Untersuchungen zum Aktiv/Passiv-Übergang von nichtrostenden Chromnickelstählen in organisch wäßrigen Medien. Teil 3. Resultate der Impedanzmessungen und Passivierungsmodell einer Legierung

Investigations into the active/passive transition of 304 stainless steel in organic media containing water and hydrogen chloride Part 3. Results of the impedance measurements and passivation model of an alloy Steady state polarization curves and electrode impedances were measured during the active/passive transition of type 304 stainless steel in dearated ethanolic solution containing hydrogen chloride and different amounts of water. The passivation potential and the critical current density for passivation strongly depend on the water content of the solution. The impedance measurements in the active/passive transition show the same sequence of diagrams independent of the water content of the solution. They indicate the onset of passivation before the maximum current density and show two time constants related to two different passivating species on the alloy surface. The experimental results were interpreted on the basis of a reaction model with parallel dissolution and passivation mechanism of the iron and the chromium compound of the alloy. The resulting total surface composition (related to the steady-state polarization curves) can be described with a reaction model of iron–the alloy behaviour is that of pure metal. The fundamental passivation reaction is described as a potential dependent equilibrium between adsorbed Me(II)- and passivating Me(III)-hydroxide, water molecules being directly involved in the formation of this primary passivating film. In the case of stainless steel this primary passivating film mainly consists of chromium (III) adsorbates. Finally, a general model for the passivation is proposed: The passivation of a pure metal or of an alloy can be understood as the coupling of the stepwise deprotonation of the water molecules at the interface metal/solution and the formation of a high cation charge density in this adsorbed hydroxide/oxide film to build up the passive layer. The effect of water content, pH, adding of passivating species to the solution or the alloying with chromium on the passivation potential and the critical current density thus can be explained.     

Untersuchungen zum Aktiv/Passiv Übergang von nichtrostenden Chromnickelstählen in organisch wäßrigen Median Teil 2: Einfluß des Wassergehalts auf die aktive Auflösung und Passivierung

Investigation into the active/passive transition of 304 stainless steel in organic media containing water Part 2: Influence of water on the active dissolution and passivation The influence of water on the corrosion and passivation of type 304 stainless steel has been studied in deaerated ethanolic solutions containing hydrogen chloride. The potentiostatic polarisation curves show that both, critical current density for passivation and passivation potential, strongly depend on the water content of the solution. A passivation model based on the assumption of a reversible primary passivation potential explains this influence of water and allows the determination of other kinetic parameters. The propounded passivation model also explains the result that the part of “passivated” surface at the maximum current density is the same for all water contents examined. The dominating influence of the water content is shown more clearly when measurements from methanolic and propanolic solutions are concerned. The passivation potential only depends on the water content and not on the type of alcohol.     

The effect of hydrogen chloride on the corrosion of an FeCrAlY alloy in simulated coal gasifier atmospheres

An iron chromium aluminium yttrium steel was exposed to a simulated coal gasifier atmosphere containing 1000 ppm and 2200 ppm hydrogen chloride at 450 °C. Increasing hydrogen chloride content was found to accelerate reaction rates, and significantly alter the microstructure and composition of the corrosion product. Tentative explanations for these results, involving vapour phase transport of metal chlorides are proposed.     

Inhibitoren der Korrosion 7 (1) Nachweis gemeinsamer Wirkungsprinzipien bei der Inhibierung der Säurekorrosion von Eisen,Zink, Aluminium (und Raney-Nickel)

Identification of mechanisms common to the inhibition of the acid corrosion of iron, zinc, aluminium (and Raney nickel) The dissolution of powder and chips of the above metals in diluted and deaerated hydrochloric acid is well inhibited by dibenzyl sulfoxide, benzyl quinolinium bromide and diphenylphosphonium chloride; triphenyl arsine chloride and tribenzylsulfonium hydrogen sulfate are less effective, while diphenyldithiophosphinic acid, thiourea, O-tolyl thiourea and mercaptobenzthiazol in low concentrations act as accelerators.     

