The equilibrium observed during modified chemical vapor deposition (MCVD) of silica glasses doped with fluorine is investigated by chemical thermodynamics. The influence of the flow rate of Freon-12 and sulfur hexafluoride on the efficiency of the incorporation of fluorine into the condensed phase is analyzed. It is revealed that, at very low flow rates of fluorinating reactants, more than 50% of fluorine can be incorporated into the glass. The refractive index and the efficiency of the conversion of SiCl 4 into the fluorine-doped silica glass are studied as functions of the vapor-gas phase composition.

The size distribution of compositional microinhomogeneities in silica glasses prepared by different methods is investigated by electron microscopy. The formation of these defects is caused by the presence of impurities introduced into the glass upon phase separation and segregation. The surface of millimeter-sized segments of silica optical fibers 125 µ m in diameter always contains inhomogeneities up to 1 µ m in size. This explains the growth of cracks to a critical size in microregions containing impurities in the course of strength tests of glass fibers.

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The compositions of fluorogermanosilicate glasses prepared by the modified chemical vapor deposition (MCVD) method are calculated in terms of equilibrium thermodynamics. The calculations are based on the assumption regarding the formation of a mixture of pure oxide particles. This assumption is confirmed by the IR transmission spectra of porous deposits.