oxidation at 550°C, in PO 2=1 atm. Mechanical loading causes a decrease of the oxygen mobility through the oxide scale (factor of 103). The oxide thicknesses on nickel undergoing mechanical loadings are different than for an unloaded sample, due to distinct contributions of the oxygen and nickel fluxes in the growing oxide. In the substrate, the ingress of oxygen becomes easier with a constant tensile load (creep). The intergranular-oxygen diffusion coefficient, Di, is increased by a factor of 102 with respect to other samples. In creep, oxygen diffusion takes place along grain boundaries of a structure with smaller grains than in unstrained Ni. A short fatigue period during creep-fatigue decreases the sensitivity of nickel to intergranular-oxygen diffusion.
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  • 52
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    Oxidation of metals 8 (1974), S. 379-391 
    ISSN: 1573-4889
    Keywords: oxidation ; sulfidation ; kinetics ; parabolic rate law
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The conditions necessary to determine the oxidation kinetics of metals and alloys are discussed quantitatively, and a new method of calculating the rational rate constants was suggested. It was shown that the size and the shape of a metal sample has an effect on the kinetics of oxidation. Further, it was established that the values of the parabolic rate constants of corrosion, calculated from the empirical Pilling and Bedworth equation, contain a serious systematic error, if changes in the metallic core surface area during the oxidation process are neglected.
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  • 53
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    Journal of materials synthesis and processing 6 (1998), S. 191-195 
    ISSN: 1573-4870
    Keywords: Transmission electron microscopy observation ; interfacial microstructure ; oxidation ; ZrC ; cubic ZrO2 ; amorphous carbon film
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Microstructure at the interface of ZrC and ZrO2 formed by oxidation of a single crystal of ZrC with 100 faces at 600°C at an oxygen pressure of 2 kPa was observed by high-resolution transmission electron microscopy and scanning electron microscopy. The ZrO2 scale was shown to consist of two subscales, zones 1 and 2. The interfacial area in zone 1 was composed of regular lattice fringes corresponding to the 111, 200, and 220 lattices of cubic ZrO2 (c-ZrO2) crystallites 2 to 10 nm in size and an amorphous phase. The growth of crystallites occurred in zone 2, which visualized the interface of zones 1 and 2. Black thin films reminiscent of zone 1 were successfully separated, which were composed of amorphous carbon in which c-ZrO2 particles 2 to 20 nm in size were included.
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  • 54
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    Oxidation of metals 43 (1995), S. 157-172 
    ISSN: 1573-4889
    Keywords: oxidation ; NiAl ; ion implantation ; TEM
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The influence of Y-ion implantation on the oxidation of β-NiAl single crystals has been investigated using SEM, TEM, and STEM. Y ions having an energy of 70 keV were implanted with a concentration of 5×1016 ions/cm2. The oxidation experiments were performed in air at 1223 K. Y-ion implantation resulted in a 45-nm disordered layer. Oxidation of Y-implanted β-NiAl leads to the formation of a fine-grain layer, consisting of γ-Al2O3 containing Y and a θ-Al2O3 layer. After further oxidation the metastable Al2O3 transformed into α-Al2O3, which started at the metal-oxide interface. Y-Al-garnet (YAG) particles were observed and Y segregation to α-Al2O3 grain boundaries has been detected.
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  • 55
    ISSN: 1573-4889
    Keywords: oxidation ; reactive-element effects ; electrodeposition ; Y2O3 ; oxide film
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Thin Y2O3 films were deposited by the electrochemical deposition-pyrolysis process on Fe−25Cr and Fe−25Cr−10Al alloys. The influence of the films on the oxidation behavior of the alloys was studied at 850°C and 1000°C. The results showed that Y2O3 films remarkably decreased the oxidation rate of Cr2O3-forming alloys and spallation of the scales, but they did not decrease the oxidation rate of the Al2O3-forming alloys, although they do reduce the spallation of Al2O3 scales. Y2O3 films remarkably change the morphology of the scales on both alloys, depending on the oxidation temperatures. These results show that the reactive-element effects of Y2O3 films on the Cr2O3 formers and Al2O3 formers are different.
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  • 56
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    Oxidation of metals 43 (1995), S. 185-215 
    ISSN: 1573-4889
    Keywords: copper ; oxidation ; direct current ; uninterrupted mode ; interrupted mode
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Oxidation kinetics of copper in the temperature range of 973–1173 K atP O 2=21.27 kPa exhibit enhancement and deceleration in the rates with changing polarity compared to normal oxidation under interrupted mode of directcurrent application. These conditions are achieved by connecting the oxidizing copper covered with an initially formed thin oxide film to the positive and negative terminal of a dc source, respectively. However, the influence of direction of the current is found to be opposite under uninterrupted mode of impressed current flow in the same temperature range. The effect of short-circuiting the metal to the outer oxide/air interface on the reaction kinetics is also reported. The rate of oxide-scale growth under normal condition, and two different modes of current applications as well as with shorting circuitry attachment conform to the parabolic growth law. The results pertaining to the two different modes of impressed current have been discussed considering both the phenomena of electrolysis of the oxide electrolyte and the polarization at the two phase boundaries. The enhancement and the reduction in rates under uninterrupted impressed current conditions are explained on the basis of increased and decreased average defect concentrations, respectively, within the oxide layer. The acceleration and deceleration in the rates under interrupted mode of current flow have been explained in the light of sustenance of a steeper and flatter electrochemical-potential gradient of defects, respectively, across the growing-oxide layer. The possible different responses of the metal/oxide and oxide/air interfaces to the impressed current brought into play by two different modes of current application, have enabled to display a better insight on the mechanistic aspects of scale growth under the influence of an externally applied current.
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  • 57
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    Oxidation of metals 43 (1995), S. 237-261 
    ISSN: 1573-4889
    Keywords: manganese ; oxidation ; ceria ; coating ; air ; low oxygen pressure ; high temperature ; manganosite ; transport mechanism ; iron ; CeFeO3 structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The kinetics, scale composition, and growth mechanism of ceria-coated and blank specimens of manganese oxidation in air were examined. The scale growth obeys the parabolic rate law at 700°C for all specimens. Lower parabolic rate constants for coated specimens are attributed to the presence of a CeO2 external scale. It constitutes a limiting factor of the oxygen activity at the gas-oxide interface. This lower-oxygen activity leads to a less-metal-deficient state of the scale. Due to this, the inner-MnO scale becomes more adherent to the substrate. Preheating at 700°C, in hydrogen (PO 2=10−24 atm), was performed in order to be placed in the MnO stability domain and try to introduce cerium in the manganese-oxide scale. This pretreatment promotes macroscopic bonding in the layer formed during subsequent oxidation in air. It ensures a better scale adherence. A new diffusional-transport mechanism in manganosite is proposed in accordance with all experimental observations of the literature and with the cerium-manganese-oxygen system studied in the present work. This model considers the high Mn3+ stability in octahedral sites of the MnO oxygen ion body. Low-oxygen partial pressure conditions permit the formation of an adherent inner-MnO scale on coated specimens. A CeO2 scale formed above the MnO scale; MnO is present as a minor component in this scale and it is located mainly at the internal interface. The difficulties in forming the cerium-orthomanganite are attributed to the very high stability of MnO related to this wide range of nonstoichiometry and to the low manganese diffusivity through the cerium-containing scale.
