Effect of electric fields on solid-state reactions between oxides

Abstract

A study of the effect of d.c. electric fields on the interdiffusion behaviour of CaO and Al₂O₃ pellets was made using scanning electron microscopy, electron microprobe analysis and X-ray diffraction. When the CaO component is positively charged, the field acts to reinforce the preferred direction of normal thermal diffusion and the thickness of the product layers is increased. The reverse occurs when the CaO component is negatively charged. A greater degree of diffusion is observed in unelectrolysed than in electrolysed samples; this unexpected result could be due to field-enhanced sintering in the latter which reduces the contribution of grain-boundary diffusion processes. The effective electrical mobility of the migrating species in the various product phases is calculated from the measured downfield shift in the diffusion profile, and compares well with estimates previously made by more approximate methods.