Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02721790 2010-10-18
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International Patent Application
For
METHODS FOR ENHANCING LUBRICITY OF SURFACES
By
Leonid V. Budaragin,
Michael M. Pozvonkov, and
Mark A. Deininger
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CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of priority under PCT Article 8 of U.S.
Provisional Application No. 61/045,593 entitled "Methods for Enhancing
Lubricity of
Surfaces" and filed on April 16, 2008, and U.S. Provisional Application No.
61/045,921
entitled "Methods for Enhancing Lubricity of Surfaces" and filed on April 17,
2008. Both
provisional applications are incorporated herein by reference in their
entireties.
FIELD OF THE INVENTION
[0002] This invention relates to methods for improving the lubricity of
surfaces,
and to articles having improved lubricity.
BACKGROUND
[0003] Friction and the resulting deformation, wear, and heat damage surfaces
throughout industry, costing billions of dollars in replacement parts and lost
production
each year. Lubricants, such as liquid oils and solids including graphite are
used to help
reduce friction and thereby increase a surface's lubricity. Also, coating a
surface with
polytetrafluoroethylene (e.g., Teflon ) having low coefficients of friction
reduces wear of
the surface. However, many lubricants degrade or lose their lubricating
ability at
temperatures above about 350 C. Compacted solid oxide glazes, sometimes
formed
when two metals rub together at high temperature in the presence of oxygen,
provide
unstable but lubricity-enhancing material on the metals' surfaces that can
exist at higher
temperatures. Other methods for making lubricity-enhancing compacted solid
oxide
glazes appear to be unknown, as do methods for making uniform surface coatings
that
function the same way.
[0004] Unexpectedly, applicants have found that forming at least one metal
oxide
on a surface can enhance the lubricity of the surface over a wide range of
temperatures
and other environmental factors to which the surface may be exposed Metal
oxides
made in accordance with the present invention, in some embodiments, provide
thin,
well-adhered coatings that improve lubricity and extend part life of the
surfaces on which
they form and contact.
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SUMMARY OF THE INVENTION
[0005] Various embodiments of the present invention are described herein.
These embodiments are merely illustrations of the present invention. Numerous
modifications and adaptations thereof will be readily apparent to those
skilled in the art
without departing from the spirit and scope of the invention.
[0006] Some embodiments of the present invention provide a method for
enhancing the lubricity of a surface, comprising:
applying at least one metal compound to the surface; and
converting at least some of the at least one metal compound to at least one
metal oxide,
thereby enhancing the lubricity of the surface. Certain embodiments further
comprise
contacting the at least one metal oxide with at least one lubricant.
Lubricants include,
but are not limited to, vegetable oils, animal oils, mineral oils,
polyolefins, esters,
silicones, fluorocarbons, other halocarbons, polytetrafluoroethylene, greases,
fats,
waxes, water, surfactants, graphite, molybdenum disulfide, tungsten disulfide,
fluid
cushions, and combinations of two or more thereof.
[0007] Other embodiments provide an article of manufacture having at least one
surface comprising at least one metal oxide made according to the process of:
applying at least one metal compound to the at least one surface; and
converting at least some of the at least one metal compound to at least one
metal oxide;
wherein the at least one surface exhibits enhanced lubricity.
[0008] Methods to show enhanced lubricity are not limited. Enhanced lubricity
means, in some embodiments, that the surface has a lower coefficient of static
friction.
In other embodiments, lubricity shows enhancement by exhibiting a lower
coefficient of
kinetic friction. In still other embodiments, lubricity shows enhancement by
exhibiting a
lower coefficient of rolling friction. Additional embodiments show enhanced
lubricity
because the surface is not as worn as a control surface subjected to the same
or similar
friction. Further embodiments show enhanced lubricity because the surface is
not as
deformed as a control surface. Still further embodiments show enhanced
lubricity
because the surface is not as hot as a control surface. Even further
embodiments show
enhanced lubricity because the part comprising the surface lasts longer than a
control
part. Yet other embodiments show enhanced lubricity because of a higher speed
compared to a control.
[0009] The at least one metal oxide can be formed on the surface by (1)
placing at
least one metal compound on the surface and (2) converting at least some of
the at least
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one metal compound into at least one metal oxide. Metal compounds useful in
the
present invention contain at least one metal atom and at least one oxygen
atom. Non-
limiting examples of useful metal compounds include metal carboxylates, metal
alkoxides, and metal R-diketonates. Converting the metal compound can be
accomplished by a wide variety of methods, such as, for example, heating the
environment around the metal compound, heating the surface under the metal
compound, heating the metal compound itself, or a combination of those three.
In other
embodiments, converting the metal compound can be accomplished by catalysis.
[0010] In some embodiments, the at least one metal compound is present in a
metal compound composition. In still other embodiments, a metal compound
composition comprises at least one rare earth metal compound, and at least one
transition metal compound.
[0011] Some embodiments of the present invention provide a method for
enhancing the lubricity of a surface in need thereof, comprising:
applying at least one metal compound to the surface; and
converting at least some of the at least one metal compound to at least one
metal oxide,
thereby enhancing the lubricity of the surface.
[0012] In some embodiments of methods of forming at least one metal oxide on a
surface, the at least one metal oxide comprises a metal oxide coating or metal
oxide
film. In other embodiments, contiguous or non-contiguous domains of metal
oxide are
formed. A metal oxide coating, film, or domain, in some embodiments, is
crystalline,
nanocrystalline, amorphous, thin film, or diffuse, or a combination of any of
the
foregoing. For example, a metal oxide domain in some embodiments of the
present
invention may comprise a film that contains both nanocrystalline and amorphous
regions. In some embodiments, a metal oxide domain at least partially diffuses
or
penetrates into the surface thereby precluding the need for any intermediate
bonding
layers.
[0013] In other embodiments, the invention relates to a surface comprising two
or
more rare earth metal oxides and at least one transition metal oxide. Further
embodiments of the invention relate to a surface comprising ceria, a second
rare earth
metal oxide, and a transition metal oxide. Some embodiments relate to a
surface
comprising yttria, zirconia, and a second rare earth metal oxide. Still
further
embodiments of the invention relate to a surface comprising alumina, silica,
ceria, or a
combination thereof. Still other embodiments relate to a surface comprising
zirconia,
ceria, yttria, and chromia.
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[0014] Additional embodiments provide a low cost means to form a useful
lubricity-enhancing material comprising alumina, silica, zirconia, yttria,
titania, nickel
oxide, chromia, or ceria, or a combination thereof, the material having a
nanocrystalline
structure.
[0015] Some embodiments provide a metal oxide domain comprising only one
metal oxide. Other embodiments provide a metal oxide domain comprising only
two
metal oxides. Still other embodiments provide a metal oxide domain comprising
only
three metal oxides. In yet other embodiments, the metal oxide domain comprises
four or
more metal oxides.
[0016] Additional embodiments of the invention provide a means to form a metal
oxide lubricity-enhancing material on an article either at the point of
manufacture or after
the article has been used. For example, a lubricity-enhancing material can be
formed on
an engine cylinder after a certain period of use in some embodiments of the
present
invention.
[0017] Other embodiments of the invention provide a method of forming a metal
oxide that is well-adhered to a surface in need of increased lubricity.
[0018] Additional embodiments of the invention provide a means to economically
form a metal oxide on a surface in need of increased lubricity. Still other
embodiments
relate to those surfaces containing metal oxides.
[0019] Some of the lubricity-enhancing materials according to the present
invention are not possible with conventional technology. Others of those
materials are
more economical than conventional materials. Still other have greater
lubricity-
enhancing activity, last longer, or a combination thereof. Still others of the
inventive
lubricity-enhancing materials show enhanced lubricity when combined with
lubricants,
including, but not limited to vegetable oils, animal oils, mineral oils,
polyolefins, esters,
silicones, fluorocarbons, other halocarbons, polytetrafluoroethylene, greases,
fats,
waxes, water, surfactants, graphite, molybdenum disulfide, tungsten disulfide,
fluid
cushion, and combinations of two or more thereof.
[0020] Other embodiments of the invention provide a method of forming multiple
domains of at least one metal oxide lubricity-enhancing material. In still
other
embodiments, the process of applying and converting can be repeated, forming
at least
one metal oxide in more than one domain. Certain additional embodiments
provide at
least one metal oxide coating having a single layer of at least one metal
oxide. Other
additional embodiments provide at least one metal oxide coating having more
than one
metal oxide layer. The metal oxides forming the various layers are alike or
different.
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Multiple layers are formed, for example, by applying at least one metal
compound to a
surface, and converting at least some of the at least one metal compound to at
least one
metal oxide to form a first layer; applying at least one metal compound to the
first layer,
and converting at least some of the at least one metal compound to at least
one metal
oxide to form a second layer.
[0021] In some embodiments of methods of the present invention, at least one
metal oxide is formed in an inert environment, including an environment
wherein no or
substantially no oxygen is present. In other embodiments, at least one metal
oxide is
formed in an aerobic environment. In still other embodiments, the at least one
metal
oxide is formed under vacuum, under argon, under nitrogen, under oxygen, under
air, or
a combination thereof.