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  • 58
    ISSN: 1573-4889
    Keywords: oxidation ; chromium coating ; laser ; oxygen diffusion
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    Notes: Abstract The oxidation of a chromium PVD coating on pure iron by a continuous 5-kW CO2 laser beam in pure oxygen at 700°C for 20 min was compared with classical furnace oxidation. Laser oxidation induces faster oxidation kinetics, especially at the beginning of oxidation, without modifying the oxide nature (Cr2O3) and morphology. Oxygen-isotopic-exchange tests show that oxygen grain-boundary diffusion does not depend on the oxidation conditions, at least after 12 min oxidation. The effec of the laser treatment is discussed with respect to oxide nucleation, metastable-oxide formation, and oxide-formation-entropy evolution. The oxidation kinetics follow a parabolic law, and the oxide-growth mechanism was attributed to countercurrent oxygen and chromium diffusion along grain boundaries. Oxygen diffusion occurred by oxygen interstitials. The oxidation constant calculated from grain-boundary diffusion in the chromia scale is smaller than the experimental oxidation constant, suggesting the presence of particular short circuits (e.g., microcracks).
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  • 59
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    Oxidation of metals 43 (1995), S. 317-328 
    ISSN: 1573-4889
    Keywords: microcrystalline ; rehealing ; oxide scales ; superalloys ; coating ; oxidation
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The rehealing ability of the protective oxide scales formed on a microcrystalline coating of the Ni-base superalloy K38G has been studied. The results indicated that the oxide scales on the coating may be rehealed when the original scales are destroyed, and the coating still has excellent resistance against high-temperature oxidation. When the original Al2O3 oxide scales spall, mixed-oxide scales of both (Al, Cr)2O3 and TiO2 can form on the surface. The mixed scales are very protective and adherent.
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  • 60
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    Oxidation of metals 43 (1995), S. 263-277 
    ISSN: 1573-4889
    Keywords: Fe−Cr−Ni alloy ; oxidation ; silica ; spallation
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In order to determine the effect of alloy grain size on the oxidation properties of silica-coated austenitic Fe-18Cr-20Ni stainless steel, both coarse-grain (100-μm grain size) and fine-grain (5-μm grain size) forms of the alloy were produced. A 1-μm-thick vitreous silica coating was deposited by chemicalvapor deposition on the alloys, which were subjected to isothermal and cyclic oxidation in air at 900°C. The coarse-grain alloys underwent widespread oxidation below the silica coating, leading to extensive coating spallation. This was attributed to the inability of the alloy to supply a sufficient outward flux of chromium to prevent oxygen penetration through microcracks in the silica coating. Due to an abundance of chromium available at the surface of the finegrain alloy, chromia formed in the microcracks within the silica layer. As a result, the silica-coated, fine-grain alloy demonstrated superior oxidation resistance and excellent adhesion of the coating.
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  • 61
    ISSN: 1573-4889
    Keywords: Ni−Cr−Al−Ti−Si bond-coating alloy ; phase stability ; oxidation ; interdiffusion
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract A novel, low-expansion experimental Ni−Cr−Al−Ti−Si bond-coating alloy was investigated in the as-cast state concerning its phase stability, oxidation resistance in air, and interdiffusion with single-crystal IN-100 at 900, 1000, and 1100°C. Isothermal oxidative thermogravimetry was employed up to 500 hr. Interdiffusion was compared to a commercial Ni−Co−Cr−Al−Y alloy on IN-100. Oxidized Ni−Cr−Al−Ti−Si specimens and diffusion couples were characterized by metallography, SEM, EDX, XRD, and XRF. The Ni−Cr−Al−Ti−Si alloy provides good oxidation resistance in air at least up to 1000°C. The alloy is an alumina former. Due to its coarse microstructure, other oxides (e.g., rutile) may form and considerably dominate the oxidation behavior. The kinetics of oxidation were correlated with temperature, formation of phases, and morphology of oxides. Interdiffusion fluxes between Ni−Cr−Al−Ti−Si and IN-100 were mainly directed to the superalloy. They were faster than in Ni−Co−Cr−Al−Y/IN-100 diffusion couples.
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  • 62
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    Oxidation of metals 43 (1995), S. 379-394 
    ISSN: 1573-4889
    Keywords: two-phase alloys ; oxidation ; scale structure
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The main possible modes of the high-temperature corrosion of binary two-phase alloys by a single oxidant under gas-phase pressures sufficient to corrode only the most-reactive alloy component are examined to compare their behavior with that of single-phase alloys. In the absence of important diffusion processes of the metal components in the alloy, the scale structures expected are different from those typical of single-phase alloys. Moreover, when diffusion in the alloy becomes important, these systems may develop an outer single-phase layer depleted in the most-reactive component, which may lead to different possible scale structures. The conditions for the transition between the various oxidation modes as well as the effect of the various parameters of kinetic, thermodynamic, and structural nature over the corrosion behavior of two-phase alloys are also examined.
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  • 63
    ISSN: 1573-4889
    Keywords: oxidation ; reactive-element effect ; reactive-element oxysulfide ; reactive-element oxide ; reactive-element orthochromite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Nickel-base alloys of nominal composition Ni-25 Wt.% Cr-(0-0.6 Wt.%) RE (RE=Y, La, and Ce) were prepared by conventional arc-melting Ni, Cr, and Y metal. The microstructure of the alloys was characterized by using electron diffraction and X-ray energy dispersive spectroscopy (XEDS) to determine the structure, morphology, and distribution of second-phase particles. Selected alloys were oxidized at 900°C and 1000°C in 1-atm air, and the resultant oxide scales were characterized using the same analytical techniques. The experimentally determined electron-diffraction data were compared with a JCPDF-EDD database, and several compounds were matched. The observed phases were RE oxysulfide, cerium orthochromite-CeCrO3, yttria-Y2O3, yttrium orthochromite-YCrO3, and Ni5Y. The significance of these observations is discussed with respect to the current level of knowledge on the role of sulfur in the reactive-element effect. The ability of the reactive elements to getter sulfur is examined with respect to the thermodynamic stability of the oxysulfide species.
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  • 64
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    Oxidation of metals 43 (1995), S. 395-409 
    ISSN: 1573-4889
    Keywords: microcrystalline film ; TiAl intermetallic compound ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation behavior of a cast TiAl intermetallic compound and its sputtered microcrystalline film was investigated at 700–900°C in static air. At 700°C, both the cast alloy and its sputtered microcrystalline film exhibited excellent oxidation resistance. No scale spallation was observed. However, at 800–900°C, the oxidation kinetics for the cast TiAl alloy followed approximately a linear rate law, which indicates that it has poor oxidation resistance over this temperature range. The poor oxidation resistance of TiAl was due to the formation of an Al2O3+TiO2 scale which spalled extensively during cooling. Nevertheless, the sputtered, TiAl-microcrystalline film exhibited very good oxidation resistance. The oxidation kinetics followed approximately the parabolic rate law at all temperatures. Although the composition of the scales was the same as that of scales formed on the cast alloy, the scales formed on the sputtered microcrystalline-TiAl film are adherent strongly to the substrate. No scale spallation was found at 700–850°C, while a small amount of spallation was observed only at 900°C. This indicates that microcrystallization can improve the oxidation resistance of the TiAl alloy.
