3,798,161 United States Patent Office Patented Mar. 5, 1974 PREPARATION OF SOL AND GEL 3 795 522 PREPARATION OF AQUEOUS REDISPERSIBLE It is known that tungstic acid exists in two forms; a GELS OR STABLE DILUTABLE SOLS CON- stable yellow form, known as a-tungstic acid, which may TAINING TUNGSTEN AND TITANIUM AND be formed by hot precipitation from tungstates and is in- TITANIUM-TUNGSTEN CARBIDES THEREFROM 5 soluble in water; and a white form, known as /3-tungstic Anthony Cecil Fox, Didcot, and Kenneth Robert Hyde, acid, which may be formed by cold precipitation from Wantage, England, assignors to United Kingdom tungstates and which goes over into the yellow form on Atomic Energy Authority, London, England prolonged standing or gentle warming. While we do not No Drawing. Filed Oct. 1, 1971, Ser. No. 185,859 wish to be bound by any theory, we believe that only a- Claims priority, application Great Britain, Oct. 5, 1970, io tungstic acid is not suitable for use in the process of this 47,314/70 invention. This belief is based on the fact that we have Int. CI. BOlj 13/00; C04b 35/56 consistently failed to make gels using commercial tungstic U.S. Cl. 106—43 18 Claims acid cake as received; on the other hand, if the tungstic acid cake is dissolved, e.g. in ammonia, and reprecipitated ABSTRACT OF THE DISCLOSURE 15 in the acid, the resulting precipitate is suitable for the Aqueous, stable, dilutable sols and aqueous, redispersible preparation of gels according to this invention. gels having a weight ratio of Ti02:W03 of at least 0.15 Alternatively the ammonium tungstate may be used di- containing tungsten and titanium and optionally other rectly, either as a solid or in aqueous solution. metals are made by mixing freshly precipitated tungstic While any water-soluble titanium salt may be used, acid or a tungstate with an aqueous solution of a titanium 20 titanium tetrachloride is preferred from the standpoints of salt. The sols and gels may be calcined at temperatures be- cost and availability. The concentration of the aqueous low 1800° C. in the presence of carbonaceous material solution is not critical, and either anhydrous TiCl4 or con- to give mixed tungsten-titanium carbides. centrated solutions which are commonly available may be used. 25 MIXED SOLS—GENERAL PREAMBLE The present invention relates to the manufacture of cer- It is advantageous to react the titanium chloride and tain mixed sols and gels suitable for the preparation of either /3-tungstic acid or a tungstate in as concentrated a mixed metal carbides. In particular, the invention provides state as is practicable. Too high concentrations produce a process for preparing a sol or gel containing tungsten and viscosities of reacting mixture which may impede reac- titanium (hereinafter referred to as a tungsten-titanium tion of the constituents. Too low concentrations consider- sol or gel), and to a method of making a mixed tungsten- ably reduce the rate of achieving sol formation and indeed titanium carbide therefrom. some sols may not be easily prepared in too dilute a con- Existing methods of preparation of mixed refractory „_ centration. metal carbides suitable for the production of hard metal The sols may be diluted, often infinitely diluted, with products include water and many inorganic aqueous solutions and also with non-aqueous liquids, e.g. alcohols, which are com- (i) carburization of mixtures of metals, or metal oxides, patible with hydrochloric acid solutions. Precipitates will with carbon, 40 form with time from extremely weak sols. (ii) heating mixtures of the pre-formed carbides, Increasing acid, e.g. hydrochloric acid, concentrations (iii) a combination of methods (i) and (ii), and produce opalescence, turbidity and finally precipitates. (iv) production of solid solutions in a fused metal bath, These precipitates will re-dissolve by further dilution to re- e.g. tungsten and titanium (or Ti02) and carbon in a duce the acid concentration. It is preferred to reduce the nickel melt at about 2000° C. 45 free acid chloride in sols to below 7 M and preferably be- low 4 M, although homogeneous liquids stable for short All of those processes require the comminution and periods of time may foe obtained at higher acidities of up mixing together of the starting materials by conventional to 12 M (see Table II). means, followed by heating the mixtures at temperatures Although an acid chloride solution is reacting with usually in excess of 1800° C. The present invention falls 50 /3-tungstic acid or a tungstate, the reaction is not con- within category (i). It is an object of this invention to sidered to be simply the formation of more soluble meta- provide sols and gels which can be used to make mixed tungstate since it