Abstract
The investigation of phase equilibrium of NiO-A2O3 system at 1650°C shows that Al2O3 dissolves by 20 mole % into spinel crystal but NiO does not dissolve. The lattice constant of the spinel is decreased continuously by the dissolution of Al2O3. The particle size of NiO, the method of preparation of NiO and additive impurities affect the rate of spinel formation but compacting pressure of NiO-Al2O3 mixture does not affect. The activation energy of spinel. formation by Jander' sequation is about 33Kcal/mole in air, and this value is approximately the same as that of electrical conductivity of spinel in air. The activation energies of the electrical conductivity of spinel in oxygen, air and vacuum are 28.9, 30.8 and 36.2 Kcal/mole respectively. The decrease in the rate of spinel formation with a decrease in the partial pressure of oxygen in the surrounding atmosphere is related to the decrease in the activation energy of the electrical conductiviiy of the spinel.
