WO2019055920A2 - Nano-additives enable advanced lubricants - Google Patents

Abstract

The presently disclosed technology relates to a nano-additives to improve the performance of lubricants, oils, and greases. More specifically, the presently disclosed technology relates to applying capped metal oxide nanoparticles, such as capped zirconia nanoparticles, in the lubricants to produce a tribofilms on the lubricating surfaces to provide wear protection to the said surfaces. Also, the interaction of the capped zirconia nanoparticles with other commonly used additives in lubricants may further optimize the performance of the resulting tribofilms.

Description

NANO-ADDITIVES ENABLED ADVANCED LUBRICANTS

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This application is partially supported by a US Dept. of Energy Corporate

Research and Development Agreement (CRADA) No. 1200801 and US Dept. of Energy

Small Business Innovation Research (SBIR) Phase I and II Grants No. DE-SC0009222.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims domestic priority benefits of U.S.

Provisional Patent Application Serial Nos. 62/559,721 filed on September 18, 2017 (Atty. Dkt. No. 2476-0201 ) and 62/559,590 filed on September 17, 2017 (Atty. Dkt. No. 2476-0185), the entire contents of each prior filed application being expressly

incorporated hereinto by reference.

FIELD

This presently disclosed technology pertains, among other things, to a lubricant containing nano-additives for oils and greases. The present disclosure provides a zirconia nanoparticles dispersion in oils with or without other additives. The function of these nano-additives is to form a protective tribofilm on contacting surfaces. The tribofilm may supplement the boundary and fluid film formed by the lubricant to provide wear and/or friction reduction and thus enable the use of lubricants with lower viscosity.

BACKGROUND AND SUMMARY

Lubricating oils and greases are commonly used in a variety of applications, for example, crankcase lubricants for internal combustion engines, lubricating oils for geared transmissions in vehicles and wind turbine drivetrains, and grease or oil lubricants for rolling element bearings. The lubricant provides protection against, among other damage including corrosion, wear of the contacting surfaces through a

pressurized fluid film and/or the formation of a solid tribofilm generated during operation. While a fluid film is governed by the viscosity of the oil, the tribofilm formation is typically provided by chemical additives that react to form a solid film on the surface. In efforts to improve efficiency of mechanical drives there is a trend to reduce the viscosity of the lubricating oils to lower the churning or viscous loses. To maintain the durability of components, the performance requirements of the lubricant additives are more demanding, specifically for friction and wear.

The chemical additives traditionally used in lubricants to provide protective tribofilms are referred to as Anti-Wear (AW) and Extreme Pressure (EP) additives.

Furthermore Friction Modifiers (FM) are used to maintain a low shear surface at the contact. These additives come in a variety of forms but most are organometallic compounds containing phosphorus, sulfur, and zinc. These compounds chemically react with the contacting surfaces to form an amorphous and/or crystalline solid tribofilm. While the mechanisms responsible for tribofilm formation from organometallics is still a topic of ongoing research, in practice it is generally observed that a certain level of shear, pressure, and/or temperature is required to nucleate and grow a tribofilm with organometallic compounds. Furthermore, in automotive applications, the phosphorus and sulfur content of these additives have been shown to have a detrimental impact on the exhaust after treatment catalysts; this has led to tighter restrictions on allowable content of these compounds in the lubricant.

Base oils suitable for use in formulating the compositions, additives and concentrates described herein may be selected from any of the synthetic or natural oils or mixtures thereof. The synthetic base oils include alkyl esters of dicarboxylic acids, polyglycols and alcohols, poly-alpha-olefins, including polybutenes, alkyl benzenes, organic esters of phosphoric acids, polysilicone oils, and alkylene oxide polymers, interpolymers, copolymers and derivatives thereof where the terminal hydroxyl groups have been modified by esterification, etherification, and the like. The synthetic oils may also include the gas to liquid synthetic oils.

Natural base oils include animal oils and vegetable oils (e.g., castor oil, lard oil), liquid petroleum oils and hydrorefined, solvent-treated or acid-treated mineral lubricating oils of the paraffinic, naphthenic and mixed paraffinic-naphthenic types. Oils of lubricating viscosity derived from coal or shale are also useful base oils. The base oil typically has a viscosity of about 2.5 to about 15 cSt and preferably about 2.5 to about 1 1 cSt at 100.degree. C.

Lubricating fluids include lubricious liquids, such as non-polar, hydrocarbon liquids comprising molecules that include from 4-60 carbons, such as from about 8-50 carbons, or from about 12-40 carbons. Lubricating fluids can include synthetic and natural oils, both naphthenic and paraffinic, and can include lubricating oils based on the American Petroleum Institute ("API") Base Stocks Group I, Group II, Group III, and Group IV. As is known in the art, the API sets minimum performance standards for lubricants. Lubricant base stocks are categorized into five groups by the API. Group I base stocks are composed of fractionally distilled petroleum which is further refined with solvent extraction processes to improve certain properties such as oxidation resistance and to remove wax. Group II base stocks are composed of fractionally distilled petroleum that has been hydrocracked to further refine and purify it. Group III base stocks have similar characteristics to Group II base stocks, except that Group III base stocks have higher viscosity indexes. Group III base stocks are produced by further hydrocracking Group II base stocks or hydroisomerized slack wax, (a byproduct of the dewaxing process). Group IV base stocks are polyalphaolefins (PAOs). Group V is a catch-all group for any base stock not described by Groups I to IV. Examples of group V base stocks include polyol esters, natural esters from seed oils and synthetic fatty esters. The lubricating fluid may also include a lubricating ester such as polyol esters, natural esters from seed oils and synthetic fatty esters, viscosity index improvers, or combinations thereof. Exemplary lubricating fluids include SAE Engine oils with SAE viscosity grades of 5W, 10W, 20, 30, 40 and 50. In certain lubricating compositions, the lubricant fluid has a kinematic viscosity (viscosity/density) at 40. degree. C. that is from about 15 cSt to about 800 cSt or that is from about 20 cSt to about 350 cSt. Other examples include SAE Gear Oils with SAE viscosity grades 75W, 80W, 85W, 90 and 140.

The use of nanoparticles as an additive to lubricants to provide AW, EP, and FM performance qualities presents an innovative approach to supplement or replace the use of organometallic compounds or other additive chemistries. The mechanisms governing the formation of a tribofilm from nanoparticles are fundamentally different than those of the chemical additives, which presents potential advantages in certain contact configurations. Therefore, inorganic nanoparticles, particles less than 100 nm in diameter, have recently been a subject of interest as friction modifier or anti-wear agent for lubricants. There have been many studies on the subject (H. Spikes, Lubr. Sci. 20 (2008), pp. 103-136; J. Tannous et al., Tribol. Lett. 41 (201 1 ), pp 55-64; A. Hernandez Batterz et al., Wear 265 (2008), pp. 422-428; H. Kato and K. Komai, Wear 262 (2007), pp 36-41 ). These studies, however, all suffer from (1 ) the lack of control on the quality of nanoparticles, i.e. the size and size distribution, and (2) lack of dispersion stability in the oils. The results, therefore, were not conclusive regarding the benefit the nanoparticle additives provided. It is now understood that to enable the advantages provided by nanoparticle additives and to avoid any detrimental consequences, the nanoparticles have to meet certain considerations include: dispersion and suspension, stability at elevated temperature, compatibility and synergy with other lubricant additives, and interaction compatibility with contacting surfaces.

In the past few years, a family of inorganic nanoparticles and nanocrystals have been developed by Pixelligent Technologies LLC which have small size (typically smaller than 10 nm diameter), with a narrow size distribution, and most importantly, an engineered surface chemistry so that they can be dispersed into common base stocks without observable impact on the appearance, viscosity, and shelf-life of the oils.

Nanoparticles will be understood to include nanocrystals. Because these developed nanoparticles are much smaller than typical asperities of almost all practical

manufactured surfaces in tribological applications, and also because of the quality and stability of the dispersion, true nano-scale control of the tribological behavior has been observed, and the benefits of the nanoparticle additives can be leveraged for reducing friction and wear.

The presently disclosed technology herein provides, among other things, that a zirconia nanoparticle dispersion in oils with or without other additives forms a protective tribofilm that is self-limiting and self-regenerating in rolling, sliding, or rolling-sliding contact. This is achieved through well-dispersed, capped nanoparticles to maintain a stable, homogeneous distribution and avoiding agglomeration of particles. The nano- scale size of the particle, 4 - 20 nm, is critical in enabling the additive to enter the contact while avoiding any unintended detrimental effects. If the nanoparticles are not capped or dispersed attractive forces bring the particles together causing agglomeration and leading to fall-out of suspension. The agglomerations lead to a non-uniform mixture in the oil and if the agglomeration is large and hard enough can lead to abrasion of the contacting surface resulting in increased wear.

In addition to having a well dispersed nanoparticle that enters the contact, this presently disclosed technology provides a nanoparticle that, once in contact, adheres strongly to the component surface and grows a thick tribofilm (30 nm to 500 nm). The nucleation of this tribofilm occurs in sliding, rolling, or rolling-sliding contacts, and at temperature ranges of -50°C to 160°C and beyond, thus extending the conditions that traditional AW and EP additives form tribofilms.

The present disclosure provides nano-additives for lubricants, oils, and greases. During operation, the said nano-additive may build protective, self-limiting, self- regenerating tribofilms in rolling, sliding, or rolling-sliding contacts. Such a tribofilm may reduce wear and/or friction at the lubricating contacts. Such a tribofilm may supplement the boundary, mixed, elasto-hydrodynamic (EHL) and/or hydrodynamic film formed by the lubricant thus allowing lubricant viscosity reduction.

The presently disclosed lubricants, oils, and greases may include any mineral and synthetic oils including synthetic hydrocarbons, esters, polyglycols, silicones, and ionic liquids.

The present disclosure provides a zirconia nanoparticle dispersion, in pure oils or oils with other lubricant additives comprising anti-wear (AW) additives such as zinc dialkyldithiophosphates (ZDDP), or friction modifiers (FM), anti-oxidants, extreme pressure (EP) additives, anti-foams, detergents, dispersants, pour point depressants, or any other commonly used lubricant additives.

The presently disclosed zirconia nanoparticles may be capped with surface capping agents as previously described in any of U.S. Patent Nos. 8,883,903;

9,328,432; 9,202,688 and 8,920,675, the entire contents of each of which are

incorporated herein by reference.

The presently disclosed zirconia nanoparticles may have size smaller than 20 nm, or smaller than 15 nm, or smaller than 10 nm, or smaller than 5 nm. The presently disclosed zirconia nanoparticle dispersion may demonstrate higher clarity. Said dispersion with 10 wt% capped zirconia nanoparticles, when measured in a cuvette with 10 mm optical path, demonstrates optical transmittance higher that 50%, or higher than 60%, or higher than 70%, or higher than 80%, or higher than 90%, or higher than 95%, or higher than 99%, when measured at 400nm.

The presently disclosed zirconia nanoparticle dispersion may demonstrate higher clarity. Said dispersion with 10 wt% capped zirconia nanoparticles, when measured in a cuvette with 10 mm optical path, demonstrates optical transmittance higher that 50%, or higher than 60%, or higher than 70%, or higher than 80%, or higher than 90%, or higher than 95%, or higher than 99%, when measured at 450nm.

The presently disclosed zirconia nanoparticle dispersion may demonstrate higher clarity. Said dispersion with 10 wt% capped zirconia nanoparticles, when measured in a cuvette with 10 mm optical path, demonstrates optical transmittance higher that 50%, or higher than 60%, or higher than 70%, or higher than 80%, or higher than 90%, or higher than 95%, or higher than 99%, when measured at 500nm.

