Electrochemical and XPS investigations of cobalt in KOH solutions

The electrochemical behaviour of cobalt in KOH solutions of different concentrations was studied. The effects of applied potential, temperature and the presence of aggressive Cl^– ions were investigated. Different electrochemical methods such as open-circuit potential measurements, polarisation techniques and electrochemical impedance spectroscopy (EIS) were used. The electrochemical behaviour of cobalt in naturally aerated KOH solutions is characterized by three different regions according to the alkali concentration. Corrosion behaviour was observed at high concentrations (0.3–1.0 M); passivation at lower concentrations (0.01–0.05 M), and at intermediate concentrations (0.1–0.2 M) corrosion followed by passivation was recorded. The corrosion parameters (i _corr, E _corr, and R _corr) under various conditions were calculated. Equivalent-circuit models for the electrode–electrolyte interface under different conditions were proposed. The experimental impedance data were fitted to theoretical data according to the proposed models. The relevance of the proposed models to the corrosion–passivation phenomena occurring at the electrode–solution interface was discussed. The electrochemical experimental results and discussions were supported by surface analytical techniques.     

Electrochemical behaviour of cobalt in aqueous solutions of different pH

A systematic study of the corrosion and passivation behaviour of cobalt in aqueous solutions of different pH was carried out. Open circuit potential measurements, polarization experiments and electrochemical spectroscopic (EIS) investigations were employed. The experimental results show that the metal surface is always covered by a native passive film which consists of CoO. The formation of the oxide film obeys a two-electron charge transfer process. The dissolution of the barrier film is controlled by the pH of the solution. In neutral and basic solutions the barrier film is stable. In these media a barrier film thickening with the formation of secondary layer is considered. In acidic solutions, the passive film is unstable and dissolves via a pure chemical process. The mechanism of the corrosion and passivation processes taking place at the electrode/electrolyte interface in the different solutions is discussed. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to confirm the electrochemical measurements and the suggested mechanisms.     

Electrochemical evaluation of the surface of chalcopyrite during dissolution in sulfuric acid solution

The dissolution of a massive chalcopyrite electrode (98.1% chalcopyrite, 1.9% siderite) was studied in 0.5 M sulfuric acid solution. Different anodic potentials were applied and the behavior of the electrode was observed by means of EIS, potentiodynamic, and Mott-Schottky techniques. Electrochemical impedance spectroscopy studies at open circuit potential (around −235 mV vs. MSE) proved the existence of a thin surface layer on the electrode. This layer was stable up to 100 mV vs. MSE and was assumed to be Cu_1−xFe_1−yS₂ (y?x) based on reports from previous studies. By increasing the potential to the range of 100-300 mV vs. MSE, the previously formed layer partially dissolved and a second layer (Cu_1−x−zS₂) formed on the surface. Both of the layers showed the characteristics of passive layers at low potentiodynamic scan rate (0.05 mV s⁻¹) while at high scan rates they acted like pseudo-passive layers. However, in the potential range of 300-420 mV vs. MSE, both of these surface layers dissolved and active dissolution of the electrode started. Further increase in potential caused the formation of a CuS layer which hindered the dissolution rate of the electrode. The formation of CuS is concomitant with Fe₂(SO₄)₃ formation and the latter may act as a nucleation precursor for jarosite at higher potentials (around 750 mV vs. MSE). Jarosite precipitation on the electrode surface hindered the dissolution of chalcopyrite at higher potentials. Different equivalent electrochemical circuits were modeled for each potential range and the model regression results compared with the experimental results of EIS to determine the proposed sequence of chalcopyrite dissolution.     

Electrochemical study of the chromium electrode behaviour in borate buffer solution

The electrochemical behaviour of the chromium electrode in borate buffer solution (pH 9.3) was studied by cyclic voltammetry and electrochemical impedance spectroscopy. Chromium passivity was observed over a broad potential region, from –1.0 to 0.5 V vs SCE. The passivation process took place in two steps: formation of a chromium oxide monolayer and transition of chromium to a higher valence state. The anodic film exhibited the properties of a p-type semiconductor. Transpassive dissolution of chromium occurred at 0.5 V vs SCE, with two reaction intermediates present, Cr_Cr ^III and Cr_ad ⁴⁺.     

