U.S. patent application number 12/007555 was filed with the patent office on 2008-09-25 for nanoparticulate based lubricants.
Invention is credited to Atanu Adhvaryu, Ajay P. Malshe, Philip Hugh McCluskey, Arpana Verma.
Application Number | 20080234149 12/007555 |
Document ID | / |
Family ID | 39775359 |
Filed Date | 2008-09-25 |
United States Patent
Application |
20080234149 |
Kind Code |
A1 |
Malshe; Ajay P. ; et
al. |
September 25, 2008 |
Nanoparticulate based lubricants
Abstract
A method of making a nanoparticulate based lubricant is
disclosed. The method includes providing solid lubricant material
with particles having a size less than or equal to about 500
nanometers, and treating the particles to create composite
nanoparticles. The composite nanoparticles includes the solid
lubricant material and at least a second material.
Inventors: |
Malshe; Ajay P.;
(Springdale, AR) ; Adhvaryu; Atanu; (Peoria,
IL) ; Verma; Arpana; (Fayetteville, AR) ;
McCluskey; Philip Hugh; (Gramado, BR) |
Correspondence
Address: |
CATERPILLAR/FINNEGAN, HENDERSON, L.L.P.
901 New York Avenue, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
39775359 |
Appl. No.: |
12/007555 |
Filed: |
January 11, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60880025 |
Jan 12, 2007 |
|
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Current U.S.
Class: |
508/150 ;
508/162; 508/166; 508/167; 508/371 |
Current CPC
Class: |
C10M 171/06 20130101;
C10M 2201/06 20130101; C10M 2223/045 20130101; C10M 2201/065
20130101; C10N 2010/08 20130101; C10M 141/10 20130101; C10N 2030/06
20130101; C10M 2219/068 20130101; C10N 2040/04 20130101; C10N
2010/02 20130101; C10M 2201/066 20130101; C10M 2223/02 20130101;
C10N 2020/06 20130101; C10M 2219/068 20130101; C10N 2010/12
20130101; C10M 2223/02 20130101; C10N 2010/02 20130101; C10M
2223/045 20130101; C10N 2010/04 20130101; C10M 2223/02 20130101;
C10N 2010/02 20130101; C10M 2219/068 20130101; C10N 2010/12
20130101; C10M 2223/045 20130101; C10N 2010/04 20130101 |
Class at
Publication: |
508/150 ;
508/371; 508/162; 508/167; 508/166 |
International
Class: |
C10M 125/24 20060101
C10M125/24; C10M 125/22 20060101 C10M125/22; C10M 125/04 20060101
C10M125/04 |
Claims
1. A method of making a nanoparticulate based lubricant comprising;
providing solid lubricant material with particles having a size
less than or equal to about 500 nanometers; and treating the
particles to create composite nanoparticles, wherein the composite
nanoparticles includes the solid lubricant material and at least a
second material.
2. The method of claim 1, wherein the step of providing includes
reducing the size of the particles to less than or equal to 500
nanometers.
3. The method of claim 1, wherein the step of providing includes
reducing the size of the particles to a range between about 50-200
nanometers.
4. The method of claim 1, wherein the composite nanoparticles
include a central core and an outer shell wherein, the central core
is substantially made of one or more materials and the outer shell
is substantially made of the second material.
5. The method of claim 4, wherein the second material includes one
of a chemical and a reaction product of the chemical.
6. The method of claim 5, wherein the chemical is selected from a
group consisting of zinc dialkyl dithio phosphate (ZDDP), sodium
tripolyphosphate, potassium diphosphate, 2-ethylhexyl molybdenum
dithiophosphate, and combinations thereof.
7. The method of claim 4, wherein the outer shell substantially
encapsulates the central core.
8. The method of claim 4, further including a third material
disposed within cavities in the central core.
9. The method of claim 8, wherein the third material includes one
of a chemical and a reaction product of the chemical.
10. The method of claim 1, wherein the step of treating includes
chemically reacting the particles with a chemical.
11. The method of claim 1, wherein the solid lubricant material is
selected from a group consisting of molybdenum disulphide, tungsten
disulphide, niobium diselinide, gold, silver, lead, tin, enhanced
pressure chemicals, and combinations thereof.
12. The method of claim 1, further including mixing the composite
nanoparticles with a base oil, wherein the base oil is selected
from a group consisting of an organic oil, a hydrocarbon based oil,
a synthetic liquid, or combinations thereof.
