Preparation of composite powders containing TiB2 and ZrB2 particles through combustion synthesis of TiO2–ZrO2–B2O3–Mg system

Abstract

Composite powders containing TiB2 and ZrB2 particles were successfully prepared through combustion synthesis of (2-x)TiO2–xZrO2–2B2O3–(10 + y)Mg system. Results showed increase in the x-value from 0 to 2 mol and y-value from 0 to 2.5 mol didn't have any considerable impact on reaction front velocity. In the case of TiO2–B2O3–Mg system with stoichiometric composition, agglomerates containing large TiB2 particles with hexagonal plate-like morphology embedded in a MgO matrix were remained after leaching. The addition of 25 wt% excess Mg (y = 2.5) to this mixture resulted in the dissolution of unwanted phases and the formation of pure submicron TiB2 particles. On the contrary, for the ZrO2–B2O3–Mg mixture (x = 2) unreacted ZrO2 remained and a ZrB2/ZrO2 composite powder was acquired. Both TiB2 and ZrB2 particles were only attained at x = 1.5 mol. The addition of 25 wt% excess Mg to this sample had an inverse effect and removed ZrB2 instead of ZrO2. Lastly, a TiB2/ZrO2 composite powder having submicron titanium boride particles was prepared after leaching process. Simultaneous thermal analyses results showed the combustion reaction sequence in the TiO2–ZrO2–B2O3–Mg system involves; dehydration of powders, melting of B2O3, reaction of molten B2O3 with solid Mg, solid-state reaction of TiO2 and Mg and the formation of Ti, partial reaction of ZrO2 with Mg and the formation of Zr and finally, development of TiB2 and ZrB2 through reaction of Ti and Zr with B element.