Surface free energy characterization of powders

Microcalorimetric measurements and contact angle measurements were conducted to study the surface chemistry of powdered minerals. The contact angle measurements were conducted on both flat and powdered talc samples, and the results were used to determine the surface free energy components using Van Oss-Chaudhury-Good (OCG) equation. It was found that the surface hydrophobicity of talc increases with decreasing particle size. At the same time, both the Lifshitz-van der Waals (γsLW) and the Lewis acid-base (γs AB) components (and, hence, the total surface free energy (γs)) decrease with decreasing particle size.; Heats of immersion measurements were conducted using a flow microcalorimeter on a number of powdered talc samples. The results were then used to calculate the contact angles using a rigorous thermodynamic relation. The measured heat of immersion values in water and calculated contact angles showed that the surface hydrophobicity of talc samples increase with decreasing particle size, which agrees with the direct contact angle measurements.; The microcalorimetric and direct contact angle measurements showed that acid-base interactions play a crucial role in the interaction between talc and liquid. Using the Van Oss-Chaudhury-Good's surface free energy components model, various talc powders were characterized in terms of their acidic and basic properties. It was found that the magnitude of the Lewis electron donor, γ _s−, and the Lewis electron acceptor, γ _s+, components of surface free energy is directly related to the particle size.; The heats of adsorption of butanol on various talc samples from n-heptane solution were also determined using a flow microcalorimeter. It was found that the total surface free energy (γ_s) at the basal plane surface of talc is much lower than the total surface free energy at the edge surface.; Furthermore, the effects of the surface free energies of solids during separation from each other by flotation and selective flocculation were studied. First, the crude kaolin was subjected to flotation and selective flocculation experiments to remove discoloring impurities (i.e., anatase (TiO₂) and iron oxides) and produce high-brightness clay with GE brightness higher than 90%. The results showed that a clay product with +90% brightness could be obtained with recoveries (or yields) higher than 80% using selective flocculation technique. (Abstract shortened by UMI.)...