HISTORICAL NOTE

cants with lower volatility, better high• temperature performance, and greater fire A History of resistance have been developed for naval craft, missiles, and other weapons. The In a civilization that depends on ma• lubricate his spindles. He found the lubri• raw materials for these synthetically pre• chines, materials that lubricate moving cant blend to be much more satisfactory pared neutral substances are plasticizers, parts are absolutely essential. A "lubri• than the straight sperm oil and continued resin polymers, and organic solvents. The cant" is any substance placed between sur• to use the new for 10 years, while most common synthetic liquid lubricants faces to decrease friction and wear, though keeping it a secret from his competitors. frequently used in aircraft turbines are di• lubricants can also act as coolants, cleans• Fifteen years later, when Colonel Edwin L. basic acid esters, which have low freezing ing agents, electrical insulators, and rust Drake drilled the first actual oil well, petro• points and excellent viscosity-temperature preventives. leum lubricants began replacing non• properties, retaining their viscocity over Primitive man probably noticed how mineral materials throughout industry. wide temperature ranges. much easier it was to haul logs that had Silicone polymers, too, have superior been stripped of bark because of the lubri• viscosity-temperature properties and are cation provided by sap oozing from the used for lubrication at high temperatures. wood. Other prehistoric lubricants were In a civilization that While fluorinated and chlorinated com• mud or crushed reeds placed under depends on machines, pounds do not have good viscosity• dragged sledges for hauling game or tim• temperature characteristics, they can be bers and rocks for building construction. materials that lubricate used in the presence of reactive com• More extensive use of lubrication was re• moving parts are pounds. Fluorinated silicones combine the quired with the invention of the wheel and best properties of fluorinated hydrocar• axle. The first carts were made with crude absolutely essential. bons and silicones. Other synthetic lubri• wooden axles and bearings. Eventually, cants include polyethylene glycols and people discovered that smearing a lump of their derivatives, and also phosphate animal on the dry and squeaking parts lubricants, like their animal esters. made the wheel run quietly and smoothly. and vegetable oil predecessors, are liquids. Modem semisolid lubricants, such as However, without the scientific concept of Liquid lubricants have an advantage over grease, consist of thickening agents in a friction, no one knew why. semisolid lubricants (such as grease and mineral oil or synthetic liquid base. Vegeta• When iron and brass replaced wood as animal fat) in that they can be drawn be• ble and animal , resins, gels, waxes, moving parts in machinery, crude lumps of tween moving parts by hydraulic action. fatty acids, saponified fats, and naphtha• animal fat proved to be inadequate lubri• The most important material property of lenic acids can be used as thickening cants. The second generation of fatty and liquid lubricants is their viscosity, or their agents; the most common are metallic oily substances were derived from animal ability to resist flow. Various methods of re• soaps made with calcium, barium, so• oils, vegetable oils, or a mixture of the two. fining petroleum byproducts created lubri• dium, or lithium. For some applications, Some of these lubricants-tallow, olive oil, cants with different ratings of viscosity. greases have a base made of synthetic liq• castor oil, peanut oil, and rape oil-are still Since early machines were relatively uid, such as fluorocarbon Liquid or silicone used for specialized purposes. After about simple, lubricants more sophisticated than liquid. the 16th century, and porpoise oil simple crude oil were unnecessary. Most When the operating conditions of tem• came into wide use. industrial shops kept a barrel of oil in the perature and pressure are too severe for liq• With the rise of the petroleum industry comer for refilling cans used to squirt oil uids or semisolids, solid lubricating in the 19th century, petroleum-based lubri• into the machines. Some employee would materials can be used. In rocket-propelled cants quickly dominated the field. Petro• get the messy job of dribbling oil into all devices, the lubricant actually comes into leum itself had been known long before bearings, using the same type of lubricant contact with oxidants and reactive fuels. this-since the ancient Assyrians and for each moving part, no matter what its Unfortunately, solid lubricants usually lack Egyptians, who used it for lighting and purpose. good adhesive properties, requiring the embalming. American Indians used crude The development of larger machines use of binder materials to bond the lubri• petroleum medicinally. The American col• used at greater speeds and with tighter cant to the surfaces of the moving parts. onists who discovered petroleum while specifications for mass production led to The most common powdered solid lubri• drilling for salt considered it a nuisance specialization in lubricating materials. A cants are graphite, tungsten disulfide, mo• and poured it away as waste. general-purpose oil that worked well lybdenum disulfide, zinc oxide, and boron One of the earliest references to crude oil enough on a simple machine could not nitride. These materials can function as lu• used as a lubricant is from a cotton spin• meet the new requirements for higher tem• bricants up to temperatures as high as ning mill in Pittsburgh, Pennsylvania, in peratures and speeds. Operational failures 650°C; with such properties, they are used 1845. The owner apparently tried a sample that could be traced directly to friction and in many hot metalworking operations. of mineral oil obtained from a salt well wear became more and more frequent. Chemists, physicists, engineers, oil re• drilled on the Allegheny River. Mineral Better lubricants, special additives, and finers, and metallurgists have all combined oils, derived from crude petroleum, con• automatic dispensing systems have been their expertise to develop new materials for sist of a complex mixture of saturated and major advances in the science of lubrica• lubrication that can withstand the most unsaturated aliphatic and aromatic hydro• tion. Applications for automobiles, air• rigorous specifications for jet engines, carbons. planes, turbojets, diesel locomotives, and space flight, and ultrafast processing, as The Pittsburgh cotton-mill owner experi• high-power machinery have led to special• well as new applications still being devel• mented with his mineral oil by mixing it ized lubricants. oped for industry and research. with the sperm oil he had been using to Since the 1950s, synthetic liquid lubri- Kevin j. Anderson

MRS BULLETIN/OCTOBER 1991 69