Der Einfluß von Kupfer auf das Korrosions und Passivierungsverhalten von Eisen-Chrom-Legierungen Teil I: Elektrochemisches Verhalten in schwefelsauren Elektrolyten

The influence of copper on corrosion and passiviation of iron-chromium-alloys Part I: Electrochemical behavior in sulfuric acid solutions The kinetic of dissolution and passivation of alloys type FeCrXCuY (X = 5; 7; 9; 11%; Y = 0; 0.5; 1%) was investigated in 1N H₂SO₄ (pH 0.3) and 0.5 M Na₂SO₄ (pH 3), using rotating disc electrodes (RDE) and hydrodynamically modulated rotating ring disc electrodes (HMRRDE). Instationary current density-potential curves (10 mV/s) were measured. For both types of electrodes the transients of current density after pulse polarisation into the passive range were investigated. The selfactivation of one hour prepassivated electrodes (open circuit breakdown) was investigated by potential scans. The dissolution of Cu bearing samples led to the formation of a visible film of copper lowering the current densities in the active and prepassive range as well as the critical current and charge densities of passiviation. Copper accelerates similar to chromium the decline of current transients after pulse passivation, whereas the partial current for film formation was increased as deduced from studies with the HMRRDE, leading to the conclusion of a larger film thickness. However, according to the accelerated open circuit breakdown of copper bearing samples, films on these alloys are less stable than expected, which is related to a faster removal of the oxide film. The results demonstrate an ambivalent effect of copper in the passive state of these alloys.     

Der Einfluß der Metallstruktur auf das Passivierungsverhalten von Nickel

The Influence of Metal Structure on the Passivation Behaviour of Nickel The results of potentiostatic anodic polarisation of deformed and undeformed nickel single crystals in 0.5 m NiSO₄ Ph 3.5 are described. With rising plastic deformation the passivation potentials become more negative and the current densities required for passivation are growing. The beginning of the transpassivation region shifts in cathodic direction also. Recrystallisation of the more deformed specimens effects a partial return of the passivation potential in to the noble direction but the beginning of transpassivation continues in falling off. The shape of the i.e. curves is discussed in connection with the changes in metal structure.     

Untersuchungen zum Einfluß von Polyphosphat auf das Korrosionsverhalten von Kupfer in Elektrolytlösungen

Experiments on the effect of polyphosphate on the corrosion behaviour of copper in electrolytic solutions Gravimetric experiments in a circulating equipment were performed on the effect of Graham salt on the corrosion behaviour of copper in electrolytic solutions by means of a high confounded 2^7?4-fractional factorial. The composition of copper samples: 99.7% Cu, 0.002% Bi, 0.005% Sb, 0.01% As, 0.05% Fe, 0.2% Ni, 0.01% Pb, 0.05% Sn, 0.01% S. The aqueous electrolytic solutions contained hydrogencarbonate-, sulphate-, chloride-, nitrate-, manganese-, calcium ions and Graham salt. It appears that Graham salt is unsuitable for the inhibition of copper corrosion. The polyphosphate promotes corrosion. Chloride-, nitrate-, sulphate- und manganese ions also increase corrosion rate whereas it is decreased by hydrogencarbonate ions. Increase of temperature also causes a decrease of corrosion rate. An existing danger of contact corrosion induced by copper cannot be removed by addition of Graham salt if copper and carbon steel, respectively galvanized steel are installed together in equipments of plant water.     

Einfluß von Kupfer auf das Korrosionsverhalten verzinkter Rohre in warmen Brauchwässern

Influence of copper on the corrosion behaviour of galvanized tubing in warm water systems Tests carried out with tap water (65°C) containing 0.1 to 0.3 mg/l Cu²⁺ have revealed that copper ions give rise to accelerated corrosion of tube walls. Corrosion takes place in the form of pitting. The intensity and frequency of pits increase as the copper content is increased and the pH value is decreased. Corrosion products formed on the zinc are predominantly a basic zinc carbonate, while copper is found in a coagulated form at the surface or embedded in the surface layer. The copper content of the corrosion products increases as the copper content of the water is increased and may attain up to 12.5%.     

