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.     

Einflüsse von Mo,V, Nb,Ti, Zr und deren Karbiden auf die Bindungszustände des Wasserstoffs in Eisen und das Bruchverhalten der Eisenlegieungen

Effects of Mo, V, Nb, Ti, Zr and their carbides on the binding states of hydrogen in iron and the fracture behaviour of the iron alloys Effects of Mo, V, Nb, Ti, Zr and their carbides on hydrogen permeation, diffusion, solubility and its distribution on different binding states in iron and iron based alloys are studied by use of the electrochemical hydrogen permeation technique. The results are analysed and described in terms of the trapping theory. The fracture behaviour of the alloys affected by hydrogen in different binding states are tested under constant elongation rate conditions. No essential specific effects of one of the alloying elements or their carbides are observed. Hydrogen diffusion and solubility, the total hydrogen content as well as the fracture behaviour are affected by the various microstructures of the alloys, thus only indirectly by the alloying elements. Crack initiation and fracture progress depend first of all on the external hydrogen activity and the grain size of the material, not on the total hydrogen content. Fine crystalline iron alloys of higher strength prove to be less sensible to hydrogen damage than coarse grain weak structures.     

Einflüsse von Legierungselementen auf die Korrosion und Wasserstoffaufnahme von Eisen in Schwefelsäure – Teil II: Korrosion und Deckschichtbildung

Effects of Alloying Elements on Corrosion and Hydrogen Uptake of Iron in Sulfuric Acid Part II: Corrosion and Formation of Surface Layers The effects of C, S, P, Mn, Si, Cr, Ni, Sn and Cu on the formation of surface layer and hydrogen uptake of iron during corrosion in 1 M H₂SO₄/N₂ were investigated using AES, XPS, SEM and electrochemical permeation techniques. Cu, Sn, P and C are enriched on the surface of iron during corrosion in H₂SO₄. Cu is enriched in the metallic form. P forms a phosphate and phosphide containing surface layer. Ni is not enriched. Cr is preferentially dissolved. Cu, Sn and Ni inhibit the dissolution of iron and thus decrease the hydrogen activity. S, P and Mn (MnS) increase the corrosion and hydrogen activity. Cr forms traps in iron which increase the hydrogen uptake.     

Einflüsse von Silicium und Kohlenstoff auf die Sulfidierung von Eisen

Effects of silicon and of carbon on the sulfidation of iron The corrosive attack of steels by H₂S under FeS formation is impeding the use of heat exchangers in processes in which sulfidizing gases occur at low oxygen pressures – the project was aimed at finding ways and means to retard or suppress the FeS growth. Thermogravimetric investigations in H₂? H₂S at 400 °C showed that during the first 100 h of sulfidation a transition takes place from the linear kinetics controlled by the phase boundary reaction H₂S ? S (in FeS) + H₂ to the parabolic kinetics controlled by solid state diffusion in the corrosion products. During this transition the linear constant decreases with time and increasing sulfur activity a_s at the FeS surface (k₁ ? 1/a_s). Upon sulfidation of Fe-6%Si an internal Fe₃Si layer is formed te sulfidation is retarded since for long time ( 100 h) the slow surface reaction at high a_s is rate determining. Carbon deposits formed in carburizing atmospheres (a_c 1) on the iron surface, have a negligible effect on the sulfidation. Only graphitization of the iron surface at 700 °C after preceding carbon saturation at 1000 °C in CH₄? H₂ has an initially retarding effect. This study demonstrated possibilities of retarding the H₂S corrosion by Si or C which, however, are rather limited.     

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.     

Der Einfluß des Salzgehaltes auf die Korrosion von Eisen und niedriglegiertem Stahl in belüfteten Lösungen

Influence of the salt content on the corrosion of iron and low-alloy steel in aerated solutions The influence of borate and carbonate on the corrosion of iron and steel was investigated in aerated, neutral electrolytes. Both salts were inhibiting the corrosion. But only borate in higher concentrations was able to prevent the corrosion by chloride. The convection of the electrolyte was of only small influence.     