Life extension of trivalent chromium passivation baths and enhanced product performance

Abstract

Although Cr (III) based passivation processes are mature, there is always pressure from end users to improve the performance of passivation films. The effect of incorporating ceramic nanoparticles into the film on the corrosion protection of steel components is reported for zinc coatings, with particular emphasis on cobalt-free processes. A novel technology based on selective ion-exchange to remove contaminants such as iron and copper as well as dissolved zinc from trivalent chromium baths is also described. Removal of these metals simultaneously without any appreciable reduction in chromium concentration rejuvenates the system and increases bath life significantly. This reduces not only the cost of frequent make-ups but also the load on the effluent treatment system, and imparts greater consistency to the life and appearance of the components processed. The concept can be extended to baths for chromating of aluminium and its alloys. Technical data generated from actual industrial installations are presented and discussed.     

Untersuchung der Potentialabhängigkeit der interkristallinen Korrosion eines sensibilisierten ferritischen Chromstahls mit rund 17% Cr

Investigations into the relationship between the potential and the inter-crystalline corrosion of a sensitized ferritic chromium steel with approx. 17 per cent, chromium Specimens of a ferritic chromium steel with 0.10 per cent. C and 17.43 per cent. Cr were used in order to ascertain, in the stable-annealed and sensitized condition, the relationship between the potential and the corrosion rate, polarisation current density and depth of penetration of the inter-crystalline corrosion attack. The tests were carried out in external potentiostatic arrangement over the potential range from E_H = + 250 mV to + 1250 mV in boiling 2 n H₂SO₄. All tests were extended over a standard period of 24 hours. Stable-annealed specimens showed no signs of corrosion attack whilst sensitized specimens showed inter-crystalline corrosion of the active-passive and passive-passive types. In the potential range of the active-passive type, the depth of penetration of the grain boundary attack decreases with increasing potential whilst, within the range of the passive-passive type, the depth is independent of the potential. The critical potential marking the boundary between active-passive and passive-passive corrosion is interpreted as the passivation potential of the zones with the greatest chromium deconcentration. With increasing sensitization, this boundary is shifted towards more positive potentials. The potential of the Strauss solution lies within the potential range most favourable for the test of the inner-crystalline corrosion of the active-passive type. The Strauss test in accordance with Steel-Iron Testing Standard 1875/61 is fully adequate for proving the grain decomposition resistance with non-stabilized 17 pC ferritic chromium steels.     

Die Lochkorrosion austenitischer Chrom-Nickel- und Chrom-Nickel-Molybdän-Stähle in schwefelsaurer Bromidlösung und ihre Inhibition durch Nitrationen

Pitting corrosion of austenitic chromium nickel and chromium nickel molybdenum steels in sulfuric acid containing bromides, and its inhibition nitrate ions In acidified bromide solution CrNi steels are attacked under pitting when a certain critical potential has been exceeded; this potential is higher than in the case of chloride containing solutions. Bromides are, consequently, less active than chlorides, but the pit density is considerably higher under idential corrosion conditions. While the pitting corrosion in chloride solutions can be considerably reduced by molybdenum addition to the steel, this effect is but little pronounced in the case of bromide solutions (with Mo additions up to 4% the potential is displaced by 0.2 V toward positive values). Mo additions around 2% are even dangerous since the pitting density is considerably increased in that range. Similar to the conditions in chloride solutions corrosion in bromide solutions is inhibited by nitrate additions; the potential limit is considerably higher in the bromide solution; this phenomenon points to stronger adsorption of bromide ions at the metal surface.     

Corrosion characteristics of nickel, copper, and stainless steel in a Lewis neutral chloroaluminate ionic liquid

Corrosion of nickel, copper, and 316 stainless steel in aluminum chloride/1-ethyl-3-methylimidazolium chloride ionic liquid (IL) is investigated by means of electrochemical techniques. SEM analyses are performed to examine the reaction mechanisms. While Ni shows good stability, Cu has high corrosion susceptibility in this IL. For 316 steel, pitting corrosion occurs at a lower potential than that of passivation. In the non-aqueous, low-oxygen, and high-ion-containing IL, the material corrosion properties are totally different from those found in conventional environments. Since ILs have found increasing potential in diverse applications, new corrosion prevention strategies are needed to overcome the IL-derived material corrosion problems.     

