Diffusion Studies in Nonmetallic System. Part I

The rate of formation of NiAl2O4 by reaction between single crystals of NiO and Al2O3 is described. In NiO the behavior of the diffusion coefficient as a function of concentration supports the Lidiard theory of diffusion by impurity-vacancy pairs. The free energy of association for pairs was calculated. The interdiffusion coefficients in the spinel showed a constant small increase with the increase of the aluminum ions dissolved in the spinel. The mechanism of the interdiffusion in systems AO-B2O3 is discussed. The experimental data obtained on interdiffusion of B(3+) ions (e.g. Cr(3+) and AL(3+) in an AO compound (e.g. MgO and NiO) implies that no association of defects occurs. This relationship was observed in systems Cr2O3-MgO and Cr2O3-NiO at temperatures higher than 1300C. From interdiffusion studies the activation energy of motion for B(3+) ions can be obtained.