U.S. patent application number 11/981720 was filed with the patent office on 2008-11-20 for lubricants with enhanced thermal conductivity containing nanomaterial for automatic transmission fluids, power transmission fluids and hydraulic steering applications.
Invention is credited to Frances E. Lockwood, Gefei Wu, Zhiqiang Zhang.
Application Number | 20080287326 11/981720 |
Document ID | / |
Family ID | 40028107 |
Filed Date | 2008-11-20 |
United States Patent
Application |
20080287326 |
Kind Code |
A1 |
Zhang; Zhiqiang ; et
al. |
November 20, 2008 |
Lubricants with enhanced thermal conductivity containing
nanomaterial for automatic transmission fluids, power transmission
fluids and hydraulic steering applications
Abstract
A lubricant composition having an enhanced thermal conductivity,
up to 80% greater than its conventional analogues, and methods of
preparation for these fluids are identified. One preferred
composition contains a base oil, nanomaterial, and a dispersing
agent or surfactant for the purpose of stabilizing the
nanomaterial. One preferred nanomaterial is a high thermal
conductivity graphite, exceeding 80 W/m in thermal conductivity.
The graphite is ground, milled, or naturally prepared to obtain a
mean particle size less than 500 nm in diameter, and preferably
less than 100 nm, and most preferably less than 50 nm. The graphite
is dispersed in the fluid by one or more of various methods,
including ultrasonication, milling, and chemical dispersion. Carbon
nanostructures such as nanotubes, nanofibrils, and nanoparticles
are another type of graphitic structure useful in the present
invention. Other high thermal conductivity carbon materials are
also acceptable. To confer long-term stability, the use of one or
more chemical dispersants or surfactants is useful. The thermal
conductivity enhancement, compared to the fluid without graphite,
is proportional to the amount of nanomaterials added. The graphite
nanomaterials contribute to the overall fluid viscosity, partly or
completely eliminating the need for viscosity index improvers and
providing a very high viscosity index. Particle size and dispersing
chemistry is controlled to get the desired combination of viscosity
and thermal conductivity increase from the base oil while
controlling the amount of temporary viscosity loss in shear fields.
The resulting fluids have unique properties due to the high thermal
conductivity and high viscosity index of the suspended particles,
as well as their small size.
Inventors: |
Zhang; Zhiqiang; (Lexington,
KY) ; Wu; Gefei; (Lexington, KY) ; Lockwood;
Frances E.; (Georgetown, KY) |
Correspondence
Address: |
David W. Carrithers;CARRITHERS LAW OFFICE, PLLC
One Paragon Centre, 6060 Dutchman's Lane, Suite 140
Louisville
KY
40205
US
|
Family ID: |
40028107 |
Appl. No.: |
11/981720 |
Filed: |
October 31, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10737731 |
Dec 16, 2003 |
|
|
|
11981720 |
|
|
|
|
10021767 |
Dec 12, 2001 |
6783746 |
|
|
10737731 |
|
|
|
|
PCT/US02/16888 |
May 30, 2002 |
|
|
|
10737731 |
|
|
|
|
60254959 |
Dec 12, 2000 |
|
|
|
60433798 |
Dec 16, 2002 |
|
|
|
Current U.S.
Class: |
508/113 |
Current CPC
Class: |
C10M 2201/041 20130101;
C10N 2020/06 20130101; C10N 2070/00 20130101; C10M 103/02 20130101;
C10M 169/04 20130101; C10N 2030/00 20130101; C10N 2030/02 20130101;
C10N 2040/042 20200501; C10N 2030/08 20130101 |
Class at
Publication: |
508/113 |
International
Class: |
C10M 169/04 20060101
C10M169/04 |
Goverment Interests
[0002] This application is part of a government project, Contract
No. W031-109-ENG-38 by the Department of Energy. The Government has
certain rights in this invention.
Claims
1. 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, comprising the
steps of: a) dissolving an effective amount of at least one of the
group consisting of a dispersant, a surfactant, a dispersant
additive package, and combinations thereof into an effective amount
of at least one base oil forming a first mixture; b) adding a high
concentration of up to 20 percent by weight of a carbon
nanomaterial into said first mixture while being strongly agitated
by high impact milling, and/or ultrasonication, to form a pasty
liquid; and c) diluting said pasty liquid with an effective amount
of a base oil.
