KR102593007B1 - Oriented humic acid film and highly conductive graphite film derived therefrom, and device comprising the same - Google Patents

Abstract

The present invention relates to an oriented humic acid film comprising a plurality of sheets of humic acid (HA) or chemically functionalized humic acid (CHA), chemically bonded or fused and substantially parallel to each other, wherein the film has a thickness of 5 nm to 500 μm. , a physical density of at least 1.3 g/cm ³ , a hexagonal carbon interplanar spacing (d002) of 0.4 nm to 1.3 nm as measured by X-ray diffraction, and a hexagonal non-carbon element content or oxygen content of less than 5% by weight. It relates to highly oriented humic acid films with carbon planes.

Description

Oriented humic acid film and highly conductive graphite film derived therefrom, and device comprising the same

This application claims priority to U.S. Patent Application No. 15/240,537, filed Aug. 18, 2016, and U.S. Patent Application No. 15/240,543, filed Aug. 18, 2016, which are incorporated herein by reference. incorporated by reference.

The present invention relates generally to the field of graphitic materials, and in particular to oriented humic acid films and graphite films derived therefrom. These novel thin film materials exhibit an unprecedented combination of exceptionally high thermal conductivity, high electrical conductivity, and high tensile strength.

Carbon is used in diamonds, fullerenes (0-D nanographitic materials), carbon nanotubes or carbon nanofibers (1-D nanographitic materials), graphene (2-D nanographitic materials), and graphite (3-D graphitic materials). It is known to have five unique crystalline structures, including: Carbon nanotubes (CNTs) refer to tubular structures grown to have single or multiple walls. Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have a diameter of several nanometers to hundreds of nanometers. Its longitudinal hollow structure gives the material unique mechanical, electrical and chemical properties. CNTs or CNFs are one-dimensional nanocarbon or 1-D nanographite materials.

Bulk native graphite is a 3-D graphitic material and each graphite grain consists of a number of grains (grains are graphite single crystals or crystallites) with grain boundaries (amorphous or defective zones) that distinguish neighboring graphite single crystals. Each grain consists of multiple graphene planes oriented parallel to each other. Graphene planes within graphite crystallites are composed of carbon atoms occupying a two-dimensional, hexagonal lattice. In a given grain or single crystal, graphene planes are stacked and bonded through van der Waals forces in the crystallographic c direction (perpendicular to the graphene plane or ground plane). Although all graphene planes within one grain are parallel to each other, typically graphene planes within one grain and graphene planes within adjacent grains are tilted in different orientations. In other words, the orientation of the various grains within a graphite particle typically varies from grain to grain.

Graphite single crystals (crystals) themselves have properties that are dramatically different when measured along the direction in the basal plane (crystallographic a- or b-axis direction) than when measured along the crystallographic c-axis direction (thickness direction). It is anisotropic. For example, the thermal conductivity of a single crystal of graphite can be approximately 1,920 W/mK (theoretical) or 1,800 W/mK (experimental) in the basal plane (crystallographic a- and b-axis directions), but not in the crystallographic c-axis direction. It is less than 10 W/mK (typically less than 5 W/mK). Additionally, multiple grains or crystallites within a graphite particle are typically all oriented along different directions. Accordingly, natural graphite particles consisting of multiple grains of different orientation exhibit average properties between these two extremes (i.e., typically not much higher than 5 W/mK).

In many applications, it is very difficult to create a thin graphitic structure with sufficiently large lateral dimensions (i.e. large length and width) and all graphene planes (or hexagonal carbon planes) essentially parallel to each other along one desired direction. It would be desirable. In other words, one large sized graphite film (e.g., a fully integrated composite of multiple graphene planes) with the c-axis orientation of all graphene planes substantially parallel to each other and with a sufficiently large length and/or width for a particular application. It is very desirable to have a layer). Up to this point, it has been very difficult to produce such oriented graphite films. Although several attempts have been made to prepare so-called oriented pyrolytic graphite (HOPG) through ultra-high temperature graphitization after tedious, energy-intensive and expensive chemical vapor deposition (CVD), the graphitic structure of HOPG is inadequately aligned. remains in its current state, and thus exhibits significantly lower properties than theoretically predicted.

The present invention provides a combination of humic acid alone or humic acid with graphene (graphene oxide, graphene fluoride, nitrated graphene, hydrogenated graphene, boron-doped graphene, other types of doped graphene, and other types of graphene). It relates to new materials science methods for designing and fabricating a novel class of materials, referred to herein as oriented humic acid films (HOHA films), from combinations of (including chemically functionalized graphene). HOHA is a thin film structure composed of aligned humic acid molecules or their derivatives (graphene- or graphene oxide-like 2D planes of hexagonal carbon atoms), where all graphene- or graphene oxide-like planes are essentially parallel to each other. do. These hexagonal carbon planes are aligned much better than conventional HOPG can achieve. These HOHA films typically have a thickness of 5 nm to 500 μm, more typically 10 nm to 200 μm, even more typically and preferably 100 nm to 100 μm. In most cases, HOGF has an oxygen content of 0.01 to 5% by weight, but may be nearly oxygen-free. Conventional HOPG does not contain oxygen.

The constituent graphene planes of graphite crystallites in natural or artificial graphite particles can be exfoliated and extracted or separated to obtain individual graphene sheets of carbon atoms if the interplanar van der Waals forces can be overcome. Separated individual graphene sheets of carbon atoms are commonly referred to as single-layer graphene. A stack of multiple graphene planes bonded through van der Waals forces in the thickness direction at a graphene interplanar spacing of approximately 0.3354 nm is commonly referred to as multilayer graphene. Multilayer graphene platelets can have up to 300 layers of graphene planes (thickness less than 100 nm), more typically up to 30 graphene planes (thickness less than 10 nm), and even more typically up to 20 graphene planes (thickness less than 10 nm). thickness of less than 7 nm), and most commonly up to 10 graphene planes (commonly referred to in the scientific community as few-layer graphene). Single-layer graphene and multilayer graphene sheets are collectively referred to as “nanographene platelets” (NGP). Graphene or graphene oxide sheets/platelets (collectively, NGPs) are a new class of carbon nanomaterials (2-D nanocarbons) distinct from 0-D fullerenes, 1-D CNTs, and 3-D graphites.

The present inventors' research group pioneered the development of early graphene materials, isolated graphene oxide sheets and related manufacturing processes as early as 2002: (1) BZ Jang and WC Huang, "Nano-scaled Graphene Plates", US patent No. 7,071,258 (07/04/2006), application filed October 21, 2002; (2) BZ Jang et al. “Process for Producing Nano-scaled Graphene Plates,” U.S. Patent Application No. 10/858,814 (06/03/2004); and (3) BZ Jang, A. Zhamu, and J. Guo, “Process for Producing Nano-scaled Platelets and Nanocomposites,” US Patent Application No. 11/509,424 (08/25/2006). Historically, Brodie first demonstrated the synthesis of graphite oxide in 1859 by adding a portion of potassium chlorate to a slurry of graphite in fuming nitric acid. In 1898, Staudenmaier improved this procedure by using fuming nitric acid as well as concentrated sulfuric acid and adding chlorate in several aliquots over the course of the reaction. This small change in procedure makes the production of oxidized graphite in a single reaction vessel significantly more practical. In 1958, Hummers reported the method most commonly used today: graphite is oxidized by treatment with KMnO ₄ and NaNO ₃ in concentrated H ₂ SO ₄ . However, these early studies failed to isolate and identify fully exfoliated and separated graphene oxide sheets. These studies also failed to disclose the isolation of pristine, non-oxidized monolayer or multilayer graphene sheets.

In practice (e.g., as illustrated in FIG. 1 ), NGP typically reacts with a strong acid and/or on native graphite particles 100 to obtain graphite intercalation compound 102 (GIC) or graphite oxide (GO). or obtained by inserting an oxidizing agent. The presence of chemical species or functional groups in the interstitial space between graphene planes serves to increase the inter-graphene spacing (d002, as measured by X-ray diffraction), thereby bringing the graphene planes together along the c-axis direction. Significantly reduces the maintaining van der Waals forces. GIC or GO is most often produced by soaking natural graphite powder in a mixture of sulfuric acid, nitric acid (oxidizing agent), and other oxidizing agents (e.g., potassium permanganate or sodium perchlorate). The resulting GIC 102 is actually some type of graphite oxide (GO) particle. These GICs or GOs are then repeatedly washed and rinsed with water to remove excess acid, resulting in a graphite oxide suspension or dispersion, containing visually distinguishable discrete graphite oxide particles dispersed in water. There are two processing paths to follow after this cleaning step:

Route 1 involves removing water from the suspension to obtain “expandable graphite”, which is essentially bulk dried GIC or dried graphite oxide particles. Upon exposing expandable graphite to temperatures typically ranging from 800 to 1,050° C. for approximately 30 seconds to 2 minutes, the GIC undergoes rapid expansion by a factor of 30 to 300 to form “graphite worms” 104, which is a collection of exfoliated but largely non-separated graphite flakes that each remain interconnected.

In Path 1A, these graphite worms (exfoliated graphite or “network of interconnected/non-separated graphite flakes”) are formed from flexible graphite sheets typically having a thickness ranging from 0.1 mm (100 μm) to 0.5 mm (500 μm). Or it can be recompressed to obtain foil 106. Alternatively, graphite worms can be simply digested for the purpose of producing so-called “expanded graphite flakes” (108) containing mostly graphite flakes or platelets thicker than 100 nm (and therefore not nanomaterials by definition). You may choose to use a low-intensity air mill or shearing machine to do this. These expanded graphite flakes can be made into paper-like graphite mat 110.

Exfoliated graphite worms, expanded graphite flakes, and recompressed agglomerates of graphite worms (commonly referred to as flexible graphite sheets or flexible graphite foils) are made of 1-D nanocarbon materials (CNTs or CNFs) or 2-D Any 3-D graphitic material that is fundamentally different and clearly distinct from nanocarbon materials (graphene sheets or platelets, NGP). Flexible graphite (FG) foil can be used as a heat spreader material, but typically has a maximum in-plane thermal conductivity of less than 500 W/mK (more typically less than 300 W/mK) and less than 1,500 S/cm. It represents the in-plane electrical conductivity of . These low conductivity values are a direct result of many defects, wrinkled or folded graphite flakes, breaks or gaps between graphite flakes, and non-parallel flakes (e.g., SEM image in Figure 2). Many flakes are tilted at very large angles to each other (eg, misorientation of 20 to 40 degrees).

