Lithium soap, often referred to simply as "lithium grease", is a lubricant grease containing a lithium derivative of soap.
Soaps are salts of fatty acids. In the domestic setting, sodium-based soaps are common for detergents, but for lubrication and as form-release agents, soaps derived from other metals are common. The most useful of the non-detergent soaps are those based on lithium. The main components of lithium soaps are lithium stearate and lithium 12-hydroxystearate.[1]
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A grease (lubricant) is a mixture of oil and a soap. The soaps are dispersed into and viscosify oils to form stable gels. Lithium grease adheres well to metal, is non-corrosive, may be used under heavy loads, and exhibits good temperature tolerance. It has a drip temperature of 190° to 220°C (350° to 400°F) and it resists moisture, so it is commonly used as lubricant in household products, such as electric garage doors. Some formulations also include PTFE and/or other substances, such as molybdenum disulfide.
Lithium soaps are not produced by saponification of triglycerides. Instead, fatty acids are treated with lithium hydroxide or lithium carbonate to form salts. The lithium salts are colourless solids that melt near 200 °C.[1]