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.     

Einfluß des entstehenden Rostes auf den Verlauf der atmosphärischen Korrosion von Stahl

Influence of incipient rust on the pattern of the atmospheric corrosion of steel The corrosion pattern with continuous rust formation has been compared with the results obtained and accumulated at certain intervals during the same time from analogous specimens. It was found, firstly, that there is a critical value of SO₂ concentration and, secondly, that the existing rust is capable of keeping certain quantities of SO₂ away from the surface. The latter effect explains the flattening-out of the corrosion rate to constant values, as well as the fact that, in pure atmosphere, the stationary conditions are reached later than in an industrial atmosphere.     

Über den Einfluß des Sauerstoffes auf die Korrosion in Dosenkonserven aus Weißblech

Influence of oxygen on the corrosion in tinplate cans The research was made with stell plate (thinnest plate, 0,07% C, from rimmed prematerial) and purest tin in a cell according to the galvanic element. Corresponding storages were made in unlaquered and laquered cans. Citrate buffer, pH 2.4, was used as electrolyte. Oxygen effects pitting corrosion on the steel surface. The corrosion activating effect connected with this pitting even then remins when oxygen is spent after some time of storage of cans. But the steel surface is protected simultanously by tin ions soluted from the tin surface, because these ions get adsorbed particularly on the endangered regions of the steel surface and inhibit the pitting corrosion. But this protection only happens in media where the steel plate is electropositive to tin. The question of the suitability of can filling free of oxygen therefore can not be answered in general, but has to be anwered individually taking into account the relations described.     

Einfluß der chemischen Zusammensetzung auf die Kinetik der atmosphärischen Korrosion von Stählen

The influence of the chemical composition on the kinetics of the atmospheric corrosion of steel A total of 19 different structural steels were exposed to urban, rural and industrial atmospheres for periods up to three years. The evaluation of the weight losses determind at certain intervals permitted the establishment of a linear relationship which can be used for assessing, within certain limits of concentration, the influence of specific alloying elements. The tests showed that the effects of the different alloys varies with the type of atmosphere and with the degree of corrosion, and may well shift from “favourable” to “detrimental”. The results are also influenced by the quantitative ratios of certain components. The corrosion behavior of the steels is consistently governed by P, S and Cu and, to a lesser extent, by C and Mn.     

Über die Einwirkung von Wasser auf Anstrichfilme

The effect of water on paint coatings The water absorption of varnishes and organic coatings is normally known as “swelling”. In many cases, however, a homogeneous water absorption through swelling of the polymer substance is of lesser importance than a heterogeneous water absorption. The latter may occur at the inner interfaces of a lacquers or plastic coating, e.g. at the interface between coating base, at the interface between polymer substance (binder) and filler (pigment), or at the interfaces within the polymer substance itself. One important cause of heterogeneous water absorption is the occurence of osmotic processes which are caused by water soluble substances present or originating at the boundaries. With such absorption, the freezing temperature of the polymer substance plays an important part. It is possible to ascertain experimentally how polymer films are absorbing the water. In this way, the influence of water on the film properties can be better evaluated than by simply ascribing all the water intake to a swelling process.     

Über einige Aspekte der atmosphärischen Korrosion von Stahl

To some aspects of the atmospheric corrosion of steel The corrosion of unalloyed steel (St 38 u 2) in pure moist air and by existence of low molecular saturated monocarbonic acids have been studied with microphotometric method. Moreover the electrochemical behaviour of this steel in adequate aqueous solutions has been characterized. It was found that steel - in distinction to pure iron - corroded already in moist air without pollutants in case the relative humidity is (RH) ≥70%. The action of the volatile monocarbonic acids on the corrosion were dependent on the pH value of water film which had been absorbed on the oxide layer of iron material. Oxygen acted as passivator above of pH_crit and the anions of these carbonic acids stabilized the surface hydroxyl groups on the strength of formation of bridging complexes. Final general conclusions about the mechanism of the atmospheric corrosion of iron materials are deduced.     

