Abstract:
Nanoparticle compositions and greaseless coatings are disclosed, including, for example, a greaseless lubricant nanoparticle coating on drill pipe threads. The lubricant coating may be multifunctional, including, for example, anti-corrosives. The coating may be a spray, or otherwise.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation application and claims the benefit of the filing date under 35 U.S.C. §120 of U.S. patent application Ser. No. 13/921,640, filed on Jun. 19, 2013. U.S. patent application Ser. No. 13/921,640 is a continuation application and claims the benefit of the filing date under 35 U.S.C. §120 of U.S. patent application Ser. No. 12/160,758, filed on Sep. 2, 2008, now U.S. Pat. No. 8,492,319 which issued on Jul. 23, 2013. U.S. patent application Ser. No. 12/160,758 is a national stage filing under 35 U.S.C. §371 and claims priority to International Application No. PCT/US2007/060506, filed on Jan. 12, 2007. International Application No. PCT/US2007/060506 claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 60/758,307, filed on Jan. 12, 2006. The contents of U.S. patent application Ser. No. 13/921,640, U.S. patent application Ser. No. 12/160,758, International Application No. PCT/US2007/060506, and U.S. Provisional Patent Application No. 60/758,307 are hereby incorporated by reference in their entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with U.S. government support under grant number NSF/DMI 0115532 awarded in part by the National Science Foundation. The U.S. government has certain rights in the invention. 
    