13. The method of claim 12, further including mixing the composite
nanoparticles with one or more lubricant additives.
14. The method of claim 1, wherein the step of providing includes
reducing the size of the solid lubricant material to a powder
having a first predetermined size greater than about 500
nanometers.
15. The method of claim 14, wherein the step of providing further
includes reducing the powder from the first predetermined size to
particles having the size less than or equal to approximately 500
nanometers.
16. A nanoparticle for lubricant applications comprising; a core
made substantially of a first material and having a size less than
or equal to about 500 nanometers wherein, the first material
includes one or more solid lubricant materials; and a shell on an
external surface of the core, wherein the shell is substantially
made of a second material.
17. The nanoparticle of claim 16, wherein the shell substantially
surrounds the core.
18. The nanoparticle of claim 16, wherein the second material is
one of a chemical agent and a reaction product of the chemical
agent.
19. A lubricant comprising; a base oil; composite nanoparticles
that include a core made of one or more materials and a shell made
of another material, wherein the shell substantially surrounds the
core; and lubricant additives.
20. The lubricant of claim 19, wherein a size of the composite
nanoparticles is less than or equal to about 500 nanometers.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from U.S. Provisional Application No. 60/880,025 to Malshe
et al. filed on Jan. 12, 2007, the entire contents of which are
incorporated herein by reference.
TECHNICAL FIELD
[0002] The present disclosure relates generally to lubricants and,
more particularly, to lubricants containing nanoparticles of a
solid lubricant.
BACKGROUND
[0003] Lubricants are introduced between contacting (sliding or
rolling) surfaces of dynamic systems to reduce the friction and
wear therebetween. Lubrication occurs when these moving surfaces
are separated by a lubricant film and an applied load is carried by
the lubricant. In general, four regimes of lubrication are broadly
defined based upon the mechanism by which the lubricant operates to
reduce friction between the moving parts. These four regimes are:
hydrodynamic lubrication, mixed lubrication, boundary lubrication,
and enhanced pressure lubrication. In the hydrodynamic and mixed
lubrication regimes, the film of lubricant (a thick film in the
case of hydrodynamic and a thin film in the case of mixed
lubrication) separates the moving surfaces. In boundary layer and
enhanced pressure regimes, lubrication is provided by a thin solid
layer of the lubricant formed on the surface of the moving parts.
This thin solid lubricant layer is formed by material sheared off
from solid lubricant particles or reaction products of additives
contained within the lubricant.
[0004] Nanoparticulate based lubricants utilize specially designed
nanometer sized solid particles to produce chemically and
physically stable solid lubricant layers at the contact zone of
dynamic systems. Under conditions of load and temperature produced
by the contacting surfaces, these nanoparticles undergo structural
deformation resulting in the formation of the thin solid lubricant
layer on the contacting surfaces, capable of shear/sliding motion.
In addition to the thin solid layer providing lubrication by
allowing for shear deformation, the nanoparticles also reduce
friction between the surfaces by acting as tiny balls in a bearing
between the contacting surfaces. The lubricating effect is enhanced
by novel properties of the nanoparticles that arise from their
curvature and size, as these particles approach molecular
dimensions (less than or equal to 500 nanometers). In contrast with
solid lubricant particles of larger dimensions, the small size of
the nanoparticles allows its permeation deep into the micro and
meso asperities of the contacting surfaces to provide
lubrication.
[0005] One application of a nanoparticle based lubricant is
described in U.S. Pat. No. 6,710,020 (hereinafter the '020 patent)
issued to Tenne et al. on Mar. 23, 2004. The '020 patent discloses
hollow fullerene-like nanoparticles of diameters between 10
nanometers and 200 nanometers, used as solid lubricants between
contacting surfaces. In the '020 patent, a composite structure
comprising a porous matrix made of a metal, alloy or a
semiconductor (base metal) and inorganic fullerene-like (IF)
nanoparticles of a metal chalcogenide are provided as the lubricant
ensemble. The IF nanoparticles are impregnated within the pores of
the base metal, which serve as a reservoir for the IF
nanoparticles, which are slowly released to the surface of the base
metal to provide lubrication. In the '020 patent, the IF
nanoparticles are synthesized in a reactor. For example, in one
embodiment, tungsten disulphide (WS.sub.2) IF nanoparticles are
prepared by reacting hydrogen sulphide (H.sub.2S) and hydrogen gas
(H.sub.2) with tungsten oxide (WO.sub.3) nanoparticles in a
fluidized bed reactor at 850.degree. C. During the reaction
process, a closed WS.sub.2 monolayer is formed on the surface of
the WO.sub.3 nanoparticle. As the reaction proceeds, the oxygen
atoms diffuse out of the WO.sub.3 and closed WS.sub.2 layers
replace the oxide core. After a few hours of the reaction process,
WS.sub.2 nanoparticles of diameter less than or equal to 200
nanoparticles are obtained. These nanoparticles are then subjected
to different cleaning and purification steps and dispersed within
an organic fluid prior to impregnation into the pores of the base
metal.
