Structural change of OH-free fused quartz tube by blowing with hydrogen–oxygen flame

The effect of blowing with a hydrogen–oxygen flame on the structure of an OH-free fused quartz tube was studied by microscopic spectroscopy. The number of OH groups increased within 1000 μm from the outside surface (OSS). The peak decomposition of the IR absorption at around 3600 cm−1 showed that most OH structures were ‘free SiOH’ without the hydrogen bond, and H2O molecules were also distributed throughout the cross section. The distribution of the fictive temperature, TF, in the cross section was measured from the peak position of infrared absorption at ≈2200 cm−1. TF before blowing was ≈1420 K, which is near the strain point, except in the region within 200 μm from the OSS, where TF steeply decreases approaching the OSS. After blowing, the values of TF became greater than those before blowing, increasing steeply from the OSS and having a maximum at ≈1000 μm. The steep change near the OSS must be caused by the shorter structural relaxation time due to the SiOH introduced by blowing and H2O vapor in the flame. The distribution of the intensities of Raman bands at 495 (D1) and 606 cm−1 (D2) derived from the planar four- and three-member rings was also measured.