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Refractory Fibers of Amorphous Alumina and Phosphorus Pentoxide

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Refractory Fibers of Amorphous Alumina and Phosphorus Pentoxide Europaisches Patentamt 0 243123 • J European Patent Office Publication number: B1 Office europeen des brevets EUROPEAN PATENT SPECIFICATION Date of publication of patent specification: 31.10.90 Intel.5: C 04 B 35/10, C 03 B 37/00, C 03 C 13/00, D 03 D 15/12, Application number: 87303421.9 B 32 B 17/02, C 03 C 25/02 Date of filing: 16.04.87 Divisional application 89124021.0 filed on 16/04/87. Refractory fibers of amorphous alumina and phosphorus pentoxide. (D Priority: 21.04.86 US 854319 Proprietor: MINNESOTA MINING AND MANUFACTURING COMPANY 3M Center, P.O. Box 33427 Date of publication of application: St. Paul Minnesota 55133 (US) 28.10.87 Bulletin 87/44 Inventor: Sowman, Harold G. c/o Minnesota Publication of the grant of the patent: Mining and 31.10.90 Bulletin 90/44 Manufacturing Company 2501 Hudson Road St. Paul Minnesota 55144-1000 (US) Inventor: Tran, Tai T. c/o Minnesota Mining and Designated Contracting States: Manufacturing Company 2501 Hudson Road DEFRGBIT St. Paul Minnesota 55144-1000 (US) References cited: Representative: Baillie, lain Cameron et al GB-A-1360200 c/o Ladas & Parry Isartorplatz 5 US-A-3 503 765 D-8000 Munchen 2 (DE) US-A-3982955 CO CM CM O Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall CL be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been 111 paid. (Art. 99(1 ) European patent convention). Courier Press. Leamington Spa, England. EP 0 243 123 B1 Description Field of the invention This invention relates to refractory fibers of alumina and phosphorus pentoxide and articles made 5 therefrom. In another aspect, it relates to a process for the preparation of such refractory fibers. The fibers are useful in the manufacture of fire-resistant materials. Background art Ceramic fibers containing aluminum/phosphorus components are known in the art. They are known to 10 be crystalline in structure which accounts for their friability. These fibers are not well suited for the manufacture of textile fabrics. Ceramic fibers containing phosphates of aluminum have been disclosed. U.S. Patent No. 4,008,299 teaches essentially crystalline filaments of aluminum phosphate. Various additives can provide some non- crystalline character. U.S. Patent No. 3,788,885 discloses a process for binding inorganic fibrous materials is which comprises applying a solution of a complex phosphate of aluminum to a fibrous material. Polycrystalline oxide fibers, including AI2O3 • P205, which melt above 1600°C are disclosed in U.S. Patent No. 3,322,865. P2O5 can be present as an additive in ceramic fibers. For example, polycrystalline alumina-silica fibers having as an additive 1 to 9% P2O5 are disclosed in U.S. Patent No. 3,503,765. An alumina fiber having P2O5 20 present as an additive is taught in U.S. Patent No. 3,950,478. GB — A— 1,360,200 discloses a fiber comprising a metal compound and polyvinyl alcohol or partially hydrolyzed polyvinyl acetate and a process therefor. U.S.— 3,982,955 discloses aluminium oxide fibers having the following composition by weight: 25 AI2O3 61—98% (preferably 76—96%) SiO2 1—20% (preferably 3—15%) P2O5 0—10% (preferably 0—5%) B2O3 0—10% (preferably 0—5%) MgO ' 0—5% (preferably 0—1 %) 30 C 0.1 — 4% (preferably 0.5—2.8%) The fibers are formed by spinning a low viscosity solution containing polyethylene oxide (having a viscosity typically of the order of 270 mPas) through a heated spinning column (in which solvent is evaporated) and heating the resulting green fibers in air to drive off organic matter. The resulting fibers 35 have an irregular cross-section. If the final heat treatment step is carried out at a temperature below 1,100°C, carbon remains in the fiber and the resulting carbon-containing filaments are stated to be amorphous to X-rays and to possess good mechanical properties. However the only amorphous fiber specifically disclosed (in Example 4) is composed of alumina, silica and carbon only and has the same tensile strength but a lower modulus than that of a comparable crystalline fiber. 40 Summary of the invention of The present invention provides a refractory fiber consisting essentially of a homogeneous mixture amorphous alumina and amorphous phosphoros pentoxide, the mole ratio of alumina to phosphorus pentoxide being in the range of 10:1 to 2:1, and said fiber being of uniform shape. 