Electrochemical study of the corrosion behaviour at the edges of electrocoated steel

Cathodic electrodeposition is currently used to protect the totality of the world automotive production against corrosion. Although this technology is highly competitive, some aspects, as the coverage of salient edges, could still be improved. Special paints containing flow modifiers have consequently been developed. Salt fog exposure on steel knife blades is the most frequently performed test to characterize the protection afforded by cataphoretic coatings against edge corrosion. In this study, a method based on electrochemical techniques, among which cathodic polarization and electrochemical impedance spectroscopy (EIS), is proposed for the special characterization of edge coverage in a faster and less restrictive way in comparison with salt fog spray. The combination of dc and ac measurements is also employed to accelerate the degradation process and to improve the fitting of EIS spectra. In order to validate these testing methods, different kinds of pretreatments and coatings were selected. The influence on edge corrosion of different parameters as the coating thickness and the amount of flow modifier were determined.     

Electrolytic production of metallic cadmium and cadmium–sodium alloys in alkali melts

Reprocessing of cadmium-containing wastes and used storage batteries produces cadmium oxide. Electrowinning of the metal from an alkali melt is proposed for processing of CdO and production of metallic cadmium or cadmium–sodium alloys. The design of a laboratory electrolyzer is discussed. Technological parameters of the electrolysis process are determined. Applied and engineering aspects of the electrowinning of cadmium and cadmium–sodium alloys are considered. Conditions of the electrolytic production of cadmium are optimized. Specific features of the electrochemical production of cadmium–sodium alloys are analyzed. Electrowinning of cadmium from an acid or chloride solution is considered. The comparison of the electrolysis of aqueous solutions and alkali melts is in favor of the latter.     

钝化工艺对HEDP镀铜层耐蚀性的影响

采用盐水浸泡试验、硝酸点滴试验以及电化学测试方法,研究了苯并三氮唑、苯并三氮唑与Cr(Ⅲ)复配、苯并三氮唑与铈盐复配、Cr(Ⅵ)以及HAD无铬钝化工艺对HEDP镀铜层耐蚀性的影响。结果表明,经苯并三氮唑复配钝化液钝化处理后,钝化膜耐蚀性较单一的苯并三氮唑钝化稍有提高,但均不及Cr(Ⅵ)钝化处理,而经HAD无铬钝化处理后,钝化膜耐硝酸点滴时间最长,在3.5%Na Cl溶液中的Rct最大,icorr最小,耐蚀性明显优于Cr(Ⅵ)钝化处理。     

Electrochemical behaviour of the antimony electrode in sulphuric acid solutions—I. Corrosion processes and anodic dissolution of antimony

The corrosion processes at open circuit conditions and in the active dissolution region of antimony, at low anodic overpotentials, have been studied in sulphuric acid solutions. It was established that antimony dissolution at open circuit is coupled to oxygen reduction, which occurs via the hydrogen peroxide route. The rate of antimony dissolution was found to increase linearly with increasing acid concentration. Based on potentiodynamic, galvanodynamic and steady-state measurements as well as ac impedance data possible mechanisms for the corrosion processes at open circuit as well as for the dissolution of antimony in the active region are proposed and discussed.     

Electrochemical behaviour of aluminium in the presence of EDTA-containing chloride solutions

The electrochemical behaviour of pure aluminium in an EDTA-containing chloride solution was investigated using potentiodynamic and potentiostatic electrochemical techniques and electrochemical impedance spectroscopy. A pronounced EDTA-induced anodic dissolution was observed in alkaline solutions, but the presence of EDTA in solution had little activating effect on the passivation properties at pH values close to 4.0. This was attributed to the relative stability of the Al(EDTA)^– complex formed at the different pH values. This EDTA-induced activation had no deleterious effect on pitting attack, in fact, higher breakdown potentials were observed in the presence of EDTA. This was attributed to the buffering action of EDTA, which inhibited the attainment of a critical pit solution composition. But, in the presence of molybdate, EDTA had no observable effect on pitting attack. The impedance spectra recorded in the presence of EDTA showed evidence for the adsorption of EDTA species during the dissolution process, which in turn, form a large capacitive network, with capacitance values of the order of 3 mF cm^–2 in the low frequency region.     