Description
[0001] This application is a Continuation-In-Part of copending U.S.
application Ser. No. 10/737,731 filed on Dec. 16, 2003 which claims
priority from U.S. application Ser. No. 10/021,767 filed on Dec.
12, 2001 which claims priority from U.S. Provisional Application
Ser. No. 60/254,959 filed on Dec. 12, 2000; PCT Application S.N.
PCT/US02/16888 filed on May 30, 2002; U.S. nonprovisional
application Ser. No. ______ filed on Dec. 8, 2003; and claims
priority from U.S. Provisional Application Ser. No. 60/433,798
filed on Dec. 16, 2002 all of which are incorporated by reference
in their entirety.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The invention relates to the field of providing lubricants
and functional fluids containing nanomaterial dispersed within
automatic transmission fluids, power transmission fluids, and
hydraulic steering fluids which exhibit enhanced thermal
conductivity as compared to conventional fluids without the
nanomaterial dispersions.
[0005] 2. Description of the Prior Art
[0006] Lubricants and coolants of various types are used in
equipment and in manufacturing processes to remove waste heat,
among other functions. Traditionally, water is most preferred for
heat removal, however, to expand it's working temperature range,
freezing point depressants such as ethylene glycol and/or propylene
glycol are added, typically at levels above 10% concentration by
volume. For example, automotive coolant is typically a mixture of
50-70% ethylene glycol, and the remainder is water. The thermal
conductivity of the freezing point depressed fluid is then about
2/3 as good as water alone, as illustrated in Table 1. In many
processes and applications, water can not be used for various
reasons, such as corrosion, temperature restriction, etc., and then
a type of oil, e.g., mineral oil, polyalphaolefin, ester synthetic
oil, ethylene oxide/propylene oxide synthetic oil, polyalkylene
glycol synthetic oil, etc. is used. The thermal conductivity of
these oils, is typically 0.12 to 0.16 W/m at room temperature, and
thus they are inferior as heat transfer agents to water, since
water has a much higher thermal conductivity, 0.61 W/m as set forth
in Table 1. Usually these oils have many other important functions,
and they are carefully formulated to perform to exacting
specifications for example for friction and wear performance, low
temperature performance, fuel efficiency performance etc. Often
designers will desire a fluid with higher thermal conductivity than
the conventional oil, but are restricted to oil due to the many
other parameters the fluid must meet.
TABLE-US-00001 TABLE 1 Thermal conductivity of various materials
(at room temperature) Thermal Conductivity Material (W/m) Mineral
oil 0.13 Typical fully- 0.12-0.16 formulated engine oil Ethylene
glycol 0.253 Water 0.613 Commercial 0.40 antifreeze Graphite
80-700
[0007] The use of graphite in fluids such as lubricants is 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, typically mean as
500-800 nm (nanometers). The thermal advantage of the graphite is
nor mentioned in the sales literature, nor is the product sold or
promoted for its thermal conductivity property.
[0008] 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 thermal
conductivity of the fluid formulated for specific applications.
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 thermal conductivity and
that reducing particle size improves thermal conductivity. While
graphite-containing automotive engine oil was once commercialized
(Arco graphite), the potential to use graphite as a heat transfer
improving material in this oil was not realized. The particle size
of graphite used was larger (mean greater than one micron) than for
the instant invention. 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.
[0009] 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. The thermal conductivity of the
Hyperion Catalysis International, Inc. material is not stated in
their product literature. However, the potential of carbon
nanotubes to convey thermal conductivity in a material is mentioned
in their patents, U.S. Pat. No. 5,165,909. Actual measurement of
the thermal conductivity of the carbon fibrils they produced was
not given in the patent, so the inference of thermal conductivity
is general and somewhat speculative, based on graphitic
structure.
