| Fourier transform infrared spectroscopy was used to determine the fictive temperature of bulk silica glass, silica glass fiber, and silica glass powders. For bulk silica glass and silica glass fiber, the fundamental asymmetric vibration band at ∼1200 cm−1 was monitored in reflection mode. For silica powders, the fundamental asymmetric vibration band at 1100 cm −1 was monitored in transmission mode. Before IR measurements were taken, as-received bulk preforms and silica powders were heat-treated in the temperature range of 900∼1200°C until the materials reached metastable equilibrium states. The calibration curves between IR wavenumber and fictive temperature were obtained, and then the fictive temperature of as-received silica glass, fibers, and powders was estimated by using calibration curves after observing IR peak wavenumbers on the as-received silica samples. The fictive temperature of as-received bulk silica glass was ∼1300°C. The fictive temperature of fiber core and inner cladding was higher for fibers processed by a faster cooling rate, higher drawing speed, lower tension force, and the fictive temperature of UV grating fiber core increased with increasing UV grating times. The fictive temperature of fumed silica with a large water content, 4.6 mol %, was ∼560°C while the fictive temperatures of fumed silica with low water content (∼1.4 mol % and ∼2.6 mol %) was ∼1400°C.; For silica glass fibers, the IR peak shifts were monitored as a function of applied stresses. The Si-O-Si bond angle increased with increasing tensile stress, but the peak at ∼1200 cm−1 decreased with increasing tensile stress (even though volume expands with tensile stress). This anomalous feature was attributed to changing force constants by applied stress.; For fumed silica powders, IR peak shifts were monitored as a function of water content. The Si-O-Si bond angle decreased with increasing water content. The structural change of silica powder due to increasing the water content is similar to the structural change of silica glass due to the decreasing fictive temperature. (Abstract shortened by UMI.)... |