[0006] Although the technique of the '020 patent may be capable of
producing nanoparticles below 200 nanometers, this technique may
have some limitations. For instance, the surface chemical
reactivity of the particles of nanometer dimensions may be high.
Therefore, the discrete nanoparticles produced by the technique of
the '020 patent may have a tendency to bind together (agglomerate).
Additionally, because the '020 patent relies on chemical synthesis
to produce the IF nanoparticles, the quantity of the nanoparticles
that may be practically produced using this technique, may be
limited. Scaling the chemical synthesis process to produce a
sufficient quantity of nanoparticles for bulk commercial
applications, may increase the cost of such lubricants making them
unviable for common applications.
[0007] The present disclosure is directed at overcoming one or more
of the shortcomings of the prior nanoparticle based lubricants.
SUMMARY OF THE INVENTION
[0008] In one aspect, the present disclosure is directed toward a
method of making a nanoparticulate based lubricant. The method
includes providing solid lubricant material with particles having a
size less or equal to about 500 nanometers, and treating the
particles to create composite nanoparticles. The composite
nanoparticles include the solid lubricant material and at least a
second material.
[0009] In another aspect, the present disclosure is directed toward
a nanoparticle for lubricant applications. The nanoparticle
includes a core made substantially of a first material and having a
size less than or equal to about 500 nanometers. The first material
includes one or more solid lubricant materials. The nanoparticle
also includes a shell on an external surface of the core, wherein
the shell is substantially made of a second material.
[0010] In yet another aspect, the present disclosure is directed
toward a lubricant. The lubricant includes a base oil and composite
nanoparticles. The composite nanoparticles include a core made of
one or more materials and a shell made of another material, wherein
the shell substantially surrounds the core. The lubricant further
includes lubricant additives.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 illustrates exemplary surfaces under frictional
contact;
[0012] FIG. 2 illustrates an enlarged view of a region of the
surfaces of FIG. 1;
[0013] FIG. 3 illustrates an exemplary process of manufacture of
the nanoparticle based lubricant of FIG. 2; and
[0014] FIG. 4 illustrates another exemplary process of manufacture
of the nanoparticle based lubricant of FIG. 2.
DETAILED DESCRIPTION
[0015] FIG. 1 illustrate exemplary surfaces 10 under frictional
contact. These surfaces 10 may be part of a machine that performs
some sort of operation associated with an industry. Non limiting
examples of surfaces 10 may include, contacting surfaces of a
piston and a cylinder within an internal combustion engine, mating
surfaces of a transmission gear assembly, etc. A lubricant 20 is
disposed between the surfaces 10 under frictional contact. The
lubricant 20 may be a substance introduced between the surfaces 10
to reduce the friction and wear therebetween. In some cases, this
reduction in friction may be accomplished by the lubricant 20
forming a protective film on the surfaces 10.
[0016] The lubricant 20 may, in some cases, be composed of several
different materials. The lubricant 20 may include a liquid such as
organic oils (for example, vegetable oils, seed oils and mineral
oils), hydrocarbon base oils (for example, fossil fuel based oils),
synthetic liquids (for example, hydrogenated polyolefin's, esters,
silicone, and fluorocarbons), and combinations of these oils, or
others. Additives may also be mixed with the lubricant 20 to
enhance desirable properties, such as improved viscosity index,
improved resistance to corrosion and oxidation, enhanced aging
characteristics, etc. The lubricant 20 may alternatively be a
mixture of a liquid and a solid lubricant. For example, the
lubricant 20 may include a suspension of a solid lubricant in a
liquid medium. In some cases, the lubricant 20 may be composed
entirely of a solid lubricant. These solid lubricants may include
dichalcogenides such as molybdenum disulphide (MoS.sub.2), tungsten
disulphide (WS.sub.2), niobium diselinide (NbSe.sub.2), soft metals
such as gold (Au), silver (Ag), lead (Pb), and tin (Sn), or any
other solid lubricant known in the industry.
