Chemical compounds that improve the lubricant performance of base oil
Oil additives are
chemical compounds that improve the
lubricant performance of base
oil (or oil "base stock"). The manufacturer of many different oils can utilize the same base stock for each formulation and can choose different additives for each specific application. Additives comprise up to 5% by weight of some oils.[1]
Nearly all commercial
motor oils contain additives, whether the oils are
synthetic or
petroleum based. Essentially, only the
American Petroleum Institute (API) Service SA motor oils have no additives, and they are therefore incapable of protecting modern
engines.[2] The choice of additives is determined by the application, e.g. the oil for a
diesel engine with
direct injection in a
pickup truck (API Service CJ-4) has different additives than the oil used in a small
gasoline-powered
outboard motor on a boat (2-cycle engine oil).
Types of additives
Oil additives are vital for the proper
lubrication and prolonged use of motor oil in modern
internal combustion engines. Without many of these, the oil would become contaminated, break down, leak out, or not properly protect engine parts at all
operating temperatures. Just as important are additives for oils used inside
gearboxes,
automatic transmissions, and
bearings. Some of the most important additives include those used for
viscosity and
lubricity, contaminant control, for the control of chemical breakdown, and for seal conditioning. Some additives permit lubricants to perform better under severe conditions, such as extreme pressures and temperatures and high levels of contamination.
Controlling chemical breakdown
Detergent additives, dating back to the early 1930s,[3] are used to clean and neutralize oil impurities which would normally cause deposits (
oil sludge) on vital engine parts. Typical detergents are magnesium sulfonates.
Corrosion or
rust inhibiting additives retard the oxidation of metals inside an engine.
Metal deactivators create a film on metal surfaces to prevent the metal from causing the oil to be oxidized.
Bases may be used to combat chemical decomposition of the base stock oil in the presence of acids. When oil is subjected to shear wear and oxidation by air and combustion gases, it will have a tendency to collect acids and increase its
Total Acid Number (TAN). For example, the breakdown acids found in used
gear oil may include carbocyclic acids, ketones, esters, and nitration and sulfation byproducts.[4] However, organic and inorganic bases and detergents are included in most formulated oils, as discussed in the following paragraph, so some (but not all) of these contaminants will be neutralized. Gear oil degradation and longevity can be measured by its TAN.
Alkaline additives are used to neutralize the acids mentioned previously, and also help prevent the formation of sulfates in a working oil. A formulated oil will often have KOH (
potassium hydroxide), a strong base, in small amounts, as it is an effective neutralizer used in refining petroleum.[5] Additives that perform a similar function in a motor oil include magnesium and calcium sulphonates, salicylates, and phenates.[4] These are the detergent additives mentioned previously. To measure the alkalinity potential of a formulated oil, it is tested to obtain the equivalent amount of KOH to arrive at the oil's
Total Base Number (TBN) with units of mg of KOH per gram of oil. As the additive package degrades, TBN will decrease until the motor oil needs to be replaced. Further use of the oil will permit sludge, varnish, and metal corrosion.[4] An important measurement of a
motor oil's degradation and longevity is its TBN relative to a new oil.
For viscosity
Viscosity modifiers make an oil's viscosity higher at elevated temperatures, improving its
viscosity index (VI). This combats the tendency of the oil to become thin at high temperature. The advantage of using less viscous oil with a VI improver is that it will have improved low temperature fluidity as well as being viscous enough to lubricate at
operating temperature. Most
multi-grade oils have
viscosity modifiers. Some synthetic oils are engineered to meet multi-grade specifications without them. Viscosity modifiers are often plastic polymers. Virtually all oils require a specific range of viscosity as a working fluid, so viscosity is the primary factor that determines if an oil is acceptable for any particular application. As oils degrade from use, their viscosity will decrease, eventually requiring their replacement.
