Korrosionsinhibierung von Aluminiumpigmenten durch Ester der Gallussäure

Corrosion inhibition of aluminium pigments by esters of gallic acid Aluminium pigments corrode in mixtures of water and butyl glycol with the evolution of hydrogen, which can easily be measured gasvolumetrically. This corrosion reaction can be inhibited with addition of esters of gallic acid (gallates). The corrosion inhibiting effect of the gallates increases with increasing chain length of the ester alcohol; this connexion between the chemical structure of the inhibitors and the evolved volumes of hydrogen can be correlated mathematically with the help of an exponential function. The best inhibitor dodecyl gallate, which is an amphiphilic molecule with a chelating head group, showed protective values of about 99 %. To corroborate the assumption, that amphiphilic molecules with chelating head groups are in general effective inhibitors for the examined corrosion reaction, a second example, the amphiphilic agaric acid (α-hexadecyl citric acid) was tested in comparison to the head group (citric acid); again the amphiphilic molecule inhibited the corrosion reaction of aluminium pigment more effectively as the head group alone.     

Korrosionsinhibierung bzw. -stimulation von Aluminiumpigmenten im alkalisch wäßrigen Medium durch Polyacrylsäuren

Corrosion inhibition resp. stimulation of aluminium pigments in aqueous alkaline medium by polyacrylic acids Flakelike aluminium pigments (aluminium content > 99.5%) are corroded in a mixture of water and butyl glycol at pH = 10 by the evolution of hydrogen. Low-molecular weight polyacrylic acids inhibit the corrosion of aluminium pigments with addition of 0.3–0.5 weight-% significantly better than high-molecular weight polyacrylic acids. By addition of very low amounts (0.05–0.1 weight-%) of polyacrylic acid the low-molecular ones show no effect whereas high-molecular polyacrylic acids stimulate the corrosion reaction. That means that high-molecular weight polyacrylic acids show a contrary action depending on their concentration. The measurement of dissolved aluminium(III) by atomic absorption spectroscopy indicates the formation of (at least partial) soluble aluminium(III)-polyacrylate-complexes whereby the solubility with addition of low-molecular weight polyacrylic acids is lower than with high-molecular.     

Korrosion und Korrosionsinhibierung von Aluminiumpigmenten im alkalisch wäßrigen Medium

Corrosion and inhibition of corrosion of aluminium pigments in alkaline aqueous medium Flakelike aluminum pigments (Al-content > 99.5%) were corroded in an aqueous alkaline mixture of water and butyl glycol in the ratio 9: 1. Chelating agents like citric acid or polyacrylic acid inhibit this corrosion reaction. The temporal progress of the corrosion reaction can be determined by volumetric analysis of the evolved hydrogen and furthermore, with addition of the corrosion inhibitors, by measuring the electrical conductivity of the solution. The corrosion reaction consists essentially of two steps:

• 1 In the latency period no or only little corrosion takes place; during this, time the protective layers (normal oxide layer or layers reinforced by reaction products of inhibitor and aluminum) were dissolved.
• 2 After that the actual corrosion reaction takes place.

It was proved that changes of the pH-value or addition of corrosion inhibitors only influence the duration of the latency period; after that period the rate of the corrosion reaction is nearly independent from the examined conditions.     

Der Einfluß des Gefügezustandes auf die Oxydationseigenschaften von Zirkonium-Vanadium-Legierungen

Influence of structure on the oxidation behaviour of zirconium vanadium alloys The oxidation of the alloys ZrV 1 and Zr V 3 has been studied on a comparative basis to zirconium after various mechanical and thermal pretreatements; the aggressive medium was steam of 300°C.It has been shown that recrystallizing annealing after cold deformation has but little influence on the oxidation resistance; a considerable diminution of the oxidation susceptibility has been achieved, however, by grain refining after a cold deformation or annealing of the martensitic structure. This type of treatment has a positive effect in particular on the structure of the protective layer. In view of the fact that the oxidation susceptibility increases with the concentration of the alloying element it may be suggested that the intermetallic compound ZrV₂ has a negative effect. Consequently, the oxidation resistance is improved by quenching from high temperatures which prevents the formation of segregations.     