DETAILED DESCRIPTION
[0022] The surfaces that can be treated in accordance with the present
invention
are not limited. A surface in need of enhanced lubricity, in some embodiments,
is a
metal surface adapted to contact, and possibly move against, another surface,
which
may be alike or different. In other embodiments, a surface is adapted to move
against a
fluid, including, but not limited to, water, sea water, air, hydraulic fluid,
or the like. In still
other embodiments, the surface is adapted to pass a product or a material,
such as, for
example, a pipe through which material flows in any suitable form, including,
but not
limited to, solid particles, chips, chunks, liquid, gel, slurry, suspension,
solution, sol,
aerosol, vapor, and the like. The metal surface in need of enhanced lubricity,
in
additional embodiments, is a surface of a piston; cylinder; o-ring; cam; cam
shaft; valve
stem; valve seat; gear; gear box or other gear housing; gear shaft; universal
joint; ball
and/or socket; artificial joint such as an artificial hip, knee, shoulder, or
elbow; roller;
bearing; bearing race; turbine; fan; motor mount; shaft seal; propeller;
airplane wing; gun
barrel, including those of firearms and artillery pieces; cartridge; receiver;
bullet or other
projectile; magazine; or the like. In some embodiments, a roller comprising at
least one
metal oxide enhancing lubricity on its surface is a roller for manufacturing
steel.
[0023] In some embodiments, the surface having enhanced lubricity is adapted
to
operate at high temperature. In other embodiments, the surface having enhanced
lubricity is adapted to operate at room temperature. In still other
embodiments, the
surface having enhanced lubricity is adapted to operate at low temperature.
Further
embodiments are adapted to provide enhanced lubricity below about -78 C,
below
about -50 C, below about -10 C, or below about 0 C. Still other embodiments
are
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adapted to provide enhanced lubricity between about -78 C and about 0 C;
from about
0 C to about 25 C; from about 25 C to about 50 C; from about 0 C to about
50 C;
from about -20 C to about 50 C; from about 50 C to about 100 C; from about
100 C
to about 250 C; from about 250 C to about 350 C; above about 350 C; from
about
350 C to about 450 C; from about 450 C to about 600 C; from about 600 C
to about
800 C; from about 800 C to about 1000 C; from about 1000 C to about 1200
C; or
above about 1200 C.
[0024] Lubricity, in some embodiments, refers to the slipperiness of the
surface.
The more slippery the surface, the less friction is produced when the surface
contacts,
and moves against, another material, in certain embodiments. Enhancing the
lubricity
means, in some embodiments, increasing the slipperiness. As stated above,
methods to
show enhanced lubricity are not limited, and some of those methods are well
known in
the art. A measure of lubricity, such as, for example, a coefficient of static
friction or a
wear rate, is enhanced by a statistically significant increment, in some
embodiments of
the present invention. In other embodiments, a measure of lubricity is
enhanced at least
1.05 times, at least 1.1 times, at least 1.5 times, at least 2 times, at least
5 times, at least
times, at least 20 times, at least 50 times, or at least 100 times.
[0025] Some embodiments provide enhanced lubricity for a surface contacting a
solid, such as, for example, metal-on-metal contact. In other embodiments, a
surface
contacts a fluid such as an airplane wing. In certain embodiments, select
portions of an
airplane wing comprise at least one metal oxide made in accordance with the
inventive
method, while other portions do not, thereby affecting the lift power of the
wing due to
the friction of air flowing past the wing. Similarly, propellers, turbines,
and similar
devices can comprise at least one metal oxide on select surfaces or portions
thereof.
[0026] Without being limited by theory, it is believed that some embodiments
of
the present invention provide enhanced lubricity to a surface by forming a
smoother
surface. In certain embodiments, any pores, cracks, bumps, steps, or other
surface
features can be filled in or smoothed over by forming at least one metal oxide
in
accordance with the present invention.
[0027] In further embodiments, it is believed that the at least one metal
oxide
provides a better platform for additional lubricants. For example, at least
one metal
oxide has micrometer-sized pores in which micrometer-sized particles of solid
lubricant
can reside and rotate. In such embodiments, the micropores of the metal oxide
act like
bearing races, and the solid lubricant particles act like ball bearings. In
still further
embodiments, the at least one metal oxide provides pores that house a
microscopic
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reservoir of liquid lubricant, thereby enhancing the lubricity of the surface
relative to the
surface in the presence of the liquid lubricant without the metal oxide. In
some
embodiments, less lubricant is used, relative to the amount of lubricant used
in the
absence of the at least one metal oxide. In other embodiments, the same amount
of
lubricant on a surface comprising at least one metal oxide exhibits enhanced
lubricity
relative to the same amount of lubricant on the surface in the absence of the
metal
oxide. Still other embodiments, a surface comprising at least one metal oxide
with a
fluid cushion such as, for example, an air cushion, exhibits enhanced
lubricity relative to
the surface with the fluid cushion in the absence of the metal oxide.
[0028] As used herein, the term "rare earth metal" includes those metals in
the
lanthanide series of the Periodic Table, including lanthanum. The term
"transition metal"
includes metals in Groups 3-12 of the Periodic Table (but excludes rare earth
metals).
The term "metal oxide" particularly as used in conjunction with the above
terms includes
any oxide that can form or be prepared from the metal, irrespective of whether
it is
naturally occurring or not. The "metal" atoms of the metal oxides of the
present
invention are not necessarily limited to those elements that readily form
metallic phases
in the pure form. "Metal compounds" include substances such as molecules
comprising
at least one metal atom and at least one oxygen atom. Metal compounds can be
converted into metal oxides by exposure to a suitable environment for a
suitable amount
of time.
[0029] As used herein, the term "phase deposition" includes any depositing
process onto a surface that is subsequently followed by the exposure of the
surface
and/or the deposited material to an environment that causes a phase change in
either
the deposited material, one or more components of the material, or of the
surface itself.
A phase change may be a physical phase change, such as for example, a change
from
fluid to solid, or from one crystal phase to another, or from amorphous to
crystalline or
vice versa.
[0030] The term alkyl, as used herein, refers to a saturated straight,
branched, or
cyclic hydrocarbon, or a combination thereof, including C1 to C24, methyl,
ethyl, n-propyl,
isopropyl, n-butyl, isobutyl, t-butyl, n-pentyl, cyclopentyl, isopentyl,
neopentyl, n-hexyl,
isohexyl, cyclohexyl, 3-methylpentyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl,
heptyl, octyl,
nonyl, and decyl.
[0031] The term alkoxy, as used herein, refers to a saturated straight,
branched,
or cyclic hydrocarbon, or a combination thereof, including C1 to C24, methyl,
ethyl, n-
propyl, isopropyl, n-butyl, isobutyl, t-butyl, n-pentyl, cyclopentyl,
isopentyl, neopentyl, n-
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hexyl, isohexyl, cyclohexyl, 3-methylpentyl, 2,2-dimethylbutyl, 2,3-
dimethylbutyl, heptyl,
octyl, nonyl, and decyl, in which the hydrocarbon contains a single-bonded
oxygen atom
that can bond to or is bonded to another atom or molecule.
[0032] The terms alkenyl and alkynyl, as used herein, refer to straight,
branched,
or cyclic hydrocarbon with at least one double or triple bond, respectively,
including, but
not limited to C1 to C24-
[0033] The term aryl or aromatic, as used herein, refers to monocyclic or
bicyclic
hydrocarbon ring molecule having conjugated double bonds about the ring. In
some
embodiments, the ring molecule has 5- to 12-members, but is not limited
thereto. The
ring may be unsubstituted or substituted having one or more alike or different
independently-chosen substituents, wherein the substituents are chosen from
alkyl,
alkenyl, alkynyl, alkoxy, hydroxyl, and amino radicals, and halogen atoms.
Aryl includes,
for example, unsubstituted or substituted phenyl and unsubstituted or
substituted
naphthyl.
[0034] The term heteroaryl as used herein refers to a monocyclic or bicyclic
aromatic hydrocarbon ring molecule having at least one heteroatom chosen from
0, N,
P, and S as a member of the ring, and the ring is unsubstituted or substituted
with one or
more alike or different substituents independently chosen from alkyl, alkenyl,
alkynyl,
hydroxyl, alkoxy, amino, alkylamino, dialkylamino, thiol, alkylthio, =0, =NH,
=PH, =S,
and halogen atoms. In some embodiments, the ring molecule has 5- to 12-
members,
but is not limited thereto.
[0035] The term hydrocarbon refers to molecules that contain carbon and
hydrogen.
[0036] "Alike or different," when describing three or more substituents for
example, indicates combinations in which (a) all substituents are alike, (b)
all
substituents are different, and (c) some substituents are alike but different
from other
substituents.
