Reaction-bonded aluminium oxide (RBAO) process: II, the solid-state oxidation of RBAO compacts

The oxidation kinetics and the fraction of aluminum that is oxidized via solid-gas reaction in reaction-bonded aluminum oxide (RBAO) compacts are shown to be strongly dependent on the oxidation temperature and the characteristics (size and green density) of the RBAO compact. Based on the Biot number, the oxidation process of RBAO compacts is controlled by convective heat transfer. Low heat transfer from the surface of the compact results in too-rapid oxidation, thermal gradients, and core-shell oxidation of the compacts. Uniform oxidation of RBAO compacts is possible by oxidizing at low temperatures (400 °-470 °C), where slow surface reaction of the aluminum particles controls the oxidation of the compact. A grain model is presented to cover both linear and nonlinear oxidation regimes during the oxidation of a RBAO compact, and this model predicts the experimental results when surface reaction of the aluminum particles is the rate-controlling mechanism and oxidation of the compact occurs uniformly.