Einfluß des pH-Wertes,des Sauerstoffgehaltes und der Strömungsgeschwindigkeit von kaltem Trinkwasser auf das Korrosionsverhalten und die Schutzschichtbildung bei feuerverzinkten Stahlrohren

Influence of pH-value, oxygen content and flow velocity of cold drinking water on corrosion behaviour and surface layer forming of galvanized steel tubes During a test program of 28 months determinations of weight loss, metallographical examinations and chemical analysis data of surface layers showed clearly that in the chosen variation range mainly the pH is important for the longterm behaviour and the expected working life of galvanized steel tubes. Lower pH-values of 6.9 lead to increased rates of Zinc attack and to inhomogene, disturbed surface layers, whereas higher pH-values of 7.9 show decreased Zinc loss and favour the forming of well protecting layers. Oxygen content and flow velocity become important only in the early stage of Zinc corrosion. Additional electrochemical measurements gave a good impression of Zinc corrosion rate development, corrosion attack morphology and properties of surface layers.     

Einfluß von weichem Talsperrenwasser auf die Inhibierende Wirkung von Polycarbonsäuren

Influence of soft storage reservoir water on inhibiting effect of polycarboxylic acids It was the intention of the project to examine the influence of soft storage reservoir water on the inhibiting effect of polycarboxylic acids on unalloyed steel, copper and AlMgSi0.5. For the investigations circuit equipments consisting of rotating thermostats and in series coupled tube test pieces were used. Several inhibitor mixtures were tested in synthetic waters of different composition and in storage reservoir water in dependence on temperature and flow velocity. At unalloyed steel tests were carried out on behaviour with heat transfer. The criterion of interpretation was first of all the weight loss rate per unit area. Furthermore, the specimens are visually estimated and metallographical examined. Polyacrylates and copolymeres alone do not sufficient retard the corrosion of unalloyed steel in soft storage reservoir water. A distinguished inhibition effect is obtained by simultaneous addition of molybdate and phosphonate. A further addition of copper inhibitors on basis of tolyltriazole renders possible the mixed installation of unalloyed steel, copper and AlMgSi 0.5 in half-open circuits. The weight loss rate of unalloyed steel was diminished to values < 0.01 mm/a. The dependence of the weight loss rate on temperature (35/60°C) and flow velocity (0.5 to 2 m/s) is small. The weight loss rate of copper is diminished to < 0.0001 mm/a. The weight loss rate of AlMgSi0.5 with and without inhibitor is about 0.003 mm/a. By visual estimation and metallographic examination local corrosion could not be determined. The behaviour of unalloyed steel with heat transfer from the metal to the inhibited medium is characterized by an increase in weight loss rate.     

Adsorption und Korrosionsinhibierung von Polyacrylsäuren auf Aluminiumpigment

Adsorption and corrosion inhibition of polyacrylic acids on aluminium pigment The inhibition of the hydrogen corrosion of aluminium pigment at pH 8 and 10 by polyacrylic acids and their adsorption is strongly influenced by the isoelectric point (IEP) of aluminium oxide (pH ≈ 9). Approximately polyacrylic acids are completely dissociated at both pH values. As expected, at pH 8 (below the IEP) polyacrylic acids are adsorbed significantly stronger as at pH 10 (above the IEP). Furthermore, the adsorbed fraction of polyacrylic acid increases with increasing molecular mass; but the protective value of polyacrylic acids decreases with increasing molecular mass. There is the surprising result that with increasing adsorption of polyacrylic acids their corrosion inhibiting effect decreases. A partial explanation of this result is the high content of carboxylat groups (calculated acid number 780 mg KOH/g) in alkaline medium, which may be responsible for specific ionic interactions with the aluminium oxide surface.     

Einfluß von Chloriden auf die Oxidation des 2¼ Cr-1 Mo-Stahls

Effects of chlorides on the oxidation of the 2¼ Cr-1 Mo steel Effects of NaCl deposited on oxide scales were investigated for the oxidation of the 2¼Cr-1 Mo steel in the temperature range 450–650 °C. The presence of NaCl causes accelerated oxidation under formation of porous and cracked Fe₂O₃ layers and of solid FeCl₂ at the metal/oxide interface. By reaction of the chloride with the oxide scale Cl₂ is formed, which penetrates into the scale and forms FeCl₂ at the inner phase boundary, this is evaporating continuously and is oxidized to iron oxide upon diffusing to the surface, whereby the chlorine is set free again. An active oxidation results which is catalysed by Cl₂. The rate of the accelerated oxidation is determined mainly by the evaporation and outward diffusion of gaseous FeCl₂ and therefore by temperature by temperature and thickness of the oxide scale. Other parameters such as the flow velocity, the area covered with NaCl or the chlorine pressure, which is present at the outer oxide scale have less effect on the overall rate.     

