GB862593A - Process for preparing fibrous and water-insoluble alkali metal titanates and new fibrous crystalline alkali metal tetratitanates - Google Patents

Abstract

Fibrous, water-insoluble titanates of alkali metals other than lithium are prepared by dissolving TiO2 or a non - fibrous titanate M2O(TiO2)2m (where M is an alkali metal other than lithium and m is 2 or 3) or compounds producing said non-fibrous titanate in situ in a molten fluoride and/or chloride of said alkali metal, crystallising said fibrous titanates therefrom and separating from the halide. The products comprise tetratitanates and hexatitanates in fibrous form: the former on long treatment with water (e.g. for 2-100 hours with water at 20-100 DEG C.) yield products also in fibrous form and with a reduced alkali metal content. All these forms have characteristic X-ray diffraction patterns, examples of which are given. The tetratitanates as formed change to hexatitanates on heating above about 1100 DEG C. After water extraction these titanates are less stable and the change occurs at above 700 DEG C. Preferred TiO2/M2O ratios in the melt lie between 2 : 1 and 8 : 1 and with ratios of 1 : 1 to 5 : 1 tetratitanates tend to form whilst 6 : 1 to 8 : 1 ratios favour hexatitanates. The fluoride:chloride ratio in the melt influences the product and 10-20% fluoride gives hexatitanates and 35-65% fluoride gives tetratitanates; tetratitanates are not formed in the absence of fluoride. The temperature of reaction should generally be below 1200 DEG C., and 750-1150 DEG C. is the preferred range: higher temperatures favour hexatitanate formation. The fibrous titanate may be separated from the halide matrix after cooling by leaching with water, or the halide remaining after removal of the titanate from the melt may be evaporated by heating in an air stream in the region of 1000 DEG C. In an example the fibres after water leaching are further purified by extracting with hydrochloric acid, and carbon entrained by the fibres during production, burnt out at 600 DEG C. to leave a nearly white product. Examples describe the preparation of the fibrous titanates by (a) dissolving the titanium component in the molten halide and cooling; (b) heating the reactants in a vertical tube, the lower end of which is maintained at a lower temperature (e.g. 150 DEG C. lower) than the top whereby fibres form at the top of the melt in the tube; (c) maintaining the melt in a cylindrical vessel divided into unequal chambers by a vertical partition extending towards the bottom of the vessel, by means of an arc between an external electrode and the bottom of the vessel and feeding the reactants in solid form to the smaller chamber; the reactants melt and sink in the smaller chamber, pass under the baffle and begin to rise in the larger vessel, in which however their flow is partly impeded by means of a horizontal baffle; the upper part of the larger vessel is thus maintained at a lower temperature and the fibrous titanate crystallises out and is removed: in a simpler method of this kind, titanium dioxide is dropped into a halide melt in a vessel heated at the bottom by means of a flame, (the temperature difference between the top and bottom of the vessel may thus be about 200 DEG C.) and fibres which form and slowly fill the melt volume are mechanically and repeatedly removed; (d) merely heating the reactants in a platinum vessel and allowing to cool slowly, e.g. in a crucible type electric resistance furnace, or by heating in a platinum tube surrounded by a porcelain tube which is then slowly passed through a tube furnace. Non-fibrous titanates, if used in the process may be prepared in situ by reaction of titanium dioxide, or a source thereof such as titanyl sulphate and a source of alkali metal oxide such as a carbonate, hydroxide, oxide or phosphate. The non-fibrous titanate may alternatively be preformed by fusion of titania with p alkali metal oxide, hydroxide or carbonate at 1200-1500 DEG C. or by heating titania and an alkali metal carbonate without fusion at 800-1000 DEG C. In Example III after mechanical removal of the fibrous titanate, a mass of blue non-fibrous potassium titanate needles is said to remain in the halide melt. The fibrous alkali metal titanates have good thermal stability and are inert to aqueous mineral acids, bases and salts at room temperature, do not dissolve in boiling 50% caustic soda and are not attacked by chlorine; they do not form hydrates and are of low bulk density: they may be incorporated into oils (e.g. silicone oil) to give lubricating greases. Specification 782,472 is referred to.ALSO:Fibrous, water-insoluble titanates of alkali metals other than lithium, prepared by crystallisation from a halide melt (see Group III) have good thermal stability, are inert and of low bulk density, and may be suspended in a viscous liquid such as glycerine to form, after filtering off the liquid, a mat or felt which may be used to filter bacteria from solutions. Specification 782,472 is referred to.