U.S. patent application number 11/194507 was filed with the patent office on 2007-12-20 for use of nanomaterials as effective viscosity modifiers in lubricating fluids.
Invention is credited to Frances E. Lockwood, Thomas R. Smith, Gefei Wu, Zhiqiang Zhang.
Application Number | 20070293405 11/194507 |
Document ID | / |
Family ID | 38862297 |
Filed Date | 2007-12-20 |
United States Patent
Application |
20070293405 |
Kind Code |
A1 |
Zhang; Zhiqiang ; et
al. |
December 20, 2007 |
Use of nanomaterials as effective viscosity modifiers in
lubricating fluids
Abstract
Nanomaterials have been used as a supplement or replacement of
traditional polymer-based viscosity modifiers for lubricants and
other related fluids. Compared with traditional polymer-based
viscosity modifiers, nanomaterials possess better viscosity-index
modification functions, i.e., more even viscosity increase across
the whole temperature range. Meanwhile, a cost-effective way of
making nanomaterials have been developed based on commercially
available graphite materials, and the resulting nanoparticles of
graphite are nanodisks (nanoplates). Furthermore, it provides a
viscosity modifier which exhibits temporary shear loss, which can
contribute to fuel economy, but no permanent shear loss.
Inventors: |
Zhang; Zhiqiang; (Lexington,
KY) ; Wu; Gefei; (Lexington, KY) ; Lockwood;
Frances E.; (Georgetown, KY) ; Smith; Thomas R.;
(Lexington, KY) |
Correspondence
Address: |
CARRITHERS LAW OFFICE, PLLC;One Paragon Centre
Suite 140
6060 Dutchman's Lane
Louisville
KY
40205
US
|
Family ID: |
38862297 |
Appl. No.: |
11/194507 |
Filed: |
August 1, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60592570 |
Jul 31, 2004 |
|
|
|
Current U.S.
Class: |
508/113 |
Current CPC
Class: |
C10M 2201/041 20130101;
C10N 2030/54 20200501; C10N 2030/02 20130101; B82Y 30/00 20130101;
C10N 2040/25 20130101; C10N 2020/06 20130101; C10N 2040/042
20200501; C10N 2040/08 20130101; C10N 2030/68 20200501; C10N
2050/01 20200501; C10M 103/02 20130101 |
Class at
Publication: |
508/113 |
International
Class: |
C10M 169/04 20060101
C10M169/04 |
Claims
1. The method of using nanomaterials as an effective viscosity
modifier for a lubricating oil, which provides better viscosity
index, and with no adverse effect to the low temperature properties
of the fluid, than the currently used polymer-based viscosity
modifiers.
2. The method of claim 1 in which the nanomaterials are made from
carbon.
3. The method of claim 1 in which the nanomaterials are carbon
nanotubes.
4. The method of claim 1 in which the nanomaterials are graphite
nanoparticles.
5. The method of claim 3 wherein said carbon nanotube is either
single-walled, double-walled, or multi-walled, with typical aspect
ratio of 100-2000.
6. The method of claim 4 wherein said graphite nanoparticles are
made by ball milling commercially available bulk graphite or
graphite powders or graphite foams into the desired particle size,
preferably with average diameter less than 500 nanometers.
7. The method of claim 4 wherein said graphite nanoparticles are in
the form of nanodisks (or nanoplates).
8. The method of claim 1 wherein said nanomaterials are used in the
final lubricating formulation in the weight percentage of from
0.001% to 50%, or more preferably from 0.01% to 25%, or more
preferably from 0.1% to 20%.
9. The method of claim 1 in which the said lubricating fluid can be
engine oil for either gasoline or diesel engines, transmission
fluid, gear oil, hydraulic fluid, shock absorber oil, or any other
lubricating fluid used in a modern vehicle.
Description
[0001] This application claims priority from U.S. Provisional
Application Ser. No. 60/592,570 filed on Jul. 31, 2004 and
Provisional Application Ser. No. 60/254,959 filed on Dec. 12, 2000
and U.S. Pat. No. 6,783,746 which issued on Aug. 31, 2004 from
application Ser. No. 10/021,767 filed on Dec. 12, 2001 and
application Ser. No. 10/929,636 filed on Aug. 30, 2004 and
application Ser. No. 10/730,762 filed on Dec. 8, 2003 which claims
priority from PCT/US02/16888 filed on May 30, 2002 and application
Ser. No. 10/737,731 filed on Dec. 16, 2003 all of which are
incorporated herein in their entirety.
TECHNICAL FIELD
[0002] The present invention relates to a novel use of nanomaterial
as a viscosity modifier for a lubricating oil and a lubricating oil
composition. More particularly, the invention relates to a novel
viscosity modifier for a lubricating oil capable of producing a
lubricating oil composition having excellent viscosity index and
lubricating oil compositions containing such a viscosity
modifier.
BACKGROUND OF THE INVENTION
[0003] The viscosity of petroleum products generally varies greatly
with temperature, and for lubricating oils for automobiles, the
temperature dependence of the viscosity is desired to be small.
Therefore, a polymer has been widely used as a viscosity modifier
having an effect of improving viscosity index for the purpose of
decreasing the temperature dependence of the lubricating oils.
[0004] Viscosity index of a fluid is defined as the relationship of
viscosity of that fluid to the temperature. It is determined by
measuring the kinematic viscosities of the oil at 40 and
100.degree. C. and then calculated by using the tables or formulas
included in ASTM D 2270. High viscosity index fluids (e.g., a base
oil with the addition of a viscosity modifier) tend to display less
change in viscosity with temperature than low viscosity index
fluids (e.g., that base oil), and the effect is illustrated in FIG.
1.
[0005] Mineral oils, which are very effective lubricants at low
temperatures, become less effective lubricants at high
temperatures. At high temperatures, their film-forming ability (in
the hydrodynamic lubrication regime) diminishes, because of a drop
in viscosity. Prior to the use of viscosity modifiers and the
introduction of multigrade oils, this problem was partly overcome
through seasonal oil changes. The principal function of a viscosity
modifier is to minimize viscosity variations with temperature.
Viscosity modifiers are typically added to a low-viscosity oil to
improve its high-temperature lubricating characteristics. These are
organic polymers that minimize viscosity change with a change in
temperature. This represents a practical means by which the
operating range of mineral oils is extended to high temperature
without adversely affecting their low-temperature fluidity. The
mechanism is explained as follows.
[0006] At low temperature, the polymer molecules occupy a small
volume (hydrodynamic volume) and therefore have a minimum
association with the bulk oil. The effect should be little
viscosity increase. The situation is reversed at high temperature
because polymer chains extend or expand as a consequence of added
thermal energy. This increases the association of the polymer with
bulk oil because of an increase in surface area. The result is an
effective increase in viscosity at this high temperature. FIG. 2
illustrates oil thickening by viscosity modifiers.
[0007] Olefin copolymers (OCP), polymethacrylates (PMA),
hydrogenated styrene-diene (STD), and styrene-polyester (STPE)
polymers are the most common types of viscosity modifiers used in
modern lubricant formulations.
[0008] However, there is always some undesired viscosity increase
at low temperature (under the operating temperature range) caused
by these viscosity modifiers. That is, the viscosity index
improvement by the polymers is limited. Moreover, these polymers
contribute to a higher extreme-low-temperature viscosity and wax
formulation.
[0009] When the surrounding temperature lowers, a wax component in
a lubricating oil is crystallized and solidified to make the
lubricating oil lose flowability, so a pour point depressant (PPD)
is usually added into the lubricating oil to depress the
solidification temperature. The pour point depressant functions to
inhibit formation of a three-dimensional network attributed to
crystallization of the wax component in the lubricating oil and to
depress the pour point of the lubricating oil. Of the
low-temperature properties of a lubricating oil containing a
viscosity modifier, having an effect of improving viscosity index,
and a pour point depressant, the viscosity at a high shear rate is
determined by compatibility of a lubricating oil base with the
viscosity modifier, but on the other hand, the viscosity at a low
shear rate is greatly influenced by the pour point depressant. It
is known that when an ethylene/.alpha.-olefin copolymer having
specific composition is used as a viscosity modifier, the effect of
the pour point depressant is markedly reduced because of an
interaction between the copolymer and the pour point depressant
(e.g., U.S. Pat. No. 3,697,429 and U.S. Pat. No. 3,551,336).