[0037] Metal compounds of the present invention can have ligands that are
alike
or different, in various embodiments. Suitable metal compounds that form metal
oxides
include substances such as molecules containing at least one metal atom and at
least
one oxygen atom. In some embodiments, metal compounds that form metal oxides
include metal carboxylates, metal alkoxides, and metal R-diketonates.
A. METAL CARBOXYLATES
[0038] The metal salts of carboxylic acids useful in the present invention can
be made
from any suitable carboxylic acids according to methods known in the art. For
example,
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U.S. Patent No. 5,952,769 to Budaragin discloses suitable carboxylic acids and
methods
of making metal salts of carboxylic acids, among other places, at columns 5-6.
The
disclosure of U.S. Patent No. 5,952,769 is incorporated herein by reference.
In some
embodiments, the metal carboxylate can be chosen from metal salts of 2-
ethylhexanoic
acid. Moreover, suitable metal carboxylates can be purchased from chemical
supply
companies. For example, cerium(III) 2-ethylhexanoate, magnesium(II) stearate,
manganese(II) cyclohexanebutyrate, and zinc(II) methacrylate are available
from Sigma-
Aldrich of St. Louis, MO. See Aldrich Catalogue, 2005-2006. Additional metal
carboxylates are available from, for example, Alfa-Aesar of Ward Hill, MA.
[0039] The metal carboxylate composition, in some embodiments of the present
invention, comprises one or more metal salts of one or more carboxylic acids
("metal
carboxylate"). Metal carboxylates suitable for use in the present invention
include at
least one metal atom and at least one carboxylate radical -OC(O)R bonded to
the at
least one metal atom. As stated above, metal carboxylates can be produced by a
variety of methods known to one skilled in the art. Non-limiting examples of
methods for
producing the metal carboxylate are shown in the following reaction schemes:
nRCOOH + Me -+ (RCOO)nMen+ + 0.5nH2 (for alkaline earth metals, alkali
metals, and thallium).
nRCOOH + Me"+(OH)n -* (RCOO)nMen+ + nH2O (for practically all metals
having a solid hydroxide).
nRCOOH + Men+(C03)0.5n -* (RCOO)nMen+ + 0.5nH2O + 0.5nCO2 (for alkaline
earth metals, alkali metals, and thallium).
nRCOOH + Men+(X)n/m (RCOO)nMen+ + n/mHmX (liquid extraction, usable for
practically all metals having solid salts).
In the foregoing reaction schemes, X is an anion having a negative charge m,
such as, e.g., halide anion, sulfate anion, carbonate anion, phosphate anion,
among
others; n is a positive integer; and Me represents a metal atom.
[0040] R in the foregoing reaction schemes can be chosen from a wide variety
of
radicals. Suitable carboxylic acids for use in making metal carboxylates
include, for
example:
Monocarboxylic acids:
[0041] Monocarboxylic acids where R is hydrogen or unbranched hydrocarbon
radical,
such as, for example, HCOOH - formic, CH3COOH - acetic, CH3CH2COOH -
propionic,
CH3CH2CH2COOH (C4H802)- butyric, C5H10O2 - valeric, C6H12O2 - caproic, C7H14 -
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enanthic; further: caprylic, pelargonic, undecanoic, dodecanoic, tridecylic,
myristic,
pentadecylic, palmitic, margaric, stearic, and nonadecylic acids;
[0042] Monocarboxylic acids where R is a branched hydrocarbon radical, such
as, fpr
example, (CH3)2CHCOOH - isobutyric, (CH3) 2CHCH2COOH - 3-methylbutanoic,
(CH3)3CCOOH - trimethylacetic, including VERSATIC 10 (trade name) which is a
mixture of synthetic, saturated carboxylic acid isomers, derived from a highly-
branched
C10 structure;
[0043] Monocarboxylic acids in which R is a branched or unbranched hydrocarbon
radical containing one or more double bonds, such as, for example, CH2=CHCOOH -
acrylic, CH3CH=CHCOOH - crotonic, CH3(CH2)7CH=CH(CH2)7COOH - oleic,
CH3CH=CHCH=CHCOOH - hexa-2,4-dienoic, (CH3)2C=CHCH2CH2C(CH3)=CHCOOH -
3,7-dimethylocta-2,6-dienoic, CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH - linoleic,
further: angelic, tiglic, and elaidic acids;
[0044] Monocarboxylic acids in which R is a branched or unbranched hydrocarbon
radical containing one or more triple bonds, such as, for example, CH=000OH -
propiolic, CH3C=CCOOH - tetrolic, CH3(CH2)4C=CCOOH - oct-2-ynoic, and
stearolic
acids;
[0045] Monocarboxylic acids in which R is a branched or unbranched hydrocarbon
radical containing one or more double bonds and one or more triple bonds;
[0046] Monocarboxylic acids in which R is a branched or unbranched hydrocarbon
radical containing one or more double bonds and one or more triple bonds and
one or
more aryl groups;
[0047] Monohydroxymonocarboxylic acids in which R is a branched or unbranched
hydrocarbon radical that contains one hydroxyl substituent, such as, for
example,
HOCH2COOH - glycolic, CH3CHOHCOOH - lactic, C6H5CHOHCOOH - amygdalic, and
2-hydroxybutyric acids;
[0048] Dihydroxymonocarboxylic acids in which R is a branched or unbranched
hydrocarbon radical that contains two hydroxyl substituents, such as, for
example,
(HO)2CHCOOH - 2,2-dihydroxyacetic acid;
[0049] Dioxycarboxylic acids, in which R is a branched or unbranched
hydrocarbon
radical that contains two oxygen atoms each bonded to two adjacent carbon
atoms,
-
such as, for example, C6H3(OH)2COOH - dihydroxy benzoic, C6H2(CH3)(OH)2COOH
orsellinic; further: caffeic, and piperic acids;
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[0050] Aldehyde-carboxylic acids in which R is a branched or unbranched
hydrocarbon
radical that contains one aldehyde group, such as, for example, CHOCOOH -
glyoxalic
acid;
[0051] Keto-carboxylic acids in which R is a branched or unbranched
hydrocarbon
radical that contains one ketone group, such as, for example, CH3COCOOH -
pyruvic,
CH3COCH2COOH - acetoacetic, and CH3000H2CH2COOH - levulinic acids;
[0052] Monoaromatic carboxylic acids, in which R is a branched or unbranched
hydrocarbon radical that contains one aryl substituent, such as, for example,
C6H5000H
- benzoic, C6H5CH2OOOH - phenylacetic, C6H5CH(CH3)COOH -
2-phenylpropanoic, C6H5CH=CHCOOH - 3-phenylacrylic, and C6H5C=CCOOH - 3-
phenyl-propiolic acids;
Multicarboxylic acids:
[0053] Saturated dicarboxylic acids, in which R is a branched or unbranched
saturated
hydrocarbon radical that contains one carboxylic acid group, such as, for
example,
HOOC-COOH - oxalic, HOOC-CH2-COOH - malonic,
HOOC-(CH2)2-COOH - succinic, HOOC-(CH2)3-COOH - glutaric,
HOOC-(CH2)4-COOH - adipic; further: pimelic, suberic, azelaic, and sebacic
acids;
[0054] Unsaturated dicarboxylic acids, in which R is a branched or unbranched
hydrocarbon radical that contains one carboxylic acid group and at least one
carbon-
carbon multiple bond, such as, for example, HOOC-CH=CH-000H - fumaric;
further:
maleic, citraconic, mesaconic, and itaconic acids;
[0055] Polybasic aromatic carboxylic acids, in which R is a branched or
unbranched
hydrocarbon radical that contains at least one aryl group and at least one
carboxylic acid
group, such as, for example, C6H4(COOH)2 - phthalic (isophthalic,
terephthalic), and
C6H3(000H)3 - benzyl-tri-carboxylic acids;
[0056] Polybasic saturated carboxylic acids, in which R is a branched or
unbranched
hydrocarbon radical that contains at least one carboxylic acid group, such as,
for
example, ethylene diamine N,N'-diacetic acid, and ethylene diamine tetraacetic
acid
(EDTA);
Polybasic oxyacids:
[0057] Polybasic oxyacids, in which R is a branched or unbranched hydrocarbon
radical
containing at least one hydroxyl substituent and at least one carboxylic acid
group, such
as, for example, HOOC-CHOH-COOH - tartronic,
HOOC-CHOH-CH2-COOH - malic, HOOC-C(OH)=CH-COOH - oxaloacetic, HOOC-
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CHOH-CHOH-COOH - tartaric, and
HOOC-CH2-C(OH) COOH-CH2COOH - citric acids.
[0058] In some embodiments, the monocarboxylic acid comprises one or more
carboxylic acids having the formula I below:
R --C(R")(R')--COON (I)
wherein:
R is selected from H or C, to C24 alkyl groups; and
R' and R" are each independently selected from H and C1 to C24 alkyl groups;
wherein the alkyl groups of R , R', and R" are optionally and independently
substituted
with one or more substituents, which are alike or different, chosen from
hydroxy, alkoxy,
amino, and aryl radicals, and halogen atoms.