    
     BACKGROUND 
     Over the years, considerable effort has been expended to develop nanostructures that can be used as lubricants, coatings, or delivery mechanisms. New ways to improve nanoparticle compositions, their method of manufacture, and their use are sought. 
     SUMMARY 
     In one aspect, a composition is described, comprising solid lubricant nanoparticles and an organic medium. 
     In another aspect, nanoparticles comprising a layered material are disclosed. 
     In a further aspect, a method of producing a nanoparticle comprising milling layered materials is provided. 
     In yet another aspect, a method of making a lubricant is disclosed, in which the method comprises milling layered materials to form nanoparticles and incorporating the nanoparticles into a base to form a lubricant. 
     Other aspects will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a method of producing solid lubricant nanoparticles. 
         FIG. 2  is a diagram illustrating one method of preparing nanoparticle based lubricants. 
         FIG. 3  shows transmission electron microscopy (TEM) micrographs of molybdenum disulfide particles. Panel (A) shows molybdenum disulfide as it is available, typically from about a few microns to submicron size. Panel (B) shows molybdenum disulfide that has been ball milled in air for 48 hours. Panel (C) is a high resolution electron microscopy image that shows molybdenum disulfide that has been ball milled in air for 48 hours. Panel (D) is a high-resolution transmission electron microscopy (HRTEM) image that shows molybdenum disulfide that has been ball milled in air for 48 hours followed by ball milling in oil for 48 hours. 
         FIG. 4  is a graph showing XRD spectra of molybdenum disulfide particles. Line (A) is the XRD spectra for molybdenum disulfide that has been ball milled in air for 48 hours followed by ball milling in oil for 48 hours. Line (B) is the XRD spectra for molybdenum disulfide that has been ball milled in air for 48 hours. Line (C) is the XRD spectra for molybdenum disulfide that has not been ball milled. 
         FIG. 5  is a graph showing XPS spectra of molybdenum disulfide particles in which the carbon peak for molybdenum disulfide that has not been ball milled is shown, as well as the carbon peak for molybdenum disulfide that has been ball milled in air for 48 hours, followed by ball milling in oil for 48 hours. 
         FIGS. 6(A)-6(D)  show graphs and bar charts depicting tribological test data for different additives in paraffin oil.  FIG. 6(A)  shows the average wear scar diameter for a base oil (paraffin oil), paraffin oil with micron sized MoS 2 , paraffin oil with MoS 2  that was milled in air for 48 hours, and paraffin oil with MoS 2  that was milled in air for 48 hours followed by milling in canola oil for 48 hours.  FIG. 6(B)  shows the load wear index for paraffin oil without a nanoparticle additive, paraffin oil with micron sized MoS 2 , paraffin oil with MoS 2  that was milled in air for 48 hours, and paraffin oil with MoS 2  that was milled in air for 48 hours followed by milling in canola oil for 48 hours.  FIG. 6(C)  shows the coefficient of friction for paraffin oil without a nanoparticle additive, paraffin oil with micron sized MoS 2  (c-MoS 2 ), paraffin oil with MoS 2  that was milled in air for 48 hours (d-MoS 2 ), and paraffin oil with MoS 2  that was milled in air for 48 hours followed by milling in canola oil for 48 hours (n-MoS 2 ).  FIG. 6(D)  shows the extreme pressure data for paraffin oil with micron sized MoS 2  (c-MoS 2 ), paraffin oil with MoS 2  that was milled in air for 48 hours (d-MoS 2 ), and paraffin oil with MoS 2  that was milled in air for 48 hours followed by milling in canola oil for 48 hours (n-MoS 2 ); in each test the solid lubricant nanoparticle additive was present in the amount of 1% by weight. 
         FIG. 7  is a TEM image showing the architecture of molybdenum disulfide nanoparticles (15-70 nm average size). Panel (a) shows the close caged dense oval shaped architecture of molybdenum disulfide nanoparticles that have been ball milled in air for 48 hours. Panel (b) shows the open ended oval shaped architecture of molybdenum disulfide nanoparticles that have been ball milled in air for 48 hours followed by ball milling in canola oil for 48 hours. 
         FIG. 8  is a graph depicting a comparison of wear scar diameters for different additives in paraffin oil. One additive is crystalline molybdenum disulfide (c-MoS 2 ). Another is molybdenum disulfide nanoparticles that were ball milled in air (n-MoS 2 ). Another additive is molybdenum disulfide nanoparticles that were ball milled in air followed by ball milling in canola oil and to which a phospholipid emulsifier was added (n-MoS 2 +Emulsifier). 
         FIG. 9  shows photographs and graphs produced using energy dispersive x-ray analysis (EDS) depicting the chemical analysis of wear scar diameters in four-ball tribological testing for nanoparticle based lubricants. Panel (a) shows paraffin oil without any nanoparticle composition additive. Panel (b) shows paraffin oil with molybdenum disulfide nanoparticles that have been ball milled in air for 48 hours followed by ball milling in oil for 48 hours and treated with a phospholipid emulsifier. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     Any numerical range recited herein includes all values from the lower value to the upper value. For example, if a concentration range is stated as 1% to 50%, it is intended that values such as 2% to 40%, 10% to 30%, or 1% to 3%, etc., are expressly enumerated in this specification. These are only examples of what is specifically intended, and all possible combinations of numerical values between and including the lowest value and the highest value enumerated are to be considered to be expressly stated in this application. 
     Herein described are compositions and methods for making compositions comprising solid lubricant nanoparticles and an organic medium. Also described are nanoparticles comprising layered materials. The nanoparticles may be solid lubricant nanoparticles. The nanoparticles may be made from starting materials or solid lubricant starting materials. Examples of solid lubricants may include, but are not limited to, layered materials, suitably chalcogenides, more suitably, molybdenum disulphide, tungsten disulphide, or a combination thereof. Another suitable layered material is graphite or intercalated graphite. Other solid lubricants that may be used alone or in combination with the layered materials are polytetrafluoroethylene (Teflon®), boron nitride (suitably hexagonal boron nitride), soft metals (such as silver, lead, nickel, copper), cerium fluoride, zinc oxide, silver sulfate, cadmium iodide, lead iodide, barium fluoride, tin sulfide, zinc phosphate, zinc sulfide, mica, boron nitrate, borax, fluorinated carbon, zinc phosphide, boron, or a combination thereof. Fluorinated carbons may be, without limitation, carbon-based materials such as graphite which has been fluorinated to improve its aesthetic characteristics. Such materials may include, for example, a material such as CF x  wherein x ranges from about 0.05 to about 1.2. Such a material is produced by Allied Chemical under the trade name Accufluor. 
