Ceramic fibers are one of the most important categories of reinforcements for composite materials. This study deals with a novel melt extraction system which has been developed to produce fine oxide ceramic fibers. Four oxide compounds were selected for the production of fibers and characterization of the extraction system. These compounds were CaO-$ rm Al sb2O sb3$ (CA), ZrO$ sb2$-$ rm Al sb2O sb3$ (ZA), ZrO$ sb2$-$ rm Al sb2O sb3$-SiO$ sb2$ (ZAS), and ZrO$ sb2$-$ rm Al sb2O sb3$-TiO$ sb2$ (ZAT). Using a 150 W CO$ sb2$ laser, these materials were melted to obtain a small molten drop, and through shallow contact with a sharpened and bevelled molybdenum wheel, fibers were extracted at various wheel velocities. At low speeds (v 000$ sp circ$C) was measured using a novel technique. Various parameters such as laser power (temperature), wheel tip radius and feed rate have been studied and their effects on the extracted fiber dimensions were investigated. It is suggested that momentum transfer controls the extracted layer thickness and fiber dimensions. The viscosity of the liquid ceramics is a crucial factor in the system, and is estimated to be $<$0.5 poise (0.05 Pa$ cdot$s) at ${ approx}2400 sp circ$C. Due to the fine fiber dimensions and strong conductive cooling of the molybdenum wheel, the extracted liquid layer was rapidly solidified, and fibers with amorphous, partially crystalline and/or metastable phases were formed. Uniform diameter fibers were amorphous, transparent, flexible and exhibited excellent tensile properties. Fine fibers with a diameter of ${ approx}$10 $ mu$m showed tensile strengths up to 3300 MPa, however, only moderate elastic moduli were achieved (95-143 GPa) due to the amorphous nature of the fibers. The rapidly solidified fibers were thermodynamically metastable, and as shown by differential thermal analysis (DTA), they devitrified in the temperature range of 930-980$ sp circ$C. Heating the fibers at higher temperatures resulted in the formation of various crystalline phases and the development of different grain morphologies.

Drew, Robin A. L. (Supervisor)