Der Einfluß von pH-Wert und Sauerstoffgehalt von Pufferlösungen auf das Korrosionsverhalten metallischer Werkstoffe

Influence of pH and oxygen content of buffer solutions on the corrosion behaviour of metallic materials The application of solutions to the decontamination of materials in nuclear installations is based on the condition that their corrosion behaviour is clearly understood. Since electrochemical corrosion is due to cathodic and anodic partial reactions which are influenced in different ways by the pH of hte solution and the oxygen content it is suggested that the results of electrochemical experiments with buffer solutions be used as a model for predicting the corrosion behaviour of materials in other solutions. In the tests described here potentiocinetic current-potential-curves have been traced and galvanic corrosion tests have been made. The results obtained in ascorbic acid, postassium hydrogen phthalate, ammonium citrate and acetate, sodium and potassium tartrate, ammonium hydrogen phosphate, sodium carbonate, hexamethylene tetramin, ethylene diamine enable – on the basis of summarized current-potential-curves – the metals studied to be classified in four groups characterized by clear differences concerning the influence of pH on the corrosino behaviour.     

Der Einfluß unterschiedlicher Nitratgehalte auf das Korrosionsverhalten von verzinkten Stahlrohren

The influence of different nitrate contents of drinking water on the corrosion behaviour of galvanized steel pipes At the water works Biblis and Alsbach of Südhessische Gas und Wasser AG, Darmstadt, field tests were performed over a period of 2 1/2 years to describe the influence of different nitrate contents in drinking water and the corrosion behaviour of different qualities of galvanized steel pipes. The results obtained showed, that weight loss and corrosion rate measurements give no information on this subject. Optical inspection and flushing tests could prove, that selective corrosion occurred in the water with higher nitrate content. Galvannealed pipes showed local corrosion attack after a certain exposition time in water with higher nitrate content, depending on flow velocity. Air blown galvanized pipes and galvannealed pipes in water with higher nitrate content additionally produce „Zinkgeriesel”︁ during flushing. The selective corrosion attack also takes place to a very small extent in galvanized steel pipes, where quality is in accordance to the German Standard DIN 2444.     

Einfluß von Oberflächenstruktur und chemischer Zusammensetzung auf die Lochfraßkorrosion von Ni-Einkristallen

Influence of surface structure and chemical composition on the pitting corrosion of nickel monocrystals With the aid of current density potential curves the pitting corrosion of nickel monocrystals (99.45–99.99 Ni) has been investigated in solutions containing 0.5 M each NiC1₂ and NiSO₄, using the pretreatment (chemical and electrochemical polishing) as a discriminating actor. As is shown by experimental results pitting is originated only at dislocations, not, however, at holidays in the passivating layer. This phenomenon is even more pronounced in the presence of impurities which may give rise to the formation of local elements. The low number of pits as compared to dislocation density can be explained in terms of special dislocation configurations required for starting pit formation.     

Der Einfluß von Martensit auf das Korrosionsverhalten von 18 Cr-10 Ni-Stahl

The effect of martensite on the corrosion properties of 18 Cr-10 Ni steel The corrosion properties of the martensitic phases formed in an austenitic matrix by (i) cooling to low temperature (-196 and ?269°C resp. ?320 and ?452°F) and (ii) cold working at room temperature was investigated for two chromium-nickel stainless steels of the 18 Cr10 Ni type. Austenite and martensite have the same chemical composition but different lattice structures. In sulfuric acid, both martensitic phases formed at low temperature and by cold working arc preferentially attacked in the active range of corrosion. The effect of potential on the corrosion attack was elucidated by potentiostatically controlled experiments with subsequent light-optical and SEM-investigation of the specimens. Selective corrosion attack of the martensitic phase was found down to a potential being 0.8 V more negative than the cathodic limiting potential of the active corrosion range of a fully austenitic steel, irrespective of the way of the martensite transformation. The preferential attack of martensite may be explained by the supposition that the deposition of cathodically protecting layers possibly consisting of nickel is rendered more difficult at the martensitic surface areas. In sulfuric acid, no differences in the corrosion properties between austenite and martensite were found in the passive and transpassive range. In chloride containing aqueous solutions, the resistance to pitting is not effected by martensite formed at low temperature. From this it is concluded that also martensite formed by cold working does not effect the pitting resistance.     