In Path 1B, the exfoliated graphite is subjected to high-strength mechanical processing to form isolated single-layer and multilayer graphene sheets (collectively referred to as NGP(112)), as disclosed in our U.S. application Ser. No. 10/858,814. Processed by shear (e.g., using an ultrasonicator, high shear mixer, high intensity air jet mill, or high energy ball mill). Single layer graphene can be as thin as 0.34 nm, while multilayer graphene can have a thickness of up to 100 nm, more typically less than 20 nm. Afterwards, the graphene sheets or platelets can be fabricated into graphene paper or membrane 114.

Path 2 involves sonicating the graphite oxide suspension for the purpose of separating/isolating the individual graphene oxide sheets from the graphite oxide particles. This is based on the concept that the inter-graphene plane separation increases from 0.3354 nm in native graphite to 0.6 to 1.1 nm in oxidized graphite oxide, significantly weakening the van der Waals forces that hold neighboring planes together. Ultrasonic power may be sufficient to further separate planar sheets of graphene to form separate, isolated, or distinct graphene oxide (GO) sheets. These graphene oxide sheets are then called "reduced graphene oxide" (which has an oxygen content of typically from 0.001% to 10% by weight, more typically from 0.01% to 5% by weight, and most typically less than 2% by weight). It can be reduced chemically or thermally to obtain RGO).

For purposes of defining the claims of this application, NGP includes single-layer discrete sheets/platelets and multilayer pristine graphene, graphene oxide, or reduced graphene oxide (RGO). Initial graphene has essentially 0% oxygen. RGO typically has an oxygen content of 0.001 to 5% by weight. Graphene oxide (including RGO) can have between 0.001% and 50% oxygen by weight.

It may be noted that flexible graphite foils (obtained by compressing and roll-pressing exfoliated graphite worms) for electronic device thermal management applications (e.g. as heat sink material) have the following main defects: (1 ) As previously specified, flexible graphite (FG) foils exhibit relatively low thermal conductivities, typically less than 500 W/mK, and more typically less than 300 W/mK. By impregnating the exfoliated graphite with a resin, the resulting composite exhibits a much lower thermal conductivity (typically well below 200 W/mK, more typically below 100 W/mK). (2) Flexible graphite foil without resin impregnated therein or coated thereon has low strength, low stiffness, and poor structural integrity. The high tendency of flexible graphite foils to tear makes them difficult to handle in the heat sink manufacturing process. In fact, flexible graphite sheets (typically 50 to 200 μm thick) are not “flexible” and therefore rigid enough to make finned component materials for finned heat sinks. (3) Another very subtle, almost ignored or overlooked, but extremely important property of the FG foil is its high tendency to easily delaminate due to graphite flakes easily escaping from the FG sheet surface and being released into other parts of the microelectronic device. These electrically conductive flakes (typically 1 to 200 μm in lateral dimension and greater than 100 nm in thickness) can cause internal shorting and failure of electronic devices.

Similarly, solid NGPs (comprising discrete sheets/platelets of pristine graphene, GO, and RGO), when packed into a film, membrane, or paper sheet 114 of a nonwoven assembly using a paper-fabrication process, , typically, these sheets/platelets are dense and do not exhibit high thermal conductivity unless the film/membrane/paper is ultra-thin (e.g. less than 1 μm, which is mechanically weak). This is reported in the inventor's earlier U.S. patent application Ser. No. 11/784,606 (April 9, 2007). However, ultra-thin films or paper sheets (less than 10 μm) are difficult to produce in large quantities and are difficult to handle when trying to introduce such thin films as heat sink materials. In general, paper-like structures or mats made from platelets of graphene, GO, or RGO (e.g., paper sheets made by a vacuum-assisted filtration process) have many defects, wrinkled or folded graphene sheets, or platelets. interruptions or gaps in between, and non-parallel platelets (e.g., SEM image in Figure 3b), resulting in relatively low electrical conductivity and low structural strength. These papers or aggregates of discrete NGP, GO or RGO platelets alone (without resin binder) also have a tendency to delaminate and release conductive particles into the air.

Other prior art graphitic materials are pyrolytic graphite films, typically thinner than 100 μm. The process begins with carbonization of a polymer film (e.g. polyimide) at a carbonization temperature of 400 to 1,500° C. under a typical pressure of 10 to 15 Kg/cm2 for 10 to 36 hours to obtain a carbonized material, followed by carbonization of a graphite film. Graphitization treatment follows at 2,500 to 3,200°C under extremely high pressure of 100 to 300 Kg/cm ² for 1 to 24 hours to form . Maintaining such extremely high pressures at such extremely high temperatures is technically extremely difficult. This is a difficult, slow, tedious, energy-intensive and extremely expensive process. Additionally, it has been difficult to produce pyrolytic graphite films thinner than 10 μm or thicker than 100 μm from polymers such as polyimide. These thickness-related issues are problematic in forming ultra-thin (<10 μm) and thick films (>100 μm) while still maintaining an acceptable degree of polymer chain orientation and mechanical strength, which requires appropriate carbonization and graphitization. Due to the difficulties inherent in this class of substances.

The second type of pyrolytic graphite is produced by high-temperature decomposition of hydrocarbon gases in vacuum followed by deposition of carbon atoms on the substrate surface. This vapor phase condensation of cracked hydrocarbons is essentially a chemical vapor deposition (CVD) process. In particular, oriented pyrolytic graphite (HOPG) is a material produced by treating CVD-deposited pyrolytic carbon under uniaxial pressure at very high temperatures (typically 3,000 to 3,300° C.). This involves bonding and simultaneous mechanical compression and thermomechanical treatment at very high temperatures for long periods of time in a protective atmosphere: a very expensive, energy-intensive, time-consuming and technically problematic process. These processes require very high temperature equipment (providing high vacuum, high pressure, or high compression) that is not only very expensive but also very expensive and difficult to maintain. Even with these extreme processing conditions, the obtained HOPG still has many defects, grain boundaries, and misorientation (neighboring graphene planes are not parallel to each other), resulting in less satisfactory in-plane properties. Typically, the best manufactured HOPG sheets or blocks typically contain many poorly aligned grains or crystals and large amounts of grain boundaries and defects.

Similarly, the most recently reported graphene thin films (<2 nm) prepared by catalytic CVD of hydrocarbon gases (e.g., C ₂ H ₄ ) on Ni or Cu surfaces are not single-grain crystals, but rather contain many grains. It is a multi-crystalline structure with boundaries and defects. When Ni or Cu is the catalyst, carbon atoms obtained through decomposition of hydrocarbon gas molecules at 800 to 1,000° C. are deposited on the Ni or Cu foil surface to form sheets of multi-crystalline single-layer or few-layer graphene. . Grains typically have sizes much smaller than 100 μm, and more typically smaller than 10 μm. Optically transparent and electrically conductive, these graphene thin films are intended for applications such as touch screens (replacing indium-tin oxide or ITO glass) or semiconductors (replacing silicon, Si). Additionally, the Ni- or Cu-catalyzed CVD process itself is not conducive to the deposition of more than 5 graphene (typically less than 2 nm), beyond which the underlying Ni or Cu catalyst can no longer provide any catalytic effect. No. There is no experimental evidence specifying that CVD graphene layers thicker than 5 nm are possible. Both CVD graphene film and HOPG are very expensive.

The above discussion clearly indicates that all prior art methods or processes for producing graphene and graphite thin films have major drawbacks. Accordingly, there is a pressing need to have a new class of carbon nanomaterials that are similar to or superior to graphene in terms of properties, but in a more cost-effective, faster, more scalable, and more environmentally friendly manner. can be produced Production processes for these novel carbon nanomaterials require reduced amounts of undesirable chemicals (or removal of these chemicals altogether), shortened process times, low energy consumption, and drainage of undesirable chemical species (e.g. sulfuric acid) or air (eg SO ₂ and NO ₂ ). In addition, these novel nanomaterials should be easily manufactured in a thin-film graphite structure that is relatively thermally and electrically conductive.

Accordingly, the object of the present invention is to provide a new class of thin-film graphite materials (thicknesses ranging from 5 nm to 500 μm) that are thermally and electrically conductive and mechanically robust, and to reduce the cost of producing this new class of graphite films. -Providing an effective method.

Humic acids (HA) are organic substances that are commonly found in soil and can be extracted from soil using bases (e.g., KOH). HA can also be extracted in high yields from a type of coal called leonardite, which is an oxidized version of lignite coal. HA extracted from leonardite contains a number of oxygenated groups (e.g., carboxyl groups) located around the edges of the graphene-like molecular center (SP2 core of the hexagonal carbon structure). These materials are somewhat similar to graphene oxide (GO), which is produced by strong acid oxidation of natural graphite. HA has a typical oxygen content of 5 to 42% by weight (the other major elements are carbon and hydrogen). HA, after chemical or thermal reduction, has an oxygen content of 0.01% to 5% by weight. For the purposes of defining the claims in this application, humic acid (HA) refers to a total oxygen content ranging from 0.01% to 42% by weight. Reduced humic acid (RHA) is a special type of HA with an oxygen content of 0.01% to 5% by weight.

The present invention surprisingly provides a novel class of graphene-like 2D materials (i.e., humic acids) that can be used alone or in combination with graphene to form graphitic films. Accordingly, another object of the present invention is to provide a cost-effective method for producing such humic acid or humic acid-graphene hybrid film-derived graphite films in large quantities. These methods or processes do not involve the use of environmentally unfriendly chemicals. Humic acid- or humic acid/graphene-derived graphite films exhibit thermal conductivity, electrical conductivity, elastic modulus and/or strength similar to or greater than conventional oriented pyrolytic graphite films. This process can produce oriented graphite films of virtually any desired thickness, from a few nanometers (nm) to hundreds of micrometers (μm).

Another object of the present invention is to provide products (e.g. devices) containing the graphite film of the present invention and methods of operating such products. The product may be a heat dissipation element in a smartphone, tablet computer, digital camera, display device, flat TV, LED lighting device, etc. These thin films exhibit an outstanding combination of thermal conductivity, electrical conductivity, mechanical strength, and elastic modulus that is not matched by any material in a similar thickness range. The oriented graphite film has an electrical conductivity greater than 12,000 S/cm, a thermal conductivity greater than 1,500 W/mK, a physical density greater than 2.1 g/cm3, a tensile strength greater than 120 MPa, and/or a tensile strength greater than 120 GPa. It can exhibit a large elastic modulus. No other material is known that exhibits this outstanding set of properties.

The present invention is a humic acid film comprising a humic acid (CHA) sheet containing a humic acid (HA) functional group, wherein the film has a thickness of 5 nm to 500 ㎛, a physical density of 1.3 g/cm ³ or more, and a thickness measured by X-ray diffraction. The case relates to an oriented humic acid film having hexagonal carbon planes with a hexagonal carbon interplanar spacing (d002) of 0.4 nm to 1.3 nm and a non-carbon element content or oxygen content of less than 5% by weight.

