Graphene embedded seal

Systems and processes for forming seals. The seals have graphene embedded in the seal. The graphene-embedded seals exhibit improved wear resistance over seals without graphene.

TECHNICAL FIELD

The present disclosure relates to a method of manufacturing a seal, specifically a seal comprising graphene.

BACKGROUND

Seals are a ubiquitous component in a wide range of devices. In many common applications, seals serve to seal an environment and are often positioned at the interface between two components. Some seals also operate in an environment where one or more components that engage the seal moves relative to the seal. The movement may take various forms, but results in wear. Traditional seal materials, such as many commercial polymers, such as polytetrafluoroethylene (“PTFE”), are susceptible to wear in part because of some of the properties that make them desirable as a seal. A material that can function as a seal while having increased, relative to the base material of the seal, wear resistance is highly desirable for a range of materials.

SUMMARY

One embodiment relates to a method of forming a graphene-embedded seal. The method comprises mixing graphene and alcohol forming a graphene alcohol solution, exposing a polymeric material to the graphene alcohol solution, and evaporating alcohol from the graphene alcohol solution, depositing graphene within the polymeric material. In one embodiment, the polymeric material is a polymer powder. In another embodiment, the polymeric material is a polymer seal.

DETAILED DESCRIPTION

Described herein are systems and processes relating to graphene-embedded seals. Methods described herein, in some embodiments, include the infiltration of graphene solution into porous polymer seals, either in their final form such as post-sintering or in an intermediate form such as by application of a graphene solution to powdered polymer precursor materials, such as monomeric powder pre-polymerization or polymeric powdered materials pre-sintering.

In one embodiment, the seals comprise organic material. For example, the seals may be, prior to embedding of the graphene, a polymeric seal, such as PTFE. In one embodiment, the graphene-embedded seal comprises polymer and carbon in the form of graphite and/or graphene. In a further embodiment, the carbon is graphene. Graphite or other non-graphene carbon may be utilized in the formation of seals to impart rigidity and strength to the final seal product. Graphene is also utilized in the formation of the seals to impart wear resistance via a reduction in friction.

In one embodiment, the graphene solution is an alcohol solution, such an alcohol in which graphene forms a solution for example ethanol. The alcohol may, in some embodiments, be an alcohol which is non-reactive with the polymer. The alcohol may, in some embodiments, be an alcohol which results in swelling phenomenon when the polymer is soaked. The graphene solution may have a concentration as desired to achieve an end result of graphene content in embedded in the seal, such as 0.1-10 mg/L, for example 0.5-1.5 mg/L, such as about 1 mg/L. The graphene may be graphene flakes (e.g., monolayer graphene flakes or platelets), such as having an average lateral size of 150-3000 nm, for example an average of about 550 nm.

FIG.1shows processes130,150,180,190for forming seals wherein graphene alcohol solution is exposed to a polymeric material, which may be, for example, polymer seals or polymer powder. In one embodiment, the graphene-embedded seal exhibits a 30-50% reduction in the coefficient of friction (“COF”) over an otherwise identical seal lacking graphene. In one embodiment, graphene is located within the bulk of the polymer rather than on the surface, such as at a subsurface within the polymer.

In one embodiment, process130illustrates a method of forming seals by graphene alcohol solution on powder. At132, graphene alcohol solution is “solution processed,” such as by applying solution to a powder polymer mix, such application may be drop-wise (i.e., dropped onto powder polymer mixture). At134, seal is formed by mixing, cold pressing and, if necessary, machining. At136, a final product is formed with carbon embedded in the seal.

In an alternative embodiment, the process150forms a “blend” product. At step152, polymeric seals precursors are formed by mixing and cold pressing the seal powders into a final seal shape according to conventional techniques. At154, the pressed seal powder is soaked in a graphene alcohol solution, such as ethanol, for example as a 1 mg/L solution of monolayer graphene flakes. The soaking proceeds for 1-7 seconds, such as 3-5 seconds, at room temperature and atmospheric pressure, for example. The graphene solution fills the pores of polymer seal. The alcohol is evaporated, such as with room temperature or via elevated temperature. At156, the soaked polymer powder is sintered to form the final graphene embedded polymer seal. The graphene remains as deposited within the pores, thus resulting in a graphene-embedded seal. In some embodiments, the soaked polymer powder may be dried separately prior to sintering, or the sintering may be utilized to evaporate the alcohol. The dried graphene-embedded seal is sintered, such as in air or nitrogen, by known techniques used for seals produced from polymer pressed powder. At136, a final blend product is formed.

