The reaction-bonded aluminum oxide (RBAO) process: II, the solid-state oxidation of RBAO compacts

The oxidation kinetics and the fraction of aluminum that is oxidized via so lid-gas reaction in reaction-bonded aluminum oxide (RBAO) compacts are show n to be strongly dependent on the oxidation temperature and the characteris tics (size and green density) of the RBAO compact. Based on the Blot number , the oxidation process of RBAO compacts is controlled by convective heat t ransfer. Low heat transfer from the surface of the compact results in too-r apid oxidation, thermal gradients, and core-shell oxidation of the compacts . Uniform oxidation of RBAO compacts is possible by oxidizing at low temper atures (400 degrees-470 degrees C), where slow surface reaction of the alum inum particles controls the oxidation of the compact. A grain model is pres ented to cover both linear and nonlinear oxidation regimes during the oxida tion of a RBAO compact, and this model predicts the experimental results wh en surface reaction of the aluminum particles is the rate-controlling mecha nism and oxidation of the compact occurs uniformly.