The present invention is an oriented humic acid film comprising a humic acid (CHA) sheet containing a humic acid (HA) functional group, wherein the film has a thickness of 5 nm to 500 ㎛, a physical density of 1.3 g/cm3 or more, and An oriented humic acid film is provided, having hexagonal carbon planes having a hexagonal carbon interplanar spacing (d002) of 0.4 nm to 1.3 nm, as measured, and a non-carbon element content or oxygen content of less than 5% by weight.

The present invention also provides a highly conductive graphite film derived from the above-described oriented humic acid film through heat treatment, wherein the graphite film has a hexagonal carbon interplanar spacing (d002) of less than 0.4 nm and an oxygen content or non-carbon content of less than 2% by weight. A hexagonal carbon plane with an elemental content, a physical density greater than 1.6 g/cm3, an in-plane thermal conductivity greater than 600 W/mK, an in-plane electrical conductivity greater than 2,000 S/cm, and a tensile strength greater than 20 MPa, A highly conductive graphite film is provided.

The oriented humic acid film may further comprise graphene sheets or molecules parallel to the HA or CHA sheets, wherein the HA-to-graphene or CHA-to-graphene ratio is between 1/100 and 100/ 1, and the graphene is graphene with 0% oxygen, graphene oxide, reduced graphene oxide, graphene fluoride, graphene bromide, graphene iodide, boron-doped graphene, nitrogen-doped is selected from graphene, or a combination thereof.

The highly conductive graphite film may further comprise a graphene sheet, wherein the graphite film has a hexagonal carbon interplanar spacing (d002) of less than 0.4 nm and an oxygen content or non-carbon element content of less than 2% by weight. The carbon is flat, has a physical density greater than 1.6 g/cm3, an in-plane thermal conductivity greater than 600 W/mK, an in-plane electrical conductivity greater than 2,000 S/cm, and a tensile strength greater than 20 MPa.

The oriented humic acid film may further comprise a polymer, wherein the HA or CHA sheets are dispersed in or bound by the polymer.

The present invention also provides an oriented humic acid film (externally A process for producing humic acid-derived graphite films (with or without added graphene sheets) and humic acid-derived graphite films is provided. This process involves (a) preparing a dispersion of humic acid (HA) or a humic acid (CHA) containing humic acid (HA) functional groups with HA or CHA sheets dispersed in a liquid medium, wherein the HA sheets contain more than 5% by weight. containing a higher oxygen content or the CHA sheet containing a non-carbon element content higher than 5% by weight; (b) dispensing and depositing the HA or CHA dispersion onto the surface of the support substrate to form a wet layer of HA or CHA, wherein the dispensing and deposition procedure includes subjecting the dispersion to an orientation-induced stress. ; (c) Partially or completely removing the liquid medium from the wetting layer of HA or CHA to form a dried hexagonal carbon plane and a hexagonal carbon interplanar spacing (d002) of 0.4 nm to 1.3 nm as measured by X-ray diffraction. forming an HA or CHA layer; and (d) the dried HA or CHA layer is formed into an oriented layer containing interconnected/fused HA/CHA molecules or thermally reduced HA or CHA sheets substantially parallel to each other at a first heat treatment temperature greater than 80°C. It includes heat treatment to produce a humic acid film. This oriented humic acid film of interconnected or fused HA or CHA sheets can be subjected to an additional compression step.

This process (with or without a compression step) (e) produces a humic acid film of reduced HA or CHA at a second heat treatment temperature higher than the first heat treatment temperature with a hexagonal carbon interplanar spacing (d002) of less than 0.4 nm and 5 further heat treating to produce a graphite film having an oxygen content or non-carbon element content of less than % by weight; and (f) compressing the graphite film to produce a highly conductive graphite film.

In certain preferred embodiments, the HA or CHA dispersion further contains graphene sheets or molecules dispersed therein, the HA-to-graphene or CHA-to-graphene ratio being between 1/100 and 100/1. These graphene sheets include graphene with 0% oxygen, graphene oxide, reduced graphene oxide, graphene fluoride, graphene bromide, graphene iodide, boron-doped graphene, and nitrogen-doped graphene. is selected from graphene, or a combination thereof.

In some embodiments, the HA or CHA sheets are present in an amount sufficient to form a liquid crystalline phase in the liquid medium. In certain particular embodiments, the dispersion contains a first volume fraction of HA or CHA dispersed in a liquid medium that exceeds the critical volume fraction (Vc) for liquid crystalline phase formation, and the dispersion is oriented in HA or CHA sheets. To improve, it is concentrated to reach a second volume fraction of HA or CHA, which is larger than the first volume fraction. The first volume fraction may be equivalent to a weight fraction of HA or CHA of 0.05% to 3.0% by weight in the dispersion. The dispersion may be concentrated to contain more than 3.0% but less than 15% by weight of HA or CHA dispersed in the liquid medium prior to step (b).

Typically, the dispersion does not contain any other polymers other than HA or CHA itself. However, in some embodiments, the dispersion may additionally contain a polymer dissolved in the liquid medium or attached to the HA or CHA.

In certain embodiments, CHA or externally added graphene sheets (if present), or both, are polymers, SO ₃ H, COOH, NH ₂ , OH, R'CHOH, CHO, CN, COCl, halides, COSH, SH, COOR', SR', SiR' ₃ , Si(--OR'--) _y R' _{3 -y} , Si(--O--SiR' ₂ --)OR', R", Li, AlR ' ₂ , Hg--X, TlZ ₂ and Mg-- Aryl, or poly(alkyl ether), R" is fluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl, or cycloaryl, X is halide, and Z is carboxylate or trifluoroacetate. , or a combination thereof.

The second heat treatment temperature may be higher than 1,500° C. for a time sufficient to reduce the hexagonal carbon interplanar spacing (d002) to a value of less than 0.36 nm and the oxygen content or non-carbon element content to less than 0.1 weight percent. In the process of the present invention, the second heat treatment temperature is preferably 1,500°C to 3,200°C.

The liquid medium may contain water and/or alcohol. The liquid medium may contain a non-aqueous solvent selected from polyethylene glycol, ethylene glycol, propylene glycol, alcohols, sugar alcohols, polyglycerols, glycol ethers, amine-based solvents, amide-based solvents, alkylene carbonates, organic acids, or inorganic acids. there is.

In certain embodiments, the dried layer of HA or CHA has a thickness of 10 nm to 200 μm or the resulting highly conductive graphite film has a thickness of 10 nm to 200 μm.

Preferably, this process is a roll-to-roll or reel-to-reel process, wherein step (b) feeds a sheet of solid substrate material from rollers to the deposition zone, and HA or depositing a layer of CHA dispersion on the surface of a sheet of solid substrate material to form a wet layer of HA or CHA dispersion thereon, and drying the HA or CHA dispersion to form a dried HA or CHA layer deposited on the substrate surface. forming and collecting the HA or CHA layer-deposited substrate sheet on a collector roller.

In the process of the present invention, the first heat treatment temperature may contain a temperature ranging from 100° C. to 1,500° C., and the oriented graphene film may have an oxygen content of less than 2.0% and a hexagonal carbon interplanar spacing (d002) of less than 0.35 nm. , a thermal conductivity of at least 800 W/mK, and/or an electrical conductivity of at least 2,500 S/cm.

In some embodiments, the first heat treatment temperature comprises a temperature ranging from 1,500° C. to 2,100° C., and the oriented humic acid film has an oxygen content of less than 1.0%, a hexagonal carbon interplanar spacing (d002) of less than 0.345 nm, and a temperature of at least 1,000 W. It has a thermal conductivity of /mK, and/or an electrical conductivity of more than 5,000 S/cm. Preferably, the first heat treatment temperature and/or the second heat treatment temperature contains a temperature higher than 2,100° C., and the oriented humic acid film has an oxygen content of less than 0.001%, an inter-graphene spacing of less than 0.340 nm, and a mosaic diffusion of less than 0.7. value, a thermal conductivity of at least 1,300 W/mK, and/or an electrical conductivity of at least 8,000 S/cm.

In processes where the dispersion contains both humic acid and graphene, the second heat treatment temperature can include a temperature of 2,500° C. or higher, and the highly conductive graphite film has an inter-graphene spacing of less than 0.336 nm, a mosaic diffusion value of less than 0.4, has a thermal conductivity greater than 1,600 W/mK, and/or an electrical conductivity greater than 10,000 S/cm.

In some embodiments, the process results in an oriented humic acid film exhibiting a degree of graphitization greater than 80% and/or a mosaic diffusion value less than 0.4. Typically, oriented humic acid films contain chemically bonded hexagonal carbon planes that are parallel to each other.

In some embodiments, the starting HA or CHA sheets have a maximum original length and the resulting oriented humic acid film contains HA or CHA sheets with a length longer than the maximum original length.

In the process of the invention comprising adding some graphene sheets to the dispersion, the oriented humic acid film is a polycrystalline graphene structure with a preferred crystalline orientation as measured by the X-ray diffraction method. In this process, heat treatment step (e) involves chemically linking, merging, or chemically bonding the HA or CHA sheets (with other HA or CHA sheets, or with graphene sheets) and/or re-graphitizing the graphitic structure. Or induce restructuring.

It is surprising to observe that under heat treatment temperature conditions, HA/CHA sheets or molecules can react or merge with other HA/CHA sheets or molecules, and even more surprisingly, these HA/CHA sheets or molecules can can react or merge with the added graphene sheets, provided that all such HA/CHA sheets/molecules and graphene sheets are well aligned and packed together such that the molecular planes are essentially parallel to each other. These properties enable the integration of HA/CHA sheets/molecules and graphene sheets into a single monolithic entity, rather than an assembly of separate sheets.

When externally added graphene sheets are present in the dispersion, the oriented graphite film has an electrical conductivity greater than 5,000 S/cm, a thermal conductivity greater than 800 W/mK, and a physical density greater than 1.9 g/cm3. , a tensile strength greater than 80 MPa, and/or an elastic modulus greater than 60 GPa. Preferably and typically, the oriented graphite film has an electrical conductivity greater than 8,000 S/cm, a thermal conductivity greater than 1,200 W/mK, a physical density greater than 2.0 g/cm, a tensile strength greater than 100 MPa, and /or has an elastic modulus greater than 80 GPa. More preferably, the oriented graphite film has an electrical conductivity greater than 12,000 S/cm, a thermal conductivity greater than 1,500 W/mK, a physical density greater than 2.1 g/cm, a tensile strength greater than 120 MPa, and/or It has an elastic modulus greater than 120 GPa.

