REACTION OF NH3 WITH TRICHLOROSILYLATED SILICA-GEL - A STUDY OF THE REACTION-MECHANISM AS A FUNCTION OF TEMPERATURE

Activation of the silica substrate with chlorosilanes increases the ammonia uptake by a factor of 5-10, compared with untreated silica. The reaction mechanism of ammonia with trichlorosilylated silica gel is examined in detail. Physisorbed NH4Cl causes a shift in the Si-NH2 stretching vibrations. Several side reactions occur during the chlorosilylation step, the ammoniation step and the thermal treatment of the reacted sample. Amine functions subsequently convert to silazanes and eventually nitrides. A novel mechanism for silazane formation is proposed. The different species on the silica surface are quantified as a function of the reaction temperature.