In an example embodiment, a process180embeds graphene into a formed polymer seal. After the polymer seal is manufactured at step172, at184, the graphene is immersed in an alcohol in which graphene is soluble (e.g., ethanol) to form a graphene-alcohol solution. The solution is deposited, such as by droplet or otherwise dispensing the alcohol and graphene, onto a polymer seal. Alternatively, or in addition the polymer seal may be immersed in the graphene alcohol solution. The graphene alcohol solution penetrates into the pores of the polymer seal. The graphene alcohol solution is allowed to dry at186such that the alcohol evaporates, leaving deposited graphene, such as within the pores of the polymer seal, forming a final 3G product.

In another embodiment, vacuum process190is utilized. After the polymer seal is manufactured at step172, the polymer seal is soaked in a vessel under pressure at step194. The polymer seal in solution may be exposed to a pressurized environment or a vacuum environment. For example, the vacuum environment may aid in facilitating the graphene alcohol solution entering the polymer pores by evacuating air from the pores. In one embodiment, the polymer seal is placed under vacuum and then the graphene alcohol solution is exposed to or used to immerse the polymer seal pressurized immersion is utilized where the dried graphene-embedded seal is immersed in a graphene alcohol solution in a pressurized vessel. The pressure-treated or vacuum-treated graphene-embedded seal is dried at step196.

For embodiments using a vacuum, the resulting seal is removed at step196to provide a final product “VAC,” as referred to below regarding testing results. It is believed the application of the vacuum aids in the penetration of the graphene into the bulk of the polymer seal as it involves infiltration of graphene alcohol solution into porous semi or final seal product. Infiltration can be done in atmospheric pressure by dipping seals into graphene alcohol solution for 5-10 seconds, removing and drying in air. Alternatively, a vacuum vessel can be used to remove air and force graphene alcohol solution into seal pores to achieve deeper penetration.

In embodiments utilizing the vacuum method, the seal is soaked into graphene alcohol solution in a vacuum vessel and air is pumped out by a rotary pump for at least 5-6 minutes. For embodiments utilizing pressure, a pressure of 2-50 atmospheres may be used for 5-15 minutes.

Experimental testing was performed on a commercially available seal without exposure to graphene (“base”), a graphene-embedded seal produced by the solution processing as described above (“3G”), and a graphene-embedded seal produced by the immersion process described above (“blend”). For the experiments described herein, the wear testing included simulation of natural gas compressor working conditions. Table 1 below illustrates a summary of the testing parameters and analytical results.

FIG.2Ais a photograph of experimental results for a commercial seal (base).FIG.2Bis a photograph of experimental results for one embodiment of a graphene-embedded seal formed by solution processing using 3 drops of graphene-alcohol solution (3G).FIG.2Cis a photograph of experimental results for one embodiment of a graphene-embedded seal formed by immersion (blend).

FIG.3is a graph of testing results for a base, blend, and 3G samples. After an initial wear-in period, the COF for the commercial “base” seal continues to fluctuate, while 3G embodiment of a graphene-embedded seal by virtue of a solution process reached near steady state rising from about 0.065-0.08 COF from 1000-7000 seconds and the blend embodiment of a graphene-embedded seal by virtue of immersion reached steady state at about 0.06. Table 2 below summaries the further results.

