Dehydroxylation time
Published time：
2021-09-17
The time required for dehydroxylation of quartz glass depends on the preparation process, specifications, size, dehydroxylation atmosphere, and temperature.
Under normal melting conditions, i.e., in an oxidizing or neutral atmosphere, such as using SiCl4 as a raw material
In quartz glass synthesized by high-temperature hydrolysis chemical vapor deposition using a hydrogen-oxygen flame as a heat source, and quartz glass made by melting crystal with a hydrogen-oxygen flame as a heat source, most hydroxyl groups are in a stable state. For products with large dimensions, even with prolonged dehydroxylation time, it is difficult to remove all hydroxyl groups. Typically, for 0.5~1.0 mm thick synthetic and gas-melted quartz glass plates under vacuum or dry N2 at 1050℃, it takes more than 140 hours to remove about 50% of the hydroxyl groups, and further extending the time hardly removes any more.
However, for quartz glass melted in a hydrogen-rich reducing atmosphere, such as quartz glass melted in a continuous melting furnace with H2 as a protective gas, due to the presence of oxygen defects, the hydroxyl groups in the quartz glass are in a metastable state and easily diffuse out as H2. For example, for 1~1.5 mm thick melted quartz glass tubes under vacuum or flowing dry N2 at 1050℃, more than 90% of the hydroxyl groups can be removed in 2 hours.
Similarly, if quartz glass is synthesized or gas-melted in a hydrogen-rich reducing atmosphere, the dehydroxylation amount can be significantly increased under the same dehydroxylation conditions.
Time, quartz glass, hydroxyl, atmosphere, removal, synthesis, N2, state, such as
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2022-01-24
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