Note: Descriptions are shown in the official language in which they were submitted.
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NANO-TRIBOLOGY COMPOSITIONS AND RELATED METHODS
INCLUDING MOLECULAR NANO-SHEETS
TECHNICAL FIELD
[0001] This specification relates to compositions and methods in the field of
tribology,
solid surface engineering, lubrication, wear, and related functions such as
corrosion
resistance, catalysis, and the like. This specification also relates to
compositions and methods
in the sub-field of nano-tribology and associated solid surface nano-
engineering, nano-
lubrication, and nano-wear.
BACKGROUND
[0002] Ttibology refers to the science and engineering of solid surfaces.
Tribology
includes the study and application of surface chemistry and structure,
friction, lubrication,
corrosion, and wear. The tribological interactions of a solid surface with
interfacing
materials and the surrounding environment may result in the loss of material
from the surface
in processes generally referred to as "wear." Major types of wear include
abrasion, friction
(adhesion and cohesion), erosion, and corrosion. Wear may be reduced by the
use of
lubricants and/or other anti-wear agents. Wear may also be reduced by
modifying the surface
properties of solids using one or more "surface engineering" processes (i.e.,
modifying the
chemical and/or structural properties of solid surfaces).
SUMMARY
[0003] In a non-limiting embodiment, a composition comprises a plurality of
nanoparticles
having open architecture, a plurality of multifunctional nano-sheets, and an
organic medium
intercalating the nanoparticles.
[0004] In another non-limiting embodiment, a method comprises contacting a
surface with
a composition. The composition comprises a plurality of nanoparticles having
open
architecture and an organic medium intercalated in the nanoparticles, The
surface and the
contacting composition are subjected to a frictional force. Constituent layers
of the
nanoparticles are delaminated to form a plurality of multifunctional nano-
sheets. The nano-
sheets deposit on the surface in a tribo-film.
[0005] It is understood that the invention disclosed and described in this
specification is not
limited to the embodiments summarized in this Summary.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0006] Various features and characteristics of the non-limiting and non-
exhaustive
embodiments disclosed and described in this specification may be better
understood by
reference to the accompanying figures, in which:
[0007] Figure 1 is a diagram illustrating a method of producing nanoparticles;
[0008] Figure 2 is a diagram illustrating one method of preparing nanoparticle
based
lubricants;
[0009] Figure 3 shows transmission electron microscopy (TEM) micrographs of
molybdenum disulfide particles; Figure 3(A) shows molybdenum disulfide as it
is available,
typically from about a few microns to submicron size; Figure 3(B) shows
molybdenum
disulfide that has been ball milled in air for 48 hours; Figure 3(C) is a high
resolution electron
microscopy image that shows molybdenum disulfide that has been ball milled in
air for 48
hours; Figure 3(D) is a high-resolution transmission electron microscopy
(HRIEM) image
that shows molybdenum disulfide that has been ball milled in air for 48 hours
followed by
ball milling in oil for 48 hours;
[0010] Figure 4 is a graph showing XRD spectra of molybdenum disulfide
particles; Figure
4(A) is the XRD spectra for molybdenum disulfide that has been ball milled in
air for 48
hours followed by ball milling in oil for 48 hours; Figure 4(B) is the XRD
spectra for
molybdenum disulfide that has been ball milled in air for 48 hours; Figure
4(C) is the XRD
spectra for molybdenum disulfide that has not been ball milled;
[0011] Figure 5 is a graph showing XPS spectra of molybdenum disulfide
particles in
which the carbon peak for molybdenum disulfide that has not been ball milled
is shown, as
well as the carbon peak for molybdenum disulfide that has been ball milled in
air for 48
hours, followed by ball milling in oil for 48 hours;
[0012] Figure 6 shows graphs and bar charts depicting tribological test data
for different
additives in paraffm oil; Figure 6(A) shows the average wear scar diameter for
a base oil
(paraffin oil), paraffin oil with micron sized MoS2, paraffin oil with MoS2
that was milled in
air for 48 hours, and paraffin oil with MoS2 that was milled in air for 48
hours followed by
milling in canola oil for 48 hours; Figure 6(B) shows the load wear index for
paraffin oil
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without a nanoparticle additive, paraffin oil with micron sized MoS2, paraffin
oil with MoS2
that was milled in air for 48 hours, and paraffin oil with MoS2 that was
milled in air for 48
hours followed by milling in canola oil for 48 hours; Figure 6(C) shows the
coefficient of
friction for paraffin oil without a nanoparticle additive, paraffin oil with
micron sized MoS2
(c-MoS2), paraffin oil with MoS2 that was milled in air for 48 hours (d-MoS2),
and paraffin
oil with MoS2 that was milled in air for 48 hours followed by milling in
canola oil for 48
hours (n-MoS2); Figure 6(D) shows the extreme pressure data for paraffin oil
with micron
sized MoS2 (c-MoS2), paraffin oil with MoS2 that was milled in air for 48
hours (d-MoS2),
and paraffin oil with MoS2 that was milled in air for 48 hours followed by
milling in canola
oil for 48 hours (n-MoS2); in each test the lubricant nanoparticle additive
was present in the
amount of 1% by weight;
[0013] Figure 7 is a TEM image showing the architecture of molybdenum
disulfide
nanoparticles (15-70 nm average size); Figure 7(A) shows the close caged dense
oval shaped
architecture of molybdenum disulfide nanoparticles that have been ball milled
in air for 48
hours; Figure 7(B) shows the open ended oval shaped architecture of molybdenum
disulfide
nanoparticles that have been ball milled in air for 48 hours followed by ball
milling in canola
oil for 48 hours;
[0014] Figure 8 is a graph depicting a comparison of wear scar diameters for
different
additives in paraffin oil; one additive is crystalline molybdenum disulfide (c-
MoS2); another
is molybdenum disulfide nanoparticles that were ball milled in air (n-MoS2);
another additive
is molybdenum disulfide nanoparticles that were ball milled in air followed by
ball milling in
canola oil and to which a phospholipid emulsifier was added (n-
MoS2+Emulsifier); and
[0015] Figure 9 shows photographs and graphs produced using energy dispersive
x-ray
analysis (EDS) depicting the chemical analysis of wear scar diameters in four-
ball
tribological testing for nanoparticle based lubricants; Figure 9(A) shows
paraffin oil without
any nanoparticle composition additive; Figure 9(B) shows paraffin oil with
molybdenum
disulfide nanoparticles that have been ball milled in air for 48 hours
followed by ball milling
in oil for 48 hours and treated with a phospholipid emulsifier.
[0016] Figures 10(A) and 10(B) show schematic diagrams of the crystal
structure of
molybdenum disulfide.
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[0017] Figure 11 shows a schematic diagram of the crystal structure of
hexagonal boron
nitride.
[0018] The reader will appreciate the foregoing details, as well as others,
upon considering
the following detailed description of various non-limiting and non-exhaustive
embodiments
according to this specification.
DESCRIPTION
[0019] Various embodiments are described and illustrated in this specification
to provide
an overall understanding of the function, operation, and implementation of the
disclosed
compositions and methods. It is understood that the various embodiments
described and
illustrated in this specification are non-limiting and non-exhaustive. Thus,
the invention is
not necessarily limited by the description of the various non-limiting and non-
exhaustive
embodiments disclosed in this specification. The features and characteristics
illustrated
and/or described in connection with various embodiments may be combined with
the features
and characteristics of other embodiments. Such modifications and variations
are intended to
be included within the scope of this specification. As such, the claims may be
amended to
recite any features or characteristics expressly or inherently described in,
or otherwise
expressly or inherently supported by, this specification. Further, Applicant
reserves the right
to amend the claims to affirmatively disclaim features or characteristics that
may be present
in the prior art. Therefore, any such amendments comply with the requirements
of 35 U.S.C.
112(a) and 132(a). The various embodiments disclosed and described in this
specification
can comprise, consist of, or consist essentially of the features and
characteristics as variously
described in this specification.