High temperature corrosion behaviour of a new Ni-30Fe-10Al-Cr-Alloy

The high temperature corrosion behaviour of a new duplex nickel-base alloy containing about 30 mass% iron, 10 miss% aluminium and 8 mass% chromium was determined in both air and hot process gases containing methane/hydrogen, sulphur dioxide and hydrogen sulphide, respectively. It was found that the corrosion resistance against carburisation, sulphidation and oxidation was excellent due to the formation of a dense, protective alumina scale. The adherence of the alumina scale was increased by an addition of 0.1 mass% hafnium. The concentration of chromium was found to have a remarkable impact on the oxidation and high temperature corrosion resistance. Alloys without chromium showed increased corrosion rates in both air and sulphur-containing gas atmospheres due to the initial formation of nickel oxides. In sulphidising SO₂- and H₂S- containing gases at least 4 mass% chromium are required to stabilise the formation of alumina and to prevent the formation of nickel/sulphur compounds.     

Zur Korrosion metallischer Werkstoffe in Tetrachlorkohlenstoff

Corrosion of metals in carbon tetrachloride Nickel, nickel alloys, titanium, the titanium-palladium alloy, carbon steel, stainless steel, zinc, aluminium und lead were immersed in the following boiling media: carbon tetrachloride dried and saturated with water and two phase mixtures of carbon tetrachloride and water. Titanium, the titanium alloy and nickel alloys of type C-4, G and 825 are high-corrosion-resistant, the alloy B-2 were only slightly corroded. Nickel, alloy 600, zinc and lead were corroded in the boiling two phase mixture. The weight loss of the stainless steel is very low, but the sensitivity of these steel grades to pitting and/or stress corrosion cracking have to be taken into account. Carbon steel and aluminium corroded heavily in contact with the boiling mixture. The composition of the gaseous phase corrosion products shows different corrosion mechanism.     

Corrosion of hot-dip-galvanised steel and zinc alloy-coated steel in ammonia and ammonium chloride

There are many potential causes of corrosion in animal buildings. Animals exhale large quantities of moisture into the air creating high relative humidity in the building if the moisture is not properly vented. High humidity increases the potential for condensation. In addition, ammonia may be found in large quantities in animal buildings. Ammonia is released from manure and urine. In addition, ammonium chloride is used as a nitrogen source in fertilisers. In this study, the atmospheric corrosion of hot-dip-galvanised steel and zinc alloy-coated steel such as zinc–aluminium and zinc–aluminium–magnesium has been studied in atmospheres containing different levels of ammonia. Investigations have also been conducted at different levels of ammonium chloride. The results are discussed in view of the mechanisms of corrosion of zinc and zinc alloy-coated steel in ammonia and ammonium chloride-containing environments.     

Elektrochemisches Verhalten und Deckschichtbildung hochlegierter Manganstähle

Electrochemical behaviour and scaling of high alloy manganese steels Passivating surface layers are considered to be one of the indispensable requirements for stress corrosion cracking of metallic materials. It is shown by potentiostatic and potentiokinetic current density-potential curves that the steel X 40 MnCrN 19 in neutral aqueous chloride solutions has a passive potential region. The passivation behaviour Of precipitation hardened samples is in agreement with the chromium depletion theory. The effect of alloying on the passivation behaviour of low carbon Mn steels is studied in 3 % NaCl solution at 20 and 100 °C Increasing proportions ε-martensite reduce the passivation of susceptibility. Increasing the Mn content has the same effect. The vital factor concerning passivation behaviour, however, is chromium content. Increasing the temperature of the corrodent results in an increased tendency to form scales of steels containing less than 8 % Cr. Long-term corrosion tests have shown, that increasing the Cr content produces a continuous transition from general localized and even pitting Corrosion. Tests made without applied current in aerated solutions have shown, that the variation in time of corrosion potentials depends from the tendency to be passivated of the materials and from the oxygen content of the solutions. In oxygen containing solutions passivable steels exhibit a pronounced corrosion in the pitting region, because with such alloys anodic dissolution current densities equal to those of the limiting diffusion current of oxygen reduction are obtained only at potentials above the pitting potential.     