The presently disclosed zirconia nanoparticle dispersion may demonstrate higher clarity. Said dispersion with 10 wt% capped zirconia nanoparticles, when measured in a cuvette with 10 mm optical path, demonstrates optical transmittance higher that 10%, or higher than 20%, or higher than 30%, or higher than 40%, or higher than 45%, or higher than 50%, or higher than 55%, or higher than 55%, when measured at 350nm.

The presently disclosed zirconia nanoparticle dispersion may demonstrate high stability. Said dispersion with 10 wt% capped zirconia nanoparticles, when measured in a cuvette with 10 mm optical path, demonstrates change in optical transmittance less than 10%, or less than 5%, or less than 1 %, after 1 month storage, or after 3 month storage, or after 6 month storage, or after 1 year storage, or after 2 year storage, or after 3 year storage.

The presently disclosed zirconia nanoparticles may form a tribofilm on

tribologically contacting surfaces in relative motion and under tribological stress. Said tribofilm may be highly dense and polycrystalline. Said tribofilm may have thickness in the range of 30 nm to 500 nm. Said tribofilm may have a hardness less than or equal to 7.3 GPa, and modulus less than or equal to about 160 GPa when measured with nano- indentation.

The small size and superb dispersibility of the nanoparticles enable them to enter the space separating asperities on the surfaces in a tribological contact. The

mechanism of the tribofilm formation may be that under tribological stress, the capping agents on the nanoparticle surface are removed, the nanoparticles are bonded to the rubbing surfaces to form nucleation sites, the nanoparticles coalesce onto the

nucleation sites, and then undergo grain coarsening to form an integral tribofilm. The tribofilm growth is stress driven and higher stress leads to faster nucleation and tribofilm growth process.

The presently disclosed tribofilm may demonstrate self-limiting thickness during its formation under a given tribological condition. The maximum film thickness may be 30 nm - 50 nm, or 50 nm - 100 nm, or 100 nm - 200 nm, or 200 nm - 300 nm, or 300 nm - 400 nm, or 400 nm - 500 nm, or 500 nm or larger.

The presently disclosed tribofilm may have surface RMS roughness equal to or less than 2 nm, or 2 nm - 5 nm, or 5nm - 10 nm, or 10 nm - 50 nm, or 50 nm - 100 nm, or 100 nm - 500 nm.

The presently disclosed tribofilm has carbon content of 10% - 15 %, or 5% - 10%, or less than 5%, as measured by EDX, EELS, or FTIR.

The presently disclosed tribofilm may have high adhesion to the substrates as measured by the tape test.

The presently disclosed tribofilm may not be removed by acid such as 10% hydrochloric acid solution, or base, such as 10% tetramethylammonium hydroxide (TMAH) solution.

The presently disclosed tribofilm may form under pure sliding, pure rolling, or mixed rolling-sliding conditions.

The presently disclosed tribofilm may form in the temperature range of - 50 °C to 160 °C, or 0 °C to 160 °C, or 20 °C to 130 °C.

The presently disclosed tribofilm may form on a steel surface, or a silicon surface, an amorphous carbon surface or a ceramic such as yttria-stabilized zirconia surface. The presently disclosed tribofilm may form on surfaces with RMS surface roughness larger than 5 nm.

The presently disclosed tribofilm may form with an oil with 10 wt% capped ZrO2 nanoparticles, or 1 wt% capped ZrO2 nanoparticles, or 0.1 wt% capped ZrO2 nanoparticles, or 0.01 wt% capped ZrO2 nanoparticles.

The presently disclosed tribofilm may form under tribological contact 10 nm or wider, or 1 urn or wider, or 150 urn or wider, or 1 mm or wider.

The presently disclosed tribofilm may be formed in the presence of ZrO2 nanoparticles together with anti-wear (AW) additives such as zinc

dialkyldithiophosphates (ZDDP), or friction modifiers (FM), anti-oxidants, extreme pressure (EP) additives, anti-foams, detergent, dispersants, pour point depressants, or any other commonly used lubricant additives.

The presently disclosed technology provides a method of forming a solid film on a lubricated surface that includes placing a lubricant in a contact region defined by two surfaces in proximity, sliding and/or rolling said surfaces so as to produce a pressure and/or shear stress on the lubricated surface in the contact region, and thereby forming the solid film in the contact region, wherein the solid film is adhered to at least one of the surfaces in the contact region, the lubricant containing at least partially capped, metal oxide nanocrystals.

Metal oxide nanocrystals of the presently disclosed technology include zinc oxide, hafnium oxide, zirconium oxide, hafnium-zirconium oxide, titanium-zirconium oxide and/or yttrium oxide.

Methods of the presently disclosed technology provide solid films that persists after formation and in the absence of said sliding and/or rolling forces.

Pressures useful in methods of the presently disclosed technology may range from 100 MPa to 5 GPa, 100 MPa to 200 MPa, 200 MPa to 400 MPa, 400 MPa to 800 MPa, 800 MPa to 1 .5 GPa, 1.5 GPa to 3 GPa, 3 GPa to 5 GPa or 5 GPa to 10 GPa.

Shear stresses useful in methods of the presently disclosed technology may range from 10 MPa to 0.5 GPa, 10 MPa to 100 MPa, 100 MPa to 200 MPa, 200 MPa to 500 MPa, or 500 MPa to 1 GPa. Methods of the presently disclosed technology provide or include lubricants having at least partially capped nanocrystals in an amount of 0.01 to 2 percent by weight of the lubricant, 0.01 to 0.05 percent by weight of the lubricant, 0.05 to 0.1 percent by weight of the lubricant, 0.1 to 0.2 percent by weight of the lubricant, 0.2 to 0.3 percent by weight of the lubricant, 0.3 to 0.4 percent by weight of the lubricant, 0.4 to 0.5 percent by weight of the lubricant, 0.5 to 0.75 percent by weight of the lubricant, 0.75 to 1 percent by weight of the lubricant, 1 to 1 .5 percent by weight of the lubricant, 1 .5 to 2 percent by weight of the lubricant, or 2 to 10 percent by weight of the lubricant.

Methods of the presently disclosed technology involve or include formation of the solid film at a temperature in a contact region during the sliding and/or rolling in the range of -100°C to 200 °C, -100 °C to -50 °C, -50 °C to -25 °C, -25 °C to 0 °C, 0 °C to 10 °C, 10 °C to 20 °C, 20 °C to 30 °C, 30 °C to 40 °C, 40 °C to 50 °C, 50 °C to 60 °C, 60 °C to 70 °C, 70 °C to 80 °C, 80 °C to 90 °C, 90 °C to 100 °C, 100 °C to 125 °C, 125 °C to 150 °C, 150 °C to 175 °C, 175 °C to 200 °C.

Lubricants of the presently disclosed technology may include a ZDDP additive, optionally present in an amount of 0.01 to 2 percent by weight of the lubricant, 0.01 to 0.05 percent by weight of the lubricant, 0.05 to 0.1 percent by weight of the lubricant, 0.1 to 0.2 percent by weight of the lubricant, 0.2 to 0.3 percent by weight of the lubricant, 0.3 to 0.4 percent by weight of the lubricant, 0.4 to 0.5 percent by weight of the lubricant, 0.5 to 0.75 percent by weight of the lubricant, 0.75 to 1 percent by weight of the lubricant, 1 to 1 .5 percent by weight of the lubricant, 1 .5 to 2 percent by weight of the lubricant, or 2 to 10 percent by weight of the lubricant.

Methods of the presently disclosed technology include forming the solid film on at least one surface or two surfaces that contains a steel composition.

Methods of the presently disclosed technology are able to form films and films formed according to the presently disclosed technology have a film hardness of 1 to 20 GPa, 100 MPa to 200 MPa, 200MPa to 500 MPa, 500 MPa to 750 MPa, 750 MPa to 1 GPa, 1 GPa to 2 GPa, 2 GPa to 3 GPa, 3 GPa to 5 GPa, 5 GPa to 7 GPa, 7 GPa to 10 GPa, 10 GPa to 15 GPa, 15 GPa to 20 GPa, or 20 GPa to 50GPa.

Methods of the presently disclosed technology are able to form films and films formed according to the presently disclosed technology have Young's modulus of 50 GPa to 300 GPa, 50 GPa to 75 GPa, 75 GPa to 100 GPa, 100 GPa to 125 GPa, 125 GPa to 150 GPa, 150 GPa to 200 GPa, or 250 GPa to 300 GPa.

Methods according to the presently disclosed technology may involve or include a sliding or rolling of the surfaces in the contact region to induce a shear rate on the lubricant in the range of 0 to 10⁷ sec^-1 , 0 to 10² sec^-1 , 10² to 10³ sec^-1 , 10³ to 10⁴ sec^-1 , 10⁴ to 10⁵ sec^-1, 10⁵ to 10⁶ sec^-1, or 10⁶ to 10⁷ sec^-1, or a shear rate that induces a tribological shear stress.

Methods of the presently disclosed technology further optionally include or involve formation of an elasto-hydrodynamic lubricant (EHL) film and/or a boundary lubricant film and/or hydrodynamic lubricant film in the contact region.

Lubricants included in the methods of the presently disclosed technology and films formed by the methods may be an oil or a grease, or a synthetic, mineral or a natural lubricant, or contain at least one of a synthetic hydrocarbon, an ester, a silicone, a polyglycol or an ionic liquid, or is an oil having a viscosity in the range of 2 to 1000 mPas (cP), 2 cP to 10cP, 10 cP to 50 cP, 50 cP to 100 cP, 100 cP to 500 cP, or 500 cP to 1000 cP, at a temperature of 100 °C.

Methods of the presently disclosed technology and films provided by the presently disclosed technology may include lubricants containing at least one of an anti- wear (AW) additive, a friction modifier such as zinc dialkyldithiophosphates (ZDDP), or friction modifiers (FM), anti-oxidants, extreme pressure (EP) additives, anti-oxidants, anti-foams, detergents, dispersants, pour point depressants, or any other commonly used lubricant additives.

The presently disclosed technology provides a solid film on a lubricated surface containing a metal oxide crystallite, the crystallite having a mean size of 5-20 nm, 5 to 100 nm, 5 nm to 10 nm, 10 nm to 20 nm, 20 nm to 30 nm, 30 nm to 40 nm, 40 nm to 50 nm, 50 nm to 60 nm, 60 nm to 70 nm, 70 nm to 80 nm, 80 nm to 90 nm, or 90 nm to 100nm, the film having an atomic ratio of carbon to metal in the range of 0.1 to 0.4.

Solid films of the presently disclosed technology optionally have a thickness of 20 to 500 nm, 20 nm to 50 nm, 50 nm to 100 nm, 100 nm to 200 nm, 200 nm to 300nm, 300 nm to 400nm, or 400nm to 500nm. Solid films of the presently disclosed technology may have a film density 1 .5-6 g/cm³, 1 .5 to 2 g/cm³, 2 to 3 g/cm³, 3 to 4 g/cm³, 4 to 5 g/cm³, or 5 to 6 g/cm³

The presently disclosed technology provides a method of delivering at least partially capped nanocrystals into the lubricated contact between two surfaces formed by sliding and/or rolling said surfaces so as to produce a pressure and/or shear stress on the lubricated surface and thereby forming a solid film, wherein the solid film is adhered to at least one of the surfaces, the lubricant comprising at least partially capped, metal oxide nanocrystals having a mean size of 3 nm to 20 nm, 3nm to 5nm, 5nm to 10nm, 10nm to 15nm, or 15nm to 20nm.

Methods of the presently disclosed technology provide solid films on at least two surfaces that may be portions of a piston ring-cylinder liner contact, a cam and lifter contact, a contact between a rolling element and races, gear teeth, or a hydrodynamic bearing shell and a rotor, or a hydrostatic bearing and stator or any other tribological contact surface with locally high pressures as described herein. The presently disclosed technology further provides a piston ring-cylinder liner contact, a cam and lifter contact, a contact between a rolling element and races, gear teeth, or a hydrodynamic bearing shell and a rotor, or a hydrostatic bearing and stator, or any other tribological contact surface with locally high pressures as described herein, containing a solid film of the presently disclosed technology.