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    Oxidation of metals 43 (1995), S. 509-526 
    ISSN: 1573-4889
    Keywords: oxidation ; kinetics ; tantalum ; oxide ; suboxide ; impurities ; diffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The kinetics, structural aspects, and phase morphologies were studied for tantalum oxidation in air from 600 to 1000°C for samples of different purity (99.15%, 99.76%, and 99.95% Ta). Regardless of purity, tantalum oxidation in the temperature range of 600–800°C as a rule is governed by a linear rate law. From 900 to 1000°C the initial-stage oxidation is governed by the parabolic rate law, which changes to the linear rate law with time. TGA, XRD, SEM, and AES methods were used. The, effect of purity on tantalum oxidation was shown to be determined by the mechanism of intermediate-oxide formation. They are TaO z (Ta2O) at 600–800°C and TaO at 900–1000°C. The final product of oxidation was β-Ta2O5.
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    Oxidation of metals 43 (1995), S. 527-542 
    ISSN: 1573-4889
    Keywords: Co−Nb alloys ; high temperature ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of two Co−Nb alloys containing 15 and 30 wt.% Nb has been studied at 600–800° C in H2−CO2 mixtures providing an oxygen pressure of 10−24 atm at 600°C and 10−20 atm at 700 and 800°C, below the dissociation pressure of cobalt oxide. At 600 and 700°C both alloys showed only a region of internal oxidation composed, of a mixture of alpha cobalt and of niobium oxides (NbO2 and Nb2O5) and at 700°C also the double oxide CoNb2O6, which formed from the Nb-rich Co3Nb phase. No Nb-depleted layer formed in the alloy at the interface with the region of internal oxidation at these temperatures. Upon oxidation at 800°C a transition between internal and external oxidation of niobium was observed, especially for Co−30Nb. This corrosion mode is associated with the development of a single-phase, Nb-depleted region at the surface of the alloy. The corrosion mechanism of these alloys is examined with special reference to the effect of the low solubility of niobium in cobalt and to the relation between the microstructures of the alloys and of the scales.
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    Oxidation of metals 44 (1995), S. 177-209 
    ISSN: 1573-4889
    Keywords: sulfidation ; oxidation ; common and refractory metals and alloys ; amorphous alloys
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The role of defect and transport properties of transition metal sulfides on the kinetics and mechanism of high-temperature sulfide corrosion of metals and alloys is discussed. It has been shown, that due to the very high concentration of defects in common metal sulfides, not only pure metals but also conventional high-temperature alloys (chromia and alumina formers) undergo very rapid degradation in highly sulfidizing environments. Refractory metals, on the other hand, are highly resistant to sulfide corrosion, their sulfidation rates being comparable with the oxidation rate of chromium. Pioneering work of Douglasset al. has shown that alloying of common metals by niobium or molybdenum, and in particular combined alloying by molybdenumand aluminum, dramatically decreases the sulfidation rate. A novel Fe−30Mo−9Al alloy has been proved to be highly resistant to sulfide corrosion, its sulfidation rate being comparable with that of pure molybdenum. Even better resistance to highly-sulfidizing environments show new amorphous Al−Mo and Al−Mo−Si alloys, these materials also being simultaneously oxidation resistant. Thus, new prospects have been created for the development of a new generation of coating materials, resistant to multicomponent sulfidizing-oxidizing atmospheres, often encountered in many branches of modern technology.
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  • 68
    ISSN: 1573-4889
    Keywords: binary alloys ; oxidation ; transient state ; kinetics
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The initial transient stage in the oxidation of binary alloys forming scales exclusively composed of the most stable oxide is examined by means of a simplified approach which avoids the numerical integration of the diffusion equation for the transport of the metal components in the alloy. At variance with previous solutions to this problem obtained by means of numerical methods, this treatment takes into account also the effect of the gas-scale reaction at the outer surface of the oxide. The concentration of the most-reactive component at the alloy surface changes gradually with time from the initial bulk value towards the corresponding steady-state value without involving any minimum, while the overall rate of the reaction presents a gradual transition from an initial nearly linear towards final parabolic behavior.
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    Oxidation of metals 47 (1997), S. 247-258 
    ISSN: 1573-4889
    Keywords: Ni3Al-base alloy ; sputtering ; nanocrystalline coating ; oxidation ; scale adhesion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Isothermal and cyclic oxidation resistance at 1000°C in air were investigated for a cast Cr-containing Ni3Al-base alloy and its sputtered nanocrystalline coating. The results indicated that both the cast Ni3Al alloy and its sputtered coating exhibit excellent isothermal oxidation resistance as a result of the formation of Al2O3 scales. However, the cast alloy possesses very poor cyclic oxidation resistance because of the spallation of the initially formed Al2O3 scale during cooling and subsequent formation of NiO. On the contrary, the sputtered Ni3(AlCr) nanocrystalline coating exhibits very good cyclic oxidation resistance due to the significant improvement of the adhesion of Al2O3.
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    Interface science 3 (1995), S. 133-141 
    ISSN: 1573-2746
    Keywords: silicon ; Si/oxide interface ; oxidation ; Monte-Carlo ; thin-films
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Experiments have shown that the early stages of silicon oxidation proceed layer by layer, so that one layer is essentially complete before another develops. Other experiments show that the mechanism does not involve step growth, the most obvious mechanism. We use a new approach to modelling the growth to show that these two observations can be understood when there is a rate-determining step which depends strongly on the local oxide thickness. The rate in question might be the sticking probability, or the rate of incorporation of adsorbed oxygen species into the oxide network. Such mechanisms are possible when transport by an ionic species dominates, contrary to the situation for thicker films. Our modelling suggests the mechanisms are driven by the image interaction, as in earlier suggestions by Stoneham and Tasker, rather than an effect of the electric field central to the Mott-Cabrera mechanism.
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  • 71
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    Journal of materials synthesis and processing 6 (1998), S. 335-338 
    ISSN: 1573-4870
    Keywords: PbZrO3 ; oxidation ; nonstoichiometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper reports the results of work function (WF) changes of undoped PbZrO3 during subsequent isothermal oxidation and reduction experiments at 500°C in the p(O2) range between 10 and 2.1 × 104 Pa. The results, obtained during three consecutive runs, indicate that heating at 500°C leads to continuous changes of surface properties resulting in a complex WF vs. time characteristic. The WF changes during the first oxidation are determined by a p(O2)-induced structural transition. The second oxidation results in two competitive processes, such as rapid increase of oxygen non-stoichiometry followed by a structural transition. Finally, the third oxidation is determined by changes of oxygen nonstoichiometry.
