₂and GO can be used. Such deposition differs from those remaining in solution, such as graphene suspended in oil, or those applied chemically. For example, those materials in solution are, obviously, in solution and not bound to the substrate surface (e.g., flowable oil with suspended particles). In contrast, solid materials that have been deposited as by spraying will not be in solution, rather such materials will be controlled by Van der Waals forces to attach the materials to the substrate. Further, there is also a structural difference between such materials and those formed as a solid on the surface of the substrate by chemical vapor deposition, atomic layer deposition, or the like. In such instances, the material is reacted (covalently bonded) with or chemisorbed to the substrate rather than merely held by Van der Waals forces. The thickness is controlled by altering the samples' exposure time to the mist. The pressure/flowrate can also effectively be used to change the amount of solid-bearing liquid carrier impinged on to the surface.

The suspension can include a functionalizing agent. The functionalizing agent could function to improve the adhesion of the coating and durability. Examples of such adhesion improving functionalizing agents are polydopamine (PDA). For example, an adhesion improving functionalizing agent (e.g. PDA) can be added to the suspension at a concentration of 0.01, or 0.02 up to 0.2, or 0.1 or 0.09 mg/ml (e.g. 0.022 mg/ml in a carrier liquid, such as ethanol, prior to solution processing). In one embodiment, PDA at a concentration of 0.042 mg/ml was added to the dispersion of the MoSGO solid lubricant such that the end concentration of MoSGO is approximately 1.021 mg/ml (such as 1 mg/ml+10%). It is believed that this type of functionalizing agent is working as a binding agent between the nanoparticles and the substrate surface. In one embodiment, the process includes forming a polymer solution. Other functionalizing agents could enhance lubricity. Examples of such alternative functionalizing agents are polytetrafluoroethylene (“PTFE”), and/or polyether ether ketone (“PEEK”). One or more functionalizing agents can be used in combination.

The thickness of the coating effective to produce (and maintain over time of usage) high lubricity (low coefficient of friction) properties depends on the usage as would be appreciated in the art. For example, lower test loads transition into very high lubricity regime more easily such that thinner coatings are sufficient, whereas thicker coatings can be required at higher loads and for longer sliding distances. A single coating layer can be used. Alternatively, subsequent coats can be applied after the initial layers have completely dried and have adhered to the substrate firmly. The thickness of the coating can be 0.5 to 2.5 micron. Also, use of an adhesion promoting functionalizing agent (e.g. PDA) is useful in a first layer to improve the adhesion of the coating to the substrate (e.g. SiC surface). Subsequent layers can comprise MoSGO without the adhesion promoting functionalizing agent. Alternatively, an adhesion promoting functionalizing agent could be used in each layer.

In some embodiments, the method of forming the low friction wear surface includes evaporating the solvent component and encapsulating or partially encapsulating the MoS₂flakes in GO in one step (i.e., by simultaneous evaporation and consequent encapsulation). Encapsulating or partially encapsulating the MoS₂flakes greatly helps the longevity and lubricity of the low friction wear surface because the flakes are passivated from or protected from ambient oxygen and moisture, such as by increasing the effective usage temperature range of the MoS₂flakes to up to about 250° C. The MoS₂flakes can be fully encapsulated or coated with the graphene oxide or can be partially encapsulated or coated with the graphene oxide. The higher density of the MoS₂enables such full encapsulation with a substantially equal weight of the less dense graphene oxide. This is ensured by virtue of the composition (wt %) of the two phases chosen. Also, this coating process can be used on large surfaces. The coating process can be used on surfaces that are not flat—e.g. patterned, textured, curved, containing recesses or projections, etc. A large-scale application of such can utilize a scanning spray nozzle to cover a large area with the graphene in solution and then vaporize the solvent.

The surface of the substrate can have a surface roughness. For example, the surface roughness, Ra, can be at least 0.1 as measured for example by ISO 4288-1996 using commercially available profilometer, such as by Taylor-Hobson® Talysurf i120. The surface roughness can be 0.05-0.4, or 0.05-0.25, or 0.1 to 0.4, or 0.1 to 0.25, or 0.2-0.4. The surface roughness can facilitate adhesion of the coating to the surface. Too high a surface roughness can degrade performance and durability over time. In case of extremely smooth substrates, the surfaces can be treated to make them amenable to the deposition techniques. Examples of such treatments include, but are not limited to, ozone treatment and doping with binders that make bonds between the substrate (e.g. Silicon carbide) and the initial layers and higher substrates (up to 400° C.) temperatures.

The substrate can comprise silicon carbide (SiC), Tungsten carbide, Boron nitride, or Silicon nitride. The substrate, (e.g. SiC) can be part of a gas seal. In experimental testing, the resultant MoSGO material achieved ultralow steady state friction and low wear in case of self-mated uncoated SiC (SiC vs SiC) and also SiC paired against DLC in presence of MoSGO at high load and high speed pin-on-disc (“POD”) tests. In one embodiment, the deposited MoSGO is utilized with an opposing wear face of MoSGO, in other embodiments the opposing wear face is DLC.

For example, experiments to determine coefficient of friction (COF) and wear for a silicon carbide disc substrate having a coating of MoS₂with graphene oxide (“MoSGO”) sliding against a diamond like coating (DLC) coated SiC ball for 120 minutes at forces and speeds consistent with those in gas seal applications. Two suspensions of the MoS₂and GO were prepared in water and ethanol and coated onto the Silicon carbide substrate. The COF was 0.019-0.02 for the coated substrates as compared to 0.715 for the uncoated substrate—a reduction of 35-38 times as compared to sliding the DLC coated SiC ball on the uncoated substrate. Ball wear was reduced by 4-5 orders of magnitude as compared to sliding the DLC coated SiC ball on the uncoated substrate. Disc wear was reduced by 6 times as compared to sliding the DLC coated SiC ball on the uncoated substrate.