BRIEF DESCRIPTION OF TABLES

TABLE 1 : Surface parameters of the samples used in Example 1 .

TABLE 2: Exemplary modulus and hardness measurement results of the tribofilm

Table 3 Chemical composition of the samples tested

BRIEF DESCRIPTION OF DRAWINGS

FIGURES 1 A and 1 B: Exemplary illustrations of the reciprocating ball-on-flat tester used in Example 1 - schematic of contact configuration - reciprocating ball-on- flat.

FIGURE 2A: Profilometric images of optical profilometric image a slide-honed cylinder liner surface. FIGURE 2B: Profilometric images of optical profilometric image a top compression ring surface.

FIGURE 3A: A photo of the Micro-Pitting Rig (MPR) used in the examples.

FIGURE 3B: A close-up photo of the MPR used in Example 1 shows the lubricant at rest covering the lower portion of the test rings.

FIGURE 4: Provides a schematic of the MPR contact configuration.

FIGURE 5A. Optical Images of Tribofilms formed by ball-on-flat test after 1 minute.

FIGURE 5B. Optical Images of Tribofilms formed by ball-on-flat test after 5 minutes.

FIGURE 5C. Optical Images of Tribofilms formed by ball-on-flat test after 20 minutes.

FIGURE 6A. Optical image of ball test scar after room temperature ball-on-flat test using PAO4 +1 wt% capped ZrO2 nanoparticles (PAO is poly-alpha-olefins).

FIGURE 6B. Optical image of flat test track after room temperature ball-on-flat test using PAO4 +1 wt% capped ZrO2 nanoparticles.

FIGURE 7A: SEM-EDX (Scanning Electron Microscopy - Energy-Dispersive X- Ray Spectroscopy) spectrum taken outside the flat wear track on the flat formed by 2 wt% capped ZrO2 nanoparticles in PAO oil showing Fe as the dominant element.

FIGURE 7B: SEM-EDX spectrum taken inside the flat wear track showing Zr as the dominant element.

FIGURE 8A: Optical profilometer image and line scan (solid lines) of a tribofilm formed by 1 wt% capped ZrO2 nanoparticles in PAO at 70 °C on a 52100 flat.

FIGURE 8B: Optical profilometer line scan showing approximately 350 nm buildup of tribofilm on the surface of the flat.

FIGURE 8C: Region evaluated for the buildup rate of the tribofilm (box).

FIGURE 9: An exemplary micrograph showing tribofilm formation on a liner after a test at 100oC using PAO10 +1 wt% capped ZrO2 nanocrystals.

FIGURE 10. EDX spectrum performed inside wear track of a flat tested with Mobil 1 10W30 and 1 wt% capped ZrO2 nanoparticles. FIGURE 1 1 : Evolution of tribofilm formation on the ring under for pure sliding during an MPR test.

FIGURE 12: Evolution of tribofilm formation on the ring up to 2 hours during an MPR test.

FIGURE 13A: SEM image of an area inside the test track on the ring after an MPR test.

FIGURE 13B: EDX spectrum of an area inside the test track on the ring after an MPR test.

FIGURE 14A: SEM image of an area inside the test track on the ring focused on a groove.

FIGURE 14B: EDX spectrum of an area inside the test track on the ring focused on a groove.

FIGURE 15: A schematic of the AFM configuration used for generating tribofilms.

FIGURE 16A: The tribofilm growth volume as function of mean contact stress, in an AFM set up, demonstrating stress-driven behavior.

FIGURE 16B: The tribofilm growth volume as function normal load, in an AFM set up, demonstrating load-driven behavior.

FIGURE 17A: An exemplary aerial view of the tribofilm generated by an AFM.

FIGURE 17B: An exemplary top view of the tribofilm generated by an AFM.

FIGURE 17C: An exemplary line scan of the tribofilm generated by an AFM.

FIGURE 18: Cross-sectional TEM image of the zirconia tribofilms at different magnification showing polycrystalline structure. The upper far right shows a fast Fourier transform of a region of one of the TEM images, demonstrating the local crystalline nature of the polycrystalline film.

FIGURE 19A: A cross-sectional TEM image of a tribofilm formed by AFM.

FIGURE 19B: Cross-sectional TEM-EDX mapping of the same tribofilm shows that zirconia tribofilms are deficient in carbon-containing capping agents and the composition of Fe and Zr formed gradients inside the tribofilm at different depth.

FIGURE 20A: Growth rates and cycles to tribofilms nucleation plotted for various sub-ambient test temperatures - under tested contact conditions, tribofilm growth is observed for all temperatures between -25°C and 25°C; some variation in growth rate is observed but films always grow.

FIGURE 20B: Growth rates and cycles to tribofilms nucleation plotted for various sub-ambient test temperatures. Reducing the interfacial temperature reduces the cycles-to-nucleation resulting in a more rapid growth initiation.

FIGURE 21 A and 21 B: Cross-sectional TEM images of a tribofilm formed by AFM using a PA04 base oil consisting of 9 wt.% zirconia with 0.8% wt.% ZDDP. Cross- sectional images show that ZDDP restricts grain coalescence and growth normally seen in pure zirconia tribofilms.

FIGURE 22: Cross-sectional TEM image of a tribofilm formed by AFM using a PA04 base oil consisting of 9 wt.% zirconia with 0.8% wt.% ZDDP (left) and EDX analysis performed across the cross-section of this tribofilms (right). EDX confirms the presence of zirconia in the tribofilms, as well as phosphorous, sulfur and zinc, which confirms that these tribofilms consist of a ZDDP phase mixed with zirconia.

FIGURE 23: An exemplary illustration of the reciprocating ball-on-flat tester - schematic of contact configuration - reciprocating ball-on-flat.

FIGURES 24A and 24B: Wear with base oil (FIGURE 24A), Wear with base oil + 1 % Zr0₂ (FIGURE 24B).

FIGURE 25: Tribofilm profile on HFRR flat.

FIGURE 26: Plots of friction coefficient vs time for several oils with and without zirconia nanocrystal additives

FIGURE 27: Optical micrographs of the test samples (ball and flat) after the HFRR tests for the oils with and without zirconia nanocrystal additives

FIGURE 28: Line scan plots from the profilometric measurements of the test sample wear track for tests with and without zirconia nanocrystal additives

FIGURE 29: Micropitting Rig and test conditions for micropitting and scuffing tests

FIGURE 30: Plot of vibration as a function of number of cycles for different oils tested in the MPR for micropitting

FIGURE 31 : Micrographs of the roller surfaces after testing in various oils, in the

MPR FIGURE 32: Profilometric images of the ring surfaces, corresponding to the images shown in Fig. 31

FIGURE 33: Plots of Traction coefficient as a function of time for three oils

FIGURE 34: Optical micrographs of roller surfaces, contrasting worn surfaces generated in the two oils

FIGURE 35: Optical and SEM micrographs of test samples received by UPenn. 35A: The sample run in Mobil SHC630 with 1 wt.% ZrO2 distinctly shows presence of a tribofilm. The area marked as A is the machined, non-contact portion of the roller while that marked B is the contact region where the tribofilm grew (light grey in optical image). 35B: Roller run in the Mobil Delvac 75W90 with 1 wt.% ZrO2 nanoparticles for 2.5M cycles did not readily reveal presence of a tribofilm under either optical microscope or SEM (fiducial markers are shown as arrows).

FIGURE 36: EDX spectra (focusing on the Zr signal at 15.75 keV) of the SHC and Delvac+1 wt.% ZrO₂, 2.5M cycles taken after 2 and 30 minutes of collection time respectively.

FIGURE 37: Chemical composition map for Zr in the SHC 630 sample, (a) optical image of the roller with a fiducial marker and the machined (A) and tribofilm (regions) indicated, (b) SEM image of the same region with the fiducial indicated, (c) EDS map of the Zr signal on the roller with the sliding direction indicated.

DETAILED DESCRIPTION

The present disclosure includes, but is not limited to, the following twenty-five (25) numbered embodiments:

1 . A method of forming a solid film on a lubricated surface comprising placing a lubricant in a contact region defined by two surfaces in proximity, sliding and/or rolling said surfaces so as to produce a pressure and/or shear stress on said lubricated surface in said contact region, and thereby forming said solid film in said contact region, wherein said solid film is adhered to at least one of said surfaces in said contact region, said lubricant comprising at least partially capped, metal oxide nanocrystals.

2. The method of embodiment 1 wherein said solid film persists after formation in the absence of said sliding and/or rolling. 3. The method of embodiment 1 wherein said pressure is in the range of 100 MPa to 5 GPa, or alternatively 100 MPa to 200 MPa, or 200 MPa to 500 MPa, or 500 MPa to 1 GPa, or 1 GPa to 2 GPa, or 2 Gpa to 3 GPa, or 3 GPa to 4 GPa, or 4 GPa to 5 GPa, or 5 GPa to 10 GPa.

4. The method of embodiment 1 wherein said shear stress is in the range of 10 MPa to 0,5 GPa, or alternatively 10 MPa to 20 MPa, or 20 MPa to 50 MPa, or 50 MPa to 100 MPa, or 100 MPa to 200 MPa, or 200 MPa to 500 MPa.

5. The method of embodiment 1 wherein the at least partially capped

nanocrystals are present in said lubricant in an amount of 0.01 to 2 percent by weight of the lubricant, or alternatively 0.01 to 0.05 percent by weight of the lubricant, or 0.05 to 0.1 percent by weight of the lubricant, or 0.1 to 0.2 percent by weight of the lubricant, or 0.2 to 0.5 percent by weight of the lubricant, or 0.5 to 1 percent by weight of the lubricant, or 1 to 1 .5 percent by weight of the lubricant, or 1 .5 to 2 percent by weight of the lubricant.

6. The method of embodiment 1 wherein the temperature in said contact region during said sliding and/or rolling is in the range of -100°C to 200 °C or alternatively -100 °C to -50 °C, or -50 °C to -25 °C, or -25 °C to 0 °C, or 0 °C to 25 °C, or 25 °C to 50 °C, or 50 °C to 75 °C, or 75 °C to 100 °C, or 100 °C to 125 °C, or 125 °C to 150 °C, or 150 °C to 175 °C, or 175 °C to 200 °C.

7. The method of embodiments 1 wherein said lubricant further comprises a ZDDP additive.

8. The method of embodiment 1 wherein at least one of said two surfaces comprises a steel composition.

9. The method of embodiment 8 wherein both of said two surfaces comprise a steel composition.

10. The method of embodiment 1 wherein said film has a hardness of 1 to 20 GPa, or alternatively 1 to 2 GPa, or 2 to 5 GPa, or 5 to 10 GPa, or 10 to 15 GPa, or 15 to 20 GPa.

1 1 . The method of embodiment 1 wherein said film has a Young's modulus of 50 to 300 GPa, or alternatively 50 to 75 GPa, or 75 to 100 GPa, or 100 to 150 GPa, or 150 to 200 GPa, or 200 to 300 GPa. 12. The method embodiment 1 wherein said film is formed to an average thickness of 30nm to 500nm, or alternatively 30 nm to 100 nm, or 100 nm to 200 nm, or 200 to 300 nm, or 300 nm to 400 nm, or 400 nm to 500 nm.

13. The method of embodiment 1 wherein said sliding or rolling of said surfaces in said contact region to induces a shear rate on said lubricant in the range of 0 to 10⁷ sec^-1, or alternatively 0 to 10 sec^-1 , or 10 to 10² sec^-1, or 10² to 10³ sec^-1 , or 10³ to 10⁴ sec^-1 , or 10⁴ to 10⁵ sec^-1 , or 10⁵ to 10⁶ sec^-1 , or 10⁶ to 10⁷ sec^-1.