[0020] Also, any numerical range recited in this specification is intended to
include all sub-
ranges of the same numerical precision subsumed within the recited range. For
example, a
range of "1.0 to 10.0" is intended to include all sub-ranges between (and
including) the
recited minimum value of 1.0 and the recited maximum value of 10.0, that is,
having a
minimum value equal to or greater than 1.0 and a maximum value equal to or
less than 10.0,
such as, for example, 2.4 to 7.6. Any maximum numerical limitation recited in
this
specification is intended to include all lower numerical limitations subsumed
therein and any
minimum numerical limitation recited in this specification is intended to
include all higher
numerical limitations subsumed therein. Accordingly, Applicant reserves the
right to amend
this specification, including the claims, to expressly recite any sub-range
subsumed within the
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ranges expressly recited in this specification. All such ranges are intended
to be inherently
described in this specification such that amending to expressly recite any
such sub-ranges
would comply with the requirements of 35 U.S.C. 112(a) and 132(a).
[0021]
[0022] The grammatical articles "one", "a", "an", and "the", as used in this
specification,
are intended to include "at least one" or "one or more", unless otherwise
indicated. Thus, the
articles are used in this specification to refer to one or more than one
(i.e., to "at least one") of
the grammatical objects of the article. By way of example, "a component" means
one or
more components, and thus, possibly, more than one component is contemplated
and may be
employed or used in an implementation of the described embodiments. Further,
the use of a
singular noun includes the plural, and the use of a plural noun includes the
singular, unless
the context of the usage requires otherwise.
[0023] The compositions and methods described in this specification may
comprise, among
other components, nanoparticles and/or nano-sheets.
[0024] The nanoparticles may comprise a transition metal chalcogenide
compound,
including sulfides, selenides, and tellurides or one or more element such as,
for example,
titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium,
molybdenum, or
tungsten. The nanoparticles may comprise a chalcogenide material such as, for
example,
molybdenum disulfide, tungsten disulfide, niobium diselenide, and/or other
materials such as,
for example, hexagonal boron nitride, graphite, metals such as copper or
silver, inorganic
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compounds such as calcium carbonate, polymers such as polytetrafiuoroethylene
(PTFE), or
dithiophosphate compounds. The compositions described in this specification
may therefore
comprise, among others, molybdenum disulfide nanoparticles, tungsten disulfide
nanoparticles, niobium diselenide nanoparticles, hexagonal boron nitride
nanoparticles,
graphite nanoparticles, copper nanoparticles, silver nanoparticles, calcium
carbonate
nanoparticles, PTFE nanoparticles, nanoparticles of dithiophosphate compounds,
or
combinations of any thereof.
[0025] In various embodiments, the nanoparticles may have an open
architecture. As used
in this specification, the term "open architecture" or "open-ended
architecture" refers to the
morphology of particles comprising fissures, separations, or other
discontinuities in the
particles' outer surfaces which provide openings to the internal portions of
the individual
particles. In embodiments comprising layered particles, the terms "open
architecture" or
"open-ended architecture" refer to the morphology of the layered particles
comprising inter-
layer defects (e.g., shearing, buckling, folding, curling, and dislocating of
constituent
molecular layers) at the surface of the particles, which increase the inter-
planar spacing
between groupings of molecular layers, thereby providing fissures,
separations, or other
discontinuities in the particles' outer surfaces and openings to the internal
portions of the
particles. As used in
this specification, the term "layered particles" or "layered
nanoparticles" refers to particles comprising generally parallel stacked
molecular layers,
wherein the inter-layer bonding comprises relatively weak bonding such van der
Waals
bonding, and wherein the intra-layer bonding comprises relatively strong
bonding such as
covalent bonding. Examples of layered particles include, but are not limited
to, graphite
particles, molybdenum disulfide particles, tungsten disulfide particles,
niobium diselenide
particles, and hexagonal boron nitride particles. It is understood that the
terms "open
architecture" and "open-ended architecture" exclude particle morphologies such
as nano-
tubes and fullerenes, which are characterized by closed particle surfaces
lacking fissures,
separations, or other discontinuities in the particles' outer surfaces.
[0026] The compositions described in this specification may also comprise an
organic
medium encapsulating/coating the nanoparticles and/or intercalated in the
nanoparticles. For
example, an organic medium may be integrated into the internal portions of
individual
nanoparticles by intercalating into the spaces formed by the fissures,
separations, or other
discontinuities in the outer surfaces of nanoparticles having an open
architecture. In various
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embodiments, the nanoparticles may be intercalated and encapsulated/coated
with an organic
medium.
[0027] The nanoparticles may have an average primary particle size of less
than or equal to
1000 nanometers, and in some embodiments, less than or equal to 500
nanometers, less than
or equal to 400 nanometers, less than or equal to 300 nanometers, less than or
equal to 200
nanometers, less than or equal to 100 nanometers, less than or equal to 75
nanometers, less
than or equal to 50 nanometers, or less than or equal to 25 nanometers.
[0028] As used in this specification, including the claims, the term "average
primary
particle size" refers to a particle size as determined by visually examining a
microscopy
image of a sample of particles, measuring the largest length dimension of the
individual
particles in the image (L e., the diameters of the smallest spheres that
completely surround the
individual particles in the image), and calculating the average of the length
dimensions
(diameters) based on the magnification of the image. A person having ordinary
skill in the
art will understand how to prepare a microscopy image (e.g., light microscopy,
transmission
electron microscopy, and the like) of the particles comprising a composition
and determine
the average primary particle size of constituent particles (or a subset of the
constituent
particles based on like particle composition) based on the magnification of
the microscopy
image. As used in this specification, the term "average primary particle size"
refers the size
of individual particles as opposed to agglomerations of two or more individual
particles.
[0029] As described above, the compositions and methods described in this
specification
may comprise, among other components, nanoparticles and/or nano-sheets. As
used in this
specification, including the claims, the term "nano-sheets" refers to planar-
shaped particles
having a thickness dimension of less than 500 nanometers and an aspect ratio
(defined as the
ratio of the largest length/width dimension to the thickness dimension) of at
least 2. In some
embodiments, for example, nano-sheets may have a thickness dimension of less
than 100
nanometers and an aspect ratio of at least 10. Nano-sheets may have a
thickness dimension
of less than 50 nanometers and an aspect ratio of at least 20. Nano-sheets may
have a
thickness dimension of less than 25 nanometers and an aspect ratio of at least
40. Nano-
sheets may have a thickness dimension of less than 10 nanometers and an aspect
ratio of at
least 100. Nano-sheets may have a thickness dimension corresponding to
approximately one
unit cell dimension and such nano-sheets may be referred to as molecular nano-
sheets. Nano-
sheets may have length and width dimensions of less than 1000 nanometers.
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[0030] Molecular nano-sheets are a sub-genus of nano-sheets in which the
thickness
dimensions of the nano-sheets correspond to approximately one unit cell
dimension.
Molecular nano-sheets may be, but are not necessarily, crystalline molecular
structures. In
some embodiments, molecular nano-sheets may have length and width dimensions
of less
than or equal to 1000 nanometers, 500 nanometers, or 100 nanometers. In some
embodiments, molecular nano-sheets may have a thickness dimension
corresponding to
approximately one unit cell dimension. Generally, a molecular nano-sheet may
comprise a
single layer of any layered nanoparticle (e.g., a graphite/graphene molecular
nano-sheet, a
molybdenum disulfide molecular nano-sheet, a tungsten disulfide molecular nano-
sheet, a
niobium diselenide molecular nano-sheet, or a hexagonal boron nitride
molecular nano-
sheet).
[0031] The crystal structure of a material (i.e., the spatial arrangement of
the atoms forming
a crystal) can be described in terms of the unit cell. A unit cell is the
smallest molecular unit
that a crystal can be divided into using crystallographic symmetry operations.
In other words,
a unit cell is the simplest repeating unit in a crystalline material. Unit
cells stacked in three-
dimensional space describe the bulk arrangement of atoms of a crystalline
material.
