WO2020023578A1 - Production sans produits chimiques de billes creuses de graphène - Google Patents

Production sans produits chimiques de billes creuses de graphène Download PDF

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Publication number
WO2020023578A1
WO2020023578A1 PCT/US2019/043148 US2019043148W WO2020023578A1 WO 2020023578 A1 WO2020023578 A1 WO 2020023578A1 US 2019043148 W US2019043148 W US 2019043148W WO 2020023578 A1 WO2020023578 A1 WO 2020023578A1
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WIPO (PCT)
Prior art keywords
graphene
balls
polymer
carbon
solvent
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PCT/US2019/043148
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English (en)
Inventor
Aruna Zhamu
Bor Z. Jang
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Global Graphene Group, Inc.
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Priority claimed from US16/044,901 external-priority patent/US11021371B2/en
Priority claimed from US16/044,878 external-priority patent/US11603316B2/en
Application filed by Global Graphene Group, Inc. filed Critical Global Graphene Group, Inc.
Publication of WO2020023578A1 publication Critical patent/WO2020023578A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/184—Preparation
    • C01B32/19—Preparation by exfoliation
    • C01B32/192—Preparation by exfoliation starting from graphitic oxides

Definitions

  • the present disclosure relates generally to the field of graphene and, more particularly, to hollow graphene balls and a process for producing same.
  • Carbon is known to have five unique crystalline structures, including diamond, fullerene (0-D nanographitic material), carbon nanotube or carbon nanofiber (l-D nanographitic material), graphene (2-D nanographitic material), and graphite (3-D graphitic material).
  • the carbon nanotube (CNT) refers to a tubular structure grown with a single wall or multi-wall.
  • Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have a diameter on the order of a few nanometers to a few hundred nanometers.
  • Their longitudinal, hollow structures impart unique mechanical, electrical and chemical properties to the material.
  • the CNT or CNF is essentially a one-dimensional nanocarbon or l-D nanographite material.
  • NGPs have been found to have a range of unusual physical, chemical, and mechanical properties. For instance, graphene was found to exhibit the highest intrinsic strength and highest thermal conductivity of all existing materials. Although practical electronic device applications for graphene (e.g., replacing Si as a backbone in a transistor) are not envisioned to occur within the next 5-10 years, its application as a nanofiller in a composite material and an electrode material in energy storage devices is imminent. The availability of processable graphene sheets in large quantities is essential to the success in exploiting composite, energy, and other applications for graphene.
  • NGPs or graphene materials include discrete sheets/platelets of single-layer and multi-layer (typically less than 10 layers), pristine graphene, slightly oxidized graphene ( ⁇ 5% by weight of oxygen), graphene oxide (> 5% by weight of oxygen), reduced graphene oxide (RGO), slightly fluorinated graphene ( ⁇ 5% by weight of fluorine), graphene fluoride (> 5% by weight of fluorine), other halogenated graphenes, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, doped graphene (e.g.
  • Pristine graphene has essentially 0% oxygen.
  • RGO typically has an oxygen content of 0.00l%-5% by weight.
  • Graphene oxide (including RGO) can have 0.00l%-50% by weight of oxygen.
  • all the graphene materials have 0.00l%-50% by weight of non-carbon elements (e.g. O, H, N, B, F, Cl, Br, I, etc.). These materials are herein referred to as non-pristine graphene materials.
  • the presently invented graphene-carbon balls can contain pristine or non-pristine graphene and the invented method allows for this flexibility.
  • Another object of the present disclosure is to provide products (e.g. devices) that contain hollow graphene balls of the present disclosure and methods of operating these products.
  • the present disclosure provides a method of producing multiple individual hollow graphene balls directly from a graphitic material and particles of a polymer. This method is stunningly simple. The method comprises:
  • step (d) of suspending the graphene-encapsulated polymer particles in a gaseous medium comprises operating a fluidized-bed apparatus. This step is essential to preventing multiple graphene balls being stuck together.
  • step (c) includes operating a magnet to separate the impacting balls or media from the graphene-coated or graphene-embedded polymer particles.
  • the solid polymer material particles can include plastic or rubber beads, pellets, spheres, wires, fibers, filaments, discs, ribbons, or rods, having a diameter or thickness from 10 nm to 10 mm. Preferably, the diameter or thickness is from 100 nm to 1 mm, and more preferably from 200 nm to 200 pm.
  • the solid polymer may be selected from solid particles of a thermoplastic, thermoset resin, rubber, semi-penetrating network polymer, penetrating network polymer, natural polymer, or a combination thereof. In an embodiment, the solid polymer is partially removed by melting, etching, or dissolving in a solvent prior to step (d).
  • the graphitic material is selected from natural graphite, synthetic graphite, highly oriented pyrolytic graphite, graphite fiber, graphitic nanofiber, graphite fluoride, oxidized graphite, chemically modified graphite, exfoliated graphite, recompressed exfoliated graphite, expanded graphite, mesocarbon microbead, or a combination thereof.
  • the graphitic material contains a non-intercalated and non-oxidized graphitic material that has never been previously exposed to a chemical or oxidation treatment prior to the mixing step (a).
