Einflüsse von Legierungselementen auf die Korrosion und Wasserstoffaufnahme von Eisen in Schwefelsäure – Teil III: Kinetik der Abscheidung und Aufnahme von Wasserstoff an binären Eisenlegierungen

Effects of Alloying Elements on Corrosion and Hydrogen Uptake of Iron in Sulfuric Acid – Part III: Kinetics of Proton Discharge and Hydrogen Uptake at Binary Iron Alloys The effects of C, S, P, Mn, Si, Cr, Ni, Sn und Cu on the kinetics of hydrogen uptake of iron in 1 M H₂SO₄ at 25°C are investigated by potentio-kinetic and steady state current density-potential measurements accompanied by hydrogen permeation measurements. The anodic dissolution of iron is increased mainly by S and P, and decreased by Ni, Sn and Cu. Hydrogen uptake is enhanced by S, P and Sn, and inhibited by Ni and Cu. The kinetics of hydrogen evolution on the surface of iron alloys investigated are controlled by a coupled discharge – chemical recombination mechanism.     

Einflüsse von Legierungselementen auf die Korrosion und Wasserstoffaufnahme von Eisen in Schwefelsäure – Teil I: Permeation,Diffusion und Löslichkeit von Wasserstoff in binären Eisenlegierungen

Effects of Alloying Elements on Corrosion and Hydrogen Uptake of Iron in Sulfuric Acid Part I: Permeation, Diffusion and Solubility of Hydrogen in Binary Iron Alloys The influence of elements in common steels like C, S, P, Mn, Si, Cr, Ni, Sn, and Cu on hydrogen uptake and permeation through iron was studied for various binary iron alloys using the electrochemical permeation method. In order to characterize the effects of the alloying additions on the hydrogen activity at the metal surface as well as on the hydrogen transport in the bulk, the hydrogen permeation coefficients, diffusion coefficients and solubilities have been determined in the temperature range of 10 to 80° C. Steady state hydrogen permeation is significantly decreased only by Si and Cr. Si reduces mainly the solubility of hydrogen in iron and decreases only slightly hydrogen diffusion. Cr additions produce strong traps for hydrogen in iron, with an average binding energy of ? 58 kJ/mol. Thus, hydrogen diffusion is retarded. The total hydrogen content is increased by Cr. Permeation measurements of commercial steels showed mainly the Si-effect.     

Einflüsse von Mo,V, Nb,Ti, Zr und deren Karbiden auf die Korrosion und Wasserstoffaufnahme von Eisen in H2S-haltigen Lösungen

Effects of Mo, V, Nb, Ti, Zr and their carbides on the corrosion and hydrogen uptake of iron in H₂S-solutions Effects of the transition metals Mo, V, Nb, Ti, Zr and their carbides as well as of phosphorous on the corrosion and hydrogen uptake of iron in acid to weakly acid NaCl solutions with and without H₂S are discussed. Investigations were carried out on binary, ternary and quaternary iron based alloys, using electrochemical and surface analytical methods. No specific effect of one of the alloying elements or the carbides on the corrosion or hydrogen uptake is observed. Due to the experimental conditions, sulphur and oxygen enriched surface scales form, by which the kinetics of the corrosion processes are determined. The alloying elements are enriched on the iron surface only as a carbide. Phosphorous is enriched as a phosphide at low pH and as a phosphate at higher pH. H₂S and phosphides increase the corrosion rate and hydrogen uptake. In pure iron or low strength iron alloys, at the very high H₂S affected hydrogen activities new lattice defects are induced permanently resulting in extremely high hydrogen concentrations.     

Die Korrosion von Kupfer-Aluminium-Legierungen in schwefelsaurer Beizlösung

Corrosion of copper-aluminium alloys in sulfuric acid containing pickling solutions Wrought copper aluminium alloys (aluminium contents between 5 and 10 weight-%, additions of Fe, Ni and Mn) have been studied by continous and alternating immersion tests in a solution containing 20% H₂SO₄ and 10% FeSO₄ at 40°C. In the as-extruded state the corrosion of monophasic alpha alloys increases with aluminium content. Larger quantities of ß' martensite exercise a negative effect. Addition of 2 weight-% Ni do not improve the corrosion resistance of the alloys with 5 and 8% Al. Cold reduction of alpha alloys give rise to a pronounced intensification of corrosion. No positive effect can be obtained by a thermal treatment of the alloys CuAl 10 Fe 4 Mn Ni and CuAl 10 Fe 4 Ni 5. The corrosion takes place under the following forms: uniform corrosion (CuAl 5), preferred corrosion of grain boundaries (CuAl*, Cual 9, Mn 2 FeNi and CuAl 10 Fe 4 Ni 5 after thermal treatment) and dealuminisation (CuAl 10 Fe 4 Mn 3 Ni). With a view to corrosion resistance the alloys CuAl 5, CuAl8 CuAl 9 Mn and - probably - CuAl 8 Fe seem to be superior to the others.     