[0032] By way of example, molybdenum disulfide predominantly exists in a
hexagonal
crystal form characterized by MoS2 layers in which the molybdenum atoms have
trigonal
prismatic coordination of six sulfur atoms with two molecules per unit cell.
Thus, the
molybdenum disulfide crystal structure comprises a tri-layer having one planar
hexagonal
layer of molybdenum atoms interspersed between two planar layers of sulfur
atoms forming
an intra-molecular covalently bonded S-Mo-S molecular layer. Bulk molybdenum
disulfide
comprises relatively weak inter-molecular van der VVaals bonds between the
adjacent sulfur
atoms of stacked S-Mo-S molecular layers.
[0033] Referring to Figure 10(A), two intra-molecular covalently bonded S-Mo-S
molecular layers 10 are shown with inter-molecular van der Waals bonds 17
between the
adjacent sulfur atoms 11 of the two stacked S-Mo-S molecular layers 10. Within
each S-Mo-
S molecular layer 10, the molybdenum atoms 13 and the sulfur atoms 11 form the
tri-layer
comprising one planar hexagonal layer of molybdenum atoms 13 interspersed
between two
planar layers of sulfur atoms 11 and forming covalent bonds 15. Referring to
Figure 10(B),
the molybdenum disulfide unit cell has a thickness dimension of approximately
3.241
angstroms across the S-Mo-S molecular layer,
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[0034] Accordingly, a molybdenum disulfide molecular nano-sheet may comprise a
molybdenum disulfide crystal having a thickness dimension corresponding to the
thickness of
the covalently bonded S-Mo-S molecular layer (without adjoining inter-
molecular van der
Waals bonded layers, Le., approximately 3.241 angstroms) and, in some
embodiments, length
and width dimensions of less than or equal to 1000 nanometers.
[0035] The crystal structure of tungsten disulfide is analogous to that of
molybdenum
disulfide and, therefore, a tungsten disulfide molecular nano-sheet may
comprise a tungsten
disulfide crystal having a thickness dimension corresponding to the thickness
of the
covalently bonded S-W-S molecular layer (without adjoining inter-molecular van
der Waals
bonded layers) and, in some embodiments, length and width dimensions of less
than or equal
to 1000 nanometers.
[0036] The crystal structure of hexagonal boron nitride is characterized by
hexagonal
coordination between three nitrogen atoms and three boron atoms forming
adjacent six-sided
rings that form intra-molecular covalently-bonded mono-layers that are
atomically thin (i.e.,
having a thickness dimension of a single atom). Referring to Figure 11, three
intra-molecular
covalently bonded B-N molecular layers 20 are shown with inter-molecular van
der Waals
bonds 27 between the adjacent B-N molecular layers 20. Within each B-N
molecular layer
20, the boron atoms 23 and the nitrogen atoms 21 form the mono-layer
comprising the
hexagonal atomic orientation within a single plane and forming the covalent
bonds 25. Thus,
the hexagonal boron nitride crystal structure comprises B-N molecular mono-
layers, and bulk
hexagonal boron nitride comprises relatively weak inter-molecular van der
Waals bonds
between the adjacent B-N molecular mono-layers. Therefore, a hexagonal boron
nitride
molecular nano-sheet may comprise a hexagonal boron nitride crystal having a
single atomic
thickness dimension and, in some embodiments, length and width dimensions of
less than or
equal to 1000 nanometers.
[0037] The crystal structure of graphite (carbon) is analogous to that of
hexagonal boron
nitride and, therefore, a graphite molecular nano-sheet may comprise a
graphene crystal
having a single atomic thickness dimension and, in some embodiments, length
and width
dimensions of less than or equal to 1000 nanometers.
[0038] In various embodiments, nano-sheets may comprise a material such as,
for example,
molybdenum disulfide, tungsten disulfide, niobium diselenide, hexagonal boron
nitride,
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graphite/graphene, metals such as copper or silver, inorganic compounds such
as calcium
carbonate, polymers such as PTFE, or dithiophosphate compounds. In some
embodiments,
the nano-sheets may comprise molecular nano-sheets comprising a material such
as, for
example, molybdenum disulfide, tungsten disulfide, niobium diselenide,
hexagonal boron
nitride, or graphene. Thus, the compositions described in this specification
may comprise
molybdenum disulfide nano-sheets, tungsten disulfide nano-sheets, niobium
diselenide nano-
sheets, hexagonal boron nitride nano-sheets, graphite nano-sheets, graphene
molecular nano-
sheets, metal (e.g., copper) nano-sheets, inorganic compound (e.g., calcium
carbonate) nano-
sheets, polymer (e.g., PTFE) nano-sheets, nano-sheets comprising
dithiophosphate
compounds, or combinations of any thereof.
[0039] It is important to recognize that layered materials such as, for
example,
molybdenum disulfide, tungsten disulfide, niobium diselenide, hexagonal boron
nitride, and
graphite, may form nano-sheets (e.g., planar-shaped particles having a
thickness dimension of
less than 500 nanometers and an aspect ratio of at least 2) or molecular nano-
sheets (e.g.,
crystalline molecular structures comprising a thickness dimension
corresponding to
approximately one unit cell dimension). In this regard, molecular nano-sheets
are a sub-
genus of nano-sheets.
[0040] In various embodiments, the nano-sheets may be functionalized. The nano-
sheets
may be functionalized with organic molecules or functional groups, inorganic
molecules or
functional groups, or both organic and inorganic molecules or functional
groups, forming
functionalized nano-sheets. The nano-sheets may be functionalized with
catalysts,
antioxidants, anti-corrosion agents, biocidal agents, or combinations of any
thereof.
Examples of antioxidants, anticorrosion agents, and biocidal agents include,
but are not
limited to, antioxidants selected from the group consisting of hindered
phenols, alkylated
phenols, alkyl amines, aryl amines, 2,6-di-tert-butyl-4-methylphenol, 4,4'-di-
tert-
octyldiphenylamine, tert-butyl hydroquinone, tris(2,4-di-tert-
butylphenyl)phosphate,
phosphites, thioesters, or combinations of any thereof; anticorrosion agents
selected from the
group consisting of alkaline earth metal bisalkylphenolsulphonates,
dithiophosphates,
alkenylsuccinic acid half-amides, or combinations thereof; and biocidal agents
material
selected from the group consisting of alkyl benzothiazole, hydroxylamine
benzothiazole, an
amine salt of an alkyl succinic acid, an amine salt of an alkenyl succinic
acid, a partial alkyl
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ester of an alkyl succinic acid, a partial alkyl ester of an alkenyl succinic
acid, or
combinations of any thereof.
[0041] In various embodiments, the nano-sheets may be fimctionalized with a
dispersant
agent. Suitable dispersant agents may comprise at least one material selected
from the group
consisting of amide compounds, borate compounds, and boride compounds. For
example, a
dispersant agent may comprise at least one of succinimide and disodium
octaborate
tetrahydrate.
[0042] In various embodiments, the nano-sheets may be coated and/or
encapsulated with an
organic medium. For instance, an organic medium may be chemically or
physically adsorbed
onto nano-sheets or otherwise chemically or physically bonded to nano-sheets.