     The methods may include milling a solid lubricant feed. In one embodiment, the solid lubricant feed may be capable of being milled to particles comprising an average dimension of about 500 nanometers (submicron size) to about 10 nanometers. Suitably, the particles may have an average particle dimension of less than or equal to about 500 nanometers, suitably less than or equal to about 100 nanometers, suitably less than or equal to about 80 nanometers, and more suitably less than or equal to about 50 nanometers. Alternatively, the ball milling may result in milled solid lubricant particles comprising a mixture, the mixture comprising particles having an average particle dimension of less than or equal to about 500 nanometers, plus larger particles. Milling may include, among other things, ball milling and chemo mechanical milling. Examples of ball milling may include dry ball milling, wet ball milling, and combinations thereof. Ball milling may refer to an impaction process that may include two interacting objects where one object may be a ball, a rod, 4 pointed pins (jack shape), or other shapes. Chemo mechanical milling may refer to an impaction process that may form a complex between an organic medium and a nanoparticle. As a result of chemo mechanical milling, the organic medium may coat, encapsulate, or intercalate the nanoparticles. 
     In another embodiment, the solid lubricant feed may be dry milled and then wet milled. An emulsifier may be mixed with a base and added to the wet milled particles. Dry milling may refer to particles that have been milled in the presence of a vacuum, a gas, or a combination thereof. Wet milling may refer to particles that have been milled in the presence of a liquid. 
     The solid lubricant nanoparticle composition may further comprise an organic medium. Examples of organic mediums include, but are not limited to, oil mediums, grease mediums, alcohol mediums, or combinations thereof. Specific examples of organic mediums include, but are not limited to, composite oil, canola oil, vegetable oils, soybean oil, corn oil, ethyl and methyl esters of rapeseed oil, distilled monoglycerides, monoglycerides, diglycerides, acetic acid esters of monoglycerides, organic acid esters of monoglycerides, sorbitan, sorbitan esters of fatty acids, propylene glycol esters of fatty acids, polyglycerol esters of fatty acids, n-hexadecane, hydrocarbon oils, phospholipids, or a combination thereof. Many of these organic media may be environmentally acceptable. 
     The composition may contain emulsifiers, surfactants, or dispersants. Examples of emulsifiers may include, but are not limited to, emulsifiers having a hydrophilic-lipophilic balance (HLB) from about 2 to about 7; alternatively, a HLB from about 3 to about 5; or alternatively, a HLB of about 4. Other examples of emulsifiers may include, but are not limited to, lecithins, soy lecithins, phospholipids lecithins, detergents, distilled monoglycerides, monoglycerides, diglycerides, acetic acid esters of monoglycerides, organic acid esters of monoglycerides, sorbitan esters of fatty acids, propylene glycol esters of fatty acids, polyglycerol esters of fatty acids, compounds containing phosphorous, compounds containing sulfur, compounds containing nitrogen, or a combination thereof. 
     A method of making a lubricant is described. The composition may be used as an additive dispersed in a base. Examples of bases may include, but are not limited to, oils, greases, plastics, gels, sprays, or a combination thereof. Specific examples of bases may include, but are not limited to, hydrocarbon oils, vegetable oils, corn oil, peanut oil, canola oil, soybean oil, mineral oil, paraffin oils, synthetic oils, petroleum gels, petroleum greases, hydrocarbon gels, hydrocarbon greases, lithium based greases, fluoroether based greases, ethylenebistearamide, waxes, silicones, or a combination thereof. 
     Described herein is a method of lubricating or coating an object that is part of an end application with a composition comprising at least one of solid lubricant nanoparticles and an organic medium. Further described is a method of lubricating an object by employing the composition comprising solid lubricant nanoparticles and an organic medium as a delivery mechanism. 
     Disclosed herein are compositions and methods of preparing nanoparticle based lubricants that, among various advantages, display enhanced dispersion stability and resistance to agglomeration.  FIG. 1  illustrates a method of preparing nanoparticle based lubricants or compositions. A solid lubricant feed is introduced via line  210  to a ball milling processor  215 . Ball milling is carried out in the processor  215  and the solid lubricant feed is milled to comprise particles having an average particle dimension of less than or equal to about 500 nanometers, suitably less than or equal to about 100 nanometers, suitably less than or equal to about 80 nanometers, and more suitably less than or equal to about 50 nanometers. Alternatively, the ball milling may result in milled solid lubricant particles comprising a mixture, the mixture comprising particles having an average particle dimension of less than or equal to about 500 nanometers, plus larger particles. The ball milling may be high energy ball milling, medium energy ball milling, or combinations thereof. Additionally, in various embodiments the ball milling may be carried out in a vacuum, in the presence of a gas, in the presence of a liquid, in the presence of a second solid, or combinations thereof. The nanoparticle composition may be removed from the processor via line  220 . The nanoparticle composition may be a nanoparticle based lubricant. 
     In alternative embodiments, the ball milling may comprise a first ball milling and at least one more subsequent ball millings, or ball milling and/or other processing as appropriate. Suitably, the ball milling may comprise dry milling followed by wet milling.  FIG. 2  illustrates a further method  100  of preparing nanoparticle based lubricants where dry milling is followed by wet milling. Feed  110  introduces a solid lubricant feed into a ball milling processor  115  where dry ball milling, such as in a vacuum or in air, reduces the solid lubricant feed to particles having an average dimension of the size described above. Line  120  carries the dry milled particles to a wet milling processor  125 . Via line  160  the dry milled particles are combined with a composite oil or an organic medium prior to entering the wet milling processor  125 . Alternatively, the organic medium and dry milled particles may be combined in the wet milling processor  125 . In further alternative embodiments (not shown), the dry milling and wet milling may be carried out in a single processor where the organic medium is supplied to the single processor for wet milling after initially carrying out dry milling. In other alternative embodiments, the balls in the ball milling apparatus may be coated with the organic medium to incorporate the organic medium in the solid lubricant nanoparticles. 
     After wet milling, line  130  carries the wet milled particles to a container  135 , which may be a sonication device. Alternatively, line  130  may carry a mixture comprising solid lubricant nanoparticles, organic medium, and a complex comprising the solid lubricant nanoparticles combined with an organic medium. 
