WO2009129380A2

WO2009129380A2 - Methods for enhancing lubricity of surfaces

Info

Publication number: WO2009129380A2
Application number: PCT/US2009/040791
Authority: WO
Inventors: Mark A. Deininger; Leonid V. Budaragin; Mikhail Pozvonkov
Original assignee: C-3 Int'l, Llc
Priority date: 2008-04-16
Filing date: 2009-04-16
Publication date: 2009-10-22
Also published as: CA2721790A1; EP2279287A2; WO2009129380A3

Abstract

The invention relates to methods for enhancing the lubricity of a surface by forming at least one metal oxide on the surface. In some embodiments, the metal oxide enhances the lubricity, and in other embodiments, the metal oxide works with another lubricant to further enhance lubricity. The wear rate of a metal surface is reduced dramatically when at least one metal oxide is formed on the surface, in some embodiments.

Description

International Patent Application

For

METHODS FOR ENHANCING LUBRICITY OF SURFACES

By

Leonid V. Budaragin,

Michael M. Pozvonkov, and

Mark A. Deininger

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 ⁰C. 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. UMMARY F 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 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 β-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. [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. ultiple layers are ormed, or 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 ⁰C, below about -50 ⁰C, below about -10 ⁰C, or below about 0 ⁰C. Still other embodiments are adapted to provide enhanced lubricity between about -78 ⁰C and about 0 ⁰C; from about 0 ⁰C to about 25 ⁰C; from about 25 ⁰C to about 50 ⁰C; from about 0 ⁰C to about 50 ⁰C; from about -20 ⁰C to about 50 ⁰C; from about 50 ⁰C to about 100 ⁰C; from about 100 ⁰C to about 250 ⁰C; from about 250 ⁰C to about 350 ⁰C; above about 350 ⁰C; from about 350 ⁰C to about 450 ⁰C; from about 450 °C to about 600 ⁰C; from about 600 ⁰C to about 800 ⁰C; from about 800 ⁰C to about 1000 ⁰C; from about 1000 ⁰C to about 1200 ⁰C; or above about 1200 ⁰C.

[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 10 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 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 Ci 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-di methyl butyl, 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 Ci 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, 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 Ci 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 O, 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, =O, =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 β-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, 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(ill) 2-ethylhexanoate, magnesium(ll) stearate, manganese(ll) cyclohexanebutyrate, and zinc(ll) 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 + Meⁿ⁺(OH)_n → (RCOO)_nMeⁿ⁺ + nH₂O (for practically all metals having a solid hydroxide). nRCOOH + Meⁿ⁺(CO₃)₀.5n → (RCOO)_nMeⁿ⁺ + 0.5nH₂O + 0.5nCO₂ (for alkaline earth metals, alkali metals, and thallium). nRCOOH + Me^π+(X)n_/m → (RCOO)_nMe⁰⁺ + n/mH_mX (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 (C₄H₈O₂)- butyric, C₅Hi₀O₂ - valeric, C₆H₁₂O₂ - caproic, C₇H₁₄ - 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≡CCOOH - 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; [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 CH₃COCH₂CH₂COOH - 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, CeH₅COOH - benzoic, C₆H₅CH₂COOH - 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-COOH - 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(COOH)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- 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')-COOH (I) wherein:

R° is selected from H or Ci to C₂₄ alkyl groups; and

R' and R" are each independently selected from H and Ci to C₂₄ alkyl groups; wherein the alkyl groups of R°, R¹, 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 R¹ 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 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, Nd₁ 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 - CsH-ioO; phenyl- propyl alcohol - CgHi₂O, 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 β-DIKETONATES

[0065] Metal β-diketonates suitable for use in the present invention contain at least one metal atom and at least one β-diketone of formula III as a ligand:

in which

R³, R⁴, R⁵, and R⁶ are alike or different, and are independently chosen from hydrogen, unsubstituted and substituted alkyl, unsubstituted and substituted 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 β-diketone of formula III may assume different isomeric and electronic configurations before and while chelated to the metal atom. For example, the free β-diketone may exhibit enolate isomerism. Also, the β-diketone may not retain strict carbon-oxygen double bonds when the molecule is bound to the metal atom. [0067] Examples of β-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 β-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 norbomadiene. [0069] Metal β-diketonates useful in the present invention can be made according to any method known in the art. β-diketones are well known as chelating agents for metals, facilitating synthesis of the diketonate from readily available metal salts. [0070] Metal β-diketonates are available from Alfa-Aesar and Gelest, Inc. Also, Strem Chemicals, Inc. of Newburyport, MA, sells a wide variety of metal β-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 β-diketonates can be chosen for some embodiments of the present invention. n ur er em o ments, a meta compoun compos t on compr ses 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 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, AI2O₃, Ceθ₂, Ce₂θ₃, TΪO2, ZrO₂ 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; β-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. [0079] The metal compound composition can applied in some embodiments in which the composition has a temperature less than about 250 ⁰C. That composition also can be applied to the surface in further embodiments at a temperature less than about 50 ⁰C. In other embodiments, the Bquid 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 ⁰C.

