Anwendung der Warburg-Technik zur Untersuchung der Korrosion von Nickel in sauerstoffhaltigen,wäßrigen Salzsäurelösungen

Application of the Warburg technique to the examination of the corrosion of nickel in aqueous hydrochloric acid solutions containing oxygen By applying the Warburg technique to corrosion phenomena, it is possible to determine the type and extent of the participation of a gaseous reagent in the reaction, provided that it is not less than 10^?8 Mols. By improving the measuring photocells, it was possible to eliminate disturbances to the stationary equilibrium caused by the measuring technique. In the present research effort, the Warburg technique has been used for determining the corrosion rate of pure nickel in aqueous hydrochloric acid solution containing oxygen, as a function of the acidity of the solution. The correlation thus found has been qualitatively discussed. It was shown that, under the prevailing conditions (Po₂ = 1 atm; O ? p_H ? 7), there is no hydrogen evolution, but always an oxygen consumption. The oxygen has been quantitatively reduced to hydrogen peroxide, dissolving the equivalent quantity of nickel.     

Zur Redoxwertigkeit des Sauerstoffs an Nickelproben in 1 n Salz-und Schwefelsäure

Redox valence of oxygen on nickel specimens in 1 n hydrochloric and sulfuric acids The ratio of dissolved nickel to oxygen consumption was studied for the corrosion of nickel in oxigen containing acid. In air saturated 1 N H₂SO₄ 4 electrons are accepted per molecule of oxygen (reduction to water). In air-saturated 1 N HCL only 2 electrons are reacting per molecule of oxygen (reduction to hydrogenperoxide) at the beginning of the reaction, in the course of the reaction (times greater than 2 hours) this value rises to 3 electrons per molecule of oxygen, according to a stationary hydrogenperoxide concentration of 7 · 10^?4 moles/l in both acid, however, the oxygen reduction leads to hydrogen peroxide as an intermediate product which in the presence of chloride ions is desorbed faster from the metal surface than it is reduced. with increasing chlorid concentration the corrosion rate decreases from H₂SO₄ to HCL solutions.It is proposed that this effect is due to different mechanisms for the anodic dissolution of the nickel.     

Anwendung der Warburg-Technik für Korrosionsmessungen an Nickelproben mit und ohne Stromdurchgang

Use of the Warburg technique to measure corrosion of nickel samples with and without passage of current The use of the Warburg technique in corrosion processes makes possible the determining of the kind and extent of gas participation in the reaction. Specially in the corrosion of pure nickel in aqueous solution of hydrochloric acid containing oxygen, it may be decided how muc of the oxygen present is reduced to hydrogen peroxide or water. The relationship of both reaction products is dependent on the passage of current through the nickel electrode. The experiments were carried out under stationary conditions, i.e. conditions similar to those in practice. Surface qualities therefore influenced the results. It could be shown that this influence mainly concerns the reduction of oxyge to water and the formation of absorbed hydrogen, whilst the extent of hydrogen peroxide formation is decisively dependent on the passage of current through the electode. The maximum formation of hydrogen peroxide lies in the steady state potetial of teh nickel sample.     

Besonderheiten im Korrosionsverhalten hochchrom- und molybdänhaltiger Legierungen in heißer 92, 5%iger Schwefelsäure

Peculiarities in the corrosion behaviour of high chromium and molybdenum containing alloys in hot 92.5% sulfuric acid In laboratory tests at temperatures above 50°C unusual high corrosion rates of passivating stainless steels and nickel alloys containing more than 26% Cr were observed in 92.5% sulphuric acid. In order to investigate the cause of this phenomenon further corrosion tests and additional chemical analyses were performed. The H₂SO₄ concentration tested displays a relative maximum of the electrical conductivity, the reason being a stronger dissociation of the sulfuric acid. Electrochemical investigations revealed an enhanced activity of the cathodic reactions which lead to higher corrosion rates. The cathodic reactions are strongly dependend on alloy constitution with special emphasis on the contents of Cr, Ni and Mo. Mo containing stainless steel show potential oscillations (of the open circuit potential) between ?50 and +550 mV_H. These alloys corrode under development of SO₂ (reduction of H₂SO₄ molecules) and formation of several sulfur compounds with different oxidation numbers (6+ and 2?). Alloys with chromium contents above 26% develop additionally hydrogen gas due to a lower hydrogen overvoltage of these alloys. With increasing nickel content the overvoltage for the reduction reaction of H₂SO₄ molecules will be lowered. This fact results in an elevation of the exchange current density for the Alloy NiCr45 and therefore to the highest corrosion rate observed. Alloy B-2 shows the best resistance, i.e. very low corrosion rates. Obviously high levels of molybdenum can compensate the influence of nickel on the overvoltage of the reduction reaction or even hinder the cathodic reaction.     