14. The method of embodiment 1 wherein said shear rate induces a tribological shear stress.

15. The method of embodiment 1 wherein an elasto-hydrodynamic lubricant (EHL) film and/or a boundary lubricant film and/or hydrodynamic lubricant film is formed in said contact region.

16. The method of embodiment 1 wherein said lubricant is an oil or a grease.

17. The method of embodiment 1 wherein said lubricant is a synthetic, mineral or a natural lubricant.

18. The method of embodiment 1 wherein the lubricant comprises at least one of a synthetic hydrocarbon, an ester, a silicone, a polyglycol or an ionic liquid.

19. The method of embodiment 1 wherein said lubricant is an oil having a viscosity in the range of 2 to 1000 mPAs (cP) at a temperature of 100 °C, or

alternatively 2 to 5 mPAs (cP) at a temperature of 100 °C, or 5 to 10 mPAs (cP) at a temperature of 100 °C, or 10 to 20 mPAs (cP) at a temperature of 100 °C, or 20 to 50 mPAs (cP) at a temperature of 100 °C, or 50 to 100 mPAs (cP) at a temperature of 100 °C, or 100 to 200 mPAs (cP) at a temperature of 100 °C, or 200 to 500 mPAs (cP) at a temperature of 100 °C, or 500 to 1000 mPAs (cP) at a temperature of 100 °C.

20. The method of embodiment 1 wherein said lubricant further comprises at least one of an anti-wear (AW) additive, a friction modifier such as zinc

dialkyldithiophosphates (ZDDP), or friction modifiers (FM), anti-oxidants, extreme pressure (EP) additives, anti-oxidants, anti-foams, detergents, dispersants, pour point depressants, or any other commonly used lubricant additives. 21 . A solid film on a lubricated surface comprising a metal oxide crystallite, said crystallite having a mean size of 5-20 nm, said film having an atomic ratio of carbon to metal in the range of 0.1 to 0.4.

22. The solid firm of embodiment 21 , with a thickness of 20 to 500 nm or alternatively 20 nm to 100 nm, or 100 nm to 200 nm, or 200 to 300 nm, or 300 nm to 400 nm, or 400 nm to 500 nm.

23. The solid film of embodiment 22, said film having a density of 1.5-6 g/cm³, or 1 .5 - 2 g/cm³, or 2 - 3 g/cm³, or 3 to 4 g/cm³, or 4 to 5 g/cm³, or 5 to 6 g/cm³.

24. A method of delivering at least partially capped nanocrystals into the lubricated contact between two surfaces formed by sliding and/or rolling said surfaces so as to produce a pressure and/or shear stress on said lubricated surface and thereby forming a solid film, wherein said solid film is adhered to at least one of said surfaces, said lubricant comprising at least partially capped, metal oxide nanocrystals having a mean size of 3 nm to 20 nm.

25. The method of embodiment 1 wherein said two surfaces are portions of a piston ring-cylinder liner contact, a cam and lifter contact, a contact between a rolling element and races, gear teeth, or a hydrodynamic bearing shell and a rotor, or a hydrostatic bearing and stator.

The present disclosure also includes, but is not limited to, the following forty-nine (49) numbered embodiments:

1 . A method of reducing wear on lubricated surfaces of rolling bearings, gears, cams, lifters and multitude of other machine components, comprising lubricating the surfaces of said rolling bearings, gears, cams, lifters and multitude of other machine components with a lubricating oil comprising nanocrystals such that said wear is reduced as compared to lubricating the surfaces with the same lubricating oil which does not contain the nanocrystals.

2. A method of reducing wear on elastohydrodynamic (EHD) contacts found in rolling bearings, gears, cams, lifters and multitude of other machine components, said method comprising lubricating said contacts with a lubricating oil comprising

nanocrystals such that said wear is reduced as compared to lubricating the surfaces with the same lubricating oil which does not contain the nanocrystals. 3. The method of embodiment 1 or embodiment 2 wherein the nanocrystals are metal oxide nanocrystals.

4. The method of embodiment 1 or embodiment 2 or embodiment 3 wherein the nanocrystals are at least partially capped nanocrystals.

5. The method of any one of embodiments 1 -3 wherein the nanocrystals comprise oxide of at least one metal selected from Groups 1 A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition metals, lanthanides, actinides, and mixtures thereof, such as metals including, but are not limited to, titanium, zirconium, hafnium, thorium, germanium, tin, niobium, tantalum, molybdenum, tungsten, uranium, cerium, the rare earth metals, copper, beryllium, zinc, cadmium, mercury, aluminum, yttrium, gallium, indium, lanthanum, manganese, iron, cobalt, nickel, calcium, magnesium, strontium, and barium.

6. The method of embodiment 5 wherein the nanocrystals do not comprise at least one of Ce, Mg, Mn, Co, graphite, or graphene, or oxides of Ce, Mg, Mn, Co.

7. The method of embodiment 1 wherein said wear is abrasive wear.

8. The method of embodiment 2 wherein said wear is abrasive wear.

9. A method of reducing pitting on lubricated surfaces of rolling bearings, gears, cams, lifters and multitude of other machine components, comprising lubricating the surfaces of said rolling bearings, gears, cams, lifters and multitude of other machine components with a lubricating oil comprising nanocrystals such that said pitting is reduced as compared to lubricating the surfaces with the same lubricating oil which does not contain the nanocrystals.

10. A method of reducing pitting on elastohydrodynamic (EHD) contacts found in rolling bearings, gears, cams, lifters and multitude of other machine components, said method comprising lubricating said contacts with a lubricating oil comprising

nanocrystals such that said pitting is reduced as compared to lubricating the surfaces with the same lubricating oil which does not contain the nanocrystals.

1 1 . The method of embodiment 9 or embodiment 10 wherein the nanocrystals are metal oxide nanocrystals.

12. The method of embodiment 9 or embodiment 10 or embodiment 1 1 wherein the nanocrystals are at least partially capped nanocrystals. 13. The method of any one of embodiments 9-12 wherein the nanocrystals comprise oxide of at least one metal selected from Groups 1 A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition metals, lanthanides, actinides, and mixtures thereof, such as metals including, but are not limited to, titanium, zirconium, hafnium, thorium, germanium, tin, niobium, tantalum, molybdenum, tungsten, uranium, cerium, the rare earth metals, copper, beryllium, zinc, cadmium, mercury, aluminum, yttrium, gallium, indium, lanthanum, manganese, iron, cobalt, nickel, calcium, magnesium, strontium, and barium.

14. The method of embodiment 13 wherein the nanocrystals do not comprise at least one of Ce, Mg, Mn, Co, graphite, or graphene, or oxides of Ce, Mg, Mn, Co.

15. A method of reducing micro-pitting on lubricated surfaces of rolling bearings, gears, cams, lifters and multitude of other machine components, comprising lubricating the surfaces of said rolling bearings, gears, cams, lifters and multitude of other machine components with a lubricating oil comprising nanocrystals such that said micro-pitting is reduced as compared to lubricating the surfaces with the same lubricating oil which does not contain the nanocrystals.

16. A method of reducing micro-pitting on elastohydrodynamic (EHD) contacts found in rolling bearings, gears, cams, lifters and multitude of other machine

components, said method comprising lubricating said contacts with a lubricating oil comprising nanocrystals such that said micro-pitting is reduced as compared to lubricating the surfaces with the same lubricating oil which does not contain the nanocrystals.

17. The method of embodiment 15 or embodiment 16 wherein the nanocrystals are metal oxide nanocrystals.

18. The method of embodiment 15 or embodiment 16 or embodiment 17 wherein the nanocrystals are at least partially capped nanocrystals.

19. The method of any one of embodiments 15-18 wherein the nanocrystals comprise oxide of at least one metal selected from Groups 1 A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition metals, lanthanides, actinides, and mixtures thereof, such as metals including, but are not limited to, titanium, zirconium, hafnium, thorium, germanium, tin, niobium, tantalum, molybdenum, tungsten, uranium, cerium, the rare earth metals, copper, beryllium, zinc, cadmium, mercury, aluminum, yttrium, gallium, indium, lanthanum, manganese, iron, cobalt, nickel, calcium, magnesium, strontium, and barium.

20. The method of embodiment 19 wherein the nanocrystals do not comprise at least one of Ce, Mg, Mn, Co, graphite, or graphene, or oxides of Ce, Mg, Mn, Co.

21 . A method of reducing scuffing, scoring, galling, or seizure on lubricated surfaces of rolling bearings, gears, cams, lifters and multitude of other machine components, comprising lubricating the surfaces of said rolling bearings, gears, cams, lifters and multitude of other machine components with a lubricating oil comprising nanocrystals such that said scuffing, scoring, galling, or seizure is reduced as compared to lubricating the surfaces with the same lubricating oil which does not contain the nanocrystals.

22. A method of reducing scuffing, scoring, galling, or seizure on

elastohydrodynamic (EHD) contacts found in rolling bearings, gears, cams, lifters and multitude of other machine components, said method comprising lubricating said contacts with a lubricating oil comprising nanocrystals such that said scuffing, scoring, galling, or seizure is reduced as compared to lubricating the surfaces with the same lubricating oil which does not contain the nanocrystals.

23. The method of embodiment 21 or embodiment 22 wherein the nanocrystals are metal oxide nanocrystals.

24. The method of embodiment 21 or embodiment 22 or embodiment 23 wherein the nanocrystals are at least partially capped nanocrystals.

25. The method of any one of embodiments 21 -24 wherein the nanocrystals comprise oxide of at least one metal selected from Groups 1 A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition metals, lanthanides, actinides, and mixtures thereof, such as metals including, but are not limited to, titanium, zirconium, hafnium, thorium, germanium, tin, niobium, tantalum, molybdenum, tungsten, uranium, cerium, the rare earth metals, copper, beryllium, zinc, cadmium, mercury, aluminum, yttrium, gallium, indium, lanthanum, manganese, iron, cobalt, nickel, calcium, magnesium, strontium, and barium. 26. The method of embodiment 25 wherein the nanocrystals do not comprise at least one of Ce, Mg, Mn, Co, graphite, or graphene, or oxides of Ce, Mg, Mn, Co.

27. The method of any one of embodiments 1 -25 wherein the lubricated surfaces are made of materials used or that could be used in machine surfaces, including but not limited to steels, copper, aluminum, magnesium, titanium, silicon, tungsten, and/or alloys, and/or ceramics, and/or oxides, and/or borides, and/or carbides, and/or nitrides, and/or mixtures thereof.

28. A method of improving protection against wear on lubricated surfaces of rolling bearings, gears, cams, lifters and multitude of other machine components comprising contacting the surfaces with a formulated oil having a viscosity in the range of 2.0 to 10,000 cSt at 40 degree C, (or alternatively 2 to 5 cSt at 40 degree C, or 5 to

10 cSt at 40 degree C„ or 10 to 20 cSt at 40 degree C, or 20 to 50 cSt at 40 degree C, or 50 to 100 cSt at 40 degree C, or 100 to 200 cSt at 40 degree C, or 200 to 500 cSt at 40 degree C, or 500 to 1 ,000 cSt at 40 degree C, or 1 ,000 to 2,000 cSt at 40 degree C, or 2,000 to 5,000 cSt at 40 degree C, or 5,000 to 10,000 cSt at 40 degree C), said formulated oil having a composition comprising a major amount of a lubricating oil base stock and a minor amount of at least partially capped metal oxide nanocrystals; wherein said at least partially capped metal oxide nanocrystals are dispersed in said lubricating

011 base stock; said at least partially capped metal oxide nanocrystals being present in an amount sufficient for the formulated oil to improve protection against wear as compared to the same formulated oil which does not contain said at least partially capped metal oxide nanocrystals.