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    Journal of materials synthesis and processing 6 (1998), S. 373-377 
    ISSN: 1573-4870
    Keywords: Zirconia ; oxidation ; preparation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper reports surface electrical properties of zirconia studied using work function measurements in the temperature range 297–1173 K during oxidation. It was found that surface preparation procedures, such as grinding and polishing, result in a change of its reactivity with oxygen. The effects produced by the preparation can be removed during thermal treatment at 1473 K.
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    Journal of materials synthesis and processing 6 (1998), S. 407-410 
    ISSN: 1573-4870
    Keywords: CaB6 ; oxidation ; weight gain ; calcium borate ; oxidation resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of CaB6 powders at high temperatures was investigated. The sample oxidized at 873 to 973 K for 25 hours exhibited weight gain with increasing oxidation temperature; the oxidation proceeded in accordance with the parabolic law during the initial oxidation stage. On the other hand, the weight gain of the sample oxidized at and above 1073 K for 4 h was approximately 80%; however even if the oxidation time was prolonged, an additional weight change did not occur. Based on the results of the X-ray diffraction analysis, calcium borate (CaB4O7) was present on the surface of the sample oxidized at 1073 K. The sample showed a good oxidation resistance at 1273 to 1373 K, because the surface film of calcium borate (CaB2O4) formed by oxidation acted as an oxidation resistant layer.
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    Oxidation of metals 44 (1995), S. 309-338 
    ISSN: 1573-4889
    Keywords: modeling ; numerical modeling ; numerical techniques ; finite-difference techniques ; oxidation ; corrosion ; carburization ; nitridation ; diffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Numerical modeling of the diffusional transport associated with high-temperature corrosion processes is reviewed. These corrosion processes include external scale formation and internal subscale formation during oxidation, coating degradation by oxidation and substrate interdiffusion, carburization, sulfidation and nitridation. The studies that are reviewed cover such complexities as concentration-dependent diffusivities, cross-term effects in ternary alloys, and internal precipitation where several compounds of the same element may form (e.g., carbides of Cr) or several compounds exist simultaneously (e.g., carbides containing varying amounts of Ni, Cr, Fe or Mo). In addition, the studies involve a variety of boundary conditions that vary with time and temperature. Finite-difference (F-D) techniques have been applied almost exclusively to model either the solute or corrodant transport in each of these studies. Hence, the paper first reviews the use of F-D techniques to develop solutions to the diffusion equations with various boundary conditions appropriate to high-temperature corrosion processes. The bulk of the paper then reviews various F-D modeling studies of diffusional transport associated with high-temperature corrosion.
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    Oxidation of metals 44 (1995), S. 399-415 
    ISSN: 1573-4889
    Keywords: Ni−Nb alloys ; high temperature ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of two Ni−Nb alloys containing 15 and 30 wt.% Nb has been studied at 600–800° C in H2−CO2 mixtures providing an oxygen pressure of 10−24 atm at 600° C and 10−20 atm O2 at 700 and 800° C, these pressures being less than the dissociation pressure of nickel oxide. The scales formed on both alloys at 600 and 700° C show only a region of internal oxidation composed of a mixture of alpha nickel and niobium oxides (Nb2O5 or/and NbO2), which formed from both the metal phases present, i.e., Ni8Nb and Ni3Nb. Only small, or even no, Nb depletion was observed in the alloys close to the interface with the zone of internal oxidation at these temperatures. On the contrary, samples of both alloys corroded at 800° C produced a continuous external scale of niobium oxides without internal oxidation. The corrosion mechanism of these alloys is examined with special reference to the effect of the low solubility of niobium in nickel.
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    Oxidation of metals 44 (1995), S. 505-525 
    ISSN: 1573-4889
    Keywords: ODS alloys ; oxidation ; scale adherence ; surface roughness ; porosity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The isothermal-oxidation behavior of three oxide-dispersion-strengthened (ODS) alloys, viz., MA 956, ODM 751, and PM 2000, has been examined in air at 1200°C for exposure times up to 4800 hr. During exposure all the alloys formed an external scale of alpha alumina (α-Al2O3). The growth rate of alumina on MA 956 was significantly faster than that formed on ODM 751 resulting in an oxide layer which was about twice as thick after 4800 hr. The oxide-grain morphology on MA 956 was essentially equiaxed containing irregularly shaped, titanium-rich particles, whereas the oxide formed on ODM 751 was slightly finer, distinctly columnar and contained elongated yttrium-rich particles. Spalling of the oxide layer occurred after approximately 2400 hr on MA 956, whereas only slight spalling occurred on ODM 751 even after the longest exposure time. Experiments revealed that the initial surface roughness of PM 2000 can contribute significantly to spalling by enabling the growth of highly convoluted scale layers which are mechanically unstable under compressive stresses (buckling). Internal porosity is also observed in all three alloys after exposure. The pores were generally spherical with small Ti-, Al-, Y-rich particles distributed over their internal surfaces. The amount of porosity increases to a maximum and then slowly decreases.
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    Oxidation of metals 45 (1996), S. 109-131 
    ISSN: 1573-4889
    Keywords: Fe−Al−C ; Fe−Al−Si−C ; inoculation ; scale ; characterization ; oxidation ; high temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Isothermal-oxidation characteristics of cast irons containing aluminum (5–15% Al) from 700 to 1000°C in air have been studied. In addition to massgain measurements, the morphology and composition of the oxide scales have been examined by SEM-EDX system and XRD analysis. A normal Fe−5Al−C alloy does not develop protective, adherent scales. Even the addition of misch metal and calcium silicide to such an alloy does not improve its oxidation resistance. But aluminum cast iron develops considerable oxidation resistance only when a sufficient quantity of silicon is also present in the alloy. Treatment of the alloy with misch, metal and calcium silicide together assists in protective scale formation. Among the alloys investigated Fe−15Al−Si−C treated with misch metal and calcium silicide shows minimum oxidation at 1000°C.
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    Oxidation of metals 45 (1996), S. 469-486 
    ISSN: 1573-4889
    Keywords: iron ; sulfur dioxide ; oxidation ; tracer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The reaction of iron with sulfur dioxide at 0.1 MPa and 1073 K was studied. The composition and morphology of the scales, transport phenomena occurring in the growing scales, and kinetics of the process were investigated. Scanning electron microscopy and various techniques of X-ray analysis were used. The transport phenomena were studied by marker and by radiotracer techniques. The scales were composed of sulfide and oxides and grew by the outward diffusion of metal. It was concluded that the process initially took place through the reaction of iron with sulfur dioxide molecules. During the next stage of the process the reaction with sulfur dioxide molecules as well as with oxygen molecules is possible.
