Lubricant
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A lubricant (colloquially, lube) is a substance (usually a liquid) introduced between two moving surfaces to reduce the friction and wear between them. Worldwide, more than 50 million tonnes of lubricants are consumed annually. Automotive engine lubricants comprise approximately 50% and hydraulic fluids with transmission oils 30% of lubricants volume-wise. In developed nations, lubricants contribute to nearly 1/4 of total pollution released to environment.
Typically lubricants contain 90% base oil (most often petroleum fractions, called mineral oils) and less than 10% additives. Vegetable oils or synthetic liquids such as hydrogenated polyolefins, esters, silicone, fluorocarbons and many others are sometimes used as base oils. Additives deliver reduced friction and wear, increased viscosity, resistance to corrosion, aging or contamination, etc.
Non-liquid lubricants include grease, powders (dry graphite, PTFE, Molybdenum disulfide, etc.), teflon tape used in plumbing, air cushion and others. An alternative way to reduce friction and wear is to use bearings such as ball bearings, roller bearings or air bearings.
In addition to automotive and industrial applications, lubricants are used for many other purposes, including personal hygiene, e.g. K-Y jelly, often used as a sexual lubricant, bio-medical applications (e.g. lubricants for artificial joints) and others.