Quartz glass deoxygenation time

The dehydroxylation time of quartz glass is influenced by several factors, including the preparation method, the size of the glass, and the atmosphere and temperature used during the dehydrogenation process.

Under normal melting conditions, such as in an oxidizing or neutral atmosphere, for example when using SiCl4 as a precursor, the hydroxyl groups present in the quartz glass are more difficult to remove. This is because the formation of hydroxyls is favored under these conditions, making it challenging to achieve complete dehydroxylation.

In contrast, quartz glass produced using an oxyhydrogen flame—created through high-temperature hydrolysis and vapor deposition—is often rich in hydroxyl groups. These types of glasses tend to be larger in size, and even after dehydroxylation, it's hard to eliminate all hydroxyls throughout the entire length. Typically, synthetic or gas-refined quartz glass sheets with thicknesses of 0.5 to 1.0 mm can lose about 50% of their hydroxyl content after 140 hours of treatment under vacuum or dry nitrogen at 1050°C. After this point, further dehydroxylation becomes minimal.

On the other hand, quartz glass melted in a hydrogen-rich reducing atmosphere, such as in a continuous furnace where H2 is used as a protective gas, tends to have a higher degree of hydroxyl removal. This is due to the presence of oxygen defects in the glass structure, which allow hydrogen to interact more effectively with the hydroxyl groups in a metastable state. For instance, a 1 to 1.5 mm thick fused quartz tube can lose over 90% of its hydroxyl groups within just 2 hours under similar vacuum or dry nitrogen conditions at 1050°C.

Similarly, if the quartz glass is synthesized or refined in a hydrogen-rich environment, applying the same dehydroxylation conditions can significantly enhance the removal of hydroxyl groups. This makes the hydrogen-rich atmosphere a key factor in achieving efficient and thorough dehydroxylation of quartz glass.