Mass spectrometric study of high-temperature dehydroxylation of disperse silicas and the interpretation of their IR spectra in the region of Si-O stretching vibrations

Field-desorption mass spectrometry has been used to determine the lower boundary of the temperature interval for the removal of surface hydroxyl groups of aerosil. Both in the regime of cation desorption and in the regime of anion desorption, at temperatures above 900/sup 0/K, OH ions of the corresponding sign are registered. It is concluded that the thermal decomposition of the surface bonds triple bond Si-OH is homolytic in character. A mechanism is proposed for the dehydroxylation of SiO/sub 2/, according to which the initially formed radical centers triple bond Si and triple bond SiO change into ions: triple bond Si/sup +/ (I) and triple bond SiO/sup -/ (II). The bands at 888 and 908 cm/sup -1/ in the IR spectra of silicas obtained at high temperatures are assigned to vibrations of Si-O bonds in I and II, respectively.