(245e) INFLUENCE OF COMPACTION ON THE SURFACE PROPERTIES OF ALUMINA (Al2O3) DETERMINED BY INVERSE GAS CHROMATOGRAPHY (IGC)

Inverse Gas Chromatography (IGC) is a convenient method for the examination of the surface properties of a solid. Due to the very small amount of probe injected, the Infinite Dilution (CGI-DI) allows neglecting inter-probe interactions. However it is important to keep in mind that with heterogeneous surfaces, the probes only see the highest energy sites on the surface and therefore tend to strongly overestimate values of surface energy. Depending on the nature of the injected probes, different components of the surface energy can be measured. The injection of linear alkanes, branched or cyclic alkanes, polar molecules allows to calculate respectively the dispersive component of the surface energy (a measure of the London interaction), the nanomorphological index (which reflects the nanomorphology of the surface), the polar component of the surface energy. In the work reported here, the solid under test, gamma-alumina, presents at the same time low particle size (around the micron) and low surface energy. So the IGC analysis requires large amounts of powder leading to high pressure losses in the column. This limitation has forced us to increase the size of the particles by compaction. The fine particles were agglomerated in a uniaxial press (Instron Press) , and gently crushed and sieved so as to separate the fraction having diameters between 200 and 400 microns. The agglomerates were made using different loads in the range 3,5-8,5 kN and the different samples allowed us to analyse the effects of the pressure level on surface properties.