Determination of Surface Free Energy of Kaolinite

Abstract

Abstract--The adsorption of n-octane and water vapor on natural kaolinite was measured. From adsorption isotherms film pressures were determined which were then used to calculate the dispersion and nondispersion components of the kaolinite surface free energy. In addition, thermodesorption of water from the kaolinite surface was determined. These results suggest that physically adsorbed water remained on the kaolinite surface, even at temperatures as great as 125"(2. Therefore, experimentally determined dispersion and nondispersion components appear to relate to the surface precovered with a film of water. These values are: ~gw) = 34.4 mJ/m 2 for dispersion interactions and ~gw) = 60.2 mJ/m 2 for nondispersion interactions. Assuming a kaolinite surface precovered with a film of water, which decreased the free energy by the work of spreading, the following components of the energy for the bare surface were calculated: ~s = 67.6 mJ/m 2 and 3'~ = 103.4 mJ/m 2, for dispersion and nondispersion components, respectively. Key Words--Adsorption, Film pressure, Free energy, Kaolinite, n-Octane, Surface, Water.Abstrakt --Zmierzono adsorpcje pary wodnej i n-oktanu na naturalnymkaolinicie. Z uzyskanych izoterm adsorpcji wyznaczono cignienia film6w i nastgpnie skladow~ dyspersyjn~ i niedyspersyjn~ swobodnej energii powierzchniowej kaolinitu. Pr6cz tego, zbadano tak2e termodesorpcj~ wody z powierzchni kaolinitu. Z tych do~wiadczefi wynika, ~e woda zaadsorbowana fizycznie pozostaje na powierzchni kaolinitu nawet do 125~ Dlatego, sugeruje si~, ~e wyznaczona do~wiadczalnie skladowa dyspersyjna i niedyspersyjna dotyczy powierzchni pokrytej filmem wody. Wyznaczone warto~ci wynosz~: ~gw) = 34.4 mJ/m 2 dla oddzialywafi dyspersyjnych i "Y~w) = 60.2 rnJ/m 2 dla oddziatywafi niedyspersyjnych. Przyjmuj0c model, w kt6rym film wody na powierzchni kaolinitu obni~a jego swobodm~ energi~ o pracg rozptywania, wyliczono skfadowe tej energii dla czystej powierzchni kaolinitu. Sk~adowe te wynosz~: ~ = 67.6 rnJ/m 2 i "r~ = 103.4 mJ/m 2.

Interactions between Talc Particles and Water and Organic Solvents

“…shown the decrease of the surface tension of alumina and -In the presence of ambient moisture, the acid sites are quartz as a function of moisture. E. Chibowski et al (58) inactive. have calculated the surface tension of kaolinite from vapor adsorption isotherm on both a nonperfectly outgassed (ther-A comparison of these results with an ab initio calculation mal treatment õ105ЊC under vacuum) and on perfectly out-(62) of the surface energy taking into account the shape of gassed kaolinite (thermal treatment ú125ЊC under vacuum).…”

Hydrophobic Nature of Organo-Clays as a Lewis Acid/Base Phenomenon

“…In view of all of these differences, a comparison of the present measurements with those of Jouany (1991), Chassin et al (1986), Jouany and Chassin (1987), and Chibowski and Staszczuk (1988) cannot be made. The use of 3 ,P is not only arbitrary with no theoretical or practical basis, it also leads to grossly aberrant results (see .…”

“…The theory of surface and interfacial thermodynamic interactions was recently reviewed by van Oss et al (1988) and only those aspects which are essential to the present discussion will be mentioned here. The surface thermodynamic properties have been deter-mined for a number of phyllosilicate minerals: hectorite (van Oss et al, 1990), talc and pyrophyllite , Ca-montmorillonite (Chassin et al, 1986), a group of natural smectite minerals (Giese et al, 1989), illite (Li et aL, 1991) and kaolinite (Chibowski and Staszczuk, 1988;Murphy et aL, 1991). In addition, the role of interfacial interactions, and especially the importance of the Lewis acid/base contribution to the flocculation of hectorite has been examined (van Oss et al, 1990); the thermodynamics of adsorption of human serum albumin on several clay minerals has been studied (Costanzo et al, 1991b); and the changes in surface properties of humic-clay complexes have been reported (Jouany, 1991).…”

“…The values of the surface tension components and parameters for these liquids are given in van Oss et al (1990). A different approach to the determination of the surface free energy of clay minerals was taken by Jouany (1991), Janczuk and Bialopiotrowicz (1988), Chassin et al (1986) and Chibowski and Staszczuk (1988). These workers reported that drops of water spread when placed on the surfaces of clay minerals either in the form of compressed powders or as films.…”

“…However, as seen in Eq. (1), 3 ,AB is determined by the Lewis acid and base parameters, -r * and 7 ~ a feature not accounted for in the work of Chassin et al (1986), Jouany and Chassin (1987), Staszczuk (1988), andJouany (1991). Further, the relation between the polar component of the interfacial tension, I~2 P, in the work of Jouany (1991), is related to the individual surface tensions, y~P and "]g2 P, by the harmonic mean:…”