Surface chemistry of silicon nitride powders: Adsorption from non-aqueous solutions

The adsorption behaviour of different silicon 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 isoclectric point in water between the three powders, to a difference in the relative site density or silanol and amino groups on the surface. It was found that the maximum concentration (T_M) of benzoic acid increased linearly while of pyridine decreased with an increase in the relative amount of amino groups on the surface.