29. The method of embodiment 28 wherein wear is abrasive wear.

30. The method of any one of embodiments 28-29 wherein the nanocrystals comprise oxide of at least one metal selected from Groups 1 A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition metals, lanthanides, actinides, and mixtures thereof, such as metals including, but are not limited to, titanium, zirconium, hafnium, thorium, germanium, tin, niobium, tantalum, molybdenum, tungsten, uranium, cerium, the rare earth metals, copper, beryllium, zinc, cadmium, mercury, aluminum, yttrium, gallium, indium, lanthanum, manganese, iron, cobalt, nickel, calcium, magnesium, strontium, and barium. 31 . The method of embodiment 30 wherein the nanocrystals do not comprise at least one of Ce, Mg, Mn, Co, graphite, or graphene, or oxides of Ce, Mg, Mn, Co.

32. A method of improving protection against pitting in bearings and/or gears lubricated with a lubricating oil by using as the lubricating oil a formulated oil having a viscosity in the range of 2.0 to 10,000 cSt at 40 degree C, (or alternatively 2 to 5 cSt at 40 degree C, or 5 to 10 cSt at 40 degree C„ or 10 to 20 cSt at 40 degree C, or 20 to 50 cSt at 40 degree C, or 50 to 100 cSt at 40 degree C, or 100 to 200 cSt at 40 degree C, or 200 to 500 cSt at 40 degree C, or 500 to 1 ,000 cSt at 40 degree C, or 1 ,000 to 2,000 cSt at 40 degree C, or 2,000 to 5,000 cSt at 40 degree C, or 5,000 to 10,000 cSt at 40 degree C), said formulated oil having a composition comprising a major amount of a lubricating oil base stock and a minor amount of at least partially capped metal oxide nanocrystals; wherein said at least partially capped metal oxide nanocrystals are dispersed in said lubricating oil base stock; said at least partially capped metal oxide nanocrystals being present in an amount sufficient for the formulated oil to improve protection against pitting as compared to the same formulated oil which does not contain said at least partially capped metal oxide nanocrystals.

33. The method of embodiment 32 wherein the nanocrystals comprise oxide of at least one metal selected from Groups 1A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition metals, lanthanides, actinides, and mixtures thereof, such as metals including, but are not limited to, titanium, zirconium, hafnium, thorium, germanium, tin, niobium, tantalum, molybdenum, tungsten, uranium, cerium, the rare earth metals, copper, beryllium, zinc, cadmium, mercury, aluminum, yttrium, gallium, indium, lanthanum, manganese, iron, cobalt, nickel, calcium, magnesium, strontium, and barium.

34. The method of embodiment 33 wherein the nanocrystals do not comprise at least one of Ce, Mg, Mn, Co, graphite, or graphene, or oxides of Ce, Mg, Mn, Co.

35. A method of improving protection against micro-pitting in bearings and/or gears lubricated with a lubricating oil by using as the lubricating oil a formulated oil having a viscosity in the range of 2.0 to 10,000 cSt at 40 degree C, (or alternatively 2 to 5 cSt at 40 degree C, or 5 to 10 cSt at 40 degree C,, or 10 to 20 cSt at 40 degree C, or 20 to 50 cSt at 40 degree C, or 50 to 100 cSt at 40 degree C, or 100 to 200 cSt at 40 degree C, or 200 to 500 cSt at 40 degree C, or 500 to 1 ,000 cSt at 40 degree C, or 1 ,000 to 2,000 cSt at 40 degree C, or 2,000 to 5,000 cSt at 40 degree C, or 5,000 to 10,000 cSt at 40 degree C), said formulated oil having a composition comprising a major amount of a lubricating oil base stock and a minor amount of at least partially capped metal oxide nanocrystals; wherein said at least partially capped metal oxide nanocrystals are dispersed in said lubricating oil base stock; said at least partially capped metal oxide nanocrystals being present in an amount sufficient for the

formulated oil to improve protection against micro-pitting as compared to the same formulated oil which does not contain said at least partially capped metal oxide nanocrystals.

36. The method of embodiment 35 wherein the nanocrystals comprise oxide of at least one metal selected from Groups 1A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition metals, lanthanides, actinides, and mixtures thereof, such as metals including, but are not limited to, titanium, zirconium, hafnium, thorium, germanium, tin, niobium, tantalum, molybdenum, tungsten, uranium, cerium, the rare earth metals, copper, beryllium, zinc, cadmium, mercury, aluminum, yttrium, gallium, indium, lanthanum, manganese, iron, cobalt, nickel, calcium, magnesium, strontium, and barium.

37. The method of embodiment 36 wherein the nanocrystals do not comprise at least one of Ce, Mg, Mn, Co, graphite, or graphene, or oxides of Ce, Mg, Mn, Co.

38. A method of improving protection against scuffing, scoring, galling, or seizure in bearings and/or gears lubricated with a lubricating oil by using as the lubricating oil a formulated oil having a viscosity in the range of 2.0 to 10,000 cSt at 40 degree C, (or alternatively 2 to 5 cSt at 40 degree C, or 5 to 10 cSt at 40 degree C„ or 10 to 20 cSt at 40 degree C, or 20 to 50 cSt at 40 degree C, or 50 to 100 cSt at 40 degree C, or 100 to 200 cSt at 40 degree C, or 200 to 500 cSt at 40 degree C, or 500 to 1 ,000 cSt at 40 degree C, or 1 ,000 to 2,000 cSt at 40 degree C, or 2,000 to 5,000 cSt at 40 degree C, or 5,000 to 10,000 cSt at 40 degree C), said formulated oil having a composition comprising a major amount of a lubricating oil base stock and a minor amount of at least partially capped metal oxide nanocrystals; wherein said at least partially capped metal oxide nanocrystals are dispersed in said lubricating oil base stock; said at least partially capped metal oxide nanocrystals being present in an amount sufficient for the

formulated oil to improve protection against scuffing, scoring, galling, or seizure as compared to the same formulated oil which does not contain said at least partially capped metal oxide nanocrystals.

39. The method of embodiment 38 wherein the nanocrystals comprise oxide of at least one metal selected from Groups 1A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition metals, lanthanides, actinides, and mixtures thereof, such as metals including, but are not limited to, titanium, zirconium, hafnium, thorium, germanium, tin, niobium, tantalum, molybdenum, tungsten, uranium, cerium, the rare earth metals, copper, beryllium, zinc, cadmium, mercury, aluminum, yttrium, gallium, indium, lanthanum, manganese, iron, cobalt, nickel, calcium, magnesium, strontium, and barium.

40. The method of embodiment 39 wherein the nanocrystals do not comprise at least one of Ce, Mg, Mn, Co, graphite, or graphene, or oxides of Ce, Mg, Mn, Co.

41 . The method of embodiment 28-40 wherein the improved protection is demonstrated in a test machine or rig, such as a MPR (micro-pitting rig), MTM (mini- traction machine) or HFRR (high frequency reciprocating rig) [PCS Instruments, 78 Stanley Gardens, London, W3 7SZ, United Kingdom], which simulates gear contacts by using appropriately designed test specimens and can measure, for example, the vibration or shock pulses that occurs as a result of pitting and micro-pitting, the comparison of surface material loss due to wear, and/or the friction coefficient change or rapid change as a result of scuffing, scoring, galling or seizure, when the formulated oil containing the at least partially capped metal oxide nanocrystals is compared with the same formulated oil not containing the at least partially capped metal oxide nanocrystals.

42. The method of embodiment 41 wherein the elastohydrodynamic contact stresses of the test machine or rig, such as a MPR, range from 100 MPa to 10 GPa.

43. The method of embodiment 41 or embodiment 42 wherein the test machine or rig, such as a MPR, is operated at a controlled temperature in the temperature range of -25C to 200 C or alternatively -100 °C to -50 °C, or -50 °C to -25 °C, or -25 °C to 0 °C, or 0 °C to 25 °C, or 25 °C to 50 °C, or 50 °C to 75 °C, or 75 °C to 100 °C, or 100 °C to 125 °C, or 125 °C to 150 °C, or 150 °C to 175 °C, or 175 °C to 200 °C. 44. The method of any one of embodiments 41 -43 wherein the mean rolling speed of the test specimens ranges from 1 mm/s to 20 m/s and the slide-roll ratio ranges from zero to infinity.

45. The method of any of embodiments 41 -44 wherein the test specimens are made of materials of a type used or could be used in machine surfaces, such as are present in rolling bearings, gears, cams and lifters, including but not limited to steels, copper, aluminum, magnesium, titanium, silicon, tungsten, and/or alloys, and/or ceramics, and/or oxides, and/or borides, and/or carbides, and/or nitrides, and/or mixtures thereof.

46. The method of any one of embodiments 1 -45 wherein the lubricated surfaces of rolling bearings, gears, cams, lifters and multitude of other machine surfaces are made of materials used or that could be used in machine surfaces, including but not limited to steels, copper, aluminum, magnesium, titanium, silicon, tungsten, and/or alloys, and/or ceramics, and/or oxides, and/or borides, and/or carbides, and/or nitrides, and/or mixtures thereof.

47. The method of any one of embodiments 1 -46 wherein the hardness of the materials range from 100 MPa to 10 GPa, or alternatively 100 MPa to 200 MPa, or 200 MPa to 500 MPa, or 500 MPa to 1 GPa, or 1 GPa to 2 GPa, or 2 Gpa to 3 GPa, or 3 GPa to 4 GPa, or 4 GPa to 5 GPa, or 5 GPa to 10 GPa.

48. The method of any one of embodiments 28-47 wherein the base oil comprises a Group I, Group II, Group III, Group IV or Group V base oil.

49. The method of embodiments 28-48 wherein said formulated oil comprises phosphorous and/or a phosphorous containing compound of a form and/or in an amount sufficient to form a protective film at a temperature lower than in the same formulated oil not containing said phosphorous and/or a phosphorous containing compound.

The present disclosure provides the following additional embodiments. EXAMPLES

Test Equipment:

Reciprocating Rig

Experiments were performed with two contact configurations (ball-on-flat and ring-on-liner) on the same reciprocating tribometer. The ball-on-flat configuration used 52100 steel counterfaces and 12.7-mm (1/2-in.) diameter balls (Grade 25) sliding against mirror-polished flats (Sq = 10 nm). The load of 15.6 N produced an initial peak Hertzian contact pressure of 1 GPa. The ring-on-liner configuration used specimens extracted from components in a commercial heavy-duty diesel engine. During all machining operations to extract test specimens, the original surfaces of the piston rings and cylinder liners were protected in order to retain the original surface roughness and honing pattern. The liners were gray cast iron with a typical honing pattern, and the ring was steel that had been coated with CrN by physical vapor deposition (PVD). The cylinder liner was mounted onto a reciprocating table on the bottom of the test rig, while the piston ring was stationary. The curvature of the ring was adjusted so that a Hertzian contact width of 10 mm was achieved. A load of 200 N produced a contact pressure of approximately 1 10 MPa, which is similar to the contact pressure experienced by the top compression ring at the top dead center (TDC) position in severe service. Schematics for the two contact configurations are shown in Figure 1 A and Figure 1 B. Figure 2A and Figure 2B shows profilometric images of the cylinder liner and top-compression ring surfaces, respectively. Their surface parameters are given in Table 1 .

The cylinder liner was mounted onto a reciprocating table on the bottom of the test rig, while the piston ring was stationary. The curvature of the ring was adjusted so that a Hertzian contact width of 10 mm was achieved. A load of 200 N produced a contact pressure of approximately 1 10 MPa, which is similar to the contact pressure experienced by the top compression ring at TDC in severe service.

A small amount of oil (0.3 ml) was applied at the interface of the test components to create a thin layer at the start of each test. The tests were conducted at 1 Hz reciprocating frequency for 1 hour using a stroke length of 20 mm. Heating elements were embedded into the reciprocating table, and the temperature was controlled by a temperature control unit. Tests were performed at 70°C, 100°C, 130°C, and 160°C respectively.

