Dispersion of Silicon Carbide Powders in Nonaqueous Solvents

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Abstract
Thirty‐two pure solvents were used to disperse laser‐synthesized SiC powder, oxidized laser‐synthesized SiC powder, and commercially available SiC powder. Five‐day sedimentation tests were used to screen the solvents. Relative turbidity of the supernatant after 1 month was used as a quantitative measure of the degree of dispersion. Coagulation kinetics were measured by photon correlation spectroscopy to determine the coagulation rate. Stabilized powders were centrifugally cast into ceramic green bodies and their green densities measured. Experimental dispersion results were correlated with various solvent properties including dielectric constant, hydrogen‐bond index, acid dissociation constant (pKa), and Lewis acid/base interaction energy. Microcalorimetry was used to measure the heat of wetting of the powders in various acidic and basic solvents. The heat of wetting was used to determine the Lewis interaction energy parameters for the powder surfaces. Oxidized SiC powder, either laser or commercial, was shown to have an acidic surface and was stabilized by basic solvents. Pure laser‐synthesized SiC powder was shown to have a basic surface and was stabilized by acidic solvents. Solvents with high hydrogen‐bond indices gave high packing densities. Other solvent properties had a much smaller influence on powder dispersibility. Good dispersibility gave ceramic green bodies with high green densities.

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