Accordingly, the viscosity modifier to be blended with a
lubricating oil which is required to have particularly excellent
low-temperature properties is desired to exhibit an excellent
effect of improving viscosity index and at the same time not to
inhibit the function of the pour point depressant.
[0010] The thickening effect of particles to a fluid base is well
known (P. C. Hiemenz and R. Rajagopalan, Principles of Colloid and
Surface Chemistry, 3.sup.rd ed., Marcel Dekker, Inc., 1997, Chapter
4). The initial theory of explaining this was developed by Albert
Einstein in 1906, and there have been various modifications and
deviations in this theory, and the details of which are obviously
out of the scope of the current invention. Nanoparticles have been
added to a fluid for the purpose of increasing thermal conductivity
(U.S. Pat. No. 6,221,275, U.S. Pat. No. 6,432,320, and U.S. Pat.
No. 6,695,974). However, there has been little or no effort in
addressing the issue of viscous thickening effect of these
nanoparticles. In most of the cases this viscous thickening effect
is undesirable, since the increased viscosity will results in more
demand for pumping power, more energy loss due to internal fluid
friction, and even malfunction or catastrophic failure of the
machinery if the viscosity is way off the desired range.
[0011] However, in the current invention, with very careful
formulation, the viscous thickening effect of the nanoparticles
could be turned into an application as a revolutionary viscosity
modifier. And because the nanoparticles are usually not polymer
based, they are not going to cause compatibility issue with other
polymeric additives/components in a lubricating fluid, and they are
usually not contributing to wax formation by themselves.
[0012] It is common understanding in the lubricant industry that
thinner fluid may provide better fuel economy if adequate film
thickness is properly maintained. The reason is that the energy
loss due to internal friction of fluid itself is less when the
viscosity is lower. Therefore, if the viscosity modifier can be
sheared down temporarily (but not permanently), fuel economy
benefit could be observed. In the event of current invention, the
nanodisks (or nanoplates) orient themselves in a laminar flow
regime (Literature cited: Y. Yang, E. Grulke, Z. Zhang, G. Wu,
Rheological Behavior of Carbon Nanotube and Graphite Dispersions,
submitted to Langmuir), which indicates that temporary shear loss
will be observed should the fluid be place in a shear field.
SUMMARY OF THE INVENTION
[0013] In this invention, the use of nanoparticles as an effective
viscosity modifier is illustrated. More specifically the use of
carbon nanomaterial will be addressed. More specifically,
cost-effective graphite materials and the process of making them
into nanoparticles will be illustrated.
[0014] The use of nanoparticles in a fluid base is well know, as
illustrated by the previous US Patents. The use of graphite in
fluids such as lubricants is also well known. The graphite is added
as a friction reducing agent, which also carries some of the load
imposed on the working fluid, and therefore helps to reduce surface
damage to working parts. In order to be low friction, it is well
known that the graphite layered structure must contain some water
or other material to create the interlayer spacing and thereby
lamellar structure. There are various commercially available
graphite suspensions, e.g., from Acheson Colloid Co., which are
specifically intended for use in lubricants. The size of the
particles is varied for different dispersions, but the minimum
average size for commercially available products is in the
submicron range or larger, typically mean as 500-800 nm. The
viscosity modification advantage of the graphite is not mentioned
in the sales literature, nor is the product sold or promoted for
its viscosity modification property.
[0015] While there have been various patents filed on lubricants
containing graphite, e.g. U.S. Pat. No. 6,169,059, there are none
which specifically rely on graphite to improve the viscosity index
of the fluid. Furthermore, there are none which teach specifically
the use of nanometer-sized graphite with mean particle size much
significantly less than 1000 nm in order to increase viscosity
index. While graphite-containing automotive engine oil was once
commercialized (Arco graphite), the potential to use graphite as a
viscosity modifying material in this oil was not realized. The
particle size of graphite used was larger (mean greater than one
micron) than for the instnt invention as shown in FIG. 3. As a
result, the graphite had some settling tendency in the fluid.
Graphite of this size also significantly affects the friction and
wear properties of the fluid, and heretofore has been used to
reduce friction and improve wear performance of the fluid, e.g. in
metalworking fluids. On the other hand, the use of graphite in
lubricants for recirculating systems was made unpopular, partly due
to evidence that micron size graphite could "pile up" in restricted
flow areas in concentrated contacts, thereby leading to lubricant
starvation. No recognition of effect of graphite particle size on
this phenomena was made.
[0016] Previously, naturally formed "nano-graphites" have not been
available in the marketplace at all. Recently, Hyperion Catalysis
International, Inc. commercialized carbon nanotubes or so-called
carbon fibrils, which have a graphitic content, e.g., U.S. Pat. No.
5,165,909. Carbon nanotubes are typically hollow graphite-like
tubules having a diameter of generally several to several tens
nanometers. They exist in the form either as discrete fibers or
aggregate particles of nanofibers.
[0017] Bulk graphite is available from POCO Graphite as a graphite
foam, and is also available from the Carbide/Graphite Group, Inc.
Graphite powders can be obtained from UCAR Carbon Company Inc., and
from Cytec Carbon Fibers LLC. These bulk or powdery materials must
be reduced to a nanometer-sized particles by various methods for
use in the instant invention.
[0018] In this invention, fluids of enhanced viscosity index are
prepared by dispersing nanometer-sized particles, especially carbon
nanomaterials, into the fluid. The term carbon nanomaterials used
in this invention refers to graphite nanoparticles, carbon
nanotubes or fibrils, and other nanoparticles of carbon with
graphitic structure. Stable dispersion is achieved by physical and
chemical treatments.
[0019] The present invention provides at a minimum, a fluid of
lubricant containing from 0.001% to 50% by weight nanoparticles,
and preferably, from 0.01% to 25% by weight, and more preferably,
from 0.1% to 20% by weight of nanoparticles. Preferably, however, a
minimum of one or more chemical dispersing agents and/or
surfactants are also added to achieve long-term stability. The term
"dispersant" in the instant invention refers to a surfactant added
to a medium to promote uniform suspension of extremely fine solid
particles, often of colloidal size. In the lubricant industry the
term "dispersant" is generally accepted to describe the long chain
oil soluble or dispersible compounds which function to disperse the
"cold sludge" formed in engines. The term "surfactanf" in the
instant invention refers to any chemical compound that reduces
surface tension of a liquid when dissolved into it, or reduces
interfacial tension between two liquids or between a liquid and a
solid. It is usually, but not exclusively, a long chain molecule
comprised of two moieties: a hydrophilic moiety and a lipophilic
moiety. The hydrophilic and lipophilic moieties refer to the
segment in the molecule with affinity for water, and that with
affinity for oil, respectively. These two terms, dispersant and
surfactant, are mostly used interchangeably in the instant
invention. The particle-containing fluid of the instant invention
will have a viscosity index higher than the conventional fluid of
the same type. The fluid can have any other chemical agents or
other type particles added to it as well to impart other desired
properties, e.g. friction reducing agents, antiwear or
anticorrosion agents, detergents, antioxidants, dispersants, or
thermal property booster. Furthermore, the term fluid in the
instant invention is broadly defined to include pastes, gels,
greases, and liquid crystalline phases in either organic or aqueous
media, emulsions and microemulsions.
