Soild-phase synthesis of MgAl2O4 powder in reducing atmosphere: effects of alumina sources and addition of carbon black

Abstract

Magnesium aluminate spinel powder was prepared by one-step carbon-bed sintering at 1400 °C for 4 h with light magnesium oxide as magnesia source, alumina/boehmite/alumina-sol as alumina source, respectively. The phase composition of synthesized powders was characterized by X_ray diffraction, and the microstructure was depicted by field-emission scanning electron microscopy. The effects of alumina type and carbon black (CB) on the phase composition and morphology of synthesized powders were studied. The results show that the type of alumina source has remarkable influence on the morphology of spinel powder. The average particle sizes of the product with both alumina and boehmite as alumina source are about 1.5 μm. However, the shape of the former is cobblestone while that of the latter is regular rhombic plate. Additionally, the morphology of boehmite was preserved in its corresponding product, implying that the spinel grows by template mechanism. The average particle sizes of the product with alumina-sol as alumina source were about 0.6–2.1 μm, and it possesses a regular octahedral structure. CB can be distributed more uniformly in the powder when polyvinylpyrrolidone (PVP) solution was used as a dispersant. The uniformly dispersed CB could significantly decrease the grain size of the product when alumina-sol was used as alumina source, but it had little effect on the particle size of products with alumina or boehmite as alumina source.