不同热解温度生物炭对溶液中镉的吸附性能研究

以玉米秸秆、枫杨树枝、花生壳为生物质材料,分别在450、550、650℃下,对3种生物质材料进行厌氧热解制备了9种生物炭,对溶液中的Cd2+进行吸附试验,研究了pH、生物炭投加量、吸附时间和Cd2+初始质量浓度对Cd2+吸附效果的影响。结果表明,吸附过程与Langmuir、Freundlich和准一级动力学方程拟合的相关性较好。pH对吸附的影响较大,吸附率与生物炭的投加量呈正比,650℃制备的3种生物炭的吸附能力更强,花生壳生物炭对溶液中的Cd2+具有更好的吸附能力。     

Electrochemical behavior of magnesium alloys as biodegradable materials in Hank's solution

The electrochemical behavior of extruded AZ31E and AZ91E alloys was investigated in Hank's solution at 37 °C. The behavior of the two alloys was studied with immersion time using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and weight loss tests. It was found that the corrosion resistance of AZ31E alloy is higher than that of AZ91E. Also, the effect of adding different concentrations of a commercial drug called glucosamine sulphate (as inhibitor) to Hank's solution was studied for AZ31E alloy. The corrosion was effectively inhibited by the addition of 0.01 mM glucosamine sulphate that reacts with AZ31E alloy and forms a protective film on its surface. The results were confirmed by surface examination via scanning electron microscope.     

Electrochemical behaviour of phenylethanolamine at gold in aqueous solution

The electrooxidation of phenylethanolamine (2-amino-1-phenylethanol) at a gold electrode in alkaline electrolyte has been studied. Measurement of the differential capacitance of the electric double layer versus the electrode potential has shown that the adsorption of phenylethanolamine at the gold-solution interface plays a significant role in the oxidation mechanism. The effect of amine concentration, electrolyte pH and potential scan rate on the electrooxidation is analysed.     

Influence of some amino acids and vitamin C on the anodic dissolution of tin in sodium chloride solution

The safety of canned foodstuffs should be evaluated not only by recognition of functional foods but also by the presence of toxicants in the human diet. In this study, the anodic dissolution of tin in 3.5% NaCl solution with and without 25–100 mM glycine, serine, methionine, vitamin C and some of their binary mixtures was studied by means of potentiodynamic and impedance techniques. The corroded tin surface was examined by SEM. The results indicated that the passive behaviour of tin is greatly improved by the presence of 50–100 mM glycine and methionine while such improvement is achieved only at 100 mM serine. Both cysteine and vitamin C showed aggressive action. The influence of the glycine/methionine mixture was found to be similar to that of the individual components, whereas the presence of cysteine in the cysteine/methionine mixture annuled the inhibiting action of methionine. The impedance results revealed that the dissolution reaction of tin in NaCl solution with and without glycine, serine and methionine is controlled by the charge transfer process while in the presence of cysteine and vitamin C, the mixed charge transfer and diffusion control is dominant. A rough, bare tin surface was observed in the presence of cysteine and vitamin C while a clean surface covered by corrosion products, in some zones, was observed in NaCl solution containing methionine. © 2001 Society of Chemical Industry     

含有机酸钠盐的废碱液中Na_2CO_3、NaOH(NaHCO_3)含量的测定

采用气提方法 ,通过间接滴定与直接滴定 ,测定了以苯为原料生产环己酮的废碱液中Na2 CO3、NaOH或Na2 CO3、NaHCO3 的含量 ,有效地避免了废碱液中有机酸钠盐的干扰。对方法的可靠性进行了验证。结果表明 ,该方法操作简便 ,测定结果准确可靠     

添加剂对镀锌层钝化膜耐蚀性的影响

利用极化曲线和交流阻抗谱,研究了不同添加剂对镀锌层烷氧基硅烷钝化膜腐蚀性能的影响,并与加速腐蚀试验结果进行了对比.实验结果表明:添加剂的加入明显改变了钝化膜层的腐蚀电位,提高钝化膜在低频区的交流阻抗值,烷氧基硅烷钝化膜的耐蚀性明显提高.     

