Sintering Mechanisms and Kinetics for Reaction Hot-Pressed ZrB₂

Sintering mechanisms and kinetics were investigated for ZrB ₂ ceramics produced using reaction hot pressing. Specimens were sintered at temperatures ranging from 1800-C to 2100-C for times up to 120 min. ZrB ₂ was the primary phase, although trace amounts of ZrO ₂ and C were also detected. Below 2000⁰C, the densification mechanism was grain-boundary diffusion with an activation energy of 241 ± 41 kJ/mol. At higher temperatures, the densification mechanism was lattice diffusion with an activation energy of 695 ± 62 kJ/mol. Grain growth exponents were determined to be ~4.5, which indicated that a grain pinning mechanism was active in both temperature regimes. The diffusion coefficients for grain growth were 1.5 x 10 ^-16 cm ⁴ /s at 1900⁰C and 2.1 x 10 ^-15 cm ⁴ /s at 2100⁰C. This study revealed that dense ZrB ₂ ceramics can be produced by reactive hot pressing in shorter times and at lower temperatures than conventional hot pressing of commercial powders.