Inorganic Fullerene-like Tungsten Disulfide (IF-WS2)
nanoparticles with a hollow
sphere (
Fullerene-like) morphology, provide extreme
lubricity, anti-friction and high impact resistance (up to 35 GPa). The IF-WS2 particles were discovered by Professor
Reshef Tenne at the
Weizmann Institute of Science. Unlike standard lubricant additives that have
platelet-like structures with moderate tribological properties, IF-WS2 particles have tens of caged concentric layers, making these particles excel under extreme pressure or load. The IF-LWS2 particles are available in dry
powder form as well as a
dispersion in oil, water, and
solvent. These dispersions are used in the formulation of various
lubricants,
grease,
metalworking fluids,
coatings,
paints, and
polymers.
For contaminant control
Metal particles released by wear are unintentional and undesirable oil additives. Most large metal particles and impurities are removed in situ using either
magnets or
oil filters.
Antimisting agents prevent the
atomization of the oil. Typical antimisting agents are silicones.[1]
Wax crystal modifiers are dewaxing aids that improve the ability of
oil filters to separate wax from oil. This type of additive has applications in the refining and transport of oil, but not for lubricant formulation.
Motor oil is manufactured with numerous additives, and there are also
aftermarket additives. A glaring inconsistency of mass-marketed aftermarket oil additives is that they often use additives which are foreign to motor oil. On the other hand, commercial additives are also sold that are designed for extended drain intervals (to replace depleted additives in used oil) or for formulating oils
in situ (to make a custom motor oil from base stock). Commercial additives are identical to the additives found in off-the-shelf motor oil, while mass-marketed additives have some of each.
Although PTFE, a solid, was used in some aftermarket oil additives, some users said that the PTFE clumped together, clogging filters. Certain people in the 1990s reported that this was corroborated by
NASA[12] and U.S. universities.[13] However, if the PTFE particles are smaller than those apparently used in the 1980s and 1990s, then PTFE can be an effective lubricant in suspension.[14] The size of the particle and many other interrelated components of a lubricant make it difficult to make blanket statements about whether PTFE is useful or harmful. Although PTFE has been called "the slickest substance known to man",[15][16] it would hardly do any good if it remains in the
oil filter.
Some mass-market engine oil additives, notably the ones containing
PTFE/
Teflon (e.g.
Slick 50)[17] and
chlorinated paraffins (e.g.
Dura Lube),[18] caused a major backlash by consumers; the U.S.
Federal Trade Commission investigated many mass-marketed engine oil additives in the late 1990s.
Although there is no reason to say that all oil additives used in packaged engine oil are good and all aftermarket oil additives are bad, there has been a tendency in the aftermarket industry to make unfounded claims regarding the
efficacy of their oil additives. These unsubstantiated claims have caused consumers to be lured into adding a bottle of chemicals to their engines which do not lower emissions, improve wear resistance, lower temperatures, improve efficiency, or extend engine life more than the (much cheaper) oil would have. Many consumers are convinced that aftermarket oil additives work, but many consumers are convinced that they do not work and are in fact detrimental to the engine. The topic is hotly debated on the
Internet.
Oil analysis – Laboratory analysis of an oil based lubricant's properties and contaminants
Tribology, the science of friction, lubrication and wear
References
^
abThorsten Bartels et al. "Lubricants and Lubrication" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Weinheim.
doi:
10.1002/14356007.a15_423
^Roger F. Sebenik et al. "Molybdenum and Molybdenum Compounds" in Ullmann's Encyclopedia of Chemical Technology 2005; Wiley-VCH, Weinheim.
doi:
10.1002/14356007.a16_655
^A
NASA research report is purported to say about PTFE oil additives, "In the types of bearing surface contact we have looked at, we have seen no benefit. In some cases we have seen detrimental effect. The solids in the oil tend to accumulate at inlets and act as a dam, which simply blocks the oil from entering. Instead of helping, it is actually depriving parts of lubricant." The source of this quote is unknown, but the quote itself appears in the magazine article referenced below.
^See
Road Rider Magazine (now Motorcycle Consumer News) article from August 1992 by Fred Rau, which has been reprinted extensively, and see
oilsfilters.htm for a contemporary discussion.
^See
Nanoflon, a PTFE that is small enough for suspension in lubricants and used commercially for that purpose.