Corrosion Dissolution Research Articles

The Effect of Sodium Thiocyanate on the Corrosion Dissolution Rate of Silver in Thiosemicarbazide Solutions

The effect of thiocyanate on the corrosion dissolution rate of silver in thiosemicarbazide (TSC) ammonium-chloride-bromide solutions was studied by using gravimetry and rotating disc electrode technique. The corrosion dissolution of silver was shown to be preceded by the formation of dithiosemicarbazide molecules due to the oxidation with iron (III) ions. The “second ligand” phenomenon is discussed, which consists in an increase in the corrosion dissolution rate of silver upon adding sodium thiocyanate (STC) to a TSC solution because of the decrease in the adsorption layer thickness. A synergism was discovered in the case of the corrosion dissolution of silver in a solution containing both thiosemicarbazide and sodium thiocyanate. The composition of the adsorption layer formed on a silver electrode and involving silver, sulfur (AgHS and Ag2S), as well as carbon, nitrogen, and oxygen forming the base of adsorption layers, was investigated by means of Auger spectrometry. The kinetic parameters (rate constants and reaction orders) were determined and a mechanism of the corrosion dissolution of silver in TSC, STC, and TSC + STC solutions is proposed.

To the theory of anticorrosion alloying of brasses

The protective effect produced by alloying was interpreted in terms of the gradient energy of the near-surface diffusion zone formed as a result of the anodic dissolution or self-dissolution of ternary phases. The general reasons for a changed tendency of such phases toward selective anodic dissolution and selective corrosion compared to nonalloyed phases were revealed. The method for quantitative estimation of the protective effect produced by small amounts of arsenic added to α-brass was proposed. A number of alloying elements (As, P, Ni, and Au) to α- and β-brasses were found to be similar in the nature of the protective effect.

Anomalous dissolution of metals and chemical corrosion

An overview is given of the anomalous behavior of some metals, in particular Fe and Cr, in acidic aqueous solutions during anodic dissolution. The anomaly is recognizable by the fact that during anodic dissolution more material dissolves than would be expected from the Faraday law with the use of the expected valence of the formed ions. Mechanical disintegration, gas bubble blocking, hydrogen embitterment, passive layer cracking and other possible reasons for such behavior have been discussed. It was shown, as suggested by Kolotyrkin and coworkers, that the reason can be, also, the chemical reaction in which H2O molecules with the metal form metal ions and gaseous H2 in a potential independent process. It occurs simultaneously with the electrochemical corrosion process, but the electrochemical process controls the corrosion potential. On the example of Cr in acid solution it was shown that the reason for the anomalous behavior is dominantly chemical dissolution, which is considerably faster than the electrochemical corrosion, and that the increasing temperature favors chemical reaction, while the other possible reasons for the anomalous behavior are of negligible effect. This effect is much smaller in the case of Fe, but exists. The possible role of the chemical dissolution reaction and hydrogen evolution during pitting of steels and Al and stress corrosion cracking or corrosion fatigue are discussed.

Kinetics and mechanism of the gold corrosion dissolution in hypochlorite solutions

Kinetics and mechanism of the gold metal dissolution by means of corrosion in chloride-hypochlorite solutions are studied. The dependences of the dissolution rate on the solution pH, sodium hypochlorite concentration, and temperature are determined. Conditions of the gold passivation surface during its corrosion in the studied solutions are discussed. The first-order rate constants of the gold dissolution (ki = 0.079–0.4030 s−1) at temperatures from 277 to 304 K and others are calculated. The equilibrium constants of the dissolution reactions in acid and alkaline chloride-hypochlorite solutions are different: 1.2 × 106 and 2.39 × 102, respectively. The activation energy calculated from the temperature dependence of the rate constants (53.43 kJ/mol) evidences a kinetic control of the gold dissolution. Quantitative data on the composition of surface adsorption films, formed by oxidation gold dissolution products, are obtained using the Auger spectroscopy

