Showing papers on "Corrosion published in 1976"

Transport Processes and the Mechanism of Pitting of Metals

Abstract: A pit model was developed on the assumption that the metal ions hydrolyze inside the pits and that the corrosion products are transported by diffusion. Concentrations of Me2+, , and H+ ions, as a function of pit depth and current density, for Zn, Fe, Ni, Co, Al, and Cr were calculated. The main reason for passivity breakdown at the initial stages of pit growth, was found to be the localized acidification due to metal ions hydrolysis. Assuming a criticalpH value for pit initiation, the following experimental facts could be explained: (i) the effect of the external pH on the pitting potential of Fe and stainless steel; (ii) the effect of sodium borate concentration on the pitting potential of Zn; (iii) the effect of weak acid salts on the pitting potential of Al; (iv) the oscillations of the electrode potential of stainless steel and nickel in solutions of ions; (v) the existence of a pitting inhibition potential ; and (vi) the existence of a pitting protection potential. Through analysis of the transport processes inside a pit it was also concluded that the pitting potential of a metal should change with the Cl− ion concentration according to the equation being the slope of the curve at room temperature.

The Polarization Resistance Technique for Measuring Corrosion Currents

Abstract: In 1938 Wagner and Traud1 published a paper: “Concerning the Evaluation of Corrosion Reactions by Superposition of Electrochemical Partial Reactions and Concerning the Potential Formation on Mixed Electrodes.” This paper is today considered the classical paper on mixed potential theory, which postulates that, even without the assumption of the existence of local anodes and cathodes, one can explain corrosion reactions by assuming that cathodic and anodic partial reactions occur at the phase boundary metal/electrolyte in constant change with statistical distribution of location and time of the individual reaction. Wagner and Traud showed further that under certain conditions (yielding certain forms of the partial potential-current curves) it is possible to calculate the rate of a given reaction using electrochemical measurements. These principles were then applied to the dissolution rate of zinc amalgam in acid solutions. Good agreement was found between corrosion rates calculated from polarization curves using the technique, which today is called “Tafel slope extrapolation” and from the amount of hydrogen evolved. These experimental results were considered proof for the general postulations of the mixed potential theory.

ESCA Study of the Passive Film on an Extremely Corrosion-Resistant Amorphous Iron Alloy

Abstract: X-ray photoelectron spectroscopy was applied to study the composition of the passive film formed on an extremely corrosion resistant amorphous Fe-10at.%Cr-13at.%P-7at.%C alloy in 1 N HCl. The passive film consists mainly of hydrated chromium oxyhydroxide which is a common major constituent of passive films on crystalline stainless steels. The extremely high corrosion resistance of the amorphous alloy can only in part be attributed to the formation of a protective hydrated chromium oxyhydroxide film.

Auger Spectroscopic Analysis of Bioglass Corrosion Films

Abstract: Auger spectroscopy and ion beam milling were used to determine surface compositional profiles on a series of bioglass implant materials after exposure to simulated body conditions. Four glasses were examined, a soda-lime-silica glass and 3 compositions produced by adding 3, 6, and 12 wt% P2O5 to the ternary glass. An SiO2-rich layer is formed on the surface of all glasses investigated. As P2O5 is added to the bulk composition, a second film rich in Ca and P forms at the SiO2-rich film-water interface. The rate of formation of the Ca-P film increases as the P2O5 content of the bulk glass increases. When glasses are corroded under identical conditions, the thickness of the Ca-P layer increases as the P2O5 content of the bulk composition is increased.