  • the energy impacting apparatus can be a vibratory ball mill, planetary ball mill, high energy mill, basket mill, agitator ball mill, cryo ball mill, micro ball mill, tumbler ball mill, continuous ball mill, stirred ball mill, pressurized ball mill, freezer mill, vibratory sieve, bead mill, nanobead mill, ultrasonic homogenizer mill, centrifugal planetary mixer, vacuum ball mill, or resonant acoustic mixer.
  • the carbon yield is the weight percentage of a polymer structure that is converted by heat to a solid carbon phase, instead of becoming part of a volatile gas.
  • the high carbon-yield polymer may be selected from phenolic resin, poly furfuryl alcohol, polyacrylonitrile, polyimide, polyamide, polyoxadiazole, polybenzoxazole,
  • polybenzobisoxazole polythiazole, polybenzothiazole, polybenzobisthiazole, poly(p-phenylene vinylene), polybenzimidazole, polybenzobisimidazole, a copolymer thereof, a polymer blend thereof, or a combination thereof.
  • the polymer can contain a low carbon-yield polymer selected from polyethylene, polypropylene, polybutylene, polyvinyl chloride, polycarbonate, acrylonitrile-butadiene (ABS), polyester, polyvinyl alcohol, poly vinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene oxide (PPO), poly methyl methacrylate (PMMA), a copolymer thereof, a polymer blend thereof, or a combination thereof.
  • a low carbon-yield polymer selected from polyethylene, polypropylene, polybutylene, polyvinyl chloride, polycarbonate, acrylonitrile-butadiene (ABS), polyester, polyvinyl alcohol, poly vinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene oxide (PPO), poly methyl methacrylate (PMMA), a copolymer thereof, a polymer blend thereof, or a combination thereof
  • the step of pyrolyzing includes carbonizing the polymer at a temperature from 200°C to 2,500°C to obtain carbon-bonded graphene sheets.
  • the carbon-bonded graphene sheets can be subsequently graphitized at a temperature from 2,500°C to 3,200°C to obtain graphite-bonded graphene sheets.
  • pyrolyzation of a polymer tends to lead to the formation of pores in the resulting polymeric carbon phase due to the evolution of those volatile gas molecules such as C0 2 and H 2 0.
  • such pores also have a high tendency to get collapsed if the polymer is not constrained when being carbonized.
  • the graphene sheets wrapped around a polymer particle are capable of constraining the carbon pore walls from being shrunk and collapsed, while some carbon species also permeate to the gaps between graphene sheets where these species bond the graphene sheets together.
  • the pore sizes and pore volume (porosity level) of the resulting hollow graphene balls depend upon the starting polymer size and the carbon yield of the polymer and, to a lesser extent, on the pyrolyzation temperature.
  • the present disclosure also provides powder mass of multiple hollow graphene balls wherein at least one of the graphene balls has a hollow core enclosed by a graphene shell.
  • the graphene shell contains single-layer or few-layer graphene sheets chemically bonded by a carbon material having a carbon material-to-graphene weight ratio from 1/200 to 1/2.
  • the few-layer graphene sheets have 2-10 layers of stacked graphene planes having an inter-plane spacing doo 2 from 0.3354 nm to 0.36 nm as measured by X-ray diffraction and the single-layer or few-layer graphene sheets contain a pristine graphene material having essentially zero % of non-carbon elements.
  • the hollow graphene ball typically has a density from 0.01 to 1.7 g/cm , and a specific surface area from 50 to 3,000 m /g.
  • the graphene shell contains stacked graphene planes having an inter-planar spacing doo 2 from 0.3354 nm to 0.40 nm as measured by X-ray diffraction. More typically, the graphene ball has a specific surface area from 200 to 2,000 m 2 /g or a density from 0.05 to 1.5 g/cm 3 .
  • Multiple graphene balls may be compacted into any desirable shape (e.g. by filling graphene balls into a mold cavity) and using a binder resin to bond the graphene balls together. The binder resin may then be thermally converted (e.g. carbonized) into a carbon material. Such an approach provides flexibility or versatility in making foam-like objects of practically any shape.
  • the graphene shell comprises few-layer graphene sheets comprising 2-10 layers of stacked graphene planes having an inter-plane spacing doo2 from 0.3354 nm to 0.36 nm as measured by X-ray diffraction.
  • the disclosure also provides an oil-removing or oil- separating device containing the invented hollow graphene balls as an oil-absorbing element.
  • the disclosure further provides a solvent-removing or solvent-separating device containing the invented hollow graphene balls as a solvent-absorbing or solvent- separating element.
  • Also provided is a method to separate oil from water comprising the steps of: (a) providing an oil-absorbing element comprising the invented hollow graphene balls; (b) contacting an oil-water mixture with the element, which absorbs the oil from the mixture; and (c) retreating the element from the mixture and extracting the oil from the element.
  • the method may further comprise a step of reusing the element.
  • the present disclosure also provides a method for separating an organic solvent from a solvent-water mixture or from a multiple-solvent mixture, the method comprising the steps of:
  • the method may further comprise a step of reusing the element.
  • the disclosure also provides a thermal management device containing the invented hollow graphene balls as a heat-conducting, heat spreading or heat dissipating element.
  • the thermal management device contains a device selected from a heat exchanger, heat sink, heat pipe, high-conductivity insert, conductive plate between a heat sink and a heat source, heat- spreading component, heat-dissipating component, thermal interface medium, or thermoelectric or Peltier cooling device.