[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 25O⁰C for a given period of time. In some embodiments, the environment of the wetted surface is heated to a temperature exceeding about 400⁰C but less than about 45O⁰C or less than about 500⁰C for a chosen period of time. In other embodiments, the environment of the surface is heated to a temperature ranging from about 400⁰C to about 65O⁰C. In further embodiments, the environment is heated to a temperature ranging from about 400⁰C to about 55O⁰C. In st urt er embodiments, the environment is heated to a temperature ranging from about 550 ⁰C to about 650 ⁰C, from about 650 ⁰C to about 800 ⁰C, or from about 800 ⁰C to about 1000 ⁰C. In one embodiment, the environment is heated to a temperature of up to about 425⁰C or about 45O⁰C. 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 empera ure gas can e pro uce y a convent ona oven, n uct on eat ng co s, eat 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:

ZrO₂ for example, at 0-90 wt%

CeO₂ for example, at 0-90 wt%

CeO₂-ZrO₂ where CeO₂ is about 10-90 wt%

Y₂O₃ Yttria-stabilized Zirconia where Y is about 1-50% mol%

TiO₂ for example, at 0-90 wt%

Fe₂O₃ for example, at 0-90 wt%

NiO for example, at 0-90 wt%

AI₂O₃ for example, at 0-90 wt%

SiO₂

Y₂O₃

Cr₂O₃

Mo₂O₃

HfO₂

La₂O₃

Pr₂O₃

Nd₂O₃

Sm₂O₃

Eu₂O₃

Gd₂O₃

Tb₂O₃

Dy₂O₃

Ho₂O₃

Er₂O₃

Tm₂O₃

Yb₂O₃

Lu₂O₃ x ures o ese compos ons are a so su a e or use n t e nvent on. [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 erms me a ox e an sur ace compr ses at east one meta ox e nc u e a o t ose 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 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 O₂, 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 ⁰C under a vacuum, introducing air and maintaining the temperature, and then increasing the temperature to about 420 ⁰C 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 n an oxygen-conta n ng atmosp ere, or 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 5 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, 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., SiO₂), a multi-metal metal oxide (e.g., SrTiOs), an impurity or interstitial inclusion in another metal oxide (e.g., Y-stabilized ZrO₂), 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 rang ng rom a out to a out 8.5 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 AI₂O₃, SiO₂, CeO₂ and ZrO₂ to metals prev ous y not t oug t poss e o being treated w t t ese 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(lll) 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 ⁰C, 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 example, low-me ting-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 ⁰C to about 1000 ⁰C, such as, for example, about 200 ⁰C to about 400 ⁰C, or about 400 ⁰C to about 500⁰C, about 500 ⁰C to about 650 ⁰C, about 650 ⁰C to about 800⁰C, or about 800 ⁰C to about 1000 ⁰C.

[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. 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 ⁰C 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 (2Og, Alfa Aesar) and heated to 70 ⁰C with stirring for 30 minutes. Then, an equal weight (3Og) 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(lll) 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 miliitorr. The coupons are heated to 450 ⁰C, 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. [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 ⁰C. 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 ⁰C 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. 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 ⁰C under nitrogen and allowed to cool. Both were treated with Ethyl Gear Test Oil before the test began.

Results:

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."

Claims

WE CLAIM:

1. 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.

2. The method of claim 1 , further comprising contacting the at least one metal oxide with at least one lubricant.

3. The method of claim 2, wherein the at least one lubricant comprises one or more vegetable oils, animal oils, mineral oils, polyolefins, esters, silicones, fluorocarbons, halocarbons, polytetrafluoroethylene, greases, fats, waxes, water, surfactants, graphite, molybdenum disulfide, tungsten disulfide, fluid cushion, and combinations of two or more thereof.

4. The method of claim 1 , wherein the at least one metal oxide comprises two or more rare earth metal oxides and at least one transition metal oxide.

5. An article of manufacture having at least one surface comprising at least one metal oxide, wherein the at least one surface exhibits enhanced lubricity.

6. The article of claim 5, wherein the at least one metal oxide was 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 the at least one metal oxide.

7. The article of claim 5, wherein the at least one metal oxide comprises zirconia, silica, and chromia.

8. The article of claim 5, wherein 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 %, relative to the total metal ion detectible in the at least one metal oxide.

9. The article of claim 5, wherein the at least one metal oxide comprises silica, sodium oxide, calcium oxide, and chromia.

10. The article of claim 5, wherein 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.

11. The article of claim 5, wherein the at least one metal oxide comprises zirconia, yttria, and chromia.

12. The article of claim 5, wherein 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.

13. The article of claim 5, wherein the at least one metal oxide comprises alumina, silica, and chromia.

14. The article of claim 5, wherein 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.

15. The article of claim 5, wherein the at least one metal oxide comprises zirconia, yttria, chromia, and titania.

. The article of claim 5, wherein 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.

17. The article of claim 5, wherein the at least one metal oxide comprises zirconia, yttria, chromia, and nickel oxide.

18. The article of claim 5, wherein 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 ranging from about 53 to about 68.5 mol %, relative to the total metal ion detectible in the at least one metal oxide.

19. The article of claim 5, wherein the at least one metal oxide comprises zirconia, yttria, chromia, and ceria.

20. The article of claim 5, wherein 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.

21. The article of claim 5, wherein the at least one metal oxide comprises zirconia and titania.

22. The article of claim 5, wherein 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.

23. T e art c e o c a m 5, w erein the at least one metal oxide is present in at least one domain having a thickness less than about 1 micron.

24. The article of claim 5, wherein the metal oxide penetrates the surface from about 100 Angstroms to about 200 Angstroms.

25. The article of claim 5, wherein the article exhibits enhanced lubricity over temperatures ranging from about -78⁰C to about 1200⁰C.