[0020] As set forth above, the nanomaterial could be of any
commercially available nanoparticles, or any material which can be
wet-milled into nanometer-sized particles using the process
developed in this invention which will be explained in detail
later. One of the preferable nanoparticles are carbon-based
materials. A preferred form of carbon nanomaterials is carbon
nanotubes. Another preferred form of carbon nanomaterials is
graphite. A preferred form of graphite is POCO Foam from POCO
Graphite. Another preferred form is graphite powders from UCAR
Carbon Company Inc. Still another preferred form of graphite is
graphite powders from Cytec Carbon Fibers LLC. Still another
preferred form of graphite is bulk graphite from The
Carbide/Graphite Group, Inc. Another preferable nanomaterial is
aluminum oxide nanoparticles from Sasol.
[0021] The nanoparticle containing dispersion may also contain a
large amount of one or more other chemical compounds, such as
polymers, antiwear agents, friction reducing agents, anti-corrosion
agents, detergents, metal passivating agents, antioxidants,
antifoaming agents, corrosion inhibitors, pour point depressants,
and additional conventional polymer-based viscosity improvers.
[0022] Furthermore, the nanomaterial dispersion can be pre-sheared,
in a turbulent flow, such as a nozzle, or a high pressure fuel
injector, a ultrasonic device, or a mill in order to achieve a
stable viscosity. This may be especially desirable in the case
where carbon nanotubes with high aspect ratio are used as the
graphite source, since they, even more than spherical particles,
will thicken the fluid but loose viscosity when exposed in
turbulent flows such as the flow regime in engines. Pre-shearing,
e.g. by milling, sonicating, or passing through a small orifice,
such as in a fuel injector, is a particularly effective way to
disperse the particles and to bring them to a stable size so that
their viscosity modifying effect will not change upon further use
in actual applications.
[0023] The milling process itself, or other pre-shearing process,
can have a rather dramatic effect on the long term dispersion
stability. It has been found that a preferred process is to mill
the particles to a thick pasty liquid of particles with mean size
less than 500 nanometers in diameter. The pasty liquid is then used
as concentrate to prepare lubricants of various viscosity grades,
and can be easily diluted to make a fluid with suitable viscosity
for an desired application as an automotive fluid, i.e., engine
oil, automatic transmission fluid, gear oil, shock absorber oil,
etc. A very effective paste can be made by mixing particles in a
viscous base fluid in a loading of 5% to 20% by weight and milling
for a period of several hours. The base fluid preferably contains
from 0% up to 100% of the dispersant/surfactant mixture with the
remainder being natural, synthetic, or mineral base oil. Once the
concentrate prepared by milling is diluted to liquid consistency
with base oil and other lubricating fluid components, the entire
fluid can (optionally) be passed through a small orifice device to
further increase the uniformity and decrease the size of dispersed
particles.
[0024] An important aspect of this invention is that the final
lubricant should be prepared to give an acceptable lubricant film
thickness at the maximum shear rate and temperature of use in the
target application. The maximum concentration of particles in the
final (diluted) lubricating fluid is limited by the relationship
between viscosity increase of the fluid caused by the particles,
and the temporary loss of viscosity (associated with the particles)
at maximum temperature and shear rate of fluid use. In general, the
viscosity of the lubricant of the instant invention will be matched
with conventional fluid at high operating temperature, typically,
100.degree. C., and the lower temperature viscosity of the
lubricant of the instant invention will be lower than that of the
conventional fluid. This means that the viscosity index of the
particle-containing lubricant of the instant invention will be
higher than that of the conventional fluid.
[0025] It is an object of the present invention to provide a
viscosity modifier for a lubricating oil, which provides better
viscosity index, and with no adverse effect to the low temperature
properties of the fluid, than the currently used polymer-based
viscosity modifiers.
[0026] It is an object of the present invention to provide a
cost-effective material as a supplement or replacement for the
conventional polymer-based viscosity modifiers.
[0027] It is an object of the present invention to development a
cost-effective processing method for making the nanomaterial to be
used as viscosity modifiers in lubricating oils.
[0028] It is an object of the present invention to use the
cost-effective graphite as the source of the nanomaterials to be
used as viscosity modifiers in lubricating oils.
[0029] It is an object of the present invention to provide a
viscosity modifier which exhibits temporary shear loss, which will
contribute to fuel economy upon use in a motor vehicle, but no
permanent shear loss.
[0030] It is an object of the present invention to provide a method
of preparing a lubricant as a stable dispersion of the carbon
nanomaterials in a liquid medium with the combined use of
dispersants/surfactants and physical agitation.
[0031] It is an object of the present invention to provide a in
which the carbon nanomaterials are made from cost-effective
high-thermal-conductivity graphite (with thermal conductivity
higher than 80 W/mK).
[0032] It is an object of the present invention to provide a method
of developing a method of forming carbon nanomaterials from
inexpensive bulk graphite.
[0033] It is an object of the present invention to provide a method
of utilizing carbon nanotube, graphite flakes, carbon fibrils,
carbon particles and combinations thereof.
[0034] It is an object of the present invention whereby the carbon
nanomaterial can optionally be surface treated to be hydrophilic at
surface for ease of dispersing into the aqueous medium.
[0035] It is an object of the present invention to provide a method
wherein the said dispersants/surfactants are soluble or highly
dispersible in the said liquid medium.
[0036] It is an object of the present invention to provide a
process for preparing a lubricant composition containing
nanomaterial by a) dissolving the said dispersants/surfactants or
dispersant additive package into the base fluid; b) adding a high
concentration (5-20% by weight) of the said carbon nanomaterials
into the above mixture while being strongly agitated by high impact
milling, and/or ultrasonication, to form a pasty liquid; and c) the
pasty liquid obtained in b) is further diluted with base oil and
additives as needed to make the final lubricant.
[0037] It is an object of the present invention to provide a method
of using a liquid medium selected from a natural oil (vegetable or
animal oil), or a synthetic oil, or a mineral oil or a combination
thereof.
[0038] It is an object of the present invention to provide a method
of defining an appropriate dispersants/surfactants for a liquid
medium of the type used in the lubricant industry, whereby it is a
surfactant or a mixture of surfactants with low
hydrophile-lipophile balance (HLB) value of 8 or less, preferably
nonionic or mixture of nonionic and ionic surfactants.
[0039] It is an object of the present invention to dissolve a
dispersant containing a surfactant a having a HLB of 8 or less in
an amount of from 0.001 to 30.0 percent by weight of a lubricant
liquid medium forming a dispersant liquid lubricant medium, adding
nanomaterial having an aspect ratio of from 500 to 5,000 in an
amount of from 0.001 to 10.0 percent by weight into the dispersant
liquid lubricant medium with agitation, and forming a uniform
suspension of colloidal size solid particles of nanomaterial having
an enhanced thermal conductivity when compared to the same
lubricant medium containing no nanomaterial.
[0040] It is an object of the present invention to dissolve a
dispersant containing a surfactant a having a HLB of 8 or less in
an amount of from 0.001 to 30.0 percent by weight of a lubricant
liquid medium forming a dispersant liquid lubricant medium, adding
carbon nanomaterial having an aspect ratio of from 500 to 5,000 in
an amount of from 0.001 to 10.0 percent by weight into the
dispersant liquid lubricant medium with agitation, and forming a
uniform suspension of colloidal size solid particles of carbon
nanomaterial having an enhanced thermal conductivity when compared
to the same lubricant medium containing no carbon nanomaterial.
[0041] It is an object of the present invention to provide that the
dispersants can be the ashless polymeric dispersants used in the
lubricant industry.
[0042] It is an object of the present invention to provide a
uniform dispersion in the form of a gel or paste with designed
viscosity of carbon nanomaterials in base oil medium.
[0043] It is an object of the present invention to provide a
uniform dispersion in a form as a gel or paste of high thermal
conductivity graphite nanoparticle in petroleum, natural, or
synthetic liquid medium.
[0044] It is an object of the present invention to provide a
uniform dispersion in its final form as an automatic transmission
fluid of relatively low viscosity (kinematic viscosity less than 10
centistokes at (100.degree. C.).
[0045] It is an object of the present invention to provide a
uniform and stable dispersion in a form containing dissolved
non-dispersing, other functional compounds in the liquid
medium.