     In another embodiment, prior to introduction of the wet milled particles into the container  135 , a base may be fed to the container  135  via line  150 . Alternatively, the base may be supplied to the wet milling processor  125  and the mixing, which may include sonicating, may be carried out in the wet milling processor  125 . In such embodiments the solid lubricant nanoparticle composition may be employed as an additive and dispersed in the base. A base may be paired with a solid lubricant nanoparticle composition according to the ability of the base and the solid lubricant nanoparticle composition to blend appropriately. In such cases the solid lubricant nanoparticle composition may enhance performance of the base. 
     In a further embodiment, an emulsifier may be mixed with the base. Emulsifiers may further enhance dispersion of the solid lubricant nanoparticle composition in the base. The emulsifier may be selected to enhance the dispersion stability of a nanoparticle composition in a base. An emulsifier may also be supplied to the container  135  via line  140 . In many embodiments, the emulsifier and base are combined in the container  135  prior to introduction of the wet milled particles. Prior mixing of the emulsifier with the base may enhance dispersion upon addition of complexes of solid lubricant nanoparticles and organic medium and/or solid lubricant nanoparticles by homogeneously dispersing/dissolving the complexes/nanoparticles. In some embodiments, the mixing of the emulsifier and base may comprise sonicating. Alternatively, the emulsifier may be supplied to the wet milling processor  125  and the mixing, which may include sonicating, may be carried out in the wet milling processor  125 . The lubricant removed from the container  135  via line  120  may be a blend comprising the wet milled particles, organic medium, and base. The blend may further comprise an emulsifier. In other alternative embodiments, additives may be added to the nanoparticle based lubricant during interaction with a mating surface. 
     In a further embodiment, antioxidants or anticorrosion agents may be milled with the solid lubricant nanoparticles. Examples of antioxidants include, but are not limited to, hindered phenols, alkylated phenols, alkyl amines, aryl amines, 2,6-di-tert-butyl-4-methylphenol, 4,4′-di-tert-octyldiphenylamine, tert-Butyl hydroquinone, tris(2,4-di-tert-butylphenyl)phosphate, phosphites, thioesters, or a combination thereof. Examples of anticorrosion agents include, but are not limited to, alkaline-earth metal bisalkylphenolsulphonates, dithiophosphates, alkenylsuccinic acid half-amides, or a combination thereof. In another embodiment, biocidals may be milled with the solid lubricant nanoparticles. Examples of biocidals may include, but are not limited to, alkyl or kydroxylamine benzotriazole, an amine salt of a partial alkyl ester of an alkyl, alkenyl succinic acid, or a combination thereof. 
     In yet another embodiment, further processing of wet milled particles may comprise removal of oils that are not a part of a complex with the solid lubricant particles. Such methods may be suitable for applications that benefit from use of dry particles of solid lubricant, such as coating applications. Oil and/or other liquids can be removed from wet milled particles to produce substantially dry solid lubricant particles and complexes. Such wet milling followed by drying may produce a solid lubricant with reduced tendency to agglomerate. In specific embodiments, an agent, such as acetone, can be added that dissolves oils that are not a part of a complex, followed by a drying process such as supercritical drying, to produce a substantially dry solid lubricant comprising particles treated by milling in an organic medium. 
     Ball milling conditions may vary and, in particular, conditions such as temperature, milling time, and size and materials of the balls and vials may be manipulated. In various embodiments, ball milling may be carried out from about 12 hours to about 50 hours, suitably from about 36 hours to about 50 hours, suitably from about 40 hours to about 50 hours, and more suitably at about 48 hours. Suitably, ball milling is conducted at room temperature. The benefits of increasing milling time may comprise at least one of increasing the time for the organic medium and solid lubricant nanoparticles to interact; and producing finer sizes, better yield of nanoparticles, more uniform shapes, and more passive surfaces. An example of ball milling equipment suitable for carrying out the described milling includes the SPEX CertiPrep model 8000D, along with hardened stainless steel vials and hardened stainless steel grinding balls, but any type of ball milling apparatus may be used. In one embodiment, a stress of 600-650 MPa, a load of 14.9 N, and a strain of 10 −3 -10 −4  per sec may be used. 
     The proportions of the components in a nanoparticle based lubricant may contribute to performance of the lubricant, such as the lubricants dispersion stability and ability to resist agglomeration. In wet milling, suitable ratios of solid lubricant nanoparticles to organic medium may be about 1 part particles to about 4 parts organic medium by weight, suitably, about 1 part particles to about 3 parts organic medium by weight, suitably, about 3 parts particles to about 8 parts organic medium by weight, suitably, about 2 parts particles to about 4 parts organic medium by weight, suitably, about 1 part particles to about 2 parts organic medium by weight, and suitably, about 1 part particles to about 1.5 parts organic medium by weight. 
     Suitable ratios of organic medium to emulsifier in a lubricant including the solid lubricant nanoparticles may be about 1 part organic medium to less than or equal to about 1 part emulsifier, suitably, about 1 part organic medium to about 0.5 parts emulsifier by weight, or suitably, from about 0.4 to about 1 part emulsifier for about 1 part organic medium by weight. 
     The amount of solid lubricant nanoparticle composition (by weight) sonicated or dispersed in the base may be from about 0.25% to about 5%, suitably 0.5% to about 3%, suitably 0.5% to about 2%, and more suitably 0.75% to about 2%. 
     The amount of emulsifier (by weight) sonicated or dissolved in the base, depending on the end application, shelf-life, and the like, may be from about 0.5% to about 10%, suitably from about 4% to about 8%, suitably from about 5% to about 6%, and suitably, from about 0.75% to about 2.25%. 
