Grinding Behaviour of Yttrium Aluminium Garnet Powders Prepared by Solution Combustion Technique

Abstract

Precursor powders for yttrium aluminium garnet (VAG) were formed by two solution combustion reactions (nitrate-urea, nitrate-glycine) followed by simple decomposition of nitrates. The precursor powders thus formed were calcined at 1100°C to form crystalline YAG. The zeta potential variations for all the calcined powders in the pH range of 1 to 7 exhibited a maximum value of >30 mV (showing stability of dispersion due to coulombic repulsion) in the pH range of 3 to 4. The slurries formulated at pH 3 with 25 volume percent of solid content showed a decrease in viscosity with increasing shear rate (pseudoplastic—showing presence of flocculates) while those with 20 volume percent solid content exhibited shear rate independent flow behaviour (Newtonian—showing absence of flocculates). Grinding studies of the powder from nitrate-glycine reaction revealed that the slurry with higher zeta potential (at pH 3) and lower viscosity (for 20 volume percent solid) led to finer powder due to better dispersion. Powders obtained through different reactions were subjected to grinding under identical conditions to compare their agglomerate strength. It was found that the powder from the nitrate-glycine reaction was the finest (softest), that from simple decomposition of nitrates the coarsest (hardest) and the same from the nitrate-urea reaction exhibited intermediate size value (intermediate in strength).