[0010] Bulk graphite with high thermal conductivity is available
from Poco Graphite as a graphite foam, with thermal conductivity
higher than 100 W/m, and is also available from the
Carbide/Graphite Group, Inc. Graphite powders can be obtained from
UCAR Carbon Company Inc., with thermal conductivity 10-500 W/m, and
typically >80 W/m, and from Cytec Carbon Fibers LLC, with
thermal conductivity 400-700 W/m. These bulk materials must be
reduced to a nanometer-sized powder by various methods for use in
the instant invention.
[0011] Utilization of these inexpensive sources of nanomaterials
have not been released in lubrication formulations before and a
point of novelty in the instant invention is the ability to reduce
the graphite to produce an inexpensive nanomaterial having a
particle size suitable for long term dispersion in lubricating
compositions and the method of dispersing same.
[0012] Automatic transmission fluids, ("ATF"), power transmission
fluids and hydraulic steering fluids have stringent requirements
for viscosity, stability to oxidation, temperature and shear, low
temperature fluidity, and static and dynamic coefficient of
friction and their relative levels over many shift cycles.
Additionally, the heat transfer requirements in transmissions and
pumps are significant. It is generally necessary to use some form
of cooling for the transmission fluid, and some designs of
transmissions are prevented due to insufficient capability to
eliminate waste heat. Because of the friction control requirements,
and the relatively large particle size of conventional graphite
dispersions, the use of graphite in these fluids is not known.
[0013] While the present invention is applicable in automatic
transmission fluids, (ATF), power transmission fluids and hydraulic
steering fluids, the examples and further discussion will focus on
automatic transmission fluids; however, the claims are applicable
to the power transmission fluids, hydraulic steering fluids, and
other types of oil based noncompressible fluids as well.
SUMMARY OF THE INVENTION
[0014] In this invention, automatic transmission fluids of enhanced
thermal conductivity are prepared by dispersing nanometer-sized
carbon nanomaterials of thermal conductivity higher than 80 W/m
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.
[0015] For example, the instant invention provides a method for
making a composition for an automatic transmission fluids that have
enhanced thermal conductivity, up to 80% greater than their
conventional analogues. One preferred composition contains an
effective amount of at least one base oil such as mineral oil,
hydrocracked mineral oil with high viscosity index, vegetable
derived oils, polyalphaolefins, poly-internal-olefins,
polyalkylglycols, polycyclopentadienes, propylene oxide or ethylene
oxide based synthetics, silicone oils, phosphate esters or other
synthetic esters, or any suitable base oil; an effective amount of
at least one type of nanomaterial, preferably graphite nanoparticle
or carbon nanotubes, and an effective amount of at least one
dispersing agents or surfactants for the purpose of stabilizing the
nanoparticles.
[0016] One preferred nanomaterial is a high thermal conductivity
graphite, exceeding 80 W/m in thermal conductivity, and ground,
milled, or naturally prepared with mean particle size less than 500
nm in diameter, and preferably less than 100 nm, and most
preferably less than 50 nm. The graphite is dispersed in the fluid
by one or more of various methods, including ultrasonication,
milling, and chemical dispersion. It is contemplated that
nanoparticles can be selected from any metal from the Group IV
elements, such as carbon materials (carbon nanotubes, fullerenes,
graphite, amorphous carbon, carbon particles, carbon fibrils and
combinations thereof, etc.), silicone carbide, and clay materials,
metal (including transition metals) particles (such as silver,
copper, aluminum, etc.), metal oxides, alloy particles, and
combinations thereof may be applicable to the instant
invention.
[0017] Carbon nanotubes with a graphitic structure are another
preferred type of nanomaterial or particles. Other high thermal
conductivity carbon materials are also acceptable as long as they
meet the thermal conductivity and size criteria set forth
heretofore.
[0018] To confer long-term stability, an effective amount of one or
more chemical dispersants or surfactants is preferred, although a
special grinding procedure in base oil will also confer long term
stability. The thermal conductivity enhancement, compared to the
fluid without graphite, is proportional to the amount of
nanomaterials added. The graphite nanoparticles or nanotubes
contribute to the overall fluid viscosity, partly or completely
eliminating the need for viscosity index improvers and providing a
very high viscosity index. Particle size and dispersing chemistry
is controlled to get the desired combination of viscosity and
thermal conductivity increase from the base oil while controlling
the amount of temporary viscosity loss in shear fields. The
resulting fluids have unique properties due to the high thermal
conductivity and high viscosity index of the suspended particles,
as well as their small size.