has been shown (see Table II below) metal carbides under somewhat less severe conditions than that a quantity of titanium ions is required to achieve those currently employed. homogeneous sols and believed to form titano-tungstic The present invention provides in one aspect a sol or gel 55 acid complexes. of titanium and tungsten, in which the titanium and tung- The temperature at which the initial sol or gel forma- sten are present in a Ti02/W03 weight ratio of at least tion is effected is not critical, and may suitably range from 0.15, and in which the molar ratio of anion/titanium is at 0° C. to 100° C., or even higher if an autoclave is used. least 1.0 divided by the valency of the anion. Preferred temperatures lie in the range of 20° C. to 80° In another aspect, the invention provides a process for 60 C. Essentially hot and cold routes of reaction produce ap- preparing a sol or gel containing tungsten and titanium, parently similar sols. Cold routes tend to take longer to which process comprises mixing freshly precipitated tung- achieve sol formation although it is not necessary to main- stic acid or a tungstate with an aqueous solution of a ti- tain as high a free acid concentration as is needed in the tanium salt so as to form the desired sol or gel. Gels so hot route where it is necessary to prevent hydrolysis of formed may be dispersed, e.g. in water, to form sols. Sols 65 titanium chloride, tantalum chloride, etc. to unpeptizable may be concentrated by evaporation to give gels. hydrated oxides. These sols and gels are good starting materials for the preparation of mixed tungsten-titanium carbides. This is MIXED GELS—GENERAL believed to be due to the fact that the tungsten and the titanium are present in the sol or gel in intimate admixture 70 Some gels are clear and glassy and pass through a clear and in a specially reactive form due to the small crystallite Vaseline appearance as they are diluted (e.g. with water) size. to produce sols, 3,795,522 Some gels are opalescent although produce clear sols MIXED SOLS AND GELS FROM A.P.T. AND on addition of water. TICL4 BY A HOT ROUTE The gels are dispersed by dilution (in for example water) to convenient concentrations. Sols prepared from It is preferable that the titanium chloride is in a suffi- ciently high free acid concentration such that the TiCU reactants containing lower ratios of Ti02/W03 and lower concentrations of free acid lead to sols with higher vis- is not hydrolyzed to unpeptizable hydrated oxides. cosities and have a thixotropic nature. The reactants may be heated in a closed vessel to 60° C. to 85° C. and maintained for short periods of time MIXED METAL SOLS AND GELS FROM (about V2 to 1 hour) at this temperature. It is not con- AMMONIUM TUNGSTATES 10 sidered essential to have reaction in a closed vessel except that in a closed system reproducible products are obtained An advantage gained from the use of ammonium tung- since no constituents are lost by evaporation. Reactions states compared with metal tungstates as starting mate- can proceed in open vessels and losses of acid and water rials, to produce mixed metal sols and gels by reaction may be made up during the hot process. with titanium chloride solution, is the same as that for 15 It is considered desirable to maintain agitation or stir- /S-tungstic acid, namely that the resultant sols or gels may ring during reaction so as to avoid local inhomogeneities be dried to yield homogeneous mixed oxides which do of components which may lead to non-dispersible mate- not contain undesirable metals such as sodium, calcium rials, e.g. a-tungstic acid, in the resultant gels. etc. The temperature is not critical although high tempera- An advantage gained by the use of ammonium tung- 20 tures can lead to irreversible hydrolysis of chlorides and state as compared with /9-tungstic acid is its ease of prep- low temperatures lead to a slow reaction. A temperature aration. a-Tungstic acid commonly produced during a of 75° C. is considered a reasonable compromise. tungsten manufacturing process may be reacted with REACTANTS aqueous ammonia to provide ammonium tungstates capa- ble of reaction with titanium chloride to give mixed tita- 25 Ammonium tungstates nium-tungsten sols and gels. (i) Ammonium tungstate solution.—To obtain a clear a-Tungstic acid may be dissolved in aqueous ammonia ammonium tungstate solution it is convenient to add aque- yielding ammonium tungstate solution which yields with ous ammonia to a slurry of a-tungstic acid in water. It titanium chloride mixed metal sols and gels. Alternatively, is desirable to cool the reactants so as to prevent the for- such an ammonium tungstate solution may be evaporated 30 mation of sparingly soluble paratungstates.