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.     

Einfluß von Natriumchlorid auf die Oxidation von hochlegierten Chrom- und Chrom-Nickel-Stählen

Effects of sodium chloride on the oxidation of high alloy Cr- and Cr-Ni-steels The effects on the oxidation were investigated of solid NaCl deposits on the oxide scales of the technical steels X10 CrMoV 12 1, X15 CrNiSi 20 12 and X10 CrNiSi 25 20 at 700°C. Independent of the alloy composition the presence of NaCl(s) initiated a markedly accelerated Fe₂O₃ growth on the surface of preoxidized samples, under formation of voluminous, nonprotective layers. Below these scales on the metallic matrix in all cases chloride was detected. The oxides grow according to the mechanism of active oxidation in which chlorine plays a catalytic role. The presence of the chloride at the oxide/metal interface reduces the adhesion of the oxide scale and leads to spalling upon cooling to room temperature. The effects observed are independent of the alloy composition, however, the thickness of the oxide scale is decisive which means the diffusion distance for the gaseous iron chloride.     

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.     

Zum Einfluß von Mangan auf die Korrosionseigenschaften von austenitischen 18.10-CrNi-Stählen

Influence of manganese on the corrosion properties of austenitic 18.10-CrNi stainless steels The influence of manganese in the range of 0.25 to 1.5 mass-% on the passivation and pitting corrosion behaviour of unstabilized and Tistabilized austenitic 18/10 CrNi stainless steels is examined by determination of useful characteristical electrochemical dates using potentiodynamical polarization measurements in H₂SO₄-acidic and neutral model electrolytes. In the case of Ti-stabilized steels, a trend to an improved ability to passivation and to an increased pitting corrosion resistance is signified with increased Mn-content. This is in agreement with the austenite stabilizing effect of manganese. In the case of unstabilized steels, a significant deterioration of the passivation and pitting corrosion behaviour is observed, if the Mn-content of the steel is increased from less than 0.7 to more than 1.0 mass-%. These observations are discussed in the viewpoint of segregation of Mn-rich sulfide inclusions in the steel, which are essentially influenced by the presence of titanium in the steel.     

Der Einfluß von CO2 auf die Korrosionskinetik von Zink in Modellwässern

Influence of CO₂ on the corrosion kinetics of zinc in water Mechanism and kinetics of Zn and Zn/Fe corrosion in water containing various contents of CO₂ is studied by impedance spectra completed by gravimetric corrosion measurements. Electrode impedance is clearly found to be a function of P, the diffusion parameter is of essential importance. A_d as a function of P yields the same curves as the rest potential dependence on CO₂ and moreover the gravimetrically measured corrosion velocity rises linearly with CO₂. –Determination of corrosion velocity according to STERN-GEARY cannot be realized in the systems under investigation. –Experimental results lead to the conclusion that the main corrosion reaction takes place at the metal/layer-phase. The corrosion mechanism is discussed.     

Untersuchungen zum Einfluß des gelösten Siliziumdioxids auf die Korrosion von Chemieemail in Salzsäure

Investigations on the Influence of Dissolved Silica on the Corrosion of Chemical Service Glass Enamel in Hydrochloric Acid At high temperatures chemical service glass enamel is being attacked by mineral acids more than expected in regard to the ion exchange theory. Taking as an example the corrosion test results of a glass enamel in 20% hydrochloric acid at 140 °C one can demonstrate that under adverse conditions all glass constituents will be dissolved almost equally during attack. This result is surprising in respect to the glass component silicon-dioxide, however, its solubility in the acid is increased to 70 ppm by the high temperature. This limit essentially determines the degree of the acid attack on the enamel. If the silica concentration of the attacking acid is low and fairly low amounts add because of short reaction times or high volume to surface ratios then the corrosion rate will be high. If the attacking acid already contains higher concentrations of silica the glass enamel corrosion will be strongly inhibited. On the basis of the quantitative results it is possible to recommend a procedure for testing glass-linings at 140 °C in 20% hydrochloric acid. For this application, too, the corrosion situation in the vapor phase and liquid phase of a technical size chemical reactor is being discussed.     

