200 Lubricant Additives: Chemistry and Applications
The difference between the two types of fi lms and other lubrication modes is best illustrated by
the data presented in Table 7.3.
7.4 CHEMISTRY OF ORGANIC FRICTION MODIFIERS
Organic FMs are generally long, slim molecules with a straight hydrocarbon chain consisting of at
least 10 carbon atoms and a polar group at one end. The polar group is one of the governing factors
in the effectiveness of the molecule as an FM. Chemically, organic FMs can be found within the
following categories [16]:
Carboxylic acids or their derivatives, for example, stearic acid and partial esters
Amides, imides, amines, and their derivatives, for example, oleylamide
Phosphoric or phosphonic acid derivatives
Organic polymers, for example, methacrylatesAnother classifi cation can be given by mode of action and FM type (Table 7.4).
Owing to the different mode of actions, the mechanism of friction reduction varies for each
category.
The next section further deals with details about their mode of action, and another section deals
with the current chemistry used as well as specifi c products.
7.4.1 FRICTION MODIFIER MECHANISMS
7.4.1.1 Formation of Reacted Layers
Similar to AW additives, protective layers are formed by chemical reaction of the additive with the
metal surface. However, the principal difference is that the reaction has to occur under the relatively
TABLE 7.3
Lubrication Modes versus Friction Coeffi cient
Lubrication Mode Friction Coeffi cient Comparison
Nonlubricated surface 0.5–7 Dragging an irregular rock over rocky ground
AW/EP fi lms 0.12–0.18 Dragging a fl at stone over a fl at rock
Friction-modifi ed fi lms 0.06–0.08 Ice skating
EHL 0.001–0.01 HydroplaningTABLE 7.4
FM Type and Mode of Action
Mode of Action/Type of FM Products
Formation of reacted layers Saturated fatty acids, phosphoric and thiophosphoric
acids, sulfur-containing fatty acids
Formation of absorbed layers Long-chain carboxylic acids, esters, ethers, amines,
amides, imides
Formation of polymers Partial complex esters, methacrylates, unsaturated fatty
acids, sulfurized olefi ns
Mechanical types Organic polymers