The effect of Cu addition on the corrosion behaviour of sintered stainless steel in H2SO4 environment

The influence of Cu addition on the corrosion behaviour of hot pressed sintered stainless steel of Type 316 in H₂SO₄ solution was investigated. It was found that Cu additions of 0.25-5 wt% enhance the passivation processes of the hot pressed sintered stainless steel. The open-circuit potential of samples containing Cu was + 200 mV(SCE) as compared to −250 mV(SCE) in the other case. The potentiodynamic measurements indicate that as a result of the Cu addition the corrosion potential is increased, and the anodic critical current density and the cathodic overpotential for the hydrogen evolution are decreased. It is suggested that the low hydrogen cathodic overpotential caused by Cu addition, combined with the active-passive basic behaviour of the 316 stainless steel matrix, arc the main factors affecting the improved corrosion resistance.     

Synopses of Papers

Abstract

The effect of anodic polarisation on dissolution of copper in hydroxylamine based chemical systems has been studied using a quartz crystal microbalance technique to evaluate their use in electrochemical mechanical planarisation processes. Copper dissolution in hydroxylamine solution increases with respect to overpotential η and dissolution rates as high as 600 nm min^–1 have been obtained at an overpotential of 750 mV. The effectiveness of benzotriazole (BTA) in inhibiting copper dissolution in these chemistries was also tested. It was found that BTA is effective in inhibiting copper dissolution only at lower overpotentials (≤250 mV).     

Dissolution, passivity and its breakdown on iron whisker crystals

The anodic polarization behaviour of iron whisker crystals was investigated in a neutral solution with or without the presence of chloride ion, with special attention to the role played by surface defects in the dissolution, the passivation and the pitting of iron. The grown whisker used was substantially dislocation-free and the defect density was varied by twisting of whisker. With increase in the angle of twisting, the anodic dissolution current increased in a chloride-free solution, whereas it decreased in a chloride-containing solution. The defect density in the substrate had no remarkable effect on passivation but the thickness of the passive film was slightly increased on twisted whiskers. The anodic polarization curve of a grown whisker in a chloride-containing solution did not exhibit a distinct pitting potential. By twisting of whisker, however, a current rise due to pitting appeared on the polarization curve and the apparent pitting potential shifted in the negative direction with increasing angle of twisting. Potentiostatic polarization experiments in a chloride-containing solution showed the emergence of random current pulses due to the breakdown of passive film and to repassivation. It is highly probable that the breakdown of the passive film occurs at the physical or chemical inhomogeneities in the passive film not associated with dislocation termini but that pitting occurs only when the breakdown occurs at emergent dislocation sites.     

Determination of electrochemical parameters and corrosion rate for carbon steel in un-buffered sodium chloride solutions using a superposition model

Corrosion of carbon steel in un-buffered NaCl solutions was studied applying linear potential sweep technique to a rotating disk electrode. Current-potential curves were obtained from linear potential sweep at a rate of 1 mV s⁻¹ in solution with concentrations in the range 0.02-1 M NaCl and rotation rates in the range 170-370 rad s⁻¹, at 22 °C. Potential sweeps, which were conducted in the potential range −700 to −100 mV/SHE, were started from the cathodic limit in order to approach the measurement of corrosion under rust-free conditions. Polarization curves were analyzed with a superimposition model developed ad hoc and implemented in a computer program, which enabled determining the corrosion rate and kinetics parameters of the underlying anodic and cathodic sub-processes. The anodic sub-process, dissolution of iron, was well described in terms of a pure charge transfer controlled reaction, while the cathodic sub-process, oxygen reduction on iron, was well described in terms of mixed mass transfer and charge transfer control. Increase of electrode rotation rate increases the limiting current of oxygen reduction, which results in an enhanced corrosion rate of carbon steel. Increase of NaCl concentration has a dual effect: the limiting current of oxygen reduction decreases as a result of the influence of NaCl concentration on solution viscosity and the anodic dissolution of iron increases due to the influence of NaCl on pitting formation. However, this last mechanism predominates and a net increase in carbon steel corrosion rate is observed in this case.     

Zinc coatings of high hardness on steel by electrodeposition from glutamate complex baths

The effect of monosodium glutamate (MSG) on zinc electrodeposition from acidic sulphate plating baths was investigated using potentiodynamic cathodic polarisation, cyclic voltammetry, cathodic current efficiency and throwing power measurements, current–time transients and in-situ anodic linear stripping voltammetry techniques, complemented with X-ray diffraction analysis and SEM measurements. Addition of MSG increases the hardness of zinc deposits by a factor of 3. Kinetic parameters such as Tafel slope, transfer coefficient and exchange current density obtained from Tafel plots, indicated that MSG had a pronounced accelerating effect on the zinc deposition process. From the voltammetric data obtained in the presence of MSG, it is clear that the overpotential of zinc deposition is significantly decreased. Chronoamperometry measurement suggested that the growth of zinc metal is a diffusion-controlled process. X-ray diffraction analysis and SEM observations revealed that MSG does not change the crystal structure of the electrodeposited zinc but strongly affected the crystallographic orientation of the crystal planes.     