As described
above, nanoparticles may be encapsulated and/or intercalated with an organic
medium. As
used herein, the term "organic medium" refers to hydrophobic/oleophilic
substances and
carbon-based compounds. For example, the organic medium may comprise at least
one
material selected from the group consisting of oil media, grease media,
alcohol media,
composite oils, mineral oils, synthetic oils, canola oil, vegetable oil,
soybean oil, corn oil,
rapeseed oil, ethyl and
methyl esters of rapeseed oil, monoglycerides, distilled
monoglycerides, diglycerides, acetic acid esters of monoglycerides, organic
acid esters of
monoglycerides, sorbitan, sorbitan esters of fatty acids, propylene glycol
esters of fatty acids,
polyglycerol esters of fatty acids, hydrocarbon oils, n-hexadecane,
phospholipids, lecithins,
amide compounds, boron-containing compounds, dithiophosphate compounds, and
combinations of any thereof. Examples of suitable dithiophosphate compounds
that may
comprise an organic medium include, but are not limited to, zinc dialkyl
dithiophosphate
(ZDDP) and molybdenum dithiophosphate (MoDTP), which may be used alone or in
combination with any other organic medium such as an oil medium. In various
embodiments, the organic medium may comprise an oil medium such as, for
example, a
composite oil, a mineral oil, a synthetic oil, canola oil, a vegetable oil,
soybean oil, corn oil, a
hydrocarbon oil, a mineral oil, or combinations of any thereof.
[0043] In addition to the nanoparticles and/or nano-sheets, the compositions
described in
this specification may also comprise a secondary or tertiary particulate
material such as, for
example, polytetrafluoroethylene; soft metals such as gold, platinum, silver,
lead, nickel,
copper; cerium fluoride; zinc oxide; silver sulfate; cadmium iodide; lead
iodide; barium
fluoride; tin sulfide; zinc phosphate; zinc sulfide; mica; boron nitrate;
borax; fluorinated
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carbon; zinc phosphide; boron; or combinations of any thereof. The secondary
or tertiary
particulate material may comprise nanoparticles. The secondary or tertiary
nanoparticles may
have an average primary particle size of less than or equal to 1000
nanometers, and in some
embodiments, less than or equal to 500 nanometers, less than or equal to 400
nanometers, less
than or equal to 300 nanometers, less than or equal to 200 nanometers, less
than or equal to
100 nanometers, less than or equal to 75 nanometers, less than or equal to 50
nanometers, or
less than or equal to 25 nanometers.
[0044] In various embodiments, the compositions described in this
specification may also
comprise a base lubricant material, which may be different than the organic
medium
described above. The nanoparticles and/or nano-sheets may be dispersed in the
base
lubricant material. The base lubricant material may comprise a material such
as, for example,
an oil, a grease, a polymer, a plastic, a gel, a wax, a silicone, a
hydrocarbon oil, a vegetable
oil, corn oil, peanut oil, canola oil, soybean oil, a mineral oil, a paraffin
oil, a synthetic oil, a
petroleum gel, a petroleum grease, a hydrocarbon gel, a hydrocarbon grease, a
lithium based
grease, a fluoroether based grease, ethylenebistearamide, or combinations of
any thereof. In
various embodiments, the base lubricant material may comprise at least one
material selected
from the group consisting of an oil, a grease, a plastic, a gel, a wax, a
silicone, and
combinations of any thereof. In various embodiments, the base lubricant
material may
comprise an oil or a grease. In various embodiments, the base lubricant
material may
comprise at least one material selected from the group consisting of a mineral
oil, a paraffin
oil, a synthetic oil, a petroleum grease, a hydrocarbon grease, a lithium
based grease, or
combinations of any thereof
[0045] In various embodiments, the compositions described in this
specification may also
comprise an emulsifier. The emulsifier may comprise at least one material
selected from the
group consisting of lecithins, phospholipids, soy lecithins, detergents,
distilled
monoglycerides, monoglycerides, diglycerides, acetic acid esters of
monoglycerides, organic
acid esters of monoglycerides, sorbitart esters of fatty acids, propylene
glycol esters of fatty
acids, polyglycerol esters of fatty acids, compounds containing phosphorous,
compounds
containing sulfur, compounds containing nitrogen, or combinations of any
thereof In various
embodiments, the emulsifier may comprise a compound containing phosphorous. In
various
embodiments, the emulsifier may comprise a phospholipid. In various
embodiments, the
emulsifier may comprise a lecithin.
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[0046] In various embodiments, the compositions described in this
specification may also
comprise one or more of an antioxidant, an anticorrosion agent, or a biocidal
that is not
bonded to or adsorbed to the surfaces of nano-sheets. For example, the
compositions may
comprise at least one antioxidant material selected from the group consisting
of hindered
phenols, alkylated phenols, alkyl amines, aryl amines, 2,6-di-tert-butyl-4-
methylphenol, 4,4'-
di-tert-octyldiphenylamine, tert-butyl hydroquinone, tris(2,4-di-tert-
butylphenyl)phosphate,
phosphites, thioesters, or combinations of any thereof. The compositions may
comprise at
least one anticorrosion agent selected from the group consisting of alkaline
earth metal
bisalkylphenolsulphonates, dithiophosphates, alkenylsuccinic acid half-amides,
or
combinations thereof. The compositions may comprise at least one biocidal
material selected
from the group consisting of alkyl benzothiazole, hydroxylamine benzothiazole,
an amine salt
of an alkyl succinic acid, an amine salt of an alkenyl succinic acid, a
partial alkyl ester of an
alkyl succinic acid, a partial alkyl ester of an alkenyl succinic acid, or
combinations of any
thereof.
[0047] The compositions described in this specification may be used to
formulate a
lubricant. For example, compositions comprising nanoparticles and/or nano-
sheets may be
used as performance-enhancing additives to off-the-shelf liquid based
lubricants.
Additionally, lubricant compositions may comprise nanoparticles and/or nano-
sheets
dispersed in a lubricant base material as described above, wherein a separate
organic medium
is intercalated in the nanoparticles, encapsulates the nanoparticles, and/or
encapsulates the
nano-sheets. Lubricant compositions comprising nanoparticles and/or nano-
sheets, with or
without an intercalating and/or encapsulating organic medium, in accordance
with the
embodiments described in this specification, will provide a synergistically
enhanced
combination of lubrication in mechanical systems.
[0048] The compositions described in this specification may be used to
formulate a coating
or solid film on a substrate or surface. For example, compositions comprising
nanoparticles
and/or nano-sheets, with or without an intercalating and/or encapsulating
organic medium,
may be physically rubbed onto substrates and surfaces to form burnished films
and coatings.
Compositions comprising nanoparticles and/or nano-sheets, with or without an
intercalating
and/or encapsulating organic medium, may also be deposited as solid films and
coatings
using pneumatic methods analogous to sandblasting. Compositions comprising
nanoparticles
and/or nano-sheets, with or without an intercalating and/or encapsulating
organic medium,
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may also be added to thermoplastic or thermosetting resinous binders to make
film-forming
coating compositions (e.g., binders based on epoxy, urethane, urea, acrylic,
phenolic, amide-
imide, polyimide, azole, and like chemical systems).
[0049] In various embodiments, compositions comprising nanoparticles and/or
nano-sheets,
with or without an intercalating and/or encapsulating organic medium, may be
used in a
method to lubricate a surface and/or deliver active materials and agents to
the surface,
including catalysts, anti-corrosion agents, antioxidants, biocidal agents, and
other functional
groups and molecules. The method may comprise applying the compositions
described in this
specification to the surface or otherwise contacting the surface with the
compositions. The
surface and the applied/contacting composition are subjected to a frictional
force, pressure, or
other mechanical stress, which causes constituent layers of the nanoparticles
to delaminate
and form a plurality of nano-sheets. In this manner, for example, nano-sheets
may be formed
in situ on a surface as the force/pressure exfoliates the constituent
molecular layers of
nanoparticles having an open architecture. In various embodiments, the
compositions may
comprise an organic medium and the organic medium coats or encapsulates the
nano-sheets
fowled in situ. The coated or encapsulated nano-sheets formed in situ may
deposit on the
surface in a tribo-fihn.
[0050] The compositions described in this specification may be made from solid
lubricant
starting or feed materials. Examples of solid lubricants may include, but are
not limited to,
layered materials such as, for example, hexagonal boron nitride and
chalcogenides, like
molybdenum disulfide, tungsten disulfide, niobium diselenide, or a combination
thereof.