The analysis of corrosion performance of car bodies coated by no nickel and low nickel zinc phosphating processes

In today's automotive industry in order to protect car bodies from corrosion, spray or immersion type zinc phosphating processes are applied. In both types, nickel and chromium are widely used though they are harmful to human health and environment. In this study, car body's corrosion performance, coated by no nickel (0 ppm) and low nickel (100, 200, 300 ppm) immersion type zinc phosphating (without chromium passivation) processes, are compared to the bodies that are coated by spray and immersion type processes including nickel (500–700 ppm) and chromium. After analyzing coating weight, composition, morphology of the crystals and salt spray test corrosion performance of car bodies specimens coated by no nickel and low nickel processes are as good as the ones coated by spray and immersion phosphating processes including nickel and chromium. In developing environment consciousness, it is inevitable to favor no nickel or low nickel processes since they give no harm to nature and human health.     

XPS study of surface film on nickel alloys in hot concentrated NaOH

X-ray photo-electron spectroscopy has been used to investigate the composition of surface films formed on Alloy 600 and Alloy 800 in 50wt. %NaOH at 120°C as a function of polarization potential. Anodic polarization from the corrosion potential successively revealed the active, primary passive, transpassive and secondary passive regions. The formation of hydrated chromium oxy-hydroxide resulted in the primary passivation; the chromium content in the passive film increased with the rise in potential. The transpassive reaction led to an abrupt decrease of chromium in the film with a consequent increase in nickel. The secondary passive film was composed exclusively of nickel hydroxide which transformed to hydrated nickelous oxy-hydroxide with an increase in potential.     

Open circuit potentials of metallic chromium and austenitic 304 stainless steel in aqueous sulphuric acid solution and the influence of chloride ions on them

Open circuit potential measurements and cyclic voltammetry of chromium and 304 stainless steel in deaerated aqueous H₂SO₄ solution of pH 1, without and containing NaCl in the concentration range 1–4 M revealed that chromium exhibits two stable open circuit potentials both having the character of a Wagner–Traud corrosion potential. One, E_corr.1, was established on the passive surface formed by previously exposing Cr to air or by potentiostatic passivation in a controlled manner, and the second one, E_corr.2, at the bare Cr surface obtained by prolonged cathodic activation. There was a small difference in the E_corr.1 values depending on the properties of the passive layer. Addition of NaCl accelerates to some extent, the hydrogen evolution reaction on the passive surface, while the same reaction on the bare surface was somewhat inhibited by NaCl. On the other hand, presence of NaCl accelerates the anodic reaction on the bare surface, and it activates the dissolution of the passive layer so that the passivation currents increase with addition of NaCl. This effect is so large that at concentrations of NaCl larger than 3 M, the destruction of the passive layer was so fast that in a matter of seconds the Cr is activated, and the only stable corrosion potential observed was E_corr.2. No pitting of Cr in the presence of NaCl was observed up to the transpassive potentials. 304 stainless steel could not be activated in sulphuric acid solution, and its open circuit potential, unlike the corrosion potential of the 400 types of stainless steel, was established by the hydrogen evolution reaction on the passive steel surface. The small anodic peak often observed on 304 stainless steel if the metal had been cathodically pre-treated is a pseudo-peak due to the anodic oxidation of hydrogen absorbed inside the metal. This finding should be elaborated more in recommendations (e.g. ASTM standards) for the application of electrochemical corrosion rate measurement to 304 stainless steel corrosion. Addition of NaCl activates the anodic dissolution of steel with the current of the passivation peak being proportional to the NaCl concentration. Unlike chromium, austenitic 304 stainless steel achieves only one corrosion potential in sulphuric acid, both in the presence and absence of NaCl, with the value of ca. −0.200 to −0.350 V (SCE) in the absence and −0.450 V (SCE) in the presence of NaCl, when steel corrodes as the active metal.     