The present invention also provides an oriented graphite film produced by the process of the present invention (with or without external addition of graphene sheets in the dispersion). The present invention also provides microelectronic devices containing the oriented graphite films of the present invention as heat-dissipating or heat-spreading components. The microelectronic device may be a smartphone, tablet computer, flat panel display, flexible display, watch, wearable electronic device, TV, or microelectronic communication device.

The present invention relates generally to the field of graphitic materials, and in particular to oriented humic acid films and graphite films derived therefrom. These novel thin film materials exhibit an unprecedented combination of exceptionally high thermal conductivity, high electrical conductivity, and high tensile strength.

1 shows a process for manufacturing isolated graphene sheets and aggregates of graphene or graphene oxide sheets in the form of graphene paper or films, as well as exfoliated graphite products (flexible graphite foil and flexible graphite composite) and pyrolytic graphite. (Bottom portion) is a flow diagram illustrating various prior art processes for manufacturing.
Figure 2 shows an SEM image of a cross-section of a flexible graphite foil, showing several graphite flakes with a non-parallel orientation to the flexible graphite foil surface plane and also showing several defects, distorted or folded flakes.
Figure 3a shows a SEMA image of HA liquid crystal-derived HOGF, in which multiple hexagonal carbon planes are uniformly fused into continuous-length graphene-like sheets or layers that can run tens of centimeters in width or length (this SEM In the image, only 50 μm wide of the 10 cm wide HOGF is shown).
Figure 3B shows an SEM image of a cross-section of a conventional graphene paper prepared from separate reduced graphene oxide sheets/platelets using a paper-making process (e.g., vacuum-assisted filtration). These images show several separate sheets of graphene that are folded or disrupted (not integrated), whose orientation is not parallel to the film/paper surface and have various defects or imperfections.
Figure 3C is a schematic diagram of a film of humic acid molecules chemically fused together and oriented to form an aligned graphite film.
Figure 4A shows the thermal conductivity values of (HA+GO)-derived HOGF, GO-derived HOGF, HA-derived HOGF, and FG foils, plotted as a function of final heat treatment temperature.
Figure 4b shows the thermal conductivity values of (HA+GO)-derived HOGF, HA-derived HOGF, and polyimide-derived HOPG, all plotted according to the final HTT.
Figure 4c shows the electrical conductivity values of (HA+GO)-derived HOGF, GO-derived HOGF, HA-derived HOGF, and FG foils, plotted as a function of final heat treatment temperature.
Figure 5a shows the inter-graphene planar spacing in HA-derived HOGF measured by X-ray diffraction.
Figure 5B depicts oxygen content in HA-induced HOGF.
Figure 5c shows the correlation between inter-graphene spacing and oxygen content.
Figure 5d shows the thermal conductivity values of (HA+GO)-derived HOGF, GO-derived HOGF, HA-derived HOGF, and FG foils, plotted as a function of final heat treatment temperature.
Figure 6 shows the thermal conductivity of HOGF samples plotted as a function of the proportion of GO sheets in the HA/GO suspension.
Figure 7A shows tensile strength values of (HA+GO)-derived HOGF, GO-derived HOGF, HA-derived HOGF, flexible graphite foil, and reduced graphene oxide paper, all plotted as a function of final heat treatment temperature. It was done.
Figure 7b shows the tensile strengths of (HA+GO)-derived HOGF, GO-derived HOGF, and HA-derived HOGF, all plotted as a function of final heat treatment temperature.

Humic acid (HA) is an organic substance commonly found in soil, which can be extracted from soil using a base (e.g. KOH). HA can also be extracted from a type of coal called leonardite, which is an oxidized version of lignite coal. HA extracted from leonardite contains a number of oxygenated groups (e.g., carboxyl groups) located around the edges of the graphene-like molecular center (SP2 core of the hexagonal carbon structure). These materials are somewhat similar to graphene oxide (GO), which is produced by strong acid oxidation of natural graphite. HA has a typical oxygen content of 5% to 42% by weight (the other major elements are carbon, hydrogen, and nitrogen). An example of a molecular structure for humic acids, with various components including quinones, phenols, catechols, and sugar moieties, is provided in Scheme 1 below (Source: Stevenson F.J. "Humus Chemistry: Genesis, Composition, Reactions," John Wiley & Sons, New York 1994):

[Scheme 1]

Non-aqueous solvents for humic acids include polyethylene glycol, ethylene glycol, propylene glycol, alcohols, sugar alcohols, polyglycerols, glycol ethers, amine-based solvents, amide-based solvents, alkylene carbonates, organic acids, or inorganic acids.

The invention provides a thickness of 5 nm to 500 μm (more typically and preferably 10 nm to 200 μm, even more typically 100 nm to 100 μm, even more typically 1 μm to 50 μm), and 1.6 g. A process for producing oriented humic acid films (with or without externally added graphene sheets) and humic acid-derived graphite films having a physical density of greater than /cm3 (up to 2.2 g/cm3) is provided. This process

(a) preparing a dispersion of humic acid (HA) or a dispersion of humic acid (CHA) comprising humic acid (HA) functional groups with HA or CHA sheets dispersed in a liquid medium, wherein the HA sheets contain oxygen higher than 5% by weight. wherein the CHA sheet contains a non-carbon element content higher than 5% by weight (in certain preferred embodiments, the HA or CHA dispersion further contains graphene sheets or molecules dispersed therein) and the HA-to-graphene or CHA-to-graphene ratio is 1/100 to 100/1. These graphene sheets include graphene with 0% oxygen, graphene oxide, reduced graphene oxide, may be selected from graphene fluoride, graphene bromide, graphene iodide, boron-doped graphene, nitrogen-doped graphene, or combinations thereof);

(b) dispensing and depositing the HA or CHA dispersion on the surface of the support substrate to form a wet layer of HA or CHA, wherein the dispersion and deposition procedure comprises subjecting the dispersion to orientation-induced stress. These orientation-controlling stresses (typically including shear stresses) enable the HA/CHA sheets (or sheet-like molecules) and graphene sheets (if present) to be aligned along the planar direction of the support substrate surface. Proper alignment of HA/CHA and graphene sheets is essential for chemical connection or merging between two or more HA/CHA sheets or between HA/CHA sheets and graphene sheets during subsequent heat treatment);

(c) liquid from the wet layer of HA or CHA to form a dried HA or CHA layer with hexagonal carbon planes and a hexagonal carbon interplanar spacing (d002) of 0.4 nm to 1.3 nm as measured by X-ray diffraction. partially or completely removing the medium; and

(d) heat treating the dried HA or CHA layer at a first heat treatment temperature greater than 80° C. to produce an oriented humic acid film containing interconnected or fused HA or CHA sheets that are substantially parallel to each other. do. These HA/CHA sheets were typically reduced thermally. These oriented humic acid films of reduced HA or CHA can be subjected to the additional step of compression.

The process (with or without a compression step) involves (e) forming a fused, reduced humic acid film of HA or CHA with a hexagonal carbon interplanar spacing (d002) of less than 0.4 nm at a second heat treatment temperature higher than the first heat treatment temperature; and further heat treating to produce a graphite film having an oxygen content or non-carbon element content of less than 5% by weight; and (f) compressing the graphite film to form a highly conductive graphite film.

In one embodiment, step (e) comprises forming the oriented humic acid film at a second heat treatment temperature higher than the first heat treatment temperature (typically greater than 300° C.) with a hexagonal carbon interplanar spacing (d002) of 0.3354 nm to 0.36 nm. and heat treatment to reduce the oxygen content or non-carbon content to less than 0.5% by weight. In a preferred embodiment, the second (or final) heat treatment temperature is at least: (A) 100 to 300°C, (B) 300 to 1,500°C, (C) 1,500 to 2,500°C, and/or (D) 2,500 to 3,200°C. Includes temperatures selected from Preferably, the second heat treatment temperature comprises a temperature in the range of 300 to 1,500° C. for at least one hour, and then a temperature in the range of 1,500 to 3,200° C. for at least another time.

Typically, when both the first heat treatment temperature and the second heat treatment temperature are below 1,500° C., the oriented humic acid (HOHA) film still contains planar molecules characteristic of humic acid molecules. Oriented humic acid (HOHA) films contain chemically bonded and fused hexagonal carbon planes, which are HA/CHA or bonded HA/CHA-graphene planes. These planes (hexagonally structured carbon atoms with small amounts of oxygen-containing groups) are parallel to each other.

Such HOHA films, when exposed to heat treatment temperatures (HTT) above 1,500°C for a sufficient length of time, typically no longer contain significant amounts of humic acid molecules, and essentially all HA/CHA sheets/molecules This was converted into graphene- or graphene oxide-like hexagonal carbon planes parallel to each other. The lateral dimensions (length or width) of these planes are large, typically several or even tens of times larger than the maximum dimensions (length/width) of the starting HA/CHA sheet. The HOHA of the present invention is essentially a “giant hexagonal carbon crystal” or a “giant planar graphene-like layer”, with all component graphene-like planes essentially parallel to each other. This has been previously discovered, developed, or developed. It is a unique and new class of materials whose possibilities are not limited.

The oriented HA/CHA layer (HOHA film without HTT > 1,500°C) itself is a very unique and new class of materials with surprisingly large cohesion (self-association, self-polymerization, and self-crosslinking abilities). This feature has not previously been taught or implied in the prior art.

Step (a) involves dispersing the HA/CHA sheet or molecule in a liquid medium, which liquid medium has a concentration of 20% to 47% by weight at the edges and/or on the plane of the HA/CHA sheet. , preferably with an oxygen content of 30% to 47% by weight), for certain HA or CHA molecules containing significant amounts of -OH and/or -COOH groups, may be water or a mixture of water and alcohol.