[0017] FIG. 2 illustrates an enlarged view of a region of the
surfaces 10 of FIG. 1. The lubricant 20 between the surfaces 10 may
include nanoparticles 22 of the solid lubricant. In the embodiment
illustrated in FIG. 2, the nanoparticles 22 of the solid lubricant
are included within a liquid medium 24. This liquid medium 24 may
include the organic oils, the hydrocarbon based oils, the synthetic
liquids, and the additives described earlier, or may include other
liquid media used in lubricants known in the art. The liquid medium
24 may be used to transport the solid lubricant nanoparticles 22 to
the contacting surfaces 10. It may also be used as the lubrication
medium in hydrodynamic lubrication and mixed lubrication regimes.
In some cases, the liquid medium 24 may also remove heat generated
by friction away from the surfaces 10. It is also contemplated that
in some cases, the liquid medium 24 may include volatile liquids
that evaporate leaving behind nanoparticles 22 of the solid
lubricant on the contacting surfaces 10. In some other embodiments,
the liquid medium 24 may be omitted from the lubricant 20.
[0018] The lubricant 20 may include a plurality of nanoparticles 22
of a solid lubricant of any shape. In this application, a
nanoparticle is defined as a multi-material composite particle
(made of more than one material) with a size less than or equal to
about 500 nanometers. Typically, the size of a nanoparticle refers
to the diameter of a sphere that superscribes the nanoparticle 22.
In some embodiments, however, the nanoparticles 22 may not exist as
discrete particles in the lubricant 20, but multiple nanoparticles
may be connected together. In these cases, the size of the
nanoparticle refers to the size of core of the nanoparticle 22. In
some embodiments, the nanoparticles 22 may have a range of sizes
less than or equal to 500 nanometers (such as, less than or equal
to 400 nanometers, or less than or equal to 400 nanometers). In
some embodiments, a majority of the nanoparticles 22 in the
lubricant 20 will have a size less than or equal to about 500
nanometers. In some other embodiments, the average size of the
nanoparticles 22 will be less than or equal to about 500
nanometers. In a preferred embodiment, the nanoparticles 22 may
have a range of sizes below about 500 nanometers with a majority of
particles having an average size below about 200 nanometers. While
the nanoparticles 22 may possess any shape, it is contemplated that
in some applications, the shape of a substantial number of
nanoparticles 22 may be tailored to a specific general shape, for
example, a generally platelet like or a generally spherical
shape.
[0019] As mentioned earlier, the nanoparticles 22 may be composed
of two or more materials. The nanoparticles 22 may include a core
32 made of one material and a shell 28 made of another material. In
some cases, the core 32 may itself be made of multiple materials
and the shell 28 made of a different material. The core 32 may
include cavities 34 that may contain another material, for
instance, the shell material. The cavities 34 in the core 32 may
include intergranular spaces and/or pores within the material. In
some embodiments, the material in the cavities 34 may be the
product of a chemical reaction between the material of the core 32
and the material of the shell 28. While in other embodiments, the
cavities 34 may contain a material different from the core 32 and
the shell 28. It is also contemplated that in some embodiments, the
core 32 may be substantially free of cavities 34, or that any
cavities 34 present may be unfilled.
[0020] The nanoparticles 22 may be made up of solid lubricants and
other chemicals that enable the nanoparticle 22 to be stable at
nanometer dimensions. The core 32 of the nanoparticle 22 may be
made of any solid lubricant material. In this disclosure, a solid
lubricant material is meant to include materials that are typically
used as solid lubricants in the industry and other metals or
chemicals that are capable of being reduced to nanometer
dimensions. For example, the core 32 may be made of molybdenum
disulphide (MoS.sub.2), tungsten disulphide (WS.sub.2), niobium
diselinide (NbSe.sub.2), metals such as gold (Au), silver (Ag),
lead (Pb), tin (Sn), enhanced pressure chemicals or salts and any
other solid lubricant known in the industry. In some applications,
the core 32 may substantially be made of one solid lubricant
material, while in other applications, the core 32 may include
multiple solid lubricant materials. It contemplated that a
lubricant 20 may include a mixture of different types of
nanoparticles 22. That is, the lubricant 20 may include
nanoparticles 22 with the core made of substantially one material,
nanoparticles 22 with the core 32 made of multiple solid lubricant
materials, and nanoparticles 22 with the core 32 made of a
different solid lubricant material. For example, some of the
nanoparticles 22 may have MoS.sub.2 included in the core 32 while
some other nanoparticles 22 may have WS.sub.2 included in the core
32.
