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  • 11
    Publication Date: 1966-08-01
    Print ISSN: 0044-2313
    Electronic ISSN: 1521-3749
    Topics: Chemistry and Pharmacology
    Published by Wiley
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Naturwissenschaften 74 (1987), S. 63-70 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 13
    ISSN: 1432-0789
    Keywords: Dehydrogenase activity ; Soil microbial activity ; Triphenyltetrazolium chloride (TTC) ; Iodonitrotetrazolium chloride (INT) ; Incubation conditions ; Extraction procedure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The triphenyltetrazolium chloride (TTC) method described by Thalmann (1968) and the iodonitrotetrazolium chloride (INT) method described by Spothelfer-Magaña and Thalmann (1992), used for measuring soil dehydrogenase activity, have been modified to overcome some methodical short-comings. Absorption maxima of 485 nm for triphenylformazan dissolved in acetone, 491 nm for iodonitrotetrazolium formazan (INTF) dissolved in tetrahydrofuran and 455 nm for INTF dissolved in N,N-dimethylformamide are recommended for measuring wavelengths. Extracting triphenylformazan twice with acetone is less toxic and proved to be at least as efficient as extraction with a mixture of 90% acetone and 10% carbon tetrachloride (Thalmann 1968 method). Tetrahydrofuran and dimethylformamide were equally good in extracting INTF from soils, but the former was less toxic. Anaerobic incubation resulted in the formation of higher amounts of triphenylformazan and INTF as well as reduced standard error. Both TTC and INT reduction showed high reproducibility and good differentiation of the microbial activity of six soils. For several reasons (more easily determined substrate dose depending on different soil types, better reduction, shorter incubation time), INT reduction seems to be a more suitable method of measuring soil microbial activity than TTC reduction.
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  • 14
    Electronic Resource
    Electronic Resource
    Springer
    Naturwissenschaften 60 (1973), S. 298-298 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 143 (1992), S. 55-60 
    ISSN: 1573-5036
    Keywords: oxidizing power ; platinum microelectrode ; rice ; rhizosphere ; soil reducing capacity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Redox potentials in microsites of the rhizosphere of flooded rice were continuously measured for several days. Close to the root tips redox potential markedly increased. The highest increase was measured in the rhizosphere of the tips of short lateral roots. Aerobic redox conditions were reached there, except in a very strongly reduced soil. Both the extension of the oxidation zone around the root tips and the maximum redox potential reached were influenced by the reducing capacity of the soil. The radius of the redox rhizosphere varied from less than 1 mm in a strongly reduced soil up to 4 mm in a weakly reduced one. The root-induced oxidation processes in the rhizosphere depended on the atmospheric oxygen supply to the roots.
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  • 16
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: With the aid of a voltage diagram, definite ranges of potential differences can be determined each of them characterising special corrosion conditions for this metal. Above the minimum corrosion potential, titanium can be rendered chemically inactive by coating with a layer of titanium-hydride (hydride-passive condition). This condition is reached normally in the presence of strong cathodic polarisation only. Exceeding a critical potential difference, the metal becomes chemically active. Corrosion and hydrogen generation take place (normal corrosion in non-oxidising acids). Exceeding the critical P.D for passivity the metal is covered with an oxide layer which again renders it inactive, (oxide-passive condition). This is the condition responsible for the excellent corrosion-resisting properties of titanium in oxidising media. With relatively high potential differences which occur only by anodic polarisation and not in oxidising media, activation is again encountered in halogenide solutions(trans-passive condition). Titanium is attacked in the forms of scars. In solutions free from halides there is no corrosion at strong anodic polarisations. The different corrosion conditions on titanium in various ranges of P.D. are explained by characteristic examples.
    Notes: Es lassen sich für Titan verschiedene Potentialbereiche an Hand eines Strom-Spannungsdiagramms festlegen, innerhalb derer ein für das Metall jeweils charakteristisches Korrosionsverhalten besteht. Oberhalb des Immunitätspotentials wird Titan durch Bedeckung mit einer Titanhydridschicht passiv (hydrid passiver Zustand). Der hydridpassive Zustand wird normalerweise nur bei starker kathodischer Polarisation erreicht. Bei Überschreiten eines kritischen Potentials wird das Metall aktiv. Es tritt Korrosion unter Wasserstoffentwicklung ein (normale Korrosion in nichtoxydierenden Säuren). Bei Überschreiten des kritischen Passivierungspotentials wird das Metall von einer Oxydschicht bedeckt und dadurch erneut passiv (oxydpassiver Zustand). Der oxydpassive Zustand ist für die ausgezeichnete Korrosionsbeständigkeit des Titans gegenüber oxydierenden Medien verantwortlich. Bei relativ hohen Potentialen, die nur durch anodische Polarisation, nicht hingegen durch Oxydationsmittel erreicht werden, tritt in halogenidhaltigen Lösungen erneut Aktivierung ein (transpassiver Zustand). Titan wird narbenförmig angegriffen. In halogenidfreien Lösungen dagegen tritt bei starker anodischer Polarisation keine Korrosion ein. An Hand einer Reihe von charakteristischen Beispielen wird das unterschiedliche Korrosionsverhalten des Titans in den verschiedenen Potentialbereichen erklärt.
