In order to correlate the biological activity of silica to its surface properties, the analysis of surface sites on three kinds of silicas of different origins and textures has been performed by adsorption calorimetry.Mechanically micronized quartz (5.2 m2g-1), an amorphous silica of low surface area ("Porasil F"; 16.1 m2g -1) and a high surface area silica obtained by ignition ("Aerosil"; 380 m2g -1) have been considered.The heat and mechanism of interaction of water vapour on the surface of quartz reveal a few highly reactive sites not present in the amorphous specimens. The surface behaviour of the latter two specimens is the same, in spite of the large difference in surface area.Radicals produced in quartz by mechanical grinding account for its reactivity and are correlated here to the fibrotic activity of quartz, as opposed to the non-fibrogenicity of amorphous silicas.The heats of interaction of amorphous and crystalline forms with proline also point to a reactivity on quartz that is absent from amorphous silica.
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