[0046] It is an object of the present invention to provide a
uniform and stable dispersion in a form without polymeric viscosity
index improvers, where all viscosity index improvement comes from
the carbon nanomaterials.
[0047] It is an object of the present invention to provide a
uniform and stable dispersion where due to the absence of polymeric
materials the dispersion exhibits no permanent, only temporary loss
in viscosity due to shear fields and turbulence.
[0048] It is an object of the present invention to provide a
uniform and stable dispersion where the carbon nanomaterials are
used to convey an extremely high viscosity index, >200, and even
>300.
[0049] It is an object of the present invention to provide a
uniform and stable dispersion where the thermal conductivity and
heat transfer capability of the fluid is at least more than 20%
improved compared to conventional mineral oil based automatic
transmission fluids.
[0050] Other objects, features, and advantages of the invention
will be apparent with the following detailed description taken in
conjunction with the accompanying drawings showing a preferred
embodiment of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] A better understanding of the present invention will be had
upon reference to the following description in conjunction with the
accompanying drawings in which like numerals refer to like parts
throughout the several views and wherein:
[0052] FIG. 1 is a graph showing the effect of viscosity modifiers
improving the viscosity index (VI) of a base oil;
[0053] FIG. 2 shows the working mechanism of a polymer-based
viscosity modifier;
[0054] FIG. 3 shows a scanning electron microscope photomicrograph
of a conventional graphite-containing oil;
[0055] FIG. 4 shows a scanning electron microscope photomicrograph
of an automatic transmission fluid (ATF) oil sample containing the
graphite nanodisks and platelets in a final automatic transmission
fluid processed by the wet-milling method; and
[0056] FIG. 5 shows an atomic force microscope, (AFM) picture of
the automatic transmission fluid of FIG. 4 wherein the grid size is
1.times.1 micron and the height is 5 nm showing the ATF oil sample
containing the graphite nanodisks and platelets in a final
automatic transmission fluid processed by the wet-milling
method.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0057] The present invention provides a nanomaterial-containing
fluid medium that possesses higher viscosity index (smaller
viscosity change tendency with temperature) compared to
conventional fluids of the same medium. In the present invention
the fluid medium is targeted in its lubrication, viscosity,
friction, antioxidant and thermal management characteristics to
perform in modern automotive machineries.
[0058] One of the preferred nanomaterials are carbon nanotubes. The
nanotubes can be either single-walled, double-walled, or
multi-walled, having a typical nanoscale diameter of 1-200
nanometers. More typically the diameter is around 10-30 nanometers.
The length of the tube can be in submicron and micron scale,
usually from 50 nanometers to 100 microns. More typical length is
500 nanometers to 50 microns. The aspect ratio of the tube (which
is defined by the average length of the tubes divided by the
average diameter) can be from hundreds to thousands, more typical
100 to 2000. The surface of the nanotube can be treated chemically
to achieve certain level of hydrophilicity, or left as is from the
production.
[0059] Another preferred form of nanomaterials are commercially
available graphite, e.g. POCO Foam, available from POCO Graphite,
Inc., and graphite powders available from UCAR Carbon Company
Inc.
[0060] POCO Foam is a high thermal conductivity foamed graphite,
thermal conductivity typically in the range 100 to 150 W/mK. A
readily commercially available graphite is graphite powders from
UCAR Carbon Company Inc. Still another preferred nanomaterial is
the high thermal conductivity bulk graphite, Part#875G, from The
Carbide/Graphite Group, Inc. Either of these graphite is prepared
for the instant invention by pulverizing to a fine powder,
dispersing chemically and physically in a fluid of choice, and then
ball milled or otherwise size-reduced until a particle size of less
than 500 nm diameter mean size is attained. Graphite nanoparticles
this small usually exhibit the morphology as "nanodisk" or
"nanoplate", i.e., disk-like or plate-like particles in the
nanometer-size scale, with average diameter much larger than the
average thickness of particles. The preferred method is to disperse
the graphite by ball milling in a viscous fluid of certain
additives (detergents, dispersants, etc.) and then diluting the
obtained concentrate with base oil and other additives as needed to
attain the final viscosity and performance characteristics. The
finer the particle size attained upon milling, the better the
viscosity thickening effect of the pasty concentrate to the final
blend. The viscous thickening effect must be carefully balanced to
attain a suitable lubricating film thickness at the maximum shear
rate and temperature of fluid use. In general, any commercially
available graphite material can be used, provided that
pulverization, milling and other described chemical and physical
methods can be used to reduce the size of the final graphite
dispersion to below a mean particle size of 500 nm (in diameter).
FIG. 4 and FIG. 5, respectively, show a scanning electron
microscopic picture and an atomic force microscopic picture of the
graphite nanodisks/nanoplates in a final automatic transmission
fluid processed by the wet-milling method.
[0061] Another preferred nanomaterial is aluminum oxide
nanoparticles from Sasol North America. These are particles
surface-treated to improve dispersability in fluid. Typical
particle size is 25 nm.
[0062] In the process of making the lubricating fluid with the
nanoparticles, the mechanical process and sequence of adding the
components are crucial in order to fully take advantage of the high
viscosity index of the nanoparticles and to make the final fluid
product with exceptionally high viscosity index. High impact mixing
is necessary to achieve a homogeneous dispersion. Ball mill is one
of the examples of a high impact mixer. In the instant invention,
an Eiger Mini Mill (Model: M250-VSE-EXP) is used as the high impact
ball mill. It utilizes high wear resistant zirconia beads as the
grinding media and circulates the dispersion constantly during
milling. To achieve the best milling effect and therefore the best
viscosity index improvement, the proper milling procedure has been
developed. Firstly if the material is in bulk state, it must first
be size reduced into powders (with average size less than 100
microns). Then a 5% to 20% by weight of powder form of the
material, and more preferably 10% by weight of the powders, in base
oil dispersion is milled into a paste state. Usually this step
takes about 3 to 4 hours. Then add appropriate amount of dispersing
agent(s), usually 1 to 2 times of the weight of particle, into the
mill. With the addition of dispersing agent(s) the paste changes
from paste into liquid almost instantly, and extended milling
becomes possible. For most cases the extended milling period is 4
hours. It should be pointed out that if the mixture in the mill
turns into a paste, the recirculation of it becomes very difficult
and thus a poor milling is resulted. It is also found that if the
dispersing agent(s) is added into the mill at the very beginning,
the viscosity index of the final nanofluids made from the milling
process is not as high.
Example of Making the Fluids
[0063] Graphite particles are obtained by pulverizing big graphite
chunks from The Carbide/Graphite Group, and size-selected through a
mesh filter to be less than 75 .mu.m. 30 grams of the above
graphite particles and 270 grams of DURASYN 162 (a commercial 2
centistokes polyalphaolefin, abbreviated hereafter as 2 cSt PAO)
were added into the EIGER Mini Mill (Model: M250-VSE-EXP). The
milling speed was gradually increased to 4000 rpm. In about 4 hours
the above mixture turned into thick paste. Discharged 60 grams of
this paste and labeled it as Paste A. For the rest of the mixture
in the mill, added 48 grams of a dispersant and inhibitor package
(DI package) from Lubrizol, LUBRIZOL 9677MX, into the mill and the
paste became very thin, and successful recirculation restored.
Stopped the mill after another 4 hours of milling and labeled the
discharged paste as Paste B. Paste C was obtained by milling a
mixture of 30 grams of graphite with diameter less than 75 .mu.m,
60 grams of LUBRIZOL 9677MX, and 270 grams of Durasyn 162 at 4000
rpm for 8 hours. Note here the dispersing agent LUBRIZOL 9677MX was
added into the mill at the very beginning. Then we formulate three
automatic transmission fluids A through C, using the above three
pastes as concentrate, and their final composition is exactly the
same: 2% graphite, 4% LUBRIZOL 9677 MX, 18% DuraSyn 162, 76%
Durasyn 166 (a commercial 6 centistokes polyalphaolefin,
abbreviated hereafter as 6 cSt PAO) (all percentage by weight).