When the volume fraction or weight fraction of HA/CHA exceeded a critical value, the obtained dispersion was found to contain a liquid crystalline phase. Preferably, the HA/CHA suspension (dispersion) contains an initial volume fraction of HA/CHA sheets that exceeds the critical or threshold volume fraction for the formation of the liquid crystalline phase prior to step (b). The inventors have observed that this critical volume fraction is typically equal to the HA/CHA weight fraction ranging from 0.2% to 5.0% by weight of the HA/CHA sheet in the dispersion. However, these low HA/CHA content ranges are not particularly applicable to the formation of desired thin films using scalable processes, such as casting and coating. The ability to create thin films via casting or coating is highly advantageous and desirable as large-scale and/or automated casting or coating systems are readily available, and the process can be relied upon for the production of polymer thin films of consistently high quality. It is known to exist. Accordingly, we have carried out in-depth and extensive studies on the suitability for casting or coating from dispersions containing HA/CHA-based liquid crystal phases. By concentrating the dispersion to increase the HA/CHA content from the range of 0.2% to 5.0% by weight of the HA/CHA sheet to the range of 4% to 16% by weight, the inventors have discovered that a thin graphene film It was found that a dispersion very suitable for large-scale production was obtained. Most importantly and unexpectedly, the liquid crystalline phase is not only preserved but often enhanced, allowing the HA/CHA sheets to be oriented along the desired orientation during casting or coating procedures. In particular, HA/CHA sheets in the liquid crystalline state containing 4 to 16 wt% of the HA/CHA sheets have the highest tendency to be easily oriented under the influence of shear stress generated by commonly used casting or coating processes. have

Accordingly, in step (b), the HA/CHA suspension is preferably formed into thin film layers under the influence of shear stresses that promote laminar flow. One example of this shearing procedure is to cast or coat thin films of HA/CHA suspension using a slot-die coating machine. This procedure is similar to coating a layer of polymer solution onto a solid substrate. The roller, “doctor blade” or wiper creates shear stresses when the film is shaped, or when there is relative motion between the roller/blade/wiper and the support substrate at a sufficiently high relative motion rate. Unexpectedly and importantly, this shearing action causes the planar HA/CHA sheets to be well aligned, for example along the shear direction. Additionally, surprisingly, this state of molecular alignment or preferred orientation is not disturbed when the liquid components in the HA/CHA suspension are subsequently removed to form a well-packed layer of at least partially dried aligned HA/CHA sheets. The dried layer has a high birefringence constant between the in-plane direction and the direction perpendicular to the plane.

The present invention involves the discovery of a facile amphiphilic self-assembly method for fabricating HA/CHA-based thin films with the desired hexagonal planar orientation. HA, which contains 5 to 46% oxygen by weight, can be considered a negatively charged amphiphilic molecule due to its bonding of hydrophilic oxygen-containing functional groups and a hydrophobic basal plane. For CHA, the functional group can be either hydrophilic or hydrophobic. Successful fabrication of HA/CHA films with unique hexagonal, graphene-like plane orientation does not require complicated procedures. Rather, this is achieved by manipulating liquid crystalline formation and modification to tune HA/CHA synthesis and enable self-assembly of HA/CHA sheets in the liquid crystalline phase.

The HA/CHA suspension was characterized using atomic force microscopy (AFM), Raman spectroscopy, and FTIR to confirm its chemical state. Finally, the existence of a lyotropic mesomorphism of HA sheets (liquid crystalline HA phase) in aqueous solution was demonstrated through cross-polarization observations.

To determine whether a 1-D or 2-D species can form a liquid crystalline phase in a liquid medium, two main aspects are considered: the aspect ratio (length/width/diameter-to-thickness ratio) and the size of this material in the liquid medium. Sufficient dispersibility or solubility. HA or CHA sheets are characterized by high anisotropy, with one- to several-atom thickness (t) and typically micrometer-scale lateral width (w). According to Onsager theory, high aspect ratio 2D sheets can form liquid crystals in the dispersion when their volume fraction exceeds a critical value:

[Equation 1]

Considering a thickness of the graphene-like plane of 0.34 nm and a width of 1 μm, the desired critical volume is = 4×0.34/1,000 = 1.36×10-3 = 0.136%. However, the initial graphene sheet is not soluble in water and does not disperse well in common organic solvents due to its strong π-π stacking attraction (maximum volume fraction, Vm, N-methylpyrrolidone ( about 0.7×10 ^-5 in NMP) and about 1.5×10 ^-5 in ortho-dichlorobenzene). Fortunately, the molecular structure of HA or CHA, due to the several oxygen-containing functional groups attached to its edges, has good resistance in water and polar organic solvents such as alcohols, N,N-dimethyl formamide (DMF) and NMP. It can be made to exhibit dispersibility. Naturally occurring HA (e.g., HA from coal) is also soluble in non-aqueous solvents for humic acids, including polyethylene glycol, ethylene glycol, propylene glycol, alcohols, sugar alcohols, polyglycerols, glycol ethers, and amine-based solvents. , amide-based solvents, alkylene carbonates, organic acids, inorganic acids, or mixtures thereof.

Perhaps, depending on theoretical predictions, the critical volume fraction of HA/CHA may be lower than 0.2% or the critical weight fraction may be lower than 0.3%, but the inventors believe that the critical weight fraction for HA/CHA sheets to form liquid crystals is 0.4. It is significantly larger than weight percent. The most stable liquid crystals exist when the weight fraction of the HA/CHA sheet is in the range of 0.6% to 5.0%, which allows for high stability over a wide temperature range. To study the effect of HA/CHA size on the formation of its liquid crystalline crystals, HA/CHA samples were prepared using pH-assisted selective precipitation technique. The lateral dimensions of HA/CHA sheets were evaluated by AFM as well as dynamic light scattering (DLS) through three different measurement modes.

During the investigation of HA/CHA liquid crystals, the inventors made an unexpected and highly important discovery: the liquid crystalline phase of HA/CHA sheets in water and other solvents is susceptible to mechanical disturbance (e.g. mechanical mixing, shear, turbulence, etc.). It can be divided or destroyed. The mechanical stability of these liquid crystals is achieved by carefully removing the liquid medium (e.g., by vaporizing it) without mechanically disturbing the liquid crystal structure, so that the concentration of the HA/CHA sheets is at least 5% (preferably between 5% and 16% by weight). % by weight), significant improvements can be achieved. The inventors have further observed that for HA/CHA weight fractions in this range of 5 to 16%, HA/CHA sheets are particularly easy to form the desired orientation during casting or coating to form thin films.

Thermodynamically, the process of amphiphilic HA/CHA self-assembly in the liquid crystalline phase is an interaction of enthalpy change (ΔH) and entropy change (ΔS) as represented by equation (2):

[Equation 2]

ΔG _{self -assembly} = ΔH _{self -assembly} - TΔS _{self -assembly}

Previous studies on the thermodynamic driving force for amphiphilic self-assembly into liquid crystalline phases indicate that the entropic contribution plays a dominant role, while the enthalpy change is unfavorable in most cases. Onsager's theory predicts that high aspect ratio particles can form liquid crystalline phases above the critical volume fraction due to a net gain in entropy, because the loss of directional entropy is compensated by increased translational entropy. In detail, high aspect ratio particles are advantageous for the formation of long-range liquid crystal phases. Another possible reason for the HA/CHA aspect ratio effect could be structural wrinkling of the HA/CHA sheet in solvent since the restoring force resulting from bending the sheet is much weaker than the restoring force along the sheet. It has been found that the degree of HA/CHA wrinkle morphology in solvent can be further improved when the aspect ratio is increased. This wrinkled configuration will significantly affect both the intra- and intermolecular interactions of HA/CHA in suspension.

To achieve long-range ordering in aqueous dispersions, well-exfoliated HA/CHA sheets with strong long-range electrostatic repulsion are required. The formation of liquid crystal structures from colloidal particles typically requires a delicate balance of long-range repulsive forces, such as electrostatic forces, and short-range attractive forces, such as van der Waals forces and π-π interactions. If the long-range repulsion is not strong enough to overcome the short-range attraction, only agglomeration of colloidal particles or weak formation of lyotropic liquid crystals with small periodicity will inevitably occur. In HA/CHA aqueous dispersions, long-range repulsive interactions are provided by the electrical double layer formed by ionized oxygen functional groups. Although HA/CHA sheets still contain a significant portion of hydrophobic domains, the attractive π-π interactions and van der Waals forces can be effectively overcome by tuning the long-range electrostatic repulsion.

The chemical composition of HA/CHA plays an important role in controlling electrostatic interactions in aqueous or organic solvent dispersions. An increase in surface charge density will cause an increase in the strength of electrostatic repulsion relative to attraction. The proportion of aromatic and oxygenated domains can be easily tuned by the level of hexagonal carbon plane oxidation or chemical modification. Fourier transform infrared spectroscopy (FTIR-ATR) results under attenuated total reflection mode of HA/CHA indicate that oxidized species (hydroxyl, epoxy, and carboxyl groups) are present on the HA/CHA surface. Thermogravimetric analysis (TGA) in nitrogen was used to probe the oxygen functional group density on the HA/CHA surface. For oxidized HA, a mass loss of about 28% by weight was observed at approximately 250° C. and was attributed to the decomposition of unstable oxygen-containing species. Below 160°C, a mass loss of approximately 16% by weight is observed, which corresponds to desorption of physically absorbed water. X-ray photoelectron spectroscopy (XPS) results for HA indicate that the C/O atomic ratio is approximately 1.9. This suggests that HA has a relatively high density of oxygen functional groups. In addition, the present inventors also prepared HA containing low density oxygen functional groups by simply varying the time and temperature of thermal or chemical reduction of oxidized HA (e.g., from leonardite coal). The inventors have observed that liquid crystals can be found to have an oxygen weight fraction preferentially ranging from 5% to 40%, more preferably from 5% to 30%, and most preferably from 5% to 20%. .

Since the Debye screening length (κ-1) can be effectively increased by reducing the concentration of free ions surrounding the HA sheets, the colloidal interactions between HA sheets can be greatly influenced by the ionic strength. As the salt concentration increases, the electrostatic repulsion of HA liquid crystals in water can decrease. As a result, more water is released from the HA interlayer space, accompanied by a decrease in d spacing. Accordingly, ionic impurities in the HA dispersion must be sufficiently removed because they are important factors affecting the formation of the HA liquid crystal structure.

However, the present inventors have also discovered that when the HA/CHA dispersion is subjected to a casting or coating operation, some minor amounts of polymer (at most 10% by weight, preferably at most 5% by weight, and most preferably at most 2% by weight) are added. ) was found to be helpful in stabilizing the liquid crystal phase. At appropriate functional groups and concentrations, GO/CFG orientation in the obtained films can be improved. This has also never been taught or implied in previous published or patent literature.

The dried HA/CHA layer can then be heat treated. A suitably programmed heat treatment procedure includes at least two heat treatment temperatures (a first temperature for a first period of time, and subsequently raised to a second temperature and maintained at this second temperature for another period of time), or an initial treatment temperature (a first temperature for a first period of time). 1 temperature) and any other combination of at least two heat treatment temperatures (HTT), including a final HTT higher than the first temperature.