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    Oxidation of metals 45 (1996), S. 507-527 
    ISSN: 1573-4889
    Keywords: oxidation ; sulfidation ; oxides ; sulfides ; Ti ; Ti-6Al-4V alloy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Pure titanium and Ti-6Al-4V were exposed at 750°C in an H2/H2O/H2S PO 2≈10−18 Pa and PS 2≈10−1 Pa), H2/H2O (PO 2≈10−18 Pa) and air environments for up to 240 hr. The corrosion kinetics, obtained by the discontinuous gravimetric method, showed that the sulfidation/oxidation kinetics were linear for Ti and linear-parabolic for Ti-6Al-4V in the H2/H2O/H2S environment. Both materials obeyed parabolic rate laws in the H2/H2O atmosphere after a transient period, and linear-parabolic rate laws in air. After exposure to the H2/H2O/H2S atmosphere, the titanium specimen displayed a double scale of TiO2 with an intervening TiS2 film between the double-layered scale of TiO2 and the substrate. Ti-6Al-4V also contained a double layer of TiO2 together with a stratum consisting of Al2S3, TiS2 and vanadium sulfide at the junction of the inner TiO2 layer and substrate. Some Al2O3 precipitated in the external portion of the outer TiO2 layer. Following oxidation in the low-PO 2 atmosphere a double-layered oxide of TiO2 scale formed on both Ti and Ti-6Al-4V. The scale on Ti-6Al-4V also contained an α-Al2O3 film situated between the outer and inner (TiO2) layers. For both materials, multilayered-scale formation characterized air oxidation. In detail a multilayered oxide scale of TiO2 formed on the air-oxidized Ti, while a multilayered oxide scale with alternating layers of Al2O3/TiO2 developed on Ti-6Al-4V oxidized in air.
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    Oxidation of metals 45 (1996), S. 487-505 
    ISSN: 1573-4889
    Keywords: sulfidation ; oxidation ; gasification ; austenitic steel alloys
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The major use of high-temperature steel alloys in gasifiers is in heat exchangers for cooling hot syngas, consisting mainly of CO and H2 with lesser amounts of H2O and CO2 and minor quantities of H2S and HCl. Metal temperatures range from 250 to 600°C, gas temperatures from 250 to 1200°C. Because of rapid cooling the composition of the gas does not change with temperature. Therefore the gas is not in equilibrium at the metal surface. Calculations show that such gases have lower oxygen and sulfur pressures than equilibrated gases at the same temperature. This makes the results of previous laboratory studies less appropriate for predicting mixed oxidant corrosion in gasifiers. For this reason the present study was carried out using nonequilibrium gas mixtures, similar to gases, produced in entrained-slagging gasifiers. Most corrosion experiments were carried out at 540°C, as this is a common temperature for superheaters and hot-gas cleanup systems. Iron-base model alloys containing 35% Ni, 20% Cr, and various minor alloying additions were studied. Three corrosion regimes were identified over the range of conditions studied, depending on the sulfur-to-oxygen pressure ratio of the gas and the alloy composition. At high PS 2/PO 2 ratios a somewhat protective FeCr2S4 scale formed on all alloys. Below this layer internal oxidation and sulfidation occurred at a slow rate. At lower PS 2/PO 2 ratios nonprotective Fe(Ni, Cr)S external scales formed. These allow rapid internal oxidation of the chromium in the alloy, resulting in high corrosion rates. Under the same conditions very low corrosion rates are obtained when silicon is added to the alloy, because the presence of SiO2 precipitates makes the internal-oxidation layer protective. Thus, the same corrosion model is operative in all three corrosion regimes: external sulfidation of iron and nickel, together with internal oxidation of chromium and other strong-oxide formers.
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    Oxidation of metals 46 (1996), S. 255-285 
    ISSN: 1573-4889
    Keywords: electron diffraction ; intermetallic ; oxidation ; TEM ; titanium aluminide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The early stages of TiAl oxidation at 900°C and 1000°C in air have been investigated by transmission electron microscopy (TEM). The investigations revealed that at the beginning of oxidation, i.e., after 4 min, TiO2 and Al2O3 grow in a preferential orientation on the γ-TiAl substrate. After 4 h of oxidation an oxide scale structure can already be found similar to that known from long-term oxidation. In addition, besides α-Al2O3, the formation of a second aluminum oxide phase and of titanium nitrides is observed. The processes at the metal-oxide interface of oxidation in the early stages, consisting of a repeated cycle of Al2O3 formation, Al2O3 dissolution, outward migration of Al through the scale, and reprecipitation of Al2O3 in the outer scale, are described by a model. The four stages observed in the kinetics of TiAl oxidation are explained on the basis of the results obtained and the structure of the oxide scale.
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    Oxidation of metals 46 (1996), S. 287-297 
    ISSN: 1573-4889
    Keywords: pure niobium ; oxidation ; sulfidation ; oxidation-sulfidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The corrosion of pure niobium has been studied at 600–800°C in various environments as part of a study of the corrosion resistance of its alloys with iron, cobalt, and nickel to atmospheres of low-oxygen and/or high-sulfur activities. The results have shown that not only the sulfidation but also the corrosion in mixed atmospheres and particularly the oxidation under low oxygen pressures of pure niobium are quite slow, with kinetics rather similar in the three types of gas mixtures used. The good corrosion resistance of niobium to attack by oxygen under low pressures is quite interesting because this element is corroded very rapidly by oxygen under high oxygen pressures, due to the formation of the nonprotective highest oxide Nb2O5 as a main corrosion product.
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    Oxidation of metals 46 (1996), S. 335-364 
    ISSN: 1573-4889
    Keywords: Fe−Cr ; oxidation ; exhaust gas ; oxide adherence ; titanium ; rare earths
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Oxidation tests of rare-earth-modified and Ti-modified Fe−20Cr alloy foils, which are under consideration for catalytic converter supports, were performed in a synthetic exhaust-gas atmosphere (N2+H2O+CO2) between 900°C and 650°C. Between 900°C and 750°C, the rare earths had no effect on oxide growth rates while Ti increased growth rates. Oxide growth rates for the rareearth alloys at 800°C and 750°C are much lower than those found in the literature for oxidation of Fe−Cr alloys or pure Cr in O2-rich atmospheres. The slow growth rates for the rare-earth alloys agree with literature data for oxidation of stainless steels containing 〉20% Cr in wet atmospheres and are caused by growth of an oxide scale only one grain thick. At temperatures ≤700°C, Fe−20Cr alloys grow massive Fe oxides; however, this can be suppressed by adding rare earths or Ti. To ensure good oxide adherence, free sulfur must be eliminated in the alloy by tying it up with a reactive-element addition. Both Ti and the rare earths can be used to tie up S, but the rare earths are more effective. For converter applications, the optimum alloy composition may contain rare earths for good oxide adherence and a small amount of Ti to suppress growth of Fe-rich oxides.
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    Oxidation of metals 46 (1996), S. 365-381 
    ISSN: 1573-4889
    Keywords: oxidation ; steel ; Raman ; scale ; transient oxides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Using Raman scattering we have investigated the oxidation, in air, of the Fe-Cr-Ni stainless steels Fe-25Cr-20Ni, Fe-25Cr-20Ni-3Zr, and Fe-24Cr-3Zr (wt.%) as a function of temperature in the range 300 to 1000°C. The Raman technique is very sensitive to, and provides a clear identification of, the oxides Fe2O3 and Cr2O3. However, the technique is insensitive to NiO, FeO, and does not give a clear identification of spinels. The Fe−Cr−Ni alloys form chromia scales at temperatures greater than ∼800°C. At lower oxidation temperatures, transient phases are observed. With a 1-h heat treatment at 300°C, we observe the formation of an unidentified scale; we speculate that it is either amorphous or consists of disordered spinel(s). Near 400°C we begin to observe hematite (Fe2O3). The intensity of the Fe2O3 signal increases with temperature to ∼600°C and then decreases, being largely replaced by the signal from Cr2O3. The thickness of the Cr2O3 scale increases with temperature up to ∼1000°C above which spallation becomes apparent. Spinel phases also apparently persist in the scale to 1000°C.