Solubility and diffusion of metallic iron in liquid Bi metal at 450 °C

Lead–bismuth (Pb–Bi) alloy is a candidate for the spallation target material in accelerator-driven system (ADS). If use of liquid metal target presents advantages for their perfect cooling of the target and their heat removal capacity, one of the main drawbacks is the corrosion and the erosion of structural materials which are in direct contact with the liquid metal at high temperatures under high flow velocities. One of corrosion processes is known as dissolution corrosion. The structural material for Pb–Bi target nowadays suggested is the modified Fe–9%Cr (at.%) steel. To evaluate the dissolution corrosion rate, the knowledge of iron solubility and diffusion coefficient in Pb–Bi is necessary. These determinations can be realized using electrochemical methods and mathematical analyzing of resulting data. The aim of this paper is to test a procedure to determine solubility and diffusion coefficient of iron in pure liquid bismuth. The experimental approach and the mathematical analysis are described. It demonstrates that combining electrochemical method and simulation lead to determine the solubility (1.85 ± 0.3 × 10 −5 mol/cm 3) and the diffusion coefficient of iron (1.0 ± 0.2 × 10 −5 mol/cm 3) in liquid Bi at 450 °C.

Anodic Dissolution and Selective Corrosion of Alloys

The mechanisms of the anodic dissolution of alloys are considered. The kinetic explanation of an abrupt increase in the corrosion resistance of the alloys, formed by metallic systems with a continuous series of solid solutions, is given. The dezincification of brasses related to the reduction of the oxidation products of copper is accounted for by the chemical conjugation of the partial ionization reactions of zinc and copper. The former reaction transmits a part of the free energy to the latter one via vacancies. As a result, the ionization of copper becomes possible at the potentials below the equilibrium potential of the individual copper. For the same reason, the oxidized copper can reduce at the brass surface to the individual copper phase. The mechanisms of the dissolution of intermetallides, used for obtaining skeleton catalysts, are discussed.

腐食環境中における６０６３アルミニウム合金の疲労挙動

Rotating bending fatigue tests were performed in distilled water and in a 3%NaCl solution using smooth specimens of 6063 aluminium alloy. The corrosion fatigue strengths were evaluated and compared with those of 2024 and 7075 alloys. Fracture mechanisms were discussed on the basis of detailed observation of crack initiation and small crack growth behaviour. The fatigue strength of 6063 alloy decreased with increasing aggressiveness of environment, but was nearly the same as those of 2024 and 7075 alloy in a 3%NaCl solution, indicating a considerably low susceptibility to the corrosive environment of 6063 alloy. There was a strong propensity that fatigue cracks were initiated at grain boundaries as environment became more aggressive. Such intergranular crack initiation was attributed to corrosive dissolution of grain boundary precipitates and a precipitation free zone. The crack growth rates of small cracks were enhanced by corrosive environments; particularly remarkable at the early stage of small crack growth following crack initiation in the 3%NaCl solution, where extensive intergranular facets were seen. Therefore, both premature crack initiation and enhanced small crack growth were responsible for the reduction in fatigue strength in the corrosive environment.

Dissolution and soldering behavior of nitrided hot working steel with multilayer LAFAD PVD coatings

Soldering and corrosive dissolution are the primary causes of die non-performance in permanent mold and die casting production of net shape parts for the transportation industry. At worst, these corrosive reactions result in core pin or sprue dissolution, and at the least, some soldered cast metal remains behind when the casting is ejected. The objective of this work was to explore the possibility of surface engineering of the die steel surface to reduce the dissolution and soldering tendencies of the surface. This paper presents a duplex surface treatment approach for dissolution resistance that consists of nitrided hot working die steel substrate coated by multi-layer titanium-based coatings applied by the large area filtered arc deposition technique. The dissolution behavior of the coating candidates is evaluated by measuring weight loss after dipping them in molten aluminum for a predetermined time. Results are compared with those of single layer coatings and surface treatments. The chemisorption and adhesion behavior is evaluated by measuring ejection force of the soldered material. The duplex coating is found to significantly reduce both the dissolution and adhesion tendencies of the coated steel surface.

