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United States Patent (19) 11 Patent Number: 4,931,316 Johnson 45 Date of Patent: Jun

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United States Patent (19) 11 Patent Number: 4,931,316 Johnson 45 Date of Patent: Jun United States Patent (19) 11 Patent Number: 4,931,316 Johnson 45 Date of Patent: Jun. 5, 1990 (54) PREPARATION OF INTERSTITIAL 56) References Cited TITANIUM CERAMIC FIBERS U.S. PATENT DOCUMENTS 2,668,284 2/1954. Dills .................................... 427/343 (75) Inventor: Robert E. Johnson, Hoboken, N.J. 3,399,979.9/1968 Hamling. ... 23/347 3,403,008 9/1968 Hamling ..... ... 23/344 3,846,527 11/1974 Winter et al. ... ... 264/63 (73) Assignee: Hoechst Celanese Corp., Somerville, 4,010,233 3/1977 Winter et al. ......................... 264/63 N.J. 4,126,652 11/1978 Oohara et al. .. ... 264/29.6 4,559,191 12/1985 Arons .................................... 264/60 4,732,750 3/1988 Olson et al. ......................... 423/609 21) Appl. No.: 240,645 Primary Examiner-Hubert C. Lorin Attorney, Agent, or Firm-Depaoli & O'Brien 22 Filed: Sep. 6, 1988 57 ABSTRACT Titanium-containing preceramic fibers are provided (51) Int. Cl. ....................... D06M 13/50; D01F 9/22 with a high loading of titanium by impregnating a poly (52) U.S. C. .................................... 427/227; 427/229; meric fiber with a liquid comprising a titanium alkoxide 427/337; 427/377; 427/380; 427/381; where the alkoxide contains at least 2 carbon atoms and 427/434.6; 264/29.1; 264/29.2; 264/83; precipitating the titanium alkoxide in the fiber as tita 264/129; 264/211 nium dioxide. Useful titanium alkoxides include tita 58 Field of Search .......................... 8/115.68, 115.69; nium tetraethoxide, titanium tetrabutoxide and titanium 427/335, 337,343,371, 227, 229,377,380,381, isopropoxide. 434.6; 264/29.1, 29.2, 82, 83, 129, 131, 60, 48, 211; 423/609; 501/38, 95, 134 20 Claims, No Drawings 4,931,316 1. 2 or nitride fibers. Use of metal salt mixtures are disclosed PREPARATION OF INTERSTITIAL TITANIUM as resulting in bimetallic oxide fibers. CERAMC FBERS Still another approach has been to disperse ceramic powders in a carrier component such as organic liquids FIELD OF THE INVENTION including low molecular weight polymers, spin the The present invention is directed to a process for dispersion into fibers and then sinter the ceramics. An preparing titanium-containing ceramic articles and, in example of this procedure for producing ceramic fibers particular, to a process for producing titanium-contain such as ferrimagnetic spinel fibers is disclosed in U.S. Pat. No. 4,559,191. ing ceramic fibers 10 U.S. Pat. No. 4,126,652 discloses a process for prepar BACKGROUND OF THE INVENTION ing metal carbide-containing molded products which Ceramic materials are of critical importance for a comprises heating a molded composition comprising at number of high temperature, high performance applica least one powdery metal selected from the group con tions such as gas turbines. These applications require a 15 sisting of B, Ti, Si, Zr, Hf, V, Nb, Ta, Mo, W, Cr, Fe, unique combination of properties such as high specific and U and having an average particle size of not more strength, high temperature mechanical property reten than 50 microns and an acrylonitrile polymer at a tem tion, low thermal and electrical conductivity, hardness perature of about 200-400 C., and then calcining the and wear resistance, and chemical inertness. Design resulting product at a temperature of about 900-2,500 reliability and the need for economical fabrication of 20 C. in an inert atmosphere to form the metal carbide. complex shapes, however, have prevented ceramic Metal carbide fibers can be formed by the process materials from fulfilling their potential in these critical which involves spinning the mixture of metal and car high temperature, high performance applications. bon-forming polymer into fiber, heating to render the The design reliability problems with ceramics, and fibers infusible and then pyrolyzing to yield the metal the resultant failure under stress, are due largely to the 25 carbide. The metals may be added together with any relatively brittle nature of ceramics. This, in combina conventional calcining aid including metal oxides. One tion with the high cost of fabricating complex shapes, example in the patent describes adding metallic tungsten has limited the usage of ceramics. and metallic silicon to a polyacrylonitrile solution and To overcome the problems associated with molding ultimately forming fiber consisting of tungsten carbide ceramic compositions into products, various alterna 30 and silicon carbide. tives have been suggested. For example, it is believed Of the ceramic fibers which have been produced by that the process of manufacturing ceramic articles from the above-mentioned processes, it appears that silicon metal-containing polymers has the potential to over carbide fiber formed from preceramic polymers is the come the problems associated with molding and sinter only ceramic fiber to gain market