ABSTRACT
Chemical modification of the disperse silica surface offers
ample scope for development of materials with pre-
assigned properties for various duties. In order to optimize
the modification processes it is necessary to know their
mechanisms and have at one’s disposal the reliable data
about such characteristics as the structure of the SiO2 surface layer, topography of its hydroxyl coating, state
of its hydration sheath depending on the conditions of syn-
thesis and pretreatment of silicas. Substantial differences
in the degree of purity, completeness of hydration, and
pore structure quite often impede establishment of corre-
lations between the aforementioned data for numerous
varieties of disperse SiO2. Quite detailed information on
the structure of surface layers has been collected in the
case of the pyrogenic silica that is distinguished by its
high purity, absence of pores and labile structural
elements. By modern physicochemical methods it has
been found that the pyrogenic SiO2 surface is formed
from sections with the structure of (111) face and, to a
lesser extent, of (100) face of b-crystobalite with terminal silanol and silanediol groups spaced 0.6-0.7 nm apart.
The bulk phase of the pyrogenic SiO2 is represented to
approximately the same extent by motifs of quartz and
crystobalite [1,2].
