Preparation of NbB{sub}2-Al{sub}2O{sub}3 in situ Composites by SHS Involving Thermite Reactions

摘要

Preparation of NbB{sub}2-Al{sub}2O{sub}3 in situ composites with a broad range of compositions was conducted by self-propagating high-temperature synthesis (SHS) involving thermite reactions. Three different thermite mixtures, including Al-Nb{sub}2O{sub}5, Al-B{sub}2O{sub}3, and Al-Nb{sub}2O{sub}5-B{sub}2O{sub}3, were adopted and mixed with Nb and/or B powders to formulate the sample compacts. Experimental observations show that the thermite reaction enhances sustainability of the synthesis reaction. Among them, the powder compact containing the thermite mixture of Al and Nb{sub}2O{sub}5 exhibited the highest flame velocity and combustion temperature. The lowest reaction propagation rate and temperature were observed in the sample with Al and B{sub}2O{sub}3 as thermite reagents. Due to insufficient reaction time for the sample containing Al and Nb{sub}2O{sub}5, the end products were composed of large amounts of two intermediate borides Nb{sub}3B{sub}4 and NbB in addition to NbB{sub}2 and Al{sub}2O{sub}3. The SHS process involving the thermite reaction of Al with B{sub}2O{sub}3 was favorable to produce NbB{sub}2-Al{sub}2O{sub}3 composites, confirmed by the least Nb{sub}3B{sub}4 and NbB left in the end products.