GB893852A - Improvements relating to alumina - Google Patents

Abstract

Fibrous alumina monohydrate having a boehmite crystal lattice is produced by heating at a temperature of between 120 DEG C. and 250 DEG C. an aqueous dispersion of alumina (one half of which can be dissolved in concentrated HCl at 98 DEG C. in less than 10 minutes), the aqueous dispersion containing a weak organic acid or the radical of a monobasic acid of dissociation constant at 25 DEG C. greater than 0,1, the molarity of the alumina calculated as Al2O3 being at least 0,05 and not over 1,6, and the molarity of the acid radical being above 0,05. The alumina may be heated in presence of hydrochloric, nitric, perchloric, iodic, hydrobromic, acetic, trichloracetic or formic acid, and other forms of alumina and acid radicals may be removed. The fibres may have one or more dimensions in the colloidal range, and may be used as colloidal sols in water or organic liquids, or such sols may be dried, e.g. by spray drying. Water may be removed in presence of a partially water-miscible organic liquid, which, if an alcohol, may effect surface esterification of the boehmite. The dry product may be redispersed to give a stable sol. The aqueous alumina dispersion may be formed from basic aluminium chloride or nitrate, aluminium hydroxide, alumina gels, or colloidal alumina solution. Basic aluminium chloride may be prepared by partly neutralizing an aluminium chloride solution, basic aluminium halide by dissolving aluminium in an aluminium halide solution, and basic aluminium nitrate either by the latter method or by heating aluminium nitrate nonahydrate to 150 DEG C. and further heating to remove oxides of nitrogen. The aqueous acidic alumina solution may also be prepared by mechanically dispersing in water freshly precipitated aluminium hydroxide which has been washed to remove salts and then adding a strong acid. Aqueous dispersions of alumina having a desired content of nitrate radicals may be prepared by the electrodialysis of aluminium nitrate solution, or sols can be used which have been prepared by the reaction of aluminium salts with ion exchangers. Soluble salts such as sodium chloride or nitrate may remain, but only small quantities of silicon, boron and molybdenum compounds are admissible, and apparatus not lined with glass or other siliceous material is preferable. Particles of highly polymerized alumina starting material should pass through a 100 mesh, preferably a 300 mesh screen. After heating, the sol may be gelled by raising the pH quickly to 8-10, preferably at above 60 DEG C., by addition to a base, salts formed may be removed by filtration and washing, and the gel redispersed in distilled water or in an acid solution. Unpolymerized alumina may also be removed as soluble aluminate by raising the pH to over 11. The washed gel may be redispersed by adding a base to adjust the pH to a value below 10. A further conversion of remaining unpolymerized alumina to fibrous alumina may be effected by withdrawing some of the acid radical, e.g. by an anion-exchanger, gelation and washing, dialysis, or by precipitation as the insoluble salt of a metal added as a base or bicarbonate, followed by heating. These steps may be repeated. Fibrous alumina may also be prepared by heating a mixture of a weak monobasic acid such as acetic or formic acid and a carbonated hydrated alumina gel to reflux temperature to cause evolution of CO2 and then heating at 140 DEG -180 DEG C. for 10 minutes to 7 hours under autogenous pressure. In Example 1, basic aluminium chloride is prepared by adding powdered aluminium to a solution of aluminium chloride hexahydrate, with initial heating. The diluted solution is heated in a sealed glass container at 160 DEG C. for 16 hours to obtain fibrous boehmite. In Example 3, the procedure is similar and a portion of the fibrous boehmite sol is transferred to n-butanol by azeotropic distillation at constant volume. The solution is heated in an autoclave to 300 DEG C. and vented to remove the alcohol and acid radical. A fluffy powder is produced. In Example 4, sodium aluminate and hydrochloric acid solutions are added slowly and simultaneously to a hydrochloric acid solution, the pH being maintained at about 4,25 and the temperature at about 95 DEG C. The aqueous alumina dispersion obtained is heated for 16 hours at 150 DEG -160 DEG C. in a sealed glass vessel, sodium chloride being removed by dialysis. Films may be made from the dialysed sol by pouring into a glass trough treated with a silicone oil parting agent and allowing to dry. In Example 5, aluminium chloride hexahydrate and ammonium hydroxide solutions are used, while a fibrous boehmite sol may also be obtained by heating a basic aluminium chloride solution in an autoclave for 1 hour at 160 DEG C., part of the chloride being removed by an ion-exchange resin. In Example 8, a basic aluminium chloride solution is diluted and heated in an autoclave for 