Ursachen und Erscheinungsformen der Korrosion in Installationssystemen

Causes and phenomenology of corrosions in domestic installations The author deals with questions concerning the operational safety of domestic installation systems for cold water distribution and warm water preparation and distribution. The investigation is concerned in particular with the conditions which in aerated waters may give rise to a prevention of corrosion of an unalloyed steel by the formation of dense and protective layers of rust and calcareous rust; in this context the role of hot-dip galvanizing is dealt with, too. The deleterious effect of aeration cells in water systems with frequent stagnation periods is emphasized and discussed. With a particular view to warm water and installations of galvanized steel the danger is pointed out which is due to the formation of hydrogen bubbles in or below the zinc coating, which may give rise to spalling. As to high-alloy steels, copper and aluminium base materials it is shown that uniform corrosion is scarcely encountered in domestic installation systems. However, attention should be paid to occasional cases of selective corrosion and stress corrosion cracking and in particular to the danger of pitting. In this context the role of the pitting potential is considered.     

Investigation on carbon dioxide corrosion behaviour of HP13Cr110 stainless steel in simulated stratum water

The carbon dioxide corrosion behaviour of HP13Cr110 stainless steel in simulated stratum water is studied by potentiodynamic curve and electrochemical impedance spectroscopy (EIS); the micro-structure and composition of the corrosion scale formed at high-temperature and high-pressure are analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that 13Cr stainless steel is in passive state in the stratum water, the passive current density increases and the passive potential region decreases with increasing temperature. The corrosion scale formed at high-temperature and high-pressure is mainly composed of iron/chromium oxides and a little amount of FeCO₃.     

Corrosion potential oscillations of nickel-containing stainless steel in concentrated sulphuric acid: II Mechanism and kinetic modelling

In the current work, the mechanism for oscillations in mixed potential of UNS S30403 Stainless steel in concentrated sulphuric acid is refined to clarify the importance of the stability limit of nickel sulphide in relation to the passivation potential of the steel. It is rationalized that the oscillation of the corrosion potential can occur spontaneously only when the nickel sulphide stability limit lies within a specific potential range above the passivation potential of the steel and below the tangent for re-activation. Two possible kinetic models are proposed and contrasted to illustrate which better explains the potential-time behaviour for depassivation.     

Electrochemical corrosion behavior of 300M ultra high strength steel in chloride containing environment

The electrochemical corrosion behavior of 300M ultra high strength steel in chloride containing environment was investigated by potentiodynamic polarization technique, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The results show that uniform corrosion occurs on 300M steel during the electrochemical measurements because no anodic passivation phenomenon is observed on polarization curves within the measurement range. The tests also show that 300M steel is highly susceptible to chloride containing solution, which is characterized by corrosion current density increasing with the addition of chlorides, and corrosion potential shifting towards positive direction and corrosion resistance decreasing, positively suggesting that chloride ions speed up the corrosion rate of 300M steel. Meanwhile corrosion products on the 300M steel surface formed during the salt spray test are too loose and porous to effectively slow down the corrosion rate. Additionally, a schematic structure of uniform corrosion mechanism can explain that 300M steel has better property of stress corrosion cracking (SCC) resistance than stainless steels.     

Passivity and Pitting Corrosion of X80 Pipeline Steel in Carbonate/Bicarbonate Solution Studied by Electrochemical Measurements

This work investigated the effects of chloride ions and hydrogen-charging on the passivity and pitting corrosion behavior of X80 pipeline steel in a bicarbonate-carbonate solution by electrochemical and photo-electrochemical techniques. It was found that a stable passivity can be established on the steel in the absence and presence of chloride ions. The hydrogen-charging does not alter the transpassive potential, but increases the passive current density. When chloride ions are contained in the solution, pitting corrosion will be initiated. The pitting potential is independent of the hydrogen-charging. Hydrogen-charging would enhance the anodic dissolution and electrochemical activity of the steel, but does not affect the pitting potential, which indicates that the charged hydrogen is not involved in the pitting initiation. However, hydrogen may accelerate the pit growth. Photo illumination could enhance the activity of the steel electrode, resulting in an increase of photo-induced anodic current density.