Spontaneous dissolution of Cu---15Zn alloy in aerated or oxygenated 2.0 M H2SO4

The corrosion rate of a Cu---15Zn α-brass rotating disc in argon-, air- or oxygen-saturated 1 M H₂SO₄ was measured in the temperature range 10–65°C. In the argon-saturated acid the sample does not corrode with any measurable rate. In the air- or oxygen-saturated acid in the temperature up to 30°C the reaction occurs in the activational control regime, in the temperature range 30–40°C in the mixed kinetics regime, and in the temperature 65°C in the diffusional regime with respect to the oxygen dissolved in the acid. The corrosion behaviour of Cu and Zn in the examined Cu---15Zn alloy is similar to that of metallic copper corroding in similar conditions.     

Effect of heat treatments on Cu-Ni 70/30 alloy pitting susceptibility in sea water at different temperatures

A series of experiments was carried out on Cu-Ni 70/30 commercial alloy specimens presenting different microstructures. The microstructure of homogeneized specimens was modified with annealing treatments by which grain size significantly increased and intermetallic compounds precipitated, thus creating some dishomogeneity in the alloy. Free corrosion and electrochemical tests were carried out at 20, 40, 60, 80°C in quiescent sea water at pH 8.2 with dissolved oxygen (D.O) content ranging from 6.5 ppm (at 20°C) to 3.0 ppm (at 80°C). The corrosion products adherent to the metallic surface were analyzed with chemical and XPS methods. The following could be observed:

• with increasing temperature, a decrease in corrosion rate and selective copper dissolution was observed in homogeneized and annealed specimens
• the annealed specimens have the highest corrosion rate in the whole temperature range and undergo pitting corrosion at low temperature.

     

The influence of radiation on the corrosion of stainless steel

The effect of γ-radiation on the electrode potential and localized corrosion of type 304L steel in 300 ppm C1- solution has been studied. In open systems with argon or Ar-20% oxygen gas blankets irradiation at a dose rate of 2 × 10³Svh⁻¹ causes the steady rest potential of the metal to increase by 200–300 mV to ca +320 mV(SCE). This increase is partly due to cathodic depolarization by oxidizing radical and molecular radiolysis products, but may also involve adsorption of these species onto the metal surface. Radiolysis products also inhibit the initiation of pitting corrosion at low electrode potentials, but have no effect on the repassivation of established pits.     

Inhibition of copper sulphidation by boron implantation

Pure polycrystalline copper and copper implanted with boron ions at a dose of 3.0 × 10¹⁷ ions cm^?2 at 25–150 keV have been exposed to hydrogen sulphide in moist air. The rate of growth of a sulphide film on the boron-implanted copper is lower than on pure copper by at least a factor of four after 18 h under the exposure conditions ([H₂S] = 3.0 ppm, T = 22.5°C, RH = 85%). The resistance of the implanted copper to sulphide corrosion is ascribed to inhibition of copper diffusion through the surface oxide layer.     

The oxidation of cupro-nickel alloys—II. The kinetics of diffusion in porous inner layers

The oxidation of cupro-nickel alloys at temperatures > 160°C produces a duplex oxide structure. In Part I, diffusion of copper across the inner nickel oxide layer was shown to be rate controlling. This conclusion is tested in this paper by examining the oxidation rate curves of a series of nine metals and alloys extending from pure copper to pure nickel. The isochronal curves are found to pass through a maximum at 75%Cu which is explained by surface diffusion of the copper through a porous nickel oxide structure extending through the metal consumption zone. The surface diffusion coefficient derived from this model is in the range 0.8–2.0 × 10^?14 m² s^?1 in accord with results of other workers.     

