$TiB_2$ particles were synthesized by a magnesio-thermal reduction process. $TiO_2$, $B_2O_3$, and Mg particles were used as starting materials. Purity and size of as-synthesized $TiB_2$ particles were carefully controlled in this study. The purity was controlled by changing the initial chemical composition of the starting materials and acid-treatment process. The size was controlled by changing the mixing method and addition of a diluent, MgO.
In the magnesio-thermal reduction process, a mixture that was composed of $TiB_2$, MgO, $Mg_3B_2O_6$, and $Mg_2TiO_4$ phases was synthesized as a product. The MgO phase in the product could be removed out by acid-treatment in a 4N H2SO4 aqueous solution. The $Mg_3B_2O_6$, and $Mg_2TiO_4$ phases in the product could be removed out by carefully controlling the initial chemical composition of the starting materials. In this study, pure $TiB_2$ particles could be prepared.
The average size of the purified $TiB_2$ particle was about 200nm. The size was controlled by the addition of a diuent, MgO. As the amount of the diluent increased, the size decreased. The size decrease could be explained by the decrease of combustion temperature as the amount of the diluent increased. The decrease of combustion temperature could be expected by considering the decrease of adiabatic temperature calculated by thermo-chemical data as the amount of the diluent increased. The size of synthesized $TiB_2$ particles depended on the mixing conditions of the starting materials. The $TiB_2$ particles synthesized from a mixture that was mixed and milled in a vibratory mill was smaller than ones synthesized from a mixture that was only mixed in a pulverizer. On considering that the Mg particles, a reagent, is crushed to be smaller particles on the vibratory milling, the initial particle size of reactants could be suggested to be an important factor to control the size of the final $TiB_2$ particles in the magnesio-thermal reaction. In this study, the size of synthesized $TiB_2$ particles could be decreased to be about 50 nm. The synthesized $TiB_2$ particles were relatively ultrafine, on considering that a representative commercial $TiB_2$ particle is about a few mm sized.
The sintering behavior of the synthesized $TiB_2$ particles was compared with a commercial $TiB_2$ particle with relatively larger particle size. The ultrafine synthesized $TiB_2$ particles showed superior densification behavior to the commercial particle. The good sinterability of the synthesized $TiB_2$ particles was originated from the smaller particle size.