Corrosion of nickel-containing stainless steel in concentrated sulphuric acid

The corrosion of UNS S30403 stainless steel was investigated in 93.5 wt% sulphuric acid at temperatures from 40 to 100 °C. Time-dependent free corrosion potential measurements demonstrate that the steel is subject to spontaneous active-passive oscillation. Studies on the effect of temperature and electrode rotation speed indicate that the oscillation is activation and transport controlled over different segments of the oscillations. It is concluded that the oscillation is caused by reversible changes in the exchange current for the cathodic reduction of sulphuric acid, depending on the presence or absence of nickel sulphide on the steel surface.     

Inhibitoren der Korrosion 25(1) – Über die Rolle der Kationen in Neutralsalzen bei der Korrosion von Eisenwerkstoffen in Gegenwart von Sauerstoff

Corrosion inhibitors 25(1) – The role of the cation in a neutral salt in the corrosion of iron in the presence of oxygen The rate of uptake of oxygen, under standard conditions, in the corrosion of 500 mg DAB6 iron powder is dependent on the nature of the cation in a neutral salt (chloride). In the presence of alkali, quaternary ammonium, quaternary phosphonium and alkali-earth chlorides, the rate of oxygen uptake is comparable. With zinc, cadmium, nickel and cobalt chlorides a marked decrease in the oxygen uptake is observed between pH5 and pH7. This is probably due to a block in the cathodic area in the iron boundary layer through precipitation of the rather insoluble basic hydroxides of zinc, cadmium, nickel and cobalt.     

Untersuchungen über den Einfluß von Schwefelwasserstoff und Schwefeldioxyd auf die Korrosion chemisch beständiger Chrom-Nickel-Stähle in schwefelsaurer Natriumsulfatlösung

Investigations into the influence of hydrogen sulphur dioxide on the corrosion of chemically resistant chrome nickel steels in a sulphuric acid chrome nickel steels in a sulphuric acid solution of sodium sulphate By measuring the current/potential curves and determining the weight losses, the influence of H₂S and SO₂ on the corrosion of an 18/8 Cr? NI steel and of an 18/8 Cr? Ni stell with 2pCMo and 2.8pC Cu in sodium sulphate solution has been investigated. H₂S and SO₂ have the effect of shifting the rest potential towards the electronegative side, compared with a solution flushed with nitrogen, enlarging the potential range of active dissolution, and greatly increasing the dissolution, and greatly increasing the corrosion rate in the active zone. From the results of the measurements, it may be concluded that the metal dissolution is catalyzed by hydrogen sulphide ions and probably by reduction products of the sulphur dioxide. This catalyzing effect is not confined to the zone of activation overpotential but also occurs in the zone of the active plateau, the shape of which is largely determined by the migration phenomena. SO₂also has the effect of increasing the dissolution rate in the passive condition.     

A study of the corrosion of aluminum alloy 2024-T3 under thin electrolyte layers

The corrosion of aluminum alloy 2024-T3 (AA2024-T3) under thin electrolyte layers was studied in 3.0 wt% sodium chloride solutions by cathodic polarization and electrochemical impedance spectroscopy (EIS) method. The cathodic polarization measurements show that, when the electrolyte layer is thicker than 200 μm, the oxygen reduction current is close to that of the bulk solution. But in the range of 200-100 μm, the oxygen reduction current is inversely proportional to the layer thickness, which shows that the oxygen diffusion through the electrolyte layer is the rate-determining step for the oxygen reduction process. In the range of 100 μm to about 58 μm, the oxygen reduction current is slightly decreased probably due to the formation of aluminum hydroxide or the change of the diffusion pattern from 2-dimensional diffusion to one-dimensional diffusion. The further decrease in electrolyte layer thickness increase the oxygen reduction current to some extent again, because the diffusion of oxygen plays more important role in thin electrolyte layers.The EIS measurements show that the corrosion is controlled by the cathodic oxygen reduction at the initial stage, showing the largest corrosion rate at the electrolyte layer thickness of 105 μm. But at the later stage of corrosion, the anodic process begin to affect the corrosion rates and the corrosion rates show a maximum at 170 μm, which may be the thickness where the corrosion changes from cathodic control to anodic control. The corrosion rate under the very thin electrolyte layer (62 μm in this study) is even smaller than that in bulk solution, this is due to that the anodic process is strongly inhibited.     