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.     

Anodisches Verhalten und Korrosion von Titan in methanolischen Lösungen

Anodic behaviour and corrosion of titanium in methanolic solutions The anodic behaviour of titanium in methanolic solutions containing halides or water in various concentrations has been investigated and the result were compared with the result obtained by corrosion tests performed on ?U”? bend specimens in similar solutions. Polarization curves can predict the susceptibility to titanium to stress corrosion cracking as in the case the metal surface is not passivable. These conditions can be obtained in the presence of low water content (i.e. 0.1% H₂O) and of activating ions as Cl^? and Br^? even in very small concentration (10^5?, 10^4? M). Presence of higher water contents and/or of F^? or I^? ions can to some extent produce passivation of the metal surface and cracking does not occur. A lower water amount in the solution (i.e. 130 ppm) eliminates any possibility of passivation of the metal surface, so that cracking can occur even in the absence of chlorides or bromides. High Cl^? concentration in the solution. (i.e. 0.1 M NaCl + 0.1% H₂O) can produce intergranular attack even in the absence of applied stress.     

Korrosion von Chemieemail in alkalischen Lösungen

Corrosion of chemical service glass-enamel in alkaline solutions Chemical service glass-enamels are high resistant, multi component silicate glasses fused onto steel yielding a compound material of mechanical and chemical stability as well. The resistance of these glass-enamels against alkali attack is investigated in laboratory tests involving gravimetric evaluation of totally glass-lined steel samples after contact with various alkaline media. Thus the influence of the following technically relevant parameters on the glass corrosion rate becomes perceptible: agitation and renewal of the medium, volume-to-surface ratio, exposure time, temperature, alkali content, glass quality; special attention is paid to inhibition effects originating e. g. from calcium(II) ions. These results may help to conceive on a laboratory scale a corrosion test for glass-linings which simulates in good approximation service conditions. In consequence, the corrosion situation in glass-lined equipment becomes more evident and appropriate measures may be considered to improve its economy.     

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.     

Über den Einfluß von Schwefelwasserstoff auf die Korrosion des Eisens in sauren Lösungen

The influence of hydrogen sulphide on the corrosion of iron in acid solutions A considerable change of the polarisation behaviour of iron electrodes in acidic perchlorate and sulphate solutions was observed if they where saturated with hydrogen sulfide gas. H₂S markedly increased the anodic current densities and increases the corrosion rates by a factor of ten. The anodic Tafel slopes d log i_A/dE are only about half as steep as those in the absence of hydrogen sulphide. It is probable that the SH^?-ions behave as catalysts of the iron dissolution reaction in a similar manner as the OH^?-ions, but are adsorbed almost to saturation.     

Einflüsse von Werkstoff und Verarbeitung auf die Spannungsrißkorrosion von Spannstählen

Influence of material and processing on stress corrosion cracking of prestressing steel In prestressed concrete constructions the highstrength prestressing steels perform essential bearing effects. The alkaline layer of concrete or mortar protects the steels against corrosion and guarantees a permanent load capacity. If the corrosion protection as a result of poor workmanship is not guaranteed from the beginning, or is lost because of lacks of construction in the course of time, or the steels are predamaged during handling, stress corrosion cracking and failure of steel and construction may occur. Also an application of unsuitable materials (prestressing steel, injection mortar, concrete) can alone or in combination with the before mentioned influences favour stress corrosion cracking. In the contribution the correlations and typical failures are discussed.     

Untersuchungen über die Kathodenwirkung von Eisensulfid und Mangansulfid auf die Korrosion von Eisen in dreiprozentiger Natriumchloridlösung

Studies on the cathodic effect of iron sulfide and manganese sulfide on the corrosion of iron in a three percent sodium chloride solution In the galvanic element iron/sodium chloride solution/iron sulfide and in the element iron/sodium chloride solution/manganese sulfide, flushed with nitrogen or air, the sulfides become the cathode and the iron is anode. Upon short circuiting the electrodes a strong cathodic polarisation of the sulfides occurs. However, only if the iron is in contact with iron sulfide in the air-flushed sodium chloride solution the corrosion of the iron is enhanced because of considerable anodic polarisation. The corrosion of the iron electrode is increased corresponding to the increase in cathodic area. According to these results inclusions of iron sulfide or manganese sulfide act as local cathodes but cannot cause pitting corrosion of unalloyed steels in a neutral chloride solution.     

