B95铝合金在铈盐溶液中形成转化膜的电极反应机理

Electrode reaction mechanism of conversion coating forming process of B95 aluminium alloy in cerium(Ⅲ) salt solution

采用电化学阻抗谱(EIS)研究B95铝合金在10 mmol/L CeCl3溶液中转化膜的形成过程,在建立稀土转化膜成膜过程三阶段机理基础上,采用电化学阻抗谱(EIS)技术研究溶液中氧含量、H2O2、pH值等各种条件变化对转化膜形成过程的影响。结果表明:O2参与的反应不是Ce转化膜形成速度的决定步骤,添加H2O2加快Ce转化膜形成速度,特别是形成过程的第一阶段;微阴极区氧主要按二电子途径还原,使局部pH上升,当pH达到或超过8.05时,Ce(Ⅲ)水合氢氧化物/氧化物开始沉积;Ce(Ⅲ)转化膜达到稳定平衡阶段,部分Ce(OH)3会被氧还原的中间产物H2O2氧化成CeO2;在中性或弱酸性溶液中,提高溶液的pH值对最终成膜有利。

The electrochemical impedance spectroscope（EIS） was used to study the conversion coating forming process of B95 aluminum alloy in 10 mmol/L CeCl3 solution. The formation process of rare earth（RE） conversion coating can be divided into three stages. Based on the three stages formation mechanism of the rare earth conversion coatings,the influences of O2 concentration,oxidant,pH etc on the formation process of conversion film were investigated. The result shows that the reaction caused by the O2 participation is not determinate step of the Ce conversion coating formation,the addition of H2O2 speeds up the formation of Ce conversion coating,especially in the first stage. The two electric ways of cathodic reaction are formed by the conversion coating on B95 aluminum alloy in CeCl3 solution,which reasonably explains the local pH rise in micro cathode area,Ce（Ⅲ） hydrous hydroxide/oxide begins to deposit when the pH reaches or exceeds 8.05. Part Ce（OH）3 can be oxidized into CeO2 by the intermediate products of H2O2 when Ce（Ⅲ） conversion coating achieves stable equilibrium. In neutral or subacidity solution,improving the pH of solution will beneficial to the final formation of the coating.