Electrochemical properties of aluminium alloys containing indium, gallium and thallium

Abstract: The electrochemical behaviour of aluminium alloyed with small amounts (up to 0.2%) of indium, gallium and thallium has been investigated. It has been found that these additions result in: (a) A considerable shift of the rest potential in the negative direction (to 1.4–1.7 V versus SCE), (b) A significant increase of the passivating current density (up to 0.1–1 Acm−2) and (c) A considerable decrease in the negative difference effect (increase of the faradaic efficiency to 99.5%) compared to the behaviour of pure aluminium. Except for the gallium alloy, the rate of corrosion of the alloys in neutral salt solutions is also decreased compared to that of pure aluminium. A ternary alloy, Al-0.01 In-0.01 Ga, exhibited a more negative rest potential than the Al-In alloy and a corrosion stability superior to that of the Al-Ga alloy. The negative difference effect was found to depend on the cation of the neutral salt in solution. The lowest effect was obtained in ammonium chloride solutions.

High Corrosion Resistance of Chromium-Bearing Amorphous Iron Alloys in Neutral and Acidic Solutions Containing Chloride

Abstract: The corrosion resistance of amorphous iron alloys, whose practical application is expected because of their outstanding mechanical properties, has been studied by total immersion tests and...

The Role of Alloyed Molybdenum in Austenitic Stainless Steels in the Inhibition of Pitting in Neutral Halide Solutions

Abstract: In the passive region of austenitic stainless steels alloyed with Mo, the formation of MoO42− ions can be expected in neutral halide solutions by the transpassive dissolution of Mo. It has...

Water radiolysis and its effect upon in-reactor zircaloy corrosion

Abstract: The well-known effects of dissolved oxygen and hydrogen in respectively increasing and reducing the corrosion rate of zircaloys irradiated in high temperature water have been attributed to changes in the course of water radiolysis.1 Computer simulation of the growth and decay of radioly tic species produced by β, γ and neutron irradiation of water at 25°C and 305°C has been performed. In general, neutron irradiation leads to greater decomposition of water, and the effect of dissolved oxygen at 305°C is to markedly increase the concentrations of oxidizing radiolytic species. Correlation of zircaloy corrosion behaviour under such conditions with predictions of water radiolysis suggests that either HO2 of O− 2 are significant contributors to the corrosion enhancement phenomenon. Possible enhancement mechanisms are briefly discussed.

X‐Ray Photoelectron Spectroscopic Study of the Aqueous Oxidation of Monel‐400

Abstract: The surface of Monel-400 alloy was exposed to high pH, aqueous corrosion at 285~ under both oxidizing and reducing conditions. After exposures lasting from 0.3 to 335 hr the surfaces were examined by x-ray photoelectron spectroscopy, scanning electron microscopy, and other techniques. Under reducing conditions, no corrosion film forms on the metal surface, but under oxidizing conditions, the first corrosion layer which forms at the solution interface is entirely Ni(OH)2. This hydroxide, which persists for long times at pH ,.~ 10 but which rapidly converts to NiO at pH ,., 14, is shown to result from a Precipitation process. The composition of the corrosion film is determined by the relative solubilities of nickel and copper at the interface. A composition profile of the corrosion layer beneath the outermost film shows :a gradual increase in cuprous ion concentration with increasing depth, probably due to solid-state migration. This suggests that the aqueous corrosion of Monel-4O0 involves both solid-state oxide growth and an ionic dissolution and precipitation mechanism.

The Electrical Properties of Protective Polymer Coatings as Related to Corrosion of the Substrate

Abstract: The effective electrical permittivity of polymer‐coated steel was measured between 200 Hz and 100 kHz as a function of time of exposure to . The real and imaginary parts of the permittivity increased over the entire frequency range as a consequence of electrolyte penetration. The development of a −1 slope on the log loss vs. log frequency curve suggested localized penetration of the dielectric coating by a conducting phase. This behavior correlated with the onset of visible localized corrosion. Results were discussed in terms of a metal/metal oxide/penetrated‐coating model.

