Mechanisms and Kinetics of Reaction‐Bonded Aluminum Oxide Ceramics

Reaction‐bonded Al 2 O 3 (RBAO) ceramics were fabricated starting from mechanically alloyed Al 2 O 3 /Al, Al 2 O 3 / Al/ZrO 2 , and Al 2 O 3 /Al/ZrO 2 /Zr mixtures. Isopressed compacts were heat‐treated in air up to 1550°C. Reaction‐bonding mechanisms, kinetics, and the influence of ZrO 2 and Zr additions are investigated. Independent of additive, oxidation of Al proceeds both as solid/gas and liquid/gas reaction, and the reaction kinetics follow a parabolic rate law. The reaction rate depends strongly on the particle size of Al. The activation energy of the reaction depends essentially on green density. Below the melting temperature of Al, in samples containing 45 vol% Al and 55 vol% Al 2 O 3 , it is 112 and 152 kJ/mol at ∼64% and ∼74% TD, respectively, while above the melting temperature, it lies in the range ∼ 26–33 kJ/mol. Zr additions reduce the activation energy to some extent. Samples with only ZrO 2 additions exhibit nearly the same activation energies as ZrO 2 ‐free samples, though ZrO 2 has a very positive effect on the microstructural development in RBAO ceramics. Microstructure evolution and some strength data of RBAO bodies are also reported.