Structural changes of various types of silica glass tube upon blowing with hydrogen–oxygen flame

Structural changes upon blowing with a hydrogen–oxygen flame were examined in three types of silica glass tube, containing <1, 200, and 1300 ppm of OH (referred to as Samples I, II and III, respectively). The samples were studied by means of microscopic spectroscopy. Upon blowing, the OH concentration near the outside surfaces of Samples I and II increased, whereas that near the outside surface of Sample III decreased. On the basis of an analysis of the SiOH absorption band (by peak decomposition), changes in the distribution of free SiOH, H ₂ O molecules, and hydrogen-bonded SiOH are discussed. The silica tube with a higher OH content has a lower fictive temperature as indicated by an IR absorption peak near 2260 cm ⁻¹. After blowing, the fictive temperature of Samples II and III remained almost constant throughout the cross-section, while that of Sample I changed, ranging from 1400 to 1700 K. The maximum fictive temperature was found at a depth of approximately 1000 μm from the outside surface.