Mechanism of Self-Propagating High-Temperature Synthesis of AlB2–Al2O3 Composite Powders

Abstract

The mechanism of self-propagating high-temperature synthesis (SHS) of AlB₂–Al₂O₃ composite powders was studied using the combustion front quenching method (CFQM). The results showed that the combustion began with fusion of B₂O₃ and Al particles followed by mutual penetration of Al and B₂O₃ in the melt. X-ray patterns exhibited reflections for Al₂O₃ that were consistent with exchange of O atoms between Al and B through the reaction B₂O₃ + 2Al → 2B + Al₂O₃. A certain amount of B₂O₃ volatilized at higher temperatures and reacted with B to form gaseous B₂O₂. Al₂O₃ and B precipitated on the Al surface. Then, the produced B dissolved in the Al melt and reacted with Al to precipitate AlB₁₂ particles. Finally, AlB₁₂ transformed into AlB₂ at the peritectic temperature during rapid cooling. Thus, the combustion could be explained by a dissolution-precipitation mechanism. The final products included AlB₂ and Al₂O₃ particles and a certain amount of Al. A model of the dissolution-precipitation mechanism was proposed. The ignition temperature of the combustion was ~800°C.