Mineralizing Spinel Formation with Boron-Containing Compounds
Spinel (MgAl2O4) formation from stoichiometric MgO and Al2O3 is strongly mineralized by B-containing compounds such as boron oxide (B2O3), lithium tetraborate (Li2B4O7) and sodium tetraborate (Na2B4O7) at 1000°C. TEM confirms that the mineralization with each compound involves borate glass which is presumably formed on cooling from liquid at 1000°C. EDS shows the boron-containing liquids formed from B2O3 and Na2B4O7-mineralized samples contain little alumina suggesting a templated grain growth whereas those in Li2B4O7-mineralized samples dissolve sufficient alumina to suggest dissolution-precipitation is occurring at this temperature. XRD shows that Li2B4O7 is the most effective mineralizer producing single- phase spinel with 3 wt% addition at 1000°C whereas B2O3 produces Mg3B2O6 at 1.5 wt% addition and both B2O3 and Na2B4O7- mineralized samples show incomplete spinelisation which may be explained by the composition of the liquids formed with these two mineralizers.
G. Bhattacharya et al., "Mineralizing Spinel Formation with Boron-Containing Compounds", Advances in Science and Technology, Vol. 45, pp. 2254-2259, 2006