| Titanium diboride and zirconium diboride powders were synthesized with TiO2(ZrO2)-B2O3-Mg by employing a magnesium thermite technique. In place of B2O3, H3BO3 was also tried as a source of boron with limited success. Removing the by-product MgO by acid leaching, metal borides of submicron size with basically spherical shape could be obtained. In the case of TiB2, a small amount of TiN was formed besides MgO during the synthesis reaction due to high temperature exposure of the reactants to air. Though ZrB2 could be similarly synthesized as TiB2 using the same technique, it was difficult to remove residual ZrO2 even after acid leaching. The presence of ZrN was not as apparent as that of TiN. The spark plasma sintering method was used to sinter the synthesized TiB2 without using any additives. At temperatures of 1600℃ and higher, relative density greater than 98% was obtained. The maximum Vickers hardness of the sintered body was 3360(32.9 GPa). Two sets of commercial powders with particle size of 3 and 16 μm respectively were tested at 2000℃ for comparison but they showed relative density less than 80%. The surface conditions of the sintered commercial powders were unfit for the hardness test. |
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