Example 1 illustrates the 100.degree. C. viscosity and viscosity
index (VI) of the fluids. It was also found that the graphite
particle size before milling was very critical on the viscosity
modification effect as well. For example, starting with graphite
smaller than 10 .mu.m (obtained as graphite powder from UCAR Carbon
Company Inc.) and following the same procedure as Paste B, a thin
Paste D was obtained.
Oil Basestocks
[0064] The petroleum liquid medium can be any petroleum distillates
or synthetic petroleum oils, greases, gels, or oil-soluble polymer
composition. More typically, it is the mineral basestocks or
synthetic basestocks used in the lube industry, e.g., Group I
(solvent refined mineral oils). Group II (hydrocracked mineral
oils), Group III (severely hydrocracked oils, sometimes described
as synthetic or semi-synthetic oils), Group IV (PAOs), and Group V
(esters, naphthenes, and others). One preferred group includes the
polyalphaolefins, synthetic esters, and polyalkylglycols.
[0065] Synthetic lubricating oils include hydrocarbon oils and
halo-substituted hydrocarbon oils such as polymerized and
interpolymerized olefins (e.g., polybutylenes, polypropylenes,
propylene-isobutylene copolymers, chlorinated polybutylenes,
poly(1-octenes), poly(1-decenes), etc., and mixtures thereof;
alkylbenzenes (e.g., dodecylbenzenes, tetradecylbenzenes,
dinonylbenzenes, di-(2-ethylhexyl)benzenes, etc.); polyphenyls
(e.g., biphenyls, terphenyls, alkylated polyphenyls, etc.),
alkylated diphenyl, ethers and alkylated diphenyl sulfides and the
derivatives, analogs and homologs thereof and the like. Alkylene
oxide polymers and interpolymers and derivatives thereof where the
terminal hydroxyl groups have been modified by esterification,
etherification, etc. constitute another class of known synthetic
oils.
[0066] Another suitable class of synthetic oils comprises the
esters of dicarboxylic acids (e.g., phtalic acid, succinic acid,
alkyl succinic acids and alkenyl succinic acids, maleic acid,
azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic
acid, alkenyl malonic acids, etc.) with a variety of alcohols
(e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl
alcohol, ethylene glycol diethylene glycol monoether, propylene
glycol, etc.). Specific examples of these esters include dibutyl
adipate, di(2-ethylhexyl) sebacate, di-hexyl fumarate, dioctyl
sebacate, diisooctyl azelate, diisodecyl azealate, dioctyl
phthalate, didecyl phthalate, dicicosyl sebacate, the 2-ethylhexyl
diester of linoleic acid dimer, the complex ester formed by
reacting one mole of sebacic acid with two moles of tetraethylene
glycol and two moles of 2-ethylhexanoic acid, and the like.
[0067] Esters useful as synthetic oils also include those made from
C.sub.5 to C.sub.12 monocarboxylic acids and polyols and polyol
ethers such as neopentyl glycol, trimethylolpropane,
pentaerythritol, dipentaerythritol, tripentaerythritol, etc. Other
synthetic oils include liquid esters of phosphorus-containing acids
(e.g., tricresyl phosphate, trioctyl phosphate, diethyl ester of
decylphosphonic acid, etc.), polymeric tetrahydrofurans and the
like.
[0068] Preferred polyalphaolefins (PAO), include those sold by
Mobil Chemical Company as SHF fluids, and those sold by Ethyl
Corporation under the name ETHYLFLO, or ALBERMARLE. PAO's include
the Ethyl-flow series by Ethyl Corporation, "Albermarle
Corporation," including Ethyl-flow 162, 164, 166, 168, and 174,
having varying viscosity from about 2 to about 460 centistokes.
[0069] MOBIL SHF-42 from Mobil Chemical Company, EMERY 3004 and
3006, and Quantum Chemical Company provide additional
polyalphaolefins basestocks. For instance, EMERY 3004
polyalphaolefin has a viscosity of 3.86 centistokes at 212.degree.
F. (100.degree. C.) and 16.75 centistokes at 104.degree. F.
(40.degree. C.). It has a viscosity index of 125 and a pour point
of -98.degree. F. and it also has a flash point of 432.degree. F.
and a fire point of 478.degree. F. Moreover, EMERY 3006
polyalphaolefin has a viscosity of 5.88 centistokes at 212.degree.
F. and 31.22 centistokes at 104.degree. F. It has a viscosity index
of 135 and a pour point of -87.degree. F. It also has a flash point
of 464.degree. F. and a fire point of 514.degree. F.
[0070] Additional satisfactory polyalphaolefins are those sold by
Uniroyal Inc. under the brand SYNTON PAO-40, which is a 40
centistokes polyalphaolefin. Also useful are the ORONITE brand
polyalphaolefins manufactured by Chevron Chemical Company.
[0071] It is contemplated that Gulf SYNFLUID 4 centistokes PAO,
commercially available from Gulf Oil Chemicals Company, a
subsidiary of Chevron Corporation, which is similar in many
respects to EMERY 3004 may also be utilized herein. MOBIL SHF-41
PAO, commercially available from Mobil Chemical Corporation, is
also similar in many respects to EMERY 3004.
[0072] Preferably the polyalphaolefins will have a viscosity in the
range of about 2-100 centistokes at 100.degree. C., with viscosity
of 4 and 10 centistokes being particularly preferred.
[0073] The most preferred synthetic base oil ester additives are
polyolesters and diesters such as di-aliphatic diesters of alkyl
carboxylic acids such as di-2-ethylhexylazelate,
di-isodecyladipate, and di-tridecyladipate, commercially available
under the brand name EMERY 2960 by Emery Chemicals, described in
U.S. Pat. No. 4,859,352 to Waynick. Other suitable polyolesters are
manufactured by Mobil Oil. MOBL polyolester P43, M-045 containing
two alcohols, and Hatco Corp. 2939 are particularly preferred.
[0074] Diesters and other synthetic oils have been used as
replacements of mineral oil in fluid lubricants. Diesters have
outstanding extreme low temperature flow properties and good
resistance to oxidative breakdown.
[0075] The diester oil may include an aliphatic diester of a
dicarboxylic acid, or the diester oil can comprise a dialkyl
aliphatic diester of an alkyl dicarboxylic acid, such as di-2-ethyl
hexyl azelate, di-isodecyl azelate, di-tridecyl azelate,
di-isodecyl adipate, di-tridecyl adipate. For instance,
Di-2-ethylhexyl azelate is commercially available under the brand
name of EMERY 2958 by Emery Chemicals.
[0076] Also useful are polyol esters such as EMERY 2935, 2936, and
2939 from Emery Group of Henkel Corporation and Hatco 2352, 2962,
2925, 2938, 2939, 2970, 3178, and 4322 polyol esters from Hatco
Corporation, described in U.S. Pat. No. 5,344,579 to Ohtani et al.,
and MOBIL ester P 24 from Mobil Chemical Company. Mobil esters such
as made by reacting dicarboxylic acids, glycols, and either
monobasic acids or monohydric alcohols like EMERY 2936
synthetic-lubricant base stocks from Quantum Chemical Corporation
and MOBIL P 24 from Mobil Chemical Company can be used. Polyol
esters have good oxidation and hydrolytic stability. The polyol
ester for use herein preferably has a pour point of about
-100.degree. C. or lower to -40.degree. C. and a viscosity of about
2-460 centistokes at 100.degree. C.
[0077] Group III oils are often referred to as hydrogenated oil to
be used as one of the preferred base oil components of the instant
invention providing superior performance to conventional
lubricating oils with no other synthetic oil base or mineral oil
base.