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    Oxidation of metals 46 (1996), S. 383-398 
    ISSN: 1573-4889
    Keywords: high temperatures ; binary alloys ; two-phase alloys ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The steady-state kinetics in the high-temperature oxidation of binary A-B alloys containing a mixture of the conjugated solid solutions of B in A (alpha phase) and A in B (beta phase) with exclusive formation of the most-stable oxide BOv have been examined, assuming that the external scale grows on top of a subsurface layer of alpha phase. The results obtained are compared with the corresponding behavior of alloys which are single phase in the whole range of composition. Under identical values of all the parameters involved the concentration of B at the alloy-scale interface is smaller for two-phase than for single-phase alloys under the same concentration of B in the alloy as a result of the restricted flux of B through the alpha-phase layer. As a consequence of this, the two-phase alloys corrode more slowly than single-phase alloys and this difference increases as the solubility of B in the alpha phase decreases. Finally, the simultaneous formation of BOv both externally and as internal oxide is more likely for two-phase than for single-phase materials.
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  • 86
    ISSN: 1573-4889
    Keywords: niobium alloys ; oxidation ; high temperatures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The corrosion of M−Nb alloys based on iron, cobalt, and nickel and containing 15 and 30 wt% Nb has been studied at 600–800°C under low oxygen pressures (10−24 atm at 600°C and 10−20 atm at 700–800°C). Except for the Co−Nb and Ni−Nb alloys corroded at 800°C, which formed external scales of niobium oxides, corrosion under low O2 pressures produced an internal oxidation of niobium. This attack was much faster than expected on the basis of the classical theory. Furthermore, the distribution of the internal oxide in the alloys containing two metal phases was very close to that of the Nb-rich phase in the original alloys. These kinetic, microstructural, and thermodynamic aspects are examined by taking into account the effects of the limited solubility of niobium in the various base metals and of the two-phase nature of the alloys.
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  • 87
    ISSN: 1573-4889
    Keywords: oxidation ; scaling ; surface temperature ; heat of reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper describes the oxidation behavior of low-carbon steel samples in binary gas mixtures of oxygen and nitrogen, at oxygen concentrations ranging between 1% and 15% and temperatures ranging between 1000 and 1250°C. Sample weight gains versus time were analyzed, along with measurements and calculations of sample heating rates due to exothermic heat of reaction at the sample surface. It was found that initial rates of oxidation depended on oxygen content in the gasmixture and that these reaction rates were linear up to oxide thicknesses of 0.4 to 0.5 mm. Calculations of linear oxidation rate constants based on equations for mass transport of oxygen in the gas mixture to the sample surface showed good agreement with those measured experimentally, indicating that the initial period of oxidation is controlled by the mass transport of oxygen to the reaction interface. The linear rate constants showed little dependency on temperature, an activation energy of approximately 17kJ/mole being obtained. Measurements of sample surface temperatures have shown that within this linear-oxidation regime, interfacial temperatures of the samples increase with increasing oxygen contents in the gas mixture, owing to exothermic heats of oxidation. Subsequent oxidation kinetics were found to be parabolic. Measured parabolic rates constants were in good agreement with previous investigations, with activation energy values of approximately 127kJ/mole.
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  • 88
    ISSN: 1573-4889
    Keywords: ODS Alloy ; oxidation ; SIMS ; microstructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Alumina-forming ODS superalloys are excellent oxidation-resistant materials. Their resistance relies upon the establishment of a stable, slow-growing, and adherent α-alumina. In the present investigation, these alloys exhibited unstable and relatively less adherent θ-alumina phase, which increased the oxidation rate in the transient stage and converted into α-alumina in the later part of the exposure. The oxide-growth process was found to depend upon various parameters such as temperature, time, and presence of an active elecment in the superalloy. Characterization carried out by XRD, SEM/EDAX, and AES on oxidized ODS and non-ODS alloys demonstrated a significant influence of the active element, Y, on the transformation of θ- to α-alumina. SIMS analysis of two-stage oxidation at 900°C for two different durations evidently showed that the change in the transport process is due to θ-to-α-alumina transformation. On the basis of these results, a new and consistent mechanism is proposed to explain the influence of θ-alumina and its transformation on growth kinetics and the effect of yttrium on the transformation leading to good scale adherence and oxidation resistance.
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  • 89
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    Oxidation of metals 47 (1997), S. 21-52 
    ISSN: 1573-4889
    Keywords: copper ; silver ; high temperature ; oxidation ; two-phase alloys
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The corrosion of three two phase Cu-Ag alloys containing 25, 50, and 75 wt% Ag has been studied at 650 and 750°C. In all cases the alloys formed external scales of copper oxides. At the same time, an internal precipitation of Cu2O within a silver matrix was also produced, with an oxide volume fraction larger for the alloys richer in Cu. Beneath this mixed layer a region of single-phase solid solution of Cu in silver formed for Cu-50Ag and especially for Cu-75Ag. Silver metal remained in the metal-consumption zone, acting essentially as an inert marker, except for a few particles with were incorporated into the growing scales. Both pure Cu and the alloys corroded parabolically, but the rate constants for the alloys decreased with increased Ag content under constant temperature. The various aspects of the corrosion of these alloys are examined by taking into account the possible effects associated with the presence of two metal phases.
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  • 90
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    Oxidation of metals 47 (1997), S. 69-89 
    ISSN: 1573-4889
    Keywords: duplex-layer formation ; dynamic oxygen-diffusion path ; Ni-Cr alloy ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The results of an investigation of oxidation of a Ni-1 at.% Cr alloy are presented. Photolithographic marker experiments revealed that the markers were found to reside at the interface between a predominantly columnar outer NiO layer and a very fine grain inner layer of NiO, indicating that substantial oxygen ingress had occurred through the columnar scale. New oxide growth at the metal-oxide interface requires the oxidant to be transported across the oxide layer. Since the measured diffusion rate of oxygen ions along grain boundaries and through the lattice is much too slow to account for the observed microstructural growth (∼1: 1 ratio of inner and outer layers), it is necessary to postulate that the oxidant traverses the scale along some type of short-circuit path other than grain boundaries. Extensive formation of elongated pores and pipelike channels was observed along columnar oxide grain boundaries. Thus, it appears that the transport of oxygen occurs via voids (pores) formed by vacancy coalescence at the columnar grain boundaries. These pores appear to open and close continuously. Formation of new fine-grained oxide in these pores was observed to have sometimes completely resealed the void, suggesting a dynamic nature of the voids.
