J. Q. Zhang

Corrosion Behavior of Anodized AZ91D Magnesium Alloy in NaCl Aqueous Solution

The corrosion behavior of anodized AZ91D magnesium alloy in neutral 1% (w) NaCl aqueous solution was investigated by salt spray test, polarization Curve, electrochemical impedance spectroscopy (E-IS), electrochemical noise (EN) and scanning electron microscope (SEM). The results showed that the corrosion behavior of Mg alloy presented characteristic changes due to anodization. For example, the unsealed anodic film Could be sustained in 5% NaCl salt spray beyond 200 h, E-corr of anodized magnesium alloy shifted up and the inductive period for pitting corrosion was obviously prolonged, and the impedance modules in high frequency of anodized alloy were several thousand times those of unanodized alloy. All these proved that anodization process made the alloy gain excellent property of anti-corrosion. The evolution of fractal dimension (D-r) was first utilized to depict the corrosion process of anodized AZ91D magnesium alloy and shown as rapid increasing in the initial, fluctuating in the medium and decreasing in the last. This evolution was related with the three different corrosion stages of anodized AZ91D magnesium alloy in 1% NaCl solution.

EIS Analysis on the Anodic Dissolution Process of Pure Aluminum in an Alkaline Solution

The EIS of the anodic dissolution process of pure aluminum in an alkaline solution was fitted using expression of Faradic admittance previously proposed by Cao([11-12]), based on which the mechanism of the process was proposed. The results show that the capacitive loop in low frequency region of EIS is caused by the reaction of Al(ss), and the inductive loop in middle frequency region is caused by the reaction of Al(OH)(ads). The time constants of Faradic admittance tau(1) and tau(2) mean the converting time of unit species Al(ss) and Al(OH)(ads) on unit bare surface site. Generally, tau(1) and tau(2) both decrease with the increase of the potential E. tau(1), > 0, tau(2) > 0, satisfy the conditions required by stability, and by Kramers-Kronig transforms as well. g(1) and g(2) relate to the variation of covering density of reactants Al(ss) and Al(OH) (ads). g(1) < 0 indicates that the aluminum surface tends to be passive when the potential increases.

Application of Dimension Analysis in Electrochemical Noise Technique

Pitting corrosion of aluminum alloy 2024-T3 in NaCl solution was studied using electrochemical noise technique. The spectral analysis results showed that the more positive the values of cut-off frequency(f(c)), the slope of high-frequency linear part of SPD (k) and white noise level(W) are, the more easily the pit initiates, but none of them can be used to depict the corrosion process individually. Two new parameters(S-E and S-G) were derived by using dimensional analysis method, and the value of S-E characterize the severity of pitting of corroding material. While the meaning of the other parameter(S-G) remains for further investigation.

Polarization Behavior of Magnesium Alloy AZ91D with Micro-Arc Oxidation Coating in NaCl Solution

The polarization curves of magnesium alloy AZ91D with a micro-arc oxidation (MAO) coating showed several typical patterns caused by differences in the composition and structure of the coating. The pattern of the polarization curve of magnesium alloy AZ91D with a MAO coating depends on the primary composition and structure of the MAO coating and many experimental factors, such as the concentration of chloride ions, pH of the electrolyte, degree of cathodic polarization, and the exposed area of the specimen. These factors change the pattern of polarization curve of magnesium alloy AZ91D with MAO coating by affecting the main composition and structure of the MAO coating because of its instability in aqueous solution. Compositional and structural changes in the MAO coating on magnesium alloy AZ91D were investigated by Fourier transform infrared microscopic mapping and the corresponding optical photographs, respectively. A model was proposed to describe the transformation of the MAO coating in aqueous NaCl solution. For magnesium alloy AZ91D with a MAO coating immersed in NaCl solution, the rate determining steps of the anodic and cathodic reactions are the mass diffusion and charge transfer steps, respectively. As a result, the corrosion current density fitted from the polarization curve is not an accurate corrosion rate.

Catalytic Oxidation of Sulfide Ion over a Spherular-Co(3)O(4) Electrode

[Lao Guo-Hong; Shao Hai-Bo; Fan Yu-Qian; Wang Jian-Ming; Zhang Jian-Qing; Cao Chu-Nan] Zhejiang Univ, Dept Chem, Hangzhou 310027, Zhejiang, Peoples R China. [Zhang Jian-Qing; Cao Chu-Nan] Chinese Acad Sci, State Key Lab Corros & Protect Met, Inst Met Res, Shenyang 110016, Peoples R China.;Shao, HB (reprint author), Zhejiang Univ, Dept Chem, Hangzhou 310027, Zhejiang, Peoples R China;shaohb@zju.edu.cn

Electrochemical Fabrication and Pseudocapacitive Performance of a Porous Nanostructured Nickel-Based Complex Film Electrode

[Kong De-Shuai; Wang Jian-Ming; Pi Ou-Yang; Shao Hai-Bo; Zhang Jian-Qing] Zhejiang Univ, Dept Chem, Hangzhou 310027, Peoples R China. [Zhang Jian-Qing] Chinese Acad Sci, Inst Met Res, State Key Lab Corros & Protect Met, Shenyang 110016, Peoples R China.;Wang, JM (reprint author), Zhejiang Univ, Dept Chem, Hangzhou 310027, Peoples R China;wjm@zju.edu.cn