Formation of TiB2 by volume combustion and mechanochemical process

Titanium diboride was produced both by volume combustion synthesis (VCS) and by mechanochemical synthesis (MCP) through the reaction of TiO{sub 2}, B{sub 2}O{sub 3} and Mg. VCS products, expected to be composed of TiB{sub 2} and MgO, were found to contain also side products such as Mg{sub 2}TiO{sub 4}, Mg{sub 3}B{sub 2}O{sub 6}, MgB{sub 2} and TiN. HCl leaching was applied to the reaction products with the objective of removing MgO and the side products. Formation of TiN could be prevented by conducting the VCS under an argon atmosphere. Mg{sub 2}TiO{sub 4} did not form when 40% excess Mg was used. Wet ball milling of the products before leaching was found to be effective in removal of Mg{sub 3}B{sub 2}O{sub 6} during leaching in 1 M HCl. When stoichiometric starting mixtures were used, all of the side products could be removed after wet ball milling in ethanol and leaching in 5 M HCl when pure TiB{sub 2} was obtained with a molar yield of 30%. Pure TiB{sub 2} could also be obtained at a molar yield of 45.6% by hot leaching of VCS products at 75 deg. C in 5 M HCl, omitting the wet ball milling step. By MCP,more » products containing only TiB{sub 2} and MgO were obtained after 15 h of ball milling. Leaching in 0.5 M HCl for 3 min was found to be sufficient for elimination of MgO. Molar yield of TiB{sub 2} was 89.6%, much higher than that of VCS. According to scanning electron microscope analyses, the TiB{sub 2} produced had average grain size of 0.27 {+-} 0.08 {mu}m.« less