Einflüsse von Mo,V, Nb,Ti, Zr und deren Karbiden auf die Korrosion und Wasserstoffaufnahme des Eisens in Schwefelsäure

Effects of Mo, V, Nb, Ti, Zr and their carbides on the corrosion and hydrogen uptake of iron in sulphuric acid The effects of Mo, V, Nb, Ti, Zr and their carbides on the corrosion and hydrogen uptake of iron in 1 M H₂SO₄/N₂/25°C were investigated by electrochemical and surface analytical methods using binary and ternary Fe-Me alloys with about 0.2 at.-%Me. Due to the experimental conditions, no protective surface layers formed. The transition metals were enriched at the iron surface only as a carbide or oxicarbide. Mo or Zr were not markedly enriched. The corrosion current density and the hydrogen activity were decreased only by Mo or Zr. Hydrogen permeation measurements were analysed in terms of the trapping theory. The average binding energy of shallow traps for hydrogen increases with increasing atomic radius of the substituted alloying elements in the order V, Mo, Ti, Nb and Zr. Correspondingly, the hydrogen diffusion coefficient (after saturation of the deep traps) decreases and the hydrogen solubility increases. The steadystate hydrogen permeation rate remains almost unaffected. The total hydrogen content is determined by the density of deep traps and thus mostly independent of the external hydrogen activity. The trapping effect of iron is strongly increased by dissolved Zr or Nb or in the presence of fine dispersed carbides as VC_x. The effect of coarse carbide particles at a lower density is small.     

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.     

Grundvorgänge der Korrosion von Metallen in organischen Lösungsmitteln II

Basic processes with the corrosion of metals in organic solvents (11) Research has been carried out into the corrosion mechanism of Zn, Fe and Ni in anhydrous primary alcohols of different chain lengths. The results can be explained from an analogy to aqueous solutions although the chain length of the plays an important part. With the corrosion of iron in the multi-components system heptane-ethanol-HCl(H₂SO₄)-O₂, a phase segregation can be observed which leads to processes similar to atmospheric corrosion. The destruction of the metal is due to a strongly acid solution phase deposited on the surface, governed by an electrolytic mechanism. The practice Of corrosion testing and corrosion Protection can be based on the Principles and methods conventionally used for corrosion in aqueous media.     

铸铁在海水中的腐蚀行为

报告了18种铸铁在天然海水和流动海水中的腐蚀试验结果,总结了它们在海水中的腐蚀行为,普通铸铁在天然海水及流动海水中的腐蚀速度与碳钢接近,低合金铸铁在海水中的腐蚀行为与普通铸铁相似。CrSbCu铸铁在海水中的腐蚀比普通铸铁轻,添加Ni,Ni-Cr,Ni-Cr-Mo,Ni－Cr-Cu,Ni-Cr-Re,Cu-Sn-Re,Cu-Cr,Cu-Al等的低合金铸铁在海水中的腐蚀速度与普通铸铁无明显差别,加入少量Ni,Cr,Mo,Cu,Sn,Sb,Re等合金元素可减小铸铁在海洋大气区的腐蚀速度,高镍铸铁在天然海水及流动海水中的腐蚀均较轻。     

Cu,P,Cr 和 Ni 对低碳钢耐蚀性的影响简

选择Cu-P-Cr-Ni钢、Cu-P-Cr钢和Q235碳钢,在0.01 mol/L的NaHSO3溶液中进行周期浸润、阻抗谱和极化曲线实验,研究了Cu-P-Cr-Ni系合金钢相比Q235碳钢在模拟工业大气(SO2)环境下的耐腐蚀性能;利用SEM,EPMA面扫描和XRD分析腐蚀锈层的形貌、组成及Cu,Cr和Ni的元素分布情况。结果表明:Cu-P-Cr-Ni系钢的腐蚀诱发敏感性最低,其次为Cu-P-Cr钢,腐蚀速率分别为Q235碳钢的59.5%和52.8%;锈层分为内、外两层,致密的内锈层明显发生Cu的颗粒状、Cr的团聚状富集,外锈层主要有Cr的富集,Ni富集不明显。Cu和Cr等的富集可形成致密的内锈层,提高低碳钢的耐蚀性。     

Corrosion of Al-Sn-Bi alloys in alcohol at high temperatures. Part I: Effects of the metallurgical structure of the alloys and the metal salt additions to alcohol

Corrosion of free machining Al alloys that contain Sn and Bi was investigated at 391-415 K in 2-(2-(2-methoxyethoxy)ethoxy)ethanol (MEEE) and 2-(2-(2-butoxyethoxy)ethoxy)ethanol (BEEE) with/without SnCl₂, Sn(OC₂H₅)₄, FeCl₃, and CuCl₂. The Al-Sn-Bi alloy displayed severe pitting corrosion in MEEE similar to the Al-Sn alloy in BEEE at 415 K, and Sn and Sn/Bi were enriched on the surface of pits. Immersion tests of pure Al in MEEE containing Sn/Cu-salts at 415 K also showed severe corrosion and the deposition of metallic Sn and Cu on the surface. The corrosion mechanisms are discussed in terms of the electro-catalytic activity of the Sn enriched on the surface.     

