THE KINETICS AND MECHANISM OF SPONTANEOUS DISPERSION OF IONIC COMPOUNDS ONTO SURFACES OF SUPPORTS

The dispersion kinetics of ionic compounds on the surfaces of supports is studied by using a temperature-programmed X-ray diffractometer. It is observed that for a given ionic compound/support mixture, there ex ists a critical dispersion temperature Tet at which the ionic compound starts to disperse onto the surface of the support at an appreciable rate. The dispersion process has 2 steps: the ions first leave the sur face of the ionic compound for the external surface of the support, an d then the ions diffuse to the whole surface of the support. For the d ispersion of ionic compounds with high melting points, the first step is rate-determining. Their critical dispersion temperatures and disper sion activation energies depend on the ionic compounds themselves and increase with their melting points, but are independent of supports. F or the dispersion of ionic compounds with low melting points, the seco nd step is rate-determining. Their critical dispersion temperatures an d dispersion activation energies depend on both the ionic compounds an d the supports.