Zum Einfluß von Heißgaskorrosion auf die Haltbarkeit von Hochtemperaturwerkstoffen

Influence of hot gas corrosion on the life of high temperature materials The study of gas turbine materials shows that behaviour is influenced by stress corrosion cracking even in the creep range. The creep strength is reduced at 1000 °C by 20–50%, depending on the salt concentration in the gas. The influence of the salt concentration is negligible only ≤ 1 ppm salt and then it is possible to base calculations on creep data obtained in air. The influence of hot gas corrosion is particularly critical between 800 and 1000 °C. The influence of general corrosion can be neglected.     

Untersuchungen zum Einfluß des Stahlgefüges auf die stationäre Wasserstoffpermeation

Investigations on the influence of microstructure of steels on steady state hydrogen permeation The effect of microstructure of iron and of a low alloyed steel on steady state hydrogen permeation is studied by means of the electrochemical permeation method adapted to hydrogen gas phase charching at p = 1 bar in the temperature range of 15 to 80 °C. In case of pure annealed iron the permeation coefficient is given by Impurities, oxide inclusions and a high density of lattice defects do not affect steady state hydrogen permeation remarkably. In steel specimens of different microstructure (pearlitic, martensitic, bainitic) hydrogen permeability is decreased by a factor 4 to 8. Carbide precipitates in tempered martensite do not change the permeation coefficient. Also cold deformation by rolling to about 15% shows no effect on steady state permeation. Cold rolling to about 40% or higher degrees decreases the steady state hydrogen flux considerably. In all cases, no essential change in temperature dependence is observed.     

Der Einfluß der Strahlenschädigung durch schnelle Neutronen auf die Spannungsrißkorrosion (SKR) von Eisen-Chrom-Nickel-Stählen

Influence of radioactive deterioration by fast neutrons on stress corrosion cracking of chromium-nickel steels Neutron irradiation has a bearing on the mechanical properties of the pure and industrial steels investigated. The creep limit is increased while the range of uniform elongation is reduced. Under an integral fast neutron flux of about 2.5.10¹⁹ n/cm² there is a defined yield strength increasing the stress corrosion susceptibility and there are indications of intercrystalline cracking in some cases. The industrial alloy has exclusively transcrystalline cracks een after neutron irradiation; the crack density is higher than in the pure alloy.     

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.     

Korrosionsinhibierung von Aluminiumpigment durch disubstituierte Benzolderivate

Corrosion inhibition of aluminium pigment by disubstituted benzene derivatives The hydrogen corrosion of aluminium pigment in aqueous alkaline media can be effectively inhibited by certain disubstituted benzene derivatives; as a rule, the corrosion inhibition is better at pH 8 as at pH 10. The following structure-efficiency-principles can be stated: • A potential chelating ortho-substitution of benzene is, as a rule, a necessary (but not sufficient) requirement for corrosion inhibition. The only exception from this rule is the strong reducing agent 1,4-dihydroxybenzene (hydroquinone). • At least one aromatic (“phenolic”) hydroxyl group seems to bee necessary for corrosion inhibition by disubstituted ortho-derivatives of benzene. In total, the best inhibitor of this work is 2-hydroxybenzyl alcohol (protective values 99 to 99.9%).     

Einfluß von Prüffrequenz und Salzgehalt des Korrosionsmediums auf die Korrosionsermüdung von Stählen bei betriebsähnlichen Lastabläufen

Influence of test frequency and NaCl-concentration on the fatigue life of steels under a realistic load sequence Because of the size and fatigue life of offshore structures the corrosion fatigue behaviour of those structures cannot be determined under service conditions. Also for the relevant corrosion fatigue tests in the laboratory using welded joints a compromise has to be found to reduce testing time to an economic justifiable amount. This compromise may be a higher stress used in the test, a higher test frequency or a higher concentration of NaCl in the seawater. The influence of test frequency and NaCl concentration on the fatigue life of fillet welded V-shaped specimens made from Fe E 355 KT was determined in artifical seawater and under a realistic load sequence. The fatigue life was separated into the crack initiation phase and the crack propagation phase as well. Mean frequencies of 0.2 Hz, 1.0 Hz and 10 Hz did not affect the fatigue life of welded joints until crack initiation, while low test frequencies of 0.2 Hz and 1.0 Hz accelerated the crack propagation. Higher NaCl-concentration of the seawater, however, had no effect on the fatigue life in both phases.