Dynamics of phase formation during combustion of Zr and Hf in air

Abstract

The processes of phase formation taking place during combustion of Zr and Hf in air have been explored by time-resolved XRD (TRXRD) at a time resolution of 0.1 s. In case of Zr combustion, the final product was found to form in two stages: first the tetragonal high-temperature modification of ZrO2 is formed (in the combustion wave) and then the latter undergoes polymorphic transition (behind the combustion wave) into its monoclinic modification. In combustion of Hf, product formation proceeds in three stages: the low-temperature monoclinic modification of α-HfO2 is formed in the combustion wave, which is followed by its transformation into the tetragonal β-HfO2 and backward conversion of the latter into α-HfO2 behind the combustion wave. The obtained data were comparatively analyzed with those reported for combustion of Ti in air.