Micro-Pitting Rig (MPR)

Figure 3A is a photo of the Micro-Pitting Rig (MPR) available at ANL. It consists of a center roller in contact with three larger rings. Figure 3B shows the lubricant at rest covering the lower portion of the test rings. The lubricant is supplied to the contact via splash lubrication. Both the rings and the barrel are uni-directionally satin ground. The contacting area is flat and approximately 1 mm wide. The roughness of a ring is approximately 150 nm. The rotation speed of the rings and roller are independently controlled allowing for a range of slide-to-roll (SRR) speed ratios. The load, speed, temperature, and SRR can all be controlled and set to a condition that is relevant for replicating gear tooth contact. Additionally, the materials and surface roughness of the samples can be tailored to match that of the gear components. During a test, the MPR is capable of measuring the friction force between the roller and the rings, as well as the vibration developed at the contact, indicating the severity of the accumulated surface damage. After a test, the roller and ring samples are analyzed to quantify the amount of surface wear. Further examination of the samples can be used to characterize the protective tribofilm that formed on the surface from the lubricant additives. MPR tests were performed to evaluate the friction and wear (and/or pitting) performance of lubricants formulated with ZrO2 nanocrystal additives.

Characterization Techniques:

Surface Profilometry

An interferometric non-contact optical profilometer (Bruker®, ContourGT, San Jose, CA) was used for measuring roughness, finish, and texture of a surface. Due to optical interference, micrographs of thin transparent films show colors that are a function of film thickness. In order to show the true surface of a tribofilm, the test components were coated with a thin layer of gold.

Microscopy

The wear tracks on the flats and cylinder liners after the tests were examined with an Olympus STM6 optical microscope, an FEI Quanta 400F scanning electron microscope (SEM), a Hitachi S-4700-II SEM, both equipped with energy dispersive x- ray spectroscopy (EDX) capability. Transmission electron microscopy (TEM) and TEM- EDX of thin cross sections of particular films were performed in a JEOL 201 OF TEM.

Nano-lndentation

A nanoindenter (Hysitron TI-950 Tribo-lndenter) was used to determine the hardness and modulus of these tribofilms formed on surfaces, under displacement control using a standard Berkovich tip. The same tip was used under scanning probe microscopy (SPM) mode to image the surface topography. The nanoindenter monitors and records the load and displacement of the indenter during indentation with a force resolution of about 1 nN and a displacement resolution of about 0.2 nm. The samples were placed on a magnetic horizontal holder and positioned with the aid of an optical microscope located above the sample. The area function parameters of the tip were calibrated using a fused quartz sample, and tip-shape calibration is based on determining the area function of the indenter tip.

EXAMPLE 1

Capped ZrO2 nanocrystals were dispersed into base oil with multiple capping agents at least as high as 10 wt% without significantly affecting the viscosity and appearance of the oil. Concentrations of 0.5 wt.%, 1 wt.%, 2 wt.% and 10%, three different capping agents, temperature (25°C, 70°C, 130°C, 160°C), time (5 mins, 20 mins, 60 mins, 4 hrs, 24 hrs), and type of oil were parameters that were investigated.

An important observation is the formation of a unique tribofilm by ZrO2 nanocrystal additives regardless of temperature. A tribofilm started to form on the flat during the ball-on-flat test only 1 minute after the test started, and a thick and dense (as judged by optical profilometry) tribofilm was fully formed on the flat 20 minutes into the test, as shown in Figure 5. Due to the relatively long stroke length, the flat experienced much less rubbing than the ball, on which a thick and dense tribofilm was fully formed after 20 minutes.

The formation of a tribofilm was also observed at room temperature using PA04 as base oil with 1 wt% capped ZrO2. nanocrystals. The ball test scar and flat test track are shown in Figure 6A and Figure 6B, respectively. A prominent zirconium peak in the SEM-EDX spectrum was found in the wear track (Figure 7B) but it was absent outside the wear track (Figure 7A), indicating that the tribofilm was zirconium-rich and the tribofilm had indeed originated from the ZrO2 nanocrystal additives.

The tribofilms were semi-transparent so a thin gold layer was coated on the ball and flat by thermal evaporation to assure the accuracy when examined with optical profilometer. An optical image of a tribofilm obtained by the optical profilometer is shown in Figure 8A. Instead of a net loss of material characteristic of wear, there was actually a net increase of material on the wear track. Line scans (vertical solid line) across the film revealed that the tribofilm has a height of about 350 nm above the flat surface (Figure 8C).

Quantitative evaluation of the area marked in the Figure 8B by a solid rectangle showed a net nanocrystal-based tribofilm build-up rate of 62,700 μm3 per mm of sliding distance per hour, approximately 1/300 of the total nanocrystal loading included in the amount of oil used in the tests. This indicated that there are significant amount of nanocrystals left to continue re-generating the tribofilm. The tribofilm was also relatively smooth, the root mean square (RMS) roughness of the tribofilm was measured to be 170 nm while for the mirror polished flat the value was 40 nm.

A tribofilm was also formed on liner segments in ring-on-liner tests at a range of conditions as shown in an exemplary image in Figure 9.

The modulus and hardness of the tribofilm were also measured using nano- indentation, and exemplary results are shown in Table 2, together with the results of the steel flat. The tribofilm possess very impressive modulus and hardness, only ~ 30% less than 52100 in both cases. A tribofilm that is hard, but slightly softer than the surface material can provide sufficient load bearing capability as a rubbing surface while serving as a protective, regenerative layer if the stress is too high.

A tribofilm also formed by adding capped ZrO2 nanoparticles in a fully formulated oil (Mobil 1 10W30). The presence of Zr was confirmed with EDX after a test. The result is shown in Figure 10.

A tribofilm formed under pure rolling conditions in an MPR test, at a load of 200 N, speed of 2 m/s, and a temperature of 70°C, as early as 15 minutes (143,000 cycles), continued to grow over time, and became more uniform throughout the test. The film was maintained up to 24 hours of testing (13.8 million cycles). The evolution of the tribofilm is shown in Figure 1 1 .

A tribofilm also formed under a combination of rolling and sliding conditions in an MPR using capped Zr02 nanocrystals loaded mineral oil. The evolution of the tribofilm is shown in Figure 12.

Figure 13A shows an SEM image of part of the tribofilm inside the test track on the ring after the MPR test. EDX analysis was performed which indicates the presence of Zr on the test track on the ring, as shown in Figure 13B. Also, grooves were observed on the tribofilm and an SEM image of the groove is shown in Figure 14A, and EDX inside the grooves showed no Zr (Figure 14B) which means that the grooves are not filled with ZrO2 nanocrystals.

EXAMPLE 2

Tribofilms with the capped ZrO2 nanocrystals were also generated in an atomic force microscope (AFM) at the interface formed by a steel microsphere (ranging between 10 and 100μm in diameter) against either a 52100 steel substrate, or a silicon substrate or a yttria-stabilized zirconia substrate (illustrated in Figure 15). The contact stress at the sliding contact was varied between 0.1 GPa and 1 GPa and normal load at the sliding interface was varied between 10 and 230 μΝ. Zirconia tribofilms exhibit a stress and loas-driven growth process where increasing the contact load and stress increases the thickness of the tribofilms (Figures 16A and 16B). Increasing surface roughness increases the rate of tribofilm growth. These tribofilms are strongly bound to the substrate and resist removal during continued sliding with the AFM probe in either base oil or in dry sliding.

Using the AFM, tribofilms with lateral dimensions as small as 2 μm and as large as 50 μm were generated, with local thickness varying from 10 nm to 200 nm (example shown in Figure 17).

Tribofilms in the AFM were generated in concentrations of capped zirconia nanoparticles ranging from 0.01 wt.% in PA04 to 10 wt.% in PA04. Additionally, tribofilms were generated in other base stocks, including mPAO SYN65. Tribofilm microstructure and chemical composition were analyzed by performing focused-ion beam (FIB) milling to produce a cross-sectional sample of the tribofilm, followed by observation in scanning electron and transmission electron microscopes (SEM/TEM).

Cross-sectional imaging of the tribofilms show a nearly fully dense microstructure with no observable voids. Diffraction analysis confirms that the tribofilms consist of a mostly polycrystalline structure, identified to be zirconia. Through cross sectional imaging, evidence of grain growth and coalescence of individual 5 nm zirconia nanoparticles to form larger grains is also seen, as shown in Figure 18.

Through these cross-sectional images and accompanying chemical spectroscopy (such as EDX, EELS and FTIR), it is confirmed that zirconia tribofilms are deficient in carbon, indicating that tribological stresses during sliding result in the removal of capping agents prior to tribofilms formation (Figure 19).

The mechanism of tribofilms growth as deduced from these images is as follows: nanoparticles undergo selective removal of surface ligands, i.e. capping agents, at the sliding contact due to tribological stresses. In the absence of dispersing ligands, the nanoparticles interact strongly with the substrate and each other and tribological stresses cause the nanoparticles to bind strongly to the substrate and to each other, resulting in the nucleation and growth of a compact tribofilm. Rough surfaces and surface scratches serve as preferred nucleation sites. Due to stress-induced growth, tribofilms grow only in the region of contact. As the film grows, stress-driven grain coarsening occurs until a self-limiting tribofilm thickness is reached. Tribofilms generated in the sliding contact of the AFM show superior mechanical properties. The modulus and hardness of these films was measured to be about 160 GPa and 7.3 GPa, respectively. These values approach known literature values of bulk zirconia.

Tribofilms in the AFM were also generated with a mixture of capped zirconia nanoparticles mixed with zinc dialkyldithiophosphates (ZDDP) anti-wear additives. In these measurements, zirconia was added to a PA04 base oil in either 9 wt.%, 1 wt.%, 0.1 wt.% or 0.01 wt.%, and mixed with 0.8 wt.% ZDDP. With this oil containing both ZDDP and capped zirconia nanoparticles, measurements were made at a variety of temperatures including 25°C, 15°C, 5°C and -5°C. For all tested temperatures, and for all concentrations of capped zirconia mixed with ZDDP additive, a tribofilm growth and formation was observed in the AFM. Similar results are expected for lower

temperatures, such as -15°C and -25°C. The growth rate and cycles to nucleation as a function of temperature are shown in figures 20A and 20B respectively; tribofilms grew between the temperatures tested of -25°C to 25°C. The surfaces of these zirconia- ZDDP tribofilms were morphologically similar to pure zirconia tribofilms. However, for identical test conditions and durations, the zirconia-ZDDP tribofilms generated had a significantly higher thickness (i.e. volume) compared to pure zirconia tribofilms, exhibiting a surprising tribofilm-forming synergy between zirconia and ZDDP. In addition, tribofilms formed within the AFM with zirconia-ZDDP mixed in PA04 were found to nucleate on the surface much more rapidly in comparison to pure zirconia tribofilms, which resulted in a significantly rapid tribofilms growth initiation.

Cross-sectional imaging of tribofilms formed in oils containing both zirconia and ZDDP exhibit zirconia nanocrystal sizes of 5 nm, which indicate that ZDDP is effective in inhibiting grain growth and coalescence as is seen in pure zirconia tribofilms (Figure 21 A). Cross-sectional images and corresponding FFT patterns (Figure 21 B) revealed the film had two layers, an amorphous Zn-rich layer at the substrate interface and an upper layer with 5 nm zirconia nanocrystals dispersed in an amorphous phase.

Chemical spectroscopy of FIB/SEM cross-sections of these ZDDP-zirconia tribofilms indicate the presence of both zirconia, as well as zinc, phosphorous and sulfur, and a relative high concentration of carbon, which confirm that these tribofilms consist of a distinct zirconia phase as well as a distinct ZDDP phase (Figure 22).

Table 1 . Surface parameters of the samples used in Example 1 .

