Liquid Structure of Magnesium Aluminates

Magnesium aluminates (MgO)x(Al2O3)1−x belong to a class of refractory materials with important applications in glass and glass–ceramic technologies. Typically, these materials are fabricated from high-temperature molten phases. However, due to the difficulties in making measurements at very high temperatures, information on liquid-state structure and properties is limited. In this work, we employed the method of aerodynamic levitation with CO2 laser heating at large scale facilities to study the structure of liquid magnesium aluminates in the system (MgO)x(Al2O3)1−x, with x = 0.33, 0.5, and 0.75, using X-ray and neutron diffraction. We determined the structure factors and corresponding pair distribution functions, providing detailed information on the short-range structural order in the liquid state. The local structures were similar across the range of compositions studied, with average coordination numbers of n¯AlO∼4.5 and n¯MgO∼5.1 and interatomic distances of rAlO=1.76−1.78 Å and rMgO=1.93−1.95 Å. The results are in good agreement with previous molecular dynamics simulations. For the spinel endmember MgAl2O4 (x = 0.5), the average Mg-O and Al-O coordination numbers gave rise to conflicting values for the inversion coefficient χ, indicating that the structural formula used to describe the solid-state order-disorder transition is not applicable in the liquid state.