     The solid lubricant nanoparticle composition may be used, without limitation, as lubricants, coatings, delivery mechanisms, or a combination thereof. The solid lubricant nanoparticle composition may be used, without limitation, as an additive dispersed in a base oil. The composition may also be used, without limitation, to lubricate a boundary lubrication regime. A boundary lubrication regime may be a lubrication regime where the average oil film thickness may be less than the composite surface roughness and the surface asperities may come into contact with each other under relative motion. During the relative motion of two surfaces with lubricants in various applications, three different lubrication stages may occur, and the boundary lubrication regime may be the most severe condition in terms of temperature, pressure and speed. Mating parts may be exposed to severe contact conditions of high load, low velocity, extreme pressure (for example, 1-2 GPa), and high local temperature (for example, 150-300 degrees C.). The boundary lubrication regime may also exist under lower pressures and low sliding velocities or high temperatures. In the boundary lubrication regime, the mating surfaces may be in direct physical contact. The composition may further be used, without limitation, as a lubricant or coating in machinery applications, manufacturing applications, mining applications, aerospace applications, automotive applications, pharmaceutical applications, medical applications, dental applications, cosmetic applications, food product applications, nutritional applications, health related applications, bio-fuel applications or a combination thereof. Specific examples of uses in end applications include, without limitation, machine tools, bearings, gears, camshafts, pumps, transmissions, piston rings, engines, power generators, pin-joints, aerospace systems, mining equipment, manufacturing equipment, or a combination thereof. Further specific examples of uses may be, without limitation, as an additive in lubricants, greases, gels, compounded plastic parts, pastes, powders, emulsions, dispersions, or combinations thereof. The composition may also be used as a lubricant that employs the solid lubricant nanoparticle composition as a delivery mechanism in pharmaceutical applications, medical applications, dental applications, cosmetic applications, food product applications, nutritional applications, health related applications, bio-fuel applications, or a combination thereof. The various compositions and methods may also be used, without limitation, in hybrid inorganic-organic materials. Examples of applications using inorganic-organic materials, include, but are not limited to, optics, electronics, ionics, mechanics, energy, environment, biology, medicine, smart membranes, separation devices, functional smart coatings, photovoltaic and fuel cells, photocatalysts, new catalysts, sensors, smart microelectronics, micro-optical and photonic components and systems for nanophotonics, innovative cosmetics, intelligent therapeutic vectors that combined targeting, imaging, therapy, and controlled release of active molecules, and nanoceramic-polymer composites for the automobile or packaging industries. 
     In some embodiments, the ball milling process may create a close caged dense oval shaped architecture (similar to a football shape or fullerene type architecture). This may occur when molybdenum disulphide is milled in a gas or vacuum. Panel (a) of  FIG. 7  shows the close caged dense oval shaped architecture of molybdenum disulphide nanoparticles that have been ball milled in air for 48 hours. 
     In other embodiments, the ball milling process may create an open ended oval shaped architecture (similar to a coconut shape) of molybdenum disulphide nanoparticles which are intercalated and encapsulated with an organic medium and phospholipids. This may occur when molybdenum disulphide is milled in a gas or vacuum followed by milling in an organic medium. Panel (b) of  FIG. 7  shows the open ended oval shaped architecture of molybdenum disulphide nanoparticles that have been ball milled in air for 48 hours followed by ball milling in canola oil for 48 hours. 
     As shown in the examples, the tribological performance of the nanoparticle based lubricant may be improved. The tribological performance may be measured by evaluating different properties. An anti-wear property may be a lubricating fluid property that has been measured using the industry standard Four-Ball Wear (ASTM D4172) Test. The Four-Ball Wear Test may evaluate the protection provided by an oil under conditions of pressure and sliding motion. Placed in a bath of the test lubricant, three fixed steel balls may be put into contact with a fourth ball of the same grade in rotating contact at preset test conditions. Lubricant wear protection properties may be measured by comparing the average wear scars on the three fixed balls. The smaller the average wear scar, the better the protection. Extreme pressure properties may be lubricating fluid properties that have been measured using the industry standard Four-Ball Wear (ASTM D2783) Test. This test method may cover the determination of the load-carrying properties of lubricating fluids. The following two determinations may be made: 1) load-wear index (formerly Mean-Hertz load) and 2) weld load (kg). The load-wear index may be the load-carrying property of a lubricant. It may be an index of the ability of a lubricant to minimize wear at applied loads. The weld load may be the lowest applied load in kilograms at which the rotating ball welds to the three stationary balls, indicating the extreme pressure level that the lubricants can withstand. The higher the weld point scores and load wear index values, the better the anti-wear and extreme pressure properties of a lubricant. The coefficient of friction (COF) may be a lubricating fluid property that has been measured using the industry standard Four-Ball Wear (ASTM D4172) Test. COF may be a dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together. The coefficient of friction may depend on the materials used. For example, ice on metal has a low COF, while rubber on pavement has a high COF. A common way to reduce friction may be by using a lubricant, such as oil or water, which is placed between two surfaces, often dramatically lessening the COF. 
     The composition may have a wear scar diameter of about 0.4 mm to about 0.5 mm. The composition may have a COF of about 0.06 to about 0.08. The composition may have a weld load of about 150 kg to about 350 kg. The composition may have a load wear index of about 20 to about 40. The values of these tribological properties may change depending on the amount of solid lubricant nanoparticle composition sonicated or dissolved in the base. 
     Various features and aspects of the invention are set forth in the following examples, which are intended to be illustrative and not limiting. 
     EXAMPLES 
     Example 1 
     Ball milling was performed in a SPEX 8000D machine using hardened stainless steel vials and balls. MoS 2  (Alfa Aesar, 98% pure, 700 nm average primary particle size) and canola oil (Crisco) were used as the starting materials in a ratio of 1 part MoS 2  (10 grams) to 2 parts canola oil (20 grams). The ball to powder weight ratio was 2 to 1. MoS 2  was ball milled for 48 hours in air followed by milling in canola oil for 48 hrs at room temperature. The nanoparticles were about 50 nm after ball milling. Table 1 summarizes milling conditions and resultant particle morphologies. It was observed that there was a strong effect of milling media on the shape of the ball milled nanoparticles. Dry milling showed buckling and folding of the planes when the particle size was reduced from micron size to nanometer size. However, the dry milling condition used here produced micro clusters embedding several nanoparticles. On the other hand, wet milling showed no buckling but saw de-agglomeration. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Milling conditions and parametric effect on particle size and shape 
               