[0019] The present invention provides at a minimum, a fluid of
lubricant containing less than 10% by weight graphite
nanoparticles. Preferably, however, a minimum of one or more
chemical dispersing agents and/or surfactants is also added to
achieve long term stability.
[0020] 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
surfactant 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 for often a surfactant has dispersing characteristics and
many dispersants have the ability to reduce interfacial
tensions.
[0021] The particle-containing fluid of the instant invention will
have a thermal conductivity higher than the neat fluid, wherein the
term `neat` is defined as the fluid before the particles are
added.
[0022] The fluid can have 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 to define a lubricant
composition suitable for use in vehicle applications or the like.
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.
[0023] For instance, U.S. Pat. No. 4,029,587 by Koch teaches the
use of a variety additives for functional fluids applicable to the
present invention and is hereby incorporated by reference in its
entirety. Moreover, U.S. Pat. No. 4,116,877 by Outten et al.
teaches the use of a variety additives for hydraulic fluids such as
automatic transmission fluids and power steering fluids applicable
to the present invention and is hereby incorporated by reference in
its entirety.
[0024] As set forth above, the preferred carbon nanomaterials are
selected from graphitic carbon structures with bulk thermal
conductivity exceeding 80 W/m. A preferred form of carbon
nanomaterials is carbon nanotubes. Another preferred form of carbon
nanomaterials is high thermal conductivity graphite. A preferred
form of the high thermal conductivity graphite is Poco Foam from
Poco Graphite. Another preferred form of high thermal conductivity
graphite is graphite powders from UCAR Carbon Company Inc. Still
another preferred form of high thermal conductivity graphite is
graphite powders from Cytec Carbon Fibers LLC. Still another
preferred form of graphite is bulk graphite from The
Carbide/Graphite Group, Inc.
[0025] Of course, one of the major drawbacks concerning commercial
use of the carbon nanotubes and other prepared carbon structures is
the cost of preparation and availability of same for commercial
applications. The instant invention has resulted in the development
of a method of reducing very inexpensive graphite to a nanomaterial
comprising particles, fabrils and flakes suitable for use and long
term dispersion in lubricant compositions.
[0026] The carbon nanomaterial 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 viscosity index improvers that are not for the
purpose of dispersing, but to achieve thickening or other desired
fluid characteristics.
[0027] Furthermore, the carbon nanomaterial dispersion can be
pre-sheared, in a turbulent flow, such as a nozzle, or high
pressure fuel injector, ultrasonic device, or 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 increasing effect will not change upon further
use.
[0028] The milling process itself, or other pre-shearing process,
can have a rather dramatic effect on the long term dispersion
stability.
[0029] A novel method has been developed whereby graphite particles
are milled to form 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 automatic transmission fluid. 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 20% up to 100% of the
dispersant/surfactant mixture with the remainder being natural,
synthetic, or mineral base oil. Once the thermally conductive
concentrate prepared by milling is diluted to liquid consistency
with base oil and other transmission fluid components, the entire
fluid can (optionally) be passed through a small orifice to further
increase the uniformity and decrease the size of dispersed
particles.
[0030] An important aspect of this invention is that the final ATF
composition should be prepared to give an acceptable lubricant film
thickness at the maximum shear rate and temperature of use in the
target transmission. The maximum concentration of particles in the
final (diluted) automatic transmission 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 heat transfer improvement with the ATF of the instant
invention will be greater at room temperature than at the highest
temperature of use due to the excellent viscosity index of the
particle-containing fluids, depending on the particle size and
their thickening effect. Viscosity index is defined as the
relationship of viscosity to the temperature of a fluid. It is
determined by measuring the kinematic viscosities of the oil at
40.degree. C. and 100.degree. C. and using the tables or formulas
included in ASTM D2270. It is important to note that the smaller
particles give the best thermal conductivity increase, and higher
viscosity index of fluid, but also contribute to higher temporary
viscosity loss in shear fields. A fluid made with heat transfer
improvement of 20% at 100.degree. C. may have an improvement of 60%
or more when compared to a conventional fluid at 40.degree. C.
