Facile synthesis of MgAl2O4 with high crystallinity from KCl–MgCl2 composite molten salts

Abstract

MgAl2O4 (MA) powder has been synthesised by heating an equimolar composition of commercial Al2O3 and calcined MgO via a molten salt synthesis (MSS) method. Phase compositions, microstructures, elements distributions, particle size and specific surface area of as-synthesised MA at various temperatures were investigated. The synthesis reaction of MA from Al2O3 and MgO is incomplete at 1000 and 1100°C for 4 h in KCl–MgCl2 molten salts. MgAl2O4 powder can be produced via the MSS method at 1200°C for 4 h, which is ∼200°C lower than that of conventional solid–solid reaction (SSR) method. Fine MA particles can be formed at 1000, 1100 and 1200°C for 4 h, and most of them aggregate. With the increase in reaction temperature from 1000 to 1200°C, the particle size of as-synthesised MA powder decreases and specific surface area increases. The average grain size and the specific surface area of the fabricated powder at 1200°C for 4 h are 7.57 μm and 0.7566 m2 g-1, respectively. Single MA crystalline phase is detected when MA powder formed at 1200°C for 4 h was further heated at 1580°C for 4 h. The MA particles, synthesised at 1000–1200°C after the heat treatment at 1580°C for 4 h, exist in spherical shape with high crystallinity and their grain size is about 2–5 μm.