El-Taib Heakal F, Abd-Ellatif W R, Tantawy N S, Taha A A
Chemistry Department, Faculty of Science, Cairo University Giza 12613 Egypt
Faculty of Women for Arts, Science and Education, Ain Shams University Cairo 11566 Egypt.
RSC Adv. 2018 Jan 19;8(7):3816-3827. doi: 10.1039/c7ra12723e. eCollection 2018 Jan 16.
The electrochemical and semiconductive properties of spontaneously formed passive films on pure Zn were investigated in alkaline carbonate/bicarbonate buffer solutions as functions of pH and temperature. The study was performed in 0.1 M (CO + HCO ) mixtures over the pH range 9.2 to 9.8 using open circuit potential, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and Mott-Schottky analysis techniques. Generally, zinc passivation is enhanced with either increasing pH or decreasing the ambient temperature. The steady state potential ( ) value reveals that in pH 9.8 buffer the propensity of Zn for passivation is superior when compared with those in the other tested buffer solutions. The total surface film resistance ( ) derived from the impedance data proves this result, which is likely attributed to changes in composition and/or microstructure of the film. In pH 9.8 buffer solution the passivation tendency always decreases with temperature increase. However, in pH 9.2 the system behaves similarly up to 25 °C; afterwards zinc passivation trend was found to re-increase once more. The apparent activation energy for the corrosion process was evaluated and discussed. Analysis of Mott-Schottky plots was found to be suitable for characterizing the semiconductor properties of the naturally deposited barrier layers which are all consistent with the well-known n-type character of the oxide film on zinc. The absence of any evidences for the p-type semiconductive behavior indicates a preponderance of oxygen vacancies and zinc interstitials over metal vacancies. Moreover, Mott-Schottky results demonstrate that the donor concentration increases with either increasing pH or deceasing temperature commensurate with the increasing trends in the passive film thickness.
在碱性碳酸盐/碳酸氢盐缓冲溶液中，研究了纯锌表面自发形成的钝化膜的电化学和半导体性质与pH值和温度的关系。该研究在0.1 M（CO₃²⁻ + HCO₃⁻）混合溶液中，pH范围为9.2至9.8，采用开路电位、电化学阻抗谱（EIS）、动电位极化和莫特-肖特基分析技术进行。一般来说，随着pH值的增加或环境温度的降低，锌的钝化作用增强。稳态电位（Eoc）值表明，在pH 9.8的缓冲溶液中，锌的钝化倾向比其他测试缓冲溶液中的更强。由阻抗数据得出的总表面膜电阻（Rt）证明了这一结果，这可能归因于膜的组成和/或微观结构的变化。在pH 9.8的缓冲溶液中，钝化倾向总是随着温度的升高而降低。然而，在pH 9.2时，该体系在25℃以下表现相似；之后发现锌的钝化趋势再次增加。评估并讨论了腐蚀过程的表观活化能。发现对莫特-肖特基图的分析适用于表征自然沉积阻挡层的半导体性质，这与锌上氧化膜众所周知的n型特性一致。没有任何p型半导体行为的证据表明氧空位和锌间隙原子比金属空位占优势。此外，莫特-肖特基结果表明，施主浓度随着pH值的增加或温度的降低而增加，这与钝化膜厚度的增加趋势一致。
