Heterogeneity analysis of the silica surface by gas adsorption

Abstract

In recent years computerised analysis methods have been developed for the determination of the distribution of adsorption energies on the surfaces of powders and precipitates from highly accurate experimental adsorption isotherms. An apparatus for the measurement of such isotherms has been constructed at Port Sunlight, and the iterative analysis method HILDA of House and Jaycock has been applied to the investigation of surface modifications of silica. The samples studied, Gasil I and TK800, are IUPAC surface-area standards and are available from the National Physical Laboratory. Results are given for a series of krypton isotherms, and the technique has been extended by the use of the nitrogen gas probe in the low-pressure range p/p₀≈ 10^–8–10^–3, enabling the detection of the very high-energy regions of the surface. The high-energy heterogeneity analysis approach is shown to be sensitive to the surface changes of Gasil I induced by heat treatment in the range 423–1170 K, and yields distinctive surface-energy distribution functions for the xerogel and Aerosil silica types.