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  • 1
    ISSN: 1573-4870
    Keywords: Thermal treatment ; leaching ; alumina ; silica ; chemical enrichment
    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 a study of the complex treatment of alumina–silica-containing materials (fly ash, low-duality bauxites, clays, kaolins, nephelines) by chemical enrichment are presented. The de-siliconization of aluminum-containing raw materials with a high silica content is based on the property of hydroaluminum silicates (which are basic silica-containing minerals) to undergo intramolecular phase changes by thermal treatment, resulting in the formation of amorphous alkali-soluble silica. Dissolution of silica is effected by leaching the heat-treated raw material with sodium hydroxide solution, whereby the alumina remains in the solid state in the form of γ-Al2O3, or α-Al2O3. The use of chemical enrichment methods enables reduction of the silica content in the raw material and utilization of the resulting material for alumina production. The effectiveness of the chemical enrichment of alumina–silica-containing material depends in large measure on the possibility of the complete and economic utilization of all valuable components of the raw material. The possible methods of utilizing silica solutions for the production of valuable materials and methods of regenerating alkali from the silica solution are also considered.
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  • 2
    ISSN: 1573-4870
    Keywords: Chemical vapor deposition ; titanium disilicide ; titanium tetrachloride ; titanium tetrabromide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Titanium silicide thin films were formed on Si substrate by reaction of TiX 4 (X=C1, Br) with Si under different experimental conditions. The Si consumption and titanium silicide obtained were calculated by the film thickness. In some reactions, titanium silicide thin film was found not only on the Si substrates but also on the SiO2 wall at the outlet of the reaction chamber. The quantity of Si consumption and the quantity of silicon-containing materials obtained on the wall of the deposition chamber varied as the reaction conditions changed. The minimum Si consumption and maximum titanium silicide obtained on silicon were the most favorable result, found in the reaction of TiBr4 with Si at 1000°C. The metallization reactions were studied in detail and the reaction pathway is proposed.
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  • 3
    ISSN: 1573-4870
    Keywords: Squeeze casting ; solidification ; Al alloy ; microstructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A 7050 (Al–6.2 wt% Zn–2.3 wt% Cu–2.3 wt% Mg) Al alloy, conventionally used for wrought products, has been successfully cast to near-net shape using direct squeeze casting. Squeeze casting with an applied pressure of 50 MPa removes the defects observed in gravity die cast billets, in particular, (1) shrinkage pipe, (2) poor die replication and waisting, and (3) microporosity. Squeeze casting results in considerable refinement of the microstructure due to an increase in cooling rate from ∼0.5°C s−1 for gravity casting to ∼11°C s−1 for squeeze casting in a tool steel die lined with porous insulation, and from ∼2.5 to ∼10°C s−1, respectively, in an uninsulated die. A normal segregation pattern of increasing eutectic toward the center of the billet is found for squeeze casting, compared to an inverse segregation pattern of increasing eutectic toward the edge of the billet for gravity casting. This change in segregation pattern is due to a higher radial temperature gradient and reduced time in the semisolid state for squeeze casting.
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  • 4
    ISSN: 1573-4870
    Keywords: Attrition milling ; processing ; cordierite ; electronic substrates
    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 cordierite powder was selected to study the particle size reduction under several attrition milling conditions. The influence of milling parameters such as the rotor speed, solid loading, and milling time on the attrition milling process was studied in terms of the particle size distributions, mean diameters, specific surface areas, and media wear contamination of the milled powders.
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  • 5
    ISSN: 1573-4870
    Keywords: Alumina ; surface ; kinetics ; diffusion ; SALK
    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 of shape evolution of a completely faceted crystal/internal void by surface diffusion was modeled. Arrays of micron-sized cavities were generated in sapphire substrates with known surface orientations using microlithography and ion beam etching and converted to internal intragranular pores of nonequilibrium shape by diffusion bonding of the etched substrate to an identical-orientation unetched sapphire substrate. Pore shape evolution rates during high-temperature anneals were monitored and found to be highly sensitive to the orientation of the substrate surface. The observed evolution rates were compared with the predictions of the kinetic model using diffusivity values for alumina that span the range from the highest to the lowest diffusion constants reported in the literature. The comparison suggests that surface-attachment-limited kinetics (SALK) play a major role in surface mass transport on stable low-index planes of alumina.