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  • 91
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    Oxidation of metals 47 (1997), S. 139-203 
    ISSN: 1573-4889
    Keywords: oxidation ; MoSi2 ; TiSi2 ; air ; oxygen ; O and Si transport in SiO2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation behavior of two MoSi2 variants, one Mo-rich and one Si-rich, and TiSi2 was investigated between 1000 and 1400°C in air, oxygen and an 80/20-Ar/O2 mixture. A protective SiO2 scale develops on MoSi2 in all atmospheres in the temperature range investigated. The SiO2 modification changes around 1300°C from tridymite to cristobalite. This change in SiO2 modification seems to cause an enhanced formation of SiO2 and evaporation of MoO3. The SiO2 grows at the MoSi2-scale interface. In air a two-layer scale grows on TiSi2 between about 1000 and 1200°C with an inner inwards growing fine-grain mixture of SiO2 + TiO2 and an outer outward-growing TiO2 partial layer. TiN formation in the transient oxidation is responsible for the formation of the inner mixed partial layer because in N -free atmospheres a scale of a SiO2 matrix with some Ti oxide precipitates inside is formed. A one-layer scale structure similar as that in N-free atmosphere is found on TiSi2 in air at T 〉 1200°C. In oxygen the TiO2 precipitates grow as needles mostly oriented perpendicular to the surface. Due to the faster oxygen transport in TiO2 compared with SiO2, these TiO2 needles act as “oxygen pipes,” causing an enhanced oxidation of TiSi2 in front of these needles. The SiO2 scale dissolves about 1–2% TiO2. This doping causes a mixed oxygenand Si transport with the consequence that the SiO2 scale on TiSi2 grows partly by oxygen transport inwards and Si transport outwards. The SiO2 modification is cristobalite over the entire temperature range investigated.
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  • 92
    ISSN: 1573-4889
    Keywords: high temperature ; oxidation ; binary alloys ; steady-state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The steady-state, high-temperature oxidation kinetics of single phase alloys rich in a most-reactive componentB in binaryA-B systems presenting a limited solubility of the two components (beta phase alloys) have been examined assuming the exclusive formation of the most-stable oxideBO v. Alloys sufficiently rich inB can form externalBO v scales directly in contact with the beta phase, while below a criticalB content the growth ofBO v involves also the appearance of an intermediate layer ofB-depleted solid solution ofB inA (alpha phase). The parabolic rate constants for the oxidation of single-phase beta alloys are lower than those of alloys of identicalB content which are single-phase over the whole range of composition (solid-solution alloys) but higher than for two-phase alpha + beta alloys under the same values of all the relevant parameters. Moreover, the tendency of single-phase beta alloys to form the most-stable oxide simultaneously as an external scale and internally to the alloy is greater than for solid-solution alloys but smaller than for two-phase alloys.
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  • 93
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    Oxidation of metals 47 (1997), S. 259-275 
    ISSN: 1573-4889
    Keywords: laser surface alloying ; aluminum ; superalloys ; oxidation ; microstructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The high-temperature oxidation resistance of laser-surface-alloyed Incoloy 800H with Al has been investigated. Several samples have been exposed to 1000°C in air and subsequently analyzed by optical microscopy, SEM, and electron microprobe X-ray fluorescence spectroscopy in order to determine their microstructure and composition. The results show that the laser-treated materials have a considerably higher oxidation resistance than the nontreated materials due to the formation of an Al-rich layer close to the surface, which acts as a barrier against oxygen diffusion into the bulk.
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  • 94
    ISSN: 1572-8978
    Keywords: Plasma polymers ; oxidation ; XPS ; photoelectron binding energy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The incorporation of oxygen into nitrogen-containing plasma deposited polymers was studied by X-ray Photoelectron Spectroscopy (XPS). As the oxygen content of the plasma polymer increased, the binding energy of the N 1s photoelectrons increased. Conversely, the binding energy of the O 1s photoelectrons was inversely proportional to the nitrogen content of the plasma polymer. The data from a large number of samples all obeyed the same “universal” correlations of photoelectron binding energy versus chemical composition. The data were described by the same curve regardless of whether the oxygen was incorporated rapidly into the thin film during plasma deposition or whether the oxygen was added slowly during spontaneous oxidation of the film in air. This implies that the same thermodynamic principles of radical reactions governed the addition of oxygen to the plasma polymer. The shift in the O 1s and N 1s photoelectron binding energies as a function of chemical composition was used to monitor the proximity of nitrogen and oxygen. By contrasting the experimental data with a simple binomial model which described the random addition of oxygen to a lattice containing carbon and nitrogen, we were able to show that oxygen was preferentially added near nitrogen-containing groups in plasma polymers.
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  • 95
    ISSN: 1572-9788
    Keywords: diversity ; genetic mapping ; Oryza sativa ; RAPDs ; rice ; inter-simple sequence repeats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Genetic variation between samples of Oryza sativa from 19 localities in Bangladesh and Bhutan was assessed using two PCR-based molecular marker systems: RAPD (random amplification of polymorphic DNA) and ISSR-PCR (inter-simple sequence repeat polymerase chain reaction). Employing RAPD, a set of 14 decanucleotides of arbitrary sequence directed the amplification of 94 reproducible marker bands, 47 (50%) of which were polymorphic. In addition, a set of 9 ISSR primers were used to direct amplification of 71 PCR products, 40 (56%) of which were polymorphic. Multivariate analyses of the two PCR-based molecular marker data sets provided evidence that the patterns of variation correspond with the classification described by Glaszmann [9] using isozyme analysis. Subtle differences in the relationships revealed between rice groups using the two types of PCR-based marker led to investigations of their map positions using an intraspecific doubled haploid mapping population. The observation that the chromosomal locations of markers can influence diversity assessments is presented and the significance of this is discussed.
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  • 96
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    Molecular breeding 5 (1999), S. 319-327 
    ISSN: 1572-9788
    Keywords: Cybrid ; cytoplasmic male sterility ; mitochondrial DNA ; protoplast fusion ; rice ; wild abortive cytoplasm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Wild abortive cytoplasmic male sterility has been extensively used in hybrid seed production in the tropics. Using protoplast fusion between cytoplasmic male sterile and fertile maintainer lines; we report here, transfer of wild abortive cytoplasmic male sterility to the nuclear background of RCPL1-2C, an advance breeding line which also served as maintainer of this cytoplasm. In total, 27 putative cybrids between V20A and RCPL1-2C and 23 lines between V20A and V20B were recovered and all of them were sterile. DNA blots prepared from the mitochondrial DNA of the cybrid lines from both the sets were probed with orf155 that is known to exhibit polymorphism between the mitochondrial DNA of the male-sterile and fertile maintainer lines. Hybridization of orf155 to 1.3 kb HindIII-digested mitochondrial DNA fragment of the cybrids showed transfer of mitochondrial DNA from wild abortive cytoplasmic male-sterile line to the maintainers, viz. RCPL 1-2C and V20B. Expression of male sterility was confirmed by the presence of sterile pollen grains and the lack of seed setting due to selfing in all the cybrid lines. These cybrids, on crossing with respective fertile maintainers set seeds that in turn, produced sterile BC1 plants. DNA blots from HindIII-digested mitochondrial DNA of these BC1 plants when probed with orf155 again exhibited localization of orf155 in wild abortive cytoplasm-specific 1.3 kb HindIII-digested mitochondrial DNA fragments. This demonstrated that the cytoplasmic male sterility transferred through protoplast fusion retained intact female fertility and was inherited and expressed in BC1 plants. Fusion-derived CMS lines, on pollination with pollen grains from restorer, showed restoration of fertility in all the lines. The results demonstrate that protoplasts fusion can be used for transferring maternally inherited traits like cytoplasmic male sterility to the desired nuclear background which can, in turn, be used in hybrid seed production programme of rice in the tropical world.