[0078] A hydrogenated oil is a mineral oil subjected to
hydrogenation or hydrocracking under special conditions to remove
undesirable chemical compositions and impurities resulting in a
mineral oil based oil having synthetic oil components and
properties. Typically the hydrogenated oil is defined as a Group
III petroleum based stock with a sulfur level less than 0.03,
severely hydrotreatd and isodewaxed with saturates greater than or
equal to 90 and a viscosity index of greater than or equal to 120,
and may optionally be utilized in amounts up to 90 percent by
volume, more preferably from 5.0 to 50 percent by volume and more
preferably from 20 to 40 percent by volume when used in combination
with a synthetic or mineral oil.
[0079] The hydrogenated oil my be used as the preferred base oil
component of the instant invention providing superior performance
to conventional motor oils with no other synthetic oil base or
mineral oil base. When used in combination with another
conventional synthetic oil such as those containing
polyalphaolefins or esters, or when used in combination with a
mineral oil, the hydrogenated oil may be present in an amount of up
to 95 percent by volume, more preferably from about 10 to 80
percent by volume, more preferably from 20 to 60 percent by volume
and most preferably from 10 to 30 percent by volume of the base oil
composition.
[0080] A Group I or II mineral oil basestock may be incorporated in
the present invention as a portion of the concentrate or a
basestock to which the concentrate may be added. Preferred as
mineral oil basestocks are the Marathon Ashland Petroleum (MAP) 325
Neutral defined as a solvent refined neutral having a Sabolt
Universal viscosity of 325 SUS at 100.degree. F. and MAP 100
Neutral defined as a solvent refined neutral having a S abolt
Universal viscosity of 100 SUS at 100.degree. F., both manufactured
by the Marathon Ashland Petroleum.
[0081] Other acceptable petroleum-base fluid compositions include
white mineral, paraffinic and MVI naphthenic oils having the
viscosity range of about 20-400 centistokes. Preferred white
mineral oils include those available from Witco Corporation, Arco
Chemical Company, PSI and Penreco. Preferred paraffinic oils
include solvent neutral oils available from Exxon Chemical Company,
HVI neutral oils available from Shell Chemical Company, and solvent
treated neutral oils available from Arco Chemical Company.
Preferred MVI naphthenic oils include solvent extracted coastal
pale oils available from Exxon Chemical Company, MVI extracted/acid
treated oils available from Shell Chemical Company, and naphthenic
oils sold under the names HYDROCAL and CALSOL by Calumet, and
described in U.S. Pat. No. 5,348,668 to Oldiges.
[0082] Finally, vegetable oils may also be utilizes as the liquid
medium in the instant invention. Soybean or rapeseed oil,
particularly of the high oleic or mid oleic genetically engineered
type, commercially available from Archer Daniels Midland Company,
are good examples of these oils. Soybean oil is of interest because
it has a high thermal conductivity itself.
Dispersants
Dispersants used in Lubricant Industry
[0083] Dispersants used in the lubricant industry are typically
used to disperse the "cold sludge" formed in gasoline and diesel
engines, which can be either "ashless dispersants", or containing
metal atoms. They can be used in the instant invention since they
are found to be an excellent dispersing agent for nanoparticles
with graphitic structure of this invention. They are also needed to
disperse wear debris and products of lubricant degradation within
the moving parts housing of an automobile.
[0084] The ashless dispersants commonly used in the automotive
industry contain an lipophilic hydrocarbon group and a polar
functional hydrophilic group. The polar functional group can be of
the class of carboxylate, ester, amine, amide, imine, imide,
hydroxyl, ether, epoxide, phosphorus, ester carboxyl, anhydride, or
nitrile. The lipophilic group can be oligomeric or polymeric in
nature, usually from 70 to 200 carbon atoms to ensure oil
solubility. Hydrocarbon polymers treated with various reagents to
introduce polar functions include products prepared by treating
polyolefins such as polyisobutene first with maleic anhydride, or
phosphorus sulfide or chloride, or by thermal treatment, and then
with reagents such as polyamine, amine, ethylene oxide, etc.
[0085] Of these ashless dispersants the ones typically used in the
petroleum industry include N-substitued polyisobutenyl succinimides
and succinates, alkyl methacrylate-vinyl pyrrolidinone copolymers,
alkyl methacrylate-dialkylaminoethyl methacrylate copolymers,
alkylmethacrylate-polyethylene glycol methacrylate copolymers, and
polystearamides. Preferred oil-based dispersants that are most
important in the instant application include dispersants from the
chemical classes of alkylsuccinimide, succinate esters, high
molecular weight amines, Mannich base and phosphoric acid
derivatives. Some specific examples are polyisobutenyl
succinimide-polyethylencpolyamine, polyisobutenyl succinic ester,
polyisobutenyl hydroxybenzyl-polyethylcncpolyamine,
bis-hydroxypropyl phosphorate. Commercial dispersants suitable for
transmission fluid are for example, LUBRIZOL 890 (an ashless PIB
succinimide), LUBRIZOL 6420 (a high molecular weight PIB
succinimide), Ethyl Hitec 646 (a non-boronated PIB succinimide).
The dispersant may be combined with other additives used in the
lubricant industry to form a "dispersant-detergent (DI)" additive
package for a lubricant, e.g., LUBRIZOL.TM. 9677MX (used in
transmission fluids), and the whole DI package can be used as
dispersing agent for the nanoparticle dispersions.
[0086] Dispersants used in the lubricant industry are typically
used to disperse the "cold sludge" formed in gasoline and diesel
engines, which can be either "ashless dispersants", or containing
metal atoms. They can be used in the instant invention since they
have been found to be an excellent dispersing agent for soot, an
amorphous form of carbon particles generated in the engine
crankcase and incorporated with dirt and grease.
[0087] The ashless dispersants commonly used in the automotive
industry contain an lipophilic hydrocarbon group and a polar
functional hydrophilic group. The polar functional group can be of
the class of carboxylate, ester, amine, amide, imine, imide,
hydroxyl, ether, epoxide, phosphorus, ester carboxyl, anhydride, or
nitrile. The lipophilic group can be oligomeric or polymeric in
nature, usually from 70 to 200 carbon atoms to ensure oil
solubility. Hydrocarbon polymers treated with various reagents to
introduce polar functions include products prepared by treating
polyolefins such as polyisobutene first with maleic anhydride, or
phosphorus sulfide or chloride, or by thermal treatment, and then
with reagents such as polyamine, amine, ethylene oxide, etc.
[0088] Of these ashless dispersants the ones typically used in the
petroleum industry include N-substituted polyisobutenyl
succinimides and succinates, allyl methacrylate-vinyl pyrrolidinone
copolymers, alkyl methacrylate-dialkylaminoethyl methacrylate
copolymers, alkylmethacrylate-polyethylene glycol methacrylate
copolymers, and polystearamides. Preferred oil-based dispersants
that are most important in the instant application include
dispersants from the chemical classes of alkylsuccinimide,
succinate esters, high molecular weight amines, Mannich base and
phosphoric acid derivatives. Some specific examples are
polyisobutenyl succinimide-polyethylenepolyamine, polyisobutenyl
succinic ester, polyisobutenyl hydroxybenzyl-polyethylenepolyamine,
bis-hydroxypropyl phosphorate. The dispersant may be combined with
other additives used in the lubricant industry to form a
"dispersant-detergent (DI)" additive package, e.g., LUBRIZOL.TM.
9802A, and the whole DI package can be used as dispersing agent for
the nanostructure suspension.
[0089] For instance, LUBRIZOL 9802A is described in the technical
brochure (MATERIAL SAFETY DATA SHEET No. 1922959-1232446-3384064)
by The Lubrizol Corporation in Wickliffe, Ohio and is hereby
incorporated by reference. LUBRIZOL 9802A is described as a motor
oil additive is believed to contain as an active ingredient a zinc
dithiophosphate and/or zinc alkyldithiophosphate.
[0090] LUBRIZOL 4999 is described in its Technical Brochure
(MATERIAL SAFETY DATA SHEET No. 1272553-1192556-3310026) by the
Lubrizol Corporation in Wickliffe, Ohio and is hereby incorporated
by reference. LUBRIZOL 9802A is described as a engine oil additive
and contains as an active ingredient from 5 to 9.9 percent of a
zinc alkyldithiophosphate.
