Formation and sintering of spinels (MgAl2O4) in reducing atmospheres

Magnesium aluminate spinel (MgAl2O4) is a mixed oxide with a cubic structure and it is considered as an excellent raw material for ceramics due to its chemical and physical properties. Most studies on formation and sintering of spinel were carried out under air atmosphere. In this work, spinel formation and sintering are studied using reducing atmospheres. Stoichiometric, alumina- and magnesia-rich spinels were prepared from calcined alumina and brucite. The spinel synthesis was studied up to 1300 °C using XRD and dilatometric techniques. Sintering was carried out on isostatically pressed pellets up to 1650 °C using: air (PO2=0.21), CO/CO2 mixture (PO2∼10−10) and pure CO gas (PO2∼10−15). Spinel formation was slightly affected by the particle size of precursors, but not by the atmosphere. The alumina-rich spinel shows the higher stability during sintering. A weight loss due to magnesium volatilization was verified in magnesia-rich spinel under CO atmosphere. The lattice parameters measured were in accordance with the weight losses and densities observed. Microstructures show microporosities due to magnesium loss.