TABLE 2Summary of results (all COF).Stan-dardNDevi-Mini-Maxi-TotalMeanationSummumMedianmumBase62340.115190.03224718.086130.039090.122130.15103Blend62340.076610.0081477.585080.036210.077010.0863G62340.062340.00496388.598270.027020.063730.06504

As a control, a commercially available seal (“base”) was analyzed both at untested portions and as subject to wear testing.FIG.4Ashows a base seal with untested areas 1, 2, and 3 indicated corresponding to the micrograph images inFIGS.4B,4C, and4D, respectively.FIG.5Ashows a base seal with tested areas 1, 2, and 3 indicated corresponding to the micrograph images inFIGS.5B,5C, and5D, respectively.FIG.6is a graph of Raman analysis results for the indicated locations inFIGS.4A-4DandFIGS.5A-5D.FIG.7is a reference Raman analysis for stock graphene flakes for comparative purposes. A comparison of Raman results illustrates that the base seal lacks graphene.

To compare the impact of graphene embedding, a “blend” embodiment example was made using a pristine graphene monolayer flakes concentration 1 mg/L and with sintering temp/time kept the same as regular seal production techniques.FIG.8Ashows a “blend” seal with a top, middle, and bottom area indicated corresponding to the micrograph images inFIG.8B,FIG.8C, andFIG.8D, respectively.FIG.9is a graph of Raman analysis results for the indicated locations inFIGS.8A-8D. The Raman spectra indicate the presence of graphene at all three locations, with a decreasing signal strength for graphene observed as one proceeds from “top” to “middle” to “bottom” of the seal cross section inFIG.8A, indicating the presence of graphene in all three locations but a decreasing amount from the top down within the seal. The distinction between the top layer and the middle and bottom layers is more pronounced than in the 3G sample, suggesting a greater relative amount of surface or near-surface graphene (i.e. less penetration for embedding) than in the blend sample given the deposition on the surface for the solution processing used in this example.

To compare the impact of graphene embedding, a “3G” embodiment example, the drop or soak process used a dipping of the seal or short exposure for 3-5 seconds and the drop-wise exposure utilized 3 drops on the seal surface.FIG.10Ashows a “blend” seal with a top, middle, and bottom area indicated corresponding to the micrograph images inFIGS.10B,10C, and10D, respectively.FIG.11is a graph of Raman analysis results for the indicated locations inFIGS.10A-10D. The Raman spectra indicate the presence of graphene at all three locations, with a decreasing signal strength for graphene observed as one proceeds from “top” to “middle” to “bottom” of the seal cross section inFIG.8A, indicating the presence of graphene in all three locations but a decreasing amount from the top down within the seal. The distinction between the top layer and the middle and bottom layers is less pronounced than in the blend sample, suggesting a relatively similar amount of surface or near-surface graphene (i.e. significant penetration for embedding) than in the 3G sample given the immersion soak used in this example.

The 3G sample that was make utilizing an immersion process illustrated a more even distribution of graphene throughout the seal and reached a more stead-state COF in the testing (seeFIGS.4A-4D) compared to the base and blended samples and at a lower COF at that. This suggests improved performance for a graphene.

Definitions

No claim element herein is to be construed under the provisions of 35 U.S.C. § 112(f), unless the element is expressly recited using the phrase “means for.”

The term “coupled” and variations thereof, as used herein, means the joining of two members directly or indirectly to one another. Such joining may be stationary (e.g., permanent or fixed) or moveable (e.g., removable or releasable). Such joining may be achieved with the two members coupled directly to each other, with the two members coupled to each other using a separate intervening member and any additional intermediate members coupled with one another, or with the two members coupled to each other using an intervening member that is integrally formed as a single unitary body with one of the two members. If “coupled” or variations thereof are modified by an additional term (e.g., directly coupled), the generic definition of “coupled” provided above is modified by the plain language meaning of the additional term (e.g., “directly coupled” means the joining of two members without any separate intervening member), resulting in a narrower definition than the generic definition of “coupled” provided above. Such coupling may be mechanical, electrical, or fluidic. For example, circuit A communicably “coupled” to circuit B may signify that the circuit A communicates directly with circuit B (i.e., no intermediary) or communicates indirectly with circuit B (e.g., through one or more intermediaries).

Although the figures and description may illustrate a specific order of method steps, the order of such steps may differ from what is depicted and described, unless specified differently above. Also, two or more steps may be performed concurrently or with partial concurrence, unless specified differently above.