Reasons for the DSA Passivation during Chlorate Electrolysis and the Means for Extending the Anode Service Life

Based on experiments and analysis of literature data, it is shown that a poor utilization of the active mass of the coating on metal oxide anodes of the DSA type during the electrochemical sodium chlorate production is due to pseudopassivation (an increase in the anodic potential due to a predominant corrosion dissolution of RuO2as compared with TiO2in the outer working zone of the coating), which develops with time. The true irreversible anode passivation, resulting from the formation of a stable barrier layer of higher titanium oxides at the coating/substrate interface, occurs when the DSA active mass wears out to a residual ruthenium content below 1.4 g/m2in it. The coating service life can be extended with no increase in the potential and with a minimum active mass consumption by using, concurrently with RuO2and TiO2, catalytically active additives with higher corrosion resistance than that of RuO2at pH 6 to 7. This prevents the anode pseudopassivation and, with an increased initial amount of the active mass, makes it possible to use the anodes until its residual content exceeds the limit below which the true passivation starts, and regenerate the coating by applying fresh mass on the residue of the existing mass.

Experimental and Theoretical studies on the Mechanism of Grignard Reagent Formation

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Electrochemical behaviour of aluminium in concentrated NaOH solutions

The corrosion–dissolution characteristics of pure aluminium were studied in a 4 M NaOH electrolyte by steady state techniques and voltammetric analysis. Delineated steady state polarization curves show that aluminium exhibits a passive state at both 25°C and 60°C. Kinetic parameters for aluminium oxidation and hydrogen evolution are consistent with those obtained in a KOH electrolyte. New information is provided by voltammetric experiments: the existence of a sharp passivation peak was demonstrated in the very negative range of potential. Such curves underline the effect of impurities contained in NaOH which increase the corrosion current. In aluminate containing electrolyte, kinetics for both partial reactions are reduced and an oscillatory phenomenon is observed at the active to passive transition.

Corrosion fatigue strength of ship structural steel butt welded joints in synthetic sea-water

Summary This paper describes an investigation into the corrosion fatigue strength of a MAG-welded 50 MPa class TMCP steel in fatigue tests carried out under a constant-amplitude load at a stress ratio of 0.1 in air and synthetic sea-water. The tests took place under natural corrosion conditions at 25°C at a cycling rate in air and sea water of 3–12 and 0.17 Hz respectively. The fatigue corrosion initiation life Nc was evaluated from the crack length measured by the DC electric potential difference method. This paper describes the S/N relationships, the macroscopic stress concentration factors and the corrosion initiation behaviour at the toes of butt welded joints. The results obtained may be summarised as follows. 1. The ΔSn/Nc relationship between the nominal stress range and the corrosion initiation life as determined in the tests made in synthetic sea-water is represented by a straight line. In the high applied stress range, the corrosion initiation life as determined in the tests made in air is virtually equal to that determined in the tests made in synthetic sea water. The ΔSn/Nc relationship found in the tests made in synthetic sea-water can be applied as the corrosion initiation life for purposes of ensuring the greatest margin of safety in tests made in air. 2. Even when a weld toe crack is present in the specimens tested in air, there is an applied stress range leading to no fatigue failure after fatigue cycling through 1 × 107 cycles. As distinct from the crack arrested at the weld toe in the tests made in air, the crack found in the specimens tested in synthetic sea-water propagates through corrosion dissolution of the crack tip. 3. The stress concentration factor at the weld toe Kt2 determined from strain gauge data is smaller than the local stress concentration factor Kt1 calculated from the two-dimensional cross section at the corrosion initiation point. Its scatter is also smaller. The ΔSt/Nc relationship of the weld toe in which the bending stress of welding angular distortion is superposed on the tensile stress of the axial force is therefore determined as ΔSt = Kt* 2ΔSn. 4. The corrosion initiation life to failure life Nc/Nf has a value of around 0.84 and 0.91 in air and synthetic sea-water, respectively. This difference is due to the effect of the environment on the crack propagation rate. 5. Fatigue cracks are always initiated in the weld toe bond and propagate at right-angles to the loading direction.

