Effect of suppression of devitrification by chlorine-containing silica glass

Characteristics of the devitrification of silica glass containing 1000 mass ppm of Cl were investigated. The magnitude of the devitrification was evaluated by the depth at the center of the crystallization area grown by putting a grain of NaCl crystal on a flat polished surface of silica glass plate. The devitrification characteristics were compared with those of various types of silica glasses containing no Cl and various amounts of OH. The slope of devitrification depth in the Arrhenius plot changes abruptly at Tc ≈1000°C; The slope at a temperature higher than Tc of the Cl-containing silica is considerably smaller than those of other silica glasses. This fact indicates that the Cl-containing silica glass is durable to devitrification, especially at temperatures higher than Tc.