Effects Of Raw Material And Chemical Oven On Phase Of AlB₂-Al₂O₃ Compound Powders Prepared By Combustion Synthesis

AlB₂-Al₂O₃ compound powders have potential application as additives in low carbon MgO-C refractory, because AlB₂ could act as antioxidant and Al₂O₃ could improve the corrosion resistance due to magnesium aluminate spinel which was generate by the reaction between Al₂O₃ and MgO. AlB₂-Al₂O₃ compound powders were prepared by combustion synthesis using Al and B₂O₃ powder as starting raw materials in this thesis. Based on thermodynamic theory, the adiabatic temperature（Tad） of Al-B₂O₃ system was calculated. The physical and chemical changes during the reaction were analyzed by differential thermal analysis and thermogravimetry（DTA-TG）. The product were characterized by X-ray diffraction（XRD）, scanning electron microscope（SEM） and energy dispersive spectrometer（EDS）, and the effects of particle size of Al powder, morphology of aluminum powder and raw material ratio on combustion parameters, phase composition and microstructure of final products were discussed. The influence of using chemical oven self-propagating high-temperature synthesis（C.O.SHS）in the phase composition of the AlB₂-Al₂O₃ compound powders were also focused on.The results of thermal analysis showed that the adiabatic temperature of Al-B₂O₃ system is 2327 K, the physical and chemical changes including lost of absorbed water when the temperature reaches 399 K, endothermic melting of B₂O₃ at 723 K, melting of Al at 937 K, the strong exothermic redox reaction between Al and B₂O₃ occurs at about1131 K, and finally forming of AlB₂-Al₂O₃ compound powders.The results showed the final synthesized products of Al-B₂O₃ system are AlB₂,Al₂O₃ and remained Al. The experimental results of phase composition of final product synthesized using spherical, irregular shape and flaky aluminum powder as raw material showed that the content of AlB₂ is the highest when the spherical Al was used as raw material. Different particle size of spherical Al was used as raw materials. The results show that the maximum combustion temperature, velocity of combustion wave spread increased, and content of AlB₂ in final product increased, with the particle size of Al decreasing. The velocity of combustion wave spread is 2.08 mm/s and the content of AlB₂ and Al₂O₃ is the highest, when the particle size of Al was 600 mesh.The content of Al₂O₃ in the product increases and then decreases with Al increasing comparing with that prepared by stoichiometric ratio. The content of Al₂O₃ is the highest, when the excessive amount Al is 30%.AlB₂-Al₂O₃ compound were prepared by C.O.SHS using Ti and C powder. It was showed that the C.O.SHS is favor for the growth of AlB₂, there are higher content of both AlB₂ and Al₂O₃, comparing with that prepared by SHS, when the excessive Al amounts of both SHS and C.O. SHS are 30%.