Untersuchungen über den Einfluß des Zinks auf das Korrosionsverhalten von Spannstählen

Investigations on the influence of zinc on the corrosion behavior of high strength steels Corrosion and fracture behavior of hot dip galvanized high strength steels with and without damaging zinc layer was studied in deionized water, in tap water, and in saturated calcium hydroxide solution through which nitrogen, air, and carbon dioxide were bubbled separately. Hydrogen permeation measurements have been carried out for steel specimens which were cathodically polarized by means of the zinc layer. It has been observed that the hydrogen activity reached to a maximum of 1-2 in neutral solutions and 4-10 in saturated calcium hydroxide solution or in dilute acid solutions containing carbon dioxide, before decreasing to low values. The decrease of hydrogen activity is due to the formation of surface layers. Constant load tests by application of a load amounting to 100-110% yield strength caused no hydrogen induced brittle fracture within 300-400 h neither with nor without damaging zinc layer. At a constant strain rate of 5· 10^?7/s only 8 mm cold drawn steel wires were found to be almost unsusceptible to hydrogen that was absorbed during the test. Under notched conditions, all the steels investigated showed macroscopic brittle fracture.     

Oberflächenanalytische Deckschichtenuntersuchung der Lochkorrosion (Typ I) an Kupfer

Surface analysis of protective layers of pitting corrosion (type I) at copper Pitting type I at copper tubes is characterized by a typical protective layer formation of the corrosion product. Electronoptical and electronspectroscopical methods of surface analysis as ESCA, SAM and AES, respectively enable a qualitative and quantitative investigation of the protective layer. Moreover, this surface analysis permits conclusions of the pitting I-formation mechanism.     

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.     

Der Einfluß programmierter Schweißtemperaturzyklen auf die Gefügeausbildung und das Korrosionsverhalten von austenitischen korrosionsbeständigen Stählen

Influence of programmed welding temperature cycles on the resulting structure and the corrosion behavior of austenitic steel Studies on corrosion resistant austenitic steels subjected to simulated welding temperature cycles have shown that even after very short annealing times the corrosion resistance is decreased. In the temperature range between 700 and 900 °C carbides are precipitated, while grain growth and twinning are observed at temperatures between 900 and 1100 °C. Above 1280 °C delta-ferrite is formed as early as after 15 sec. Potentiokinetic current density/potential curves have been traced on the basis of tests in 1 N sulfuric acid at room temperature. The passivation current density has turned out to be a suitable corrosion resistance criterion.     

Einfluß der Legierungszusammensetzung auf das Oxidations- und innere Nitrierungsverhalten von Nickelbasis-Superlegierungen

Influence of the alloy composition on the oxidation and internal-nitridation behaviour of nickel-base superalloys Internal nitridation of nickel-base superalloys takes place as a consequence of the failure of protecting oxide scales (Al₂O₃ and Cr₂O₃, respectively) and leads to a deterioration of the material properties due to near-surface embrittlement caused by the nitrides precipitated (TiN and AlN, respectively) and due to near-surface dissolution of the γ′ phase. By using thermogravimetric methods in a temperature range between 800 °C and 1100 °C supplemented by microstructural examinations, the failure potential due to internal nitridation could be documented. A quantification was carried out by extending the experimental program to thermogravimetric studies in a nearly oxygen-free nitrogen atmosphere which was also applied to various model alloys of the system Ni-Cr-Al-Ti. It could be shown that the nitrogen diffusivity and solubility in nickel-base alloys is influenced particularly by the chromium concentration. An increasing chromium content leads to an enhanced internal-nitridation attack.     

Einfluß und Wirkungsweise von Inhibitoren auf das Korrosionsverhalten von Reineisen und Stahl in praxisnahen Korrosionsmedien

Influence of inhibitors on the corrosion behaviour of pure iron and steel in practical media The present paper summarizes the experimental and theoretical results obtained in the BMFT-R & D project F 5.4/2. The electrochemical impedance spectroscopy (EIS) is found to be a very useful in-situ measuring technique for complicated corrosion systems giving information which are not available by conventional electrochemical or non-electrochemical methods. The influence of 3-D surface inhomogeneities on local corrosion processes of iron and steel in neutral aerated media and practical systems are analyzed in terms of transfer function analysis of EIS-data. A new concept is presented to classify corrosion inhibitors as interface and interphase ones. On the basis of the results obtained a systematic development of interphase corrosion inhibitors will be supported in the future.     

