Mechanical pretreatment clarifiers

For the modification of silica with aminosilanes, the liquid phase procedure is usually applied. Only few studies have described the vapour phase APTS modification.6,7 The modification proceeds in three steps, (i) A thermal pretreatment of the silica determines the degree of hydration and hydroxylation of the surface, (ii) In the loading step, the pretreated substrate is stirred with the silane in the appropriate solvent, (iii) Curing of the coating is accomplished in a thermal treatment. On industrial scale ethanol/water is used as a solvent, on lab-scale an organic solvent is used. The reasons for this discrepancy is the increased control on the reaction processes, possible in an organic solvent. This will be clarified by the discussion of the modification mechanism in aqueous solvent and the effect of water in the different modification steps. 

The last chemical pretreatment step is the electrolytic or fine degreasing, in which the chemical cleaning power of an alkaline cleaner is enhanced by an electric current. The underlying mechanisms have not been fully clarified. Saponification of the esters of fatty acids may play a role. Furthermore, the evolving gas bubbles will tear off the last traces of contaminants from the surface. 

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