             
          
           
               
                   
                 Shape of the particles 
                 Shape of the clusters 
               
               
                   
                   
               
             
          
           
               
                 Dry Milling 
                   
                   
               
               
                 12 hours 
                 Plate-like with sharp edges 
                 Sharp and irregular 
               
               
                 24 hours 
                 Plate-like with round edges 
                 More or less rounded 
               
               
                 48 hours 
                 Spherical 
                 Globular clusters 
               
               
                 Wet Milling 
               
               
                 12 hours 
                 Thin plates with sharp edges 
                 Thing plates with sharp 
               
               
                   
                   
                 edges 
               
               
                 24 hours 
                 Thin plates with sharp edges 
                 Thin plates with sharp 
               
               
                   
                   
                 edges 
               
               
                 48 hours 
                 Thin plates with sharp edges 
                 Thin plates with sharp 
               
               
                   
                   
                 edges 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Effect of milling media on resultant size (starting size sub-micron) 
               
               
                 shape, and agglomeration of particles 
               
             
          
           
               
                   
                   
                   
                   
                 Dry milled 
               
               
                 Properties 
                 Dry 
                 Alcohol 
                 Oil 
                 and oil milled 
               
               
                   
               
               
                 Clusters size (nm) 
                 100 
                 300 
                 200 
                 100 
               
               
                 Particle size (nm) 
                  30 
                  80 
                  80 
                  30 
               
               
                 Agglomeration 
                 High 
                 Very less 
                 Very less 
                 Very less 
               
               
                 Shape of the 
                 Spherical 
                 Platelet 
                 Platelet 
                 Spherical 
               
               
                 particles 
               
               
                   
               
             
          
         
       
     