[0059] Some suitable alpha branched carboxylic acids typically have an average
molecular weight in the range 130 to 420. In some embodiments, the carboxylic
acids
have an average molecular weight in the range 220 to 270. The carboxylic acid
may
also be a mixture of tertiary and quaternary carboxylic acids of formula I.
VIK acids can
be used as well. See U.S. Patent No. 5,952,769, at col. 6, II. 12-51.
[0060] Either a single carboxylic acid or a mixture of carboxylic acids can be
used to
form the metal carboxylate composition. In some embodiments, a mixture of
carboxylic
acids is used. In still other embodiments, the mixture contains 2-
ethylhexanoic acid
where R is H, R" is C2H5 and R' is C4H9 in formula (I) above. In some
embodiments,
this acid is the lowest boiling acid constituent in the mixture. When a
mixture of metal
carboxylates is used, the mixture has a broader evaporation temperature range,
making
it more likely that the evaporation temperature of the mixture will overlap
the metal
carboxylate decomposition temperature, allowing the formation of a solid metal
oxide.
Moreover, the possibility of using a mixture of carboxylates avoids the need
and
expense of purifying an individual carboxylic acid.
B. METAL ALKOXIDES
[0061] Metal alkoxides suitable for use in the present invention include at
least one metal
atom and at least one alkoxide radical -OR2 bonded to the at least one metal
atom.
Such metal alkoxides include those of formula II:
M(OR2)Z (II)
in which M is a metal atom of valence z+;
z is a positive integer, such as, for example, 1, 2, 3, 4, 5, 6, 7, and 8;
R2 can be alike or different and are independently chosen from unsubstituted
and
substituted alkyl, unsubstituted and substituted alkenyl, unsubstituted and
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substituted alkynyl, unsubstituted and substituted heteroaryl, and
unsubstituted
and substituted aryl radicals,
wherein substituted alkyl, alkenyl, alkynyl, heteroaryl, and aryl radicals are
substituted with one or more alike or different substituents independently
chosen
from halogen, hydroxy, alkoxy, amino, heteroaryl, and aryl radicals.
In some embodiments, z is chosen from 2, 3, and 4.
[0062] Metal alkoxides are available from Alfa-Aesar and Gelest, Inc., of
Morrisville, PA.
Lanthanoid alkoxides such as those of Ce, Nd, Eu, Dy, and Er are sold by
Kojundo
Chemical Co., Saitama, Japan, as well as alkoxides of Al, Zr, and Hf, among
others.
See, e.g., http://www.kojundo.co.jp/English/Guide/material/lanthagen.html.
[0063] Examples of metal alkoxides useful in embodiments of the present
invention
include methoxides, ethoxides, propoxides, isopropoxides, and butoxides and
isomers
thereof. The alkoxide substituents on a give metal atom are the same or
different.
Thus, for example, metal dimethoxide diethoxide, metal methoxide
diisopropoxide t-
butoxide, and similar metal alkoxides can be used. Suitable alkoxide
substituents also
may be chosen from:
1. Aliphatic series alcohols from methyl to dodecyl including branched and
isostructured.
2. Aromatic series alcohols: benzyl alcohol - C6H5CH2OH; phenyl-ethyl alcohol -
C8H100; phenyl- propyl alcohol - C9H120, and so on.
[0064] Metal alkoxides useful in the present invention can be made according
to many
methods known in the art. One method includes converting the metal halide to
the metal
alkoxide in the presence of the alcohol and its corresponding base. For
example:
MXZ + zHOR2 -_)~ M(OR2)Z + zHX
in which M, R2, and z are as defined above for formula II, and X is a halide
anion.
C. METAL [3-DIKETONATES
[0065] Metal [3-diketonates suitable for use in the present invention contain
at least one
metal atom and at least one [3-diketone of formula III as a ligand:
O 0
R3 R6 (III )
R4 R5
in which
R3, R4, R5, and R6 are alike or different, and are independently chosen from
hydrogen, unsubstituted and substituted alkyl, unsubstituted and substituted
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alkoxy, unsubstituted and substituted alkenyl, unsubstituted and substituted
alkynyl, unsubstituted and substituted heteroaryl, unsubstituted and
substituted
aryl, carboxylic acid groups, ester groups having unsubstituted and
substituted
alkyl, and combinations thereof,
wherein substituted alkyl, alkoxy, alkenyl, alkynyl, heteroaryl, and aryl
radicals are
substituted with one or more alike or different substituents independently
chosen
from halogen atoms, hydroxy, alkoxy, amino, heteroaryl, and aryl radicals.
[0066] It is understood that the (3-diketone of formula III may assume
different isomeric
and electronic configurations before and while chelated to the metal atom. For
example,
the free 3-diketone may exhibit enolate isomerism. Also, the P-diketone may
not retain
strict carbon-oxygen double bonds when the molecule is bound to the metal
atom.
[0067] Examples of (3-diketones useful in embodiments of the present invention
include
acetylacetone, trifluoroacetylacetone, hexafluoroacetylacetone, 2,2,6,6-
tetramethyl-3,5-
heptanedione, 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, ethyl
acetoacetate, 2-methoxyethyl acetoacetate , benzoyltrifluoroacetone,
pivaloyltrifluoroacetone, benzoyl-pyruvic acid, and methyl-2,4-dioxo-4-
phenylbutanoate.
[0068] Other ligands are possible on the metal R-diketonates useful in the
present
invention, such as, for example, alkoxides such as -OR2 as defined above, and
dienyl
radicals such as, for example, 1,5-cyclooctadiene and norbornadiene.
[0069] Metal 13-diketonates useful in the present invention can be made
according to any
method known in the art. 3-diketones are well known as chelating agents for
metals,
facilitating synthesis of the diketonate from readily available metal salts.
[0070] Metal (3-diketonates are available from Alfa-Aesar and Gelest, Inc.
Also, Strem
Chemicals, Inc. of Newburyport, MA, sells a wide variety of metal (3-
diketonates on the
internet at http://www.strem.com/code/template.ghc?direct=cvdindex.
[0071] In some embodiments of the present invention, a metal compound
comprises a transition metal atom. In other embodiments, a metal compound
comprises
a rare earth metal atom. In further embodiments, a metal compound composition
comprises a plurality of metal compounds. In some embodiments, a plurality of
metal
compounds comprises at least one rare earth metal compound and at least one
transition metal compound, while in other embodiments, a plurality of metal
compounds
comprises other than at least one rare earth metal compound and at least one
transition
metal compound. Metal carboxylates, metal alkoxides, and metal R-diketonates
can be
chosen for some embodiments of the present invention.
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[0072] In further embodiments, a metal compound composition comprises one
metal compound as its major component and one or more additional metal
compounds
which may function as stabilizing additives. Stabilizing additives, in some
embodiments,
comprise trivalent metal compounds. Trivalent metal compounds include, but are
not
limited to, chromium, iron, manganese, and nickel compounds. A metal compound
composition, in some embodiments, comprises both cerium and chromium
compounds.
[0073] In some embodiments, the metal compound that is the major component of
the metal compound composition contains an amount of metal that ranges from
about
65 to about 97% by weight or from about 80 to about 87% by weight of the total
weight
of metal in the composition. In other embodiments, the amount of metal forming
the
major component of the metal compound composition ranges from about 90 to
about
97% by weight of the total metal present in the composition. In still other
embodiments,
the amount of metal forming the major component of the metal compound
composition
ranges from about 97 to about 100% by weight of the total metal present in the
composition.
[0074] The metal compounds that may function as stabilizing additives, in some
embodiments, may be present in amounts such that the total amount of the metal
in
metal compounds which are the stabilizing additives is at least 3% by weight,
relative to
the total weight of the metal in the metal compound composition. This can be
achieved
in some embodiments by using a single stabilizing additive, or multiple
stabilizing
additives, provided that the total weight of the metal in the stabilizing
additives is greater
than 3%. In other embodiments, the amount of the stabilizing metal is less
than 3 %
relative to the total weight of metal in the metal compound composition. In
yet other
embodiments, the total weight of the metal in the stabilizing additives ranges
from about
3% to about 35% by weight. In still other embodiments, the total weight for
the metal in
the stabilizing additives ranges from about 3 to about 30% by weight, relative
to the total
weight of the metal in the metal compound composition. In other embodiments,
the total
weight range for the metal in the stabilizing additives ranges from about 3 to
about 10%
by weight. In some embodiments, the total weight range for the metal in the
stabilizing
additives is from about 7 to about 8% by weight, relative to the total weight
of the metal
in the metal compound composition. Still other embodiments provide the
stabilizing
metal in an amount greater than about 35 % by weight relative to the total
weight of the
metal in the metal compound composition.
[0075] The amount of metal in the metal compound composition, according to
some embodiments, ranges from about 20 to about 150 grams of metal per
kilogram of
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metal compound composition. In other embodiments, the amount of metal in the
metal
compound composition ranges from about 30 to about 50 grams of metal per
kilogram of
metal compound composition. In further embodiments, the metal compound
composition can contain from about 30 to about 40 grams of metal per kg of
composition. Amounts of metal less than 20 grams of metal per kilogram of
metal
compound composition or greater than about 150 grams of metal per kilogram of
metal
compound composition also can be used.