The first heat treatment temperature is for chemical coupling and thermal reduction of HA/CHA, at a first temperature of greater than 80°C (can be up to 1,000°C, preferably up to 700°C, and most preferably up to 300°C). It is carried out. This is referred to herein as Regime 1:

Regime 1 (up to 300° C.): In this temperature range, chemical bonding, polymerization (edge-to-edge fusion), and cross-linking between adjacent HA/CHA sheets (initial chemical linkage and thermal reduction regime) begin to occur. Multiple HA/CHA sheets are packed side-by-side and edge-to-edge and chemically bonded to form an integrated layer of graphene oxide-like entities. Additionally, the HA/CHA layer reduces its oxygen content to approximately 5% or less, primarily through thermally induced reduction reactions. This treatment results in a reduction of the inter-graphene spacing from approximately 0.8 to 1.2 nm (dry) to approximately 0.4 nm, and an increase in the in-plane thermal conductivity from approximately 100 W/mK to 500 W/mK. Even in this low temperature range, some chemical linkage between HA/CHA sheets occurs. Although the HA/CHA sheets are well aligned, the graphene interplanar spacing is relatively large (0.4 nm or greater). A large number of O-containing functional groups remain.

The highest or final HTT experienced by GO materials can be divided into three distinct HTT regimes:

Regime 2 (300° C. to 1,500° C.): Primarily in this chemical linking regime, additional thermal reduction and extensive chemical combination, polymerization, and cross-linking between adjacent HA/CHA sheets occur. Chemical linkage between HA/CHA and graphene sheets (e.g. GO sheets) (if present) also occurs. The oxygen content is typically reduced to less than 1% after chemical linkage, resulting in a reduction of the inter-graphene spacing to approximately 0.35 nm. This is in stark contrast to conventional graphitizable materials (e.g., carbonized polyimide films), which typically require temperatures as high as 2,500°C to initiate graphitization, with some initial graphitization already starting at such low temperatures. It implies that something has happened. This is another distinct feature of the graphene film-bonded metal foil of the present invention and its manufacturing process. This chemical linkage reaction results in an increase in the in-plane thermal conductivity of the graphene thin film to 850 to 1,250 W/mK and/or the in-plane electrical conductivity to 3,500 to 4,500 S/cm.

Regime 3 (1,500 to 2,500° C.): In this ordering and re-graphitization regime, extensive graphitization or graphene plane fusion occurs, resulting in a significantly improved degree of structural ordering. As a result, the oxygen content is typically reduced to 0.01% and the inter-graphene spacing is reduced to approximately 0.337 nm (depending on the actual HTT and length of time, achieving a degree of graphitization of 1% to approximately 80%). The improved degree of alignment is also reflected by an increase in the in-plane thermal conductivity to over 1,300 to 1,500 W/mK and/or the in-plane electrical conductivity to 5,000 to 7,000 S/cm.

Regime 4 (higher than 2,500°C): In this recrystallization and completion regime, extensive movement and removal of grain boundaries and other defects occurs, resulting in nearly perfect single or polycrystalline graphene crystals with massive grains, which start from It may be larger than the original grain size of the HA/CHA sheet. The oxygen content is essentially eliminated and is typically 0.01% to 0.1%. The inter-graphene spacing is reduced to approximately 0.3354 nm (graphitization degree of 80% to nearly 100%), which corresponds to the inter-graphene spacing of a fully graphitic single crystal. Very interestingly, graphene polycrystals all have graphene planes that are closely packed and bonded, with all planes aligned along one direction, perfect orientation. Such a perfectly oriented structure is not produced even by HOPG produced by simultaneously treating pyrolytic graphite at ultra-high temperature (3,400°C) under ultra-high pressure (300 Kg/cm2). Oriented graphene structures can achieve this highest degree of perfection at significantly lower temperatures and ambient (or slightly higher compression) pressures. The structures thus obtained exhibit an in-plane thermal conductivity of slightly more than 1,500-1,700 W/mK up to an in-plane electrical conductivity of 15,000-20,000 S/cm.

The oriented HA-derived structures of the invention comprise at least the first regime (typically requiring 1 to 24 hours in this temperature range), more typically the first two regimes (1 to 10 hours being preferred). , even more typically the first three regimes (preferably regime 3 for 0.5 to 5 hours), and most typically all four regimes (regime 4 for 0.5 to 2 hours may be run to achieve the highest conductivity) ) can be obtained by heat treating the HA/CHA layer with a temperature program including.

X-ray diffraction patterns were obtained with an X-ray diffractometer equipped with CuKcv radiation. The shift and broadening of the diffraction peaks were calibrated using silicon powder standards. The degree of graphitization (g) was calculated from the )am. These equations are only valid when d002 is approximately 0.3440 nm or less. HOHAs with d002 higher than 0.3440 nm indicate the presence of oxygen-containing functional groups (e.g., -OH, >O, and -COOH) on the graphene molecular planar surface, which act as spacers to increase the inter-graphene spacing. reflect

Another structural index that can be used to characterize the degree of ordering of the HOHA-derived graphite films of the present invention and conventional graphite crystals is "mosaic diffusion", which is defined as the fluctuation curve of (002) or (004) reflection ( X-ray diffraction intensity) is expressed in terms of full width at half maximum. This degree of ordering characterizes the graphite or graphene crystal size (or grain size), the amount of grain boundaries and other defects, and the degree of preferred grain orientation. Almost perfect single crystals of graphite are characterized by mosaic diffusion values of 0.2 to 0.4. Most of our HOHA-derived graphite samples have mosaic diffusion values in this range (when formed with a heat treatment temperature (HTT) above 2,500° C.) of 0.2 to 0.4. However, some values range from 0.4 to 0.7 for HTT between 1,500 and 2,500°C and from 0.7 to 1.0 for HTT between 300 and 1,500°C.

HA or graphene can be functionalized through various chemical pathways. In a preferred embodiment, the obtained functionalized HA or functionalized graphene (collectively denoted as Gn) may have the following general formula:

[Gn]--R _m

where m is the number of different functional group types (typically 1 to 5) and R is SO ₃ H, COOH, NH ₂ , OH, R'CHOH, CHO, CN, COCl, halide, COSH, SH, COOR ', SR', SiR' ₃ , Si(--OR'--) _y R' _{3 -y} , Si(--O--SiR' ₂ --)OR', R", Li, AlR' ₂ , is selected from Hg--X, TlZ ₂ and Mg-- ), R" is fluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl or cycloaryl, X is halide, and Z is carboxylate or trifluoroacetate.

Given that polymers, for example epoxy resins, and HA or graphene sheets can be combined to produce a coating composition, the functional group -NH ₂ is particularly taken into account. For example, a commonly used curing agent for epoxy resins is diethylenetriamine (DETA), which may have two or more -NH2 groups. One of the -NH ₂ groups may be bonded to the edge or surface of the graphene sheet, and the remaining unreacted -NH ₂ group will be available for later reaction with the epoxy resin. This arrangement provides good interfacial bonding between the HA (or graphene) sheet and the resin additive.

Other useful chemical functional groups or reactive molecules include amidoamines, polyamides, aliphatic amines, modified aliphatic amines, cycloaliphatic amines, aromatic amines, anhydrides, ketimine, diethylenetriamine (DETA), and triethylene-tetramine (TETA). ), tetraethylene-pentamine (TEPA), polyethylene polyamine, polyamine epoxy adduct, phenolic curing agent, non-brominated curing agent, non-amine curing agent, and combinations thereof. These functional groups are multifunctional, having the ability to react with at least two chemical species from at least two ends. Most importantly, it can bind to the edge or surface of graphene or HA using one of its ends and, during the subsequent curing step, react with the resin at one or two other ends.

[Gn]--Rm described above may have additional functional groups. The obtained CFG has a composition of the formula:

[Gn]--A _m ,

In the above formula, A is OY, NHY, O=C--OY, P=C--NR'Y, O=C--SY, O=C--Y, --CR' ₁ --OY, N' is selected from Y or C'Y, where Y is a suitable functional group of a protein, peptide, amino acid, enzyme, antibody, nucleotide, oligonucleotide, antigen, or enzyme substrate, enzyme inhibitor, or transition state analog of an enzyme substrate, or R'- -OH, R'--NR' ₂ , R'SH, R'CHO _, R'CN, R'X, R'N+(R') ₃ OR'--) _y R' _{3 -y} , R'Si(--O--SiR' ₂ --)OR', R'--R", R'--N--CO, (C ₂ H ₄ O--) _w H, (--C ₃ H ₆ O--) _w H, (--C ₂ H ₄ O) _w --R', (C ₃ H ₆ O) _w --R', is selected from R', and w is an integer greater than 1 and less than 200.

HA and/or graphene sheets can also have functional groups to form compositions with the formula:

[Gn]--[R'--A] _m

In the above formula, m, R' and A are as defined above. The composition of the present invention also includes CHA to which certain cyclic compounds are adsorbed. These include compositions of substances of the formula:

[Gn]--[X--Ra] _m

where a is 0 or a number less than 10, Preferred cyclic compounds are planar. More preferred cyclic compounds for adsorption are porphyrins and phthalocyanines. The adsorbed cyclic compound may have functional groups. These compositions include compounds of the formula:

[Gn]--[X--Aa] _m

In the above formula, m, a, X and A are as defined above.

HA or graphene with the functional groups of the present invention can be prepared directly by sulfonation, electrophile addition to the deoxygenated GO surface, or metallization. Graphene or HA sheets can be treated before contacting them with functionalizing agents. This treatment may include dispersing the graphene or HA sheets in a solvent. In some cases, the sheet may subsequently be filtered and dried prior to contact. One particularly useful type of functional group is the carboxylic acid moiety, which is naturally present on the surface of HA when prepared from the acid insertion route discussed above. If additional amounts of carboxylic acid are needed, the HA sheets can be oxidized with chlorate, nitric acid, or ammonium persulfate.

Carboxylic acid functionalized graphene sheets are particularly useful because they can serve as a starting point for preparing graphene or HA sheets with other types of functional groups. For example, alcohols or amides can be easily coupled to acids to obtain stable esters or amides. If the alcohol or amine is part of a di- or polyfunctional molecule, the linkage through O- or NH- leaves the other functionality as a pendant group. This reaction can be carried out using any method developed for esterifying or amifying carboxylic acids with alcohols or amines, as is known in the art. Examples of such methods can be found in G. W. Anderson, et al., J. Amer. Chem. Soc. 96, 1839 (1965), which is hereby incorporated by reference in its entirety. The amino group is treated with nitric acid and sulfuric acid to obtain nitrated fibrils, and the nitrated form is then treated with a reducing agent, such as sodium dithiamine, to obtain amino-functionalized fibrils. It can be introduced directly onto graphite fibrils by chemical reduction to onite.

The present inventors have discovered that the above-mentioned functional groups can be attached to the surface or edge of HA or graphene sheets for one or several of the following purposes: (a) improved oxidation of graphene or HA in the desired liquid medium; for dispersion; (b) enhanced solubility of graphene or HA in a liquid medium such that a sufficient amount of graphene or HA sheets can be dispersed in such liquid exceeding the critical volume fraction for liquid crystalline phase formation; (c) improved film-forming capabilities so that thin films of graphene or other discrete sheets of HA can be coated or cast; (d) improved ability of graphene or HA sheets to orient due to modifications to the flow behavior; and (e) enhanced ability of graphene or HA sheets to chemically connect and fuse within larger or wider graphene planes.

