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Lubricants like mineral oil or synthetic oil are used to reduce the friction and wear between sliding

parts. A lot of additives are used in base oil to enhance the lubricating performance like anti wear,
anti rust, anti corrosion, anti friction, extreme pressure, pour point, viscosity modifier and many
other types additives. Different composition of additives are used in base oil according to need of
lubricating oil such as ball and sliding bearings, sliding members, ball screw, different types of
gears, friction assemblies, joints, auto mobile engine and other many application where friction
and wear to be reduced. Function of these additives in base oil is not to reduce the friction and
wear but also to enhance the life of machine and also used for heat dissipation between mating
surfaces, enhance the thermal conductivity of fluid.
On the other hand from last few decades there is a lot of other additives are proposed and
recommended to use in mineral oil or synthetic oil and grease to increased the performance of
lubricating oil such as micro size particle and nano size particle. While using these particle in base
oil the substance consisting of nano sized particle attribute good tribological properties as
compared to micro sized particle.
Nano lubricant
Nano lubricants is a new class of lubricants, in which a nano sized particle are disperse in base oil
to enhance the tribological properties of lubricating oil. Many researchers has been shown that
when some nano sized particle are added into base oil, ther tribological properities of lubricating
oil improved as other conventional oil. Due to good tribological properties of nano size particle in
base oil it attains a great interest of scientist and engineers. Also many researchers showed that the
nano size particle lubricating oil improved the load carrying capacity heat dissipation, heat transfer
co-efficient and thermal conductivity oil.
Mechanism of nano sized particle.
The actual mechanism of nano size particle in base oil is still in process but many researcher
hypothesis that it is due to colloidal effect, rolling effects, protection effect and third body effect in
base oil under boundary condition regime. When nano sized particle are added in base oil it will
improved the tribological properties lubricating oil and it was found that various mechanism are
effect a) ball bearing effect of particle existed between rubbing surface b) surface polish c)
increasing surface hardness
Effect of nano particle size
The effect of nano particle size on tribological properties are based on
1) the size nano particle determine their intrinsic mechanical and physicochemical properties that
influence the tribological properties. The hardness of particle increase while decreasing the
size of particle. While at critical grain size below than 10nm become softer and exhibit poor
tribological properties.
2) Nano particle based lubrication system needs to stay in contact zone during load and shearing
to protect the rubbing surface. From this point of view the effect of nano particles size cab
comes into play an important role when we consider the asperities of rubbing surface contact
as physical barriers that keep nano particles within the contact zone.
3) Third, homogeneity of nano particle size that strongly controls its ability to perform reliably
and smoothly is strongly influenced by collidal effect. It paly an important role of stability and
dispersonability of nnao particle in base oil.

The effect of nano particle shape

The shape of nanoparticles is an very important parameter that may be effect the tribological
behavior of lubricating oil. different shape of particle are used in base oil like spherical, nano
sheets and elliptical. The hape of particle determines the pressure experienced while loading. For
example nano sphere particle experienced good pressure under large load while nano sheets
experience bad pressure under high load.
The effect of nanostructure
The internal structure of nano particles can influence the mechanical properties and also their
tribological behavior. For instance the vacancies within the nano materials act as pinning centers
inhibiting the dislocation motion, thereby enhancing the mechanical strength within a certain
concentration. Thus the presence of a limited amount of atomic vacancies can enhance the
tribologival behavior. But exssive amount of cavities or vacancies are disadvantges for tribological
The effect of surface fictionalization
The effect of rubbing surface also paly an important role on tribological behavior of nano particle
lubrication. When the rubbing surfaces are well finished and smooth then the tribological behavior
of nano particle lubrication is good as compared to unsteady and rough rubbing surface.
The effect of nano aprticle concentration
The concentration of nanoparticles within base oil strongly influence the tribological behavior of
lubricating system. In general a optimum concentration of nano particles gives minimum coefficient of friction and wear loss. If the concentration of nano particle is above or below the
optimum ratio its behavior on tribologicsl properties is not good.