Influence of Drawing Conditions on the Properties of Bismuth Borate Glass Fibers
New York State College of Ceramics at Alfred University. Kazuo Inamori School of Engineering.
In this study the influence of forming conditions, namely draw temperature and draw speed, on thermal properties of glass fibers of the composition 0.25 Bi2O3 – 0.75 B2O3 were examined using mainly DSC measurements and confocal micro – Raman spectroscopy. Glass fibers were drawn at temperatures of 525, 550 and 575°C and draw speeds ranging from 1 to 10 m/sec. DSC measurements were performed to measure glass transition, heat capacity, fictive temperature, and pre – Tg exotherm, both in strength and the onset. Concurrently micro – Raman measurements were used to identify the structural borate groups present in the fibers and their change with forming conditions. Several trends could be observed. As draw speed increases the glass transition decreases, indicating a more disordered structure. Pre – Tg exotherms show a local maximum at draw speeds of 4 m/s. Raman spectroscopy indicates the presence of [BiO6] octahedra that are becoming more distorted as the draw speed increases. The local maximum in both the pre – Tg exotherm and the corresponding Raman peak show that there is an optimal distortion. Pre – Tg exotherm onset temperatures show a linear decrease with draw speeds. All this supports the conclusion that there is no major structural rearrangement. Heat capacity shows no overall trends of behavior dependant on forming conditions. These glass fibers also show a decrease in glass transition height during reheating that indicates a decreasing amount of glass. This can either be due to crystallization or phase separation. Finally the aspect ratio of the glass fibers seems to have a direct influence on heat capacity. As the aspect ratio increases the heat capacity of the glass fibers increases suddenly by a factor of two. The exact mechanism for this effect is unclear at this point.
Advisory committee members: Matthew Hall, William Lacourse, James Shelby. Dissertation completed in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Materials Science and Engineering at the Kazuo Inamori School of Engineering, New York State College of Ceramics at Alfred University