Über den Einfluß von Thioharnstoff und Thioharnstoff-Derivaten als Beizinhibitoren auf die Wasserstoffaufnahme,die Inhibitorwirksamkeit und die Wechselbiegefestigkeit von Kohlenstoffstahl bei der Säurebeizung

Influence of thiourea and its derivatives as pickling inhibitors on hydrogen pickup, degree of inhibition and fatigue load of carbon steel during pickling in acids The influence of additions of thiourea (TU), N-methyl-TU, N, N′-tetramethyl-TU, N-phenyl-TU, N, N′-diethyl-TU and N, N′-diphenyl-TU upon the acid pickling of mild steel (1,0 M H₂SO₄ at 50° C) was investigated. Measured were inhibitor efficiency, uptake of hydrogen and alternating bending strength of the samples as functions of inhibitor type and inhibitor concentration. With all inhibitors a maximum of inhibitor efficiency and alternating bending strength and a minimum of hydrogen uptake was found in the same inhibitor concentration range of about 0,001 M. Compared to pickling in pure sulfuric acid at this optimum concentration the inhibitor efficiency is between 95,2 and 98,4%, the decrease of the hydrogen uptake between 8,6 and 63,3% and the increase of the alternating bending strength between 20,0 and 43,4%, depending upon the kind of inhibitor. The alternating bending strength increases roughly linearly with decreasing hydrogen content of the samples. In the optimum concentration range the inhibitor efficiency and the alternating bending strength increase, the hydrogen uptake decreases roughly linearly with increasing adsorption area or increasíng molecular weight of the inhibitors.     

Über den Einfluß von Kohlenstoff und Stickstoff auf die Empfindlichkeit niedriglegierter Stähle gegen Spannungsrißkorrosion

The influecne of carbon and nitrogen on the sensitivity of low-alloyed steels to stress corrosion Application of stress to steels under the influence of certain media produces stress-corrosion cracking. This can be examined through experimental methods only, by which the specimens are kept under constant stress. The cracking time required for the specimen is then a measure of resistance of stress-corrosion failure. In this way it is possible to investigate the influence of alloying metals and the heat treatment on susceptibility of steels, by considering the respective strenght. Experiments were carried out to determine the effect of carbon content and the combined effect of carbon and nitrogen in a series of medium frequency and vacuum steels. It is found that increasing carbon content improves the resistance of specimens, taking also the higher strength into account. A higher nitrogen content shortens the cracking time. This shortening of resistance due to nitrogen content was much more note worthy in the case of high-carbon steels than in the case of low-carbon steels which were already sensitive in this respect. Comparing an open-hearth steel with the above steels, it seems as if there are other alloying metals which make the steels susceptible to stress-corrosion cracking. The effect of these alloying metals shall be investigated further.     

Über den Einfluß des Gefüges von Zinklegierungen auf die Schutzfähigkeit von Zinkanoden in Seewasser

Influence of the structure of zinc alloys on the protective capacity of zinc anodes in sea water The use of zinc for cathodic protection duties in sea water is restricted because of the considerable polarisation of zinc. The behaviour is due in particular to cathodically active additions of lead, copper and iron. The microcouples then formed give rise to considerable zinc dissolution and to the formation of a thick and dense passivation layer. Since, however, any reduction of the iron content in zinc involves high cost it is more economical to add small quantities of Al, Cd, Si, Hg, Sn or Mn. These additions produce a considerable grain refinement and thus reduce the tendency to form microcouples even in the presence of iron.     

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.     

Einfluß der Mikrogeometrie auf den Korrosionseffekt III. Atmosphärische Korrosion bei kapillarer Kondensation

The influence of microgeometry on corrosion - (III)Atmospheric corrosion with capillary condensation While there is no condensation on a smooth surface, such a condensation can take place even at relative humidities below 100% in the case of complex and in particular capillary surface. The conditions existing on such a surface can be approximated by a model involving hemi-spherical elevation in contact with each other. On the basis of this model it is possible to calculate the rate to be expected in terms of the geometrical parameter. It is shown that the corrosion effect at the contact points increases as the radius of the hemi-spheres is increased, while the overall corrosion is reduced since the overall number of hemispheres per unit surface is reduced in this case.     

Über den Einfluß der Austenitstabilität von 18/8-Chrom-Nickel-Stählen auf die Verformungseigenschaften und auf das Korrosionsverhalten dieser Stähle

Influence of austenite stability of 18-8 Cr-Ni-steels on the cold working and corrosion properties of these steels The martensite formed during cold working has a negative effect on uniform corrosion only when the specimen is active in the particular medium; if so, corrosion current density increases with the degree of cold working. The martensite generated by cold working reduces on the other hand the susceptibility to intercrystalline corrosion and – in amounts up tn 2% – increases the time to failure in stress corrosion cracking (15 and 45 kp/mm²). The pitting potential is not shifted by the martensite, but pit density increases with the martensite content. In the Kesternich test no negative effect of the martensite is found. It is therefore concluded that reducing the Ni content in 18-8 steels improves workability without having a pronounced deleterions bearing on corrosion behaviour.     