    Additional Material: 4 Ill.
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  • 17
    Electronic Resource
    Electronic Resource
    Weinheim [u.a.] : Wiley-Blackwell
    Materials and Corrosion/Werkstoffe und Korrosion 45 (1994), S. 654-662 
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Charakterisierung von in wäßrigen chlorid- und sulfathaltigen Elektrolyten gebildeten Reaktionsschichten auf KupferKupfer ist in einem Potentialbereich von 50 mVH bis etwa 300 mVH durch Ausbildung einer dünnen Deckschicht aus Kupfer(I)-Korrosionsprodukten passiv. Diese Schicht hemmt die anodische mehr als die kathodische Teilreaktion der Korrosion. Der steile anodische Durchbruch im transpassiven Bereich führt zur Oxidation von Kupfer und der Bildung sekundär gefällter Deckschichten.In sulfathaltigen Elektrolyten entstehen voluminöße Deckschichten aus kristallinem Kupfer(I)-oxid, die keine korrosionsschützende Wirkung haben. Als Folge wird flächenmäßiger Abtrag beobachtet. In chloridhaltigen Elektrolyten bildet sich eine zweilagige Deckschicht aus. Dem Durchbruch vorgelagert ist die Bildung von Kupfer(I)-chlorid. Durch dessen Protolyse entstehende filmartige Kupfer(I)-oxid-Schichten hemmen die anodische Metallauflösung, ein gleichförmiger Flächenangriff wird unterbunden und repassivierender Lochfraß tritt auf.
    Notes: Copper is in a passive state in a potential range of 50 mVH to about 300 mVH in contact with an aqueous electrolyte at neutral pH caused by the formation of a thin tarnishing layer consisting of copper(I)-corrosion products. This layer inhibits more the anodic than the cathodic partial reaction of the corrosion process. The steep threshold in the transpassive range leads to the oxidation of copper and the formation of secondarily formed reaction layers.In sulphate containing electrolytes voluminous reaction layers of crystalline non-protective copper(I)-oxide are formed. The manifestation of corrosion is general attack. In chloride containing electrolytes a two-fold reaction layer is formed, copper(I)-chloride underneath copper(I)-oxide. This amorphous copper(I)-oxide is formed via hydrolysis of copper(I)-chloride and inhibits anodic metal dissolution. The only observed manifestation of corrosion is repassivating pitting.
    Additional Material: 18 Ill.
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  • 18
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: The influence of extra-cellular polymeric substances in microbiologically influenced corrosionUnexpected pitting failures in copper potable water installations have occurred in some countries (Germany, Sweden, Scotland, South-West England, Saudi-Arabia) in the mid-eighties. These failures could not be expected in a single case based on the chemical composition of the potable water. Further typical manifestation characteristics of this microbiologically influenced corrosion have been i.) an uptake of dissolved and undissolved copper species in an obsolete, non regular fashion, ii.) black layers of copper(II)-oxide on the inner tube surface, accompanied by posniakite and malachite in the pitting areas, and, iii.) the detection of extracellular polymeric substances (EPS). These EPS consist partly of polysaccharides. They could either be produced by microorganisms within the potable water installation or be transported in a dissolved or undissolved state into the installation. Consequently, they sediment on the inner surfaces of the copper tubes. The physico-chemical properties of some kinds of EPS, especially their membrane properties and their cation selectivity, play a key role in this corrosion process. This is shown exemplarily performing diffusion potential measurements and contact corrosion experiments.
    Notes: In der Mitte der achtziger Jahre traten in einigen Ländern (Deutschland, Schweden, Schottland, Süd-West England, Saudi-Arabien) unerwartete Lochfraßschäden an Trinkwasser-Installationen aus Kupfer auf. Die Zusammensetzung der Trinkwässer ließ in keinem Fall solche Schäden erwarten. Als typische Merkmale einer mikrobiologisch beeinflußten Korrosion war neben den Perforationen der Rohre sporadisch eine hohe Konzentration von Kupferkorrosionsprodukten in gelöster und ungelöster Form im Trinkwasser zu finden, außerdem schwarze Schichten aus Kupfer(II)-oxid auf der Rohrinnenoberfläche mit Pusteln aus Posnjakit oder Malachit im Lochfraßbereich sowie das Auftreten extrazellulärer polymerer Substanzen (EPS). Die EPS, die zu einem wesentlichen Teil aus Polysacchariden bestehen, müssen nicht notwendigerweise innerhalb der Installation durch Mikroorganismen produziert, sondern können auch in gelöster oder ungelöster Form mit dem Trinkwasser in die Installation transportiert werden, wo sie sich während der Stagnationsphasen auf den Rohrinnenoberflächen absetzen. Den physikochemischen Eigenschaften einiger Arten der EPS, insbesondere den Membraneigenschaften und der Kationenselektivität kommt in diesem Korrosionsprozeß eine Schlüsselrolle zu. Das wird exemplarisch anhand von Diffusionspotentialmessungen und Kontaktelementmessungen belegt.
