STRUCTURE-ANALYSIS OF SOL GEL-DERIVED SIO2 GELS BY NEUTRON-DIFFRACTION

The structures of sol-gel-derived SiO2 gels were investigated using the neutron diffraction technique, and compared with that of melt-derived SiO2 glass. It was found that, in the structure factor, S(Q), of gels, the first sharp diffraction peak (FSDP) appearing at low momentum transfer (Q = 1.0-1.5 angstrom-1) shifted toward high Q value and its intensity was considerably less compared with that Of SiO2 glass. In the pair correlation function curve, G(r), given by the Fourier transformation of the S(Q), some difference between gel and glass was observed in the intermediate atomic distance of 4 approximately 6 angstrom. These two facts suggested a difference in the arrangement of SiO4 tetrahedra in the network between gel and glass. It was assumed that the decrease in intensity and the shift toward high Q value of FSDP in S(Q) of gel, and differences in the Fourier transform curves are due to the formation of small siloxane ring units such as fourfold rings in the sol-gel-derived gels instead of sixfold rings in the SiO2 glass.