Electrochemical behaviour of tin in bicarbonate solution at pH 8

The anodic oxidation of tin in 0.1 to 1M bicarbonate solutions at pH 8 has been studied. The process may be divided into three potential regions: (1) a short active dissolution (Tafel) region; (ii) a dissolution-precipitation region; and (iii) a large region of electrode passivity. The rate-determining step of the reaction in the active-dissolution region is attributed to the diffusion of an ionic species into the solution, the diffusing species being generated at the metal surface. In the region of the first oxidation peak, the reaction rate is controlled by diffusion of CO ₃ ^2– species in solution. When the potential becomes more positive than –0,1 V_sce, a highly passivating (most likely SnO₂) film is formed on the electrode surface.     

Electrochemical behaviour and electrowinning of rhodium in acidic chloride solution

The electrochemical behaviour and recovery of rhodium in an acidic solution were investigated using a rotating disc electrode system and a modified electrochemical cyclone cell, respectively. The electrochemical polarization data indicated that the Rh³⁺ ions were reduced to metallic Rh below ?0.1 V, and the limiting current density for rhodium deposition was observed at around ?0.3 V (vs. SCE) with a diffusion coefficient of 6.3 × 10^?6 cm² s^?1 using the Levich equation. The effects of the applied voltage and the initial concentration of rhodium were examined using the modified cyclone cell, and more than 91 % of the rhodium in solution was recovered within 2 h under the optimal conditions.     

镀锌及低铬钝化锌镀层的电化学行为

本文在３％ＮａＣｌ溶液中采用线性极化及交流阻抗技术测定了镀锌层和钝化后的锌镀层的极化电阻,实验表明：低铬钝化后腐蚀电阻明显增大,是纯锌的２－６倍,同时利用Ｓｔｅｒｎ－Ｇｅａｒｙ方程,根据极化电阻Ｒｐ和Ｔａｆｅｌ斜率计算腐蚀电流,同时探讨了纯化后的镀锌层在静止电位下的交流阻抗行为。     

High Rate Anodic Dissolution of 100Cr6 Steel in Aqueous NaNO 3 Solution

The high rate anodic dissolution of 100Cr6 steel in NaNO₃ electrolytes of various concentrations and at different temperatures was investigated. Galvanostatic flow channel experiments were used to examine the current efficiency of the steel substrate. Below 6 A cm^–2(zone A), oxygen evolution dominates, while at higher current densities iron dissolution prevails (zone C). Potentiodynamic polarization studies indicated a complete substrate surface passivation up to +1.8V (vs NHE), and periodic fluctuations of the current density at higher anode potentials (> +1.8 V) due to severe oxygen evolution. Rotating cylinder measurements served for polarization studies at lower current densities in the region of dominating oxygen evolution. Scanning electron micrographs revealed a correlation between the current efficiency and the coverage of the substrate surface with an electronically conductive film at current densities of 2, 9 and 20 A cm^–2. The microstructure of the black, solid surface film developing during the high rate anodic dissolution of the steel was found to be heterogeneous and very porous. The main film components, as determined by X-ray diffraction and Auger electron spectroscopical measurements, were amorphous iron oxides, Fe _x O _y , and inert carbides, M₃C, originating from the steel matrix. An activation–repassivation process is proposed, which is responsible for the development of the complex multilayer (multiphase) structure observed at the steel substrate surface.     

HEDP镀铜液在铜电极上的电化学行为

采用测量开路电位-时间曲线和阴极极化曲线的方法,研究了铜电极上HEDP镀铜的电化学行为.结果表明,HEDP体系的溶液组成与温度都会影响铜电极的稳定开路电位,电镀铜过程的阴极极化(镀层结晶质量)与极化度(镀液分散能力).溶液中HEDP浓度升高,则稳定开路电位变负,阴极极化和极化度增大,有利于电沉积铜的电极过程.溶液pH升高时,稳定开路电位变负,电沉积铜的阴极极化增大.溶液温度降低时,电沉积铜的阴极极化增大.阴极极化较小时的极化度较大,且随pH的升高或温度的降低而明显增大.