A similar experiment using an uncoated SiC ball showed COF reduction of 16 times, (0.043 for the coated substrate as compared to 0.697 for the uncoated substrate). While disc wear reduction of 16 times and ball wear of reduction of 3-4 times were observed as compared to an uncoated substrate.

Friction plots indicate immediate action of MoSGO and steady state ultralow friction is maintained. In case of baseline tests without MoSGO, coating wear on the disc is observed and large wear is noticed along with large friction coefficient. Further, following the initial evaluation of the solid lubricant MoSGO on SiC, the lubricant was tested for its ability to reduce torque. The solid lubricant adhesion was observed to not be optimal.

Additional experiments where the suspension includes PDA and the coating is tested by sliding against an uncoated SiC ball showed the COF was reduced by 22 times (0.032 vs 0.697) and disc wear was reduced by 25 times as compared to an uncoated substrate

Further, disc on disc tests were run where a disc surface is rotated relative to another disc surface (disc on disc test). Torque is measured rather than coefficient of friction. Specifically, a mat-lapped silicon carbide mating ring was rotated relative to a mat-lapped silicon carbide primary ring, bearing a MoSGO lubricant coating modified with PDA in dry nitrogen. A reduction in torque of 84% was observed in dry nitrogen and of 60% in ambient air.

In another test, both a mat-lapped mating ring and a polished (i.e. smooth) primary ring were coated with an MoSGO coating and a disc on disc test. After the test, inspection of the wear tracks by scanning electron microscope and Raman spectroscopy revealed that the polished surface no longer included the MoSGO lubricant while the mat lapped surface retained the MoSGO layer. Mat lapped surface roughness is about 0.15 Ra. Polished surface is about 0.055 Ra.

Combinations

The MoSGO coating can be used in combination with another coating. For example, an opposing surface can have a diamond like coating (DLC). A particular coating including nanodiamonds can comprise MoS₂with nanodiamonds (MoSND) as a lubricant for the substrate, e.g. a SiC substrate in rotational facing with a substrate coated with MoSGO. Carbon nano-onions can be formed during interaction of the lubricant with the substrates as the sliding interfaces. To form the MoSND coating, a solution-processed material (MoS₂) can be placed into a solution in the proportion of 50-1000 mg of nanodiamonds per 1 L of solution applied to the SiC material, such as by spraying or drop casting.

Seal Assembly

As noted, the coatings disclosed herein can be used in dry gas seal or non-contacting seal applications.

For Example, FIG. 2 shows a cross-section of a seal assembly 600 that can be placed between a rotating shaft 604 and a housing 606 with an outer wall 610 and a bore 609. The seal assembly includes a mating ring 614 with a mating ring seal face adjacent to and facing a primary ring seal face of a primary ring 616. At least one of the mating ring seal face and the primary ring seal face bear a coating comprising molybdenum disulfide and nanodiamonds or comprising molybdenum disulfide and graphene oxide as described herein.

The seal 600 is shown as a single seal configuration but it shall be understood that the seal assembly 600 could be used in combination with another seal form a dual dry gas seal assembly.

The seal assembly 600 can operate by developing a layer of gas between the mating ring seal face and the primary ring seal face due to relative motion between the mating ring 614 and the primary ring 616. In particular, the layer of sealing gas can keep gas within a chamber 608 from escaping therefrom along a shaft 604. The seal assembly 600 can also optionally include a biasing member 638 that urges the primary ring 616 towards the mating ring 614. One of the mating ring seal face and the primary ring seal face can comprise a surface feature textured area (e.g. recesses) such that the rotation of the rings relative to one another facilitates a sealing gas to reside between the faces. The surface texture features can be configured such that they draw gas in from an outer diameter of one of the faces towards it center/inner diameter. Such a configuration is applicable to situations where pressure at the outer diameter is greater than at the inner diameter. In the opposite case (e.g., where the pressure is higher at the inner diameter), the surface texture patterns an extend outwardly from the inner diameter to the outer diameter.

There can be coating on only one of the seal faces or on both of the seal faces. The coating on each seal face can be the same or different. For example, the coating on one seal face can comprise molybdenum disulfide and graphene oxide and optionally a functionalizing agent such as polydopamine (MoSGO) as described herein while the other seal face can be uncoated, coated with nanodiamonds, coated with MoSND, or coated with molybdenum disulfide and graphene oxide and optionally a functionalizing agent such as poly dopamine.

The seal assembly 600 can also include a sleeve ring 615 that can be mated to the rotating shaft 604 that enables the mating ring 614 to rotate with the shaft 604. The mating ring seal face can include grooves thereon. The seal assembly 600 can include an optional retainer 602 with a body 668 and surfaces 672, 674, 676, 678.

The MoSND or MoSGO coating can be applied to a seal face after formation of the texture (i.e. recesses) in the seal face. Alternatively, the coating can be applied to the seal face and then the seal face etched to form recesses.

Definitions

While the present teachings have been described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments or examples. On the contrary, the present teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those of skill in the art.

While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” Any ranges cited herein are inclusive.

The terms “substantially” and “about” used throughout this specification are used to describe and account for small fluctuations. For example, they may refer to less than or equal to ±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as less than or equal to ±0.05%.