Other suitable layered materials include graphite. Other solid lubricant
starting or feed
materials that may be used alone or in combination with the layered materials
include, but are
not limited to polytetrafluoroethylene, soft metals (such as, for example,
silver, lead, nickel,
copper), cerium fluoride, zinc oxide, silver sulfate, cadmium iodide, lead
iodide, barium
fluoride, tin sulfide, zinc phosphate, zinc sulfide, mica, boron nitrate,
borax, fluorinated
carbon, zinc phosphide, boron, or a combination thereof. Fluorinated carbons
may be,
without limitation, carbon-based materials such as graphite which has been
fluorinated to
improve its aesthetic characteristics. Such materials may include, for
example, a material
such as CF x wherein x ranges from about 0.05 to about 1.2. Such a material is
produced, for
example, by Allied Chemical under the trade name Accufluor.
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[0051] The methods of making the nanoparticles encapsulated and/or
intercalated with the
organic medium, and the nano-sheets, may include, for example, the milling of
a solid
lubricant feed material. In various embodiments, the solid lubricant feed
material may be
capable of being milled to particles comprising an average primary particle
size of about
1000 nanometers or less (submicron size), for example, from about 500
nanometers to about
nanometers. The particles may have an average primary particle size of less
than or equal
to about 500 nanometers, less than or equal to about 100 nanometers, less than
or equal to
about 75 nanometers, and less than or equal to about 50 nanometers.
Alternatively, the
milling may result in milled lubricant particles comprising a mixture, the
mixture comprising
particles having an average primary particle size of less than or equal to
about 500
nanometers, plus larger particles. Additionally, the milling may result in
milled nano-sheets
in combination with nanoparticles.
[0052] The milling may include, among other techniques, ball milling and chemo-
mechanical milling. Examples of ball milling may include dry ball milling, wet
ball milling,
and combinations thereof. Ball milling may refer to an impaction process that
may include
two interacting objects where one object may be a ball, a rod, 4 pointed pins
(jack shape), or
other shapes. Chemo-mechanical milling may refer to an impaction process that
may form an
integrated complex between the organic medium and the nanoparticles, and
between the
organic medium and the nano-sheets. As a result of chemo-mechanical milling,
the organic
medium may coat, encapsulate, and/or intercalate the nanoparticles, and coat
and/or
encapsulate the nano-sheets. In various embodiments, chemo-mechanical milling
may be
performed using a ball milling technique.
[0053] In various embodiments, the solid lubricant feed material may be dry
milled and
then wet milled. An emulsifier may be mixed with a lubricant base material and
added to the
wet milled particles. Dry milling may refer to particles that have been milled
in the presence
of a vacuum, a gas, or a combination thereof. Wet milling may refer to
particles that have
been milled in the presence of a liquid.
[0054] As described above, the lubricant nanoparticle composition may farther
comprise an
organic medium. Examples of organic media include, but are not limited to, oil
media,
grease media, alcohol media, or combinations thereof. Specific examples of
organic media
include, but are not limited to, composite oil, eanola oil, vegetable oils,
soybean oil, corn oil,
ethyl and methyl esters of rapeseed oil, distilled monoglycerides,
monoglycerides,
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diglycerides, acetic acid esters of monoglycerides, organic acid esters of
monoglycerides,
sorbitan, sorbitan esters of fatty acids, propylene glycol esters of fatty
acids, polyglycerol
esters of fatty acids, n-hexadecane, hydrocarbon oils, phospholipids, or a
combination
thereof. Many of these organic media may be environmentally acceptable.
[0055] The compositions described in this specification may contain
emulsifiers,
surfactants, or dispersants. Examples of emulsifiers may include, but are not
limited to,
emulsifiers having a hydrophilic-lipophilic balance (HLB) from about 2 to
about 7; a HLB
from about 3 to about 5; or a HLB of about 4. Examples of emulsifiers may
include, but are
not limited to, lecithins, soy lecithins, phospholipid lecithins, detergents,
distilled
monoglycerides, monoglycerides, diglycerides, acetic acid esters of
monoglycerides, organic
acid esters of monoglycerides, sorbitan esters of fatty acids, propylene
glycol esters of fatty
acids, polyglycerol esters of fatty acids, compounds containing phosphorous,
compounds
containing sulfur, compounds containing nitrogen, or a combination thereof.
[0056] Examples of surfactants that may be included in the compositions
described in this
specification include, but are not limited to, 2-alkyl-succinic acid 1-propyl
ester, canola oil,
dialkyl hydrogen phosphite, glycerol mono oleate, lecithin, octadecylamine,
oleic acid,
oleylamide, oleylamine, poly(methyl methacrylate), sodium stearate, Span 80,
stearic acid,
thiocarbamates (molybdenum dithiocarbamate or MoDTC), thiophosphates
(molybdenum
dithiophosphate or MoDTP, zinc dialkyl dithiophosphate or ZDDP),
frioctylphosphine oxide,
Tween 20 or combinations of any thereof.
[0057] Examples of dispersants that may be included in the compositions
described in this
specification include, but are not limited to, polyisobutylene succinimides
(PIBS), succinic
anhydrides, PIBS anhydrides, succiniate esters, metal sulfonates, polymeric
detergents,
polymeric dispersants, polyoxyethylene alkyl ethers, polyoxyethylene
dialkylphenol ethers,
polyalphaolefins (PAO), alkylglycoside, polyoxyethylene fatty acid esters,
sucrose fatty acid
esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid
esters, borate esters,
phosphate esters, phosphate amines, fatty acid alkanolamide, and combinations
thereof. In
various embodiments, amine-containing dispersants, such as, for example,
phosphate amines,
may comprise reaction products of amines including, but not limited to,
ethylenediamine,
diethylenetriamine, pentaethylenehexamine, polyethyleneamine,
tetraethylenepentamine,
triethylenetetramine, or combinations of any thereof.
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[0058] A method of making a composition, such as, for example, a lubricant
additive or a
primary lubricant formulation, is described. The composition may be used as an
additive
dispersed in a lubricant base material or as a component of a primary
lubricant formulation.
Examples of lubricant base materials may include, but are not limited to,
oils, greases,
plastics, gels, sprays, or a combination thereof. Specific examples of bases
may include, but
are not limited to, hydrocarbon oils, vegetable oils, corn oil, peanut oil,
canola oil, soybean
oil, mineral oil, paraffin oils, synthetic oils, petroleum gels, petroleum
greases, hydrocarbon
gels, hydrocarbon greases, lithium based greases, fluoroether based greases,
ethyl enebistearamide, waxes, silicones, or a combination thereof.
[0059] Described in this specification is a method of lubricating or coating
an object that is
part of an end application with a composition comprising nanoparticles and/or
nano-sheets,
with or without an intercalating and/or encapsulating organic medium. Further
described is a
method of lubricating an object by employing nanoparticles and/or nano-sheets,
with or
without an intercalating and/or encapsulating organic medium, as a delivery
mechanism.
[0060] The compositions and methods described in this specification exhibit,
among
various advantages, enhanced dispersion stability, resistance to
agglomeration, and corrosion
resistance. Figure 1 illustrates a method of preparing nanoparticle based
lubricants or
compositions. A solid lubricant feed is introduced via line 210 to a ball
milling processor
215. Ball milling is carried out in the processor 215 and the solid lubricant
feed is milled to
comprise particles having an average primary particle size of less than or
equal to about 1000
nanometers, less than or equal to about 500 nanometers, less than or equal to
about 100
nanometers, less than or equal to about 80 nanometers, or less than or equal
to about 50
nanometers. Alternatively, the ball milling may result in milled lubricant
particles
comprising a mixture, the mixture comprising particles having an average
particle dimension
of less than or equal to about 1000 nanometers or less than or equal to about
500 nanometers,
plus larger particles. The ball milling may be high energy ball milling,
medium energy ball
milling, or combinations thereof. Additionally, in various embodiments the
ball milling may
be carried out in a vacuum, in the presence of a gas, in the presence of a
liquid, in the
presence of a second solid, or combinations thereof. The nanoparticle
composition may be
removed from the processor via line 220. The nanoparticle composition may be a
nanoparticle based lubricant.