Therefore the heat transfer improvement due to the particles may be
twofold, due to the higher thermal conductivity of the particles,
and also due to the exceptional viscosity index of the
particle-containing fluid.
[0031] 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.
[0032] 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/m).
[0033] It is an object of the present invention to provide a method
of developing a method of forming carbon nanomaterials from
inexpensive bulk graphite.
[0034] 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.
[0035] It is an object of the present invention to provide a method
of using carbon nanotubes which are either single-walled, or
multi-walled, with typical aspect ratio of 500-5000.
[0036] 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.
[0037] 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.
[0038] It is an object of the present invention to provide a
process for preparing a lubricant composition containing
nanomaterial by
[0039] 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.
[0040] 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.
[0041] 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 HLB value (<8),
preferably nonionic or mixture of nonionic and ionic
surfactants.
[0042] It is an object of the present invention to provide that the
dispersants can be the ashless polymeric dispersants used in the
lubricant industry.
[0043] 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.
[0044] 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.
[0045] 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.).
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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
[0052] 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:
[0053] FIG. 1 is an atomic force microscopy (AFM) picture of an
automatic transmission fluid composition showing the graphite
nanoparticles as flakes or plate-like structures with an average
diameter of around 50 nm and thickness around 5 nm.
[0054] FIG. 2 is a diagram of a hot-wire rig constructed to obtain
the absolute measurement of the thermal conductivity of
electrically conducting liquids by the transient hot-wire
method.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0055] The present invention provides a graphitic dispersion in
fluid medium that gives a high thermal conductivity and improved
heat transfer capability compared to conventional fluids of the
same medium. In the present invention the fluid medium is targeted
in its viscosity, friction, and antioxidant characteristics to
perform in modern automatic transmissions.
[0056] One preferred type of graphitic particles are carbon
nanotubes, the nanotubes can be either single-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 500 nanometers to 500 microns. More typical length is
1 micron to 100 microns. The aspect ratio of the tube can be from
hundreds to thousands, more typical 500 to 5000. The surface of the
nanotube can be treated chemically to achieve certain level of
hydrophilicity, or left as is from the production. Unfortunately,
the commercial availability of the prepared nanotubes is limited
making them too expensive for incorporation into commodity type
lubricants at this time.
[0057] Therefor, a novel method has been developed to form
nanomaterials suitable for use with commodity type lubricants at a
low cost and capable of being produced in a large quantity using
readily available equipment. Other acceptable form of graphite is a
high-thermal-conductivity graphite commercially available, e.g.
POCO FOAM, available from Poco Graphite, Inc., and graphite powders
available from UCAR Carbon Company Inc. POCO FOAM is a high thermal
conductivity foamed graphite, thermal conductivity typically in the
range 100 to 150 W/m. A readily commercially available graphite is
graphite powders from UCAR Carbon Company Inc., thermal
conductivity of 10 to 500 W/m, and typically >80 W/m. Still
another acceptable form of graphite is the
high-thermal-conductivity graphite, Part#875G, from The
Carbide/Graphite Group, Inc.
[0058] These graphite are 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 particle, flake, fibril or combinations thereof
produce nanomaterial of a size of less than 500 nm mean size is
attained. The preferred method is to disperse the graphite by ball
milling in a viscous fluid of most 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 thermal conductivity
increase but also the more viscosity thickening effect of the pasty
concentrate on the final blend. These effects must be balanced to
attain a suitable lubricating film thickness at the maximum shear
rate and temperature of fluid use. In general, any high thermal
conductivity graphite 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 or less.
[0059] In the process of making lubricating fluid such as the
automatic transmission fluid with the nanomaterial, the mechanical
process and sequence of adding the components are important in
order to fully take advantage of the high viscosity index of the
nanoparticles an 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.
[0060] To achieve the best milling effect and therefore the best
viscosity index improvement, the proper milling procedure has been
developed. Firstly a 5% to 20% by weight of graphite powders, and
more preferably 10% by weight of graphite powders, in base oil
dispersion is milled into a paste state. Usually this step takes
about 3 to 4 hours. Then add the appropriate effective amount of at
least one dispersing agent(s), usually 1 to 2 times of the weight
of graphite, 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(are) added into the
mill at the very beginning, the viscosity index of the final
nanofluids made from the milling process is not as high.