Inhibierung der Korrosion von Kupfer in salzsauren Lösungen

Inhibition of copper corrosion in hydrochloric solutions Furfural is one of the best corrosion inhibitors of copper in hydrochloric acid. The inhibition effect ranges from 90 to 100 per cent. With increasing acid concentration, the quantity of furfural required for effective corrosion inhibition becomes smaller. By means of polarisation measurements, it can be found that, in 0.2 n and 1.0 n HCl, the inhibitor has an essential anodic effect and the cathode becomes depolarised whilst, in 2.0 n and 3.0 n HCl, the anodic zone is virtually unchanged and there is a considerable polarisation in the cathodic zone. The protective effect of furfural is probably due to its resin forming capacity.     

Einfluß von Mo2C und P auf die Wasserstoffdiffusion und Löslichkeit im System Fe-Mo-C-P

Effect of Mo₂C and P on hydrogen diffusion and solubility in the Fe-Mo-C-P system In Fe-Mo-C-P alloys at moderately high temperatures, phosphorus favors the precipitation of Mo₂C particles in the matrix. In the vicinity of these precipitates, the dislocation density is increased and phosphorus is enriched by trapping. The effect of this microstructure on the steady state hydrogen permeation is negligible. The hydrogen solubility is increased and the hydrogen diffusion is decreased according to interactions between hydrogen and the traps which are formed along with the carbides. The average binding energy of the deep traps for hydrogen was found to be about ?54 kJ/mol H. This value corresponds to the interaction energy between hydrogen and the deep traps at dislocations. If phosphorus is enriched in the vicinity of Mo₂C, the average binding energy of the deep traps decreases.     

Untersuchungen zum Einfluß von Sulfid- und Sulfationen auf die Korrosion des Eisens in alkalischer Lösung

Investigation into the influence of sulfide and sulfate ions on the corrosion of iron in alcaline solution The corrosion behaviour of Armco iron as well as that of a technical high-strength steel was investigated in sulphide - and sulphate-containing electrolytes of pH ～ 12.6. Current density - potential curves show that iron, after successful passivation, remains passive and protected against corrosion in a solution saturated with CaS, CaSO₄ and Ca(OH)₂ at potentials up to 800 mV(EH). Passivation experiments conducted by changing from the active region to various anodic potentials yielded a critical potential region around 300 mV(EH), above which corrosion appeared. Up to E_H = 200 mV complete passivation was observed. The same critical potential region was observed in experiments of repassivation after mechanical damaging of a protective passive layer. Additional tensile stresses of 85%· σ_0,2 caused no stress corrosion cracking at a potential of 500 mV(EH). After damaging the passive layer, through scratching of the stressed wires fracture occured at and above potentials of 300 mV(EH). At 200 mV(EH) repassivation was observed even under tensile load. In a sulphate-free Na₂S/Ca(OH)₂ solution of the same sulphide ion concentration no stress corrosion cracking of the samples occured at any potential up to 800 mV(EH) even after scratching the steel samples. The observed stress corrosion in sulphide - and sulphate-containing electrolytes is to be ascribed to the action of sulphate and not to sulphide ions.     

