ISSN:0947-5117    

DOI:10.1002/maco.19800310502

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

摘要:

AbstractDepending on etching, iron in chloride or sulphate solutions and in some degree copper in perchlorate solution can be made to follow one or the other of two clearly different dissolution behaviours. This is attributed to the establishment of two alternative states of the metal surface. For both metals the transitions (at constant potential) between the two states can be followed by means of cd‐time curves, and one of these transitions can be described in terms of the Avrami equation. The rates of the transitions are dependant on potential and on the composition of the electrolyte solution, but because of the great number of details influencing these phenomena a complete interpretation is not yet available. However, sources of some experimental errors are discussed in detail, and for iron electrodes it is shown that other fundamental phenomena than the relaxation of pit shape must be assumed as the basis of the transition

ISSN:0947-5117    

DOI:10.1002/maco.19800310503

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

摘要:

AbstractIn Form eines Überblicks wird das Problem der selektiven Auflösung unedler Legierungskomponenten erörtert. Am Beispiel der Korrosion edelmetallhaltiger Legierungen werden dabei charakteristische Stromspannungskurven besprochen und die derzeit diskutierten Mechanismen der selektiven Korrosion homogener Legierungen vorgestellt. Der kritische Vergleich verschiedener experimenteller Ergebnisse ergibt einige Gesichtspunkte, die für das Vorherrschen eines Oberflächendiffusionsmechanismus sprechen. Ein unlängst unternommener Versuch zur Berechnung der anodischen Stromspannungskurven edelmetallhaltiger Legierungen wird erl

ISSN:0947-5117    

DOI:10.1002/maco.19800310504

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

摘要:

AbstractThe formation of Fe2+‐ions is studied in 0.5 M H2SO4and 1 M HClO4during changes of the potential of passivated iron specimen with the rotating‐ring‐disk technique. An Fe2+‐pulse is found during the decrease of the electrode potential serving as an indicator for the short exposure of small areas of bare metal to the electrolyte. In the presence of aggressive anions the repassivation of these defects is prevented leading to the formation of pits. The increase of the pit nucleation after potential changes coincides qualitatively with the occurrence of the Fe2+transients. The adsorption mechanism may be excluded for these conditions because it postulates the action of aggressive anions for the very beginning of the breakdown

ISSN:0947-5117    

DOI:10.1002/maco.19800310505

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

摘要:

AbstractThe polarization behaviour of iron in perchlorate, chloride and sulphate base electrolytes at pH values ranging from 0.3 ≤ pH ≤ 3.5 was found to be changed drastically by the addition of small amounts of the heavy metal ions Mez+= Pb2+, Tl+to the electrolyte solutions. At potentials positive to the corresponding Me/Mez+‐electrode a strong inhibition of the active iron dissolution process as well as the charge transfer controlled hydrogen evolution was observed. This effect can be explained by an underpotential deposition of Mez+leading to a complete coverage of Me‐adsorbate on the iron surface. In deaerated solution an inhibition factor of 98% can be obtained, whereas in aerated solutions especially under rotating conditions the corrosion rate was not decreased. In the latter case the corrosion process is dominantly determined by the limiting diffusion controlled oxygen reduction reaction which was found to be not markedly inhibited by the metal adsorbates. In acid chloride solutions a competetive adsorption of Cl−must be taken int

ISSN:0947-5117    

DOI:10.1002/maco.19800310506

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

摘要:

AbstractThe coulostatic method avoids some of the essential short‐comings of the polarization resistance method; in particular, it enables the time to be reduced because in most cases it is sufficient to follow potential decay down to 50% of the original value (this requires less than 0.1 sec). Experiments in 1 n sulfuric acid (with iron) in deionized water, in aerated and deaerated 0.1 m sodium chloride solutions and in an aerated solution containing 0.05 m NaCl + 0.1 m sodium hydrogen carbonate + 0.03 m sodium sulfate (with steel) yield corrosion losses which are well reproducible with the results of other methods, even when surface layers are formed on the metals. Tests with steel 304 in ferric chloride solution and (under crevice corrosion conditions) with steel 403 in 5% NaCl‐solution show that the coulostatic method yields reproducible results even in the case of local corrosion with very small amounts of corrosion products being formed. Reliable results are obtained under the conditions of subsurface corrosion, too, so that a rapid screaming of the protective value of various coatings systems becomes feasi

ISSN:0947-5117    

DOI:10.1002/maco.19800310507

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

摘要:

AbstractSulfidation appears to be considerably more suitable than oxidation for studying the high‐temperature behaviour of metals. Sulfide scales are formed at considerably higher rates and at lower temperatures, in addition it is much easier to work with the radioactive sulfide isotope. The experiments can be conducted in sulfur vapour or in hydrogen/hydrogen sulfide mixtures; differences are due only to different sulfur partial pressures. Sulfide scale is formed on pure metals (e. g. Cu, Ag, Ni) as well as in binary or ternary alloys. (e. g. FeNi, NiCr, CuZn, CoCr, FeCrAl) with consistantly reproducible results. Irrespective of scale thickness and structure the reaction rates are always controlled by outward diffusion with the high defect concentration favouring high reaction rates. Since various metals tend to form low melting metal/metal sulfide eutectics, it is necessary to keep temperatures below the particular melting point. Contrary to inner oxidation there is no inner sulfidation. The protective action of sulfide scale is considerably inferior to that of oxide scale. According to the results of the present compilation no material has become available which combines sufficient scaling resistance with good high‐temperature mechanical properties. Solution of this problem may perhaps be found by adding rare earth met

ISSN:0947-5117    

DOI:10.1002/maco.19800310508

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

摘要:

AbstractIn der Praxis entstehen bei rostfreien Stählen, die in chloridhaltigem Wasser eingesetzt werden, immer wieder Schäden durch Spaltkorrosion. Es wurden Korrosionsversuche in einem Spaltmodell mit dem Stahl AISI 304 L angestellt und die Zusammensetzung des Spaltelektrolyten bestimmt. Anhand potentiostatischer Langzeitversuche in Natriumchloridlösungen verschiedener Konzentration und Temperatur wurden in einer Spaltkorrosionszelle die kritischen Potentiale für Spaltkorrosion (US) folgender Stähle bestimmt: 22 CrMo V 121, X 22 CrNi 17 und AISI 304 L.Analog zu den kritischen Potentialen für Lochkorrosion (UL) zeigte USeine starke Abhängigkeit vom Chloridgehalt der Außenlösung. Bei hohen Konzentrationen lagen beide Potentiale nahe beisammen, bei tiefen Chloridkonzentrationen war UStiefer als UL. Die Kenntnis der kritischen Potentiale erlaubt, bei bekanntem Ruhepotential UReines Stahles in einem Elektrolyten bekannter Chloridkonzentration Rückschlüsse auf die Gefährdung durch Loch‐ und Spaltkorrosion zu ziehen.Die Methode eignet sich auch für andere passivi

ISSN:0947-5117    

DOI:10.1002/maco.19800310509

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

ISSN:0947-5117    

DOI:10.1002/maco.19800310510

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

ISSN:0947-5117    

DOI:10.1002/maco.19800310511

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY