U.S. patent application number 11/981768 was filed with the patent office on 2009-12-03 for enhancing thermal conductivity of fluids with graphite nanoparticles and carbon nanotube.
Invention is credited to Frances E. Lockwood, Zhiqiang Zhang.
Application Number | 20090298725 11/981768 |
Document ID | / |
Family ID | 33160075 |
Filed Date | 2009-12-03 |
United States Patent
Application |
20090298725 |
Kind Code |
A1 |
Zhang; Zhiqiang ; et
al. |
December 3, 2009 |
Enhancing thermal conductivity of fluids with graphite
nanoparticles and carbon nanotube
Abstract
Fluid compositions that have enhanced thermal conductivity, up
to 250% greater than their conventional analogues, and methods of
preparation for these fluids are identified. The compositions
contain at a minimum, a fluid media such as oil or water, and a
selected effective amount of carbon nanomaterials necessary to
enhance the thermal conductivity of the fluid. One of the preferred
carbon nanomaterials is a high thermal conductivity graphite,
exceeding that of the neat fluid to be dispersed therein in thermal
conductivity, and ground, milled, or naturally prepared with mean
particle size less than 500 nm, and preferably less than 200 nm,
and most preferably less than 100 nm. The graphite is dispersed in
the fluid by one or more of various methods, including
ultrasonication, milling, and chemical dispersion. Carbon nanotube
with graphitic structure is another preferred source of carbon
nanomaterial, although other carbon nanomaterials are acceptable.
To confer long term stability, the use of one or more chemical
dispersants is preferred. The thermal conductivity enhancement,
compared to the fluid without carbon nanomaterial, is somehow
proportional to the amount of carbon nanomaterials (carbon
nanotubes and/or graphite) added.
Inventors: |
Zhang; Zhiqiang; (Lexington,
KY) ; Lockwood; Frances E.; (Georgetown, KY) |
Correspondence
Address: |
WOOD, HERRON & EVANS, LLP
2700 CAREW TOWER, 441 VINE STREET
CINCINNATI
OH
45202
US
|
Family ID: |
33160075 |
Appl. No.: |
11/981768 |
Filed: |
October 31, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10730762 |
Dec 8, 2003 |
7348298 |
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11981768 |
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PCT/US02/16888 |
May 30, 2002 |
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10730762 |
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Current U.S.
Class: |
508/118 ;
204/157.62; 508/113; 508/116; 508/130; 508/131; 977/742; 977/750;
977/752 |
Current CPC
Class: |
C10M 2205/0285 20130101;
C10N 2020/06 20130101; C10M 125/02 20130101; C10N 2070/00 20130101;
B82Y 30/00 20130101; C10M 141/06 20130101; C10N 2020/063 20200501;
C10M 2215/28 20130101; C10M 169/04 20130101; Y10S 977/742 20130101;
C10M 2201/041 20130101; Y10S 977/745 20130101 |
Class at
Publication: |
508/118 ;
508/113; 508/130; 508/116; 508/131; 204/157.62; 977/742; 977/750;
977/752 |
International
Class: |
C10M 125/02 20060101
C10M125/02; C10M 169/04 20060101 C10M169/04; B01J 19/10 20060101
B01J019/10 |
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 thermally enhanced fluid composition, comprising: an effective
amount of a selected neat fluid having a selected thermal
conductivity; an effective amount of a selected carbon nanomaterial
dispersed into said selected neat fluid, said selected carbon
nanomaterial having a thermal conductivity greater than the thermal
conductivity of said selected neat fluid in which the carbon
nanomaterial is dispersed; and an effective amount of at least one
chemical dispersing agent;
2. The composition of claim 1 wherein said carbon nanotube is
either single-walled, or multi-walled, with typical aspect ratio of
500-5000.
3. The composition of claim 1 wherein said carbon nanotube is
surface treated to be hydrophilic at surface for ease of dispersing
into the aqueous medium.
4. The composition of claim 1 wherein the said dispersant is
soluble in the said liquid medium.
5. The composition of claim 1 wherein said liquid medium is
selected from the group consisting of a petroleum distillate and a
synthetic petroleum oil.
6. The composition of claim 1, wherein said chemical dispersing
agent is a surfactant
7. The composition of claim 6, wherein said surfactant is selected
from the group consisting of a ionic surfactant and a mixture of a
nonionic and ionic surfactant.
8. The composition of claim 1, wherein said dispersing agent is a
dispersant-detergent (DI) additive package.
9. The composition of claim 1 wherein said liquid medium is a water
based solution.
10. The composition of claim 9, wherein said dispersant is a
nonylphenoxypoly(ethyleneoxy)ethanol-type surfactant.
12. The composition of claim 1 wherein said fluid is a uniform
dispersion in a form as a gel or paste.
14. The composition of claim 1, wherein said fluid is a grease.
15. The composition of claim 1, wherein said carbon nanomaterial
comprises carbon nanotubes and graphite nanoparticles.
16. The composition of claim 1, wherein said carbon nanomaterial is
selected from the group consisting of carbon nanotubes, graphite
nanoparticles, and combinations thereof.
17. The thermally enhanced fluid composition of claim 1, wherein an
effective amount of a selected carbon nanomaterial to obtain the
desired thermal enhancement is up to 20 percent by weight.
18. The thermally enhanced fluid composition of claim 1, wherein an
effective amount of a selected carbon nanomaterial to obtain the
desired thermal enhancement is from 0.001 to 10 percent by
weight.
19. The thermally enhanced fluid composition of claim 1, wherein an
effective amount of a selected carbon nanomaterial to obtain the
desired thermal enhancement is from 0.01 to 5 percent by
weight.
20. The thermally enhanced fluid composition of claim 1, including
a selected amount of oil.
21. The thermally enhanced fluid composition of claim 1, including
a selected amount of water.
22. The thermally enhanced fluid composition of claim 1, wherein
said effective amount of a selected carbon nanomaterial is up to 90
percent by weight.
23. The thermally enhanced fluid composition of claim 1, wherein
said effective amount of a selected carbon nanomaterial is up to 10
percent by weight.
24. The thermally enhanced fluid composition of claim 1, wherein
said effective amount of a selected carbon nanomaterial is from
0.001 to 2.0 percent by weight.
25. The thermally enhanced fluid composition of claim 1, wherein
said selected carbon nanomaterial has a thermal conductivity
exceeding 80 W/m-K.
26. The thermally enhanced fluid composition of claim 1, wherein
said selected carbon nanomaterial has a thermal conductivity
exceeding that of said selected neat fluid.
27. The thermally enhanced fluid composition of claim 1, wherein
said neat fluid comprises a petroleum liquid medium selected from
the group consisting of a petroleum distillate, a synthetic
petroleum oil, a grease, a gel, a oil-soluble polymer composition,
and combinations thereof.
28. The thermally enhanced fluid composition of claim 1, wherein
said neat fluid is selected from the group comprising Group I
(solvent refined mineral oils), Group II (hydrocracked mineral
oils), Group III (severely hydrocracked hydrogenated oils), Group
IV (polyalphaolefins), and Group VI (esters, naphthenes, and
polyalkylglycols), and combinations thereof.
29. The thermally enhanced fluid composition of claim 1, wherein
said neat fluid is selected from the group of synthetic hydrocarbon
oils, halo-substituted hydrocarbon oils, polymerized and
interpolymerized olefins, polybutylenes, polypropylenes,
propylene-isobutylene copolymers, chlorinated polybutylenes,
poly(1-octenes), poly(1-decenes), alkylbenzenes, dodecylbenzenes,
tetradecylbenzenes, dinonylbenzenes, di-(2-ethylhexyl)benzenes,
polyphenyls, biphenyls, terphenyls, alkylated polyphenyls,
alkylated diphenyl, ethers and alkylated diphenyl sulfides, and
combinations thereof.
30. The thermally enhanced fluid composition of claim 1, wherein
said neat fluid is selected from the group comprising the esters of
dicarboxylic acids selected from the group consisting of 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, with an alcohols
selected from the group consisting of butyl alcohol, hexyl alcohol,
dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol diethylene
glycol monoether, propylene glycol, 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 combinations thereof.
31. The thermally enhanced fluid composition of claim 1, wherein
said neat fluid is selected from the group comprising esters made
from C.sub.5 to C.sub.12 monocarboxylic acids and polyols and
polyol ethers such as neopentyl glycol, trimethylolpropane,
pentaerythritol, dipentaerythritol, tripentaerythritol, and
combinations thereof.
32. The thermally enhanced fluid composition of claim 1, wherein
said neat fluid is selected from a polyalphaolefins having a
viscosity of up to 100 centistoke at 100.degree. C.
33. The thermally enhanced fluid composition of claim 1, wherein
said neat fluid is selected from the group of synthetic based oil
ester additives consisting of polyolesters, diesters, di-aliphatic
diesters of alkyl carboxylic acids, di-2-ethylhexylazelate,
di-isodecyladipate, di-tridecyladipate, and combinations
thereof.
34. The thermally enhanced fluid composition of claim 1, wherein
said neat fluid is selected from the group of diesters consisting
of an aliphatic diester of a dicarboxylic acid, a dialkyl aliphatic
diester of an alkyl dicarboxylic acid, a di-2-ethyl hexyl azelate,
a di-isodecyl azelate, a di-tridecyl azelate, a di-isodecyl
adipate, a di-tridecyl adipate, and combinations thereof.
35. The thermally enhanced fluid composition of claim 1, wherein
said neat fluid is selected from a hydrogenated oil having a sulfur
level less than 0.03 with saturates greater than or equal to 90 and
a viscosity index of greater than or equal to 120.
36. The thermally enhanced fluid composition of claim 1, wherein
said neat fluid is a hydrogenated oil having a viscosity of from 2
to 60 CST at 100 degrees centigrade.
37. The thermally enhanced fluid composition of claim 1, wherein
said neat fluid is a hydrogenated oil present in an amount of up to
99 percent by volume.
38. The thermally enhanced fluid composition of claim 1, wherein
said neat fluid is selected from the water-based group consisting
of an alcohol and its derivatives.
39. The thermally enhanced fluid composition of claim 1, wherein
said neat fluid is selected from the water-based group consisting
of an ethylene glycol, a propylene glycol, a methyl alcohol, an
ethyl alcohol, a propyl alcohol, an isopropyl alcohol, and
combinations thereof.
40. The thermally enhanced fluid composition of claim 1, wherein
said dispersants are selected from the group consisting of an
lipophilic hydrocarbon group, and a polar functional hydrophilic
group.
41. The thermally enhanced fluid composition of claim 1, wherein
said polar functional hydrophilic group is selected from the class
of carboxylate, ester, amine, amide, imine, imide, hydroxyl, ether,
epoxide, phosphorus, ester carboxyl, anhydride, or nitrile.
42. The thermally enhanced fluid composition of claim 1, wherein
said dispersant is an ashless dispersant typically used in the
petroleum industry selected from the group consisting of
N-substituted polyisobutenyl succinimides and succinates, allyl
methacrylate-vinyl pyrrolidinone copolymers, alkyl
methacrylate-dialkylaminoethyl methacrylate copolymers,
alkylmethacrylate-polyethylene glycol methacrylate copolymers, and
polystearamides.
43. The thermally enhanced fluid composition of claim 1, wherein
said dispersant is an oil-based dispersants selected from the group
consisting of alkylsuccinimide, succinate esters, high molecular
weight amines, Mannich base derivatives, phosphoric acid
derivatives, polyisobutenyl succinimide-polyethylenepolyamine,
polyisobutenyl succinic ester, polyisobutenyl
hydroxybenzyl-polyethylenepolyamine, and bis-hydroxypropyl
phosphorate.
44. The thermally enhanced fluid composition of claim 1, wherein an
effective amount of said dispersant present in an amount of from
0.001 to 30 percent by weight.
45. The thermally enhanced fluid composition of claim 1, wherein an
effective amount of said dispersant present in an amount of from
between 0.5 percent to 20 percent weight.
46. The thermally enhanced fluid composition of claim 1, wherein an
effective amount of said dispersant present in an amount of from
between 2 to 6 weight percent by weight.
47. The thermally enhanced fluid composition of claim 1, wherein an
effective amount of said nanomaterial present is in an amount of
0.0001 up to 50 percent by weight.
48. The thermally enhanced fluid composition of claim 1, wherein
said dispersant is selected from the group consisting of a high
molecular weight polyamine dispersion inhibitor package, a high
molecular weight succinimide dispersion inhibitor package, a mixed
dispersant comprising a high molecular weight succinimide and an
ester, a bis-succinimide, a nonylphenoxy poly(ethyleneoxy), OLOA
9061 dispersant, LUBRIZOL 4999 dispersant, LUBRIZOL 9802A
dispersant, LUBRIZOL 9802AC dispersant, INFINEUM C9231 dispersant,
INFINEUM C9232 dispersant, INFINEUM C9235 dispersant, LUBRIZOL
QS154250 dispersant.
49. The thermally enhanced fluid composition of claim 1, including
an effective amount of a viscosity improver selected from the group
consisting of an olefin copolymers (OCP), a polymethacrylates
(PMA), a hydrogenated styrene-diene (STD), a styrene-polyester
(STPE) polymers, and an olefin copolymer.
50. The thermally enhanced fluid composition of claim 1, including
an effective amount of at least one pour point depressant selected
from the group consisting of an alkylnaphthalene, an acrylic
copolymer, a polymethacrylate, a polyfumarates, a styrene ester, an
oligomerized alkylphenol, a phthalic acid ester, an ethylenevinyl
acetate copolymer, and other mixed hydrocarbon polymers.
51. The thermally enhanced fluid composition of claim 1, including
an effective amount of a rust and oxidation inhibitor.
52. The thermally enhanced fluid composition of claim 1, including
an effective amount of a demulsifier.
53. The thermally enhanced fluid composition of claim 1, including
an effective amount of a foam inhibitor.
54. The thermally enhanced fluid composition of claim 1, including
an effective amount of a seal swelling agent.
55. A method of thermally enhancing the conductivity of a fluid
composition, comprising the steps of: selecting a neat fluid having
a selected thermal conductivity; selecting a carbon nanomaterial;
dispersing said selected carbon nanomaterial having a thermal
conductivity greater than the thermal conductivity of said selected
neat fluid in which the carbon nanomaterial is dispersed into said
neat fluid; and adding at least one chemical dispersing agent
thereto.
56. The method of thermally enhancing the conductivity of a fluid
composition of claim 55, including the step of pre-shearing said
dispersed nanomaterial solution.
57. The method of thermally enhancing the conductivity of a fluid
composition of claim 56, wherein said step of pre-shearing is
selected from the group consisting of creating a turbulent flow
through a nozzle, creating a turbulent flow thorough a high
pressure fuel injector, an ultrasonic device, and combinations
thereof to achieve a stable viscosity.
58. A method of thermally enhancing the conductivity of a fluid
composition, comprising the steps of: selecting a neat fluid having
a selected thermal conductivity; selecting a carbon nanomaterial;
selecting at least one chemical dispersing agent; dissolving said
dispersant into said neat fluid forming a liquid medium; adding
said carbon nanoparticle into said liquid medium while being
agitated or ultrasonicated.
59. The method of thermally enhancing the conductivity of a fluid
composition of claim 58, including the step of pre-shearing said
dispersed nanomaterial solution.
60. The method of thermally enhancing the conductivity of a fluid
composition of claim 59, wherein said step of pre-shearing is
selected from the group consisting of creating a turbulent flow
through a nozzle, creating a turbulent flow thorough a high
pressure fuel injector, an ultrasonic device, and combinations
thereof to achieve a stable viscosity.
61. A method of thermally enhancing the conductivity of a fluid
composition, comprising the steps of: selecting a neat fluid having
a selected thermal conductivity; selecting a carbon nanomaterial;
selecting at least one chemical dispersing agent; dissolving said
carbon nanomaterial into said neat fluid forming a liquid medium;
adding said chemical dispersing agent into said liquid medium while
being agitated or ultrasonicated.
62. The method of thermally enhancing the conductivity of a fluid
composition of claim 61, including the step of pre-shearing said
dispersed nanomaterial solution.
63. The method of thermally enhancing the conductivity of a fluid
composition of claim 62, wherein said step of pre-shearing is
selected from the group consisting of creating a turbulent flow
through a nozzle, creating a turbulent flow thorough a high
pressure fuel injector, an ultrasonic device, and combinations
thereof to achieve a stable viscosity.
Description
[0001] This application is a Continuation of application Ser. No.
10/730,762 filed on Dec. 8, 2003 as a Continuation-In-Part of
pending PCT Patent Application Serial No. PCT/US02/16888 filed on
May 30, 2002 all of which are hereby incorporated by reference in
their entirety.
BACKGROUND OF THE INVENTION
[0003] 1. Technical Field
[0004] Fluids of enhanced thermal conductivity are prepared by
dispersing carbon nanomaterials of a selected thermal conductivity
into the fluid serving as the liquid medium. Dispersion is achieved
by physical and chemical treatments. Methods are described and
fluid compositions are identified which exhibit enhanced thermal
conductivity due to the dispersion of carbon nanomaterials in
aqueous and/or petroleum liquid medium utilizing selected
dispersants and mixing methods to form stable carbon 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 range, freeze
depressants such as ethylene glycol and/or propylene glycol are
sometimes added, typically at levels above 10% concentration by
volume, for example, automotive coolant is typically a mixture of
50-70% ethylene glycol, the remainder water. The thermal
conductivity of the freeze depressed fluid is then about 2/3 as
good as water alone. In many processes and applications, water can
not be used for various reasons, and then a type of oil, e.g.
mineral oil, polyalpha olefin oil, ester synthetic oil, ethylene
oxide/propylene oxide synthetic oil, polyalkylene glycol synthetic
oil, etc. are used. The thermal conductivity of these oils, is
typically 0.1 to 0.17 W/m-K at room temperature, and thus they are
inferior to water, with comparable thermal conductivity of 0.61
W/m-K, as heat transfer agents. Usually these oils have many other
important functions, and they are carefully formulated to perform
to exacting specifications for example for friction, wear
performance, low temperature 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.
[0007] The use of graphite solids 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;
however, the thermal conductivity property of the graphite is not
an important consideration in conventional applications. 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.
[0008] 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 (on the order of one to
several microns) than for the instant invention. As a result, the
graphite incorporated in the aforementioned automotive engine oil
had strong settling tendency in the fluid. Graphite of this size
also significantly effected 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. The use
of graphite in lubricants for recirculating systems was made
unpopular, partly due to the publication by NASA that graphite
could pile up in restricted flow areas in concentrated contacts,
thereby leading to lubricant starvation. No recognition on the
effect of graphite particle size on this phenomena was ever
established. Furthermore, none of the prior art references teach
the use of utilizing nano-sized graphite particles with mean
particle size less than 500 nm to enhance thermal conductivity in
fluids.
[0009] Carbon nanotubes are a new form of the nanomaterial formed
by elemental carbon, which possesses different properties than the
other forms of the carbon materials. It has unique atomic
structure, very high aspect ratio, and extraordinary mechanical
properties (strength and flexibility), making them ideal
reinforcing fibers in composites and other structural
materials.
[0010] Carbon nanotubes are characterized as generally to rigid
porous carbon three dimensional structures comprising carbon
nanofibers and having high surface area and porosity, low bulk
density, low amount of micropores and increased crush strength and
to methods of preparing and using such structures. The instant
process is applicable to nanotubes with or without amorphous
carbon.
[0011] The term "nanofiber" refers to elongated structures having a
cross section (e.g., angular fibers having edges) or diameter
(e.g., rounded) less than 1 micron. The structure may be either
hollow or solid. Accordingly, the term includes "bucky tubes" and
"nanotubes". The term nanofibers also refers to various fibers,
particularly carbon fibers, having very small diameters including
fibrils, whiskers, nanotubes, buckytubes, etc. Such structures
provide significant surface area when incorporated into a structure
because of their size and shape. Moreover, such fibers can be made
with high purity and uniformity. Preferably, the nanofiber used in
the present invention has a diameter less than 1 micron, preferably
less than about 0.5 micron, and even more preferably less than 0.1
micron and most preferably less than 0.05 micron. Carbon nanotubes
are typically hollow graphite tubules having a diameter of
generally several to several tens nanometers which exist in many
forms either as discrete fibers or aggregate particles of
nanofibers
[0012] The term "internal structure" refers to the internal
structure of an assemblage including the relative orientation of
the fibers, the diversity of and overall average of fiber
orientations, the proximity of the fibers to one another, the void
space or pores created by the interstices and spaces between the
fibers and size, shape, number and orientation of the flow channels
or paths formed by the connection of the void spaces and/or pores.
The structure may also include characteristics relating to the
size, spacing and orientation of aggregate particles that form the
assemblage. The term "relative orientation" refers to the
orientation of an individual fiber or aggregate with respect to the
others (i.e., aligned versus non-aligned). The "diversity of" and
"overall average" of fiber or aggregate orientations refers to the
range of fiber orientations within the structure (alignment and
orientation with respect to the external surface of the
structure).
[0013] Carbon fibrils can be used to form a rigid assemblage or be
made having diameters in the range of 3.5 to 70 nanometers. The
fibrils, buckytubes, nanotubes and whiskers that are referred to in
this application are distinguishable from continuous carbon fibers
commercially available as reinforcement materials. In contrast to
nanofibers, which have desirably large, but unavoidably finite
aspect ratios, continuous carbon fibers have aspect ratios (L/D) of
at least 10.sup.4 and often 10.sup.6 or more. The diameter of
continuous fibers is also far larger than that of fibrils, being
always >1.0 microns and typically 5 to 7 microns. Continuous
carbon fibers are made by the pyrolysis of organic precursor
fibers, usually rayon, polyacrylonitrile (PAN) and pitch. Thus,
they may include heteroatoms within their structure. The graphitic
nature of "as made" continuous carbon fibers varies, but they may
be subjected to a subsequent graphitization step. Differences in
degree of graphitization, orientation and crystallinity of graphite
planes, if they are present, the potential presence of heteroatoms
and even the absolute difference in substrate diameter make
experience with continuous fibers poor predictors of nanofiber
chemistry. Carbon nanofibrils are vermicular carbon deposits having
diameters less than 1.0 micron, preferably less than 0.5 micron,
even more preferably less than 0.2 micron and most preferably less
than 0.05 micron. They exist in a variety of forms and have been
prepared through the catalytic decomposition of various
carbon-containing gases at metal surfaces.
[0014] Carbon nanotubes are typically hollow graphite tubules
having a diameter of generally several to several tens nanometers.
Carbon nanotubes exist in many forms. The nanofibers can be in the
form of discrete fibers or aggregate particles of nanofibers. The
former results in a structure having fairly uniform properties. The
latter results in a structure having two-tiered architecture
comprising an overall macrostructure comprising aggregate particles
of nanofibers bonded together to form the porous mass and a
microstructure of intertwined nanofibers within the individual
aggregate particles. For instance, one form of carbon fibrils are
characterized by a substantially constant diameter, length greater
than about 5 times the diameter, an ordered outer region of
catalytically grown, multiple, substantially continuous layers of
ordered carbon atoms having an outside diameter between about 3.5
and 70 nanometers, and a distinct inner core region. Each of the
layers and the core are disposed substantially concentrically about
the cylindrical axis of the fibril. The fibrils are substantially
free of pyrolytically deposited thermal carbon with the diameter of
the fibrils being equal to the outside diameter of the ordered
outer region.
[0015] Moreover, a carbon fibril suitable for use with the instant
process defines a cylindrical carbon fibril characterized by a
substantially constant diameter between 3.5 and about 70
nanometers, a length greater than about 5 times the diameter, an
outer region of multiple layers of ordered carbon atoms and a
distinct inner core region, each of the layers and the core being
disposed concentrically about the cylindrical axis of the fibril.
Preferably the entire fibril is substantially free of thermal
carbon overcoat. The term "cylindrical" is used herein in the broad
geometrical sense, i.e., the surface traced by a straight line
moving parallel to a fixed straight line and intersecting a curve.
A circle or an ellipse are but two of the many possible curves of
the cylinder. The inner core region of the fibril may be hollow, or
may comprise carbon atoms which are less ordered than the ordered
carbon atoms of the outer region. "Ordered carbon atoms," as the
phrase is used herein means graphitic domains having their c-axes
substantially perpendicular to the cylindrical axis of the fibril.
In one embodiment, the length of the fibril is greater than about
20 times the diameter of the fibril. In another embodiment, the
fibril diameter is between about 7 and about 25 nanometers. In
another embodiment the inner core region has a diameter greater
than about 2 nanometers.
[0016] Dispersing the nanotubes into organic and aqueous medium has
been a serious challenge. The nanotubes tend to aggregate, form
agglomerates, and separate from the dispersion.
[0017] Some industrial applications require a method of preparing a
stable dispersion of a selected carbon nanomaterials in a liquid
medium. For instance, U.S. Pat. No. 5,523,006 by Strumban teaches
the user of a surfactant and an oil medium; however, the particles
are Cu--Ni--Sn--Zn alloy particles with the size from 0.01 .mu.m
and the suspension is stable for a limited period of time of
approximately 30 days. Moreover, the surfactants do not include the
dispersants typically utilized in the lubricant industry.
[0018] U.S. Pat. No. 5,560,898 by Uchida et al. teaches that a
liquid medium is an aqueous medium containing a surfactant;
however, the stability of the suspension is of little consequence
in that the liquid is centrifuged upon suspension.
[0019] U.S. Pat. No. 5,853,877 by Shibuta teaches dispersing
disentangled nanotubes in a polar solvent and forming a coating
composition with additives such as dispersing agents; however, a
method of obtaining a stable dispersion is not taught.
[0020] U.S. Pat. No. 6,099,965 by Tennent et al. utilizes a kneader
for mixing a dispersant with other reactants in a liquid medium,
yet sustaining the stability of the dispersion is not taught.
[0021] The potential of carbon nanotubes to convey thermal
conductivity in a material is mentioned in U.S. Pat. No. 5,165,909;
however, 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. Bulk graphite with high
thermal conductivity is available from POCO GRAPHITE as a graphite
foam having a thermal conductivity of greater than 100 W/m-K, and
from Carbide having a high thermal conductivity as well. These bulk
materials must be reduced to a powder of nanometer size by various
methods for use in the instant invention.
SUMMARY OF THE INVENTION
[0022] In this invention, fluids of enhanced thermal conductivity
are prepared by dispersing carbon nanomaterials of a selected
thermal conductivity measured in W/m-K into a selected neat fluid
which serve as a liquid solvent medium or carrier. Dispersion of
the nanomaterials throughout the selected liquid medium is achieved
by physical and chemical treatments to yield a fluid composition
having an enhanced thermal conductivity as compared to the neat
fluid alone.
[0023] Fluid compositions that have enhanced thermal conductivity,
up to 250% greater than their conventional analogues, and methods
of preparation for these fluids are identified. The compositions
contain at a minimum, a fluid media such as oil or water, and a
selected effective amount of particles necessary to enhance the
thermal conductivity of the fluid. The graphite is a high thermal
conductivity graphite, exceeding that of the neat fluid to be
dispersed therein in thermal conductivity, and ground, milled, or
naturally prepared with mean particle size less than 500 nm, and
preferably less than 200 nm, and most preferably less than 100 nm.
The graphite is dispersed in the fluid by one or more of various
methods, including ultrasonication, milling, and chemical
dispersion. Carbon nanotube with graphitic structure is another
preferred source of carbon nanomaterials, although other
nanomaterials are acceptable. To confer long term stability, the
use of one or more chemical dispersants is preferred. The thermal
conductivity enhancement, compared to the fluid without carbon
nanomaterial, is somehow proportional to the amount of carbon
nanomaterial added.
[0024] The present invention provides a fluid containing up to 90%
carbon nanomaterials. Very good results were obtained with
nanomaterial loadings in a range of up to 20 percent by weight and
more particularly from 0.001 to 10 percent by weight, and more
typically from 0.01 to 2.5 percent by weight. Well dispersed stable
nanotube/nanoparticle in oil suspensions with up to 2.5 percent by
weight carbon nanomaterials resulted in surprising good enhancement
of the thermal characteristics of the fluids developed according to
the present invention. Preferably, a minimum of one or more
chemical dispersing agents and/or surfactants is 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 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 are mostly used interchangeably in
the instant invention. The particle-containing fluid of the instant
invention will have a thermal conductivity higher than the neat
fluid, in this case the term neat is defined as the fluid before
the particles are added. 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
anti-corrosion agents, detergents, antioxidants, etc. Furthermore,
the term fluid in the instant invention is broadly defined to
include pastes, gels, greases, foam, and liquid crystalline phases
in either organic or aqueous media, emulsions and
microemulsions.
[0025] As set forth above, the preferred carbon nanomaterial is
restricted to any graphitic nanomaterials with bulk thermal
conductivity exceeding that of the neat fluid to be enhanced. For
instance, the thermal conductivity of oil is about 0.2 W/m-K; the
thermal conductivity of antifreeze (water and alcohol and/or glycol
mixtures) is usually about 0.4 W/m-K; and the thermal conductivity
of water is about 0.6 W/m-K. For most applications, a carbon
nanomaterial in the form of a carbon nanotube or graphite
nanoparticle is chosen having a thermal conductivity exceeding 80
W/m-K. A preferred form of carbon nanomaterial is carbon
nanotubes.
[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, etc. that are not for the purpose of dispersing, but
to achieve thickening or other desired fluid characteristics.
[0027] Furthermore, the dispersed nanomaterial solution can be
pre-sheared, in a turbulent flow such as a nozzle, or high pressure
fuel injector, or ultrasonic device, in order to achieve a stable
viscosity. This may be desirable in the case where carbon nanotubes
with high aspect ratio are used as the carbon nanomaterial source,
since they will thicken the fluid but loose viscosity when exposed
in turbulent flows such as engines.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] The present invention provides a carbon nanomaterial
dispersion in fluid medium that gives a high thermal conductivity
compared to conventional fluids of the same medium.
[0029] The preferred carbon nanomaterials are carbon nanotubes, the
nanotubes can be either single-walled, or multi-walled, having a
typical nanoscale diameter of 1500 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. Other acceptable carbon nanomaterials are available,
e.g. POCOFOAM, available from PocoGraphite, Inc., located in
Decatur, Tex., POCOFOAM is a high thermal conductivity foamed
graphite, thermal conductivity from 100 to 150 W/m-K. To prepare it
for the instant invention, it must be pulverized to a fine powder,
dispersed chemically and physically in the fluid of choice, and
then ball milled or otherwise size reduced until a particle size of
less than 500 nm mean size is attained. The finer the particle size
attained upon milling, the better. 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 particles to below a
mean particle size of 500 nm.
Oil Basestocks
[0030] 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 VI (esters, naphthenes, and others). One preferred group
includes the polyalphaolefins, synthetic esters, and
polyalkylglycols.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] Polyalphaolefins (PAO), useful in the present invention
include those sold by BP Amoco Corporation as DURASYN fluids, those
sold by Exxon-Mobil Chemical Company, (formerly 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.
[0036] MOBIL SHF-42 from Exxon-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 (cSt) at
212.degree. F. (100.degree. C.) and 16.75 cSt 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 about
432.degree. F. and a fire point of about 478.degree. F. Moreover,
EMERY 3006 polyalphaolefin has a viscosity of 5.88 cSt at
+212.degree. F. and 31.22 cSt at +104.degree. F. It has a viscosity
index of 135 and a pour point of -87.degree. F.
[0037] Additional satisfactory polyalphaolefins are those sold by
Uniroyal Inc. under the brand SYNTON PAO-40, which is a 40
centistoke polyalphaolefin.
[0038] It is contemplated that Gulf Synfluid 4 cSt PAO,
commercially available from Gulf Oil Chemicals Company, a
subsidiary of Chevron-Texaco 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.
[0039] Especially useful are the polyalphaolefins will have a
viscosity in the range of up to 100 centistoke at 100.degree. C.,
with viscosity of 2 and 10 centistoke being more preferred.
[0040] The most preferred synthetic based 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 polyolester P-43, NP343 containing
two alcohols, and Hatco Corp. 2939 are particularly preferred.
[0041] 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
residence to oxidative breakdown.
[0042] 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.
[0043] 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 Exxon-Mobil Chemical Company. Esters 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
Exxon-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 to 100 centistoke at
100.degree. C.
[0044] A hydrogenated oil is a mineral oil subjected to
hydrogennation or hydrocracking under special conditions to remove
undesirable chemical compositions and impurities resulting in a
base oil having synthetic oil component and properties. Typically
the hydrogenated oil is defined by the American Petroleum Institute
as a Group III base oil with a sulfur level less than 0.03 with
saturates greater than or equal to 90 and a viscosity index of
greater than or equal to 120. Most useful are hydrogenated oils
having a viscosity of from 2 to 60 CST at 100 degrees centigrade.
The hydrogenated oil typically provides superior performance to
conventional motor oils with no other synthetic oil base. The
hydrogenated oil may be used as the sole base oil component of the
instant invention providing superior performance to conventional
mineral oil bases oils or used as a blend with mineral oil and/or
synthetic oil. An example of such an oil is YUBASE-4.
[0045] 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
utilized as the oil base stock in an amount of up to 100 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.
[0046] 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 ASHLAND 325 Neutral defined as a
solvent refined neutral having a SABOLT UNIVERSAL viscosity of 325
SUS @ 100.degree. F. and ASHLAND 100 Neutral defined as a solvent
refined neutral having a SABOLT UNIVERSAL viscosity of 100 SUS @
100.degree. F., manufactured by the Marathon Ashland Petroleum.
[0047] 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 API Group I and II oils available from Exxon-Mobil Chemical
Company, HVI neutral oils available from Shell Chemical Company,
and Group II oils available from Arco Chemical Company. Preferred
MVI naphthenic oils include solvent extracted oils available from
Equilon Enterprises and San Joaquin Refining, hydrotreated oils
available from Equilon Enterprises and Ergon Refining, and
naphthenic oils sold under the names HYDROCAL and CALSOL by
Calumet, and described in U.S. Pat. No. 5,348,668 to Oldiges.
[0048] Finally, the thermal conductivity of vegetable oils may also
be enhanced and utilized as the liquid medium in the instant
invention.
Aqueous Medium
[0049] A selected aqueous medium is water, or it can be any
water-based solution including alcohol or its derivatives, such as
ethylene glycol, propylene glycol, or any water-soluble inorganic
salt, e.g. molybdate salts, nitrates, nitrites, methyl alcohol,
ethyl alcohol, propyl alcohol, isopropyl alcohol, and combinations
thereof, or organic compounds, such as aromatic and/or aliphatic
carboxylate acids more, particularly short chain mono- and
di-carboxylic acids. Such solutions are typically utilized as
antifreeze constituents and may include other corrosion resistant
additives together with the carbon nanomaterial dispersed therein
providing enhance thermal properties.
Dispersants
Dispersants Used in Lubricant Industry
[0050] 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.
[0051] 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.
[0052] 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. For instance, bis-succinimide is a
dispersant based on polybutene and an amine which is suitable for
oil based dispersions and is commercially available under the
tradenames of INFINEUM C9231, INFINEUM C9232, and INFINEUM C9235
which is sold by Infineum, USA, L.P. The C9231 is borated while the
C9232 and C9235 are not; however, all are bis-succinimides which
differ due to their amine to polymer ratio.
[0053] 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/or the concentrated package
(LUBRIZOL.TM. 9802AC), which are mixed Dispersants having a high
molecular weight succinimide and ester-type dispersant as the
active ingredient, and which also contains from about 5 to 9.9
percent by weight of zinc alkyldithiophosphate, from 1 to 4.9
percent by weight of a substituted phenol, from 1 to 4.9 percent of
a calcium sulfonate, and from 0.1 to 0.9 percent by weight of a
diphenylamine; wherein the whole DI package can be used as
dispersing agent for the carbon nanomaterial dispersion.
[0054] Another preferred dispersant package is LUBRIZOL OS#154250
which contains from about 20 to 29.9 percent by weight of a
polyolefin amide alkeneamine, from 0.5 to 1.5 percent by weight of
an alkylphosphite, about 1.1 percent by weight of a phosphoric
acid, and from 0.1 to 0.9 percent by weight of a diphenylamine,
with primary active ingredient believed to be polyisobutenyl
succinimides and succinates. Another preferred dispersant package
is a high molecular weight succinimide DI package for diesel
engines LUBRIZOL.TM. 4999 which also contains from about 5 to 9.9
percent zinc alkyldithiophosphate by weight.
Other Types of Dispersants
[0055] 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.
[0056] The dispersant for the water based carbon nanomaterial
dispersion, more specifically carbon nanotube dispersion, should be
of high HLB value (typically less than or equal to 10), preferable
nonylphenoxypoly(ethyleneoxy)ethanol-type surfactants are
utilized.
[0057] In both the water and oil based cases, the dispersants
selected should be soluble or dispersible in the liquid medium.
[0058] The dispersant can be in a range of up from 0.001 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 1.0 to 8.0
percent, and most preferably in a range of from between 2 to 6
weight percent.
[0059] The carbon nanotube or graphite nanoparticles can be of any
desired weight percentage in a range of from 0.0001 up to 50
percent by weight providing for an effective amount to obtain the
desired thermal enhancement of the selected fluid media. For
practical application an effective amount of carbon nanomaterials
is usually in a range of from between 0.01 percent to 20 percent,
and more preferably in a range of from 0.02 to 10 percent, and most
preferably in a range of from between 0.05 percent to 5 percent.
The remainder of the formula is the selected medium comprising oil,
water, or combinations thereof together with any chemical additives
deemed necessary to provide lubricity, corrosion protection,
viscosity, or the like.
[0060] It is believed that in the instant invention the dispersant
functions by adsorbing onto the surface of the carbon nanotube.
Other Chemical Compounds
[0061] 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.
[0062] 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.
[0063] Other compounds which can be used in the instant invention
in either the aqueous medium or 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.
[0064] Other chemical additives used in lubricants such as pour
point depressant can also be used in the instant invention. Most
pour point depressants are organic polymers, although some
nonpolymeric substances have been shown to be effective. Commercial
pour point depressants include alkylnaphthalenes,
polymethacrylates, polyfumarates, styrene esters, oligomerized
alkylphenols, phthalic acid esters, ethylenevinyl acetate
copolymers, and other mixed hydrocarbon polymers. The treatment
level of these additives is usually low. In nearly all cases, there
is an optimum concentration above and below which pour point
depressants become less effective.
[0065] Acrylic copolymers such as manufactured by Supeleo Inc. in
Bellefonte, Pa. as Acryloid 3008 is a pour point depressant useful
in the present invention.
[0066] Still other chemical additives used in lubricants, such as
rust and oxidation inhibitors, demulsifiers, foam inhibitors, and
seal-swelling agents can also be used in the instant invention.
Physical Agitation
[0067] 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.
[0068] Ultrasonication is the most preferred physical method in the
instant invention since it is less destructive to the carbon
nanomaterial, more specifically, carbon nanotube, structure than
the other methods described. Ultrasonication can be done either in
the bath-type ultrasonicator, or by the tip-type ultrasonicator.
More typically, tip-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.
[0069] 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.
[0070] The instant method of forming a stable suspension of carbon
nanomaterials in a solution consist of two steps. First select the
appropriate dispersant for the carbon nanomaterials, which include
carbon nanotube or graphite nanoparticles, and the medium, and
dissolve the dispersant into the liquid medium to form a solution,
and second add the carbon nanotube or graphite nanoparticles into
the dispersant-containing solution while agitating, ball milling,
or ultrasonicating the solution or any combination of physical
methods named.
EXAMPLES
[0071] 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.
Example 1
TABLE-US-00001 [0072] Weight Components Description percentage
Carbon nanotube Surface untreated, aspect ratio 2.5 2000, diameter
25 nm, length 50 .mu.m Dispersant High Mol. Wt. Polyammine DI
package 4.88 ORONITE (OLOA 9061) Liquid solvent
Poly(.alpha.-olefin), 6 cSt 92.62 Sonication FISHER SCIENTIFIC 550
Sonic Dismembrator, 15 minutes
[0073] As set forth in Example 1, the thermal conductivity of the
above dispersion was 0.380 Wm-K for the fluid (solution of the
dispersant and solvent) containing the thermally enhancing
nanotubes, as compared to a thermal conductivity of 0.146 W/m-K for
the fluid (solution of the dispersant and solvent) without the
thermally enhancing nanotubes.
Example 2
TABLE-US-00002 [0074] Weight Components Description percentage
Carbon nanotube Surface untreated, aspect ratio 2000, 0.1 diameter
25 nm, length 50 .mu.m Dispersant High mol. Wt. Succinimide DI
package 4.8 for diesel engines LUBRIZOL .TM. 4999 Liquid solvent
Poly(.alpha.-olefin), 6 cSt 95.1 Sonication FISHER SCIENTIFIC 550
Sonic Dismembrator, 15 minutes
Example 3
TABLE-US-00003 [0075] Weight Components Description percentage
Carbon nanotube Surface untreated, aspect ratio 2000, 0.1 diameter
25 nm, length 50 microns Dispersant Mixed Dispersant (high mol. Wt.
4.8 Succinimide and ester-type dispersant) DI package LUBRIZOL .TM.
9802A Liquid solvent Poly(.alpha.-olefin), 6 cST 95.1 Sonication
FISHER SCIENTIFIC 550 Sonic Dismembrator, 15 minutes
Example 4
TABLE-US-00004 [0076] Weight Components Description percentage
Carbon nanotube Surface untreated, aspect ratio 0.10 2000, diameter
25 nm, length 50 .mu.m Dispersant Bis-succinimide dispersant 4.80
(INFINEUM C9231) Liquid solvent Poly(.alpha.-olefin), 6 cSt 95.10
Sonication FISHER SCIENTIFIC 550 Sonic Dismembrator, 15 minutes
Example 5
TABLE-US-00005 [0077] Weight Components Description percentage
Carbon nanotube Surface untreated, aspect ratio 0.10 2000, diameter
25 nm, length 50 .mu.m Dispersant Bis-succinimide dispersant 4.80
INFINEUM C9232) Liquid solvent Poly(.alpha.-olefin), 6 cSt 95.10
Sonication FISHER SCIENTIFIC 550 Sonic Dismembrator, 15 minutes
Example 6
TABLE-US-00006 [0078] Weight Components Description percentage
Carbon nanotube Surface untreated, aspect ratio 0.10 2000, diameter
25 nm, length 50 .mu.m Dispersant Bis-succinimide dispersant 4.80
(INFINEUM C9235) Liquid solvent Poly(.alpha.-olefin), 6 cSt 95.10
Sonication FISHER SCIENTIFIC 550 Sonic Dismembrator, 15 minutes
Example 7
TABLE-US-00007 [0079] Weight Components Description percentage
Carbon nanotube Surface treated 0.10 Dispersant nonylphenoxy
poly(ethyleneoxy) 5.00 ethanol, branched Liquid solvent Water 94.90
Sonication FISHER SCIENTIFIC 550 Sonic Dismembrator, 15 minutes
[0080] The dispersions in examples 1-7 are very uniform, and have
not shown any sign of separation or aggregation for a year.
Example 8
TABLE-US-00008 [0081] Weight Components Description percentage
Graphite POCOFOAM after milling 2.0 nanoparticles Dispersant
Lubrizol .TM. OS#154250 7.55 VI Improver and Polyalkylmethacrylate,
ACRYLOID 10.9 Other Chemicals 3008 .TM. acrylic copolymer and red
dye Liquid solvent Group III Base oil 79.55 Sonification FISHER
SCIENTIFIC 550 Sonic Dismembrator, 15 minutes indicates data
missing or illegible when filed
[0082] In Example 8, the graphite particles were obtained through
pulverizing and milling the high thermal conductivity graphite foam
(bulk thermal conductivity as 100 to 150 W/MK), known as POCOFOAM,
to the desired nanometer size range. It was first ground into
coarse particles, and then dispersed into an oil solution with
dispersants and other chemicals. The dispersion is then milled in a
horizontal mill. The final dispersion after the milling is
sonicated to achieve homogeneity.
[0083] As set forth in Example 8, the thermal conductivity of the
above dispersion was 0.175 Wm-K for the fluid containing the
thermally enhancing graphite particles, as compared to a thermal
conductivity of 0.140 W/m-K for the base fluid (solution of the
dispersant, viscosity index improver, and solvent) without the
thermally enhancing graphite particles.
[0084] 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.
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