Einflüsse von HCl und N2 auf die Hochtemperaturkorrosion in Atmosphären mit niedrigem Sauerstoffdruck

Influence of HCl and N₂ on high temperature corrosion in atmospheres with low oxygen pressures The effects of HCl and N₂ on the high temperature corrosion in atmospheres with low oxygen pressures were investigated. Investigations of the alloy Fe-20Cr in He-H₂-H₂-O-HCl atmospheres at 1173 K under conditions, where no condensed chlorides could be formed, show the simultaneous growth of Cr₂O₃ and evaporation of CrCl₂. The kinetics of the reactions can be described by growth of Cr₂O₃ according to the parabolic rate law and transport of CrCl₂ in the gas flow following a linear rate law. During heating of the samples in He-H₂-H₂O-HCl condensed chlorides are formed which decrease the adherence of the oxide layers and cause oxide spallation during cooling. This can be avoided either by preoxidation in H₂-H₂O or heating in dry hydrogen. The porosity of Cr₂O₃ layers is not enhanced when HCl is added to the gas atmosphere. The oxidation and evaporation is enhanced in N₂-H₂-H₂O-HCl atmospheres compared to He-H₂-H₂O-HCl atmospheres. The Cr₂O₃ scales are coarse grained and poros. The enhanced porosity is caused by the nucleation and growth of chromium nitrides in the transient state of oxidation.     

Zur Korrosion von Eisen und Aluminium in wässerigen Lösungen von Ammoniak und Kohlensäure – 2. Mitteilung: Elektrochemische Untersuchungen

Contributionto the corrosion of iron and aluminum in aqueous solutions of ammonia and carbonic acid. 2nd Communication: Electrochemical investigations Corrosion potential-time curves and current density-potential curves as well as polarization resistances and other electrochemical methods have been used to characterize the corrosion behaviour of aluminum and iron base materials in an aqueous solution of 11% ammonia and 7% carbon dioxide (leaching solution applied in hydrometallurgical nickel raffination) at 50 °C. For comparisonal purposes the behaviour of the same materials has been investigated in ammonia, sodium carbonate and sodium hydroxide solutions at constant pH. Despite of the relatively elevated pH value aluminum is protected against corrosion in the ammonia-carbon dioxide-water-mixture through selfpassivation (fast repassivation of mechanically destroyed passive layer). In contrast, the stability of iron and mild steel in the same solution is seriously impaired by easy activation. Permanent passivation is only achieved through anodic protection by means of an external current source.     

Einflüsse kleiner Zusätze von Niob oder Cer auf Korrosion und Kriechen von Incoloy 800 in Co-H2O-H2-Atmosphären

Effects of small alloying additions of niobium or cerium on the corrosion and creep of Incoloy 800 in CO-H₂O-H₂-atmospheres In oxidizing and carburizing atmospheres at high temperatures Fe-Ni-Cr-alloys are carburized under creep conditions by carbon transfer through cracks in the oxide layer. In creep experiments in CO-H₂O-H₂ atmospheres at 1000 °C with several alloys based on Incoloy 800 the carburization could be related to the strain of the specimens. Alloying additions of Nb in the range 0.2 to 1% caused changes in the creep rate, a decrease for >0.35% and an increase for >0.35% Nb. The creep resistance for the high Nb concentrations could be improved by solution annealing at high temperatures (1200 °C). Niobium strongly decreases the carburization - this effect can be explained by the formation of an internal layer of Al- and Nb-oxides beneath the outer Cr₂O₃ layer. An alloying addition of Ce (0.06%) also has beneficial effects on the creep resistance and carburization resistance of Incoloy 800.     

Elektrochemische Untersuchungen über die Korrosion des Eisens in sulfidhaltigen Lösungen

Electro-chemical investigations into the corrosion of iron in solutions containing sulphides In order to investigate the corrosion behaviour of steel reinforcements in concrete containing sulphides, measurements have been carried out of electro-chemical current potentials. The electrode material consisted of carbonyl iron; the air-less electrolyte solutions had varying contents of H₂S, HS^. and S^?, with a PH value ranging from 4 to 12.6. The tests showed that, with PH= 12.6, iron remains protected by a passive oxide film even in a solution containing sulphur. However, from about PH = 10-11 downwards, the passive film is replaced by a non-protective iron sulphide layer. But at least down to PH = 9, the corrosion rate is still very low due to the strong inhibition of the cathodic part-reaction of the hydrogen segregation. The kinetics of the hydrogen segregation due to H₂S reduction are discussed.