[0076] The metal compound may be present in any suitable form. Finely divided
powder, nanoparticles, solution, suspension, multi-phase composition, gel,
vapor,
aerosol, and paste, among others, are possible.
[0077] A metal compound composition may also include nanoparticles in the size
range of less than 100 nm in average size and being composed of a variety of
elements
or combination thereof, for example, A1203, CeO2, Ce203, Ti02, Zr02 and
others. In
some cases, the nanoparticles can be dispersed, agglomerated, or a mixture of
dispersed and agglomerated nanoparticles. Nanoparticles may have a charge
applied
to them, negative or positive, to aid dispersion. Moreover, dispersion agents,
such as
known acids or surface modifying agents, may be used.
[0078] The applying of the metal compound composition may be accomplished by
various processes, including dipping, spraying, flushing, vapor deposition,
printing,
lithography, rolling, spin coating, brushing, swabbing or any other means that
allows the
metal compound composition to contact the surface to be treated. In this
regard, the
metal compound composition may be liquid, and may also comprise a solvent. The
optional solvent may be any hydrocarbon and mixtures thereof. In some
embodiments,
the solvent can be chosen from carboxylic acids; toluene; xylene; benzene;
alkanes,
such as for example, propane, butane, isobutene, hexane, heptane, octane, and
decane; alcohols, such as methanol, ethanol, n-propanol, isopropanol, n-
butanol, and
isobutanol; mineral spirits; 1i-diketones, such as acetylacetone; ketones such
as
acetone; high-paraffin, aromatic hydrocarbons; and combinations of two or more
of the
foregoing. Some embodiments employ solvents that contain no water or water in
trace
amounts or greater, while other embodiments employ water as the solvent. In
some
embodiments, the metal compound composition further comprises at least one
carboxylic acid. Some embodiments employ no solvent in the metal compound
composition. Other embodiments employ no carboxylic acid in the metal compound
composition.
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[0079] The metal compound composition can applied in some embodiments in
which the composition has a temperature less than about 250 C. That
composition also
can be applied to the surface in further embodiments at a temperature less
than about
50 C. In other embodiments, the M quid metal compound composition is applied
to the
surface at room temperature. In still other embodiments, that composition is
applied at a
temperature greater than about 250 C.
[0080] Following application, the at least one metal compound is at least
partially
converted to at least one metal oxide. In some embodiments the at least one
metal
compound is fully converted to at least one metal oxide.
[0081] Suitable environments for converting the at least one metal compound
into
at least one metal oxide include vacuum, partial vacuum, atmospheric pressure,
high
pressure equal to several atmospheres, high pressure equal to several hundred
atmospheres, inert gases, and reactive gases such as gases comprising oxygen,
including pure oxygen, air, dry air, and mixtures of oxygen in various ratios
with one or
more other gases such as nitrogen, carbon dioxide, helium, neon, and argon, as
well as
hydrogen, mixtures of hydrogen in various ratios with one or more other gases
such as
nitrogen, carbon dioxide, helium, neon, and argon, also other gases such as,
for
example, nitrogen, NH3, hydrocarbons, H2S, PH3, each alone or in combination
with
various gases, and still other gases which may or may not be inert in the
converting
environment. In some embodiments, a suitable environment for converting the at
least
one metal compound into at least one metal oxide is free or substantially free
of oxygen.
[0082] The environment may be heated relative to ambient conditions by
suitable
methods, in some embodiments. In other embodiments, the environment may
comprise
reactive species that cause or catalyze the conversion of the metal compound
to the
metal oxide, such as, for example, acid-catalyzed hydrolysis of metal
alkoxides. In still
other embodiments, the metal compound is caused to convert to the metal oxide
by the
use of induction heating, lasers, microwave emission, or plasma, as explained
below.
[0083] The conversion environment may be accomplished in a number of ways.
For example, a conventional oven may be used to bring the wetted surface up to
a
temperature exceeding approximately 250 C for a given period of time. In some
embodiments, the environment of the wetted surface is heated to a temperature
exceeding about 400 C but less than about 450 C or less than about 500 C for a
chosen
period of time. In other embodiments, the environment of the surface is heated
to a
temperature ranging from about 400 C to about 650 C. In further embodiments,
the
environment is heated to a temperature ranging from about 400 C to about 550
C. In
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still further embodiments, the environment is heated to a temperature ranging
from
about 550 C to about 650 C, from about 650 C to about 800 C, or from about
800 C
to about 1000 C. In one embodiment, the environment is heated to a
temperature of up
to about 425 C or about 450 C. Depending on the amount of surface, the time
period
may be extended such that sufficient conversion of a desired amount of the
metal
compound to metal oxides has been accomplished.
[0084] In some applications, the oxidation of the surface being treated or
other
material is not desired. In these cases, an inert atmosphere may be provided
in the
conversion environment to prevent such oxidation. In the case of heating the
surface in
a conventional oven, a nitrogen or argon atmosphere can be used, among other
inert
gases, to prevent or reduce the oxidation of the surface or other material
prior to or
during the conversion process.
[0085] The conversion environment may also be created using induction heating
through means familiar to those skilled in the art of induction heating. For
example, a
metal compound composition can be applied to the interior surface of a piston
cylinder.
Then, one or more induction wands can pass proximate to the cylinder, heating
the
cylinder and thereby causing the conversion of the metal compound into metal
oxide on
the cylinder walls. Alternatively, the conversion environment may be provided
using a
laser applied to the surface for sufficient time to allow at least some of the
metal
compounds to convert to metal oxides. In other applications, the conversion
environment may be created using an infra-red light source which can reach
sufficient
temperatures to convert at least some of the metal compounds to metal oxides.
Some
embodiments may employ a microwave emission device to cause at least some of
the
metal compound to convert. Still other embodiments employ a plasma to provide
the
environment for converting the metal compound into metal oxide. In the case of
induction heating, microwave heating, lasers, plasmas, and other heating
methods that
can produce the necessary heat levels in a short time, for example, within
seconds, 1
minute, 10 minutes, 20 minutes, 30 minutes, 40 minutes, or one hour.
Accordingly, in
some embodiments, the conversion environment can be created without the use of
an
inert gaseous environment, thus enabling conversion to be done in open air,
outside of a
closed system due to the reduced time for undesirable compounds to develop on
the
material's surface in the presence of ambient air.
[0086] The gas above the metal compound on the surface can be heated, in
some embodiments, to convert the metal compound to the metal oxide. Heating
can be
accomplished by introducing high temperature gases, for example. This high
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temperature gas can be produced by a conventional oven, induction heating
coils, heat
exchangers, industrial process furnaces, exothermic reactions, microwave
emission, or
other suitable heating method.
[0087] In some embodiments a feed of an inert gas may be provided to create a
non-oxidizing atmosphere for the conversion process.
[0088] In other embodiments of the present invention, similar or differing
metal
oxides can be formed on the surface to make the lubricity-enhancing material.
Representative metal oxide compositions that have been found to be suitable in
embodiments of the present invention include, but are not limited to:
Zr02 for example, at 0-90 wt%
CeO2 for example, at 0-90 wt%
Ce02-ZrO2 where CeO2 is about 10-90 wt%
Y203 Yttria-stabilized Zirconia where Y is about 1-50% mol%
TiO2 for example, at 0-90 wt%
Fe203 for example, at 0-90 wt%
NiO for example, at 0-90 wt%
A1203 for example, at 0-90 wt%
Si02
Y203
Cr203
Mo203
Hf02
La203
Pr203
Nd203
Sm203
Eu203
Gd203
Tb203
DY203
H0203
Er203
Tm203
Yb203
Lu203
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Mixtures of these compositions are also suitable for use in the invention.
[0089] Oxides of the following elements also can be used in embodiments of the
present
invention: Lithium, Beryllium, Sodium, Magnesium, Aluminum, Silicon,
Potassium,
Calcium, Scandium, Titanium, Vanadium, Chromium, Manganese, Iron, Cobalt,
Nickel,
Copper, Zinc, Gallium, Germanium, Arsenic, Bromine, Rubidium, Strontium,
Yttrium,
Zirconium, Niobium, Molybdenum, Technetium, Ruthenium, Rhodium, Palladium,
Antimony, Tellurium, Silver, Cadmium, Indium, Tin, Cesium, Barium, Lanthanum,
Cerium, Praseodymium, Neodymium, Promethium, Samarium, Europium, Gadolinium,
Terbium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium, Lutetium, Hafnium,
Tantalum, Tungsten, Rhenium, Osmium, Iridium, Platinum, Gold, Mercury,
Thallium,
Lead, Bismuth, Radium, Actinium, Thorium, Protactinium, Uranium, Neptunium,
Plutonium, Americium, Curium, Berkelium, Californium, Einsteinium, Fermium,
Mendelevium, Nobelium, and Lawrencium. Oxides containing more than one of the
foregoing elements, and oxides containing elements in addition to the
foregoing
elements, also can be used in embodiments of the present invention. For
example,
SrTiO3 and MgAI2O4 are included. Those materials are likely to form at least
in small
amounts when appropriate metal compounds are used, depending on the conditions
of
the conversion process. In some embodiments, the molar ratio of metal
compounds
deposited on the surface corresponds to the molar ratio of metal oxides after
conversion.