  • FIG. 1 A flow chart showing the most commonly used prior art process of producing highly oxidized NGPs that entails tedious chemical oxidation/intercalation, rinsing, and high- temperature exfoliation procedures.
  • FIG. 2(A) A flow chart showing the presently invented process for producing graphene balls.
  • FIG. 2(B) Schematic of the heat-induced conversion of polymer into carbon, which bonds
  • FIG. 3 Thermal conductivity values vs. specific gravity of a carbon-bonded graphene ball
  • FIG. 4 Thermal conductivity values of carbon-bonded graphene ball compacts
  • FIG. 5 Thermal conductivity values of carbon-bonded graphene ball compacts and pristine
  • graphene foam (prepared by casting with a blowing agent and then heat treating) plotted as a function of the final (maximum) heat treatment temperature.
  • FIG. 6 Electrical conductivity values of carbon-bonded graphene ball compacts
  • FIG. 7 The amount of oil absorbed per gram of graphene ball compacts, plotted as a function of the oxygen content in the foam having a porosity level of approximately 97% (oil separation from oil-water mixture).
  • FIG. 8 The amount of oil absorbed per gram of integral carbon-bonded graphene ball compacts, plotted as a function of the porosity level (given the same oxygen content).
  • FIG. 9 The amount of chloroform absorbed out of a chloroform-water mixture, plotted as a function of the degree of fluorination.
  • FIG. 10 Schematic of heat sink structures (2 examples).
  • the present disclosure provides a method of producing individual (isolated or separated) hollow graphene balls directly from particles of a graphitic material and particles of a polymer.
  • the method begins with mixing multiple particles of a graphitic material and multiple particles of a solid polymer carrier material to form a mixture, which is enclosed in an impacting chamber of an energy impacting apparatus (e.g. a vibratory ball mill, planetary ball mill, high energy mill, basket mill, agitator ball mill, cryo ball mill, micro ball mill, tumbler or tumbler ball mill, continuous ball mill, stirred ball mill, pressurized ball mill, freezer mill, vibratory sieve, bead mill, nanobead mill, ultrasonic homogenizer mill, centrifugal planetary mixer, vacuum ball mill, or resonant acoustic mixer).
  • an energy impacting apparatus e.g. a vibratory ball mill, planetary ball mill, high energy mill, basket mill, agitator ball mill, cryo ball mill, micro ball mill, tumbler or tumbler ball mill, continuous ball mill, stirred ball mill, pressurized ball mill, freezer mill, vibratory sieve, bead mill, nanobead mill, ultrasonic homogenizer mill,
  • a plurality of impacting balls or media can be added to the impacting chamber of the energy impacting apparatus. These impacting balls, accelerated by the impacting apparatus, impinge upon the surfaces/edges of graphite particles with a high kinetic energy at a favorable angle to peel off graphene sheets from graphite particles. These graphene sheets are tentatively transferred to surfaces of these impacting balls. These graphene- supporting impacting balls subsequently collide with polymer particles and transfer the supported graphene sheets to the surfaces of these polymer particles. This sequence of events is herein referred to as the“indirect transfer” process. These events occur in very high frequency and, hence, most of the polymer particles are covered by graphene sheets typically in less than one hour.
  • step (c) includes operating a magnet to separate the impacting balls or media from the graphene-coated polymer particles.
  • the method then includes recovering the graphene-coated polymer particles from the impacting chamber.
  • the graphene-coated polymer particles are then pyrolyzed to thermally convert the polymer into carbon or graphite that bonds the graphene sheets together while the particles are being suspended in a gaseous medium.
  • a main purpose of suspending these graphene-coated polymer particles while being heat-treated is to keep individual particles separated so that the resulting hollow graphene balls are not aggregated and bonded together.
  • a fluidized bed apparatus or a properly configured pattern of a gas stream can be used for this purpose.
  • polymer particles that have a high carbon yield or char yield (e.g. > 30% by weight of a polymer being converted to a solid carbon phase; instead of becoming part of a volatile gas).
  • the high carbon-yield polymer may be selected from phenolic resin, poly furfuryl alcohol, polyacrylonitrile, polyimide, polyamide, polyoxadiazole, polybenzoxazole, polybenzobisoxazole, polythiazole, polybenzothiazole, polybenzobisthiazole, poly(p-phenylene vinylene), polybenzimidazole, polybenzobisimidazole, a copolymer thereof, a polymer blend thereof, or a combination thereof.
  • phenolic resin poly furfuryl alcohol, polyacrylonitrile, polyimide, polyamide, polyoxadiazole, polybenzoxazole, polybenzobisoxazole, polythiazole, polybenzothiazole, poly(p-phenylene vinylene), polybenzimidazole, polybenzobisimidazole, a copolymer thereof, a polymer blend thereof, or a combination thereof.
  • the polymer can contain a low carbon-yield polymer selected from polyethylene, polypropylene, polybutylene, polyvinyl chloride, polycarbonate, acrylonitrile-butadiene (ABS), polyester, polyvinyl alcohol, poly vinylidiene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene oxide (PPO), poly methyl methacrylate (PMMA), a copolymer thereof, a polymer blend thereof, or a combination thereof.