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[0061] In various embodiments, the ball milling may comprise a first ball
milling and at
least one more subsequent ball millings, or ball milling and/or other
processing as
appropriate. The ball milling may comprise dry milling followed by wet
milling. Figure 2
illustrates a further method 100 of preparing nanoparticle based lubricants
and other
compositions where dry milling is followed by wet milling. Feed 110 introduces
a solid
lubricant feed into a ball milling processor 115 where dry ball milling, such
as in a vacuum or
in air, reduces the solid lubricant feed to particles having an average
dimension of the size
described above. Line 120 carries the dry milled particles to a wet milling
processor 125.
Via line 160 the dry milled particles are combined with a composite oil or an
organic medium
prior to entering the wet milling processor 125. Alternatively, the organic
medium and dry
milled particles may be combined in the wet milling processor 125. In further
alternative
embodiments (not shown), the dry milling and wet milling may be carried out in
a single
processor where the organic medium is supplied to the single processor for wet
milling after
initially carrying out dry milling. In other alternative embodiments, the
balls in the ball
milling apparatus may be coated with the organic medium to incorporate the
organic medium
in the nanoparticles and/or onto the nano-sheets.
[0062] After wet milling, line 130 carries the wet milled particles to a
container 135, which
may be a sonication device. Alternatively, line 130 may carry a mixture
comprising
nanoparticles and/or nano-sheets, organic medium, and a complex comprising
nanoparticles
combined with an organic medium and/or nano-sheets combined with an organic
medium.
[0063] In another embodiment, prior to introduction of the wet milled
particles into the
container 135, a lubricant base material may be fed to the container 135 via
line 150.
Alternatively, the base may be supplied to the wet milling processor 125 and
the mixing,
which may include sonicating, may be carried out in the wet milling processor
125. In such
embodiments the lubricant nanoparticle and/or nano-sheet composition may be
employed as
an additive and dispersed in the lubricant base material. A lubricant base
material may be
paired with a lubricant nanoparticle and/or nano-sheet composition according
to the ability of
the base material and the lubricant nanoparticle and/or nano-sheet composition
to blend
appropriately. In such cases the lubricant nanoparticle and/or nano-sheet
composition may
enhance the performance characteristics of the base.
[0064] In various embodiments, an emulsifier may be mixed with the lubricant
base
material. Emulsifiers may further enhance dispersion of the lubricant
nanoparticle and/or
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nano-sheet composition in the lubricant base material. The emulsifier may be
selected to
enhance the dispersion stability of a nanoparficle or nano-sheet composition
in a base. An
emulsifier may also be supplied to the container 135 via line 140. In some
embodiments, the
emulsifier and base are combined in the container 135 prior to introduction of
the wet milled
particles. Prior mixing of the emulsifier with the base material may enhance
dispersion upon
addition of nanoparticles, nano-sheets, and/or complexes thereof with an
organic medium, by
homogeneously dispersing the nanoparticles/nano-sheets/ complexes. In some
embodiments,
the mixing of the emulsifier and base may comprise sonicating. The emulsifier
may be
supplied to the wet milling processor 125 and the mixing, which may include
sonicating, may
be carried out in the wet milling processor 125. The lubricant removed from
the container
135 via line 170 may be a blend comprising the wet milled particles, organic
medium, and
base. The blend may further comprise an emulsifier.
[0065] In various embodiments, antioxidants or anticorrosion agents may be
milled with
the nanoparticles and/or nano-sheets or added to prior-milled nanoparticles
and/or nano-
sheets. Examples of antioxidants include, but are not limited to, hindered
phenols, allcylated
phenols, alkyl amines, aryl amines, 2,6-di-tert-butyl-4-methylphenol, 4,4'-di-
tert-
octyldiphenylamine, tert-Butyl hydroquinone, tris(2,4-di-tert-
butylphenyl)phosphate,
phosphites, thioesters, or combinations of any thereof. Examples of
anticorrosion agents
include, but are not limited to, alkaline-earth metal
bisalkylphenolsulphonates,
dithiophosphates, alkenylsuccinic acid half-amides, or combinations of any
thereof. In
various embodiments, biocidals may be milled with the nanoparticles and/or
nano-sheets or
added to prior-milled nanoparticles and/or nano-sheets. Examples of biocidals
may include,
but are not limited to, alkyl or hydroxylamine benzotriazole, an amine salt of
a partial alkyl
ester of an alkyl, alkenyl succinic acid, or a combination thereof.
[0066] In various embodiments, further processing of wet milled nanoparticles
and/or
nano-sheets may comprise removal of oils that are not a part of a complex with
the lubricant
particles or nano-sheets. Such methods may be suitable for applications that
benefit from use
of dry particles and sheets of lubricant, such as coating applications. Oil
and/or other liquids
can be removed from wet milled nanoparticles and/or nano-sheets to produce
substantially
dry lubricant particles, sheets, and complexes having intercalated and/or
encapsulated organic
media. Such wet milling followed by drying may produce a lubricant with
reduced tendency
to agglomerate. In specific embodiments, an agent, such as acetone or other
suitable solvent,
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may be added that dissolves oils that are not a part of a complex with the
nanoparticles or
nano-sheets, followed by a drying process such as supercritical drying, to
produce a
substantially dry lubricant comprising particles or sheets treated by milling
in an organic
medium.
[0067] Ball milling conditions may vary and, in particular, conditions such as
temperature,
milling time, and size and materials of the balls and vials may be
manipulated. In various
embodiments, ball milling may be carried out from about 12 hours to about 50
hours, from
about 36 hours to about 50 hours, from about 40 hours to about 50 hours, or
for about 48
hours ( 1 hour, 2 hours, or 3 hours). Ball milling may be conducted at
room temperature
or elevated temperatures. The benefits of increasing milling time may comprise
at least one
of increasing the time for the organic medium and nanoparticles to interact,
integrate, and
complex; and producing finer sizes, better yield of nanoparticles, more
uniform shapes, and
more passive surfaces. An example of ball milling equipment suitable for
carrying out the
described milling includes the SPEX CertiPrep model 8000D, along with hardened
stainless
steel vials and hardened stainless steel grinding balls, but any type of ball
milling apparatus
may be used. In some embodiments, a stress of 600-650 MPa, a load of 14.9 N,
and a strain
of 10"3-104 per second may be used.
[0068] In various embodiments, a hybrid milling process may produce a mixture
of both
nanoparticles encapsulated and/or intercalated with an organic medium and nano-
sheets
coated and/or encapsulated with an organic medium. The hybrid milling process
may
produce combinations of nanoparticles and nano-sheets that are functionalized,
for example,
with catalysts, antioxidants, anti-corrosion agents, biocidals, or
combinations of any thereof.
[0069] The proportions of the components in a nanopartiele and/or nano-sheet
based
lubricant or other composition may contribute to performance of the
composition, such as the
composition's dispersion stability and ability to resist agglomeration. In wet
milling, suitable
starting ratios of solid lubricant feed particles to organic medium may be
about 1 part
particles to about 4 parts organic medium by weight, about 1 part particles to
about 3 parts
organic medium by weight, about 3 parts particles to about 8 parts organic
medium by
weight, about 2 parts particles to about 4 parts organic medium by weight,
about 1 part
particles to about 2 parts organic medium by weight, or about 1 part particles
to about 1.5
parts organic medium by weight.
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[0070] Suitable ratios of organic medium to emulsifier in a composition
including
nanoparticles and/or nano-sheets may be about 1 part organic medium to less
than or equal to
about 1 pail, emulsifier, about 1 part organic medium to about 0.5 parts
emulsifier by weight,
or from about 0.4 to about 1 part emulsifier for about 1 part organic medium
by weight.
[0071] The amount of lubricant nanoparticle and/or nano-sheet composition (by
weight)
sonicated or dispersed in a lubricant base material may comprise from about
0.25% to about
5%, about 0.5% to about 3%, about 0.5% to about 2%, or about 0.75% to about
2%, based on
total weight of the composition.
