Improved method for measuring specific surface areas of clays using ethylene glycol monoethyl ether (EGME)

摘要

An improved method for determining the specific surface area of clays using ethylene glycol monoethyl ether (EGME) is proposed that uses reduced amounts of EGME and CaCl_2 at the optimum ratio of these agents to keep EGME vapor pressure constant in a desiccator. The optimum ratio was 2.0 cm_3 EGME to 14.4 g CaCl_2 for clay samples of about 0.5 g. About 20 times the expected adsorption volume of EGME was dropped on to the sample, the rest being added to the CaCl_2 in a separate vessel. The desiccator was evacuated to seal it for about one minute so as not to change the ratio of the agents and not to contaminate the air in the laboratory with EGME vapor. Desorption equilibrium was reached in 2 approx 4 days. The final EGME retention in the desorption process agreed well with that in the adsorption process. Accordingly, the relative vapor pressure of EGME was found to be very close to the pressure which completes monomolecular layer adsorption. A fairly good linear relationship was found between EGME retention and the specific surface area for three different kinds of clays that retained 0.264 mg EGME on each square meter of surface. Effects of the specific surface area and CEC on EGME retention were estimated separately. The effect of CEC was not significant in this method.