Table 2: Exemplary Modulus and Hardness Measurement Results of the Tribofilm

EXAMPLE 3

The following tasks were conducted:

• High Frequency Reciprocating Rig (HFRR) for tribofilm formation and friction

• Energy-Dispersive X-ray spectroscopy (EDX) for film composition

• Profilometry for film profiles and thickness

Findings on ZrO2 nanocrvstal tribofilms:

• Form under pure sliding, pure rolling and rolling-sliding

• Form at temperatures from minus 25°C to over 100°C

• Constant coefficient of friction of around 0.12

• Films form in a variety of lubricant formulations - synergistic with other P based additives.

• Provide micro-pitting and scuffing protection

Innovative, high-performing lubricants can be formulated with ZrO2

Oils and greases for longer life rolling bearings and gears Synergistic antiwear benefits with reduced phosphorus formulations HFRR Formulation studies:

The tribofilms were observed using HFRR under the following conditions:

Load: 15.6 N = 1 GPa. Room temperature.

Reciprocating frequency: 60 rpm = 1 Hz

Test duration: 1 hour or 24 hoursTribofilms reduced wear on the ball. Wear Volume was 3, 165 x 10³ μm³ with Base Fluid only. Wear Volume was reduced to 10.1 x 10³ μηι³ with Base Fluid + 1 wt% ZrO2 as shown in figure 24 a (base fluid only) and b (Base Fluid + 1 wt% ZrO2). Tribofilm profile on HFRR flat is shown in Figure 25. A variety of engine oil formulations and additive component studies were conducted in the HFRR.

General observations:

• With ZrO2 particles present, the friction coefficient was ~0.12 independent of formulation as shown by Figure 26.

• Tribofilms formed in a wide range of formulations and did not depend on base stock or formulation chemistry as shown by Figure 27.

• Profilometry showed tribofilm thicknesses of several hundred nanometers,

sufficient to give wear protection as shown by Figure 28.

EXAMPLE 4

Micropitting Protection

Pictures of the Micropitting Rig and test conditions for micropitting and scuffing tests are shown in Figure 29. Capped zirconia nanoparticles were tested to see if tribofilm formation would protect against micropitting. Four tests were run:

Baseline: Mobil Delvac™ Synthetic Gear Oil 75W-90 (2.5 million cycles)

Mobil Delvac™ SGO 75W-90 + 0.1 wt% ZrO2 (2.5 million cycles)

Mobil Delvac™ SGO 75W-90 + 1 .0 wt% ZrO2 (2.5 million cycles)

Mobil Delvac™ SGO 75W-90 + 1 .0 wt% ZrO2 (1 1 million cycles)

Results:

The MPR uses a vibration cut-off to denote failure. As seen in Figure 30 below, Mobil Delvac™ 75W90 ("Delvac", baseline) oil exhibited high vibration at approximately 2.5M cycles. The results were identical to the Delvac™ oil baseline with the addition of 0.1 wt.% Zr02. However, the addition of 1.0 wt.% delayed micro-pitting on the roller surface. A longer test was performed to examine when the oil containing Zr02 would cause a significant level of micropitting. The test lasted for about 1 1 M cycles at which point the surface of the roller was covered in micropits. That can be seen in Figure 31 .

Micropitting Results:

Mobil Delvac™ SGO 75W-90 oil (micropitting 2.5 M cycles)

Delvac™ oil + 0.1 wt% Zr02 (micropitting 2.5 M cycles)

Delvac™ oil + 1 .0 wt% Zr02 (No micropitting 2.5 M cycles)

Delvac™ oil + 1 .0 wt% Zr02 (micropitting at ~1 1 M cycles)

Surface profilometry of the ring surfaces showed no noticeable change in topography within or outside wear track for the 2.5M cycle tests. However, some wear was observed for the 1 1 M cycle test, indicating that the micro-pitting resistance might be a result of mild polishing wear. This can be seen in Error! Reference source not found..

Scuffing Protection

The scuffing tests were performed with the following oils:

1 . Mobil Delvac™ 75W90 synthetic gear oil

2. Mobil SHC630 VG 220

3. Mobil SHC630 VG 220 + 1 .0 wt.% Zr02

When scuffing occurs on the MPR, it is associated with a dramatic increase in the traction coefficient. The Delvac™ 75W90 oil formulation prevented scuffing. Figure 33 shows that as the load and slide-to-roll increased, the traction coefficient either remained relatively constant, or decreased. Therefore, a different oil that could exhibit scuffing was used, namely the Mobil SHC630 VG220. The Mobil SHC630 VG220 exhibited scuffing at a SRR ratio of 90%. A dramatic increase in the traction coefficient occurred and that can be seen in Figure 33. The addition of 1 .0 wt.% Zr02 significantly improved its scuffing performance. The formulation containing Zr02 exhibited no scuffing compared to baseline Mobil SHC630 oil. The surface of the roller was greatly damaged when the baseline Mobil SHC630 oil was used. Therefore, only micrographs of the roller surface of the Delvac™ 75W90 oil and Mobil SHC630 VG 220 oil + 1 .0 wt.% Zr02 are shown in Figure 34.

Characterization of tribofilms formed during the tests run in the Mobil Delvac™ oil micropitting tests were performed, as well as the Mobil SHC 630 oil scuffing test that was performed. Since no scuffing was observed in Mobil Delvac™ oil, detailed analysis was not conducted on the Delvac™ oil scuffing test samples. Although optical images that were taken clearly showed presence of a tribofilm on the SHC sample, the presence of a tribofilm on any of the Delvac™ oil samples was not apparent, as seen in the optical images in Figure 35. Energy Dispersive X-Ray Spectroscopy (EDX) was performed on the samples using a scanning electron microscope (SEM). These measurements did reveal the presence of Zr in all samples except the Delvac baseline sample, which contained no nanoparticles. However, a far lower concentration of Zr was detected on the samples run in Mobil Delvac™ oil with 1 wt.% ZrO2 relative to the sample run in the Mobil SHC oil with 1 wt.% ZrO2. Specifically, to achieve a signal to background strength comparable to the SHC sample, the Delvac™ oil + ZrO2 samples required fifteen times more collection time. Figure 36 shows spectra of the SHC sample after 2 minutes of collection and the Delvac™ oil + 1 wt.% ZrO2, 2.5M cycles sample after 30 minutes of collection time. Error! Reference source not found, lists the chemical composition of each sample. Figure 37 shows an area map of the Zr signal in the SHC 630 sample.

Table 3 Chemical composition of the samples tested

A key finding of this work is that SHC 630, which is very similar to Delvac™ 75W90 oil except for differences in additives and an order of magnitude (in cSt) lower viscosity, forms thick tribofilms while the Delvac™ oil lubricant forms only a weak film at best. We hypothesize that the film-forming additive already present in Delvac™ 75W-90 oil, olefin sulfide, plays a major role in inhibiting the formation of the tribofilm. As the chemical composition table shows (Error! Reference source not found.), there was sulfur on the surface of samples run in Delvac™ oil, while there was no sulfur in the SHC 630 tribofilm. Sulfur is surface active and rapidly and strongly adsorbs on steel surfaces. It is possible that the adsorbed sulfur either prevents the initial removal of the capping agent and/or passivates the steel surface, preventing strong adsorption of the zirconia nanoparticles. Although we would need more evidence to strongly support this hypothesis, it is promising that a gear lubricant such as SHC 630 induces a tribofilm when mixed with ZrO2. Finally, further evidence of synergy between phosphorus and ZrO2 was seen. In the sample run in SHC 630, the Zr signal was correlated with the P signal, suggesting that the film is composed of both elements.

Key findings:

• ZrO2 nanocrystals have been shown to develop thick, self-limiting tribofilms when used as additives in lubricants. • Capping agents make nanocrystal dispersions stable at high concentrations.

• Tribofilms >100 nm thick form under pure sliding, pure rolling and rolling- sliding

• Films can form rapidly at temperatures from minus 25°C to over 100°C.

• Films form in a variety of lubricants, independent of formulation.

• MPR tests demonstrate micro-pitting and scuffing protection.

• Synergistic with ZnDTP (and potentially other P based additives) as ZrO2 nanocrystals are incorporated into ZnDTP-based tribofilm

The foregoing description is given primarily for clearness of understanding and no unnecessary limitations are to be understood therefrom, for modification will become obvious to those skilled in the art upon reading this disclosure arid may be made upon departing from the spirit and scope of any specific embodiments. Accordingly, this disclosure is not intended to be limited by the specific exemplification presented herein above. Rather, what is intended to be covered is within the spirit and scope of the entirety of the present disclosure.

The contents of all references referred to herein are incorporated in their entirety in this disclosure.

Claims

We Claim:

1 . A method of reducing wear on lubricated surfaces of rolling bearings, gears, cams, lifters and multitude of other machine components, comprising lubricating the surfaces of said rolling bearings, gears, cams, lifters and multitude of other machine components with a lubricating oil comprising nanocrystals such that said wear is reduced as compared to lubricating the surfaces with the same

lubricating oil which does not contain the nanocrystals.

2. A method of reducing wear on elastohydrodynamic (EHD) contacts found in

rolling bearings, gears, cams, lifters and multitude of other machine components, said method comprising lubricating said contacts with a lubricating oil comprising nanocrystals such that said wear is reduced as compared to lubricating the surfaces with the same lubricating oil which does not contain the nanocrystals.

3. The method of claim 1 or claim 2 wherein the nanocrystals are metal oxide

nanocrystals.

4. The method of claim 1 or claim 2 or claim 3 wherein the nanocrystals are at least partially capped nanocrystals.

5. The method of any one of claims 1 -3 wherein the nanocrystals comprise oxide of at least one metal selected from Groups 1 A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition metals, lanthanides, actinides, and mixtures thereof, such as metals including, but are not limited to, titanium, zirconium, hafnium, thorium, germanium, tin, niobium, tantalum, molybdenum, tungsten, uranium, cerium, the rare earth metals, copper, beryllium, zinc, cadmium, mercury, aluminum, yttrium, gallium, indium, lanthanum, manganese, iron, cobalt, nickel, calcium, magnesium, strontium, and barium.

6. The method of claim 5 wherein the nanocrystals do not comprise at least one of Ce, Mg, Mn, Co, graphite, or graphene, or oxides of Ce, Mg, Mn, Co.

7. The method of claim 1 wherein said wear is abrasive wear.

8. The method of claim 2 wherein said wear is abrasive wear.

9. A method of reducing pitting on lubricated surfaces of rolling bearings, gears, cams, lifters and multitude of other machine components, comprising lubricating the surfaces of said rolling bearings, gears, cams, lifters and multitude of other machine components with a lubricating oil comprising nanocrystals such that said pitting is reduced as compared to lubricating the surfaces with the same lubricating oil which does not contain the nanocrystals.

10. A method of reducing pitting on elastohydrodynamic (EHD) contacts found in rolling bearings, gears, cams, lifters and multitude of other machine components, said method comprising lubricating said contacts with a lubricating oil comprising nanocrystals such that said pitting is reduced as compared to lubricating the surfaces with the same lubricating oil which does not contain the nanocrystals.

1 1 . The method of claim 9 or claim 10 wherein the nanocrystals are metal oxide

nanocrystals.

12. The method of claim 9 or claim 10 or claim 1 1 wherein the nanocrystals are at least partially capped nanocrystals.

13. The method of any one of claims 9-12 wherein the nanocrystals comprise oxide of at least one metal selected from Groups 1 A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition metals, lanthanides, actinides, and mixtures thereof, such as metals including, but are not limited to, titanium, zirconium, hafnium, thorium, germanium, tin, niobium, tantalum, molybdenum, tungsten, uranium, cerium, the rare earth metals, copper, beryllium, zinc, cadmium, mercury, aluminum, yttrium, gallium, indium, lanthanum, manganese, iron, cobalt, nickel, calcium, magnesium, strontium, and barium.

14. The method of claim 13 wherein the nanocrystals do not comprise at least one of Ce, Mg, Mn, Co, graphite, or graphene, or oxides of Ce, Mg, Mn, Co.