[0090] The invention relates, in some embodiments, to diffused domains of
metal
oxide. As used herein, "diffused" means that metal oxide molecules,
nanoparticles,
nanocrystals, larger domains, or more than one of the foregoing, have
penetrated the
surface. The diffusion of metal oxides can range in concentration from rare
interstitial
inclusions in the surface, up to the formation of materials that contain
significant
amounts of metal oxide. A thin film is understood to indicate a layer, no
matter how thin,
composed substantially of metal oxide. In some embodiments, a thin film has
very little
or no surface material present, while in other embodiments, a thin film
comprises atoms,
molecules, nanoparticles, or larger domains of surface ingredients. In some
embodiments, it may be possible to distinguish between diffused portions and
thin films.
In other embodiments, a gradient may exist in which it becomes difficult to
observe a
boundary between the diffused domain and the thin film. Furthermore, some
embodiments may exhibit only one of a diffused domain and a thin film. Still
other
embodiments include thin films in which one or more species have migrated from
the
surface into the thin film. Additional embodiments provide contiguous domains
of metal
oxide on a surface, while other embodiments provide non-contiguous domains.
The
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terms "metal oxide" and "surface comprises at least one metal oxide" include
all of those
possibilities, including diffused coatings, thin films, stacked thin films,
contiguous and
non-contiguous domains, and combinations thereof. The term "metal oxide
coating"
includes, for example, diffused coatings, thin films, stacked thin films, and
combinations
thereof.
[0091] The diffused domains of some embodiments of the invention provide
increased performance, in part, because the metal oxide penetrates the surface
to a
depth providing a firm anchor to the surface without the need for intermediate
bonding
layers. In some embodiments, the diffused domain penetrates the surface to a
depth of
less than about 100 Angstroms. In other embodiments, the diffused metal oxide
penetrates from about 100 Angstroms to about 200 Angstroms, from about 200
Angstroms to about 400 Angstroms, from about 400 Angstroms to about 600
Angstroms,
and greater than about 600 Angstroms, and in some embodiments from about 200
to
about 600 Angstroms. This diffused metal oxide allows much thinner domains [in
some
embodiments around 0.1 to 1 microns in thickness (or about 0.5 microns when
approximately 6 layers are used)] to be applied. This, in turn, allows for
less metal oxide
to be used, reducing significantly the cost of materials attaching to the
surface. Thus,
some embodiments of the present invention provide a domain, such as a coating,
no
thicker than about 5 nm. Other embodiments provide a domain no thicker than
about 10
nm. Still other embodiments provide a domain no thicker than about 20 nm.
Still other
embodiments provide a domain no thicker than about 100 nm. Other embodiments
provide a domain having a thickness less than about 25 microns. Still other
embodiments provide a domain having a thickness less than about 20 microns.
Still
other embodiments provide a domain having a thickness less than about 10
microns.
Yet other embodiments provide a domain having a thickness less than about 5
microns.
Some embodiments provide a domain having a thickness less than about 2.5
microns.
Even other embodiments provide a domain having a thickness less than about 1
micron.
[0092] In some embodiments of the invention, the metal oxide can contain other
species, such as, for example, species that have migrated from the surface
into the
metal oxide. In other embodiments, those other species can come from the
atmosphere
in which the at least one metal compound is converted. For example, the
conversion
can be performed in an environment in which other species are provided via
known
vapor deposition methods. Still other embodiments provide other species
present in or
derived from the at least one metal compound or the composition comprising the
compound. Suitable other species include metal atoms, metal compounds
including
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those metal atoms, such as oxides, carbides, nitrides, sulfides, phosphides,
and
mixtures thereof, and the like. The inclusion of other species can be
accomplished by
controlling the conditions during conversion, such as the use of a chosen
atmosphere
during the heat conversion process, for example, a partial vacuum or
atmosphere
containing 02, N2, NH3, one or more hydrocarbons, H2S, alkylthiols, PH3, or a
combination thereof.
[0093] Some embodiments of the present invention provide metal oxides that are
substantially free of other species. For example, small amounts of carbides
may form
along side oxides when, for example, metal carboxylates are converted, if no
special
measures are taken to eliminate the carbon from the carboxylate ligands. Thus,
converting metal compounds in the presence of oxygen gas, air, or oxygen mixed
with
other gases reduces or eliminates carbide formation in some embodiments of the
present invention. Also, rapid heating of the conversion environment, such as,
for
example, by induction heating, microwave heating, lasers, plasmas, and other
heating
methods that can produce the necessary heat levels in a short time, reduces or
eliminates formation of other species, in other embodiments. At least one
rapid heating
technique is used in combination with an oxygen-containing atmosphere in still
other
embodiments.
[0094] Additional embodiments employ various heating steps to reduce or
eliminate the formation of other species. For example, carbide formation can
be
lessened during metal oxide formation in some embodiments by applying a metal
compound composition containing a metal carboxylate to a surface, subjecting
the
surface to a low-temperature bake at about 250 C under a vacuum, introducing
air and
maintaining the temperature, and then increasing the temperature to about 420
C under
vacuum or inert atmosphere to convert the metal carboxylate into the metal
oxide.
Without wanting to be bound by theory, it is believed that the low-temperature
bake
drives off most or all of the carboxylate ligand, resulting in an oxide
substantially free of
metal carbide.
[0095] Still other embodiments employ more than one application to achieve at
least one metal oxide substantially without other species. For example, in
some
embodiments, a base of at least one metal oxide is formed from at least one
metal
carboxylate under an inert atmosphere. Such a base may contain metal carbides
due to
the initial presence of the carboxylate ligands. Moreover, such a base may
exhibit good
adhesion and strength, for example, when the surface comprises a carbon steel
alloy.
Then, one or more subsequent metal compounds are repeatedly applied and
converted
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in an oxygen-containing atmosphere, for example, and the subsequent layers of
metal
oxide form substantially without metal carbides. In some embodiments, six or
more
layers are formed on the base.
[0096] In addition, the effect of any mismatches in physical, chemical, or
crystallographic properties (particularly with regard to differences in
thermal expansion
coefficients) may be minimized by the use of much thinner coating materials
and the
resulting films. Furthermore, the smaller crystallite structure of the film (3-
6 nanometers,
in some embodiments) increases Hall-Petch strength in the film's structure
significantly.
[0097] The thermal stability of the metal oxide can be tested, in some
embodiments, by exposing the treated surface to thermal shock. For example, a
surface
having a metal oxide coating can be observed, such as by microscopy. Then the
surface can be exposed to a thermal shock, such as by rapid heating or by
rapid cooling.
Rapid cooling can be caused by, for example, dunking the room-temperature or
hotter
surface into liquid nitrogen, maintaining the surface under liquid nitrogen
for a time, and
then removing the surface from the liquid nitrogen. The surface is then
observed again,
to look for signs that the metal oxide coating is delaminating, cracking, or
otherwise
degrading because of the thermal shock. The thermal shock test can be repeated
to
see how many shock cycles a given metal oxide coating can withstand before a
given
degree of degradation, if any, is observed. Thus, in some embodiments of the
present
invention, the at least one metal oxide coating withstands at least one, at
least five, at
least ten, at least twenty-five, at least fifty, or at least one hundred
thermal shock cycles
from room temperature to liquid nitrogen temperature.
[0098] The nanocrystalline grains of metal oxide resulting from some
embodiments of the methods of the present invention have an average size, or
diameter, of less than about 50 nm. In some embodiments, nanocrystalline
grains of
metal oxide have an average size ranging from about 1 nm to about 40 nm or
from
about 5 nm to about 30 nm. In another embodiment, nanocrystalline grains have
an
average size ranging from about 10 nm to about 25 nm. In further embodiments,
nanocrystalline grains have an average size of less than about 10 nm, or less
than about
nm.
[0099] In other embodiments, the invention relates to metal oxide domains
(whether diffused, thin film, contiguous, non-contiguous, or a combination
thereof) and
articles comprising such domains, in which the domains contain two or more
rare earth
metal oxides and at least one transition metal oxide. Further embodiments of
the
invention relate to metal oxide domains (and articles comprising them),
containing ceria,
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WO 2009/129380 PCT/US2009/040791
a second rare earth metal oxide, and a transition metal oxide. Some
embodiments
relate to metal oxide domains (and articles comprising them), containing
yttria, zirconia,
and a second rare earth metal oxide. Still other embodiments relate to metal
oxide
domains (and articles comprising them), containing alumina, silica, and
combinations
thereof. Additional embodiments relate to metal oxide domains (and articles
materials
comprising them), containing zirconia, ceria, alumina, nickel oxide, titania,
and
combinations thereof. For example, one embodiment comprises zirconia, titania,
yttria,
and chromia. Another embodiment comprises zirconia and nickel oxide. Yet
another
embodiment comprises zirconia and alumina, while another embodiment comprises
zirconia and ceria. A further embodiment comprises zirconia, titania, nickel
oxide, and
ceria.
