Determination of specific surface area by krypton adsorption, comparison of three different methods of determining surface area, and evaluation of different specific surface area standards

Abstract

A method for the measurement of the specific surface area of powder samples weighing between 1 and 50 mg is described. The method is based on 85Kr adsorption. A ratio test demonstrated that the method gives self-consistent data for samples of less than 10 mg. A cross-check, using 50-mg samples of uranium dioxide, demonstrated agreement to ±5% with results obtained using nitrogen as adsorbate and a vacuum microbalance. The suitability of materials as specific surface area standards is discussed. All the oxides studied gave c values between 50 and 300 for adsorption of nitrogen, and Type 2 isotherms, indicating applicability of the Brunauer, Emmett, and Teller (BET) method of calculating nitrogen-specific surface area. Samples of titanium dioxide and aluminum oxide were found to be uniform with respect to specific surface area. However, the values obtained for titanium dioxide standards were influenced by the temperature to which samples were heated prior to the determination of adsorption properties. Specific surface areas of three standard powder samples of different specific surface areas were measured by a vacuum microbalance, a flowing gas thermal conductimetric method, and a 85Kr adsorption technique. Values obtained were found to be independent of both the method employed and the operator. Data for successive determinations on samples of fused aluminosilicate particles demonstrated a precision of ±2% for 5-mg samples, but an accuracy of only ±20%. Cell design and blank corrections are discussed.