电容器铝箔交流腐蚀扩面机理研究

Study on the Mechanisms of Extending Surface Area of Aluminum Capacitor Foil Etched by Alternating Current

实现铝电解电容器小型化的关键是铝电极箔电解腐蚀扩面过程的人为设计。为实现这一目标，本文就目前尚不清楚的交流腐蚀扩面机制进行了系统分析研究。首先研究了高纯铝箔在水溶液中的热力学和在盐酸溶液中的动力学行为，接着详细地研究了铝在交流电的负半周所发生的变化，以及这些变化对交流正半周铝的点蚀的萌生和生长的影响，并从理论上推导出控制交流负半周腐蚀膜形成的数学关系式。在此基础上，提出了铝在交流负半周发生的四种变化，以及交流腐蚀扩面机理。根据这一机理，提出了铝箔的交流腐蚀工艺优化原则，并用实验对这一原则进行了初步验证。本论文的主要内容如下：

The micro-volume of aluminum electrolytic capacitor has been drawn more and more attention in recent years due to the high rate development of microelectronic technology. The dissertation focus attention on the mechanisms of extending surface area of aluminum electrode foil etched by altemating current in hydrochloric acid solutions because a thorough grasp of the mechanism can advance the electroetching technology. The corrosion behavior of aluminum in aqueous and chloride solutions were investigated roundly as viewed from chemical thermodynamics and kinetics. And the surface changes of aluminum during the negative half-cycle of AC and it's effects on the pitting of anodic aluminum in 2 mol/L have been experimented by using voltammetric technology and SEM observation. Moreover, an experiential formula for predicting the possibilities of etch film formation in the negative half-cycle of AC has been driven from the principle of mass transfer in HCl solutions. Finally, a mechanism of AC etching for aluminum foil in HCl and a theoretical rule for choosing electroetching conditions were suggested on the results. The details as follows． 1. A corrosion electrochemical measurement system, which consists of personal computer. DAC, ADC, Potentiostat, and the software written in Turbo C, has been assembled on the basis of the corrosion requirements. The system can meet well the needs of the measurement of electrochemical experiments in steady-state and transient-state because of the variable sampling rate of 20 to 200 K SPS provided by the system． 2. The reactions possibilities of aluminum and it's oxide in aqueous solutions were analysed by calculated the Gibbs standard energy and equilibrium constants. The results show that corrosion can occur on aluminum at ordinary conditions, the end corrosion product of aluminum in aqueous solutions depends on the pH of solutions. The aluminum oxide with Bayerite structure on aluminum is thermodynamically stability in solutions with pH range of 5.1 to 8.8 by which aluminum shows chemical inert in some extent in ordinary aqueous solutions． 3. The dissolution kinetics of aluminum foil in HCl solutions was investigated by potentiostat polarization. The results show that the Tafel slopes of anodic and cathodic are 19.8 mV/decade and 120 mV/decade, respectively. Aluminum anodic dissolution rate is proportional to the 2.5th power of hydrogen ion concentrations and to the 3th power of chloride ion concentrations, and the rate of cathodic hydrogen evolution is proportional to the lth power of hydrogen ion concentration and to the 0.56th power of chloride ion concentration. The reaction mechanisms of aluminum dissolution and cathodic hydrogen evolution are also proposed on the basis of the empirical rate expressions． 4. The effects of cathodic polarization conditions including cathodic potential and the periods of cathodic half-cycle on pitting behavior of aluminum foil in 2 mol/L HCl solutions have been determined by using voltammetric and SEM technologies. It was found that the anodic pitting of aluminum depends mainly on cathodic potentiaI, A discussion on the phenomena was also carried out． 5. The influence of cathodic hydrogen evolution on anodic pitting of aluminumin 2 mol/L HCl solutions has been studied based on the chronocurrent and chronopotential plots and surface morphologies of aluminum foil etched under different hydrogen evolution current density. The experimental results clearly show that the process of cathodic hydrogen evolution exerts a double-effect of promotion and inhibition on the anodic pitting. And also, the double-effect mechanisms of cathodic hydrogen evolution were discussed． 6. A experiential formula for estimating the formation possibility of etch film during the negative half-cycle of ac electroetching of aluminum foil in HCl solutions was derived by taking into account diffusion and electrical migration of H+ in the e1ectrolyte, as well as the variations of electrode morphology with electroetching frequency. The result indicates that the precipitation of Al3+ wil