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  • 6
    ISSN: 1573-4870
    Keywords: CeO2–Sm2O3 ; alkali element ; calcia ; oxide ionic conductivity ; solid oxide fuel cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Ceria–samaria (CeO2–Sm2O3) is one of the most interesting fluorite oxides since its ionic conductivity is higher than that of yttria-stabilized zirconia in air. However, these CeO2 -based oxides are partially reduced and develop electronic conductivity under fuel cell operating conditions. In their application to the SOFC system, their current densities and power densities are not at a satisfactory level. For the development of high-performance CeO2 electrolytes, it is important that the fluorite lattice of CeO2-based oxide be improved from the viewpoint of crystallography. In this study, it is assumed that the reduction of Ce4+ in the fluorite lattice was inhibited by expansion of the CeO2 lattice. In order to investigate the contribution of the expanded CeO2 lattice to reduction resistance, CeO2–Sm2O3 solid solution, calcia-doped CeO2–Sm2O3 solid solution, and a small amount of alkali element-doped CeO2–Sm2O3 -based oxide were prepared for comparison. It was found that the calcia or a small amount of alkali element-doped CeO2 solid solution enhanced the oxide ionic conductivity. The power density of the latter showed a high value at 800°C. It is concluded that the improved fuel cell performance can be attributed to the good reduction resistance in the fuel cell atmosphere.
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  • 7
    ISSN: 1573-4870
    Keywords: Lithium antimony oxide ; chemical bath deposition ; thermal decomposition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Well-crystallized LiSb(OH)6 powders with a hexagonal structure were prepared by chemical bath deposition. The thermal decomposition of as-prepared samples was examined. In order to obtain LiSb(OH)6 powders, it was essential to use tartaric acid as a stabilizing agent for antimony ion and to add LiOH above pH 9 into the precursor solution. The crystal structure of the samples obtained was of hexagonal phase. The increase in pH value and keeping temperature indicated that the shape of samples changed from granule particles to plate-like particles. The granule particles heated at 800°C consisted of orthorhombic LiSbO3. However, the plate-like particles resulted in the coexistence of both orthorhombic LiSbO3 and tetragonal Li3SbO4
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  • 8
    ISSN: 1573-4870
    Keywords: Mullite–zirconia composite powder ; preparation ; ultrasonic spray pyrolysis technique ; sintering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Sinterabilities of mullite (3Al2O3·2SiO2–zirconia (ZrO2)composite powders prepared by ultrasonic spray pyrolysis techniques (USPTs) were examined. Starting mullite powders containing ∼18.5 mol% (∼15.0 vol%) of zirconia (ZrO2) were prepared by single-nozzle (SN) and double-nozzle (DN) USPT. In SN-USPT, the composite powder was prepared by spray pyrolysis of a water–ethanol solution in an Al(NO3)3–Si(OC2H5)4–ZrOCl2–YCl3 system at 900°C, using one ultrasonic vibrator. In DN-USPT, the composite powder was prepared by simultaneous spray pyrolyses of a water–ethanol solution in an Al(NO3)3–Si(OC2H5)4 system and one in a ZrOCl2–YCl3 system at 900°C, using two ultrasonic vibrators. When these composite compacts were fired at a temperature between 1400 and 1700°C for 5 h, the relative densities attained maxima, i.e., 87.2% (SN-USPT) and 95.5% (DN-USPT), at the firing temperature of 1500°C. Densification of the DN-USPT-derived powder compact proceeded more markedly than that of the SN-USPT-derived powder compact.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-4870
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 10
    ISSN: 1573-4870
    Keywords: Hollandite-type catalyst ; photo-oxidation ; photo-reduction ; trichloro ethylene ; nitrate ion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The photocatalytic activity of new hollandite compounds was investigated for the oxidative decomposition of trichloro ethylene (ClHC=CCl2) and the selecive reduction of nitrate ion (NO 3 - ) with methanol in water under UV irradiation. The ClHC=CCl2 and the NO 3 - in water are hazardous chemicals to humans. Social interest is put on the development of effective processes to remove these nuisances. The hollandite compounds have a one-dimensional tunnel structure and are well known as alkali ion conductors. In this study, their distinctive catalytic properties in gas phase under heating were applied to photocatalytic reactions. The hollandite catalysts which were prepared by the powder mixing method or sol-gel method had activities for the oxidation of ClHC=CCl2 and the selective reduction of NO 3 - with methanol in water under UV irradiation. The selective reduction of NO 3 - with a reducing agent in the presence of dissolved oxygen in water would be the new way which has not been reported for ordinary photocatalysts such as titanium dioxide (TiO2). Therefore, it was expected that this type of compound had a possibility as a new type of photocatalyst.
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