[0021] The shell 28 may include a chemical agent. The chemical
agent may impart desirable properties to the lubricant 20. This
chemical agent may be phosphate based, amine based, sulphate based,
or boron based. Non-limiting examples of materials that may be used
as a chemical agent may include zinc dialkyl dithio phosphate
(ZDDP), sodium tripolyphosphate, potassium diphosphate,
2-ethylhexyl molybdenum dithiophosphate, and combinations thereof.
In some cases, more than one chemical agent may also be used. In
some embodiments, the chemical agent may be made of a material that
may be converted to a stable boundary film in a lubrication
application. In some embodiments, the shell 28 may serve as a
surface stabilization agent for the core 32. That is, the chemical
agent may react with the surface of the core 32, and form a shell
around the core 32. This shell 28 may reduce the surface energy of
the core 32, thereby reducing the tendency of discrete
nanoparticles 22 to agglomerate and grow in size. In cases where
the chemical agent reacts with the core material, the shell 28 may
be made as the reaction product of the chemical agent and the core
material. In some other embodiments, the chemical agent may settle
on the surface of the core and harden. In these embodiments, the
shell 28 may be made of the material of the chemical agent. It is
also contemplated that the shell 28 may be a reaction product of
the chemical agent and other reactants.
[0022] The chemical agent may seep into the core 32 and may fill
cavities 34 and other spaces within the core 32. In some
embodiments, the chemical agent that seeps into the core 32 may
react with the core material to form a reaction product. In these
embodiments, a cross-section of the nanoparticle 22 may exhibit a
layered appearance with the proportion of the chemical agent (or
the reaction product of the chemical agent and the core material)
increasing towards the exterior of the nanoparticle 22.
[0023] The size of the nanoparticles 22 may change over time. For
instance, the size of the nanoparticles 22 may decrease over time.
This decrease in size may be the result of material transfer from
the nanoparticle 22 to the contacting surfaces 10 through
delamination processes at the contact zone. The material
delaminated from the nanoparticle 22 may form a solid lubricant
layer 26 on the surfaces 10. The solid lubricant layer 26 may start
accumulating over parts of the surfaces 10 and may increase in
coverage over time. In some embodiments, the accumulated solid
lubricant layer 26 may cover substantial areas of the surfaces 10,
over time. The composition of the nanoparticles 22 may also change
with time. The changing composition may also be due to the transfer
of material from the nanoparticle 22 to the solid lubricant layer
26. Alternatively or additionally, the chemical agent that soaked
into the core 32 of the nanoparticle 22 may leak out, thereby,
changing the composition of the nanoparticle 22 over time.
[0024] FIG. 3 illustrates an exemplary process of manufacture of
the nanoparticle 22 based lubricant 20. Solid lubricant material 35
may be loaded into a chemical-mechanical grinding machine 40. The
chemical-mechanical grinding machine 40 may be any means capable of
grinding (reducing the physical size of) the solid lubricant
material 35 to a powder and enabling a chemical reaction between a
chemical agent and the solid lubricant material 35. The
chemical-mechanical grinding machine 40 may include a mechanical
ball mill, rod mill, SAG mill, autogenous mill, pebble mill, high
pressure grinding rolls, buhrstone mill, or any other grinding
means capable of grinding solid lubricant material into a powder. A
chemical agent 65 may also be fed into the chemical-mechanical
grinding machine 40. The chemical agent 65 may be a solid, liquid
or a gelatinous type material. It is also contemplated that, in
some application, the chemical agent 65 may be a gaseous material.
In some embodiments, commercially available solid lubricant
material 35 in the form of a coarse powder may partially fill a
tumbler of the chemical-mechanical grinding machine 40, along with
the chemical agent 65 and a grinding medium. The grinding medium
may include, for example, stainless steel or ceramic balls. The
tumbler may then be rotated or agitated, causing the grinding media
to grind the solid lubricant material 35 into a powder. The
chemical agent 65 may further react with the powder to form
nanoparticles 22 with a core 32 and a shell 28. In some
embodiments, the solid lubricant powder and the chemical agent 65
may also be subjected to one or more heating steps during grinding.
