Novel sol-gel process depositing alpha-Al2O3 for the improvement of graphite oxidation-resistance

Anhydrous Al2O3 sol was prepared from aluminum isopropoxide as the raw mate rial and diethylene glycol monoethyl ether as the solvent. Peptization of t he raw material in the organic solvent was accomplished using acetic acid, which produced a clear, viscous, and stable sol. The spinnable sol, prepare d within 30 min, has remained stable for over a year, and crystallizes in t he alpha -Al2O3 structure at 950 degreesC via a single transition phase, ga mma -Al2O3. The deposited films synthesized using a modified dip-coating pr ocess, were uniform and crack-free, and provided an excellent oxidation res istance for graphite pre-coated with a silicon oxide layer. (C) 2001 Elsevi er Science B.V. All rights reserved.