The wetting of silicon carbide surfaces

Abstract

Abstract Silicon carbide fibers, 3 mil in diameter, produced by thermal decomposition of dichloromethylsilane on a tungsten substrate, have a relatively smooth surface. This is shown by close agreement of the measured specific surface area, 0.016 m 2 /gm ± 0.02 m 2 /gm with the calculated geometric specific surface area, 0.04 m 2 /gm and is supported by evidence from surface electron micrographs. Electron microprobe analysis of the fibers qualitatively showed the presence of oxygen on the fiber surface, indicating that surface oxidation of silicon carbide takes place quite readily. The critical surface tension of silicon carbide coated graphite coupons, prepared similarly to the fibers was found to be 52 ± 5 dyne/cm. The critical surface tension was not altered by exposure of the coupons to highly oxidizing conditions or to hydrofluoric acid. However, high temperature surface oxidation (air, 500°C) followed by boiling water treatment increased the critical surface tension to greater than 70 dynes/cm. The critical surface tension of a room temperature cured epoxy resin was found to be 45 ± 5 dyne/cm, indicating that an epoxy resin has a lower energy surface than untreated, oxidized, or oxidized-hydrated silicon carbide. Adhesion tension measurements between treated silicon carbide coupons and coupling agents showed that (i) oxidation and oxidation-hydration promote good adhesion of certain coupling agents to the silicon carbide surfaces, (ii) the adsorbed films are retained on the oxidized silicon carbide surfaces under rigid desorption conditions, and (iii) the “bond” between oxidized-hydrated silicon carbide surface and 4,4′-methylenedianiline was improved considerably over the “bond” between oxidized silicon carbide surface and the same compound.