[0061] Graphite nanomaterials are obtained by pulverizing big
graphite chunks weight several pounds or kilograms obtained from
The Carbide/Graphite Group. The resulting pulverized material is
size-selected through a mesh filter to be less than 75 Thirty (30)
grams of the above pulverized graphite particles and 270 grams of a
base oil, DURASYN 162 (a commercial 2 centistokes polyalphaolefin)
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. About 60 grams of this
paste was discharged and labeled Paste `A`. Forty-eight (48) grams
of a dispersant package from Lubrizol, LUBRIZOL 9677MX, was added
to the rest of the mixture in the mill. The paste became very thin,
and successful recirculation was 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 7560 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 three automatic transmission fluids were
formulated, A through C, using the above three pastes as
concentrates respectively. The final compositions were exactly the
same by weight and ingredients except for the graphite material: 2%
graphite, 4% LUBRIZOL 9677 MX, 18% DURASYN 162, 76% DURASYN 166 (a
commercial 6 centistokes polyalphaolefin base oil) (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 an important variable to
control the viscosity modification effect as well. For example,
starting with graphite smaller than 10 (obtained as graphite powder
from UCAR Carbon Company Inc.) and following the same procedure as
Paste B, a thin Paste D was obtained. An automatic transmission
fluid D was formulation with the same composition as ATF A and
result is list in Example 1 as well. The particle size is measured
by atomic force microscopy (AFM), and FIG. 1 illustrates an AFM
picture of ATF B. The graphite nanoparticles appear to be flakes or
a plate-like structure, with average diameter of around 50 nm and
thickness around 5 nm.
Oil Basestocks
[0062] 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 (polyalphaolefins),
and Group V (esters, naphthenes, and others). One preferred group
includes the polyalphaolefins, synthetic esters, and
polyalkylglycols.
[0063] 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(l-octenes), poly(l-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.
[0064] 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.
[0065] Esters useful as synthetic oils also include those made from
C 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.
[0066] 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 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.
[0067] 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 (100.degree.
C.) and 16.75 centistokes at (40.degree. C.). It has a viscosity
index of 125 and a pour point of -98.degree. C. Moreover, EMERY
3006 polyalphaolefin has a viscosity of 5.88 centistokes at
212.degree. C. and 31.22 centistokes at 104.degree. C. It has a
viscosity index of 135 and a pour point of -87.degree. C.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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. Mobil polyolesters P-43, M O45
containing two alcohols, and Hatco Corp. 2939 are particularly
preferred.
[0072] 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.
[0073] 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.
[0074] 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 basestocks 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.
[0075] Group III oils are often referred to as hydrogenated oil to
be used as the sole base oil component of the instant invention
providing superior performance to conventional ATFs with no other
synthetic oil base or mineral oil base.
[0076] 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 hydrotreated 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.
[0077] The hydrogenated oil my be used as the sole 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.
[0078] 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. C. and MAP 100
Neutral defined as a solvent refined neutral having a Sabolt
Universal viscosity of 100 SUS at 100.degree. C., both manufactured
by the Marathon Ashland Petroleum.
[0079] 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.
[0080] 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 Used in Lubricant Industry
[0081] 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 transmission.
[0082] 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.
[0083] Of these ashless dispersants the ones typically used in the
petroleum industry include N-substituted 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-polyethylenepolyamine, polyisobutenyl
succinic ester, polyisobutenyl hydroxybenzyl-polyethylenepolyamine,
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 ispersant-detergent (DI) additive
package for transmission fluids, e.g., LUBRIZOL 9677MX, and the
whole DI package can be used as dispersing agent for the
nanoparticle dispersions.
Other Types of Dispersants
[0084] 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.
[0085] 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 20 percent, more preferably in a range of from between 1
to 15 percent, and most preferably in a range of from between 2 to
13 percent. The carbon nanomaterials can be of any desired weight
percentage in a range of from 0.001 up to 10 percent. For practical
application it is usually in a range of from between 0.01 percent
to 10 percent, and most preferably in a range of from between 0.1
percent to 5 percent. The remainder of the formula is the selected
medium.