Hemmung der sauren Korrosion unterschiedlicher Kohlenstoffstähle unter Verwendung von Thioharnstoff

Inhibition of the acid corrosion of various carbon steels In the present paper the influence of carbon content in steel (0.002–1.05%C) on the corrosion rate in deacerated 2.0 M sulphuric acid containing thiourea in a concentration of 0.003-0.4% has been studied. The measuring effects of spontaneous dissolution and the potentiostatic measuring results for two different stirring rates of the disk electrode have been shown. It was found that the thiourea represses the corrosion of steel to a certain optimal concentration above which a corrosion stimulation takes place. The optimal concentration of the thiourea depends on the carbon content in steel and in a smaller degree on the stirring rate. In the absence of thiourea the anodic and cathodic polarisation curves have a run considerably depending on the carbon content in steel. The polarisation curves at the thiourea concentration of 0.010 and 0.100% show a Tafel run with an elevation practically independent on the carbon content in steel. The run of the polarisation curves as well as the metallographic observations allow to admit that the cementit and also the ferrite undergo an anodic dissolution at the presence of thiourea.     

The electrochemical reduction of oxygen on copper in dilute sulphuric acid solutions

The electrolytic reduction of O₂ on Cu was studied in dilute H₂SO₄ at 25°C by steady-state and transient electrochemical techniques. A distinctive hump (i.e. a current maximum) is observed in the steady-state potentiostatic polarization curve approximately 50 mV negative to the open-circuit corrosion potential. Results of transient studies, of varying the solution agitation, and varying the concentrations of oxygen, sulphuric acid, and sulphate ions indicate that the hump is due to cathodic film formation which inhibits the rate of oxygen reduction. The inhibiting film appears to be composed of intermediates from the O₂ reduction process and also may contain adsorbed sulphate ions. The film is removed under corrosion conditions by rapid dissolution of the substrate copper. Extrapolation of the cathodic Tafel curve to the corrosion potential yields corrosion rates lower than those measured because of the cathodic passivation.     

纯钛表面Mo-N共渗改性层在稀H2SO4溶液中的腐蚀行为

利用等离子技术在纯钛表面制备Mo-N改性层,对改性层组织进行观察,测试改性层的元素分布、XRD衍射谱,采用极化曲线法和失重法考核改性层在稀硫酸溶液中的腐蚀性能.结果表明,改性层由渗层和扩散层组成,改性层在稀硫酸中的耐蚀性得到改善.     

Intergranular corrosion resistance of stainless steel diffusion‐bonded joints with B‐containing amorphous insert metal

Summary

This paper describes an investigation of the intergranular corrosion resistance of austenitic stainless steel joints diffusion‐bonded with an amorphous insert metal containing 1.5 mass% boron, in order to clarify optimum bonding conditions for austenitic stainless steel pipes joined by a high‐speed diffusion bonding system. The sulphuric acid/copper sulphate test is conducted to evaluate the intergranular corrosion of bonded joints caused by a Cr depletion zone. Joints diffusion‐bonded with lower bonding pressure and shorter bonding time are more sensitive to intergranular corrosion. Under such bonding conditions, Cr boride and Cr carboboride precipitates causing selective corrosion are found in the bonding layer. Joints diffusion‐bonded under higher bonding pressure and with longer bonding time, however, show no intergranular corrosion and few precipitates in the bonding layer. With regard to the B‐containing amorphous insert metal used in the present investigation, the optimum bonding conditions for prevention of intergranular corrosion are a bonding temperature of 1473 K, bonding pressure of > 9.8 MPa, and bonding time of > 180 sec.     

Inkristalline Korrosion der Nickellegierung NiCr 20 TiAl

Intercrystalline corrosion of the nickel alloy NiCr 20 TiAl The corrosion behaviour of NiCr 20 TiAl shows a clear dependence from the carbon content. In Strauss solution the alloys containing 0.007% C are not susceptible to intercrystalline corrosion, while with carbon contents of 0.036 to 0.078% intercrystalline corrosion occurs similar to that in 18-8 steels. In boiling nitric acid the corrosion susceptibility further depends from the heat treatment. After cooling from the temperature of solution annealing in air high weight losses are found which even increase after ageing, while they are reduced by quenching in water and then can be found with the alloys having higher carbon contents only. The intercrystalline corrosion is attributed to a formation at the grain boundaries.     

The influence of various major and minor alloying elements on the corrosion of an Fe-40 %Cr Superferritic stainless steel in sulphuric acid

The corrosion resistance of an Fe-40%Cr superferritic alloy containing various major and minor alloying additions, e. g. nickel, molybdenum, aluminium, zirconium, nitrogen, niobium, titanium and ruthenium, as well as various combinations of them, was investigated in dilute sulphuric acid. Although small nickel and molybdenum additions alone cannot cause spontaneous passivation of the Fe-40%Cr alloy to which they are added, a combination of these two alloying elements result in an Fc-40%-Cr superferritic stainless steel which can passivated spontaneously in dilute sulphuric acid. Further additions of minor alloying elements like Ti, Nb, Ru and N have an influence on the time required to achieve spontaneous passivation and the final open-circuit potential eventually reached. Further additions of Al and Zr to the Fe-40%Cr-2%Ni-2%Mo alloy did not have much of an effect on the final open-circuit potential reached, and only affected the time required before this potential was reached in each case.     

