Surface heterogeneity of passively oxidized silicon carbide particles: Hydrophobic-hydrophilic partition

The surface of silicon carbide (SiC) particles previously subjected to pass ive oxidation has been characterized using various techniques such as adsor ption of positively and negatively charged surfactants in aqueous solution, immersion microcalorimetry in three probe liquids, and flow microcalorimet ry in organic media. Adsorption data show that around one quarter of the su rface appears negatively charged and thus hydrophilic, while three quarters appear uncharged and hydrophobic. This is attributed to dissociation of si lanols groups. Immersion calorimetry in liquids having well-defined polar a nd nonpolar components of surface energy shows that the Lifshitz-van der Wa als component of SiC is very high and that the acid and basic components ar e weak. The experimental results appear to be consistent with both computat ions of surface energy using Lifshitz theory and experimental data previous ly obtained with other minerals. The three indexes are discussed and it is argued that they represent different terms of the solid surface energy (C) 2000 Academic Press.