[0086] It is believed that in the instant invention the dispersant
functions by adsorbing onto the surface of the carbon
nanomaterials.
Other Chemical Compounds
[0087] 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 thickening or other desired
fluid characteristics. These can be added but reduce the amount of
particulate that can be used without excessive thickening.
[0088] The viscosity improvers used in the lubricant industry can
be used in the instant invention for the oil medium, 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.
[0089] 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 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.
[0090] 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, Adipate, 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 oieate, 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.
[0091] Antioxidants are an important part of transmission fluids.
General classes include zinc
dialkyldithiophosphates, alkyl and aryl phenols, alkyl and aryl
amines, and sulfurized olefins. Commercial examples are Ciba L57
(phenyl amine) and Etnyl Hitec 1656.
[0092] 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.
[0093] Friction Modifiers are used to control friction and torque
characteristics of the fluid. Commercial examples include LUBRIZOL
8650 and HITEC 3191.
Physical Agitation
[0094] 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.
[0095] Ball milling is the most preferred physical method in the
instant invention since it is effective at rapidly reducing the
graphite 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
transmission. 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 reduces the carbon nanotube average aspect
ratio. A detailed description has been given in an earlier section
of the instant invention.
[0096] Ultrasonication is another physical method in the instant
invention since it is less destructive to the carbon nanomaterial
structure than the other methods described. Ultrasonication can be
done either in the bath-type ultrasonicator, or by the horn-type
ultrasonicator. 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.
[0097] The instant method of forming a stable dispersion of carbon
nanomaterials in a solution consist of three steps. First select
the appropriate concentrate of dispersant or mixture of dispersing
and other additives for the carbon nanomaterials, and the 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 carbon nanomaterials into the
dispersant-containing solution, initiate strongly agitating, 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
oil and additives to give the final desired concentrations of
additives and the desired final viscosity.
EXAMPLES
[0098] The following examples describe preferred embodiments of the
invention. Other embodiments within the scope of the claims herein
will be apparent to one skilled in the art from consideration of
the specification or practice of the invention as disclosed herein.
It is intended that the specification, together with the examples,
be considered exemplary only, with the scope and spirit of the
invention being indicated by the claims which follow the examples.
In the examples all percentages are given on a weight basis unless
otherwise indicated. 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.
Example 1
Automatic Transmission Fluids and Viscosity Data
TABLE-US-00002 [0099] ATF A B C D E* From Concentrate Paste Paste
Paste Paste N/A A B C D Kinematic 7.55 19.68 10.83 7.48 7.15
viscosity at 100.degree. C., cSt Kinematic vis- 28.44 29.32 28.77
27.85 33.67 cosity at 40.degree. C., cSt Viscosity Index 254 634
395 257 183 *E is an off-the-shelf regular commercial ATF (MERCON
V).
[0100] Thermal conductivity is measured by a transient hot-wire rig
constructed by the inventors in-house according to Nagasaka et al.
(Y. Nagasaka and A. Nagashima, Absolute measurement of the thermal
conductivity of electrically conducting liquids by the
transient
R H T E F = ( k k 0 ) 0.67 ( .eta. .eta. 0 ) - 0.52 ( .rho. .rho. 0
) 0.57 ( C P C P , 0 ) 0.33 ##EQU00001##
hot-wire method, Journal of Physics E: Sci. Instrum. 1981, 14,
1435-1440). A diagram of the rig is shown in FIG. 2. The relative
heat transfer efficiency factor (RHTEF) of a test fluid versus a
another test fluid (denoted by subscript 0) is evaluated by the
above equation.
Example 2
TABLE-US-00003 [0101] Components Description Weight percentage
Carbon nanomaterial Graphite (The 2.0 Carbide/Graphite Group, Inc.)
