Most modern lubricating oils require the use of chemical additives to improve their performance capabilities beyond those of the base oils used. There are hundreds of additives which when blended with base oils change their characteristics significantly the following are general definitions of some of the major types of the additive used in the manufacturers of modern lubricating oils
- Antifoam Agents – promote more rapid break-down of foam bubbles by weakening oil films between them.
- Antiseptic Agents/bactericides – prevent the growth of micro-organisms and bacteria in oil/water emulsions.
- Antistatic Additive- increases the conductivity of a hydrocarbon fuel to hasten the dissipation of electrostatic charges during high speed dispensing, thereby reducing the fire explosion hazard
- Antiwear Agents-are usually added to oils to reduce wear of machine or engine parts operating under boundary lubrication conditions.
- Color Stabilizers-react chemically with the base oil to stabilize its color.
- Corrosion Inhibitor- Additive that protects lubricated metal surfaces from chemical attack by water or other contaminant.
- Demulsive assist the natural ability of the oil to separate rapidly from water these agents are also helpful in rust inhibition.
- Detergent- dispersant Agents – prevent the formation of deposits on metal surfaces. Detergents suspend contaminants by reacting with them to form compounds which remain in suspension in the oil. Dispersants absorb onto contaminants, keeping them dispersed in the oil
- Emulsifiers-are surface-active chemicals added to base oils to reduce intermolecular forces and permit intimate mixing of very small oil droplets in water
- Extreme Pressure Additives – react with rubbing metal surfaces which are not sufficiently separated by the oil film, to form antiweld compound which prevent complete seizure
- Friction Modifiers – Modifies wax crystal formation to reduce interlocking thus enabling lubricant to flow at low temperatures
- Pour Point Depressant – Modifies wax crystal formation to reduce interlocking thus enabling lubricant to flow at low temperatures
- Inhibitor – additive that improves the performance of a petroleum product by controlling undesirable chemical reactions, i.e., oxidation inhibitor, rust inhibitor, etc.
- Metal Deactivators- form a film over metal surfaces to prevent participation of these metals as catalysts in promoting oxidation of the oil
- Oxidation Inhibitors – prevent or retard oxidation of the oil thereby reducing viscosity increase and the formation of sludge, varnish, and acids
- Pour Point Depressants – lower the pour point of paraffinic oil by modifying the form of wax crystallization.
- Rust and Corrosion Inhibitors – prevent rust and corrosion of metal surfaces in contact with the lubricant
- Tackiness Agents – improve the adhesive qualities of an oil
- Viscosity Index Improvers – are high molecular weight polymers added to oils to increase the viscosity index