Mechanism of Self-Propagating High-Temperature Synthesis of AlB2–Al2O3 Composite Powders
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.
KeywordsAlB2–Al2O3 composite powders dissolution-precipitation mechanism self-propagating hightemperature synthesis (SHS)
The work was sponsored by the National Natural Science Foundation of China (Grant No. 51272203 and No. 51572212).
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