Über den Einfluß verschiedener Chloridionenkonzentrationen auf die Aktiv-Passiv-Korrosionsempfindlichkeit von Stahl in gesättigter Kalziumhydroxidlösung

Influence of various chloride ion concentrations on the active-passive corrosion susceptibility of steel in saturated calcium hydroxide solution The corrosion of steel in concrete is caused mainly by the presence of chlorides. This effect was investigated by measuring potentiodynamic current-voltage-curves and by potentiostatic experiments of stressed (55 or 77% σ_B) plain steel electrodes in saturated Ca(OH)₂-solution with varying chloride concentrations. The results show that down to Cl′-concentrations of 100 mg/l there is a significant statistical probability of corrosion within 48 hours, and that for longer times the threshold concentration may be even lower. The microscopical examination of corroded samples shows that under the experimental conditions only pitting corrosion is the cause of failure and that this pitting is promoted by the applied stress.     

Über den Einfluß des Flächenverhältnisses auf die Stromdichte in galvanischen Zellen und Belüftungszellen

Influence of the area ratio on the current density in galvanic and aeration cells With a view to corrosion phenomena on conventional metal combinations the corrosion current density has been studied as a function of the cathode: anode area ratio in aeration cells (Fe/Zn, Fe/Fe, Zn/Zn, with Na-sulfate and NaCl as electrolytes) and in galvanic cells (Cu/Fe, Cu/Zn, with Cu? , ammonium and zinc sulfate as electrolytes). It was the aim of the investigation to find out the extent to which the theoretical ideas of Mansfeld and Akimov concerning film rupture and diffusion control may be applicable. It is found that mansfeld's concept must be extended to include the effective electrode potentials in order to allow an interpretation of corrosion current density in aeration cells. In the case of galvanic cells, however, there is a limitation attributable to the cell resistance which is determined by independent resistance measurements. The corrosion behaviour of the metals studied is interpreted in terms of the measured current densities.     

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.     

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.     

Zum Einfluß der Oberflächenbearbeitung und der chemischen Zusammensetzung auf die Korrosion von Dental-Amalgamen

Influence of mechanical treatment of the surface and of chemical composition on the corrosion of dental amalgams The influence of mechanical treatment of the surface and of chemical composition of amalgams on the corrosion behaviour is examined in artificial saliva by determination of useful characteristical dates using potentiodynamical polarization measurements on little (0.03 V min^?1) and high (0.6 V min^?1) polarization rate. In the case of the amalgams the corrosion resistance increase with smaller roughness of the surface and smaller concentration of γ₂-phase. The concentration of γ₂-phase is influenced by the chemical composition and to a certain extent by the mechanical treatment of surface. Therefore dental amalgam with little or without γ₂-phase and polishing of amalgam are required for therapy of filling.     

Über die Wirkung des Magnetits beim atmosphärischen Rosten und beim Unterrosten von Anstrichen

The effect of magnetite on atmospheric rusting and underrusting of paint coats The corrosion products formed during atmospheric rusting of steel can, under suitable conditions, form magnetite; this conversion takes place by preference at the ferrous sulfate nests where FeOOH is reduced by metallic iron. Contrary to the current view about the protective effect of magnetite, this conversion considerably increases the ultimate rusting rate, even below paint coats. The conversion behaviour of natural rust affords a possibility for evaluating the ultimate rusting susceptibility of a rusted surface. To that end the rust as formed under natural conditions in the atmosphere is kept in an atmosphere of oxygen free nitrogen at 97% rel. humidity of several weeks and the proportion of magnetite then formed is determined. This proportion may, according to experimental results, amount to more than 90% and can increase the ultimate rusting rate to several times the original value; oxygen concentrations below 1 vol.% are then sufficient for maintaining the high corrosion rate. This method of assessment affords a better characterization of the substrate than a characterization by age, thickness and origin of rust alone.     

Über den Einfluß der Bewitterung auf das Korrosionsverhalten unlegierter und niedriglegierter Stähle

Influence of weathering on the corrosion behaviour of unalloyed and low-alloy steels Accelerated weathering tests with plain carbon steel and low-alloy steels show that the influence of weathering is of considerable importance for the atmospheric corrosion. Attention has to be paid that the steel surfaces are never wet over a longer period of time. The faster the steels will be dry, the better is the long time behaviour of these materials. Frequent short wet periods, followed by dry phases lead to the formation of an increasingly better protective layer. By favorable weathering conditions the influence of the composition of the alloys is comparatively small. Metallographic and electrochemical tests further show that the corrosion protection is not only due to the formation of a compact macroscopic layer. Local passivation effects are significant as well.     

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.