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  • 97
    ISSN: 1572-9788
    Keywords: physical mapping ; rice ; YAC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Genomic libraries of rice,Oryza sativa L. cv. Nipponbare, in yeast artificial chromosomes were prepared for construction of a rice physical map. High-molecular-weight genomic DNA was extracted from cultured suspension cells embedded in agarose plugs. After size fractionation of theEco RI- andNot I-digested DNA fragments, they were ligated with pYAC4 and pYAC55, respectively, and used to transformSaccharomyces cerevisiae AB1380. A total of 6932 clones were obtained containing on average ca. 350 kb DNA. The YAC library was estimated to contain six haploid genome equivalents. The YACs were examined for their chimerism by mapping both ends on an RFLP linkage map. Most YACs withEco RI fragments below 400 kb were intact colinear clones. About 40% of clones were chimeric. Genetic mapping of end clones from large size YACs revealed that the physical distance corresponding to 1 cM genetic distance varies from 120 to 1000 kb, depending on the chromosome region. To select and order YAC clones for making contig maps, high-density colony hybridization using ECL was applied. With several probes, at least one and at most ten YAC clones could be selected in this library. The library size and clone insert size indicate that this YAC library is suitable for physical map construction and map-based cloning.
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  • 98
    ISSN: 1572-9788
    Keywords: Bacillus thuringiensis ; Chilo suppressalis ; biolistic ; rice ; Scirpophaga incertulas ; transformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Rice cultivars of isozyme group V include high-quality, aromatic rices that are difficult to improve by traditional methods because of the loss of quality characters upon sexual hybridization. Their low-tillering plant type predisposes them to economic loss from attack by stem borers, a group of insects to which they are susceptible. We report here the enhancement of stem borer resistance in cv. Tarom Molaii through transformation by microprojectile bombardment. Embryogenic calli derived from mature seeds were bombarded with gold particles coated with plasmid pCIB4421, carrying a synthetic truncated toxin gene based on the cryIA(b) gene from Bacillus thuringiensis, and plasmid pHygII, carrying the hygromycin phosphotransferase (hpt) selectable marker gene. Inclusion of 50 mg/l hygromycin B in culture media from bombardment through to rooting of plantlets eliminated escapes. The procedure generated three independent hpt transformants of which two also contained the cryIA(b) gene. One such line (No. 827) produced truncated (67 kDa) CryIA(b) protein equivalent to about 0.1% of total soluble protein. The cryIA(b) gene was controlled by the promoter of the maize C4 PEP carboxylase gene and was expressed in leaf blades but was not expressed to a detectable level in dehulled mature grain. Line 827 contained about 3 copies of the cryIA(b) gene which segregated as a single dominant Mendelian locus in the second (T1) and third (T2) generations and co-segregated with enhanced resistance to first-instar larvae of striped stem borer (Chilo suppressalis) and yellow stem borer (Scirpophaga incertulas). T2 line 827-6 homozygous for the cryIA(b) gene showed no dead hearts or whiteheads after infestation with stem borers, whereas T2 line 827-25 lacking the gene averaged 7 dead hearts per plant and 2.25 whiteheads per plant. These results establish that transformation of high-quality rices of group V is a feasible alternative to sexual hybridization.
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  • 99
    ISSN: 1573-5036
    Keywords: Bradyrhizobium japonicum ; ecology ; N2-fixation ; nodulation ; rice ; soybean
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effect of rice culture on changes in the number of a strain of soybean root-nodule bacteria, (Bradyrhizobium japonicum CB1809), already established in the soil by growing inoculated soybean crops, was investigated in transitional red-brown earth soils at two sites in south-western New South Wales. At the first site, 5.5 years elapsed between the harvest of the last of four successive crops of soybean and the sowing of the next. In this period three crops of rice and one crop of triticale were sown and in the intervals between these crops, and after the crop of triticale, the land was fallowed. Before sowing the first rice crop, the number of Bradyrhizobium japonicum was 1.32×105 g−1 soil. The respective numbers of bradyrhizobia after the first, second and third rice crops were 4.52 ×104, 1.26×104 and 6.40×102 g−1 soil. In the following two years the population remained constant. Thus sufficient bradyrhizobia survived in soil to nodulate and allow N2-fixation by the succeeding soybean crop. At the second site, numbers of bradyrhizobia declined during a rice crop, but the decline was less than when the soil was fallowed (400-fold cf. 2200-fold). Multiplication of bradyrhizobia was rapid in the rhizosphere of soybean seedlings sown without inoculation in the rice bays. At 16 days after sowing, their numbers were not significantly different (p〈0.05) from those in plots where rice had not been sown. Nodulation of soybeans was greatest in plots where rice had not been grown, but yield and grain nitrogen were not significantly different (p〈0.05). Our results indicate that flooding soil has a deleterious effect on the survival of bradyrhizobia but, under the conditions of the experiments, sufficient B. japonicum strain CB 1809 survived to provide good nodulation after three crops of rice covering a total period of 5.5 years between crops of soybean.
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  • 100
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    Plant and soil 189 (1997), S. 145-153 
    ISSN: 1573-5036
    Keywords: coleoptile ; cultivar ; direct sowing ; flooded soil ; rice ; seedling establishment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Seedling establishment of direct sown rice plants is less successful in flooded soil than in drained soil. This study was conducted to clarify the difference in morphogenesis of rice seeds sown in flooded and drained soils and to identify the morphological characteristics responsible for successful establishment of cultivars in flooded soil. Rice cultivars ASD1 and IR41996–50–2–1–3, superior in seedling establishment in flooded soil, and Mahsuri and IR72, non-superior (control), were sown at a depth of 25 mm in soil flooded with 25 mm of water or in drained soil. The coleoptile and 1st leaf emerged from the soil surface simultaneously in drained soil while in flooded soil the coleoptile emerged first. The coleoptile of superior cultivars, unlike the controls, elongated more in flooded soil than in drained soil. In flooded soil, the development of mesocotyl, 1st leaf, and roots were inhibited to a greater extent in the controls, than in the superior cultivars. In sealed flasks in which gas containing 0–21% O2 was exchanged daily, the superior cultivars developed longer coleoptiles than the controls at lower O2 concentrations. These findings suggest that the reason superior cultivars grow better in flooded soil than the controls is that the coleoptile elongates faster and longer in hypoxia and is able to reach the soil surface where O2 is available.
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