TiO2纳米管沉积NiMo合金纳米阵列制备高效HER催化剂

制备高效稳定的非贵金属催化剂对于电解水生产高纯度氢气的发展至关重要。本实验通过简单的阳极氧化法和电沉积方法制备NiMo/TNAs复合催化剂,将NiMo合金颗粒通过电沉积方法稳固包覆于TNAs独特的弯曲有序界面上,当沉积电流和电解液Mo离子浓度变化时,NiMo的沉积状态和催化能力也随之改变,经过研究表明,在沉积电流密度15mA.cm_^-2,Mo离子浓度4g.L_^-1条件下沉积1min制备的样品具有更高的HER催化性能。通过更大活性表面积,更便捷的离子传输通道和增强的结构稳定性,获得了优异的催化活性的NiMo/TNAs电催化剂。NiMo/TNAs催化剂的起始过电位仅为50mV,分别在110mV和227mV低过电势下获得10mA.cm_^-2和100mA.cm_^-2的电流密度。因此得到结论,将NiMo合金颗粒沉积在TNAs纳米阵列,制备NiMo/TNAs催化剂为制备廉价高效电催化剂提供了新途径。     

Studies on copper-semiconducting layer-electrolyte systems—II. Galvanostatic anodic polarization of Cu/Cu2S/S2− applying stationary and rectangular pulse techniques

Copper sulphide layers formed by anodically polarizing copper in a Na₂S bath were investigated electrochemically using galvanostatic techniques. The variation in potential of unpolarized copper/copper sulphide electrodes with pS suggested a film of cuprous sulphide containing some cupric sulphide. The overpotential measurements indicated sulphide films of low porosity, deficient in Cu⁺ ions. The transfer coefficients and exchange currents computed from the results were interpreted as a system involving an impervious layer of cuprous sulphide overlayered with a film of cupric sulphide. The influence of Cu²⁺, S^2? and OH^? on the anodic processes are also discussed.     

Changes in mass and stress during anodic oxidation and cathodic reduction of the Cu/Cu2O multilayer film

The anodic oxidation and cathodic reduction processes of the Cu/Cu₂O multilayer film and pure Cu film in pH 8.4 borate buffer solution were analyzed by electrochemical quartz crystal microbalance (EQCM) for gravimetry and bending beam method (BBM) for stress measurement. The mass loss of the multilayer film during anodic oxidation at 0.8 V (SHE) in the passive region was less than that of the pure Cu film. The comparison between current transients and mass changes during anodic oxidation has succeeded in separating the anodic current density into two partial current densities of oxide film growth, i_O^2-, and of Cu²⁺ dissolution through the passive film, i_Cu²⁺. As a result, in the case of the pure Cu film, the anodic current density was mainly due to i_Cu²⁺, while in the case of the multilayer film, i_Cu²⁺ was almost equal to i_O^2-. The compressive stress for the multilayer film was generated during anodic oxidation, while the tensile stress for the pure Cu film was generated.The mass loss of the multilayer film during cathodic reduction at a constant current density (i_c = −20 μA cm⁻²) was significantly less than that estimated from coulometry, suggesting that H₂O produced by cathodic reduction remained in the multilayer film. The compressive stress was generated during cathodic reduction of the multilayer film, which was ascribed to H₂O remained in the multilayer film.     

A SERS investigation of the electrodeposition of Au in a phosphate solution

The spectroelectrochemical behaviour of cyanide and phosphate ions adsorbed on a Au electrode during electrodeposition and corrosion in a KAu(CN)₂ phosphate bath was studied by in situ SERS (Surface Enhanced Raman Spectroscopy) and cyclic voltammetry. SERS spectra exhibiting features corresponding to CN⁻ and PO₄⁻ vibrations were recorded under potentiostatic control in an interval from − 1600 to + 1500 mV vs. Ag/AgCl. Surface CN⁻ species are the dominating ones under both cathodic and anodic polarisations. As far as the phosphate vibrations are concerned, bands related to PO₄⁻ are visible in both cathodic and anodic conditions. A fluorescence background was evident in the potential range − 1300 ÷ + 1300 mV. At cathodic potentials phosphate ion adsorption on electrode surface prevails over cyanide for potentials more cathodic than − 1000 mV. At − 700 mV a discontinuity is noticed in the Stark tuning of CN⁻, probably due to a change of Au(CN)₂⁻ adsorption mechanism. At anodic potentials bands due to cyanide oxidation could be observed.     