Dispersant Lubrizol 9677MX 4.0 Base oil Durasyn 166 76.0 Base oil
Durasyn 162 18.0 Process Pulverize to <75 and then Eiger mini
mill Viscosity 40 (cSt) 28.4 Viscosity 100 (cSt) 7.55 Viscosity
Index (VI) 254 (vs. 183 for conventional ATF) Thermal conductivity
0.1776 (vs. 0.132 for conventional ATF) (W/m) RHTEF at 40 1.4 (vs.
conventional ATF)
Example 3
TABLE-US-00004 [0102] Components Description Weight percentage
Carbon nanomaterial Graphite powder 2.0 (UCAR) Dispersant Lubrizol
9677MX 4.0 Base oil Durasyn 166 76.0 Base oil Durasyn 162 18.0
Process Eiger mini mill Viscosity 40 (cSt) 27.85 Viscosity 100
(cSt) 7.48 Viscosity Index (VI) 257 (vs. 183 for conventional ATF)
Thermal conductivity 0.1926 (vs. 0.132 for conventional ATF) (W/m)
RHTEF at 40 1.5 (vs. conventional ATF)
Example 4
TABLE-US-00005 [0103] Components Description Weight percentage
Carbon nanomaterial Poco Foam (Poco 2.5 Graphite) Dispersant
Lubrizol 9677MX 7.5 Base oil SK Yubase 4 42.5 Base oil SK Yubase 3L
42.5 Viscosity modifier Lubrizol 7720C 5.0 Process Eiger mini mill
Viscosity 40 (cSt) 43.12 Viscosity 100 (cSt) 9.55 Viscosity Index
(VI) 215 (vs. 183 for conventional ATF) Thermal conductivity 0 . .
. 2092 vs. 0.132 for conventional ATF) (W/m) RHTEF at 40 1.6 (vs.
conventional ATF)
Example 5
TABLE-US-00006 [0104] Components Description Weight percentage
Carbon nanomaterial Graphite (The 2.0 Carbide/Graphite Group, Inc.)
Dispersant Lubrizol 9677MX 5.0 Base oil Durasyn 162 18.0 Base oil
Hatco HXL-7156 37.5 Base oil SK Yubase L3 37.5 Process Pulverize to
<75 then EIGER mini-mill Viscosity 40 (cSt) 35.18 Viscosity 100
(cSt) 10.48 Viscosity Index (VI) 306 (vs. 183 for conventional ATF)
Thermal conductivity 0.1889 vs. 0.132 for conventional ATF) (W/m)
RHTEF at 40 1.3 (vs. conventional ATF)
Example 6
TABLE-US-00007 [0105] MerconV MaxLife Parameters ATF ATF Fluid #1
Fluid #2 Fluid #3 Fluid #4 % Graphite (UCAR) 0 0 2.0 0 2.0 0 %
Graphite (Poco Foam) 0 0 0 2.0 0 2.0 % DI Package 10.5 10.5 4.0 6.5
10.5 10.5 40 Vis (cSt) 36.2 34.56 27.89 27.44 16.01 16.96 100 Vis
(cSt) 7.7 7.12 7.48 7.35 7.57 7.37 Viscosity Index 190 175 257 255
527 475 100 C.sub.p (J/g) 2.1801 1.9706 2.255 2.277 2.0867 2.1578
20 Density (g/cm 0.8632 0.8389 0.8244 0.8294 0.8213 0.8226 40
Density (g/cm 0.8502 0.8288 0.8151 0.8191 0.8099 0.8114 100 Density
(g/cm 0.8115 0.7921 0.7781 0.7828 0.7746 0.7758 RHTEF at 40 1
(baseline) N/A 1.46 1.54 1.8 1.82 RHTEF at 100 1 (baseline) N/A
1.27 1.34 1.17 1.24
Example 7
TABLE-US-00008 [0106] Components Description Weight percentage
Carbon nanomaterial Multi-walled carbon 0.2 nanotubes Dispersant
Oronite OLOA 9061 4.8 Base oil Durasyn 166 95.0 Process
Ultrasonicate for 15 minutes and then pass the dispersion through a
fuel injector shear nozzles 20 cycles Viscosity 40 (cSt) 46.08
Viscosity 100 (cSt) 9.89 Viscosity Index (VI) 208 (vs. 183 for
conventional ATF) Thermal conductivity 0.1522 vs. 0.132 for
conventional ATF) (W/m) RHTEF at 40 1.2 (vs. conventional ATF)
[0107] 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.
* * * * *