A viscous solution or dispersion of soluble or dispersed metal compounds is extruded from a spinnerette, the resulting continuous green fibers are drawn in air (preferably as a strand) and allowed to continuously accumulate or collect in a free-form, relaxed manner in the configuration of offset or superimposed loops on a moving belt which is continuously passed through a furnace to remove volatiles and burn off organic material, and the resulting continuous refractory fibers are continuously pulled in a straight or linear form through a furnace at higher temperature to densify, strengthen, straighten and/or modify the microstructure of the fibers or develop desired crystalline species therein.
A method for dry-spinning a metal alkoxide sol to form fibers which may be gathered and wound in a conventional manner, wherein the atmosphere in the spin chamber comprises ammonia to dry the fibers to a non-sticky state.
In the production of aluminum oxide fibers comprising dry spinning an aluminum-containing solution to produce fiber and thereafter heat treating the fiber, the improvement which comprises applying to the fiber prior to heat treatment a solution of polyvinyl acetate in a solvent which is inert to the fiber. Advantageously the polyvinyl acetate is present in its solution in a concentration of about 0.1 to 10% by weight and is applied to the fiber in about 0.1 to 3 % by weight. The spinning solution may also contain SiO.sub.2 and polyethylene oxide, and the polyvinyl acetate solution may also contain di-n-butyl phthalate as a plasticizer for the polyvinyl acetate. The fiber bundles are characterized by increased strength and resistance to breaking during further processing.
Filamentary shaped bodies, such as strands, fibers, ribbons and the like, are formed by extruding an extensible high solids forming mix through an orifice and thereafter stretch casting the mix under the force of gravity through zones of controlled environment to form a continuous filamentary body which may thereafter be separated into discrete fibers or collected in its continuous form. The preferred high solids constituent include those metallic compounds capable of undergoing reduction so that shaped bodies made therefrom may be reduced and sintered into metallic filamentary articles.
A high temperature, preferably polycrystalline, ceramic fiber having a selectable diameter of between 1 and 200 microns. The fiber is stable in an inert atmosphere at a temperature above about 1700.degree. C. and is often stable even in air at a temperature above 1500.degree. C. The fiber comprises a sintered ceramic powder having a maximum particle size less than the diameter of the fiber and an average particle size less than 0.2 times the diameter of the fiber. The ceramic powder is also stable in an inert atmosphere at a temperature above about 1700.degree. C. At least 90% of the ceramic is selected from borides, nitrides, carbides, and silicides. The fiber is characterized by a smooth surface and is preferably out of round. The invention further comprises a textilable sinterable filament, comprising a flexible polymer matrix containing high temperature sinterable ceramic powder particles. The ceramic powder particles are selected from ceramic borides, nitrides, carbides, and silicides. The diameter of the filament is from 2 to 300 microns. The invention also comprises the method for making textilable filament by fiberizing a mixture of a polymer and a sinterable non-oxide fiber and the method wherein the high temperature ceramic fiber is prepared by sintering the textilable sinterable filament as previously described. The invention also includes composites containing such filaments.
An improved process is provided for the formation of metal ion containing carbon fibers which particularly are suited for utilization in electron shielding applications. An acrylic fibrous material is formed having substantially uniformly dispersed therein a halide of a transition metal. The metal halide (e.g. a chloride) present within the fibrous material is (1) converted to an oxide, (2) the fibrous material containing the metal oxide is heated in an oxygen-containing atmosphere until thermally stabilized, and (3) the thermally stabilized fibrous material is carbonized or carbonized and graphitized at a more highly elevated temperature in an appropriate atmosphere. The resulting product comprises ions of a transition metal substantially uniformly dispersed in an amorphous carbon or graphitic carbon matrix. The halide of a transition metal may be incorporated into the acrylic precursor by co-spinning and/or padding prior to thermal stabilization. The conversion of the halide of a transition metal to an oxide prior to thermal stabilization may be conducted by contact with a base or with an oxidizing agent as described.