  • a low carbon-yield polymer selected from polyethylene, polypropylene, polybutylene, polyvinyl chloride, polycarbonate, acrylonitrile-butadiene (ABS), polyester, polyvinyl alcohol, poly vinylidiene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene oxide (PPO), poly methyl methacrylate (PMMA), a copolymer thereof, a polymer blend thereof, or a combination thereof
  • the carbon phase can get graphitized to further increase both the electric conductivity and thermal conductivity.
  • the amount of non-carbon elements is also decreased to typically below 1% by weight if the graphitization time exceeds 1 hour.
  • an organic polymer typically contains a significant amount of non carbon elements, which can be reduced or eliminated via heat treatments.
  • pyrolyzation of a polymer causes the formation and evolution of volatile gas molecules, such as C0 2 and H 2 0, which lead to the formation of pores in the resulting polymeric carbon phase.
  • volatile gas molecules such as C0 2 and H 2 0
  • such pores also have a high tendency to get collapsed if the polymer is not constrained when being carbonized (the carbon structure can shrink while non-carbon elements are being released).
  • the graphene sheets wrapped around a polymer particle are capable of constraining the carbon pore walls from being collapsed.
  • some carbon species also permeate to the gaps between graphene sheets where these species bond the graphene sheets together.
  • the pore sizes and pore volume (porosity level) of the resulting graphene balls mainly depend upon the starting polymer size and the carbon yield of the polymer.
  • the graphitic material as a source of graphene sheets, may be selected from natural graphite, synthetic graphite, highly oriented pyrolytic graphite, graphite fiber, graphitic nanofiber, graphite fluoride, oxidized graphite, chemically modified graphite, exfoliated graphite, recompressed exfoliated graphite, expanded graphite, mesocarbon microbead, or a combination thereof.
  • natural graphite synthetic graphite, highly oriented pyrolytic graphite, graphite fiber, graphitic nanofiber, graphite fluoride, oxidized graphite, chemically modified graphite, exfoliated graphite, recompressed exfoliated graphite, expanded graphite, mesocarbon microbead, or a combination thereof.
  • Graphene sheets can be peeled off from natural graphite by using polymer particles alone, without utilizing the heavier and harder impacting balls (such as zirconium dioxide or steel balls commonly used in a ball mill, for instance).
  • the peeled-off graphene sheets are directly transferred to polymer particle surfaces and are firmly wrapped around the polymer particles.
  • Impacting polymer particles are capable of peeling off graphene sheets from artificial graphite, such as mesocarbon microbeads (MCMBs), which are known to have a skin layer of amorphous carbon.
  • MCMBs mesocarbon microbeads
  • a certain desired degree of hydrophilicity can be imparted to the graphene-carbon hybrid shell if the starting graphite is intentionally oxidized to some degree (e.g. to contain 2-15% by weight of oxygen).
  • oxygen-containing functional groups can be attached to the carbon phase if the carbonization treatment is allowed to occur in a slightly oxidizing environment.
  • the graphitic material may be selected from a non-intercalated and non-oxidized graphitic material that has never been previously exposed to a chemical or oxidation treatment prior to being placed into the impacting chamber.
  • the graphene balls can be subjected to a heat treatment at a temperature higher than 2,500°C for graphitization of the carbon material converted from the polymer.
  • the resulting material is particularly useful for thermal management applications (e.g. for use to make a finned heat sink, a heat exchanger, or a heat spreader).
  • the graphene shells having a i/002 higher than 0.3440 nm reflects the presence of oxygen- or fluorine-containing functional groups (such as -F, -OH, >0, and -COOH on graphene molecular plane surfaces or edges) that act as a spacer to increase the inter-graphene spacing.
  • oxygen- or fluorine-containing functional groups such as -F, -OH, >0, and -COOH on graphene molecular plane surfaces or edges
  • Another structural index that can be used to characterize the degree of ordering of the stacked and bonded graphene planes in the shell of graphene balls and conventional graphite crystals is the“mosaic spread,” which is expressed by the full width at half maximum of a rocking curve (X-ray diffraction intensity) of the (002) or (004) reflection.
  • This degree of ordering characterizes the graphite or graphene crystal size (or grain size), amounts of grain boundaries and other defects, and the degree of preferred grain orientation.
  • a nearly perfect single crystal of graphite is characterized by having a mosaic spread value of 0.2-0.4. Most of our graphene walls have a mosaic spread value in this range of 0.2-0.4 (if produced with a heat treatment temperature (HTT) no less than 2,500°C).
  • the shell of the hollow graphene ball contains single-layer or few-layer graphene sheets chemically bonded by a carbon material having a carbon material-to-graphene weight ratio from 1/100 to 1/2, wherein the few-layer graphene sheets have 2-10 layers of stacked graphene planes having an inter-plane spacing doo 2 from 0.3354 nm to 0.36 nm as measured by X-ray diffraction and the single-layer or few-layer graphene sheets contain a pristine graphene material having essentially zero % of non-carbon elements, or a non-pristine graphene material having 0.01% to 25% by weight of non-carbon elements (more typically ⁇ 15%) wherein the non-pristine graphene is selected from graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, or a combination thereof.
  • the hollow graphene balls may have a density from 0.001 to 1.7 g/cm , a specific surface area from 50 to 3,000 m /g, a thermal conductivity of at least 200 W/mK per unit of specific gravity, and/or an electrical conductivity no less than 2,000 S/cm per unit of specific gravity.
