Synthesis andcharacterisation of nanocrystalline MgAl 2 O 4 ceramic powders by use of molten salts

Nanocrystalline MgAl₂O₄ powders were prepared by a thermal decomposition method, i.e. by use of molten salts. This method involves co-melting stoichiometric amounts of magnesium nitrate hydrate Mg(NO₃)₂.6H ₂O and aluminium nitrate hydrate Al(N O₃) ₃.9H₂O at 500°C. The spinel content of the co-melted and calcined powders at different firing temperatures up to 1000°C was determined by chemical analysis and the powders were characterised with respect to spinel formation, crystallite and particle sizes by X RD, T EM, and IR spectroscopy. The results obtained revealed that the co-melted materials were amorphous. After heat treatment of the amorphous materials at up to 1000°C, pure spinel powder was obtained, reaching over 98% spinel content. During calcination at different firing temperatures up to 1000°C the amorphous material progressively crystallised, forming nanocrystalline spinel with a maximum crystallite size of about 10 nm and particle size of around 300 nm. Bands in IR spectra were observed corresponding to the ex istence of AlO₆ groups prior to magnesium spinel formation, which was the only crystalline phase at 1000°C.