The Study Of Self-propagating High-temperature Synthesis Of TiB₂ By The Reduction Of Magnesium

This paper synthesizes TiB2 powder with the self-propagating high-temperature synthesis by the reduction of magnesium, and analyses the influence on synthesis by adiabatic temperature, reaction free energy and initial conditions with the thermodynamic calculation. The experiment study the influence on structure and production efficiency by the initial conditions, and analyses the composing and granularity distributing of the production with x-ray,SEM, PL granularity equipment.The thermodynamic analysis show that: at the same preheating temperature, the adiabatic temperature will reduce with the increasing of the amount of the diluents; in the same system with the same amount of diluents, the adiabatic temperature will increase with the increasing of preheating temperature. The calculation of the reaction free energy shows that: in the Mg-TiO2 system, there are four ways for the reductive reaction of the TiO2, but the reaction of 2MgO+2TiO2=Mg2TiO4+Ti has the lowest reaction free energy and the highest possibility to react; in the Mg-B2O3 system, the reaction of B2O3+3Mg=2B+3MgO as the lowest reaction free energy and the highest possibility to react, but the free energy of the reaction are tend to be positive with the increasing of the reaction temperature; in the Mg-B2O3-TiO2 system, at the balance condition, the main reaction of TiO2 +B2O3+5Mg =5MgO +TiB2 has the highest possibility to react. So, we can add diluents and excessive Mg in the system to low down the adiabatic temperature to promote the reaction to go on the right way; at the same time, the excessive Mg can make up the some evaporation of Mg.The experiment results show that the production synthesized by SHS by the reduction of magnesium was treated with ache ,then we can get the TiB2 powder with average granularity of 20.55μm;at the same time the initial conditions such as molding pressure, the amount of Mg and diluents affect the structure, production efficiency of TiB2 and the evaporation of Mg. When the molding pressure is up to12MPa, the combustion wave is interrupt and the reaction can't go on; when the excessive Mg is up to 10%, the production efficiency of TiB2 is highest; when the content of diluents MgO exceed 20wt%, the combustion wave is interrupt and the reaction can't go on.