  • the shell contains stacked graphene planes having an inter-planar spacing doo 2 from 0.3354 nm to 0.40 nm as measured by X-ray diffraction.
  • the graphene balls can be used in the following forms for various applications:
  • the graphene balls may be compacted together (with or without a binder resin) to
  • TIM thermal interface material
  • the graphene balls can be filled into odd-shaped spaces as a heat spreader per se due to its high thermal conductivity.
  • the light weight (low density adjustable between 0.001 and 1.7 g/cm ), high thermal conductivity per unit specific gravity or per unit of physical density, and high structural integrity (graphene sheets being bonded by carbon) make the graphene balls (coupling with a binder or matrix material) an ideal material for a durable heat exchanger.
  • the matrix or binder material can be a polymer, a metal (e.g. Cu and Al), a pitch (e.g.
  • the hollow graphene balls can be a thermally conductive additive of a conductive coating or paint formulation.
  • the high thermal emissivity of the invented graphene balls enables good radiation-based heat dissipation.
  • the substantially spherical shape of graphene balls can result in a heat-dissipator or heat sink surface having micro-grooves for micro-convective flow for faster heat dissipation.
  • the graphene ball-based thermal management or heat dissipating devices include a heat exchanger, a heat sink (e.g. finned heat sink), a heat pipe, high-conductivity insert, thin or thick conductive plate (between a heat sink and a heat source), thermal interface medium (or thermal interface material, TIM), thermoelectric or Peltier cooling plate, etc.
  • a heat exchanger is a device used to transfer heat between one or more fluids; e.g. a gas and a liquid separately flowing in different channels.
  • the fluids are typically separated by a solid wall to prevent mixing.
  • the presently invented graphene balls, along with a resin binder, may be sprayed over surfaces of a heat exchanger as a heat dissipation-enhancing coating, for instance.
  • Heat exchangers are widely used in refrigeration systems, air conditioning units, heaters, power stations, chemical plants, petrochemical plants, petroleum refineries, natural-gas processing, and sewage treatment.
  • a well-known example of a heat exchanger is found in an internal combustion engine in which a circulating engine coolant flows through radiator coils while air flows past the coils, which cools the coolant and heats the incoming air.
  • the solid walls e.g. that constitute the radiator coils
  • the presently invented graphene balls having either a higher thermal conductivity or higher specific surface area, are a superior alternative to Cu and Al, for instance.
  • heat exchangers There are many types of heat exchangers that are commercially available: shell and tube heat exchanger, plate heat exchangers, plate and shell heat exchanger, adiabatic wheel heat exchanger, plate fin heat exchanger, pillow plate heat exchanger, fluid heat exchangers, waste heat recovery units, dynamic scraped surface heat exchanger, phase-change heat exchangers, direct contact heat exchangers, and microchannel heat exchangers. Every one of these types of heat exchangers can take advantage of the exceptional high thermal conductivity and specific surface area of the presently invented graphene ball material.
  • the presently invented solid graphene balls can also be used in a heat sink.
  • Heat sinks are widely used in electronic devices for heat dissipation purposes.
  • the central processing unit (CPU) and battery in a portable microelectronic device such as a notebook computer, tablet, and smart phone
  • CPU central processing unit
  • a portable microelectronic device such as a notebook computer, tablet, and smart phone
  • a metal or graphite object e.g. Cu foil or graphite foil
  • TIM thin thermal interface material mediates between the hot surface of the heat source and a heat spreader or a heat- spreading surface of a heat sink.
  • a heat sink usually consists of a high-conductivity material structure with one or more flat surfaces to ensure good thermal contact with the components to be cooled, and an array of comb or fin like protrusions to increase the surface contact with the air, and thus the rate of heat dissipation.
  • a heat sink may be used in conjunction with a fan to increase the rate of airflow over the heat sink.
  • a heat sink can have multiple fins (extended or protruded surfaces) to improve heat transfer. In electronic devices with limited amount of space, the shape/arrangement of fins must be optimized such that the heat transfer density is maximized.
  • cavities inverted fins may be embedded in the regions formed between adjacent fins. These cavities are effective in extracting heat from a variety of heat generating bodies to a heat sink.
  • an integrated heat sink comprises a heat collection member (core or base) and at least one heat dissipation member (e.g. a fin or multiple fins) integral to the heat collection member (base) to form a finned heat sink.
  • the fins and the core are naturally connected or integrated together into a unified body without using an externally applied adhesive or mechanical fastening means to connect the fins to the core.
  • the heat collection base has a surface in thermal contact with a heat source (e.g. a LED), collects heat from this heat source, and dissipates heat through the fins into the air.
  • FIG. 10 provides a schematic of two heat sinks: 300 and 302.
  • the first one contains a heat collection member (or base member) 304 and multiple fins or heat dissipation members (e.g. fin 306) connected to the base member 304.
  • the base member 304 is shown to have a heat collection surface 314 intended to be in thermal contact with a heat source.
  • the heat dissipation member or fin 306 is shown to have at least a heat dissipation surface 320.
  • a particularly useful embodiment is an integrated radial heat sink 302 comprising a radial finned heat sink assembly that comprises: (a) a base 308 comprising a heat collection surface 318; and (b) a plurality of spaced parallel planar fin members (e.g. 310, 312 as two examples) supported by or integral with the base 308, wherein the planar fin members (e.g. 310) comprise the at least one heat dissipation surface 322. Multiple parallel planar fin members are preferably equally spaced.