电沉积Ni-P合金镀层在酸性介质中耐蚀性能的研究

研究了Ni-P合金镀层在盐酸、硫酸、硝酸三种介质中的耐蚀性能。通过浸泡实验,得出不同磷含量镀层的腐蚀数据,同时还与纯镍镀层、1Gr18Ni9Ti不锈钢进行了比较。对腐蚀后镀层表面纯化膜成分的AES分析表明,Ni-P合金镀层的耐蚀机理与表面磷化钝化膜的生成及溶解有关。     

Teilstromdichte Potentialkurven von Nickelelektroden in luftgesättigter Salzsäure in Anwesenheit verschiedener Amine

Partial current density-potential curves of nickel electrodes in air saturated hydrochloric acid in the presence of various amines The corrosion-rate of nickel electrodes (99,8% purity) was determined potentiostatically and manometrically by the “Warburg” -method in In hydrochloric acid saturated with air. It was split up into the partial current density-potential curves of nickel dissolution, oxygen reduction and evolution of hydrogen. Addition of several aliphatic and aromatic amines to the electrolyte shows that these compounds decrease the diffusion limiting current of oxygen reduction. They also inhibit the chargetransfer reaction of hydrogen and oxygen in different ways. At the equilibrium rest potential all these amines inhibit the nickel dissolution slightly; at cathodic potentials only the aromatic amines show this effect.     

Die Bedeutung einer Deckschichtbildung bei der Spannungsrißkorrosion

The importance of the formation of a cover with stress corrosion cracking Many metals and alloys, when exposed to corrosive agents, from covering layers which have a considerable influence on the corrosion process. This applies, in particular, to covering layers with protective effect. The significance of the formation of electro-positive cover films in stress corrosion cracking is illustrated by the example of the formation of cracks in unalloyed steels in nitrate solutions and alkali solutions as well as in austenitic steels in solutions containing chloride and in sulphuric acid. As with pit corrosion, the incomplete or disturbed formation of such layers is the cause of the occurrence of localized corrosion where, under the influence of tensile stresses, the local anodes become the points where the cracks originate. Tension crack corrosion must therefore be regarded as a special problem of the corrosion of metals with incomplete cover films.     

Vorrichtung zur kontinuierlichen Messung der unter Sauerstoffreduktion verlaufenden Korrosion

Apparatus for continuous measurement of corrosion rate by oxygen reduction An equipment is described for continuous measurement of corrosion rates by oxygen reduction. The basic principle involves the measurement of quantity of oxygen produced in electrolysis to compensate the quantity consumed during the corrosion. The quantity of electricity consumed for oxygen evolution can be conveniently measured and thus shows the progress of the corrosion process.     

Hydrogen induced stress corrosion cracking in low and high strength ferritic steels of different phosphorus content in acid media

Hydrogen induced stress corrosion cracking (HSCC) resistance and mode of fracture in various low and high strength steels (yield strength 120 to 960 MPa) and containing different levels of phosphorus content were studied using constant extension rate test method in various acid media viz. sulphuric acid solutions under cathodic polarisation, hydrogen sulphide saturated solutions of sodium chloride + acetic acid (NACE solution) and synthetic sea water (BP solution). In case of low strength steels (yield strength 120–265 MPa), the HSCC susceptibility in sulphuric acid increased with phosphorus content and became very high irrespective of phosphorus content in hydrogen sulphide saturated solutions. The susceptibility was directly related to different hydrogen activities measured in these solutions. No significant dependence of HSCC susceptibility on the phosphorus segregation as high as 20 atom % at the grain boundaries was found and the fracture mode was always transgranular. In contrast, a similar segregation of phosphorus in high strength steels (yield strength 875–960 MPa) caused a reduction in HSCC resistance and changed the fracture mode to intergranular.     

Corrosion of Hydrides of Nickel and Cu30Ni Alloy in Oxygen Containing Solutions

Corrosion behavior of nickel hydride is studied in alkaline, neutral, and weakly acidic oxygen-containing solutions by compensating oxygen consumed in corrosion and spectrophotometric analysis of solution for nickel. It is shown that in the course of nickel hydride corrosion in alkaline solutions, oxygen is consumed solely in its interaction with hydrogen formed at hydride decomposition, while nickel remains at the surface. It is concluded that, in a pH range from 7 to 14, hydrogen oxidation is limited by its solid-phase diffusion, whereas the rate of nickel hydride decomposition is pH-independent. The difference in the corrosion behavior of the original alloy and its hydride is attributed to the fact that the original alloy evolves copper ions, whereas the hydride evolves hydrogen.__________Translated from Zashchita Metallov, Vol. 41, No. 4, 2005, pp. 390–394.Original Russian Text Copyright © 2005 by Markos’yan, Sirota, Pchel’nikov.