Quartz Glass And Raw Materials In The Hydroxyl,

Hydroxyl group is the main structural defects in silica glass, which affects the properties and manufacture of silica glass. As the developing of science and technology, the roles of hydroxyl group becomes important for the application of silica glass, particularly in the areas of optical fiber, laser, optical waveguide and aerospace, etc. In this paper, the formation, diffusion and structural characters of the hydroxyl group in silica glass were studied.According to the quality's needs and manufactural process of quartz glass, the quartz minerals are allowed to exist low impurity content in crystal lattices and less fluid inclusions. High temperature of leaching with HF acid can be applied to dissolve the impurity companion minerals (mica or feldspar) with vein quartz.The bulbs in quartz glass depend on the temperature of it's melting process and the impurity in raw materials. The characters of fluid inclusions in quartz, such as: numbers, volume, homogenization temperature, were observed under microscope. The component and density were calculated by the thermodynamic principles of fluid inclusions. Furthermore, the effects of the inclusions' characters on the bulbs in quartz glass were studied.The infrared spectra show the existence of hydroxyl group in quartz, which are different from the molecular water in quartz. The concentration of stable hydroxyl in quartz glass becomes higher with the increasing of concentration of hydroxyl group or water in raw materials. The relationship of hydroxyl's heredity between raw materials and quartz glass melted under hydrogen atmosphere were studied by analyzing the isotope content (8D) of gases released from quartz glass and its raw materials. The results indicated that stable hydroxyl correlates with the structural site E'-center that can transmitted from raw materials to quartz glass.The hydroxyl can be removed from the quartz glass at the temperature range of 700~1200癈, at the same time, hydrogen and water are released from the silica glass, which had been measured by quadrupole mass spectrometry. The data of diffusion coefficient and activation energy of the dehydroxylation process were calculated, and the results indicated the changes of mechanism for dehydroxylation with the heat-treatment temperature. The main process of dehydroxylation in the temperature range of 700~900癈 belongs to a second order opposite reaction. The structural relaxation and defeats in quartz glass can affect the mechanism of dehydroxylation. The characters of hydroxyl groups in doped quartz glass were also discussed.Both the stretching band of Si-O-Si and the numbers of oxygenvacancy defects are different according to the melting process for silica glass. The difference on the structural defects of four kinds silica glasses can be reduced after heat-treated. IR, ESR and MAS NMR were used to study the structural characters of hydroxyl group, and analyze the effect of E' center on the NMR spectra of silica glass. The results indicated: hydrogen can exist in silica glass as Si-OH with hydrogen bond, Si-OH pairs, isolate Si-OH, Si-OH/Si~H pairs, Si-OH / E'center pairs and E' defects with hydrogen.