[0072] The amount of emulsifier (by weight) sonicated or dissolved in a
lubricant base
material, depending on the end application, shelf-life, and the like, may
comprise from about
0.5% to about 10%, from about 4% to about 8%, from about 5% to about 6%, or
from about
0.75% to about 2.25%, based on total weight of the composition.
[0073] The compositions described in this specification may be used, without
limitation, as
lubricants, coatings, delivery mechanisms, or combinations of any thereof. The
compositions
may be used, without limitation, as an additive dispersed in a base oil or
other lubricant
composition. The compositions may also be used, without limitation, to
lubricate a boundary
lubrication regime. A boundary lubrication regime may be a lubrication regime
where the
average lubricant film thickness may be less than the composite surface
roughness and the
surface asperities may come into contact with each other under relative
motion. During the
relative motion of two surfaces with lubricants in various applications, three
different
lubrication stages may occur, and the boundary lubrication regime may be the
most severe
condition in terms of temperature, pressure and speed. Mating parts may be
exposed to
severe contact conditions of high load, low velocity, extreme pressure (for
example, 1-2
GPa), and high local temperature (for example, 150-300 degrees C.). The
boundary
lubrication regime may also exist under lower pressures and low sliding
velocities or high
temperatures. In the boundary lubrication regime, the mating surfaces may be
in direct
physical contact.
[0074] The compositions may further be used, without limitation, as a
lubricant or coating
in machinery applications, manufacturing applications, mining applications,
aerospace
applications, automotive applications, pharmaceutical applications, medical
applications,
dental applications, cosmetic applications, food product applications,
nutritional applications,
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health related applications, bio-fuel applications or a combination thereof.
Specific examples
of uses in end applications include, without limitation, machine tools,
bearings, gears,
camshafts, pumps, transmissions, piston rings, engines, power generators, pin-
joints,
aerospace systems, mining equipment, manufacturing equipment, or a combination
thereof.
Further specific examples of uses may be, without limitation, as an additive
in lubricants,
greases, gels, compounded plastic parts, pastes, powders, emulsions,
dispersions, or
combinations thereof. The compositions may also be used as a lubricant that
employs the
lubricant nanoparticle and/or nano-sheet composition as a delivery mechanism
in
pharmaceutical applications, medical applications, dental applications,
cosmetic applications,
food product applications, nutritional applications, health related
applications, bio-fuel
applications, or a combination thereof. The various compositions and methods
may also be
used, without limitation, in hybrid inorganic-organic materials. Examples of
applications
using inorganic-organic materials, include, but are not limited to, optics,
electronics, ionics,
mechanics, energy, environment, biology, medicine, smart membranes, separation
devices,
functional smart coatings, photovoltaic and fuel cells, photocatalysts, new
catalysts, sensors,
smart microelectronics, micro-optical and photonic components and systems for
nanophotonics, innovative cosmetics, intelligent therapeutic vectors that
combined targeting,
imaging, therapy, and controlled release of active molecules, and nanoceramic-
polymer
composites.
[0075] In some embodiments, the dry ball milling operations may create a close
caged
dense oval shaped architecture (similar to a football shape or fullerene type
architecture).
This may occur when solid lubricant feed materials are milled in a gas or
vacuum. Figure
7(A) shows the close caged dense oval shaped architecture of molybdenum
disulfide
nanoparticles that have been ball milled in air for 48 hours.
[0076] In some embodiments, the wet ball milling operation may create an open
architecture (as described above), which may be encapsulated and/or
intercalated with an
organic medium. This may occur when solid lubricant feed materials are milled
in a gas or
vacuum followed by milling in an organic medium. Figure 7(B) shows the open
architecture
of molybdenum disulfide nanoparticles that have been ball milled in air for 48
hours followed
by ball milling in canola oil for 48 hours. In other embodiments, the ball
milling operations
may create nano-sheets, which may be coated and/or encapsulated with an
organic medium,
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or functionalized with catalysts, antioxidants, anti-corrosion agents,
biocidals, or
combinations of any thereof.
[0077] As shown in the examples, the tribological perfoimance of a
nanoparticle based
lubricant may be improved. The tribological performance may be measured by
evaluating
different properties. An anti-wear property may be a lubricating fluid
property that has been
measured using the industry standard Four-Ball Wear (ASTM D4172) Test. The
Four-Ball
Wear Test may evaluate the protection provided by a lubricant under conditions
of pressure
and sliding motion. Placed in a bath of the test lubricant, three fixed steel
balls may be put
into contact with a fourth ball of the same grade in rotating contact at
preset test conditions.
Lubricant wear protection properties may be measured by comparing the average
wear scars
on the three fixed balls. The smaller the average wear scar, the better the
protection.
Extreme pressure properties may be lubricating fluid properties that have been
measured
using the industry standard Four-Ball Wear (ASTM D2783) Test. This test method
may
cover the determination of the load-carrying properties of lubricating fluids.
The following
two determinations may be made: 1) load-wear index (formerly Mean-Hertz load)
and 2)
weld load (kg). The load-wear index may be the load-carrying property of a
lubricant. It
may be an index of the ability of a lubricant to minimize wear at applied
loads. The weld
load may be the lowest applied load in kilograms at which the rotating ball
welds to the three
stationary balls, indicating the extreme pressure level that the lubricants
can withstand. The
higher the weld point scores and load wear index values, the better the anti-
wear and extreme
pressure properties of a lubricant. The coefficient of friction (COF) may be a
lubricating
fluid property that has been measured using the industry standard Four-Ball
Wear (ASTM
D4172) Test. COF may be a dimensionless scalar value which describes the ratio
of the force
of friction between two bodies and the force pressing them together. The
coefficient of
friction may depend on the materials used. For example, ice on metal has a low
COF, while
rubber on pavement has a high COF. A common way to reduce friction may be by
using a
lubricant which is placed between two surfaces.
[0078] The compositions described in this specification may have a wear scar
diameter of
about 0.4 mm to about 0.5 mm. The composition may have a COF of about 0.06 to
about
0.08. The composition may have a weld load of about 150 kg to about 350 kg.
The
composition may have a load wear index of about 20 to about 40. The values of
these
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tribological properties may change depending on the amount of lubricant
nanoparticle and/or
nano-sheet composition sonicated or dissolved in the lubricant base material.
[0079] The non-limiting and non-exhaustive examples that follow are intended
to further
describe various non-limiting and non-exhaustive embodiments without
restricting the scope
of the embodiments described in this specification,
EXAMPLES
Example 1:
[0080] Ball milling was performed in a SPEX 8000D machine using hardened
stainless
steel vials and balls. MoS2 (Alfa Aesar, 98% pure, 700 mu average primary
particle size) and
canola oil (Crisco) were used as the starting materials in a ratio of 1 part
MoS2 (10 grams) to
2 parts canola oil (20 grams). The ball to powder weight ratio was 2 to 1.
MoS2 was ball
milled for 48 hours in air followed by milling in canola oil for 48 hrs at
room temperature.
The nanoparticles were about 50 nm after ball milling. Table 1 summarizes
milling
conditions and resultant particle morphologies. It was observed that there was
a strong effect
of milling media on the shape of the ball milled nanoparticles. Dry milling
showed buckling
and folding of the planes when the particle size was reduced from micron size
to nanometer
size. However, the dry milling condition used here produced micro clusters
embedding
several nanoparticles. On the other hand, wet milling showed no buckling but
saw de-
agglomeration.