Study of inhibition mechanism and efficiency of indole-5-carboxylic acid on corrosion of copper in aerated 0·5M H2 SO4

Abstract

Inhibition of the corrosion of copper in aerated 0·5M sulphuric acid solutions containing various concentrations of indole-5-carboxylic acid was studied in the temperature range 25–55°C using potentiodynamic curves (Tafel lines), weight loss, analytical methods, and determination of double layer capacitance. The corrosion rates reveal good corrosion inhibition, up to 95% in the concentration range of 1 × 10^-4–4 × 10^-3M. Tafel anodic slopes in inhibited acid solutions are considerably higher than those in uninhibited acid solutions. This points to a change in the corrosion mechanism of copper in the presence of indole-5-carboxylic acid. Under these conditions, copper could electro-oxidise primarily to Cu⁺ rather than to Cu²⁺, forming slightly soluble [Cu–(indole-5-carboxylic)_n ]⁺_(ads) complexes. Corrosion rates determined by the weight loss method in both the absence and presence of inhibitor are much higher (on average by a factor of about 6) than those obtained with the potentiodynamic method. This points to a limitation of the Tafel line extrapolation method in corrosion rate determination. The double layer capacitance–potential curves indicate considerable adsorption of the inhibitor over a wide potential range (-600 to +200 mV with regard to E_corr ).     

The possibility for formation of macro‐cell corrosion in a liquid with low electrical conductivity

The possibility of electrochemical corrosion of carbon steel at the rate of 3.25 × 10^?5 A/cm² in water was examined under the conditions present during an accidental pipe rupture at the Mihama nuclear power plant: liquid conductivity, 7.5 µS/cm; dissolved oxygen concentration, 5 ppb or less; pH 8.6～9.3; ferrous ion concentration, 20 ppb or less; temperature, 142 °C. The corrosion rate of iron in a micro‐cell with a dissolved oxygen reduction cathode was estimated to be only 1/400 of the preceding rate. On the other hand, that in a micro‐cell with a hydrogen ion reduction cathode was estimated to be as high as 1/10 of the preceding rate, that is, 3.25 × 10^?6 A/cm². Two important factors may have influenced the corrosion rate: the remarkable wall thinning, which must have been the direct cause of the rupture of the pipe, was located close to, and downstream from, an orifice; and, the water temperature was in the range at which carbon steel makes a transition from the active to the passive state. Taking these facts into consideration, it appears possible that micro‐cells with different corrosion rates might be generated and integrated into a macro‐cell, where the iron dissolution rate might be accelerated to as much as 10 times that of the micro‐cell.     

The influence of carbonaceous surface impurities on excrescence initiation in the rimming steel/CO2/CO system

The influence of surface carbon contamination in determining the sites of excrescence growth has been studied, for the reaction of rimming steel in carbon dioxide containing 1·5%CO + 1000 ppm H₂O + 10 ppm CH₄ at 17·25 × 10⁶ N m^?2 and 450°C. Patterns visible in the oxide layer in the early stages of oxidation can be attributed to hydrocarbon impurities remaining on surfaces not rigorously cleaned. The impurity can accumulate at specific areas on the surface and can then accelerate oxidation such that excrescences start growing early in the normally protective stage. Surface cleaning procedures and their limitations for corrosion studies are discussed.     

Effect of sulphides on corrosion of Cu–Ni–Fe–Mn alloy in sea water

Abstract

The corrosion behaviour of Cu–30Ni–2Fe–2Mn commercial alloy (similar to C71640) in quiescent, hermetically closed sulphide polluted and unpolluted natural sea water at 25°C was investigated. The corrosion resistance was examined using free corrosion and electrochemical tests and the surface film was characterised by chemical analysis and X-ray photoelectron spectroscopy. The different susceptibilities to corrosion were closely linked to the initial sulphide concentration; the accelerated attack occurring with an initial sulphide concentration of 4 ppm correlated with the amount of dissolved oxygen in solution and with the chemical composition of the corrosion layer.     

Influence of hydrostatic pressure on pitting of aluminium in sea water

Abstract

The effect of hydrostatic pressure on the corrosion of aluminium in sea water oj pH 8·2 containing 7ppm dissolved oxygen has been investigated at 20°C. On increasing the pressure from 1 to 300 atm, the corrosion rate increased, an effect attributable to an increase in the rate of the anodic reaction while the cathodic rate remained unchanged. The observed increased susceptibility to pitting corrosion with increasing pressure was found to correlate with the presence of increasing quantities of SO^2?₄ and Cl^? ions in the oxidation layer. The introduction of electron acceptors such as SO^2?₄ and Cl^? into n type compounds such as aluminium oxides increases the density of lattice dejects and promotes breakdown oj the barrier provided by the oxidation layer.     

