Surface modification and processing of silicon nitride

Silicon nitride powder was modified with different alkoxysilanes. The chemisorption of the silanes at the Si3N4 powder surface was established by the DRIFT spectroscopy. Furthermore the surface properties of the modified powders were characterized by acid base titration and by indirect contact angle measurements. The results show that the functional group of the silane determines the surface properties of the modified powder. The calculated surface free energies of the modified powders are lower than those of the unmodified powder. As a result of the silane adsorption the powder surface charge density in an aqueous suspension increases substantially. Simultaneous the point of zero charge shifts from pH=5.3 for the unmodified powder to pH=9.9 respectively pH=3.2 for the modified powders. Aqueous slips of the modified powders were characterized by viscosity measurements.