[0091] LUBRIZOL 7720C in amounts of about 40% and LUBRIZOL 5186B in
amounts of up to about 1% are especially useful for shock absorber
nanofluids containing nanostructures.
[0092] OLOA 9061 is described in Technical Brochure "MATERIAL
SAFETY DATA SHEET No. 006703" by Chevron Chemical Company LLC and
is hereby incorporated by reference. OLOA 9061 is described as zinc
alkyl dithiophosphate compound.
[0093] IGEPAL CO-630 is described in Technical Brochure "MATERIAL
SAFETY DATA SHEET" from Rhodia Inc. and is hereby incorporated by
reference. IGEPAL CO-630 is described as a nonylphenoxy
poly(ethyleneoxy) ethanol, branched compound.
Other Types of Dispersants
[0094] Alternatively a surfactant or a mixture of surfactants with
low HLB value (typically less than or equal to 8), preferably
nonionic, or a mixture of nonionics and ionics, may be used in the
instant invention.
[0095] The dispersant for the oily liquid medium is a surfactant
with low hydrophile-lipophile balance (HLB) value (HLB <8) or a
polymeric dispersant of the type used in the lubricant industry. It
is preferably nonionic, or a mixture of nonionics and ionics. A
preferred dispersant for the aqueous liquid medium is of high HLB
value (HLB >10), preferably a
nonylphenoxypoly(ethyleneoxy)ethanol-type surfactant. Of course,
other alcohol based glycols having a high HLB value can be used as
well. The uniform dispersion of nanotubes is obtained with a
designed viscosity in the liquid medium. The dispersion of
nanotubes may be obtained in the form of a paste, gel or grease, in
either a petroleum liquid medium or an aqueous medium.
[0096] The dispersants selected should be soluble or dispersible in
the liquid medium. The dispersant can be in a range of up from 0.01
to 30 percent, more preferably in a range of from between 0.5
percent to 25 percent, more preferably in a range of from between 1
to 20 percent, and most preferably in a range of from between 2 to
15 percent. The nanoparticle material can be of any desired weight
percentage in a range of from 0.001 up to 50 percent. For practical
application it is usually in a range of from between 0.01 percent
to 25 percent, and most preferably in a range of from between 0.1
percent to 20 percent. The remainder of the formula is the selected
medium and other desired additives.
[0097] It is believed that in the instant invention the dispersant
functions by adsorbing onto the surface of the nanoparticle
material.
Other Chemical Compounds
[0098] This dispersion may also contain a large amount of one or
more other chemical compounds, preferably polymers, not for the
purpose of dispersing, but to achieve additional thickening or
other desired fluid characteristics. These can be added but reduce
the amount of particulate that can be used without excessive
thickening.
[0099] The viscosity improvers used in the lubricant industry can
be used in the instant invention for the oil medium for the purpose
of achieving additional thickening, which include olefin copolymers
(OCP), polymethacrylates (PMA), hydrogenated styrene-diene (STD),
and styrene-polyester (STPE) polymers. Olefin copolymers are
rubber-like materials prepared from ethylene and propylene mixtures
through vanadium-based Ziegler-Natta catalysis. Styrene-diene
polymers are produced by anionic polymerization of styrene and
butadiene or isoprene. Polymethacrylates are produced by free
radical polymerization of alkyl methacrylates. Styrene-polyester
polymers are prepared by first co-polymerizing styrene and maleic
anhydride and then esterifying the intermediate using a mixture of
alcohols.
[0100] Other compounds which can be used in the instant invention
in the oil medium include: acrylic polymers such as polyacrylic
acid and sodium polyacrylate, high-molecular-weight polymers of
ethylene oxide such as Polyox.RTM. WSR from Union Carbide,
cellulose compounds such as carboxymethylcellulose, polyvinyl
alcohol (PVA), polyvinyl pyrrolidone (PVP), xanthan gums and guar
gums, polysaccharides, alkanolamides, amine salts of polyamide such
as Disparlon AQ series from King Industries, hydrophobically
modified ethylene oxide urethane (e.g., Acrysol series from
Rohmax), silicates, and fillers such as mica, silicas, cellulose,
wood flour, clays (including organoclays) and nanoclays, and resin
polymers such as polyvinyl butyral resins, polyurethane resins,
acrylic resins and epoxy resins.
[0101] Chemical compounds such as seal swell agents or plasticizers
can also be used in the instant invention and may be selected from
the group including phthalate, adipates, sebacate esters, and more
particularly: glyceryl tri(acetoxystearate), epoxidized soybean
oil, epoxidized linseed oil, N,n-butyl benzene sulfonamide,
aliphatic polyurethane, epoxidized soy oil, polyester glutarate,
polyester glutarate, triethylene glycol caprate/caprylate, long
chain alkyl ether, dialkyl diester glutarate, monomeric, polymer,
and epoxy plasticizers, polyester based on adipic acid,
hydrogenated dimer acid, distilled dimer acid, polymerized fatty
acid trimer, ethyl ester of hydrolyzed collagen, isostearic acid
and sorbian oleate and cocoyl hydrolyzed keratin, PPG-12/PEG-65
lanolin oil, dialkyl adipate, alkylaryl phosphate, alkyl diaryl
phosphate, modified triaryl phosphate, triaryl phosphate, butyl
benzyl phthalate, octyl benzyl phthalate. alkyl benzyl phthalate,
dibutoxy ethoxy ethyl adipate, 2-ethylhexyldiphenyl phosphate,
dibutoxy ethoxy ethyl formyl, diisopropyl adipate, diisopropyl
sebacate, isodecyl oleate, neopentyl glycol dicaprate, neopenty
giycol diotanoate, isohexyl neopentanoate, ethoxylated lanolins,
polyoxyethylene cholesterol, propoxylated (2 moles) lanolin
alcohols, propoxylated lanoline alcohols, acetylated
polyoxyethylene derivatives of lanoline, and dimethylpolysiloxane.
Other plasticizers which may be substituted for and/or used with
the above plasticizers including glycerine, polyethylene glycol,
dibutyl phthalate, and 2,2,4-trimethyl-1,3-pentanediol
monoisobutyrate, and diisononyl phthalate all of which are soluble
in a solvent carrier. Other seal swelling agents such as LUBRIZOL
730 can also be used.
[0102] Antioxidants are an important part of transmission fluids.
General classes include zinc dialkyldithiophosphates, alkyl and
aryl phenols, alkyl and aryl amines, and sulfuinzed olefins.
Commercial examples are CIBA L57 (phenyl amine) and ETHYL HITEC
1656.
[0103] Pour point depressants, either of polymethyl methacrylate or
ethylene propylene olefin co-polymer type are useful to decrease
the low temperature Brookfield viscosity of the ATF. Examples
include ROHMAX 3008, ROHMAX 1-333, LUBRIZOL 6662A.
[0104] Friction Modifiers are used to control friction and torque
characteristics of the fluid. Commercial examples include LUBRIZOL
8650 and HITEC 3191.
Physical Agitation
[0105] The physical mixing includes high shear mixing, such as with
a high speed mixer, homogenizers, microfluidizers, a Kady mill, a
colloid mill, etc., high impact mixing, such as attritor, ball and
pebble mill, etc., and ultrasonication methods or passing through a
small orifice such as a fuel injector. Turbulent flows of any type
will assist mixing.
[0106] Ball milling is the most preferred physical method in the
instant invention since it is effective at rapidly reducing
particles to very small size while simultaneously dispersing them
into a concentrated paste as previously described. The concentrate
can then be diluted with base oil and other additives to hit a
final target viscosity, depending on the maximum temperature and
shear conditions anticipated in the target vehicle application. For
further size reduction and reducing particle maximum size the
diluted oil can be passed through a small orifice such as a fuel
injector. The raw material mixture may be pulverized by any
suitable known dry or wet grinding method. One grinding method
includes pulverizing the raw material mixture in the fluid mixture
of the instant invention to obtain the concentrate, and the
pulverized product may then be dispersed further in a liquid medium
with the aid of the dispersants described above. However,
pulverization or milling modifies the average aspect ratio of
rod-like nanomaterials, e.g., carbon nanotubes. A detailed
description has been given in an earlier section of the instant
invention.
