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Additives in lubricant: Types and chemical composition of lubricant additives Semira Hajrlahovic Mehic, M.Sc. Inspector Counsellor Chemicals Office of the Republic of Slovenia 1 Content • • • • • Lubricant function Formulation of lubricants Types of additives Main reasons to add additives Typical additives 2 Lubricant function • Modern equipment must be lubricated in order to prolong its lifetime • A lubricant performs a number of critical functions: – lubrication, cooling, cleaning, suspending, – protecting metal surfaces against corrosive damage…. 3 Formulation of lubricants • Lubricant comprises a base and an additive package • The primary function of the base fluid: – to lubricate and act as a carrier of additives • The function of additives: – to enhance an already existing property of the base fluid • viscosity, viscosity index, pour point, oxidation resistance – to add a new property • cleaning/suspending ability, antiwear performance, corrosion control 4 Formulation of lubricants • Typically lubricants contain 90% base oil and less than 10% additives • Base : – most often petroleum fractions (called mineral oils) – vegetable oils or synthetic liquids such as hydrogenated polyolefins, esters, silicones, fluorocarbons are sometimes used as base oils 5 Formulation of lubricants • Non-liquid lubricants include grease, powders (dry graphite, molybdenum disulfide, tungsten disulfide) • Dry lubricants such as graphite, molybdenum disulfide and tungsten disulfide offer lubrication at temperatures (up to 350 °C) • The amount of additive used varies from a few hundredths of a percent to 30% or more 6 Lube oil base and additives logic • The lube oil base is the building block – which appropriate additives are selected and properly blended – to achieve a balance in performance characteristics of the finished lubricant • To achieve the highest levels of performance in finished lubricants: – understanding of the interactions of base oil and additives – matching those to requirements of machinery and operating conditions 7 Types of additives • Some additives impart new and useful properties to the lubricant • Some enhance properties already present • Some act to reduce the rate at which undesirable changes take place in the product during its service life 8 Main reasons to add additives • To impart desirable characteristics • Improvements in lubricating oil over the last decades • Are organic compounds like: – chlorine (as in chlorinated esters), – sulphur (as in sulphurized oils) – phosphorus (as in tricresyl phosphate) 9 Main reasons to add additives • To protect the lubricant in service by limiting the chemical change and deterioration • To protect the mechanism from – harmful combustion products – malfunctioning combustion products and – malfunctioning lubricating oil • To improve existing physical properties and to create new beneficial characteristics 10 Typical additives • Increase oil and machinery life – effect many oil and surface characteristics • Decrease sludge on surface (metal), varnish the metal parts, clean the surface • Some are multifunctional: – certain viscosity index improvers also have function as pour point depressants – dispersants or anti-wear agents have also function as oxidation inhibitors 11 Typical additives • • • • • • • • • • • Friction modifiers Anti-wear agents Extreme-pressure additives Anti-oxidation additives Rust and corrosion inhibitors Foam inhibitors Oiliness agents Detergents and dispersants Alkaline agents Pour point depressants (PPD) Viscosity index improvers 12 Friction modifiers • Added to lubricants to reduce the surface friction of the lubricated parts • Mechanism similar to rust and corrosion inhibitors – form durable low resistance lubricant films via adsorption on surfaces and via association with the oil • Polar chemical compounds with high affinity for metal surfaces and possessing long alkyl chains – long-chain fatty acids, their derivatives, and the molybdenum compounds 13 Anti-wear agents • Protect rubbing surfaces operating with film boundary lubrication – Organo-sulfur and organo-phosphorus compounds: • organic polysulfides • phosphates, dithiophosphates • dithiophosphates (ZDDP) –Also antioxidant 14 Extreme-pressure additives • Form extremely durable protective films by thermo-chemically reacting with the metal surfaces • The film can withstand extreme temperatures and mechanical pressures and minimizes direct contact between surfaces • Anti-wear agents have a lower activation temperature than the extreme-pressure 15 Extreme-pressure additives • Chlorinated paraffins – 2,3,4,5,6,8-hexachlorodecane (short-chained chlorinated paraffin) • Sulphurized fats • Zinc dialkyldithiophosphate (ZDDP) • Molybdenum disulfide (MoS2) 16 Anti-oxidation additives • One of the most important aspects of lubricating oils • Engine's metal parts (copper and iron) act as effective oxidation catalysts – engine oils are probably more susceptible to oxidation • High temperature, high pressure, high friction, and high metal concentration in motors, lead to oxidation of lubricating oil • Oxidation generally increase oil viscosity and results in formation of resins, lacquers and acidic compounds 17 Anti-oxidation additives • Protect by forming the oxidation of metal component – Sulfur compounds – Phosphorus compounds – Sulfur-phosphorus compounds – Aromatic amine compounds – Hindered phenolic compounds – Organo-zinc compounds (Zn- dithiophosphate ZDDP) – Organo-copper compounds – Organo-molybdenum compounds 18 Rust and corrosion inhibitors • Rust inhibitors: compounds with high polar attraction toward metal surfaces • By physical or chemical interaction at the metal surface, they form a continuous film that prevents water from reaching the metal surface • Amino salts and salts of sulphonic acids (functional group R-SO3−) 19 Rust and corrosion inhibitors • Form a protective film on the bearing surfaces – prevents the corrosive materials from reaching or attacking the metal • The film may be adsorbed on the metal or chemically bonded to it • Inclusion of highly alkaline materials in the oil help to neutralize strong acids, greatly reducing this corrosion 20 Rust and corrosion inhibitors • • • • Alkaline compounds Organic acids Esters Amino-acid derivatives 21 Foam inhibitors • Foaming of lubricants is a very undesirable effect – can cause enhanced oxidation by the intensive mixture with air • Dimethylsilicones (dimethylsiloxanes) 22 Oiliness agents • Reduce friction seizure point and wear rates • Glycerin monooleate (GMO) • • Pentaerythritol Monooleate (PMO) 23 Detergents • Tend to neutralize the deposits • before formation under high temperature and pressure conditions, or • as a result of using a fuel with high sulphur content • The organic portion of the detergent (“soap”), has the ability to – associate with the salts to keep them suspended in the bulk lubricant – to suspend nonacidic oxygenated products, such as alcohols, aldehydes, and resinous oxygenates • To keep surfaces clean 24 Detergents 25 Detergents in lubricants • Phenolates, sulphonates and phosphonates of alkaline and alkaline-earth elements – calcium (Ca), magnesium (Mg), sodium (Na) or Ba (barium) salts • Sodium dodecylbenzenesulfonate 26 Dispersants • Used to disperse or suspend the deposits forming contaminants • More effective than detergents due to higher molecular weight • Molecules have a polar charge at one end which attracts and holds the deposits • Polyesters and benzlamides 27 Dispersants • Long chain hydrocarbons succinimides (such as polyisobutylene succinimides) 28 Detergents and dispersants • Together make about 45–50%, of the total volume of the lubricant additives manufactured • Differences: – Dispersants are metal-free, detergents contain metals (magnesium, calcium) – Dispersants have little or no acid-neutralizing ability, but detergents do – Dispersants are much higher in molecular weight, (approx. 4–15 times higher) than the organic portion (soap) of the detergent 29 Alkaline agents • Alkaline level (total base number=TBN) must m atch the acidity of the lubricant • Neutralize acids of the oil and include additives such as dispersants and detergents • Acid neutralizing alkalis are present in the detergents – failure to keep an oil alkaline can lead to damage to bearings due to acidic attack as well as increased liner wear 30 Pour point depressants (PPD) • Pour point: • The lowest temperature at which the oil is fluid • Improve low temperature viscosity – Polymethacrylate (PMA) – Styrene Esters • Oils used under low-temperature conditions must have low pour points 31 Pour point depressants (PPD) • Two general types: – Alkylaromatic polymers adsorb on the wax crystals as they form, preventing them from growing and adhering to each other – Polymethacrylates co-crystallize with wax to prevent crystal growth • The additives do not entirely prevent wax crystal growth, but rather lower the temperature at which a rigid structure is formed 32 Viscosity index improvers • Probably the most important single property of a lubricating oil • Viscosity varies with temperature → it is necessary to consider the actual operating temperature of the oil in the machine • Different oils have different rates of change of viscosity with temperature – a distillate oil from a naphthenic base crude shows a greater rate of change of viscosity than a distillate oil from a paraffin crude 33 Viscosity index improvers • Can be blended into oils to increase V.I. – But not always stable in lubricating environments exposed to shear or thermal stressing • Methacrylate polymers and copolymers 34 Viscosity index improvers • Acrylate polymers • Olefin polymers and copolymers • Styrene butadiene copolymers 35 General capabilities expected from an engine lubricant • Dispersivity or capacity to keep the cold parts of an engine clean • Detergency or capacity to keep hot parts of an engine clean • Thermal strength or capacity to withstand temperature changes • Anti-oxidant or capacity to resist the action of oxygen 36 General capabilities expected from an engine lubricant • Anti-wear or capacity to contain wear • Anti-scuffing or capacity to preserve oil film even in the presence of high pressures • Alkalinity reserve/capacity to neutralize acids formed during combustion • Deemulsibility or capacity to separate contaminants 37 General capabilities expected from an engine lubricant • Resistance to hydrolysis or capacity to withstand the action of water which can affect additives • Centrifuge ability and filterability or capacity to separate insoluble elements • Anti-rust, anti-corrosive and anti-foam – just some of the other properties which protect the metalic object from wear down 38 Thank you! semira.hajrlahovic-mehic @gov.si 39