[00100] In some embodiments, the metal compound applied to the surface
comprises a cerium compound, and the metal oxide comprises cerium oxide (or
ceria).
In other embodiments, the metal compound applied to the surface comprises a
zirconium compound, and the metal oxide comprises zirconia. In yet other
embodiments, a solution comprising both a cerium compound and a zirconium
compound is applied, and the resulting metal oxide comprises ceria and
zirconia. In
some cases, the zirconia formed by the process of the invention comprises
crystal grains
having an average size of about 3-9 nm, and the ceria formed by the process of
the
invention comprises crystal grains having an average size of about 9-18 nm.
The
nanostructured zirconia can be stabilized in some embodiments with yttria or
other
stabilizing species alone or in combination. In still other embodiments, the
metal oxide
comprises zirconia, yttria, or alumina, each alone or in combination with one
or both of
the others.
[00101] Thus, in some embodiments, a surface comprises at least one metal
oxide
comprising zirconia, silica, and chromia. For example, the at least one metal
oxide
comprises zirconium ion detectible in an amount ranging from about 35 to about
45 mol
%, silicon ion detectible in an amount ranging from about 52 to about 64 mol
%, and
chromium ion detectible in an amount ranging from about 1 to about 3 mol %,
each mol
% (molar percent) being relative to the total metal ion detectible in the at
least one metal
oxide. The metal ion can be detectable according to any suitable method, such
as, for
example, X-ray fluorescence techniques including energy dispersive X-ray
spectroscopy. A detected metal ion can be present in any suitable species,
such as a
single metal metal oxide (e.g., Si02), a multi-metal metal oxide (e.g.,
SrTiO3), an impurity
CA 02721790 2010-10-18
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or interstitial inclusion in another metal oxide (e.g., Y-stabilized Zr02),
solid solutions,
and the like.
[00102] In further embodiments, a surface comprises at least one metal oxide
comprising silica, sodium oxide, calcium oxide, and chromia. For example, the
at least
one metal oxide comprises silicon ion detectible in an amount ranging from
about 57 to
about 70 mol %, sodium ion detectible in an amount ranging from about 10 to
about 20
mol %, calcium ion detectible in an amount ranging from about 10 to about 20
mol %,
chromium ion detectible in an amount ranging from about 1 to about 3 mol %,
relative to
the total metal ion detectible in the at least one metal oxide.
[00103] In still further embodiments, a surface comprises at least one metal
oxide
comprising zirconia, yttria, and chromia. For example, the at least one metal
oxide
comprises zirconium ion detectible in an amount ranging from about 85 to about
94 mol
%, yttrium ion detectible in an amount ranging from about 5 to about 10 mol %,
and
chromium ion detectible in an amount ranging from about 1 to about 5 mol %,
relative to
the total metal ion detectible in the at least one metal oxide.
[00104] Additional embodiments provide a surface comprising at least one metal
oxide that comprises alumina, silica, and chromia. For example, the at least
one metal
oxide comprises aluminum ion detectible in an amount ranging from about 25 to
about
35 mol %, silicon ion detectible in an amount ranging from about 60 to about
74 mol %,
and chromium ion detectible in an amount ranging from about 1 to about 5 mol
%,
relative to the total metal ion detectible in the at least one metal oxide.
[00105] Yet additional embodiments provide a surface comprising at least one
metal oxide, wherein the at least one metal oxide comprises zirconia, yttria,
chromia,
and titania. For example, the at least one metal oxide comprises zirconium ion
detectible in an amount ranging from about 20 to about 30 mol %, yttrium ion
detectible
in an amount ranging from about 1 to about 6 mol %, chromium ion detectible in
an
amount ranging from about 0.5 to about 3 mol %, and titanium ion detectible in
an
amount ranging from about 61 to about 78.5 mol %, relative to the total metal
ion
detectible in the at least one metal oxide.
[00106] Still further embodiments provide a surface comprising at least one
metal
oxide, wherein the at least one metal oxide comprises zirconia, yttria,
chromia, and
nickel oxide. For example, the at least one metal oxide comprises zirconium
ion
detectible in an amount ranging from about 30 to about 40 mol %, yttrium ion
detectible
in an amount ranging from about 1 to about 5 mol %, chromium ion detectible in
an
amount ranging from about 0.5 to about 2 mol %, and nickel ion detectible in
an amount
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WO 2009/129380 PCT/US2009/040791
ranging from about 53 to about 68.5 mol %, relative to the total metal ion
detectible in
the at least one metal oxide.
[00107] Another set of embodiments provides a surface having at least one
metal
oxide thereon, wherein the at least one metal oxide comprises zirconia,
yttria, chromia,
and ceria. For example, the at least one metal oxide comprises zirconium ion
detectible
in an amount ranging from about 35 to about 45 mol %, yttrium ion detectible
in an
amount ranging from about 1 to about 5 mol %, chromium ion detectible in an
amount
ranging from about 0.5 to about 3 mol %, and cerium ion detectible in an
amount ranging
from about 47 to about 63.5 mol %, relative to the total metal ion detectible
in the at least
one metal oxide.
[00108] Still further embodiments provide a surface comprising at least one
metal
oxide, wherein the at least one metal oxide comprises zirconia and titania.
For example,
the at least one metal oxide comprises zirconium ion detectible in an amount
ranging
from about 20 to about 30 mol %, and titanium ion detectible in an amount
ranging from
about 70 to about 80 mol %, relative to the total metal ion detectible in the
at least one
metal oxide.
[00109] As explained herein, additional metal oxides, which can be the same or
different, can be added. In some embodiments, the at least one metal oxide
serves as a
bond base for at least one additional material. Such additional materials need
not be
formed according to the present invention. Some embodiments provide a metal
oxide
bond base that allows an additional material that would not adhere to the
surface as well
in the absence of the bond base. In still other embodiments, at least one
metal oxide
serves as a bond base for at least one other metal oxide. Additional
embodiments
provide the bond base in the form of a coat. In addition, the surface can be
subjected to
a thermal treatment, either before or after a metal oxide is formed on the
surface. For
example, a surface having a metal oxide in accordance with the present
invention can
be annealed at high temperature to strengthen the surface. In another example,
a
surface can be held near absolute zero before or after a metal oxide coating
is formed
on the surface. Suitable temperatures for thermal treatment range from nearly
0 K to
several thousand K, and include liquid hydrogen, liquid helium, liquid neon,
liquid argon,
liquid krypton, liquid xenon, liquid radon, liquid nitrogen, liquid oxygen,
liquid air, and
solid carbon dioxide temperatures, and temperatures obtained by mixtures,
azeotropes,
and vapors of those and other materials.
[00110] The process of the invention may permit the use of metal oxides on a
wide
variety of materials, including application of AI203, Si02, CeO2 and Zr02 to
metals
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WO 2009/129380 PCT/US2009/040791
previously not thought possible of being treated with these materials. Some
embodiments of the present invention provide a relatively low temperature
process that
does not damage or distort many surfaces, does not produce toxic or corrosive
materials, and can be done on site, or "in the field" without the procurement
of expensive
capital equipment.
[00111] In some embodiments of the present invention, a surface in need of
enhanced lubricity is placed within a vacuum chamber, and the chamber is
evacuated.
Optionally, the surface can be heated or cooled, for example, with gas
introduced into
the chamber or by heat transfer fluid flowing through the surface mounting
structure. If a
gas is introduced, care should be taken that it will not alter the surface in
an unintended
manner, such as by oxidation of a hot iron-containing surface by an oxygen-
containing
gas. Introduced gas optionally can be evacuated once the surface achieves the
desired
temperature. Vapor of one or more metal compounds, such as cerium(III) 2-
hexanoate,
enters the vacuum chamber and deposits on the surface. A specific volume of a
fluid
composition containing the metal compound can provide a specific amount of
compound
to the surface within the vacuum chamber, depending on the size of the chamber
and
other factors. Optionally, a chosen gas is vented into the chamber and fills
the vacuum
chamber to a chosen pressure, in one example, equal to one atmosphere. The
chamber
is heated to a temperature sufficient to convert at least some of the
compounds into
oxides, for example, 450 C, for a discrete amount of time sufficient for the
conversion
process, for example, thirty minutes. In this example, ceria domains form on
the
surface. Optionally, the process can be repeated as many times as desired,
forming
contiguous domains, a uniform coating, or even a thicker coating of ceria on
the surface.
In certain embodiments, a uniform coating will form from the first application
of the metal
compound composition. In some embodiments, the component can be cooled
relative
to ambient temperature, such as, for example, to liquid nitrogen temperature,
to aid the
deposition process. In other embodiments, a reducing atmosphere may be used to
convert at least a portion of the metal oxides to metal.
