Clay-thickened grease

Non-soap greases using finely divided solids as thickeners are useful as lubricants at elevated temperatures. Materials used include organO Clays such as dimethyldioctyl-decyl-ammonium bentonite (Bentone greases) or selected dyestuffs which produce brightly coloured greases. 

These are generally reserved for specialist applications, and are in the main more costly than conventional soap-based greases. The most common substances used as nonsoap thickeners are silica and clays prepared in such a way that they form gels with mineral and synthetic oils. Other materials that have been used are carbon black, metal oxides and various organic compounds. 

Since 1977 several new thickener types have become widely used, including complex (sodium, lithium, calcium or aluminium), polyurea, modified clays, and other non-soap thickeners. To bring the picture up-to-date, Risdon carried out an evaluation in 1986 of three of the newer grease types not inciuded in the previous programme. They were lithium complex, aluminium complex and polyurea. They included one EP (extreme pressure) and one non-EP grease for each type of thickener, and all were of the same consistency grade, NLGI No 2. 

Hydrogels of silica were milled into oil with an oleophilic surfactant such as a long Chain quaternary ammonium- compound, dimethyldioctadecylammonium chloride, or metal soaps. Clays were used but the process also applied to fine silica (599). This was only one of many patents relating to grease thickeners made from bentonite-type clays (600). 

Bingham plastics These fluids do not flow unless the stress applied exceeds a certain minimum value refened to as the yield stress and then show a linear shear stress versus shear rate relationship. Thickened hydrocarbon greases Certain asphalts and bitumen Water suspensions of clay/fly ash/metallic oxides Sewage sludges Jellies Tomato ketchup Toothpaste... 

Other uses - Hormite clays are also used as thickeners in grease, polyesters, and vinyl plastisols, odor absorbents, bleaching (decolorizing) agents for petroleum, mineral, and vegetable oils, fdter aids, anticaking agents, pharmaceutical absorbents, acicular fillers in rubber (sepiolite), catalyst supports (sepiolite), and cosmetic/pharmaceutical thickeners and emulsion stabilizers. 

---