Table 1: Milling conditions and parametric effect on particle size and shape
Dry Milling Shape of the particles Shape of the clusters
12 hours Plate-like with sharp edges Sharp and irregular
24 hours Plate-like with round edges More or less rounded
_
48 hours Spherical Globular clusters
Wet Milling Shape of the Particles Shape of the clusters
12 hours Thin plates with sharp edges Thing plates with sharp
edges
= 24 hours Thin plates with sharp edges Thin plates
with sharp edges
=
48 hours Thin plates with sharp edges Thin plates with sharp
edges
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Table 2: Effect of milling media on resultant size (starting size sub-micron),
shape, and
agglomeration of particles
Properties Dry Alcohol Oil Dry milled and
oil milled
Clusters size (nm) 100 300 200 100
Particle size (urn) 30 80 80 30
Agglomeration High Very less Very less Very less
Shape of the particles Spherical , Platelet Platelet Spherical
[0081] Figure 3 shows TEM micrographs of the as-available (700 nm), air
milled, and
hybrid milled (48 hrs in air medium followed by 48 hours in oil medium) MoS2
nanoparticles. Figure 3(A) represents micron-sized particle chunks of the as-
available MoS2
sample off the shelf. These micrographs, particularly Figure 3(B), represent
agglomerates of
nanoparticles when milled in the air medium. Figure 3(B) clearly demonstrates
size
reduction in air milled MoS2. Higher magnification (circular regions) revealed
formation of
the disc shaped nanoparticles after milling in the air medium. From Figures
3(C) and 3(D) it
may be concluded that the particle size was reduced to less than 30 nm after
milling in air and
hybrid conditions. Regardless of the occasionally observed clusters, the
average size of the
clusters is less than or equal to 200 nm.
[0082] Hybrid milled samples were dispersed in paraffin oil (from Walmart) and
remained
suspended without settling. However, the dispersion was not uniforu after a
few weeks. To
stabilize the dispersion and extend the anti-wear properties, phospholipids
were added.
Around 2% by weight of soy lecithin phospholipids (from American Lecithin) was
added in
the base oil.
[0083] Figures 4 and 5 show the XRD and XPS spectra of MoS2 before and after
ball
milling, respectively. XRD spectra revealed no phase change as well as no
observable
amorphization in the MoS2 after milling. This observation is consistent with
the continuous
platelets observed throughout the nanoparticle matrix in TEM analysis for
milled material.
Broadening of peaks (FWHM) was observed in XRD spectra of MoS2 ball milled in
air and
hybrid media, respectively. The peak broadening may be attributed to the
reduction in
particle size. The estimated grain size is 6 nm. This follows the theme of
ball milling where
clusters consist of grains and sub-grains of the order of 10 nm. XPS analysis
was carried out
to study the surface chemistry of the as-available and hybrid milled MoS2
nanoparticles. As
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shown in Figure 5, a carbon (C) peak observed at 285 eV in the as-available
MoS2 sample
shifted to 286.7 eV. Bonding energies of 286 eV and 287.8 eV correspond to C-0
and C=0
bond formation, respectively. The observed binding energy level may
demonstrate that a thin
layer containing mixed C-0 and C=0 groups encapsulates the MoS, particles.
[0084] Preliminary tribological tests on the synthesized nanoparticles were
perfotmed on a
four-ball machine by following ASTM 4172. The balls used were made of AISI
52100
stainless steel and were highly polished. Four Ball Wear Scar measurements
using ASTM
D4172 were made under the following test conditions:
Test Temperature, C 75 ( 1.7)
Test Duration, min 60 (+ 1)
Spindle Speed, rpm 1,200 (*0)
Load, kg 40 (1 0,2)
Wear scar diameter (WSD, mm) of each stationary ball was quantified in both
vertical and
horizontal directions. The average value of WSD from 3 independent tests was
reported
within 0.03 mm accuracy.
[0085] Four Ball Extreme Pressure measurements using ASTM D2783 were made
under
the following test conditions:
Test Temperatures 'V 23
Test Duration, min 60 ( 1)
Spindle Speed, rpm 1,770 ( 60)
Load, kg Varies, 10-sec/stage
Ball Material AISI-B52100
,
Hardness 64-66
Grade 25EP
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[0086] Three different particles (in w/w ratio) were evaluated for their anti-
wear properties
as additives in paraffin oil. Figure 6(A) shows the average wear scar
measurements for
paraffin oil without a nanoparticle additive, paraffin oil with micron sized
MoS2, paraffin oil
with MoS2 that was milled in air for 48 hours, and paraffin oil with MoS2 that
was milled in
air for 48 hours followed by milling in canola oil for 48 hours. Figure 6(B)
shows the load
wear index for paraffin oil without a nanoparticle additive, paraffin oil with
micron sized
MoS2, paraffin oil with MoS2 that was milled in air for 48 hours, and paraffin
oil with MoS2
that was milled in air for 48 hours followed by milling in canola oil for 48
hours. Figure 6(C)
shows the COP for paraffin oil without a nanoparticle additive, paraffin oil
with micron sized
MoS2, paraffin oil with MoS2 that was milled in air for 48 hours, and paraffin
oil with MoS2
that was milled in air for 48 hours followed by milling in canola oil for 48
hours. Figure 6(D)
shows the extreme pressure data for paraffin oil with micron sized MoS2,
paraffin oil with
MoS2 that was milled in air for 48 hours, and paraffin oil with MoS2 that was
milled in air for
48 hours followed by milling in canola oil for 48 hours. In each test the
nanoparticle additive
was present in the amount of 1% by weight.
Test data from nanoparticle composition additive in base oil
Lubricant Four Ball Tests at 40 kg Four Ball Extreme
Load Pressure
(ASTM D4172) (ASTM D-2783)
All dispersions diluted to WSD (mm) COP Weld Load FIG.
6(A)
x% by wt. in reference Load (kg) Wear and 6(b)
base oil Index
Paraffin oil 1.033 0.155 126 12.1 A
Nanoparticles of MoS2 1.012 0.102 100 16.1
without organic medium
(0.5%)
Nanoparticles of MoS2 0.960 0.114 126 20.8
without organic medium
(1.0%)
Nanoparticles of MoS2 0.915 0.098 126 22.0
without organic medium
(1.5%)
Conventional available 1.009 0.126 160 22.0
micro particles (0.5%)
Conventional available 0.948 0.091 126 19.1
micro particles (1.0%)
Conventional available 0.922 0.106 126 16.5
micro particles (1.5%)
NanoGli de: 0.451 0.077 160 24.8
Nanoparticles
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of MoS2 with organic
medium (0.5%)
NanoGlide: 0.461 0.069 200 25.9
Nanoparticles
of MoS2 with organic
medium (1.0%)
NanoGlide: 0.466 0.075 315 34.3
Nanoparticles
of MoS2 with organic
medium (1.5%)
[0087] The transfer film in the wear scar, studied using energy dispersive x-
ray analysis
(EDS), identified the signatures of phosphates in addition to molybdenum and
sulfur. Figure
9(a) depicts the base case of paraffin oil without a nanoparticle additive.
Figure 9(b) depicts
paraffin oil with the molybdenum disulfide nanoparticles and the emulsifier.
It shows the
early evidences of molybdenum (Mo)-sulfur (S)-phosphorous (P) in the wear
track. Iron (Fe)
is seen in Figures 9(a) and 9(b), as it is the material of the balls (52100
steel) in the four-ball
test. The molybdenum and sulfur peaks coincide and are not distinguishable
because they
have the same binding energy. Elemental mapping also showed similar results.
[0088] This specification has been written with reference to various non-
limiting and non-
exhaustive embodiments. However, it will be recognized by persons having
ordinary skill in
the art that various substitutions, modifications, or combinations of any of
the disclosed
embodiments (or portions thereof) may be made within the scope of this
specification. Thus,
it is contemplated and understood that this specification supports additional
embodiments not
expressly set forth in this specification. Such embodiments may be obtained,
for example, by
combining, modifying, or reorganizing any of the disclosed steps, components,
elements,
features, aspects, characteristics, limitations, and the like, of the various
non-limiting and
non-exhaustive embodiments described in this specification. In this manner,
Applicant
reserves the right to amend the claims during prosecution to add features as
variously
described in this specification, and such amendments comply with the
requirements of 35
U.S.C. 112(a) and 132(a).
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