Effects of PTFE activation and excess Al on combustion synthesis of SiC- and ZrC-Al2O3 composites

Fabrication of SiC- and ZrC-Al2O3 composites was studied in PTFE-added SiO2/Al/C and ZrO2/Al/C combustion systems. PTFE acted as not only a reaction promoter to initiate and sustain self-propagating combustion, but a carburizing agent to facilitate evolution of carbides. Excess Al was required to improve thermite reduction of oxide precursors. Based upon the dependence of flame-front velocity on combustion temperature, the activation energies of 149.8 and 104.0 kJ/mol were respectively deduced for synthesis of SiC- and ZrC-Al2O3 composites from PTFE-assisted combustion. The SiC-Al2O3 composite with the least amount of minor phases was produced from the SiO2/Al/C system with PTFE of 6.2 wt% and extra Al of 25%. The best yield of the ZrC-Al2O3 composite was obtained from the ZrO2/Al/C system with PTFE of 3 wt% and 25% excess Al.