1.Definition of lubrication

　  Lubrication is the process, or technique employed to reduce wear of one or both surfaces in close proximity, and moving relative to each another, by interposing a substance called lubricant between the surfaces to carry or to help carry the load (pressure generated) between the opposing surfaces. The interposed lubricant film can be a solid, (eg graphite, MoS₂)[1] a solid/liquid dispersion, a liquid, a liquid-liquid dispersion (greases) or exceptionally a gas.
　  In the most common case the applied load is carried by pressure generated within the fluid due to the frictional viscous resistance to motion of the lubricating fluid between the surfaces.
　  Lubrication can also describe the phenomenon such reduction of wear occurs without human intervention (aquaplaning on a road).
　  The science of friction, lubrication and wear is called tribology.
　  Adequate lubrication allows smooth continuous operation of equipment, with only mild wear, and without excessive stresses or seizures at bearings. When lubrication breaks down, metal or other components can rub destructively over each other, causing destructive damage, heat, and failure.

2. Lubrication theory

　  A branch of fluid dynamics, lubrication theory is used to describe the flow of fluids (liquids or gases) in a geometry in which one dimension is significantly smaller than the others.
　  Interior flows are those where the boundaries of the fluid volume are known, and include those inside bearings. Here a key goal of lubrication theory is to determine the pressure distribution in the fluid volume, and hence the forces on the bearing components. The working fluid in this case is often termed a lubricant.
　  Free film lubrication theory is concerned with the case in which one of the surfaces containing the fluid is a free surface. In that case the position of the free surface is itself unknown, and one goal of lubrication theory is then to determine this. Surface tension may then be significant, or even dominant. Issues of wetting and dewetting then arise. For very thin films (thickness less than one micrometre), additional intermolecular forces, such as disjoining forces, may become significant.

3. Lubricant

　  A lubricant (sometimes referred to as "lube") is a substance (often a liquid) introduced between two moving surfaces to reduce the friction between them, improving efficiency and reducing wear. They may also have the function of dissolving or transporting foreign particles and of distributing heat.
One of the single largest applications for lubricants, in the form of motor oil, is to protect the internal combustion engines in motor vehicles and powered equipment.
　  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, silicones, fluorocarbons and many others are sometimes used as base oils. Additives deliver reduced friction and wear, increased viscosity, improved viscosity index, resistance to corrosion and oxidation, aging or contamination, etc.
　  Lubricants such as 2-cycle oil are also added to some fuels. Sulfur impurities in fuels also provide some lubrication properties, which has to be taken in account when switching to a low-sulfur diesel; biodiesel is a popular diesel fuel additive providing additional lubricity.
Non-liquid lubricants include grease, powders (dry graphite, PTFE, Molybdenum disulfide, tungsten disulfide, etc.), teflon tape used in plumbing, air cushion and others. Dry lubricants such as graphite, molybdenum disulfide and tungsten disulfide also offer lubrication at temperatures (up to 350 °C) higher than liquid and oil-based lubricants are able to operate. Limited interest has been shown in low friction properties of compacted oxide glaze layers formed at several hundred degrees Celsius in metallic sliding systems, however, practical use is still many years away due to their physically unstable nature.
　  Another approach to reducing friction and wear is to use bearings such as ball bearings, roller bearings or air bearings, which in turn require internal lubrication themselves, or to use sound, in the case of acoustic lubrication.
　  In addition to industrial applications, lubricants are used for many other purposes. Other uses include bio-medical applications (e.g. lubricants for artificial joints) and the use of personal lubricant for sexual purposes.

4. Purposes of lubricants

Keep moving parts apart	Reduce friction	Transfer heat	Carry away contaminants and debris
Transmit power	Protect against wear	Prevent corrosion	Seal for gasses

5. Types of lubricants

Gaseous lubricants	Liquid lubricants	Lanolin	Water
Mineral oil	Vegetable (natural) oils	Synthetic oils

6. Solid lubricants

Teflon or PTFE

Non-metals

Metal/alloy

7.Major publications

Peer reviewed 
　  Tribology Transactions 
　  Journal of Synthetic Lubricants

Trade periodicals 

Tribology and Lubrication Technology	Fuels & Lubes International	Oiltrends	Lubes n’ Greases
Compoundings	Chemical Market Review	Machinery lubrication

Reference:

[1] www.engineersedge.com/lubrication/applications_solid_lubrication.htm - 14k

(From:http://en.wikipedia.org)