Chariot axles were greased with soap more than 3,000 years ago
Traces of calcium soap have been found on chariot axles dating to 1400 BC, and the builders of the Egyptian pyramids slid their stones over timber soaked in oil. People have been fighting friction for millennia. Modern engine oil simply fights it with a far more elaborate chemistry set.
A lubricant reduces friction between touching surfaces, which in turn cuts heat, wear, noise and vibration. Most often it works by laying a thin film between moving parts, but it can also carry away debris, transmit force, or heat and cool surfaces. The science of it is called tribology. Romans relied on olive oil, rapeseed oil and animal fats. The Industrial Revolution and its metal machinery sped things up, and whale oil remained in use as an additive in automatic transmission fluid until late in the 20th century. Early in the 1900s petroleum took over, helped by vacuum distillation, which made it possible to purify the heavy, non-volatile compounds lubricants need.
The scale is huge. About 37,300,000 tons were consumed worldwide in 1999, with vehicles the biggest users, and liquids dominating over solids and gases. Most lubricants are chiefly a base oil, either refined from crude or synthetic, graded by the American Petroleum Institute according to purity and how well viscosity holds up with temperature. Compressor and hydraulic oils may contain nothing else, while greases, gear oils and metalworking fluids can be up to 30 percent additives.
A modern car oil may carry as many as ten additives making up a fifth of its volume. Detergents keep engine parts free of deposits; pour point depressants stop wax crystals forming in the cold; silicone anti-foaming agents discourage bubbles; viscosity index improvers keep the oil thick when hot; antioxidants slow its breakdown; alkaline corrosion inhibitors soak up acids; and anti-wear agents such as zinc dithiophosphates lay protective films on metal.
Solids can lubricate too. Graphite, molybdenum disulfide and similar materials keep working at high temperatures, though molybdenum disulfide degrades above 350 °C in air. Grease is typically about 80 percent oil held in a sponge-like soap thickener.
Source: Lubricant