It is also contemplated that the grinding and/or the reaction step
may be conducted under a selected ambient condition, for example,
under an inert gas, or at an elevated temperature.
[0025] In another embodiment, the chemical-mechanical grinding
machine 40 may include multiple machines, and the conversion of the
solid lubricant material 35 to the nanoparticles 22 may occur in
multiple stages. For example, a first chemical-mechanical grinding
machine may grind the solid lubricant material 35 to a powder of a
predetermined size greater than about 500 nanometers under a
selected ambient condition. This powder may be then be ground in
the same or a second chemical-mechanical grinding machine/operation
further. The second chemical-mechanical grinding machine/operation
may be similar to the first chemical-mechanical grinding
machine/operation, or it may be different. For instance, the first
chemical-mechanical grinding machine may be a dry grinding machine
and the second chemical-mechanical grinding machine may be a wet
grinding machine that grinds the powder output from the first
chemical-mechanical grinding machine in the presence of a liquid
chemical agent 65. Grinding the powder in the presence of the
liquid chemical agent 65 may produce the nanoparticles 22.
Measurement and filtration processes may also be incorporated
between the multiple grinding operations.
[0026] Any combination of grinding processes and chemical processes
may be used to manufacture the nanoparticles 22. For instance, in
one embodiment, two solid lubricant materials are ground separately
(in the same or different chemical-mechanical grinding machines) to
form two groups of solid lubricant powders. These powders may be
mixed with chemical agents (the same or different chemical agents)
separately and subjected to another grinding process to form two
groups of nanoparticles 22. These groups of nanoparticles 22 may
then be mixed together. In another embodiment, the two groups of
solid lubricant powders, that are formed by grinding the solid
lubricant materials separately, are first mixed together and then
treated with a chemical agent 65. The mixed powders are further
ground in the presence of the same or a different chemical agent to
form the nanoparticles 22.
[0027] The nanoparticles 22 that are output from the
chemical-mechanical grinding machine 40 may then be mixed with a
liquid medium 24 in a mixing machine 90. The mixing machine 90 may
include any means capable of producing a well mixed suspension of
the nanoparticles 22 in the liquid medium 24. The mixing machine 90
may include a mechanical mixer, an ultrasonic mixer or any other
mixer known in the art. In embodiments where a solid lubricant is
desired, the nanoparticles 22 output from the chemical mechanical
grinding machine 40 may be used as the lubricant 20.
[0028] The liquid medium 24 may include any organic oil, a
hydrocarbon based oil, or a synthetic liquid described earlier.
Various additives may be also be mixed with the liquid medium 24.
These additives may enhance the desirable properties of the
lubricant 20. For example, the additives may protect the lubricated
surfaces 10 from rust and/or wear, enhance the properties of the
lubricant 20 for specific applications, and protect the lubricant
20 from oxidizing. These additives may include acid neutralizers,
antifoam agents, antioxidants, antirust agents, corrosion
inhibitors, detergents, dispersants, emulsifiers, extreme pressure
additives, oiliness enhancers, pour point depressants, tackiness
agents, viscosity index improvers, and/or any other lubricant
additives that are known in the art. Additionally or alternatively,
in some embodiments, the additives may be pre-mixed with the
chemical agent 65.
[0029] In some embodiments, the lubricant 20 containing the
nanoparticles 22 may be further subjected to various measurement
processes and purification processes (not shown). The measurement
processes may measure various physical and/or chemical
characteristics, such as viscosity, nanoparticle loading,
lubricity, etc., of the lubricant 20. In some embodiments, the
suspension may be routed back to the chemical-mechanical grinding
machine 40 or the mixing machine 90 for further processing based on
the readings of the various measurement processes. The purification
processes may involve removal of contaminants and other undesirable
materials from the lubricant 20.
[0030] FIG. 4 shows another embodiment of the process of
manufacture of the nanoparticle 22 based lubricant 20. In the
embodiment shown in FIG. 4, the solid lubricant powder 45, output
from the first grinding machine, may be passed through a filtration
device 50. The filtration device 50 may separate large particle
size powder 55, where the average particle size is greater than a
desired value, from the nanoparticles 22. The filtered large
particle size powder 55 may be routed back to the
chemical-mechanical grinding machine 40 for further grinding, while
the nanoparticles 22 may be routed downstream for further
processing. It is also contemplated that other sensing or
separation devices or techniques may be used in addition to or in
place of the filtration device 50 to detect the size of the solid
lubricant powder 45.