[00112] In other embodiments, the surface can be kept at lower temperatures
sufficient to prevent the degradation of the surface during the heating
process, for
example, at liquid nitrogen temperatures while the metal compound converts to
the
oxide due to any technique that heats the metal compound but not the surface
to a
significant degree. Examples of such heating techniques include flash lamps,
lasers,
and microwave heating. In addition, materials that would become degraded by
exposure
to high temperatures can be kept at lower temperatures using the same
techniques. For
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example, low-melting-temperature metals and similar surfaces can be kept
cooler while
the at least one metal compound is converted to at least one metal oxide.
[00113] As used herein in reference to process gases used to carry out the
process
of the invention, the term "high temperature" means a temperature sufficiently
high to
convert the metal compound to metal oxide, generally in the range of about 200
C to
about 1000 C, such as, for example, about 200 C to about 400 C, or about
400 C to
about 500 C, about 500 C to about 650 C, about 650 C to about 800 C, or
about 800
C to about 1000 C.
[00114] In some embodiments of the invention, a lubricity-enhancing material
may
be formed on a surface by applying a liquid metal compound composition to the
surface
using a dipping process, spraying, vapor deposition, swabbing, brushing, or
other known
means of applying a liquid to surface. This liquid metal compound composition
comprises at least one rare earth metal salt of a carboxylic acid and at least
one
transition metal salt of a carboxylic acid, in a solvent, in some embodiments.
The
surface, once wetted with the composition is then exposed to a heated
environment that
will convert at least some of the metal compounds to metal oxides, thereby
forming a
lubricity-enhancing material on the surface.
EXAMPLES
Example 1
[00115] Several 2" x 2" coupons of mirror-finish SS304 steel (McMaster-Carr)
or
tool steel are individually designated as indicated below. At least some of
those
compositions mimic chemically and thermally inert materials by the same names
known
in nature and industry, in an inventive manner. A wide range of similar
materials can
suggest additional compositions to be used as embodiments of the present
invention.
The "Uncoated" coupon is given no coating, to function as the control. Each of
the other
coupons are washed in soapy water, sonicated, rinsed with water, placed in
ethanol, air
dried, and coated on one side with the following compositions in accordance
with
embodiments of the present invention:
Zircon: Zirconium 2-ethylhexanoate (28 % wt. of the final composition, Alfa-
Aesar),
silicon 2-ethylhexanoate (33.5 % wt., Alfa-Aesar) and chromium 2-
ethylhexanoate (1 %
wt., Alfa-Aesar) are mixed into 2-ethylhexanoic acid (37.5 % wt., Alfa-Aesar),
and the
composition is spin-coated onto the steel surface.
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Glass: Silicon 2-ethylhexanoate (74 % wt., Alfa-Aesar), sodium 2-
ethylhexanoate (5.2 %
wt., Alfa-Aesar), calcium 2-ethylhexanoate (11 % wt., Alfa-Aesar), and
chromium 2-
ethylhexanoate (1.4 % wt., Alfa-Aesar) are mixed into 2-ethylhexanoic acid
(8.4 % wt.,
Alfa-Aesar), and the composition is spin-coated onto the steel surface.
YSZ: Yttrium 2-ethylhexanoate powder (2.4 % wt., Alfa-Aesar) is dissolved into
2-
ethylhexanoic acid (60 % wt., Alfa-Aesar) with stirring at 75-80 C for one
hour. Once
the composition is cooled to room temperature, zirconium 2-ethylhexanoate
(36.6 % wt.,
Alfa-Aesar) and chromium 2-ethylhexanoate (1 % wt., Alfa-Aesar) are mixed in.
The
composition is spin-coated onto the steel surface.
Clay: Aluminum 2-ethylhexanoate (15 % wt., Alfa-Aesar), silicon 2-
ethylhexanoate (45 %
wt., Alfa-Aesar), and chromium 2-ethylhexanoate (2 % wt., Alfa-Aesar) are
mixed into 2-
ethylhexanoic acid. This composition is handbrushed onto the surface, due to
the
viscosity of the composition. The composition apparently reacts with moisture
in the air
and began to solidify, making application difficult.
Zirconia-Titania: An equal weight of the YSZ liquid composition described
above is
combined with an equal weight of titanium 2-ethylhexoxide (Alfa Aesar, item
no. 44,678)
as received with stirring. The composition is spin-coated onto the steel
surface.
Zirconia-Nickel Oxide: Nickel 2-ethylhexanoate powder (10g, Alfa Aesar) is
mixed into 2-
ethylhexanoic acid (20g, Alfa Aesar) and heated to 70 C with stirring for 30
minutes.
Then, an equal weight (30g) of the YSZ liquid composition described above is
mixed in
with stirring. The composition is spin-coated onto the steel surface.
Zirconia-Ceria: An equal weight of the YSZ liquid composition described above
is mixed
together with an equal weight of cerium(Ill) 2-ethylhexanoate (Alfa Aesar,
item no.
40,451) as received. The composition is spin-coated onto the steel surface.
[00116] The coated steel coupons are placed in a vacuum oven, and evacuated to
about 20-60 millitorr. The coupons are heated to 450 C, and then allowed to
cool to
room temperature. The process of depositing and heating is repeated to apply
eight
coatings of the appropriate composition on each coupon.
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[00117] The coupons coated with the various compositions can be tested
according to any suitable method to measure lubricity relative to the uncoated
coupon.
Example 2
[00118] A roller, useful as a side roller for conducting hot steel sheets into
compression rollers, was coated with four layers of yttria-stabilized zirconia
made from a
composition containing yttrium (III) 2-ethylhexanoate (7.5 mol %), chromium 2-
ethylhexanoate (2 mol %), and zirconium (IV) 2-ethylhexanoate (90.5 mol %).
The
ingredients were mixed together and applied to the roller using an airbrush,
and the
roller was heated under nitrogen to 450 C. After the roller cooled
sufficiently, the
process was repeated three times for a total of four layers on the surface. An
identical
roller remained unheated and uncoated and functioned as a control. Both
rollers were
weighed and placed in a steel mill production process, in which they
functioned as side
rollers to conduct freshly-manufactured 3" thick steel sheets into compression
rollers that
thinned the steel to 3/8". After one week of running the rollers in the
production process,
the uncoated roller had to be replaced, which is common for such rollers. The
coated
roller, however, continued in the production process for 10.2 weeks, and the
mass
losses of the two rollers were compared. Even though the coated roller faced
approximately 10 times more process than the uncoated roller, the coated
roller
exhibited approximately 1/5th of the mass loss of the uncoated roller. In
other words,
the wear rate was reduced to 1 /50th by just four coats of metal oxide. That
result shows
unexpected and dramatic enhancement of the lubricity of the surface of the
roller in an
actual industrial process.
Example 3
[00119] A sample of extrusion dyes for extruding aluminum was coated with 6-8
coats of the same yttria-stabilized zirconia composition described in Example
2. The
composition was applied to the dye, heated to 450 C under nitrogen, allowed
to cool,
and then the process was repeated for the total number of layers desired.
Another
extrusion dye remained uncoated as a control. Compared to the control dye, the
coated
dye appeared smoother and shinier. Aluminum was extruded through the dyes in
the
usual manner. The coated dyes allowed a 10% increase in production of
aluminum. In
addition, the coated dyes lasted approximately two to three times longer than
the
uncoated dye. That result shows unexpected enhanced lubricity of the extrusion
dyes
allowing increased production and lengthened lifetime.
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Example 4
[00120] Two steel coupons, one uncoated and the other coated with a Zirconia-
Titania made from a composition containing zirconium (IV) 2-ethylhexanoate (50
% wt.)
and titanium (IV) ethoxide (50 % wt.), were tested to measure friction and
wear due to
sliding friction. The composition was applied to one coupon using a lint-free
towel
wetted with the composition. Then the wetted coupon was heated to 450 C under
nitrogen and allowed to cool. Both were treated with Ethyl Gear Test Oil
before the test
began.
Results:
Coupon Coefficient of Wear Scar Wear Rate
Friction (mm) mm3/Nm
Uncoated 0.083 0.85 5x10"
Zirconia-Titania 0.075 0.60 1 0-9
The foregoing data show unexpected and dramatic improvement in the lubricity
of the
surface by an embodiment of the present invention over the use of a
conventional
lubricant alone.
[00121] As previously stated, detailed embodiments of the present invention
are
disclosed herein. However, it is to be understood that the disclosed
embodiments are
merely exemplary of the invention that may be embodied in various forms, and
do not
imply limitation. It will be appreciated that many modifications and other
variations that
will be appreciated by those skilled in the art stand within the claims set
forth below
without departing from the teachings, spirit, and intended scope of the
invention.
Furthermore, the foregoing description of various embodiments does not
necessarily
imply exclusion. For example, "some" embodiments may include all or part of
"other"
and "further" embodiments within the scope of this invention. In addition, "a"
means "at
least one" and does not necessarily mean "one and only one."
32