15. A method of reducing micro-pitting on lubricated surfaces of rolling bearings, gears, cams, lifters and multitude of other machine components, comprising lubricating the surfaces of said rolling bearings, gears, cams, lifters and multitude of other machine components with a lubricating oil comprising nanocrystals such that said micro-pitting is reduced as compared to lubricating the surfaces with the same lubricating oil which does not contain the nanocrystals.

16. A method of reducing micro-pitting on elastohydrodynamic (EHD) contacts found in rolling bearings, gears, cams, lifters and multitude of other machine

components, said method comprising lubricating said contacts with a lubricating oil comprising nanocrystals such that said micro-pitting is reduced as compared to lubricating the surfaces with the same lubricating oil which does not contain the nanocrystals.

17. The method of claim 15 or claim 16 wherein the nanocrystals are metal oxide nanocrystals.

18. The method of claim 15 or claim 16 or claim 17 wherein the nanocrystals are at least partially capped nanocrystals.

19. The method of any one of claims 15-18 wherein the nanocrystals comprise oxide of at least one metal selected from Groups 1 A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition metals, lanthanides, actinides, and mixtures thereof, such as metals including, but are not limited to, titanium, zirconium, hafnium, thorium, germanium, tin, niobium, tantalum, molybdenum, tungsten, uranium, cerium, the rare earth metals, copper, beryllium, zinc, cadmium, mercury, aluminum, yttrium, gallium, indium, lanthanum, manganese, iron, cobalt, nickel, calcium, magnesium, strontium, and barium.

20. The method of claim 19 wherein the nanocrystals do not comprise at least one of Ce, Mg, Mn, Co, graphite, or graphene, or oxides of Ce, Mg, Mn, Co.

21 . A method of reducing scuffing, scoring, galling, or seizure on lubricated surfaces of rolling bearings, gears, cams, lifters and multitude of other machine components, comprising lubricating the surfaces of said rolling bearings, gears, cams, lifters and multitude of other machine components with a lubricating oil comprising nanocrystals such that said scuffing, scoring, galling, or seizure is reduced as compared to lubricating the surfaces with the same lubricating oil which does not contain the nanocrystals.

22. A method of reducing scuffing, scoring, galling, or seizure on elastohydrodynamic (EHD) contacts found in rolling bearings, gears, cams, lifters and multitude of other machine components, said method comprising lubricating said contacts with a lubricating oil comprising nanocrystals such that said scuffing, scoring, galling, or seizure is reduced as compared to lubricating the surfaces with the same lubricating oil which does not contain the nanocrystals.

23. The method of claim 21 or claim 22 wherein the nanocrystals are metal oxide nanocrystals.

24. The method of claim 21 or claim 22 or claim 23 wherein the nanocrystals are at least partially capped nanocrystals.

25. The method of any one of claims 21 -24 wherein the nanocrystals comprise oxide of at least one metal selected from Groups 1 A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition metals, lanthanides, actinides, and mixtures thereof, such as metals including, but are not limited to, titanium, zirconium, hafnium, thorium, germanium, tin, niobium, tantalum, molybdenum, tungsten, uranium, cerium, the rare earth metals, copper, beryllium, zinc, cadmium, mercury, aluminum, yttrium, gallium, indium, lanthanum, manganese, iron, cobalt, nickel, calcium, magnesium, strontium, and barium.

26. The method of claim 25 wherein the nanocrystals do not comprise at least one of Ce, Mg, Mn, Co, graphite, or graphene, or oxides of Ce, Mg, Mn, Co.

27. The method of any one of claims 1 -25 wherein the lubricated surfaces are made of materials used or that could be used in machine surfaces, including but not limited to steels, copper, aluminum, magnesium, titanium, silicon, tungsten, and/or alloys, and/or ceramics, and/or oxides, and/or borides, and/or carbides, and/or nitrides, and/or mixtures thereof.

28. A method of improving protection against wear on lubricated surfaces of rolling bearings, gears, cams, lifters and multitude of other machine components comprising contacting the surfaces with a formulated oil having a viscosity in the range of 2.0 to 10,000 cSt at 40 degree C, said formulated oil having a composition comprising a major amount of a lubricating oil base stock and a minor amount of at least partially capped metal oxide nanocrystals; wherein said at least partially capped metal oxide nanocrystals are dispersed in said lubricating oil base stock; said at least partially capped metal oxide nanocrystals being present in an amount sufficient for the formulated oil to improve protection against wear as compared to the same formulated oil which does not contain said at least partially capped metal oxide nanocrystals.

29. The method of claim 28 wherein wear is abrasive wear.

30. The method of any one of claims 28-29 wherein the nanocrystals comprise oxide of at least one metal selected from Groups 1 A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition metals, lanthanides, actinides, and mixtures thereof, such as metals including, but are not limited to, titanium, zirconium, hafnium, thorium, germanium, tin, niobium, tantalum, molybdenum, tungsten, uranium, cerium, the rare earth metals, copper, beryllium, zinc, cadmium, mercury, aluminum, yttrium, gallium, indium, lanthanum, manganese, iron, cobalt, nickel, calcium, magnesium, strontium, and barium.

31 . The method of claim 30 wherein the nanocrystals do not comprise at least one of Ce, Mg, Mn, Co, graphite, or graphene, or oxides of Ce, Mg, Mn, Co.

32. A method of improving protection against pitting in bearings and/or gears

lubricated with a lubricating oil by using as the lubricating oil a formulated oil having a viscosity in the range of 2.0 to 10,000 cSt at 40 degree C, said formulated oil having a composition comprising a major amount of a lubricating oil base stock and a minor amount of at least partially capped metal oxide nanocrystals; wherein said at least partially capped metal oxide nanocrystals are dispersed in said lubricating oil base stock; said at least partially capped metal oxide nanocrystals being present in an amount sufficient for the formulated oil to improve protection against pitting as compared to the same formulated oil which does not contain said at least partially capped metal oxide nanocrystals.

33. The method of claim 32 wherein the nanocrystals comprise oxide of at least one metal selected from Groups 1A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition metals, lanthanides, actinides, and mixtures thereof, such as metals including, but are not limited to, titanium, zirconium, hafnium, thorium,

germanium, tin, niobium, tantalum, molybdenum, tungsten, uranium, cerium, the rare earth metals, copper, beryllium, zinc, cadmium, mercury, aluminum, yttrium, gallium, indium, lanthanum, manganese, iron, cobalt, nickel, calcium,

magnesium, strontium, and barium.

34. The method of claim 33 wherein the nanocrystals do not comprise at least one of Ce, Mg, Mn, Co, graphite, or graphene, or oxides of Ce, Mg, Mn, Co.

35. A method of improving protection against micro-pitting in bearings and/or gears lubricated with a lubricating oil by using as the lubricating oil a formulated oil having a viscosity in the range of 2.0 to 10,000 cSt at 40 degree C, said formulated oil having a composition comprising a major amount of a lubricating oil base stock and a minor amount of at least partially capped metal oxide nanocrystals; wherein said at least partially capped metal oxide nanocrystals are dispersed in said lubricating oil base stock; said at least partially capped metal oxide nanocrystals being present in an amount sufficient for the formulated oil to improve protection against micro-pitting as compared to the same formulated oil which does not contain said at least partially capped metal oxide nanocrystals.

36. The method of claim 35 wherein the nanocrystals comprise oxide of at least one metal selected from Groups 1 A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition metals, lanthanides, actinides, and mixtures thereof, such as metals including, but are not limited to, titanium, zirconium, hafnium, thorium, germanium, tin, niobium, tantalum, molybdenum, tungsten, uranium, cerium, the rare earth metals, copper, beryllium, zinc, cadmium, mercury, aluminum, yttrium, gallium, indium, lanthanum, manganese, iron, cobalt, nickel, calcium,

magnesium, strontium, and barium.

37. The method of claim 36 wherein the nanocrystals do not comprise at least one of Ce, Mg, Mn, Co, graphite, or graphene, or oxides of Ce, Mg, Mn, Co.

38. A method of improving protection against scuffing, scoring, galling, or seizure in bearings and/or gears lubricated with a lubricating oil by using as the lubricating oil a formulated oil having a viscosity in the range of 2.0 to 10,000 cSt at 40 degree C, said formulated oil having a composition comprising a major amount of a lubricating oil base stock and a minor amount of at least partially capped metal oxide nanocrystals; wherein said at least partially capped metal oxide nanocrystals are dispersed in said lubricating oil base stock; said at least partially capped metal oxide nanocrystals being present in an amount sufficient for the formulated oil to improve protection against scuffing, scoring, galling, or seizure as compared to the same formulated oil which does not contain said at least partially capped metal oxide nanocrystals.

39. The method of claim 38 wherein the nanocrystals comprise oxide of at least one metal selected from Groups 1 A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition metals, lanthanides, actinides, and mixtures thereof, such as metals including, but are not limited to, titanium, zirconium, hafnium, thorium,

germanium, tin, niobium, tantalum, molybdenum, tungsten, uranium, cerium, the rare earth metals, copper, beryllium, zinc, cadmium, mercury, aluminum, yttrium, gallium, indium, lanthanum, manganese, iron, cobalt, nickel, calcium,

magnesium, strontium, and barium.

40. The method of claim 39 wherein the nanocrystals do not comprise at least one of Ce, Mg, Mn, Co, graphite, or graphene, or oxides of Ce, Mg, Mn, Co.

41 . The method of claim 28-40 wherein the improved protection is demonstrated in a test machine or rig, such as a MPR (micro-pitting rig), MTM (mini-traction machine) or HFRR (high frequency reciprocating rig) [PCS Instruments, 78 Stanley Gardens, London, W3 7SZ, United Kingdom], which simulates gear contacts by using appropriately designed test specimens and can measure, for example, the vibration or shock pulses that occurs as a result of pitting and micro-pitting, the comparison of surface material loss due to wear, and/or the friction coefficient change or rapid change as a result of scuffing, scoring, galling or seizure, when the formulated oil containing the at least partially capped metal oxide nanocrystals is compared with the same formulated oil not containing the at least partially capped metal oxide nanocrystals.

42. The method of claim 41 wherein the elastohydrodynamic contact stresses of the test machine or rig, such as a MPR, range from 100 MPa to 10 GPa.

43. The method of claim 41 or claim 42 wherein the test machine or rig, such as a MPR, is operated at a controlled temperature in the temperature range of -25C to 200 C.

44. The method of any one of claims 41 -43 wherein the mean rolling speed of the test specimens ranges from 1 mm/s to 20 m/s and the slide-roll ratio ranges from zero to infinity.

45. The method of any of claims 41 -44 wherein the test specimens are made of materials of a type used or could be used in machine surfaces, such as are present in rolling bearings, gears, cams and lifters, including but not limited to steels, copper, aluminum, magnesium, titanium, silicon, tungsten, and/or alloys, and/or ceramics, and/or oxides, and/or borides, and/or carbides, and/or nitrides, and/or mixtures thereof.

46. The method of any one of claims 1 -45 wherein the lubricated surfaces of rolling bearings, gears, cams, lifters and multitude of other machine surfaces are made of materials used or that could be used in machine surfaces, including but not limited to steels, copper, aluminum, magnesium, titanium, silicon, tungsten, and/or alloys, and/or ceramics, and/or oxides, and/or borides, and/or carbides, and/or nitrides, and/or mixtures thereof.

47. The method of any one of claims 1 -46 wherein the hardness of the materials range from 100 MPa to 10 GPa.

48. The method of any one of claims 28-47 wherein the base oil comprises a Group I, Group II, Group III, Group IV or Group V base oil.

49. The method of claims 28-48 wherein said formulated oil comprises phosphorous and/or a phosphorous containing compound of a form and/or in an amount sufficient to form a protective film at a temperature lower than in the same formulated oil not containing said phosphorous and/or a phosphorous containing compound.