45 The alumina-phosphorus pentoxide fibers of the invention are typically solid, smooth, and can be invention have transparent to visible light. The fired alumina-phosphorus pentoxide fibers of the present unusual textile handling properties in that they can be repeatedly rubbed between the fingers with little evidence of friability and are useful for the manufacture of fireproof fabrics. The fibers can be modified by the addition of small amounts of additives to the precursor composition such as polyvinylpyrrolidone to so provide softer fiber or other oxide components to produce a variety of colors. These physical The characteristics are in contrast to those fibers disclosed in the prior art which are crystalline in structure. textile crystalline fibers of the prior art can be friable and are not as well suited for the manufacture of fabrics. The fabrics prepared from fibers of the present invention are particularly well suited for consumer textiles rather than solely industrial applications as are crystalline fiber fabrics. The invention also provides a method for preparing a refractory fiber having a homogeneous 55 the composition consisting essentially of amorphous alumina and amorphous phosphorus pentoxide, mole ratio of alumina to phosphorus pentoxide being in the range of 10:1 to 2:1, comprising the steps: and a) preparing a viscous precursor liquid mixture comprising an alumina precursor a phosphorus and a viscosity in pentoxide precursor having an oxide solid content in the range of 25 to 55 weight percent 60 the range of 10 to 1,000 Pas, b) shaping said viscous concentrate in a fiber form by drawing or spinning, and fiber c) evaporatively gelling or hydrolyzing the resultant formed fiber to provide a green comprising said homogeneous composition of alumina and phosphorus pentoxide, and sufficient to provide a tired d) firing said green fiber to a temperature of at most 1000°C and for a time and amorphous phosphorus 65 fiber consisting essentially of a homogeneous mixture of amorphous alumina EP 0 243123 B1 pentoxide, said temperature and time being insufficient to provide a polycrystalline fiber. Heating and firing the shaped green fiber in step d) of the above process removes water, decomposes and volatilizes undesired fugitive constituents, and converts it into the refractory fiber of the invention. In this application: 5 "ceramic" means inorganic nonmetallic material consolidated by the action of heat, such as metal and nonmetal oxides; "sol" means a fluid solution or a colloidal suspension; "non-melt" means that the mixture is not melted although one of the components may be; "homogeneous" means of uniform composition; io- "non-vitreous" means not formed from a melt of the oxide mixture; "green" refers to the ceramic articles which are unfired, that is, not in their final ceramic form; "amorphous" means a material having a diffuse x-ray diffraction pattern without definite lines to indicate the presence of a crystalline component; "refractory" means resistant to high temperatures, e.g., up to 900 — 1000°C; is "dehydrative gelling" or "evaporative gelling" mean that sufficient water and volatile material are removed from the shaped green fibers so that the form or shape of the fiber is sufficiently rigid to permit handling or processing without significant loss or distortion of the desired fibrous form or shape. Therefore, all the water in the shaped fiber need not be removed. Thus, in a sense, this step can be called partial dehydrative gelling. The shaped fibers in their green form are generally transparent to visible light 20 and clear under an optical microscope; "continuous fiber" means a fiber (or multi-fiber article such as a strand) which has a length which is infinite for practical purposes as compared to its diameter; Detailed description which, can 25 To prepare the fibers of the invention, aluminum and phosphorus-containing compounds contain soluble salts, sols or dispersible colloids or mixtures are mixed together with other optional iron, nickel, chromium, components, such as polyvinylpyrrolidone or precursors of oxides such as copper, mixture. The etc. for color or other property modifications to form a homogeneous liquid precursor concentrated to a fiber-forming consistency (i.e., when a rod is inserted and pulled out, a components are To 30 fiber is formed) by evaporation of solvent or removal of solvent from the precursor liquid mixture. the of facilitate spinning of continuous fibers it is preferable that the concentrate has a viscosity in range 50,000 to 100,000 mPas. For spinning of staple form fibers (as by use of spinning discs or blowing of least processes) much lower viscosities, i.e., down to 10,000 mPas, are usable. Drying or removal at part non- of the water from the shaped fiber causes it to gel or become rigid. The resulting shaped "green or 1000 C 35 refractory amorphous fiber can be further heated and fired at temperatures up to (higher result in the formation of phosphates of aluminum) which removes the remaining water temperatures fiber. A decomposes and volatilizes the undesired fugitive constituents and converts it into a refractory At particularly desirable composition comprises a molecular equivalent of 4 AI2O3:1 P2O5.
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