Oxidation of copper at high temperatures

The kinetics and mechanism of copper oxidation have been measured over the temperature range 900–1050°C and the pressure range 5×10^?3 to 8×10^?1 atm. It has been shown that, at the pressures lower than the dissociation pressure of CuO, the oxide scale formed on flat fragments of the copper specimens is compact and composed of a single layer, adhering closely to the metallic base. Growth of the scale proceeds under these conditions by outward diffusion of metal. The rate of the process under the conditions for which single-phase scales are formed increases with increasing oxygen pressure according to the equation: $${\text{k''}}_{\text{p}}^{} = const {\text{p}}_{{\text{O}}_{\text{2}} }^{{\text{1/3}}{\text{.9}}} $$ . the activation energy for oxidation is 24 ± 2 kcal/mole. On the basis of theFueki-Wagner method and the method proposed in the present work, the self-diffusioncoefficients of copper in cuprous oxide were calculated as a functionof oxygen pressure and temperature. It has been shown that distribution of thedefect concentration in the growing layer of the scale is linear.     

超音速大气等离子喷涂TiB2-SiC涂层的抗氧化性及耐熔盐腐蚀性能

采用超音速大气等离子喷涂制备全包覆TiB₂-SiC涂层,研究了TiB₂-SiC涂层在400和800 ℃的氧化性能,并探究其氧化机理。对TiB₂-SiC涂层在900 ℃下的抗铝熔盐腐蚀性能进行研究,并探讨其耐熔盐腐蚀机理。结果表明,超音速大气等离子喷涂制备的TiB₂-SiC涂层具有良好的抗氧化性,在400 ℃的氧化速率常数为1.92×10^-5 mg²·cm^-4·s^-1,在800 ℃的氧化速率常数为1.82×10^-4 mg²·cm^-4·s^-1。超音速大气等离子喷涂制备的TiB₂-SiC涂层在900 ℃下具有良好的抗熔盐腐蚀性能,熔盐腐蚀后TiB₂-SiC涂层都保持致密结构,未发生涂层的开裂及剥落。     

Corrosion studies under conditions of thermal desalination. II. The influence of oxygen content,pH value,flow rate and impurities on the corrosion rates of unalloyed and low alloyed steels

Corrosion rates determined on the basis of weight loss and polarization resistance are considerably lower for a 6% chromium steel than for an unalloyed steel C 15 (DIN 17210), a base-melt and a 5.5% Ni steel. The results of a 100 hrs test and a short duration parameter studies at various oxygen concentrations show that above 100°C there is a minimum corrosion rate at 10 ppb oxygen. At oxygen concentrations above 20 ppb there is a transition from uniform corrosion to pitting. The dependence of corrosion rate on pH is in accordance with expectations; the same is true with the dependence on flow rate. Sulphides as impurities in sea-water become corrosion stimulators only below pH 7, but are highly active even in the ppm range. Addition of 1 ppm copper ions gives rise to considerable stimulation, too. The results obtained in this study enable conclusions to be drawn with respect to the operation of sea-water desalination plant.     

On size effect of rate of corrosion of copper nanowire ensemble: Part 2. Size effect of rate of corrosion of copper in pyrophosphate solution

The corrosion of specimens of copper produced by electroplating on disc electrodes 10–500 μm in diameter from a pyrophosphate electrolyte is studied in this electrolyte (without added copper ions) using polarization curve measurements. It is found that the rate of corrosion of the microelectrodes with a radius of 5 μm is eight times higher than that of the microelectrodes with a radius of 25 μm; the measured rate of corrosion remains unchanged when varying the radius of the microelectrode in a range of 25–250 μm. It is shown that the process under investigation is corrosion with oxygen depolarization; the rate of reduction (of dissolved oxygen) increases eightfold when varying the radius of the microelectrode in a range of 5–25 μm. The experimental results are confirmed by the calculations of diffusion currents for the microelectrodes, which show that the size effect, i.e., an increase in the diffusion current density with decreasing area of the electrode surface, should be observed for electrodes with a radius less than 20–30 μm.     