INDUSTRIAL APPLICABILITY
[0031] The disclosed nanoparticulate based lubricants 20 can be
used to reduce the friction and/or wear between any moving parts.
The lubricant 20 contains nanoparticles 22 that act as spacers to
separate the surfaces 10 of the moving parts. The nanoparticles 22
may also reduce friction between the surfaces 10 by acting as a
ball bearing between the surfaces 10. The lubricating effect may
also be enhanced by novel properties of the nanoparticles 22 that
arise from their curvature and molecular dimensions. The
nanoparticles 22 may have a composite structure and may possess an
internal core 32 made of a solid lubricant material and an outer
shell 28 made of a chemical agent that imparts desirable properties
to the lubricant 20. The chemical agent may also serve as a surface
stabilization agent that reacts with the surface of the solid
lubricant core 32 to form a shell 28 that reduces the tendency of
the nanoparticles 22 to agglomerate and grow in size.
[0032] Under conditions of friction between the surfaces 10, the
nanoparticles 22 may undergo structural deformation, resulting in
material delaminating from the nanoparticle 22 and forming a solid
lubricant layer 26 on the surfaces 10 that is capable of
accommodating sliding/shear motion. This phenomenon of formation of
a lubricating film on the surfaces 10 may also lead to reduced
friction and wear between components in the boundary and enhanced
pressure lubrication regime.
[0033] The process of manufacture the nanoparticulate based
lubricant 20 includes reducing the size of commercially available
solid lubricant particles to nanometer dimensions by mechanical
means, and surface stabilization by reacting these particles with a
chemical agent. The resulting nanoparticles 22 may possess a
composite structure with a solid lubricant core 32 surrounded by a
shell 28 of the chemical agent. These nanoparticles 22 may be used
as a solid lubricant powder, or may be dispersed in a liquid medium
24 to create a liquid lubricant.
[0034] To illustrate the process of manufacture of a
nanoparticulate based lubricant 20, an example case will be
described. Commercially available MoS.sub.2 powder, between about
700 nanometers and about 1 micron (1000 nanometers) in size, may be
subjected to mechanical milling in a SPEX CertiPrep model 8000D
ball milling machine. Milling may be conducted in the presence of a
liquid chemical media of zinc dialkyl dithio phosphate (ZDDP) using
a grinding media of hardened stainless steel grinding balls. The
resulting slurry of the nanoparticles 22 in the chemical media may
contain particles ranging in sizes between about 20 nanometers and
200 nanometers. Some of the nanoparticles contained in the slurry
may possess a MoS.sub.2 core and a phosphate based shell. Some of
the nanoparticles 22 may also show penetration of the chemical
media into the cavities 34 of the MoS.sub.2 core. This slurry
containing nanoparticles 22 can be used as a lubricant paste or can
be mixed with a base oil to serve as a liquid lubricant.
[0035] In the nanoparticles 22 formed using this technique, the
surface energy of the nanometer sized particles may dissipate by
reaction with the chemical agent. The resulting composite structure
of the nanoparticles 22 with a solid lubricant core 32 and an
encapsulating shell 28 may reduce the tendency of the nanoparticles
22 to agglomerate and grow in size. The composite structure of the
nanoparticles 22, therefore, may help maintain the nanometer
dimensions of the nanoparticles 22, while retaining the novel
properties arising out of the small dimensions of the nanoparticles
22.
[0036] Since the manufacture of the nanoparticles 22 involves
mechanical grinding processes that are routinely used in industry,
the manufacturing technique is well suited for bulk production.
Commonly available mechanical grinding machines can also be easily
incorporated into conventional production lines. The capability of
the technique to bulk produce the nanoparticles, and the ability to
incorporate the required machinery into production lines may make
the lubricants produced by this technique, cost effective.
[0037] It will be apparent to those skilled in the art that various
modifications and variations can be made to the disclosed
nanoparticulate based lubricants 20. Other embodiments will be
apparent to those skilled in the art from consideration of the
specification and practice of the disclosed nanoparticulate based
lubricants 20. It is intended that the specification and examples
be considered as exemplary only, with a true scope being indicated
by the following claims and their equivalents.
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