造船用鋼突合せ溶接継手の人工海水中疲労強度

MAG welding was applied to the butt welded joint for a 500 MPa class TMCP steel. Fatigue tests were performed under a constant-amplitude load with the stress ratio of 0.1 in air and in synthetic seawater. In particular, corrosion fatigue tests were carried out under a natural corrosion condition with the cycling rate of 0.17 Hz at 25°C. The fatigue crack initiation life, Nc, was evaluated from a crack length measured by a DC electric potential difference method.In this paper, the S/N relations, macroscopic stress concentration factors and crack initiation behaviors at a toe of weld are discussed. The results obtained are as follows:(1) It was found that there exists a linear relation between ΔSn and Nc when tested in the seawater, where the ΔSn is a nominal stress range. The Nc-value tested under a higher applied stress range in the air agrees well with that observed in the seawater. It may be, therefore, quite reasonable to apply the ΔSn/Nc relation obtained in the seawater as the most safety crack initiation life in the air.(2) There is an applied stress range in which no fatigue failure arises even after 1×107 cycles in spite of the existence of a crack at the toe of weld when tested in the air. On the other hand, the crack at the toe of weld grows in the seawater due to corrosion dissolution of the crack tip.(3) The macro-stress concentration factors at the toe of weld, Kt2, obtained from strain gages were smaller than the localized stress concentration factor, Kt, , estimated from two-dimensional cross section at the crack initiation point. The scattering of the Kt2 was also small. The ΔSt in the ΔSt/Nc relation evaluated at the toe of weld, where bending stress components caused by the angular deformation as well as tensile stress components of the axial force exist, can be estimated as ΔSt=Kt2*ΔSn.(4) The ratio of crack initiation life to failure life, Nc/Nf, was about 0.84 in the air, and about 0.91 in the seawater. This difference may be caused by an environmental effect on crack growth rates.(5) The fatigue crack always initiates at the toes of weld, and propagates in a direction perpendicular to the loading direction.

Erosive dissolution of InP substrates during liquid phase heteroepitaxy

The erosive dissolution of AIIIBV substrates is one of many effects appearing during liquid phase heteroepitaxy. This effect concerns particularly heterostructures with a significant mismatch in the lattice parameters. The mechanisms leading to such a phenomenon are analysed for the case of the GaInPAs/InP heteropair. It is found that the erosion instability of the interface depends mainly on the configuration energy of the lattice in the interface region.

３％ＮａＣｌ水溶液中におけるＡｌ‐Ｌｉ合金の疲労挙動

Rotating bending fatigue tests have been conducted in a 3%NaCl solution using under-aged, peak-aged and over-aged materials of two aluminum-lithium alloys, 2090 and 8090. Detailed observations on corrosion pit, fatigue crack initiation and growth have been made, and the results obtained were compared with those of conventional aluminum alloys, 2024 and 7075. The corrosion fatigue strength of Al-Li alloys significantly reduced when compared with the fatigue strength in laboratory air, but was independent of aging condition. However, the peak-aged material showed relatively higher sensitivity to corrosion environment than the other aged materials. In comparison with 2024 and 7075 alloys, Al-Li alloys exhibited better corrosion fatigue strength. It was found that the corrosion fatigue process in Al-Li alloys consisted of corrosion pit initiation and growth, and fatigue crack initiation and subsequent growth. The density and size of corrosion pits in Al-Li alloys were much higher and smaller, respectively, than those in 2024 and 7075 alloys, and the configuration was extremely irregular. Corrosion fatigue cracks initiated from such corrossion pits and then grew. The crack growth of Al-Li alloy was enhanced in 3%NaCl solution at both low and high Kmax regions, due to corrosion dissolution and crack coalescence, respectively. Furthermore, the crack growth resistance of Al-Li alloys was almost the same as that of 7075 alloy, but was higher than that of 2024 alloy.