A study on cobalt electrodeposition onto a carbon steel electrode

Abstract

The electrodeposition of cobalt on to a carbon steel working electrode was studied through the comparison between theoretical and experimental polarisation curves. The former was obtained using the Butler–Volmer equation with electrochemical parameters, such as Tafel slope values, exchange current densities, cathodic limit current densities and equilibrium potential values. The following results were obtained: the anodic region refers to the iron oxidation with a Tafel slope of about 0·055 V decade^?1, which is near the theoretical value (0·059 V decade^?1); the experimental cathodic region represents the cobalt and hydrogen ion reduction; the limiting current density (?1 × 10^?3 to ?1 × 10^?2 A cm^?2) obtained was near the calculated value, ?3·7 × 10^?3 A cm^?2.     

Mechanism of Pitting Corrosion of Copper in Supply Waters

Abstract

Detailed examination of a large number of copper water tanks and pipes showing pitting corrosion (taken from certaind is districts to which pitting is confined) revealed features that could not be reconciled with the conventiona1 explanation based on the presence of large cathodic areas surrounding small anodic corrosion Sites. A new theory of pitting corrosion of copper is proposed which explains the features observed Pitting arises when a pocket of cuprous chloride forms beneath a porous electrically conducting membrane (usually cuprous oxide). The anodic and cathodic processes occur on the inner andouter surfaces of the memberane. Dissolution of copper occurs by reaction with the anodic product beneath the membrane and deposition of calcium carbonate occurs by reaction of hardness salts in the water with the cathodic product above the membrane.

Pockets of cuprous chloride capable of developing into corrosion pits can only form if the potential of the copper rises above 90mV EH during the period of film formation. Control of the potential below this value by coupling to a small sacrificial aluminium anode has been shown to prevent formation of pits in copper tanks and cylinders in service.     

ELECTROCATALYTIC BEHAVIORS OF CER ON SOME METAL OXIDES IN CHLORIDE MELT AT 700℃

１ＩＮＴＲＯＤＵＣＴＩＯＮＥｌｅｃｔｒｏｃｈｅｍｉｃａｌｉｎｄｕｓｔｒｙｉｓｉｎｇｅｎｅｒａｌａｈｕｇｅｅｎｅｒｇｙｃｏｎｓｕｍｅｒ．Ｅｌｅｃｔｒｏｃａｔａｌｙｓｉｓ,ａｓａｐｏｗｅｒｆｕｌｗｅａｐｏｎｉｎｌｏｗｅｒｉｎｇｏｖｅｒｐｏｔｅｎｔｉａｌ,...     

Anodic and cathodic behaviour of tin in acidic sulphate solutions

Kinetic parameters for the Sn/Sn²⁺-electrode in acidic sulphate solutions have been determined by steady state measurements. The anodic and cathodic current density potential curves exhibited Tafel behaviour over rather small regions where the slopes corresponded to ± RT/2F.The electrochemical reaction orders with respect to the OH^?- and Sn²⁺-ions have been determined. Both the anodic and the cathodic reaction orders with respect to OH^? as well as the cathodic reaction order with respect to Sn²⁺, were found to be about 2. These results are consistent with a mechanism similar to the one proposed by Heusler¹ for iron.     

铜离子对银电解的影响

采用电导率仪测定不同Cu2+浓度下AgNO3溶液的电导率,应用扫描伏安法研究Cu2+对阴极极化的影响,通过恒电流电解精炼研究Cu2+浓度对电解银粉含铜量的影响。结果表明:AgNO3溶液的电导率随着Cu2+浓度的增加而逐渐升高;Cu2+对银的析出具有抑制作用,随着其浓度的增加银的析出电位负移;电解液Cu2+浓度超过21.3 g/L时,银粉铜含量便会超标;银电解液中的Cu2+浓度在10~20 g/L范围时,对银粉中其他杂质元素Bi、Fe、Pb、Te的析出具有抑制作用。     

The influence of copper upon the atmospheric corrosion of iron

The atmospheric corrosion of pure iron and the binary alloy Fe-0.5Cu has been analyzed by a simultaneous measurement of the anodic current density of the metal dissolution and the cathodic current density of the O₂ reduction reaction during several wet/dry cycles using a magnetic and a gas volumetric technique, respectively. The results show three typical stages of the atmospheric corrosion: stage 1 (wetting of a dry surface): rapid corrosion with rust reduction as cathodic process; stage 2 (wet surface): slow corrosion with O₂ reduction as cathodic process; and stage 3 (drying out of the surface): very rapid corrosion with O₂ reduction as the cathodic process during critical wetting of the surface. The effect of copper is restricted to stage 3, where the corrosion rate is much smaller for the Fe-0.5Cu alloy than for pure iron. Two models are discussed to explain these results.     