Effects of Hydrostatic Pressure on the Corrosion of Copper in Sea Water

Abstract

A study has been made of the effect of hydrostatic pressure, ranging from 1 to 300 atm. (0·102 to 30·6 N.mm^?2) on the corrosion of copper in sea water at pH 7·8 and at a temperature of 10°c. The experimental technique ensured that the content of dissolved oxygen in the sea water was virtually constant over the pressure range, at a value of 7·0 ppm. The same test series was also carried out in a 3·5% NaCl solution.

The weight loss of the copper was found to increase with increase in pressure, both in sea water and in NaCl, and reached a maximum at a pressure of 150 atm. (～15 N.mm^?2) in both solutions. The increased pressure has no influence on the anodic dissolution process for copper, but accelerates the cathodic process. Protective films adhering to the corroded surfaces are identical for the two solutions at ambient pressure. However, at higher pressures adherent corrosion products form only in NaCl solutions. These products were found to be the same as those formed at ambient pressure.     

Relationship between coking and metal dusting

Metal dusting is a severe form of corrosive degradation that Fe, Co and Ni base high temperature alloys undergo when subjected to environments supersaturated with carbon (a_c > 1). This corrosion process leads to the break-up of bulk metal into metal powder. The present study focuses on the fundamental understanding of the corrosion of Fe and Ni in carbon-supersaturated environments over the temperature range, 350–1050 °C. Building on earlier research, the role of deposited carbon in triggering corrosion is further clarified. For Fe, the corrosion rate peaked at ∼ 575 °C with a sharp decrease in rate on either side of the maximum. High-resolution electron microscopy revealed, in addition to metal particles, a mixture of graphitic carbon, amorphous carbon and filamentous carbon in the corrosion product. While the presence of a surface layer of Fe₃C was characteristic of corrosion up to 850 °C, such a layer was absent at the higher temperatures. The corrosion rate maximum that typified the metal dusting of Fe was absent in the case of Ni where no surface carbide occurs until temperatures well below 350 °C. The mechanistic differences between iron corrosion and nickel corrosion are compared and contrasted.     

Slow strain rate stress corrosion testing at elevated temperatures and high pressures

Slow strain rate stress corrosion cracking experiments have been performed on single phase and duplex phase 304 stainless steels at 290°C. Environmental variables included chloride concentrations (0–1000 ppm), oxygen concentration (0–2 ppm) and potential (?_corr to + 500 mV vs Ag/AgCl). These experiments have shown that s.c.c. resistance is relatively unaffected by Cl^? if O₂ concentrations approach zero. However, at 2 ppm O₂ concentration, there is a large decrease in resistance with increasing Cl^? concentrations. Anodic polarization of the steels during straining in solutions containing 100 ppm Cl^? and 0 ppm O₂ showed a threshold potential for s.c.c. at ～ 500 mV more noble than the corrosion potential (? 650 ± 60 mV vs Ag/AgCl at temperature).     

Bestimmung der Abtragungsraten von Zirconium,Tantal und der Legierung Tantal-40Niob in fluoridhaltiger azeotroper Salpetersäure mit Hilfe der Radiotracer-Methode

