GB1264973A - - Google Patents

Abstract

1,264,973. Ceramic articles; oxide fibres. E.I. DU PONT DE NEMOURS & CO. 28 Feb., 1969 [23 Dec., 1968], No. 10799/69. Headings C1A and C1J. Polycrystalline ceramic oxide articles comprise at least 60 wt. per cent of aluminium oxide and/or solid solutions thereof with one or more other refractory oxides and exhibit at least one dimension less than 0À01 inch; a crystallinity greater than 85%, a porosity less than 10%; a distribution of grain size such that substantially all have average diameters of less than 3 microns, at least 30% are less than 0À5 micron and at least 10% are larger than 0À04 micron; and a maximum roughness height not greater than 8 x 10<SP>-5</SP> inches and a roughness period less than 0À012 inch. The articles are made from an extrudable two-phase system comprising (1) solid particles comprised of at least 10 wt. per cent oxide e.g. clays and of which at least 92 wt. per cent have equivalent spherical diameters between 0À02 and 3 microns, and (2) an aqueous phase having dissolved therein at least :one precursor of aluminium oxide or of another refractory oxide capable of forming ;a solid solution with aluminium oxide and in which the oxides in said solid particles comprise between 13 and 97% of the total weight of available oxides in the system. The solid particles can comprise aluminium oxide, bentonite, kaolin and other aluminium silicates and optionally other oxides such as chromium oxide, magnesium oxide, thorium oxide, iron oxide, nickel oxide, cobalt toxide, cerium oxide, uranium oxide, zirconium oxide, beryllium oxide, hafnium oxide, titanium oxide. Suitable precursors of refractory oxides are aluminium chlorohydroxide, chloride, nitrate and acetate, chromium chlorohydroxide and chloride, ferric chloride, nickel nitrate, magnesium chloride, and mixtures of these. The extrudable system can also contain up to 35% of boron oxide, silica, phosphorus pentoxide, arsenic trioxide and/or tellurium dioxide, hydrochloride acid, and up to 5% cif a modifier such as silicic acid, boric acid, boehmite, phosphoric acid, zirconyl nitrate, poly-(ethylene oxide) or lithium chloride. 'The mix can be extruded as filaments through a spinneret or as films through a die, dried, and fired. The as spun filaments can be coated with a 20 wt. per cent solution of ethyl laurate in perchloroethylene or of paraffn wax in toluene to minimize contraction on firing. The spun filaments are attenuated by pulling way from the spinneret either mechanically or by an air jet. The filaments can be fired by heating in a propane-air flame.