Effect of phosphate ions on electrochemical behaviour of copper in sulphate solutions

Abstract

The effect of phosphate ions on the corrosion behaviour of copper in sulphate solutions was investigated at different temperatures (293, 313, 333, and 353 K) and at different pH values (pH = 2·1, 7·2, and 12·3). A three electrode electrochemical technique was used for the measurements, using a saturated calomel electrode (SCE) for reference purposes. Both anodic and cathodic polarisation curves were established, from which the anodic and cathodic Tafel constants were determined. Corrosion potentials were determined by extra trapolation of the anodic and cathodic Tafel lines to the point of zero current density. The results showed that for a pH value of 2·1, the corrosion rate of copper showed a marked tendency to increase with increasing temperature in solutions containing either sulphate alone or sulphate plus phosphate. However, at pH values of 7·2 and 12·3, this tendency became less pronounced in solutions containing sulphate alone and in solutions containing sulphate plus phosphate together, max imum corrosion rates were greatly reduced and showed less tendency to increase with increasing temperature. Anodic and cathodic reaction mechanisms are proposed to explain the observations for the corrosion of copper.     

Preparation and electrochemical corrosion behaviour of 3D large-sized nanocrystalline copper bulk in solutions with chloride ions

ABSTRACT

A 3D large-sized nanocrystalline (NC) copper bulk was prepared by inert gas condensation and in situ warm compress, the density of which was 99.51% of theoretical value. Electrochemical methods and XRD、EDS、SEM technique were used to investigate the anodic polarisation behaviour of NC copper in solutions with chloride ions. NC copper exhibited a different anodic polarisation behaviour from its coarse-grain (CG) counterpart in 0.47?wt-% NaCl solution. No second passivity was observed for NC copper, while there was a notable second passivity for CG copper. Compared with CG copper, the corrosion resistance of NC copper decreased. The anodic polarisation behaviour of NC copper changed significantly when 10^4?ppm Cl^? was added in 0.3% Na₂SO₄ solution. Attributed to the CuCl protective film on NC copper, the critical current intensity decreased and the decreasing rate of anodic current intensity lowed notably in activity-passivity zone.     

Corrosion of Metals by Applied Alternating Currents

Abstract

The corrosion of mild steel in 0·05 M NaCl at 30°c under the influence of an applied square wave a.c. signal was studied. A mechanism for a.c. corrosion is presented, stressing the importance of reactions during a preceding cathodic half-cycle to the reactions during an anodic half-cycle and vice versa.

The corrosion rates of copper, lead and zinc under applied a.c. were also determined for comparative purposes.

It has been established that for 50 Hz sine wave a.c. applied to mild steel a peak current density of 471 mA.cm^?2 must be exceeded before serious corrosion sets in. This has been verified by a comparison of the corrosion rates as encountered in two electrode boilers operating at current densities above and below this critical value.     

Partial Electrode Processes at AC-Polarized Copper in Chloride and Nitrate Media

The dissolution of a copper electrode by passing a rectangular alternating current of an infralow frequency (1/6 Hz) was studied by chronopotentiometric method. The near-electrode concentrations of copper oxidation products were calculated by the numerical solution of the boundary problem of transient diffusion. In concentrated chloride electrolytes, the shape of the E vs. t plot was found to be determined by transient mass transfer. The ratio of the copper reduced during the cathodic half-period to its amount dissolved in the anodic half-period was estimated experimentally. This ratio was used to determine the distribution of faradaic charges between different partial electrode processes. In nitrate electrolytes, cathodic process significantly affects the anodic dissolution of copper.     

用含KBH_4碱液处理改善MINi_(3.7)Co_(0.6)Mn_(0.4)Al_(0.3)贮氢合金电极的动力学性能

研究了用表面改性处理对ＭＩＮｉ３．７Ｃｏ０．６Ｍｎ０．４Ａｌ０．３贮氢合金电极动力学性能的影响．结果表明：用含 ＫＢＨ４碱液处理合金粉末可有效地提高氢化物电极的高倍率放电能力 ＨＲＤ,交换电流密度Ｉ０,极限电流密度ＩＬ和α相中氢的扩散系数Ｄ等各项动力学性能,而且ＫＢＨ４的浓度越高（＜０．０３ ｍｏｌ／Ｌ）,动力学性能提高得也越大当碱液中所含 ＫＢＨ。浓度相同时氢在相中的扩散系数Ｄ的增加要小于交换电流密度Ｉ０的增加． ＫＢＨ４碱液处理对 ＭＩＮｉ３．７Ｃｏ０．６Ｍｎ０．４Ａｌ０．３贮氢合金电极动力学性能的改善导致合金电极的阴、阳极极化明显减小