Chemical reactivity of hot-pressed Si3N4–ZrB2 ceramics at 1500–1700 °C

Abstract

Chemical reactivity of hot-pressed Si3N4–ZrB2 ceramics at 1500–1700°C under N2 and Ar atmosphere is investigated by X-ray diffraction, thermodynamic calculation, and phase diagram. Results show that there are chemical reactions in Si3N4–ZrB2 ceramics. The chemical reactions accelerate the decomposition and phase transformation of Si3N4. The reaction products include ZrN, BN, ZrSi2, SiC or Si, which strongly depend on the atmosphere or temperature. The source of N2 for ZrN and BN products is both atmosphere and decomposition of Si3N4 at 1600°C or above, whereas that is only atmosphere at 1500°C. There is no reaction in Si3N4–ZrB2 ceramics at 1500°C under Ar. The MgO–Lu2O3 sintering adds lead to the significant increase of relative density of Si3N4–ZrB2 from 48% to 94% at 1500°C in Ar. Therefore, it is possible that dense Si3N4–ZrB2 ceramics with no reaction could be achieved at 1500°C or below in Ar.