Processing parameter effects on the reaction bonding of aluminum oxide process

The reaction bonding of aluminum oxide (RBAO) process was analyzed from the milling of the precursor mixtures to the sintering of the reaction bonded alpha-alumina as a function of precursor powder composition, Al particle si ze, temperature, and heating rate. The RBAO process involves both solid-gas (T < T-M,T-Al) and liquid-gas (T > T-M,T-Al) oxidation of Al + alpha-Al2O3 powder compacts. It has been demonstrated that maximum Al content of the p recursor powder is limited to 60 vol %. In addition, it was observed that t he initial Al particle size affects the oxidation behavior significantly an d hence final properties of alpha-Al2O3 compacts. Therefore, the initial Al particle size is very critical for the RBAO process. The critical Al parti cle size (i.e., the largest Al particle size can be used to obtain dense ce ramic materials by the RBAO process) was determined as similar to 1.5 mu m. It has been demonstrated that heating rate can be used to im prove the fin al microstructures of RBAO ceramics. Although there is no large (>4 vol %) amount of ZrO2 addition, alpha aluminum oxide ceramics with 97% TD have bee n produced by optimizing the processing parameters such as fine (<1.5 mu m) Al particles and slower heating rate during the liquid-gas oxidation. (C) 1999 Kluwer Academic Publishers.