Promotion of the Corrosion Protection of Thin Aluminum Film by Silane Coupling Treatment

Abstract

This study investigated shortening of the treatment time to improve corrosion（pitting）resistance of a thin aluminum film using 1, 2-Bis（triethoxysilyl）ethane（BTSE）and Bis（triethoxysilyl）propyltetrasulfide（BTSPS）. During silane coupling processing using BTSPS, the processing time can be shortened by adding hydrogen peroxide or by combining the processing with electrolysis, especially cathode polarization. Using both treatments decreased the processing time to approximately 1/20 of its usual length. The degree of time decrease depends on the shift of potential to the noble side and the decrease of pH by hydrogen peroxide addition. Both increase the formation rate of the BTSPS layer on Al. A weakly acidic Al metal surface is created by removing oxide and hydroxide, depending on the increased potential and the decreased pH. Because BTSPS is a soft base, the HSAB principle suggests that the Al metal surface and BTSPS become combined easily. Reduction of the dissolved O₂ changes the Al surface to an alkali environment. Therefore, processing time reduction by cathodal electrolysis is explained by promotion of the hydrolytic reaction of BTSPS. Adding H₂O₂ to BTSE produces no time-shortening effect. Furthermore, no pitting resistance is observed even if Al is immersed for a long time.