Example 1 : Humic acid and reduced humic acid from leonardite

By dispersing leonardite in a basic aqueous solution (pH of 10), humic acid can be extracted from leonardite in very high yield (in the range of 75%). Subsequent acidification of the solution precipitated the humic acid powder. In one experiment, 3 g of leonardite was dissolved by 300 ml of double deionized water containing 1 M KOH (or NH4OH) under magnetic stirring. The pH value was adjusted to 10. The solution was then filtered to remove any large particles or any residual impurities.

The obtained humic acid dispersions containing HC alone or in the presence of graphene oxide sheets (GO prepared in Example 3, described below) were cast onto a glass substrate to form a series of films for subsequent heat treatment. formed.

Example 2 : Preparation of humic acid from coal

In a typical procedure, 300 mg of coal was suspended in concentrated sulfuric acid (60 ml) and nitric acid (20 ml), followed by cup sonication for 2 hours. The reaction was then stirred and heated in an oil bath at 100 or 120° C. for 24 hours. The solution was cooled to room temperature and poured into a beaker containing 100 ml ice, followed by the addition of NaOH (3 M) until the pH value reached 7.

In one experiment, the neutral mixture was then filtered through a 0.45-mm polytetrafluoroethylene membrane, and the filtrate was dialyzed in a 1,000 Da dialysis bag for 5 days. For larger humic acid sheets, the time can be shortened to 1 to 2 hours using cross-flow ultrafiltration. After purification, the solution was concentrated using rotary evaporation to obtain a solid humic acid sheet. These humic acid sheets alone and their mixtures with graphene sheets were redispersed in solvents (ethylene glycol and alcohol, separately) to obtain several dispersion samples for subsequent casting or coating.

Example 3 : Preparation of graphene oxide (GO) and reduced graphene oxide (RGO) sheets from natural graphite powder

Natural graphite from Ashbury Carbons was used as starting material. GO was obtained by the following well-known modified Hummer method involving two oxidation steps. In a typical procedure, the first oxidation was achieved under the following conditions: 1100 mg of graphite was placed in a 1000 mL boiling flask. Afterwards, 20 g of K2S2O8, 20 g of P2O5, and 400 ml of concentrated aqueous solution of H ₂ SO ₄ (96%) were added to the flask. The mixture was heated under reflux for 6 hours and then left undisturbed for 20 hours at room temperature. The oxidized graphite was filtered and washed with abundant distilled water until a pH value above 4.0 was reached. At the end of this first oxidation a wet cake-like material was recovered.

For the second oxidation process, the previously collected wet cake was placed in a boiling flask containing 69 mL of a concentrated aqueous solution (96%) of H ₂ SO ₄ . The flask was kept in an ice bath while 9 g of KMnO ₄ was slowly added. Care was taken to avoid overheating. The resulting mixture was stirred at 35° C. for 2 hours (sample color changed to dark green), after which 140 mL of water was added. After 15 minutes, the reaction was stopped by adding 420 mL of water and 15 mL of a 30% by weight aqueous solution of H ₂ O ₂ . At this stage the color of the sample changed to light yellow. To remove metallic ions, the mixture was filtered and washed with 1:10 aqueous HCl solution. The collected material was gently centrifuged at 2700 g and washed with deionized water. The final product was a wet cake containing 1.4% GO by weight, estimated from the dry extract. Subsequently, a liquid dispersion of GO platelets was obtained by lightly sonicating the wet cake material, diluted in deionized water.

Separately, GO at various GO ratios (1%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 99%), as illustrated in Figure 3c. A water suspension containing a mixture of and humic acid was prepared and slot-die coated to form thin films of various compositions.

Example 4 : Preparation of an oriented film containing initial graphene sheets (0% oxygen) mixed with humic acid.

In a typical procedure, 5 grams of graphite flakes ground to a size of approximately 20 μm or less were dispersed in 1,000 mL of deionized water (containing 0.1% by weight of dispersant, Zonyl® FSO from DuPont) to obtain a suspension. An ultrasonic energy level of 85 W (Branson S450 sonicator) was used for exfoliation, separation, and size reduction of the graphene sheets for 15 minutes to 2 hours. The resulting graphene sheets are pristine graphene that has not been oxidized and is oxygen-free and relatively defect-free. Primary graphene is essentially free of any non-carbon elements.

The suspension after sonication contains the initial graphene sheets dispersed in water and the surfactant dissolved therein. Humic acid was then added to the suspension, and the resulting mixture suspension was further sonicated for 10 minutes to facilitate uniform dispersion and mixing.

Example 5 : Preparation of oriented graphite film from mixture of graphene fluoride sheets and humic acid

Although several processes have been used by the inventors to form GF, only one process is described herein as an example. In a routine procedure, exfoliated graphite (HEG) was prepared from the intercalated compound C ₂ F·xClF ₃ . HEG was further fluorinated with vapor of chlorine trifluoride to give fluorinated exfoliated graphite (FHEG). A pre-cooled Teflon reactor was charged with 20 to 30 mL of liquid pre-cooled ClF ₃ , the reactor was closed and cooled to liquid nitrogen temperature. Afterwards, 1 g or less of HEG was placed in a container equipped with a hole for entry of ClF ₃ gas and placed inside the reactor. On day 7, a grey-beige product with the approximate formula C2F was formed.

Subsequently, a small amount of FHEG (approximately 0.5 mg) was mixed with 20-30 mL of organic solvent (methanol and ethanol, separately) and sonicated (280 W) for 30 min to form a homogeneous yellow dispersion. Humic acid was then added to this dispersion at various HA-to-GF ratios. The dispersion was then prepared into a thin film using comma coating. The oriented HA film was then heat treated at various temperatures to obtain a highly conductive graphite film.

Example 6 : Preparation of HOHA containing nitrided graphene sheets and humic acid

Graphene oxide (GO) synthesized in Example 3 was finely ground with different fractions of urea, and the pelleted mixture was heated in a microwave reactor (900 W) for 30 seconds. The product was washed several times with deionized water and dried in vacuum. In this method, graphene oxide was simultaneously reduced and doped with nitrogen. Products were obtained with graphene:urea mass ratios of 1:0.5, 1:1 and 1:2, designated as NGO-1, NGO-2 and NGO-3, respectively, and the nitrogen content of these samples was determined by elemental analysis. In this case, it is 14.7, 18.2 and 17.5% by weight, respectively. These nitrided graphene sheets remain dispersible in water. Various amounts of HA with oxygen content between 20.5% and 45% were added to the suspension. The resulting suspension of nitrided graphene-HA dispersion is then coated on a plastic film substrate to form a wet film, which is then dried, peeled off from the plastic film, and heat treated at various heat treatment temperatures from 80 to 2,900°C. To obtain an oriented humic acid (HOHA) film (if the final HTT is less than 1,500°C) or an aligned and conductive graphite film (if the final HTT is above 1,500°C).

Example 7 : Preparation of nematic liquid crystal from humic acid sheet

Humic acid aqueous dispersions were prepared by dispersing HA sheets in deionized water by mild sonication. Any acidic or ionic impurities in the dispersion were removed by dialysis, which is an important step for liquid crystal formation.

Low-concentration dispersions (typically 0.05 to 0.6% by weight) immobilized for sufficiently long periods of time (usually more than two weeks) undergo macroscopic phase-separation into two phases. Although the low-density upper phase was optically isotropic, the high-density lower phase exhibited significant optical birefringence between the two crossed polarizers. A typical nematic schlieren texture consisting of dark and light brushes was observed on the bottom. This is a biphasic behavior, where isotropic and nematic phases coexist. The composition range for the above is quite wide due to the large polydispersity of the HA molecule. It can be noted that ionic strength and pH value significantly affect the stability of HA liquid crystals. Electrostatic repulsion from dissociated surface functional groups such as carboxylates plays an important role in the stability of HA liquid crystals. Accordingly, reduction of repulsive interactions by increasing ionic strength or lowering pH value increased the aggregation of HA sheets.

The inventors observed that when HA sheets account for a weight fraction of 1.1%, virtually all of the HA sheets form a liquid crystalline phase, and that the liquid crystals can be preserved by gradually increasing the concentration of HA up to the range of 6% to 16%. did. The prepared humic acid dispersion exhibited a macroscopically heterogeneous, chocolate-milk-like appearance. This milky appearance may be mistaken for agglomeration or precipitation of graphene oxide, but it is actually a nematic liquid crystal.

By dispensing and coating the HA suspension on a polyethylene terephthalate (PET) film in a slurry coater and removing the liquid medium from the coated film, the inventors obtained thin films of dried HA. Each film was then subjected to a different heat treatment, typically chemical coupling and thermal bonding at a first temperature of 80° C. to 300° C. for 1 to 10 hours and a second temperature of 1,500° C. to 2,850° C. for 0.5 to 5 hours. Includes reduction treatment. Through this heat treatment, and under compressive stress, the HOHA film was transformed into a highly conductive graphite film (HOGF).

At different heat treatment stages, the internal structures (crystal structure and orientation) of several dried HA layers (HOHA films) and HOGF were investigated. X-ray diffraction curves of the dried layer of HOHA before heat treatment, the HOHA film thermally reduced at 150°C for 5 hours, and the obtained HOGF were obtained. The peak at approximately 2θ = 12° of the dried HOHA layer corresponds to an intergraphene spacing (d002) of approximately 0.75 nm. Upon partial heat treatment at 150°C, the dried film shows the formation of a hump centered at 22°, indicating the beginning of the process of reducing the interplanar spacing, and the initiation of the chemical linking and alignment process. do. With respect to a heat treatment temperature of 2,500°C for 1 hour, the hexagonal carbon interplanar spacing (d002) decreased to approximately 0.336, close to 0.3354 nm for graphite single crystals.

With respect to a heat treatment temperature of 2,750° C. for 1 hour, the hexagonal carbon interplanar spacing (d002) is reduced to approximately 0.3354 nm, identical to that of a graphite single crystal. Additionally, a second diffraction peak with high intensity appears at 2θ = 55°, corresponding to X-ray diffraction from the (004) plane. The (004) peak intensity relative to the (002) intensity in the same diffraction curve, or the I(004)/I(002) ratio, is a good indication of the degree of crystal integrity and preferred orientation of the graphene plane. It is well known in the art that for all common graphitic materials heat treated at temperatures lower than 2,800°C, the (004) peak is absent or relatively weak and the I(004)/I(002) ratio is less than 0.1. there is. The I(004)/I(002) ratio for graphitic materials heat treated at 3,000 to 3,250° C. (e.g., oriented pyrolytic graphite, HOPG) ranges from 0.2 to 0.5. In contrast, HOGF prepared from HA liquid crystal-based films with a final HTT of 2,750 °C for 1 h exhibits an I(004)/I(002) ratio of 0.77 and a mosaic diffusion value of 0.21, which is of an exceptionally high degree. It represents a practically complete graphene single crystal with a preferred orientation.