The radiotracer technique as a means to investigate the corrosion of zirconium, tantalum, and a Ta-40Nb alloy in fluoride containing azeotropic nitric acid Zirconium and tantalum as well as the tantalum 40% niobium alloy are of considerable technical importance due to their high corrosion resistance against numerous corrosive media. With respect to corrosion testing in analytically pure azeotropic nitric acid in the temperature range between 20 and 121°C, corrosion rates were determined for zirconium: 7 · 10^?6 to 5 · 10^?4 mm/y, for tantalum: 10^?8 to 4 · 10^?6 mm/y, and for the Ta-40Nb alloy: 2 · 10^?7 to 8 · 10^?6 mm/y [1]. These corrosion rates will be markedly increased by adding small amounts of fluorides or by fluoride impurities. The radiotracer method after neutron activation was applied to determine the corrosion rates in azeotropic fluoride containing nitric acid. Even minute additions of fluorides strongly affect the corrosion resistance of zirconium. In the range between 0.15 and 10 ppm F^? and at a temperature of 108°C, corrosion rates between 5.3 · 10^?3 and 3.1 mm/y were measured. It was impossible to establish a limit for the fluoride concentration, below which the corrosion rate of zirconium will not be adversely influenced. The corrosion rates of tantalum and the Ta-40Nb alloy are considerably increasing above a fluoride concentration of 10 ppm. The highest corrosion rates measured were between 8.4 · 10^?3 mm/y at 50°C/280 ppm F^? and 1.4 · 10^?2 mm/y at 110°C/320 ppm F^?. Within the range of this investigation, the corrosion resistance of tantalum was higher than that of the Ta-40Nb alloy by one order of magnitude. The corrosion resistance of zirconium and tantalum was not influenced by any treatment of the samples before testing.     

The corrosion of copper by atmospheric sulphurous gases

The sulfurization of copper by atmospheric gases is widely recognized, but the importance of the potential causative agents of sulfurization and the mechanisms involved have remained unresolved. In this work, polycrystalline copper has been exposed to the atmospheric gases hydrogen sulfide (H₂S), carbonyl sulfide (OCS), carbon disulfide (CS₂), and sulfur dioxide (SO₂) in humidified air under carefully controlled laboratory conditions. At room temperature, the rates of sulfurization by H₂S and OCS are comparable, and are some two orders of magnitude greater than those by CS₂ and SO₂. Given the atmospheric concentrations of these gases, it is clear that OCS is the principal cause of atmospheric sulfurization of copper except near sources of the gases where high concentrations may render H₂S (and possibly SO₂) important. At constant absolute humidity, the sulfurization rate of copper by OCS is found to be inversely proportional to temperature over the range 21–80°C, a property attributed to reduced quantities of surface water at high temperatures and the subsequent decrease in the rate of hydrolytic transformation of OCS into a reactive form. In a final series of experiments, the initial sulfurization of copper by 2.2 ± 0.2 ppm H₂S in humidified air at 22°C has been studied in detail. The first stages of sulfurization involve rapid attack by H₂S at surface defect sites. As these corrosive mounds spread and merge, diffusion of copper to the surface is impeded and the fraction of H₂S molecules striking the surface that become incorporated into the corrosion film drops sharply from ～ 5 × 10^?5 (at t = 5 s) to ～ 8 × 10^?7 (at t = 72 h).     

Superplastic deformation behaviour of friction stir processed 7075Al alloy

Commercial 7075Al rolled plates were subjected to friction stir processing (FSP) with different processing parameters, resulting in two fine-grained 7075Al alloys with a grain size of 3.8 and 7.5 μm. Heat treatment at 490 °C for 1 h showed that the fine grain microstructures were stable at high temperatures. Superplastic investigations in the temperature range of 420–530 °C and strain rate range of 1×10⁻³–1×10⁻¹ s⁻¹ demonstrated that a decrease in grain size resulted in significantly enhanced superplasticity and a shift to higher optimum strain rate and lower optimum deformation temperature. For the 3.8 μm 7075Al alloy, superplastic elongations of >1250% were obtained at 480 °C in the strain rate range of 3×10⁻³–3×10⁻² s⁻¹, whereas the 7.5 μm 7075Al alloy exhibited a maximum ductility of 1042% at 500 °C and 3×10⁻³ s⁻¹. The analyses of the superplastic data for the two alloys revealed a stress exponent of 2, an inverse grain size dependence of 2, and an activation energy close to that for grain boundary self-diffusion. This indicates that grain boundary sliding is the main deformation mechanism for the FSP 7075Al. This was verified by SEM examinations on the surfaces of deformed specimens.