Effect of heat treatment conditions on the growth of MgAl2O4 nanoparticles obtained by sol-gel method

MgAl2O4 nanoparticles (NPs) were prepared by sol-gel method using aluminium nitrate, magnesium nitrate and citric acid as starting materials, phenolic formaldehyde resin and carbon black as additives. Growth of MgAl2O4 NPs in different heat treatment conditions (temperature, atmosphere, carbon additives and in Al2O3-C system) was investigated. MgAl2O4 NPs were formed at 600 degrees C in air atmosphere with serious agglomeration of nanoparticles having diameter of approximate 30 nm. The size of MgAl2O4 NPs increased greatly from 40 to 50 nm to several hundreds of nanometres as the temperature was raised from 800 degrees C to 1400 degrees C. Partial sintering of NPs was observed upon heating at temperatures higher than 1200 degrees C in air. In reducing atmosphere, the size of MgAl2O4 NPs (about 30-50 nm) changed slightly with increasing temperature. This was attributed to the dispersion of carbon inclusions in the MgAl2O4 grain boundaries, inducing a steric hindrance effect and inhibiting the growth of particles. MgAl2O4 NPs (30-50 nm) in the Al2O3-C system were in-situ formed at high temperatures with the use of dried precursor gels. MgAl2O4 NPs can contribute to improving the thermal shock resistance of Al2O3-C materials.