[0107] Ultrasonication is another physical method in the instant
invention since it may be less destructive to the nanomaterial
structure than the other methods described. Ultrasonication can be
done either in the bath-type ultrasonicator, or by the horn-type
ultrasonicator (or called the "wand"). More typically, horn-type
ultrasonication is applied for higher energy output. Sonication at
the medium-high instrumental intensity for up to 30 minutes, and
usually in a range of from 10 to 20 minutes is desired to achieve
better homogeneity.
[0108] The instant method of forming a stable dispersion of
nanomaterials in a solution consist of three steps. First select
the appropriate concentrate of dispersant or mixture of dispersing
and other additives for the nanomaterial, and the oily medium, and
dissolve the dispersant into the liquid medium to form a
concentrate solution (keeping in mind the final additive
concentrations desired following dilution); secondly add a high
concentration of the nanomaterials, e.g., graphite nanoparticles or
carbon nanotubes, into the dispersant-containing solution, initiate
strong agitation: ball milling, or ultrasonicating, or any
combination of physical methods named; following an agitation time
of several hours, the resulting paste will be extremely stable and
easily dilutable into more base oils and additives to give the
final desired concentrations of additives and the desired final
viscosity.
EXAMPLES
[0109] Specific compositions, methods, or embodiments discussed are
intended to be only illustrative of the invention disclosed by this
specification. Variation on these compositions, methods, or
embodiments are readily apparent to a person of skill in the art
based upon the teachings of this specification and are therefore
intended to be included as part of the inventions disclosed herein.
Reference to documents made in the specification is intended to
result in such patents or literature cited are expressly
incorporated herein by reference, including any patents or other
literature references cited within such documents as if fully set
forth in this specification.
[0110] An automatic transmission fluid D was formulation with the
same composition as automatic transmission fluid (ATF) A and result
is list in Example 1 as well. The particle size is measured by
atomic force microscopy (AFM), and FIG. 5 illustrates an AFM
picture of ATF B. The graphite nanoparticles are plate-like
structure, with average diameter is around 50 nm and thickness
around 5 nm (as we described earlier, nanodisk or nanoplate).
Example 1
Automatic Transmission Fluids and Viscosity Data
[0111] TABLE-US-00001 ATF A B C D E* From Concentrate Paste A Paste
B Paste C Paste D N/A Kinematic viscosity at 7.55 19.68 10.83 7.48
7.15 100.degree. C., cSt Kinematic viscosity at 28.44 29.32 28.77
27.85 33.67 40.degree. C., cSt Viscosity Index 254 634 395 257 183
*E is an off-the-shelf regular commercial ATF (MERCON V).
Example 2
Engine Oil
[0112] TABLE-US-00002 Product Conventional Nanoparticle-containing
Engine Oil Engine oil Composition Valvoline 90% DURABLEND 5W-30
DURABLEND 5W-30 9% DURASYN 162 1% Graphite Process Bulk graphite is
pulverized, and milled in DURASYN 162 to obtain a paste. The paste
is added to DURABLEND 5W-30 Viscosity 10.66 10.90 @ 100.degree. C.
Viscosity 61.14 54.34 @ 40.degree. C. Viscosity 166 197 Index
Example 3
Shock Absorber Oil
[0113] TABLE-US-00003 Product Conventional Nanoparticle-containing
Shock Oil Shock oil Composition VISTA LPA 62.40 77.70 210 LUBRIZOL
36.87 20.66 7720C LUBRIZOL 0.30 0.30 5186B Tricresyl 0.22 0.22
phosphate F-655C 0.20 defoamer Blue Dye 0.01 0.01 Graphite 1.11
Process Graphite obtained as powders (UCAR), and milled in VISTA
LPA 210/LZ 7720C to obtain a concentrate. Then the other
ingredients are added to make the final formulation Viscosity 8.97
7.77 @ 100.degree. C. Viscosity 29.75 12.45 @ 40.degree. C.
Viscosity 307 732 Index
Example 4
Automatic Transmission Fluid (ATF)
[0114] TABLE-US-00004 Product Conventional Nanoparticle-
Nanoparticle- Mercon V containing containing ATF ATF #1 ATF #2
Composition 2 cSt PAO 36.00 34.00 4 cSt PAO 51.50 53.50 LUBRIZOL
10.50 10.50 ATF DI Package Graphite 2.00 2.00 Process Graphite
obtained Graphite foam as powders (UCAR), (POCO) was and milled in
pulverized, and 2 cSt PAO/DI milled in 2 cSt package to obtain
PAO/DI package a concentrate. to obtain a Then other concentrate.
ingredients are Then other added to make ingredients are the final
added to make formulation the final formulation Viscosity 7.70 7.57
7.37 @ 100.degree. C. Viscosity 36.20 16.01 16.96 @ 40.degree. C.
Viscosity 190 527 475 Index
Example 5
Gear Lubricant
[0115] TABLE-US-00005 Product Conventional Nanoparticle-containing
Gear Oil Gear Oil Composition YUBASE 100N 47.70 4 cSt PAO 15.00
9.00 6 cSt PAO 67.00 LUBRIZOL 10.00 10.00 Gear Oil DI Package
LUBRIZOL 26.30 12.00 3174 VISCOPLEX 1.00 1.00 0-112 Graphite 1.00
Process Graphite obtained as powders (UCAR), and milled in 4 cSt
PAO/DI package to obtain a concentrate. Then the other ingredients
are added to make the final formulation Viscosity 14.21 14.79 @
100.degree. C. Viscosity 98.63 65.06 @ 40.degree. C. Viscosity 148
240 Index
[0116] To demonstrate the temporary shear loss effect, a regular
DEXRON III ATF and a nanofluid ATF were tested for
high-temperature-high-shear (HTHS) viscosity, ASTM D 4683. This
technique measures the high-temperature (150.degree. C.)
high-shear-rate viscosity of motor oils; very high shear rates
(10.sup.6 s.sup.-1) are obtained by using an extremely small gap
between the rotor and stator wall. Low number means more temporary
shear loss under the test conditions.
Example 6
HTHS Viscosity of a DEXRON III ATF and a Nanofluid ATF
[0117] TABLE-US-00006 DEXRON III ATF Nanofluid ATF Graphite
nanodisk 0 2% 100.degree. C. Kinematic Viscosity 7.2 cSt 7.55 cSt
HTHS Viscosity (150.degree. C., 2.06 cP 1.74 cP 10.sup.6
s.sup.-1)
[0118] To demonstrate that there is no permanent shear loss to
these nanodisk-containing fluids, a standard European gear
lubricant test, CEC L-45-T-93, was run on a SYNPOWER 75W-90 and on
a nanofluid gear oil. This test is designed to permanently shear
down the non-shear-stable polymers in the formulation through a
special taper roller bearing rig.
Example 7
Permanent Shear Test Data on a SYNPOWER 75W-90 and a Nanofluid Gear
Oil
[0119] TABLE-US-00007 SYNPOWER Nanofluid Gear 75W-90 Oil Graphite
nanodisk 0 1% 100.degree. C. 14.90 cSt 18.14 cSt Kinematic
Viscosity before shear 100.degree. C. 13.96 cSt 17.47 cSt Kinematic
Viscosity after shear Percent Viscosity 6.31 3.69 Loss due to
shear
[0120] The foregoing detailed description is given primarily for
clearness of understanding and no unnecessary limitations are to be
understood therefrom, for modification will become obvious to those
skilled in the art upon reading this disclosure and may be made
upon departing from the spirit of the invention and scope of the
appended claims. Accordingly, this invention is not intended to be
limited by the specific exemplification presented herein above.
Rather, what is intended to be covered is within the spirit and
scope of the appended claims.
* * * * *