Effect Of Additive On AlB₂-Al₂O₃ Compound Powders Prepared By Combustion Synthesis

The AlB₂-Al₂O₃ compound powders were prepared using Al and B₂O₃ as raw materials by the method of combustion synthesis（CS）, using La、S、Mg as additive and NaCl 、 KCl 、 KBF₄ 、 NaCl-KCl 、 NaCl-KCl-KBF₄ as salt. The combustion temperature was recorded by temperature-time recorder, and the combustion wave velocity was calculated. The phases of product were characterized by XRD. The changes of raw materials in the heating process were studied by DSC-TGA. The microscopic morphology of products was characterized by FESEM and EDS. The effects of different additive and their addition amounts on the phase of product were studied.The results showed that Mg is the best additive because there is no AlB₂ in AlB₂O₃-La system products and Al-B₂O₃-S system needed more energy and produced H2 S. Combustion temperature of Al-B₂O₃-Mg system is 1953 K,the combustion temperature decreased with increasing amount of Mg, while its combustion wave velocity increased. DSC-TGA show that the ignition temperature is 909℃when adding6 wt.%Mg, the synthesized products of Al-B₂O₃-Mg system contain Al₂O₃, AlB₂,MgAl2O4 solid solution and Al. With increasing of Mg, the content of MgAl2O4 solid solution and Al increases while the contents of Al₂O₃ decreased, and the content of AlB₂ reached its highest value when adding 6wt.%Mg; SEM show that Al₂O₃ is spherical particles with the size of 2 4 μm, and AlB₂ is hexagonal-shaped particles with the size of 5 10 μm, MgAl2O4 solid solution is continuous unshaped matrix.The results showed that the ignition temperature is 879℃when adding salt, the synthesized products contain Al₂O₃,Al、Al B₂. There are vestigial salt in products when single salt amount reached 20 wt.%. The product contain a little of boride when adding KBF₄ in reactant, and the content of boride increases with increasing amount of KBF₄. SEM show that the microstructure of the combustion product is a small amountof AlB₂ with a particle size of about 5 μm, which is dispersed in a mixture of Al and Al₂O₃ with a particle size of about 2 μm.