SURFACE-CHEMISTRY OF SILICON-NITRIDE POWDERS - ADSORPTION FROM NONAQUEOUS SOLUTIONS

The adsorption behaviour of different si]icon nitride powders in cyclohexane has been studied. Adsorption isotherms of organic probe molecules covering a wide spectrum of Lewis acidity/basicity showed large variations in adsorption behaviour between the different probes. Mathematical analysis showed that the adsorption data could be described by a Langmuir-Freundlich type of isotherm. Using a previously presented model of the silicon nitride surface, it was possible to relate the variation of the isoelectric point in water between the three powders, to a difference in the relative site density of silanol and amino groups on the surface. It was found that the maximum concentration (GAMMA(M)) of benzoic acid increased linearly while GAMMA(M) of pyridine decreased with an increase in the relative amount of amino groups on the surface.