Components of Surface Free Energy of Some Clay Minerals

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Abstract
The wetting contact angle was measured for water drops settled on the surface of pressed discs of kaolinite, alumina, bentonite, marble, montmorillonite, and quartzite immersed in hexane, octane, dodecane, cis-decalin, and air. Minimum and maximum values of the contact angle were obtained for the given systems of solid-water drop-hydrocarbon, depending on the manner of disc preparation. Using both minimum (0min) and maximum (0m~x) values of the contact angle, values of the dispersion component (3,s ~) of surface free energy of these solids were calculated from the equation which was derived on the basis of an equilibrium state of the system solid-water drop-hycrocarbon for two different hydrocarbons. The values of3,s ~ for kaolinite, alumina, bentonite, marble, montmorillonite, and quartzite obtained from Oma, are 83.5, 98.1, 98.9, 80.2, 95.9, and 89.7 mJ/m 2, and from Om~x are 73.1, 85.0, 84.4, 75.8, 85.5, and 75.5 mJ/m 2. These values for marble and quartzite are similar to those in the literature (marble = 67.7 mJ/ma; quartzite = 71.3 and 76.0 m J/m2). The values of the dispersion components of surface free energy for marble and quartzite covered with a water film (q, sf a) were found to be: 41.8, 36.9; 49.2, 42.5; 49.6, 42.2; 40.2, 38.1; 48.1, 42.8; and 44.9, 38.0 mJ/m 2, respectively. Values of ~/s~ for kaolinite, bentonite, and montmorillonite agreed well with those obtained from hydrocarbon adsorption isotherms determined by differential thermal analysis (35.5, 36.5, and 37.4 mJ/m2). Using values of ~/sf ~ and contact angles measured in the system solid-water drop-air, the nondispersion component of the surface free energy of solids with adsorbed water film (~sr n) was calculated from the modified Young equation. The values of ~sf" for kaolinite and quartzite are as follows: 55.8, 69.0; 85.6, 94.0; 52.1, 75.0; 64.7, 68.9; 54.9, 71.3; and 59.2, 74.4 mJ/m z. The values of the nondispersion components determined for kaolinite, bentonite, and montmorillonite agreed well with those obtained by differential thermal analysis (67.6, 78.3, and 65.5 mJ/m 2, respectively). Further, based on the assumption that the adsorbed water film decreased the surface free energy of these solids by the value of the work of spreading wetting, the nondispersion component ('ys n) of the surface free energy of the solids was calculated to be: 86.9, 129.6; 169.5,187.7; 67.1,144.8; 117.5,129.3; 83.0, 135.7 and 100.2, 143.4 mJ/m 2. These calculated values of the nondispersion component of marble and quartzite surface free energy agree with those obtained from adsorption isotherms determined by chromatographic and differential thermal analysis (marble = 103.8, 106.4; quartzite = 112, 115, 153.6 mJ/m2).

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