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 α-alumina as a function of precursor powder composition, Al particle size, temperature, and heating rate. The RBAO process involves both solid-gas (T < T_M,Al) and liquid-gas (T > T_M,Al) oxidation of Al + α-Al₂O₃ powder compacts. It has been demonstrated that maximum Al content of the precursor powder is limited to 60 vol%. In addition, it was observed that the initial Al particle size affects the oxidation behavior significantly and hence final properties of α-Al₂O₃ compacts. Therefore, the initial Al particle size is very critical for the RBAO process. The critical Al particle size (i.e., the largest Al particle size can be used to obtain dense ceramic materials by the RBAO process) was determined as approx. 1.5 μm. It has been demonstrated that heating rate can be used to improve the final microstructures of RBAO ceramics. Although there is no large (>4 vol%) amount of ZrO₂ addition, alpha aluminum oxide ceramics with 97% TD have been produced by optimizing the processing parameters such as fine (< 1.5 μm) Al particles and slower heating rate during the liquid-gas oxidation.