Influence of some anions on the stress corrosion of low alloy steels in aqueous solutions

Polarization and stress corrosion behaviour of two types of low alloy steels, AISI 4130X and AISI 4145, were studied in agitated 0.05 M sodium acetate and 0.05 M trisodium phosphate solutions saturated with natural gas at room temperature. The magnitude of currents, shown in potentiokinetic polarization curves in the range of —0.8 V(SCE) to +0.8 V(SCE) in these media, is very small compared with earlier results obtained in sulphate and chloride solutions. Stress corrosion experiments conducted using a slow strain rate technique under cathodic conditions indicate the onset of hydrogen embrittlement on both types of steel in sulphate, chloride, acetate and phosphate solutions. Under anodic conditions, the results in 0.05 M sodium acetate solutions indicate strong susceptibility to stress corrosion compared with no susceptibility in 0.05 M trisodium phosphate solutions if there is no onset of pitting. These results are in contrast with results showing strong anodic dissolution and consequent absence of stress corrosion under anodic conditions in sulphate and chloride media. Results of Auger and IR analyses of anodic surface films formed in acetate and phosphate solutions are presented and discussed in relation to their observed mechanical behaviour.

The Development of a Mechanistic Basis for Modelling Fuel Dissolution and Container Failures Under Waste Vault Conditions

ABSTRACTDue to the long containment periods required for radionuclides in a nuclear waste disposal vault, the justification that a particular containment system is acceptable will be based on relatively short-term experimental data used to support predictive models. To justify this approach, we must possess a sound mechanistic understanding of processes such as fuel dissolution, radionuclide release and container corrosion. Since these processes are driven by oxidants in the vault, it is natural to study them by electrochemical techniques. In this paper, we have reviewed a number of electrochemical methods used in the study of waste vault reactions. More detailed descriptions are given of the development of predictive models for the dissolution of UO2, the crevice corrosion of titanium alloys and the uniform dissolution of copper.

Effects of stress rising time, discending time and hold time on corrosion fatigue crack growth rate and corrosion fatigue fracture toughness.

The effect of stress wave form, that is, fast-slow (tR<tD), slow-fast (tR>tD), symmetrical (tR=tD) wave form on corrosion fatigue crack growth rate was studied, where tR is rising time and tD is descending time. When tR is smaller than tD+tH, tD is not so effective on crack growth rate and tR is much more of a controlling factor. Where tH is stress holding time, corrosion fatigue fracture toughness is constant independent of tR, tH and tD, and takes the same value of that in air, while corrosion fatigue crack growth rate is remarkably effected by tR and tH. So, the effect of stress wave form motivates local corrosion dissolution at the crack tip and accelates crack growth rate, but does not affect material damage so much.

The electrochemical behaviour of INCOLOY 800 and AISI 304 steel in solutions that are similar to those within occluded corrosion cells

Occluded corrosion cell solutions were synthesized by a mixture of iron, nickel and chromium chloride salts, the concentration of which was proportionally the same as that of the alloy matrix. The overall chloride concentration varied between 0.01 and the saturation of one of these salts. The variation of open-circuit electrode potential and of the potential-dynamic anodic polarization curves with increasing overall chloride concentration indicated that the corrosion behaviour of INCOLOY 800 and AISI 304 steel changes from the passive to the active dissolution corrosion mechanism. The threshold chloride concentration is close to 0.5 g ion 1−1 for both alloys. It was noticed that, even for a very concentrated medium, the dissolution rate was independent of mass transport. It was also found that the anodic behaviour of these alloys depended essentially on the chloride concentration and pH of the solution. Hence, an acidified NaCl solution, which is much easier to prepare than a synthetic occluded corrosion cell solution, can be used in kinetic studies on the propagation of localized corrosion.

Chemiphoresis of montmorillonite particles

AbstractThe chemiphoresis of montmorillonite saturated with Na, K, Li or Ca was studied in a system where corrosive dissolution of Al, Fe, Zn or Cu metal plates took place in the presence of HF and H2O2. The deposition of the clay as well as metal dissolution were found to be a function of indicating that the electrochemical reaction is controlled principally by diffusion of the reacting species to the metal-liquid interface. The deposition increased with clay concentration and was lower for Ca-clay than for Na-, K- or Li-clay. It is shown that chemiphoresis alone does not provide sufficient data for the calculation of particle mobility and that other types of measurement are necessary. A relationship between particle deposition and electrical conductivity was developed, and examined experimentally with satisfactory results.