Einfluß der Hydrodynamik auf die Korrosion von Eisen und Stahl in neutralen belüfteten NaCl- und Na2SO4-Lösungen

Influence of hydrodynamics on the corrosion of iron and steel in neutral aerated NaCl and Na₂SO₄ solutions The corrosion behaviour of iron and steel in aerated neutral NaCl and Na₂SO₄ solutions is mainly determined by the transport-controlled cathodic oxygen reduction. Its reaction zone depends on the physical and chemical properties of the 3-D layer formed on the corroding surface. The influence of hydrodynamics is restricted to the transport of the dissolved oxygen to the reaction zone. The obtained results are independent of laminar or turbulent flow conditions.     

Zur Korrosion von unlegiertem Stahl und Aluminium in wäßrigen Lösungen von Ammoniak und Kohlensäure — 1. Mitteilung: Korrosionsprodukte

Corrosion of unalloyed steel and aluminium in aqueous solution of ammonia and carbonic acid-1. Communication:Corrosion products Two new corrosion products were detected in testing of pure iron, rimming unalloyed steel, aluminium (99,9) and Al-Mg 1,5 in aerated aequous solutions of 130 g/l NH₃ and 80/l Co₂ at 60°. On iron and unalloyed steel the compound (NH₄)₂Fe₂(OH)₄(CO)₃ · H₂O was formed and on aluminium or Al-Mg 1,5 NH₄Al(OH)₂CO₃ · H₂. Both compounds were synthesized and compared by X-ray diffraction, IR spectrum, thermoanalysis, and chemical analysis with published literature. For NH₄Al(OH)₂CO₃ · H₂O the unit cell was calculated which changes somewhat with for the corrosion product are a = 6,64 Å; b = 11,99 Å; c = 5,76 Å. Orthorhombic lattice, aspect C*c*, or (a*) = 13.29 Å; C* = 11,99 Å (hexagonal lattice, pseudohexagonal?). The measured density = 2.03 g · the calculated 2,29 g · cm for Z = 4. The infrared spectrum was partly newly coordinated. Between aluminium metal and NH₄Al(OH)₂CO₃H₂O epitaxial relations are possible, which could explain the higher resistance against corrosion in comparison with steel in the test solution.     

Der Einfluß von Kupfer auf das Korrosions- und Passivierungsverhalten von Eisen-Chrom-Legierungen Teil II: Oberflächenanalytische Untersuchungen

The influence of copper on corrosion and passivation of iron-chromium alloys Part II: Surface analytical examinations The formation and the breakdown of potentiostatically in 1N H₂SO₄ generated passive layers of Fe/Cr alloys (7 resp. 11% Cr) and those with 1% Cu has been studied by XPS analysis and angular dependent XPS. After 1 h passivation the layer thicknes reaches 1 to 4 nm. In accordance with the current densities of layer formation the thickness is increased by copper and decreased by higher Cr contents. The mean thickness of the residual layers measured immediately after selfactivation shows the same tendencies. Passive layers have higher Cr- but lower Fe-contents than the alloys, especially in the presence of copper. Copper is only detectable in the metallic state. It causes raising amounts of γ-Fe₂O₃, leading to the assumption, that copper accelerates passivation via oxidation, of Fe-II-cations in the-oxide lattice by means of the initially existing Cu-II-ions. Concentration depth profiles show that the Cr-enrichment is localised at the oxide/electrolyte interface. Copper is somewhat enriched near the layer/alloy interface, resulting from the initial alloy dissolution. Self activation leads to strong enrichment of copper, raising from the lower to the upper part of layer. The ambivalent effect of copper in regard of improving passivation but accelerating self activation of FeCr-alloys in H₂SO₄ is discussed.     

