GB675301A - Aerogels and grease compositions made therefrom - Google Patents

Abstract

A lubricating grease composition comprises a major proportion of an organic liquid possessing lubricating properties and a minor proportion of a non-collapsed soap aerogel. The organic liquid possessing lubricating properties may be mineral lubricating oil, a synthetic hydrocarbon, an organic ester, an organic polymer or a fluorinated hydrocarbon, and a list of suitable liquids is given. The soaps from which the non-collapsed soap aerogels can be made may be metal or organic base salts of fatty materials and mixtures thereof. Saponifiable materials which may be used to form soaps are fats and oils of animal, vegetable, marine or fish origin, fatty acids derived from such fats and oils, the hydrogenated or sulphurized products of such fatty acids, and the substitution derivatives of such fatty acids for example the mercapto amino or halogen substituted fatty acids. Saponifiable materials from other sources such as napthenic acids, tall oil fatty acids, rosin acids and acids produced by the oxidation of petroleum hydrocarbons, may also be used. A list of specific saponifiable materials which can be used to form soaps is given, while a list of metals and organic bases whose soaps may be employed is also given. In addition to non-collapsed soap aerogel, the lubricating grease composition may contain non-collapsed aerogels of silica, ferric oxide or cellulose, and a list is given of suitable mixtures of aerogels and lubricating liquids. The lubricating grease compositions may be acid, alkaline or neutral and may contain stabilizing agents, oxidation inhibitors, corrosion inhibitors, extreme pressure agents, anti-wear agents, viscosity index improvers, oiliness agents or pour point depressors. Details of suitable polymers of alkylene oxides, esters and ethers of such polymers and polymers of alkylene thioglycols, which may be employed as the stabilizing or anti-bleeding agents, are given. Suitable oxidation inhibitors of the amine and phenol types are listed while dicyclohexylamine nitrite and amino nitroso compounds are given as examples of suitable corrosion inhibitors. Phosphorus, sulphur or halogen containing organic compounds which may be employed as extreme pressure agents are specified. The anti-wear agents may be oil-soluble urethanes, oil-soluble substitution products of urea or thiourea such as the allophanates, carbazides and carbazones, rubber, polyisobutylene or polyvinyl esters, while the viscosity index improvers may be polyisobutylene having a molecular weight of about 800, voltolized paraffin wav or polymerized unsaturated esters of fatty acids and monohydric alcohols. Suitable oiliness agents are stearic and oleic acids, while a suitable pour point depressor is chlorinated naphthalene. In the examples, lubricating greases having as the base oil mineral lubricating oil (with or without polyethylene glycol), dimethyl silicone polymer or dioctyl phthalate, are described. The non-collapsed soap aerogel employed in these examples is made from the sodium soap obtained from a mixture of hydrogenated fish oil fatty acids and hydrogenated castor oil. The fish oil fatty acids are obtained from a mixture of menhaden and sardine oils. Specifications 672,650 and 672,651 are referred to. Preparation of non-collapsed soap aerogels.-These aerogels are obtained by removing the liquid from a soap gel, comprising a soap phase and a liquid phase, under such conditions that the collapse of the gel structure is prevented. Thus the liquid may be removed (1) by raising the temperature of the gel above the critical temperature of the liquid (the pressure being maintained above the critical pressure during heating) and then releasing the pressure at this raised temperature. Alternatively the liquid may be removed (2) by cooling the gel to below the freezing point of the liquid and then subliming the solidified liquid under vacuum. According to method (1) the soap may be formed in situ in or introduced into a hydrocarbon solvent such as a lubricating oil, n-cetane or methyl naphthalene and the mixture heated to a grease-making temperature (300-500 DEG F or higher) with agitation. The resulting gel is cooled and the solvent removed by extraction with another liquid having a lower critical temperature than the hydrocarbon solvent, for example a low boiling paraffin hydrocarbon or a liquefied gas such as liquefied CO2. The temperature of the soap-liquid system is raised above the critical temperature of the liquid and the pressure then released as described above. In this way fibres of non-collapsed soap aerogel are obtained. According to method (2) a soap gel may be prepared in a hydrocarbon liquid such as p-xylene, benzene, naphthalene or hexamethyl ethane or in water or a benzene-water or mineral oil-water mixture and the liquid removed by freezing and sublimation as described above. In an example of method (1) the saponifiable materials are reacted with aqueous caustic soda in presence of mineral oil and the soap slurry formed is heated to drive off water. During this heating, additional mineral oil is added, the mixture heated to 390 DEG F and then cooled to form a grease. The mineral oil is then extracted from the grease with isobutylene after which the isobutylene is displaced by ethylene at ice temperature and 700-800 pounds per square inch pressure. The ethylene is released from the ethylene-soap mixture after heating to above the critical temperature of the ethylene.