acceptance. How ing inorganic ceramic compositions. Thus, polymers 35 ever, the metal-containing polymers are typically of based on silicon, carbon and/or nitrogen and oxygen low molecular weight and it has been found difficult to have been developed. See for example, "Siloxanes, Si maintain a threadline during spinning such ceramic lanes and Silazanes in the Preparation of Ceramics and precursors into fiber. It has also been found that trying Glasses" by Wills et al, and "Special Heat-Resisting to spin a polymeric dope containing ceramic particles is Materials from Organometallic Polymers' by Yajima, quite difficult, in particular, due to the necessity of in Ceramic Bulletin, Vol 62, No. 8, pages 893-915 loading the polymers with high levels of inorganic sub (1983), and the references cited therein. Typically, the stances, which high loadings vastly increase the viscos organosilicon preceramic polymers are pyrolyzed in an ity of the spinning dopes. On the other hand, impregnat inert gas to form silicon carbide and/or silicon nitride ing polymeric fibers and the like with aqueous solutions containing articles, especially fibers. It is believed that 45 of metal salts has been unsatisfactory in view of the the formation of silicon carbide fibers is the only com small loadings of metals which are obtained in the fiber. mercial product formed by this technology. Accord The impregnation method, however, has an advantage ingly, there is a need to develop ceramic articles from over forming ceramic fibers from spinning dopes which other metal-containing polymers, especially ones that contain ceramic or metallic particles, since in the im exhibit superior resistance to high temperature oxida 50 pregnation method, the fiber is spun from known fiber tion. forming organic materials and, thus, there are no spin Another process for producing ceramic articles, in ning and handling problems with regard to the prece cluding fibers, is disclosed in U.S. Pat. Nos. 3,399,979 ramic fiber. However, to make the impregnation and 3,403,008. According to these patents, a preformed 55 method for forming ceramic fibers practical, methods of organic polymeric material is impregnated with a solu obtaining higher loadings of the metal into the poly tion of a metal compound, the impregnated material meric substrate must be found. heated to leave a carbonaceous relic containing the It is thus one of the objects of the present invention to metal in finely dispersed form and further heated at provide a novel process for producing titanium-contain 1,000-2,000 C. in a nonoxidizing atmosphere to form 60 ing ceramic articles. the metal carbide or metal nitride depending on the Another and important object of the present inven atmosphere utilized. A similar approach has been taken tion is to provide an improved process for producing in the formation of metal oxide fibers. Thus, as disclosed titanium ceramic fibers which contain an increased in U.S. Pat. Nos. 3,846,527 and 4,010,233 metal salts are titanium content. incorporated into polymeric spinning solutions, the 65 These and other objects, aspects and advantages, as solutions spun into fibers, and the fibers calcined in air well as the scope, nature and utility of the present inven to yield metal oxide fibers. Use of alternative calcina tion, will be apparent from the following description tion atmospheres leads to the formation of metal carbide and appended claims. 4,931,316 3 4. The molecular weight of the acrylonitrile polymer is SUMMARY OF THE INVENTION usually in a range of about 30,000 to 300,000. More In accordance with the present invention, titanium particularly, it may be preferably chosen in such a man containing ceramic fibers are produced by passing a ner that the viscosity at the molding step becomes from spun organic fiber through a liquid bath containing a about 50 to 10,000 poise. titanium alkoxide to impregnate the fiber with the tita Other suitable polymers include polyisobutylene, nium compound and, subsequent to impregnation, con polyisoprene, polystyrene, polymethyl methacrylate, tacting the impregnated fiber with a bath of ammonium polyvinyl alcohol, polyacrylamide, polyacrylic acid, hydroxide to precipitate titanium dioxide in the fiber. It polyethylene oxide, cellulose, carboxymethyl cellulose, has been found that the loading level of titanium dioxide 10 hydrolyzed starch, dextran, guar gum, polyvinylpyrrol in the green fiber can reach as high as about 30 wt.%, idone, polyurethane, polyvinyl acetate, and the like, and which represents about a threefold improvement over mixtures thereof. TiO2 loading using previous metal loading techniques The source of titanium to be used in impregnating the such as the use of a solution of metal halide as the imbi spun organic fiber or molded article comprises titanium bation agent. The titanium alkoxides utilized in this alkoxides in which the alkoxy group is formed from an invention are liquids at room temperature and, thus, a alkyl radical containing at least two carbon atoms. Pref bath of the neat reagent can be used.
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