  • the presently invented graphene balls can be an additive in the structure of any finned heat sink element, or simply an ingredient of a heat-dissipating coating of any element.
  • the graphene balls being highly elastic and resilient, are a good thermal interface material and a highly effective heat spreading element as well.
  • these high-conductivity graphene balls can also be used as an insert for electronic cooling and for enhancing the heat removal from small chips to a heat sink. Because the space occupied by high conductivity materials is a major concern, it is a more efficient design to make use of high conductivity pathways that can be embedded into a heat generating body.
  • the elastic and highly conducting graphene balls herein disclosed meets these requirements perfectly.
  • the high elasticity and high thermal conductivity make the presently invented solid graphene balls (made into a compact with or without a binder) a good conductive thick plate to be placed as a heat transfer interface between a heat source and a cold flowing fluid (or any other heat sink) to improve the cooling performance.
  • the heat source is cooled under the thick graphene ball-based plate instead of being cooled in direct contact with the cooling fluid.
  • the thick plate of graphene balls can significantly improve the heat transfer between the heat source and the cooling fluid by way of conducting the heat current in an optimal manner. No additional pumping power and no extra heat transfer surface area are required.
  • the graphene balls may also be coated onto selected surfaces of a heat pipe.
  • graphene balls can be used as a wick material inside a heat pipe.
  • a heat pipe is a heat transfer device that uses evaporation and condensation of a two-phase working fluid or coolant to transport large quantities of heat with a very small difference in temperature between the hot and cold interfaces.
  • a conventional heat pipe consists of sealed hollow tube made of a thermally conductive metal such as Cu or Al, and a wick to return the working fluid from the evaporator to the condenser.
  • the pipe contains both of the saturated liquid and vapor of a working fluid (such as water, methanol or ammonia), all other gases being excluded.
  • the heat pipe for electronics thermal management can have a solid graphene foam envelope and wick, with water as the working fluid.
  • Graphene/ methanol may be used if the heat pipe needs to operate below the freezing point of water, and graphene/ammonia heat pipes may be used for electronics cooling in space.
  • Peltier cooling plates operate on the Peltier effect to create a heat flux between the junction of two different conductors of electricity by applying an electric current. This effect is commonly used for cooling electronic components and small instruments. In practice, many such junctions may be arranged in series to increase the effect to the amount of heating or cooling required.
  • the solid graphene balls may be used to improve the heat transfer efficiency.
  • the graphene balls and a solid compact element containing graphene balls compacted together can contain microscopic pores ( ⁇ 2 nm) or mesoscaled pores having a pore size from 2 nm to 50 nm. They can also be made to contain micron-scaled pores (1-500 pm). Based on well- controlled pore size alone, the instant graphene ball products can be an exceptional filter material for air or water filtration.
  • the graphene shell chemistry and the bonding carbon phase chemistry can be independently controlled to impart different amounts and/or types of functional groups to either or both of the graphene sheets and the carbon binder phase (e.g. as reflected by the percentage of O, F, N, H, etc. in the foam).
  • the concurrent or independent control of both pore sizes and chemical functional groups at different sites of the internal structure provide unprecedented flexibility or highest degree of freedom in designing and making graphene balls (i.e. graphene/carbon hybrid balls) that exhibit many unexpected properties, synergistic effects, and some unique combination of properties that are normally considered mutually exclusive (e.g.
  • some part of the structure is hydrophobic and other part hydrophilic; or the compact structure containing graphene balls can be both hydrophobic and oleophilic).
  • a surface or a material is said to be hydrophobic if water is repelled from this material or surface and that a droplet of water placed on a hydrophobic surface or material will form a large contact angle.
  • a surface or a material is said to be oleophilic if it has a strong affinity for oils and not for water. The present method allows for precise control over hydrophobicity, hydrophilicity, and oleophilicity of an object containing multiple types of graphene balls.
  • the present disclosure also provides an oil-removing, oil- separating, or oil-recovering device, which contains the presently invented graphene balls as an oil-absorbing or oil- separating element. Also provided is a solvent-removing or solvent-separating device containing the graphene balls as a solvent-absorbing element.
  • a major advantage of using the instant graphene-carbon hybrid balls as an oil-absorbing element is its structural integrity. Due to the notion that graphene sheets in the shell are chemically bonded by the carbon material, the resulting foam would not get disintegrated upon repeated oil absorption operations. In contrast, we have discovered that graphene-based oil absorbing elements prepared by hydrothermal reduction, vacuum-assisted filtration, or freeze drying get disintegrated after absorbing oil for 2 or 3 times. There is just nothing (other than weak van der Waals forces existing prior to first contact with oil) to hold these otherwise separated graphene sheets together. Once these graphene sheets are wetted by oil, they no longer are able to return to the original shape of the oil-absorbing element.
  • Another major advantage of the instant technology is the flexibility in designing and making oil-absorbing elements that are capable of absorbing oil up to an amount as high as 400 times of its own weight yet still maintaining its structural shape (without significant expansion). This amount depends upon the specific pore volume of the foam, which can be controlled mainly by the ratio between the amount of original carrier polymer particles and the amount of graphene sheets prior to the heat treatment.
