High-Temperature Fibers and Core-Sheath Fiber Development

摘要

A composite ceramic-glass fiber of core-sheath configuration was formed by drawing the fiber from melts of the core and sheath materials metered through concentric orifices. The objective was to develop a continuous high-modulus (over 20 million psi) fiber produced by sheathing a high-modulus polycrystalline core material with a high-strength, high-temperature glass. Indirect heating was found to be most satisfactory on the basis of temperature control, bushing configuration, and fiber forming. Investigations of bushing materials proved that tungsten was superior to boron nitride and that high-alumina core materials which react with tungsten with time should be contained in iridium. Research on high-modulus core materials included pure alumina, alumina modified with calcium oxide and magnesium oxide, dispersions of high-modulus microcrystals and whiskers in a matrix glass, and nucleating-crystallizing glass ceramics. Most promising were pure alumina, spinel (Al2O3-MgO), and calcium aluminates. Tungsten dual-melt bushing fiber forming studies disclosed a problem in interaction kinetics between the molten core and sheath materials, but this can be handled by appropriate concentric orifice design. Continuous core-sheath fiber forming was accomplished at temperatures between 3600F and 4000F. With feasibility established and the required high-temperature melt containment problem solved, the task remaining is to develop the concept to achieve higher core-to-sheath volume ratios, consistent with continuous fiber formation. (Author)