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Physico-chemical Properties of Sols and Gels of Na-montmorillonite with and without Adsorbed Hydrous Aluminum Oxide¹

ABSTRACT

Sodium-montmorillonite was prepared with and without adsorbed hydrous aluminum oxide and called Na/Al-clay and Na-clay, respectively. The two clays were mixed with 10^-4N NaCl solution in different proportions. Measurements of shear stress at different shear rates showed that the clay content at which gelation began, as indicated by an increase in viscosity and the initiation of non-Newtonian and hysteretic behavior, was lower for the Na/Al-clay than for the Na-clay ( 2% clay vs. 4% clay). Theoretical considerations indicated that both strong and weak bonds were present in the gels but only weak bonds were present in the sols.

Specific heat capacities of the mixtures were determined in a Calvet microcalorimeter and were found to differ from those calculated from the known proportions and specific heat capacities of clay and water. Differences were greater for the Na/Al- than for the Na-clay. A detailed analysis indicated that these differences could be attributed to clay-water interaction.

EMF measurements, made with sodium glass and Ag/AgCl electrodes, showed that the relative partial molar free energy of NaCl changed with clay content in somewhat different ways for the Na/Al- and Na-clay mixtures. The changes were correlated with changes in other properties of the mixtures. It was concluded that adsorbed hydrous aluminum oxide does influence the physico-chemical properties of sols and gels of Na-montmorillonite.

¹ Journal Paper no. 3895, Purdue Univ. Agr. Exp. Sta., Lafayette, Ind. Contribution from the Agronomy Dept. Presented before Div. S-2, Soil Science Society of America at Washington, D.C., Nov. 1967. This research was supported by the National Aeronautics and Space Administration.

² Formerly Post-Doctoral Research Associate and Professor of Agronomy, respectively. Present address of the senior author is Dept. of Soil Science, University of Sydney, Sydney, N.S.W., Australia.

Received for publication November 29, 1969. Accepted for publication November 10, 1970.