    Additional Material: 7 Ill.
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  • 19
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: The influence of alloying admixtures on the corrosion behaviour of titaniumMeasurements of potentials on welded titanium and titanium oxygen alloys have shown that, with increasing oxygen content of the weld or alloy, the potential is shifted to the electropositive side provided that the oxygen content does not exceed 0.6 per cent. This does not affect the corrosion rate of the titanium oxygen alloys. With higher oxygen contents, however, corrosion in boiling 2½ pC. sulphuric acid is increased. But as such corrosion is, in any case, already high, this fact is, in practice, without interest. Conditions are similar with titanium nitrogen alloys. The higher degree of corrosion here encountered with welded specimens could be ascribed to the effect of heat treatment which causes an inadmissibly high degree of corrosion even with non-welded specimens. Oxidizing solutions do not even attack titanium weld joints. By adding 0.2 pC or more Pd, the corrosion resistance in non-oxidizing media can be improved. With the aid of potential measurements and current potential curves, the corrosion behaviour of Ti Pd alloys is explained.
    Notes: Potentialmessungen an geschweißtem Titan und an Titan-sauerstoff-Legierungen zeigten mit zunehmendem Sauerstoffgehalt der Schweiße bzw. der Legierung eine Potentialveredlung, wenn der Sauerstoffgehalt 0,6% nicht übersteigt. Die Korrosionsgeschwindigkeit der Titan-Sauerstoff-Legierungen ändert sich hierdurch nicht. Höhere Sauerstoffgehalte dagegen bewirken i siedender 2,5%iger Schwefelsäure eine verstärkte Korrosion. Dies ist allerdings in Anbetracht des an sich schon hohen Angriffs für die Praxis ohne belang. Ähnlich liegen die Verhältnisse bei Titan-Stickstoff-Legierungen. Die auftretende verstärkte Korrosion bei geschweißten Proben konnte auf einen Einfluß der Wärmebehandlung zurückgeführt werden, die auch bei ungeschweißten Proben einen unzulässig starken Angriff hervorrufen. Oxydierende Lösungen greifen auch Titan-Schweißnähte nicht an. Durch einen Zusatz von 0,2% und mehr Pd kann die Korrosionsbeständigkeit in nicht oxydierenden Medien verbessert werden. An Hand von Potentialmessungen und Stromspannungskurven wird das Korrosionsverhalten der TiPd-Legierungen erklärt.
    Additional Material: 15 Ill.
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  • 20
    Electronic Resource
    Electronic Resource
    Weinheim [u.a.] : Wiley-Blackwell
    Materials and Corrosion/Werkstoffe und Korrosion 17 (1966), S. 477-485 
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Anodic protection through local cathodesIf passivation-prone metals are brought into contact with local cathodes, it is possible to achieve an anodic passivation protection if the critical density of the passivating current is produced by the accelerated cathode process (e.g., accelerated reduction of H+ ions as a result of a reduction of the hydrogen over-potential). Particularly suitable local cathodes are the platinum metals but also carbon and semi-conducting oxides. Generally, small quantities of these are already sufficient. The cathodically acting components may be alloyed with the metal to be protected. But they may also be brought into contact with the metal surface from outside. Finally, it is also possible to add ions of electropositive metals to the corrosive agent. In this case, such ions initially act, because of their high redox potential, as oxidants and settle down on the surface after reduction so that the local cathode effect can commence. Anodic protection can also be obtained by contact with oxidant solids, e.g. manganese oxide. Particularly well suited metals or alloys are the stainless steels and titanium, but also lead.
    Notes: Durch Kontakt von passivierbaren Metallen mit Lokalkathoden kann ein anodischer Passivschutz erreicht werden, wenn die kritische Passivierungsstromdichte durch den beschleunigten Kathodenvorgang (z.B. beschleunigte Reduktion von H+-Ionen als Folge der Senkung der Wasserstoffüberspannung) aufgebracht wird. Geeignete Lokalkathoden sind besonders die Platinmetalle, aber auch Kohlenstoff und halbleitende Oxide. Es reichen meistens schon kleine Mengen hiervon aus. Die kathodisch wirksamen Komponenten können dem zu schützenden Metall zulegiert werden. Sie können aber auch von außen mit der Metalloberfläche in Kontakt gebracht werden. Schließlich ist auch ein Zusatz von Edelmetallionen zu dem Angriffsmittel möglich. In diesem Fall wirken die Edelmetallionen wegen ihres hohen Redoxpotentials zunächst oxydierend und schlagen sich nach Reduktion oberflächlich nieder, so daß die Lokalkathodenwirkung einsetzen kann. Auch eine Kontaktierung mit oxydierend wirkenden Feststoffen wie z.B. Mangandioxid, bewirkt einen anodischen Schutz. Besonders für den anodischen Schutz geeignete Metalle bzw. Legierungen sind die nichtrostenden Stähle und Titan, aber auch Blei.
    Additional Material: 15 Ill.
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