  • the disclosure also provides a method to separate/recover oil from an oil-water mixture (e.g. oil-spilled water or waste water from oil sand).
  • the method comprises the steps of (a) providing an oil-absorbing element comprising the invented graphene balls; (b) contacting an oil- water mixture with the element, which absorbs the oil from the mixture; and (c) retreating the oil-absorbing element from the mixture and extracting the oil from the element.
  • the method comprises a further step of (d) reusing the element.
  • the disclosure provides a method to separate an organic solvent from a solvent-water mixture or from a multiple-solvent mixture.
  • the method comprises the steps of (a) providing an organic solvent-absorbing element comprising multiple graphene balls, separately or bonded together; (b) bringing the element in contact with an organic solvent-water mixture or a multiple- solvent mixture containing a first solvent and at least a second solvent; (c) allowing this element to absorb the organic solvent from the mixture or absorb the first solvent from the at least second solvent; and (d) retreating the element from the mixture and extracting the organic solvent or first solvent from the element.
  • the method contains an additional step (e) of reusing the solvent-absorbing element.
  • lkg of polypropylene (PP) pellets, 50 grams of flake graphite, 50 mesh (average particle size 0.18mm; Asbury Carbons, Asbury NJ) and 250 grams of magnetic steel balls were placed in a high-energy ball mill container.
  • the ball mill was operated at 300 rpm for 2 hours.
  • the container lid was removed and stainless steel balls were removed via a magnet.
  • the polymer carrier material was found to be coated with a dark graphene layer. Carrier material was placed over a 50 mesh sieve and a small amount of unprocessed flake graphite was removed.
  • a sample of the coated carrier material was then submitted to air flow suspension in a heating chamber, wherein the graphene-coated PP particles were heat-treated at 350°C and then at 600°C for 2 hours to produce individual (isolated/separated) graphene balls.
  • the carrier material for graphene ball production is not limited to PP. It could be any polymer (thermoplastic, thermoset, rubber, wax, mastic, gum, organic resin, etc.) provided the polymer can be made into a particulate form. It may be noted that un-cured or partially cured thermosetting resins (such as epoxide and imide-based oligomers or rubber) can be made into a particle form at room temperature or lower (e.g. cryogenic temperature). Hence, even partially cured thermosetting resin particles can be used as a polymer carrier.
  • PP polypropylene
  • EXAMPLE 2 Graphene balls using expanded graphite (> 100 nm in thickness) as the graphene source and ABS as the polymer solid carrier particles
  • EXAMPLE 3 Production of graphene balls from mesocarbon microbeads (MCMBs as the graphene source material) and polyacrylonitrile (PAN) fibers (as solid carrier particles)
  • MCMBs mesocarbon microbeads
  • PAN polyacrylonitrile
  • EXAMPLE 4 Particles of cured phenolic resin as the polymer carrier in a freezer mill
  • a mass of graphene-coated resin particles was subjected to air stream-assisted pyrolyzation to produce graphene balls.
  • EXAMPLE 5 Natural graphite particles as the graphene source, polyethylene (PE) or nylon 6/6 beads as the solid carrier particles, and ceramic or glass beads as added impacting balls
  • a mass of graphene-coated PE pellets and a mass of graphene-coated nylon beads were separately subjected to pyrolyzation (by heating the compacts in a chamber from l00°C to 650°C) while being suspended in a nitrogen gas stream for producing graphene balls.
  • SEM examination of these structures indicates that carbon phases are present near the edges of graphene sheets and these carbon phases act to bond the graphene sheets together.
  • the carbon- bonded graphene sheets form a shell of a graphene ball.
  • Graphene balls are schematically illustrated in FIG. 2(B).
  • the experiment began with preparation of micron-sized rubber particles.
  • a mixture of methylhydro dimethyl-siloxane polymer (20 g) and polydimethyisiloxane, vinyldimethyl terminated polymer (30 g) was obtained by using a homogenizer under ambient conditions for 1 minute.
  • Tween 80 (4.6 g) was added and the mixture was homogenized for 20 seconds.
  • Platinum-divinyl-tetramethyl-disiloxane complex (0.5 g in 15 g methanol) was added and mixed for 10 seconds. This mixture was added to 350 g of distilled water and a stable latex was obtained by homogenization for 15 minutes. The latex was heated to 60°C for 15 hours. The latex was then de-emulsified with anhydrous sodium sulfate (20 g) and the silicone rubber particles were obtained by filtration under a vacuum, washing with distilled water, and drying under vacuum at 25°C. The particle size distribution of the resulting rubber particles was 3-11 pm.
  • Some GO ball samples were mixed with different proportions of urea and the mixtures were heated in a microwave reactor (900 W) for 0.5 to 5 minutes. The products were washed several times with deionized water and vacuum dried. The products obtained were nitrogenated graphene balls. The nitrogen contents were from wt. 3% to 17 wt. %, as measured by elemental analysis.
  • oxidized graphene-carbon balls are particularly effective as an absorber of oil from an oil-water mixture (i.e. oil spilled on water and then mixed together).
  • the compacted graphene balls (0-15% by wt. oxygen), having graphene sheets bonded by carbon in the shell, are both hydrophobic and oleophilic (FIG. 7).