Transport processes and the mechanism of pitting of metals

Abstract: A pit model was developed on the assumption that the metal ions hydrolyze inside the pits and that the corrosion products are transported by diffusion. Concentrations of Me2+, , and H+ ions, as a function of pit depth and current density, for Zn, Fe, Ni, Co, Al, and Cr were calculated. The main reason for passivity breakdown at the initial stages of pit growth, was found to be the localized acidification due to metal ions hydrolysis. Assuming a criticalpH value for pit initiation, the following experimental facts could be explained: (i) the effect of the external pH on the pitting potential of Fe and stainless steel; (ii) the effect of sodium borate concentration on the pitting potential of Zn; (iii) the effect of weak acid salts on the pitting potential of Al; (iv) the oscillations of the electrode potential of stainless steel and nickel in solutions of ions; (v) the existence of a pitting inhibition potential ; and (vi) the existence of a pitting protection potential. Through analysis of the transport processes inside a pit it was also concluded that the pitting potential of a metal should change with the Cl− ion concentration according to the equation being the slope of the curve at room temperature.

Nucleation and Repassivation of Corrosion Pits for Pitting on Iron and Nickel

Abstract: Pit nucleation and repassivation on iron and nickel has been examined by potentiostatic transient measurements. Very short times for the nucleation of corrosion pits of some ms to some 100 ms for prepassivated specimens have been observed. Addition of picrate to the electrolyte can stop pit nucleation for well prepassivated specimens at all potentials completely, but cannot prevent the corrosion of already existing pits. The results are explained by the adsorption- and film breaking theory but give contradiction to the penetration mechanism. The repassivation of corrosion pits in an early stage of development takes Δ Tr = 1 ms to some 100 ms according to the pitting time Δ tp and the pit current density. A relation Δ Tr = k(Δtp)2 has been found. The transport of the accumulated aggressive anions from the pit electrolyte to the bulk solution is postulated as the rate determining process for repassivation.

Mechanical fracture predictions for sensitized stainless steel piping with circumferential cracks. [BWR]

Abstract: Circumferential intergranular stress corrosion cracks have been discovered in the heat-affected zones of girth welds in the Type 304 stainless steel recirculation bypass piping systems of several boiling water reactor (BWR) plants. These cracks initiate at the inner surface of the pipe wall and grow through the thickness by combined stress corrosion and fatigue. The work given in this report is based on the supposition that such a crack has been detected and that its size and shape are known. To determine the residual strength of the cracked pipe, an integrated program of small-scale laboratory experiments, full-scale pipe tests, finite-element computations, and a mechanical failure analysis was conducted. After investigating several candidates, the work has shown that a simple plastic collapse criterion can most effectively be used to predict failure in Type 304 stainless steel pipes with circumferential cracks.

The Mechanism of Corrosion of Poly butadiene-Coated Steel in Aerated Sodium Chloride

Abstract: Polybutadiene-coated steel exhibits highly localized corrosion sites that spread with time. Delamination of the coating occurs in the cathodic areas immediately adjacent to the anodic corrosion sites. Data obtained from electrical measurements, corrosion potentials, and literature sources were used to arrive at an overall mechanism of corrosion.

The corrosion and oxidation of metals (second supplementary volume)

Abstract: This volume is the third in a series on this subject, presenting especially new information published during the period 1968-75. The topics dealt with include simple oxidation, electrochemical, anodic, acid and crystalographic corrosion. A chapter contains information on soluble inhibitors and two chapters deal with protection against corrosion by paints, non-metallic coatings, metallic coatings and metal pigmented paints. A section is included on the corrosion of the motor car, with reference to corrosion due to salt on roads and precautions to combat this reaction. Information is also given concerning corrosion of exhaust systems, car interiors and brake-fluid lines. Brief reference is made to anti-corrosion treatment of steel bridges. /TRRL/

Corrosion of Silicon Carbide in Gases and Alkaline Melts

Abstract: The corrosion behavior of sintered SiC in gaseous environments and alkaline melts was investigated at 900°C. In oxidizing atmospheres such as normally exist in a gas turbine, SiC forms a dense coherent surface film of SiO2 which is not corroded by thin layers of condensed sodium sulfate. However, under some conditions, especially when very low oxygen pressures are maintained at the SiC surface or when basic salt melts or slags containing carbonaceous material are present, rapid corrosion of the ceramic can occur. On the other hand, SiC is inert in pure N2, H2, or H2-H2S mixtures at 900°C. These different modes of behavior are discussed in the context of possible high- temperature applications of SiC ceramics.