1 hour at 160 DEG C. The sol is treated with the bicarbonate form of an anion-exchange resin, and then may be further treated to convert remaining unpolymerized alumina by raising the temperature to 160 DEG C. in 2 1/2 hours and holding at this temperature for 1 hour. In Example 9, a portion of a dispersion obtained by heating a diluted basic aluminium chloride solution is transferred azeotropically to n-butanol and heated to 300 DEG C. with venting, the dry product containing butoxy groups, while another part of the dispersion may be freed from anions by gelling with ammonium hydroxide to pH 10 and washing with hot distilled water, followed by further adjustment of the pH to 10 with ammonia. The filter cake may be dispersed in water and freeze-dried to obtain a fluffy powder, or may be pelleted, or may be azeotropically distilled with n-butanol to remove water, when the product contains butoxy groups. In Example 15, aluminium nitrate nonahydrate is heated for 8 hours at 275 DEG C., micropulverized, slurried with water, and autoclaved at 160 DEG C. for 3 hours. The sol may be de-ionized by treating with a mixture of the hydrogen form of Nalcite HCR resin and the bicarbonate form of "Amberlite" (Registered Trade Mark) IRA 400 resin, or the sol may be gelled by adding dilute ammonium hydroxide to a pH of 8,3 and dried. In Example 19, sols prepared as in Example 3 may be stabilized by the addition of acetic, formic, propionic, hydriodic, hydrobromic, nitric or perchloric acid. In Example 20, deionizing is effected by a mixture of the hydrogen form of a polystyrene sulphonic acid resin and the bicarbonate form of a polystyrene quaternary amine resin, the step being repeated and being followed by treatment with the second resin only. In Example 21, an alumina gel prepared by reacting aluminium sulphate and sodium carbonate solutions is filtered and washed, slurried with distilled water, mixed with dilute acetic acid (or with iodic, trichloracetic, perchloric or hydrobromic acid), heated to boiling and refluxed, and transferred to a stainless steel autoclave and heated to 160 DEG C. in 24 minutes and held at that temperature for 1 hour. In Example 22, the sol of Example 21 is spray-dried to give a powder containing some acetate groups. Fibrous anhydrous alpha-alumina is prepared by igniting fibrous boehmite at above 1000 DEG C. The dehydrated fibrous boehmite may be compressed, preferably with a small amount of aluminium acetate or a metal stearate, before firing. Dry fibrous boehmite may be mixed with one or more dry lubricants such as graphite, molybdenum sulphide, talc or powdered mica. Lubricants can be formed by mixing fibrous boehmite, either dry or in a suitable organic solvent, with kerosene, gasoline, naphtha, benzene, carbon tetrachloride, stearic and other long-chain fatty acids, polymeric esters, diesters such as di-2-ethylhexyl sebacate, or with oils such as hydrocarbon, fluorocarbon, silicone, whale, cottonseed, castor, or polyethylene oxide oils. Sodium or lithium stearates or hydroxystearates may also be added. The fibrous boehmite may be coated with a monomolecular layer of a long-chain soap. A grease may be prepared by milling a solvent-treated petroleum oil or a silicone oil with 13% by weight of fibrous boehmite. Chromic oxide supported on a dehydrated fibrous boehmite or on pellets or mats formed by dehydrating a gel formed by mixing a fibrous boehmite sol with a silica sol may be used as a catalyst for the low-pressure polymerization of 1-olefins, e.g. ethylene.ALSO:The strength and/or abrasion resistance of a rubber-like polymeric material, e.g. natural and synthetic rubber, neoprene, butyl rubber, GR-S type styrene-butadiene copolymers, butadieneacrylonitrile copolymers, polybutadienes, polyisoprenes, chlorosulphonated polyethylene, fluorocarbon rubbers, polyester rubber, silicone rubber, and polyurethane rubber, are improved by the incorporation of 1 to 30% by weight of fibrous alumina monohydrate having a boehmite crystal lattice. The fibrous boehmite may be incorporated at any point in the manufacture, including the original formation of the polymer. The load carrying capacity of a finished sponge or foam of natural or synthetic rubber or other elastomer may be improved by treatment with an aqueous fibrous boehmite sol. The hydrophobic surface of a polyurethane sponge may be made hydrophilic by treatment with 0,5-10% of a fibrous boehmite followed by drying at 50 DEG -110 DEG C. The tensile and/or impact strength of urea-formaldehyde, melamine-formaldehyde, phenol-formaldehyde, polyester, alkyd, epoxy, polyvinyl acetate, polyvinyl acetal, polyvinyl alcohol, polyethylene, polyacrylic ester, polyacrylonitrile and silicone resins of regenerated cellulose are improved by the incorporation of 1-40% of fibrous boehmite. The materials may be in the form of films, foils, or textiles, and the fibrous boehmite may be added to aqueous dispersion of the resins or incorporated i