Thermal syntheses of magnesium borate compounds from high-energy milled MgO-B₂O₃ and MgO-B(OH)₃ mixtures

The comparative effects of high-energy milling on solid-state thermal syntheses of different magnesium borate compounds from MgO-B₂O₃ and MgO-B(OH)₃ mixtures were investigated for initial MgO:B₂O₃ mole ratios of 1:0.125, 1:0.25, 1:0.5, 1:1, 1:2 at temperatures between 500 and 900 °C. It was observed that magnesium oxide-boric acid mixtures react only by high-energy milling to form hydrous magnesium borates. Following high-energy milling of the initial solid mixtures, anhydrous magnesium borate compounds started to form at temperatures as low as 500 °C, and purer and more crystalline phases were obtained at higher temperatures compared to unmilled compositions.