A fast and low-cost room temperature process for TiB2 formation by mechanosynthesis

Nanometric particles of titanium diboride can be produced by solid state room temperature reduction of boron(III) oxide, titanium dioxide with magnesium metal. The reaction is driven by high-energy ball milling powder mixtures of easily available materials like B2O3, TiO2 and Mg and involves a thermite route that allows for very short reaction times (lower than 2 h) under the proper milling conditions. The two thennite reactions, one between TiO2 and Mg and the other between B2O3 and Mg are nearly-instantaneous, the one starting first providing sufficient heat for reaching the ignition temperature for the other reaction to take place, and are immediately followed by reaction between elemental Ti and B to provide titanium diboride. The evolution of the reaction was followed as a function of time by X-ray diffraction (XRD), showing a gradual decrease in crystallite size of the reactant TiO2, with formation of intermediate reaction products, and once a near-instantaneous reaction takes place it produces mostly MgO and TiB2 as final products. Intermediate reaction products like less stable borides are also produced, but prolonged milling time for 1 h more results in the most stable boride TiB2 and MgO as only products. MgO was removed by leaching in diluted HCl and pure titanium diboride was obtained with a typical molar yield of 81%. The TiB2 powders are formed of impact welded aggregates of small particles of homogeneous dimension of about 50-100 nm. (C) 2004 Elsevier B.V. All rights reserved.