  • a surface or a material is said to be hydrophobic if water is repelled from this material or surface and that a droplet of water placed on a hydrophobic surface or material will form a large contact angle.
  • a surface or a material is said to be oleophilic if it has a strong affinity for oils and not for water.
  • the compression strength of the samples having an average density of 0.51 g/cm was measured to be 3.6 MPa and the compression modulus was measured to be 74 MPa.
  • the compression strength and compressive modulus of the presently invented graphene ball compact bonded by a phenolic resin having a comparable physical density are 5.5 MPa and 95 MPa, respectively.
  • CVD graphene is essentially pristine graphene that has never been exposed to oxidation and should have exhibited a high thermal conductivity compared to our graphene ball compacts.
  • the carbon phase of the hybrid shell is in general of low degree of crystallinity (some being amorphous carbon) and, thus, has much lower thermal or electrical conductivity as compared with graphene alone.
  • the carbon phase is coupled with graphene sheets to form a graphene ball compact produced by the presently invented method, the resulting product exhibits a higher thermal conductivity as compared to an all-pristine graphene foam.
  • graphene balls exhibit values from 250 to 500 W/mK per unit of specific gravity; but those of other types of foam materials are typically lower than 250 W/mK per unit of specific gravity.
  • FIG. 4 shows the thermal conductivity values of the presently invented graphene foam compact and hydrothermally reduced GO graphene foam. Electrical conductivity values of graphene foam compacts and the hydrothermally reduced GO graphene foam are shown in FIG. 6.
  • the internal structures (crystal structure and orientation) of several series of graphene- carbon foam materials were investigated using X-ray diffraction.
  • the graphene walls of the hybrid foam materials exhibit a doo 2 spacing typically from 0.3345 nm to 0.40 nm, but more typically up to 0.34 nm.
  • the doo2 spacing is decreased to approximately to 0.3354 nm, identical to that of a graphite single crystal.
  • the (004) peak intensity relative to the (002) intensity on the same diffraction curve, or the /(004)//(002) ratio, is a good indication of the degree of crystal perfection and preferred orientation of graphene planes.
  • the (004) peak is either non-existing or relatively weak, with the 7(004 )//(002) ratio ⁇ 0.1, for all graphitic materials heat treated at a temperature lower than 2,800°C.
  • the 7(004)//(002) ratio for the graphitic materials heat treated at 3,000-3,250°C e.g., highly oriented pyrolytic graphite,
  • HOPG HOPG
  • a graphene foam prepared with a final HTT of 2,750°C for one hour exhibits a 7(004)//(002) ratio of 0.78 and a Mosaic spread value of 0.21, indicating the pore walls being a practically perfect graphene single crystal with a good degree of preferred orientation (if prepared under a compression force).
  • The“mosaic spread” value is obtained from the full width at half maximum of the (002) reflection in an X-ray diffraction intensity curve.
  • This index for the degree of ordering characterizes the graphite or graphene crystal size (or grain size), amounts of grain boundaries and other defects, and the degree of preferred grain orientation.
  • a nearly perfect single crystal of graphite is characterized by having a mosaic spread value of 0.2-0.4.
  • Some of our graphene foams have a mosaic spread value in this range of 0.3-0.6 when produced using a final heat treatment temperature no less than 2,500°C.
  • harder polymer particles e.g. PE, PP, nylon, ABS, polystyrene, high impact polystyrene, etc. and their filler-reinforced versions
  • softer polymer particles e.g. rubber, PVC, polyvinyl alcohol, latex particles
  • polymer particles are generally capable of
  • the instant disclosure provides processes that generate graphene ball compacts having a density that can be as low as 0.001 g/cm and as high as 1.7 g/cm .
  • the pore sizes can be varied from microscopic ( ⁇ 2 nm), through mesoscaled (2-50 nm), and up to macro-scaled (e.g. from 1 to 500 pm).
  • the presently invented method also allows for convenient and flexible control over the chemical composition (e.g. F, O, and N contents, etc.), responsive to various application needs (e.g. oil recovery from oil-contaminated water, separation of an organic solvent from water or other solvents, heat dissipation, etc.).
  • chemical composition e.g. F, O, and N contents, etc.
  • application needs e.g. oil recovery from oil-contaminated water, separation of an organic solvent from water or other solvents, heat dissipation, etc.

Abstract

L'invention concerne une masse de poudre de multiples billes creuses de graphène individuelles, au moins l'une des billes creuses de graphène ayant une enveloppe de graphène composée de feuilles de graphène liées par un matériau de carbone et un noyau creux entouré par l'enveloppe de graphène. Ces feuilles de graphène creuses peuvent être utilisées dans un large éventail d'applications, telles que la gestion thermique, la séparation d'un solvant organique d'un mélange solvant-eau et la séparation huile-eau. L'invention concerne également un procédé de production de multiples billes creuses de graphène individuelles.
PCT/US2019/043148 2018-07-25 2019-07-24 Production sans produits chimiques de billes creuses de graphène WO2020023578A1 (fr)

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US16/044,901 US11021371B2 (en) 2018-07-25 2018-07-25 Hollow graphene balls and devices containing same
US16/044,878 US11603316B2 (en) 2018-07-25 2018-07-25 Chemical-free production of hollow graphene balls
US16/044,901 2018-07-25

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