Oxidation protection of mild steel by coatings made with aluminum alkyls

Abstract

The deposition of Al on 1010 steel from mixtures of trimethyl (TMA) and triethyl (TEA) aluminum alkyls in argon and hydrogen was studied. Unlike earlier work with SiH4/H2 no aluminum diffusion onto the steel was observed even when the samples were heated to 800°C. Coatings obtained with TEA at temperatures between 300-400°C resulted in overlays of elemental Al or Al oxide after exposure to ambient conditions. No deposition was obtained at temperatures higher than 400°C in a hot-wall reactor due to rapid decomposi tion of TEA on the walls of the reactor. Deposition with TMA at temperatures between 400-800°C resulted in overlays of Al carbide. For deposition at tem peratures higher than 500°C, a cold-wall reactor was used. The Al overlay coatings resulting from TMA were dense, homogeneous, and adhered well to the steel. Both kinds of coatings provided oxidation protection to the steel in air at 800°C. The performance of the coatings produced with TMA was superior to the coatings produced with TEA and similar to the performance of an Alonized steel. © 1991 Plenum Publishing Corporation.