       FIG. 3  shows TEM micrographs of the as-available (700 nm), air milled, and hybrid milled (48 hrs in air medium followed by 48 hours in oil medium) MoS 2  nanoparticles. Panel (A) represents micron-sized particle chunks of the as-available MoS 2  sample off the shelf. These micrographs, particularly panel (B), represent agglomerates of lubricant nanoparticles when milled in the air medium. Panel (B) clearly demonstrates size reduction in air milled MoS 2 . Higher magnification (circular regions) revealed formation of the disc shaped nanoparticles after milling in the air medium. From panels (C) and (D) it may be concluded that the particle size was reduced to less than 30 nm after milling in air and hybrid conditions. Regardless of the occasionally observed clusters, the average size of the clusters is less than or equal to 200 nm. 
     Hybrid milled samples were dispersed in paraffin oil (from Walmart) and remained suspended without settling. However, the dispersion was not uniform after a few weeks. To stabilize the dispersion and extend the anti-wear properties, phospholipids were added. Around 2% by weight of soy lecithin phospholipids (from American Lecithin) was added in the base oil. 
       FIGS. 4 and 5  show the XRD and XPS spectra of MoS 2  before and after ball milling, respectively. XRD spectra revealed no phase change as well as no observable amorphization in the MoS 2  after milling. This observation is consistent with the continuous platelets observed throughout the nanoparticle matrix in TEM analysis for milled material. Broadening of peaks (FWHM) was observed in XRD spectra of MoS 2  ball milled in air and hybrid media, respectively. The peak broadening may be attributed to the reduction in particle size. The estimated grain size is 6 nm. This follows the theme of ball milling where clusters consist of grains and sub-grains of the order of 10 nm. XPS analysis was carried out to study the surface chemistry of the as-available and hybrid milled MoS 2  nanoparticles. As shown in  FIG. 5 , a carbon (C) peak observed at 285 eV in the as-available MoS 2  sample shifted to 286.7 eV. Bonding energies of 286 eV and 287.8 eV correspond to C—O and C═O bond formation, respectively. The observed binding energy level may demonstrate that a thin layer containing mixed C—O &amp; C═O groups enfolds the MoS 2  particles. 
     Preliminary tribological tests on the synthesized nanoparticles were performed on a four-ball machine by following ASTM 4172. The balls used were made of AISI 52100 stainless steel and were highly polished. Four Ball Wear Scar measurements using ASTM D4172 were made under the following test conditions: 
                                                 Test Temperature, ° C.   75 (±1.7)           Test Duration, min   60 (±1)             Spindle Speed, rpm   1,200 (±60)             Load, kg   40 (±0.2)                        
Wear scar diameter (WSD, mm) of each stationary ball was quantified in both vertical and horizontal directions. The average value of WSD from 3 independent tests was reported within ±0.03 mm accuracy.
 
     Four Ball Extreme Pressure measurements using ASTM D2783 were made under the following test conditions: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Test Temperature, ° C. 
                 23 
               
               
                   
                 Test Duration, min 
                 60 (±1) 
               
               
                   
                 Spindle Speed, rpm 
                 1,770 (±60)   
               
               
                   
                 Load, kg 
                 Varies, 10-sec/stage 
               
               
                   
                 Ball Material 
                 AISI-E52100 
               
               
                   
                 Hardness 
                 64-66 
               
               
                   
                 Grade 
                 25EP 
               
               
                   
                   
               
             
          
         
       
     
     Three different particles (in w/w ratio) were evaluated for their anti-wear properties as additives in paraffin oil.  FIG. 6(A)  shows the average wear scar measurements for paraffin oil without a nanoparticle additive, paraffin oil with micron sized MoS 2 , paraffin oil with MoS 2  that was milled in air for 48 hours, and paraffin oil with MoS 2  that was milled in air for 48 hours followed by milling in canola oil for 48 hours.  FIG. 6(B)  shows the load wear index for paraffin oil without a nanoparticle additive, paraffin oil with micron sized MoS 2 , paraffin oil with MoS 2  that was milled in air for 48 hours, and paraffin oil with MoS 2  that was milled in air for 48 hours followed by milling in canola oil for 48 hours.  FIG. 6(C)  shows the COF for paraffin oil without a nanoparticle additive, paraffin oil with micron sized MoS 2 , paraffin oil with MoS 2  that was milled in air for 48 hours, and paraffin oil with MoS 2  that was milled in air for 48 hours followed by milling in canola oil for 48 hours.  FIG. 6(D)  shows the extreme pressure data for paraffin oil with micron sized MoS 2 , paraffin oil with MoS 2  that was milled in air for 48 hours, and paraffin oil with MoS 2  that was milled in air for 48 hours followed by milling in canola oil for 48 hours. In each test the nanoparticle additive was present in the amount of 1% by weight. 
     
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
               
               
                 Test data from nanoparticle composition additive in base oil 
               
             
          
           
               
                   
                 Solid Lubricant 
               
             
          
           
               
                   
                 Four Ball Tests 
                   
                   
               
               
                   
                 at 40 kg Load 
                 Four Ball Extreme Pressure 
               
               
                   
                 (ASTM D4172) 
                 (ASTM D-2783) 
               
             
          
           
               
                 All dispersions diluted to x % 
                 WSD 
                   
                 Weld Load 
                 Load Wear 
                 FIG. 6(A) 
               
               
                 by wt. in reference base oil 
                 (mm) 
                 COF 
                 (kg) 
                 Index 
                 and 6(B) 
               
               
                   
               
               
                 Paraffin oil 
                 1.033 
                 0.155 
                 126 
                 12.1 
                 A 
               
               
                 Nanoparticles of MoS 2  without 
                 1.012 
                 0.102 
                 100 
                 16.1 
                 B 
               
               
                 organic medium (0.5%) 
               
               
                 Nanoparticles of MoS 2  without 
                 0.960 
                 0.114 
                 126 
                 20.8 
                 C 
               
               
                 organic medium (1.0%) 
               
               
                 Nanoparticles of MoS 2  without 
                 0.915 
                 0.098 
                 126 
                 22.0 
                 D 
               
               
                 organic medium (1.5%) 
               
               
                 Conventional available micro 
                 1.009 
                 0.126 
                 160 
                 22.0 
                 E 
               
               
                 particles (0.5%) 
               
               
                 Conventional available micro 
                 0.948 
                 0.091 
                 126 
                 19.1 
                 F 
               
               
                 particles (1.0%) 
               
               
                 Conventional available micro 
                 0.922 
                 0.106 
                 126 
                 16.5 
                 G 
               
               
                 particles (1.5%) 
               
               
                 NanoGlide: Nanoparticles 
                 0.451 
                 0.077 
                 160 
                 24.8 
                 H 
               