Amorphous metal alloys and products thereof

Abstract: A class of amorphous metal alloys is provided in which the alloys are rich in iron, nickel, cobalt, chromium and/or manganese. These alloys contain at least one element from each of three groups of elements and are low in metalloids compared to previously known liquid quenched amorphous alloys rich in iron, nickel, cobalt, chromium and/or manganese. The alloys can be readily formed in the amorphous state and are characterized by high hardness, high elastic limit and, for selected compositions, good corrosion resistance. Products made from these alloys include cutting tools, such as razor blades.

Duplex coating for thermal and corrosion protection

Abstract: A duplex coating and method for making same wherein a primary layer of metals or metal alloys is deposited on a superalloy substrate to seal the substrate against oxidation. A second layer of low density oxide is deposited on the surface of the primary layer. The primary layer has a rough surface so as to provide an adherent surface for the oxide layer.

Method for rendering substrates resistant to abrasion

Abstract: A method for rendering a surface of a substrate resistant to abrasion comprising applying to the substrate and then curing a composition comprising: (1) a reactive silane and (2) a metal ester. Certain compositions can be cured by means of heat, ultraviolet light, or electron beam irradiation. Cured coatings are also corrosion and solvent resistant.

Metal/environment reactions

Abstract: Principles environments ferrous metals ferrous metals (continued) rarer metals the noble metals high temperature effect of mechanical factors design and economic aspects of corrosion cathodic and anodic protection pretreatment and design for metal finishing methods of applying metallic coatings protection by metallic coatings protection by paint coatings chemical conversion coatings miscellaneous coatings conditioning the environment non-metallic materials corrosion testing, monitoring and inspection diagnostic and research techniques useful information.

The Transport of Radioactive Corrosion Products in High-Temperature Water II. The Activation of Isothermal Steel Surfaces

Abstract: A mathematical model to describe the contamination of steel surfaces by 60Co in high-temperature water is developed. The model assumes that 60Co is incorporated into the growing oxide film on the s...

The oxygen electrode. Part 6.—Oxygen evolution and corrosion at iridium anodes

Abstract: A comparison of the anodic behaviour of iridium and platinum using both current and corrosion-rate measurements at various potentials showed that the rate of oxygen evolution was considerably faster on iridium in both acidic and basic media. Under constant potential conditions a continuous decrease in current with time was observed in the case of platinum, under all conditions, and in the case of iridium, in base. It is assumed that this effect is due to continuous slow oxidation of the metal substrate with consequent inhibition of electron transfer or of radical reaction at the electrode surface. A sharp break on the Tafel plot for iridium in acidic solution was observed at 1.57 V and was attributed to a change in the rate-determining step, the reaction occurring via hydroxyl radical intermediates both above and below the break. A large increase in current was also observed on this plot at 1.8 V and was attributed to a further change in mechanism, the evolution reaction at higher potentials involving a cyclic change in the oxidation state of iridium ions in the oxide film. The latter change was accompanied by the onset of slow corrosion of the electrode—again suggesting a change in the nature of the anodic film. The corrosion current contributed only a very small fraction of the overall current and gave a linear Tafel plot, the slope of which was twice that of the corresponding plot for total current over the same region of potential. It is postulated that the corrosion reaction and the oxygen evolution reaction in this region involve a common intermediate.

Acoustic Emission Method for Monitoring Corrosion Reactions

Abstract: There is a continuing need for new test techniques to follow corrosion reaction processes and to predict long-term materials performance in aggressive environments. Additionally, there is ...