Korrosionsprobleme in chlorhaltigen Medien: Lösungsmöglichkeiten durch einige nichtrostende Spezialstähle

Corrosion problems in chloride containing media: possible solution by some stainless special steels The increasing water pollution forces the chemical industry to use water with increasing chloride content for cooling and other purposes. This trend brings about increasing corrosion danger, in particular pitting, stress corrosion cracking and corrosion fatigue as well as crevice corrosion. The present paper deals with some steels characterized by resistance to these specific corrosion phenomena. A steel containing (%) 21 Cr., 7.5 Ni, 2.5 Mo, 1.5 Cu, to 2 Mn, to 1 Si and 0.06 C is particularly resistant to stress corrosion cracking. It contains 30 to 50% ferrite in an austenitic matrix. Even in Mg chloride solutions it may be kept under a load of 7 kg/mm² without stress corrosion occurring (with a steel of the 18 10 CrNiMo type the admissible load is only 2 kg/mm²). A steel containing (%) 25 Ni, 21 Cr, 4.5 Mo, 1.5 Cu, to 1 Si, to 2 Mn, and 0.02 C has a broad passivity range and is resistant to general corrosion in acid reducing media and phosphoric acid of all concentrations. A ferritic steel containing (%) 26 Cr. 1 Mo and minor additions of C, Mn, Si, Cu, Ni and nitrogen is resistant to stress corrosion cracking in neutral chloride solutions and general corrosion in oxidizing and neutral media, even against hydrogen sulfid and organic acids; it is beyond that lergely resistant to pitting in chloride solutions.     

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.     

Korrosion von Aluminium in Salzgemischen und Korrosionseinfluß von Kupferionen

Corrosion of aluminium in mixtures of salts and effect of copper ions Corrosion of aluminium has been studied in stagnant condition, in mixtures of salts, NaCl + NaHCO₃, Na₂CO₃ + NaHCO₃ and NaCl + Na₂CO₃; effect of addition of copper ions has also been studied. It has been found that (shallow) pits are formed only when both chloride and bicarbonate are present. Addition of copper ions occasionally increases the numbers of pits but may some times decrease corrosion.     

Corrosion behavior of Cr/Cu-coated Mg alloy (AZ91D) in 0.1 M H2SO4 with different concentrations of NaCl

An electroplating process was proposed for obtaining a protective Cr/Cu deposit on the two-phase Mg alloy AZ91D. The corrosion behavior of Cu-covered and Cr/Cu-covered AZ91D specimens was studied electrochemically in 0.1 M H₂SO₄ with different NaCl concentrations. Experimental results showed that the corrosion resistance of an AZ91D specimen improved significantly after Cr/Cu electrodeposition. The corrosion resistance of Cr/Cu-covered AZ91D decreased with increasing NaCl concentration in 0.1 M H₂SO₄ solution. After immersion in a 0.1 M H₂SO₄ with a NaCl-content above 3.5 wt.%, the surface of Cr/Cu-covered AZ91D suffered a few blisters. Cracks through the Cr deposit provided active pathways for corrosion of the Cu and the AZ91D substrate. Formation of blisters on the Cr/Cu-covered AZ91D surface was confirmed based on the results of an open-circuit potential test, which detected an obvious potential drop from noble to active potentials.     

Zur Korrosion von Lötverbindungen

Corrosion of brazed joints A soldered electrical PtNi contact was attacked in air with formation of Pb (OH)₂ · (PbCO₃)₂. This corrosion product, because of its dielectric properties, deteriorated the contact performance of the Pt? Ni couple. It is therefore recommended not to use lead containing alloys for soldering electrical contacts.     

Über den beschleunigenden Einfluß von Schwefeldioxid und Wasser auf die atmosphärische Korrosion von verrosteten Eisen

The accelerating effect of sulphur dioxide and water on the atmospheric corrosion of rusty iron The atmospheric corrosion process of rusty steel was observed in the laboratory in an atmosphere with 1, 10 and 100 p.p.m. SO₂, respectively, at a temperature of 30°C. It was found that the correlation of the corrosion rate with humidity can, in the range between critical humidity and nearly 100 per cent. Relative humidity, be represented by a rising quadratic parabolic equation. The differences in the three SO₂ concentrations had no influence on the corrosion kinetics, which is explained by the fact that, under the testing conditions, the rust was fully saturated with SO₄^2?. On the strength of these and earlier results, the authors submit a new working theory concerning the atmospheric corrosion of already rusty steel, introducing the theories of Heusler and Florianovitsch-Kolotyrkin into the sphere of atmospheric corrosion.     

Untersuchungen zur H-induzierten Rißkorrosion – Teil 2: Vergleichende Untersuchungen zur Wasserstoffpermeation und Spannungsrißkorrosion

Investigation into the hydrogen induced cracking corrosion – Part 2: Comparative investigations into hydrogen permeation Creep specimens of cold rolled pure iron with different strengths have been stressed in H₂SO₄ + As₂O₃ undercathodic polarisation. The critical stress level for stress corrosion cracking is proportional to the yield strength ranging about 60% ys. At higher stresses the life times decrease with increasing strengths. No correlation exists with permeation rate and hydrogen content, but with time lag. Low alloy steel types show similar relationships in the same and in H₂S containing environments. Metallographic examinations show no relation between stress corrosion cracks and surface or inside blisters. SEM examinations show manyfold types of fracture surfaces without systematics.