APPLICATION OF INVERSE GAS CHROMATOGRAPHY TO THE STUDY OF THE SURFACE PROPERTIES OF SLATES

Invers e gas chromatography (IGC) at zero surface coverage was used for determining the surface characteristics of a slate sample. Previously this sample had been characterized by means of X-ray diffraction (XRD), chemical analysis, infrared (IR) spectroscopy and nitrogen adsorption. Quartz, mus- covite and chlorite were the minerals foming the slate. A well-defined mesoporous structure with pores of 15 /~ of interlayer distance was observed. Chemical analysis and IR spectroscopy corroborated the X-ray results. The surface characteristics of the slate were defined in relation to nonspecific and specific interactions with organic molecules. In accordance with the nonspecific interactions, the London com- ponent ('~s D) of the surface free energy gave an estimation of the surface energy of the slate sample. The obtained values for ~s ~ were 140.0, 124.8, 108.2 and 96.8 mN m i at 100, 110, 120 and 130 ~ respec- tively. These values were characteristic of an inorganic sample of high surface energy. The values of the thermodynamic variables--differential heat of adsorption, free energy and entropy of adsorption--were in accordance with these results. At the same time, specific interactions were characterized by the e~ parameter and the acid-base (KA, Ks) indices. The positive value of e, (0.09 kJ mol 1) indicated the presence of Lewis acidic sites on the slate surface. The value of K A (acid index) of 1.17 was higher than the value of K B (base index) of 0.37; this result confirmed the acidic nature of the studied slate's surface.