Der Einfluß von Bakterien auf die Eisenkorrosion in Brack- und Meerwasser

Influences of bacteria on iron corrosion in brackish and sea waters The corrosion of steel in seawaters is subject to seasonal variations; the corrosion maxma being in spring and autumn. The variations are not attribuable to changes in water temperature, salt concentration or oxygen content but are due to the co-action of biotic and abiotic factors, the former givin rise to temperature dependent variations of corrosion. The activity of bacteria becomes bovious only at temperatures above 10 °C; at these temperatures metablolism is activated and the products of matabolism may attack iron (or bac-     

Einfluß korrosiver Medien auf das Verhalten von glasfaserverstärkten Verbundwerkstoffen

Influence of corrosive media on the behaviour of FR composites Aqueous media are absorbed by resins and composites. It is possible to describe the sorption behaviour of glass fiber reinforced composites knowing the sorption behaviour of the resin fraction and the absorption in the volume of interfaces and flaws. Concentration changes lead to dimensional changes; these swelling strains of anisotropically reinforced layers can be determined from the swelling behaviour of the matrix resin. In general concentration distributions during diffusion processes cause residual stresses (swelling stresses). Swelling strains and swelling stresses have to be superimposed to a mechanical load. The phenomenon of the ?stress-crack-corrosion”? also occurring in polymers can be explained by residual stresses due to diffusion processes.     

Der Einfluß von Zusatzelementen auf die Zunderfestigkeit von Heizleiterlegierungen

Influence of elemental additions on the scaling resistance of electrical heater alloys The influence of trace elements on the useful life of heater alloys is discussed; this influence had first been recognized by W. Hessenbruch almost 40 years ago and had been systematically studied. It is known from Hessenbruch's work, that in particular cerium and calcium increase the scaling resistance of heater alloys. A short discussion is devoted to metallurgical problems in connection with the addition of these highly reactive elements. Although it is generally known that alloy additions increase the useful life of the alloys and although this effect is largely utilized on an industrial level, a definitive clarification of the mechanism of action of these improving elements is still lacking. Opinions diverge already with respect to the question for the form — metallic or oxidic — in which these elements enter into action. The opinions maintained with respect to this phenomenon are discussed. A new experimental technique has enabled to give an answer in terms of an action of elements dissolved in their metallic state.     

Der Einfluß von Chlorid auf das Korrosionsverhalten von Nicrofer 3033 (1.4591) in mittelkonzentrierter heißer Schwefelsäure

The influence of chloride on the corrosion behaviour of Alloy 33 in medium concentrated hot sulfuric acid In the concentration-temperature field of 15 to 80 mass-% p. a. grade sulfuric acid and temperatures of 50 to 90 °C in which Alloy 33 is either corrosion resistant without and with small additions of Fe³⁺, the influence of chloride concentration on the degradation of its corrosion resistance has been determined. The evaluation of the critical chloride content has been carried out by gravimetrical means in tests of 7 days duration. For comparison materials used in sulfuric acid applications as Alloy 20 (2.4660) and Alloy 31 (1.4562) have been examined in form of random tests in the above mentioned concentration-temperature field. Based on polarization tests the influence of chloride ions in sulfuric acid solutions could be evaluated for the conditions of presence and absence of the oxidant Fe³⁺. The chloride concentration, which can be tolerated, diminishes with increasing acid concentration and temperature. If the oxidant Fe³⁺ is present in the sulfuric acid solution, higher chloride concentrations can be tolerated. Alloy 20 (2.4660) will in comparision to Alloy 33 (1.4591) be activated at significantly lower chloride concentrations. Compared to Alloy 33 (1.4591) the range of application of Alloy 31 (1.4562) is mainly restricted in Fe³⁺ containing sulfuric acid.     

Einfluß des pH auf Natriumdiäthyldithiocarbamat als Inhibitor der Korrosion von Kupfer

Influence of the PH value on sodium diethylcarbamate as a corrosion inhibitor for copper In aqueous solutions down to PH values of 5.1, sodium diethylcarbamate has a very good inhibiting effect on the corrosion of electrolyte copper. In solutions with PH values below 5.1, however, the application of this inhibitor has the effect of greatly increasing the rate of copper corrosion.     

Einfluß von bituminösen Dachbelagsmaterialien auf das Korrosionsverhalten von Dachentwässerungssystemen aus Zink und verzinktem Stahl

Influence of bitumineous roof coverings on corrosion behaviour of roof draining systems made of zinc and galvanized steel In long time weathering and laboratory tests on a number of different bitumineous roof coating materials it was confirmed that they are the cause of damage on zinc roof draining systems. The acidic corrosion capacity rain_water is very increased by the formation of acids in bitumineous materials. The formation of acids is almost independent of the different types of bitumineous base materials, but can be reduced by adequate gravel or state covering. But only alkaline mineral coverings, found in a few cases, give sufficient protection against corrosion of zinc. Further important influence which cause corrosion damages is the relation of bitumineous roof area to zinc area and the particular conditions of water draining.