Process for producing continuous alumina multifilament yarns which comprises preparing an aqueous spinning mix containing selected alumina particles and water-soluble precursors of alumina in selected amounts, spinning filaments from the mix, forming a continuous filament package on a collapsible, refractory bobbin at a windup speed which attenuates the filaments, firing the package in a furnace at selected temperatures in either one or two steps, and then firing the yarn while backwinding it. A bobbin is obtained which is wound with strong substantially straight yarn of at least five aligned polycrystalline .alpha.-alumina continuous filaments, which yarn can be backwound from the bobbin.
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of copending application Ser. No. 301,504, filed Oct. 27, 1972, which is a continuation-in-part of application Ser. No. 155,737, filed June 23, 1971, now abandoned.
Disclosed is a process for continuously producing highly flexible long .alpha.-alumina fibers of small diameter according to the slurry spinning technique. Also disclosed are a specific spinnable slurry containing an alumina powder having an average particles diameter of 0.1 .mu.m or less, the specific thermophysical conditions under which the slurry is spun into a multifilament yarn, and the well-balanced residence time conditions under which the multifilament yarn running as a single continuous fiber is prefired and fired to form a long .alpha.-alumina fiber.
.alpha.-Alumina fibers are produced by a sol-gel process using aluminum nitrate as a starting material. A reaction mixture including aluminum nitrate, water and aluminum particles is refluxed until the aluminum particles are completely dissolved to obtain an aluminum hydroxide sol. The aluminum hydroxide sol is then aged to increase the viscosity thereof, spun, dried and sintered to obtain .alpha.-alumina crystalline fibers.
A heat-resistant alumina fiber mat contains an accumulated mass of alumina staple fibers and continuous alumina filaments. The accumulated mass is sewn with the continuous alumina filaments. A process for producing a heat-resistant alumina fiber mat comprises accumulating a precursor of alumina staple fibers to obtain an accumulated mass, sewing the accumulated mass with continuous filaments to give a sewn mass and then sintering the sewn mass. The continuous filaments may be continuous alumina filaments or a precursor thereof.
A fibre product comprising fine-diameter inorganic oxide fibres, for example alumina fibres, which can be compressed to increase the volume fraction of fibres to at least 0.25 without excessive damage to the fibres. In a preferred embodiment the fibres are nominally-continuous and essentially-aligned and such a product is made by blow-spinning through a converging duct and collection on a wind-up drum. The product may be in the form of a mat or blanket, a tape or a woven material.
A method is described for producing hard, dense, finely crystalline fired bodies from alumina gels of solids content greater than 45%, by the use of high pressure in mixing and/or presssure extrusion together with seeding of the gel by submicron alpha alumina particles.