               
                 of MoS 2  with organic medium 
               
               
                 (0.5%) 
               
               
                 NanoGlide: Nanoparticles 
                 0.461 
                 0.069 
                 200 
                 25.9 
                 I 
               
               
                 of MoS 2  with organic medium 
               
               
                 (1.0%) 
               
               
                 NanoGlide: Nanoparticles 
                 0.466 
                 0.075 
                 315 
                 34.3 
                 J 
               
               
                 of MoS 2  with organic medium 
               
               
                 (1.5%) 
               
               
                   
               
             
          
         
       
     
     The transfer film in the wear scar, studied using energy dispersive x-ray analysis (EDS), identified the signatures of phosphates in addition to molybdenum and sulfur. Panel (a) of  FIG. 9  depicts the base case of paraffin oil without a nanoparticle additive. Panel (b) of  FIG. 9  depicts paraffin oil with the molybdenum disulfide nanoparticles and the emulsifier. It shows the early evidences of molybdenum (Mo)-sulfur (S)-phosphorous (P) in the wear track. Iron (Fe) is seen in panels (a) and (b) of  FIG. 9 , as it is the material of the balls (52100 steel) in the four-ball test. The molybdenum and sulfur peaks coincide and are not distinguishable because they have the same binding energy. Elemental mapping also showed similar results. 
     Prophetic Examples 
     Examples 2-23 are made using a similar method as Example 1, unless specified otherwise. 
     Example 2 
     MoS 2  (Alfa Aesar, 98% pure, 700 nm average particle size) and canola oil from ADM are used as the starting materials. The MoS 2  powder is ball milled for various time conditions, variable ball/powder ratios, and under various ambient conditions, starting with air, canola oil and the subsequent combination of milling in air followed by milling in canola oil. It is also ball milled in different types of organic media. For example, one organic medium that is used is canola oil methyl ester. The processing of this will be similar to the above mentioned example. 
     Different types of ball milling processes can be used. For instance, in the first step, cryo ball milling in air followed by high temperature ball milling in an organic medium is used. 
     After the ball milling, the active EP-EA (extreme pressure—environmentally acceptable) particles are treated with phospholipids that have been mixed with a base oil such as paraffin oil. 
     Example 3 
     Molybdenum disulphide is ball milled with boron using a ratio of 1 part molybdenum disulphide to 1 part boron. This mixture is then ball milled with vegetable oil (canola oil) using a ratio of 1 part solid lubricant nanoparticles to 1.5 parts canola oil. An emulsifier is added using a ratio of 1 part solid lubricant nanoparticle composition (MoS 2 -boron-canola oil) to 2 parts emulsifier. This is added to the base oil (paraffin oil). 
     Example 4 
     Molybdenum disulphide is ball milled with copper using a ratio of 1 part molybdenum disulphide to 1 part metal. This mixture is then ball milled with vegetable oil (canola oil) using a ratio of 1 part solid lubricant nanoparticles to 1.5 parts canola oil. An emulsifier is added using a ratio of 1 part solid lubricant nanoparticle composition (MoS 2 -copper-canola oil) to 2 parts emulsifier. This is added to the base oil (paraffin oil). 
     Example 5 
     A molybdenum disulphide/graphite (obtained from Alfa Aesar) mixture in the ratio of 1:1 is ball milled. This mixture is then ball milled with vegetable oil (canola oil) using a ratio of 1 part solid lubricant nanoparticles to 1.5 parts canola oil. An emulsifier is added using a ratio of 1 part solid lubricant nanoparticle composition (MoS 2 -graphite-canola oil) to 2 parts emulsifier. This is added to the base oil paraffin oil). 
     Example 6 
     A molybdenum disulphide/boron nitride (Alfa Aesar) mixture in the ratio of 1:1 mixture is ball milled. This mixture is then ball milled with vegetable oil (canola oil) using a ratio of 1 part solid lubricant nanoparticles to 1.5 parts canola oil. An emulsifier is added using a ratio of 1 part solid lubricant nanoparticle composition (MoS 2 -boron nitride-canola oil) to 2 parts emulsifier. This is added to the base oil (paraffin oil). 
     Example 7 
     A molybdenum disulphide/graphite/boron nitride mixture in the ratio 1:1:1 is ball milled. This mixture is then ball milled with vegetable oil (canola oil) using a ratio of 1 part solid lubricant nanoparticles to 1.5 parts canola oil. An emulsifier is added using a ratio of 1 part solid lubricant nanoparticle composition (MoS 2 -graphite-boron nitride-canola oil) to 2 parts emulsifier. This is added to the base oil (paraffin oil). 
     Example 8 
     A molybdenum disulphide/graphite mixture in the ratio of 1:1:1 is ball milled. This mixture is then ball milled with vegetable oil (canola oil) using a ratio of 1 part solid lubricant nanoparticles to 1.5 parts canola oil. An emulsifier is added using a ratio of 1 part solid lubricant nanoparticle composition (MoS 2 -graphite-boron-canola oil) to 2 parts emulsifier. This is added to the base oil (paraffin oil). 
     Example 9 
     A molybdenum disulphide/graphite mixture in the ratio of 1:1 is ball milled with copper using a ratio of 1 part molybdenum disulphide/graphite to 1 part metal. This mixture is then ball milled with vegetable oil (canola oil) using a ratio of 1 part solid lubricant nanoparticles to 1.5 parts canola oil. An emulsifier is added using a ratio of 1 part solid lubricant nanoparticle composition (MoS 2 -graphite-copper-canola oil) to 2 parts emulsifier. This is added to the base oil (paraffin oil). 
     Example 10 
     A molybdenum disulphide/boron nitride mixture in the ratio of 1:1 is ball milled with boron using a ratio of 1 part molybdenum disulphide/boron nitride to 1 part metal. This mixture is then ball milled with vegetable oil (canola oil) using a ratio of 1 part solid lubricant nanoparticles to 1.5 parts canola oil. An emulsifier is added using a ratio of 1 part solid lubricant nanoparticle composition (MoS 2 -boron nitride-boron-canola oil) to 2 parts emulsifier. This is added to the base oil (paraffin oil). 
     Example 11 
     A molybdenum disulphide/boron nitride mixture in the ratio of 1:1 mixture is ball milled with copper using a ratio of 1 part molybdenum disulphide/boron nitride to 1 part metal. This mixture is then ball milled with vegetable oil (canola oil) using a ratio of 1 part solid lubricant nanoparticles to 1.5 parts canola oil. An emulsifier is added using a ratio of 1 part solid lubricant nanoparticle composition (MoS 2 -boron nitride-copper-canola oil) to 2 parts emulsifier. This is added to the base oil (paraffin oil). 
     Example 12 
     A molybdenum disulphide/boron nitride/graphite mixture in the ratio of 1:1:1 is ball milled with boron using a ratio of 1 part molybdenum disulphide/boron nitride/graphite to 1 part metal. This mixture is then ball milled with vegetable oil (canola oil) using a ratio of 1 part solid lubricant nanoparticles to 1.5 parts canola oil. An emulsifier is added using a ratio of 1 part solid lubricant nanoparticle composition (MoS 2 -boron nitride-graphite-boron-Canola oil) to 2 parts emulsifier. This is added to the base oil (paraffin oil). 
     Example 13 
     A molybdenum disulphide/boron nitride/graphite in the ratio of 1:1:1 is ball milled with copper using a ratio of 1 part molybdenum disulphide/boron nitride/graphite to 1 part metal. This mixture is then ball milled with vegetable oil (canola oil) using a ratio of 1 part solid lubricant nanoparticles to 1.5 parts canola oil. An emulsifier is added using a ratio of 1 part solid lubricant nanoparticle composition (MoS 2 -boron nitride-graphite-copper-canola oil) to 2 parts emulsifier. This is added to the base oil (paraffin oil). 
     Example 14 
     Molybdenum disulphide is ball milled with polytetrafluoroethylene (Teflon®) in a ration of 1 part molybdenum disulphide to 1 part Teflon®. This mixture is then added to the base oil (paraffin oil) with a phospholipid emulsifier (soy lecithin). 
     Example 15 
     Molybdenum disulphide is ball milled with polytetrafluoroethylene (Teflon®) in a ration of 1 part molybdenum disulphide to 1 part Teflon®. This mixture is then added to the base oil (paraffin oil) with a phospholipid emulsifier (soy lecithin). 
     Example 16 
     Molybdenum disulphide is ball milled with metal additives like copper, silver, lead etc. in a ratio of 1 part molybdenum disulphide to 1 part metal additive. This mixture is further ball milled in vegetable oil based esters (canola oil methyl esters) in a ratio of 1 part solid lubricant nanoparticles to 1.5 parts esters. An emulsifier is added using a ratio of 1 part solid lubricant nanoparticle composition (MoS 2 -esters) to 2 parts phospholipid emulsifier. This is added to the base oil (paraffin oil). 
     Example 17 
     Molybdenum disulphide is ball milled with metal additives like copper, silver, lead etc. in a ratio of 1 part molybdenum disulphide to 1 part metal additive. This mixture is further ball milled in vegetable oil based esters (canola oil methyl esters) in a ratio of 1 part solid lubricant nanoparticles to 1.5 parts esters. This is added to the base oil (paraffin oil). 
     Example 18 
     Molybdenum disulphide is ball milled. The solid lubricant nanoparticles are further ball milled in vegetable oil based esters (canola oil methyl esters) in a ratio of 1 part solid lubricant nanoparticles to 1.5 parts esters. An emulsifier is added using a ratio of 1 part solid lubricant nanoparticle composition (MoS 2 -esters) to 2 parts phospholipid emulsifier. This is added to the base oil (paraffin oil). 
     Example 19 
     Molybdenum disulphide is ball milled. The solid lubricant nanoparticles are further ball milled in vegetable oil based esters (canola oil methyl esters) in a ratio of 1 part solid lubricant nanoparticles to 1.5 parts esters. This is added to the base oil (paraffin oil). 
     Example 20 
     Molybdenum disulphide is ball milled with metal additives like copper, silver, lead etc. in a ratio of 1 part molybdenum disulphide to 1 part metal additive. This mixture is further ball milled in fatty acids (oleic acid) in a ratio of 1 part solid lubricant nanoparticles to 1.5 parts fatty acids. An emulsifier is added using a ratio of 1 part solid lubricant nanoparticle composition (MoS 2 -oleic acid) to 2 parts phospholipid emulsifier. This is added to the base oil (paraffin oil). 
     Example 21 
     Molybdenum disulphide is ball milled with metal additives like copper, silver, lead etc. in a ratio of 1 part molybdenum disulphide to 1 part metal additive. This mixture is further ball milled in fatty acids (oleic acid) in a ratio of 1 part solid lubricant nanoparticles to 1.5 parts fatty acids. This is added to the base oil (paraffin oil). 
     Example 22 
     Molybdenum disulphide is ball milled. The solid lubricant nanoparticles are further ball milled in fatty acids (oleic acid) in a ratio of 1 part solid lubricant nanoparticles to 1.5 parts fatty acids. An emulsifier is added using a ratio of 1 part solid lubricant nanoparticle composition (MoS 2 -oleic acid) to 2 parts phospholipid emulsifier. This is added to the base oil (paraffin oil). 
     Example 23 
     Molybdenum disulphide is ball milled. The solid lubricant nanoparticles are further ball milled in fatty acids (oleic acid) in a ratio of 1 part solid lubricant nanoparticles to 1.5 parts fatty acids. This is added to the base oil (paraffin oil).