“Mosaic diffusion” values were obtained from the full width at half maximum of the (002) reflection within the X-ray diffraction intensity curve. This index for degree of ordering characterizes the graphite or graphene crystal size (or grain size), the amount of grain boundaries and other defects, and the degree of preferred grain orientation. Almost perfect single crystals of graphite are characterized by mosaic diffusion values of 0.2 to 0.4. Most of the HA-derived HOGFs of the present invention have mosaic diffusion values in this range of 0.2 to 0.4 when produced using final heat treatment temperatures of 2,500°C or higher.

It can be noted that the I(004)/I(002) ratios for all of the dozens of flexible graphite samples investigated are all well below 0.05 and, in most cases, virtually non-existent. The I(004)/I(002) ratio for all graphene paper/membrane samples prepared by the vacuum-assisted filtration method is less than 0.1 even after heat treatment at 3,000°C for 2 hours. These observations demonstrate that the HOHA films of the present invention are novel and fundamentally different from papers/films/membranes of random pyrolytic graphite (PG), flexible graphite (FG), and conventional graphene/GO/RGO sheets/platelets (NGP). It further confirms the already established concept of a separate class of substances.

The intergraphene spacing values of both HA liquid crystal suspension-derived HOGF samples obtained by heat treatment at various temperatures over a wide temperature range are summarized in Figure 5a. The corresponding oxygen content values are shown in Figure 5b. To show the correlation between inter-graphene spacing and oxygen content, the data from Figures 5A and 5B were replotted in Figure 5C. A thorough examination of Figures 5A-5C shows that there are four HTT ranges (100 to 300°C; 300 to 1,500°C; 1,500 to 2,000°C; and >2,000°C) resulting in four respective oxygen content ranges and intergraphene spacing ranges. shows that The thermal conductivities of samples of HA liquid crystal-induced HOGF specimens and corresponding flexible graphite (FG) foil sheets plotted as a function of the same final heat treatment temperature range are also summarized in Figure 5d. All these samples have similar thickness values.

It is important to note that heat treatment temperatures as low as 500°C are sufficient to bring the average interplanar spacing below 0.4 nm, getting closer and closer to native graphite or graphite single crystals. The advantage of this approach is the concept that this HA liquid crystalline suspension strategy allows to reorganize, reorient, and chemically fuse planar HA sheets into a unified structure with all graphene pseudo-planes, where all graphene planes are now lateral. They are larger in dimensions (considerably larger than the length and width of the hexagonal carbon planes in the original HA molecule) and are essentially parallel to each other. This already results in a thermal conductivity of 300 to 400 W/mK at an HTT of 700°C (with an HTT of 500°C) and >623 W/mk (from HA alone) or >900 W/mk (from a mixture of HA + GO). This result is at least 3 to 4 times greater than the value of the corresponding flexible graphite foil (200 W/mK). Additionally, the tensile strength of HOGF samples can reach 90 to 125 MPa (Figure 7a).

For HTTs as low as 1,000°C, the resulting oriented HA films exhibit thermal conductivities of 756 W/mK (from HA alone) and 1,105 W/mK (from HA-GO mixture), respectively. This contrasts with the observed 268 W/mK for flexible graphite foil with the same heat treatment temperature. In fact, no matter how high the HTT is (e.g. even as high as 2,800° C.), flexible graphite foils only exhibit thermal conductivities lower than 600 W/mK. At HTT of 2,800 °C, the HOGF layer of the present invention exhibits a thermal conductivity of 1,745 W/mK compared to the layer derived from a mixture of HA and GO (Figures 4a and 5d). As specified in Figure 4a, it can be further noted that the thermal conductivity values of the HA/GO mixture-derived graphite films are consistently higher than those of the corresponding graphite films derived from graphene oxide. This surprising effect is further discussed in Example 8.

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) photographs of lattice imaging of graphene layers, as well as selected area electron diffraction (SAD), bright field (BF), and dark field (DF) images were also obtained for single graphene layers. This was performed to characterize the structure of the fin material. For measurement of the cross-section of the films, samples were embedded in a polymer matrix, sliced using a hypermicrotome, and etched with Ar plasma.

A thorough inspection and comparison of FIGS. 2A, 3A, and 3B shows that the graphene-like layers in HOGF are oriented substantially parallel to each other; This is not the case for flexible graphite foil and graphene oxide paper. The tilt angle between two discernible layers in a highly conductive graphite film is generally less than 10 degrees, and most often less than 5 degrees. In contrast, there are many folded graphite flakes, kinks, and misorientations in flexible graphite, with many angles between two graphite flakes being greater than 10 degrees, some as high as 45 degrees (Figure 2). Not bad at all, the misorientation between graphene platelets in the NGP paper (Figure 3b) is also high and there are many gaps between platelets. HOGF entities are essentially gapless.

Figure 4A shows the thermal conductivity values for each of the HA/GO-derived film, GO-derived film, HA suspension-derived HOGF, and FG foil, all plotted as a function of final HTT. These data clearly demonstrate the superiority of the HA/GO-derived HOGF of the present invention in terms of achievable thermal conductivity at the given heat treatment temperatures.

1) HA/GO liquid crystal suspension-derived HOGF was found to be superior to GO gel-derived HOGF in thermal conductivity at similar final heat treatment temperatures. Excessive oxidation of graphene sheets in GO gels can cause high defect population on the graphene surface even after thermal reduction and re-graphitization. However, it appears that the presence of HA molecules can help heal defects or bridge gaps between GO sheets.

2) Although oriented films derived from HA alone show slightly lower thermal conductivity values than those derived from GO alone, HA as a material is abundant in nature, which makes the use of undesirable chemicals to form HA does not require HA is ten times cheaper than natural graphite (the raw material for GO) and one hundred to ten thousand times cheaper than GO.

3) For comparison, the inventors also obtained a universally oriented pyrolytic graphite (HOPG) sample from the polyimide (PI) carbonization route. The polyimide film was carbonized in an inert atmosphere at 500°C for 1 hour, at 1,000°C for 3 hours, and at 1,500°C for 12 hours. The carbonized PI film was then graphitized under compressive force at a temperature ranging from 2,500 to 3,000° C. for 1 to 5 hours to form a universal HOPG structure.

Figure 4b shows the thermal conductivity values of HA/GO suspension-derived HOGF, HA suspension-derived HOGF, and polyimide-derived HOPG, all plotted as a function of final graphitization temperature. These data show that universal HOPG produced using the carbonized polyimide (PI) route consistently exhibits lower thermal conductivity compared to HA/GO-derived HOGF, given the same HTT for the same heat treatment time. For example, HOPG from PI exhibits a thermal conductivity of 820 W/mK after graphitization at 2,000°C for 1 hour. At the same final graphitization temperature, HA/GO-derived HOGF exhibits a thermal conductivity value of 1,586 W/mK. It may be noted that PI is much more expensive than HA and the production of PI involves the use of several environmentally undesirable organic solvents.

4) These observations demonstrated a clear and important advantage of using the HA/GO or HA suspension method to produce HOGF materials compared to the common PG method for producing oriented graphite crystals. In fact, no matter how long the graphitization time takes for HOPG, the thermal conductivity is always lower than that of HA/GO liquid crystal-derived HOGF. Additionally, it was surprisingly discovered that humic acid molecules can chemically link together to form a strong, highly conductive graphite film. Oriented HA films (including oriented HA/GO films), and subsequently heat treated versions, are similar to flexible graphite (FG) in terms of chemical composition, crystal and defect structure, crystal orientation, morphology, production process and properties. It is clear that it is fundamentally different and clearly distinct from foil, graphene/GO/RGO paper/membrane, and pyrolytic graphite (PG).

5) The above conclusion is supported by the data in Figure 4c, which shows that the electrical conductivity values of HA/GO suspension-derived and HA suspension-derived HOGF HOGF are much better than that of FG foil sheets over the entire range of final HTTs investigated. It is further supported.

Example 8 : Effect of graphene addition on the properties of HA-based HOHA and oriented graphite films

Various amounts of graphene oxide (GO) sheets were added to the HA suspension to obtain a mixture suspension in which HA and GO sheets were dispersed in a liquid medium. The same procedure as described above was subsequently performed to form HOGF samples of various GO fractions. The thermal conductivity data for these samples are summarized in Figure 6, which shows that the thermal conductivity values of HOGF formed from the HA-GO mixture are higher than those of HOGF films formed from either single component alone.

More surprisingly, a synergistic effect can be observed when both HA sheets and GO sheets coexist in an appropriate ratio. It appears that HA can help heal GO sheets (known to have defects) from their otherwise defective structures. It is also possible that HA molecules, which are significantly smaller in size than GO sheets/molecules, can fill the gaps between GO molecules and react with them to bridge the gaps. These two factors may significantly improve conductivity.

Example 9 : Tensile Strength of Various Graphene Oxide-Derived HOHA Films

A series of HA/GO dispersion-derived HOGF, GO dispersion-derived HOGF, and HA-derived HOGF films were prepared by using similar final heat treatment temperatures for all materials. The tensile properties of these materials were determined using a universal testing machine. The tensile strength and modulus of these various samples prepared over a range of heat treatment temperatures are shown in Figures 7A and 7B, respectively. For comparison, some tensile strength data of RGO paper and flexible graphite foil are also summarized in Figure 7A.

These data show that the tensile strength of graphite foil-induced sheets increases slightly (from 14 to 29 MPa) with final heat treatment temperature, and that the tensile strength of GO paper (compressed/heat treated sheets of GO paper) increases with final heat treatment temperature of 700 MPa. It was proven that the temperature increased from 23 to 52 MPa when the temperature increased to 2,800°C. In contrast, the tensile strength of HA-derived HOGF increases significantly from 28 to 93 MPa over the same range of heat treatment temperatures. Most significantly, the tensile strength of HA/GO suspension-derived HOGF increases significantly from 32 to 126 MPa. These results are very surprising, and show that HA/GO and HA dispersions contain oriented/aligned, chemically active HA/GO and HA sheets/molecules that can chemically connect and associate with each other during heat treatment, whereas in conventional GO papers they do not. It further reflects the fact that the graphite flakes in fin platelets and FG foils are essentially dead platelets. HA or HA/GO-based oriented films and subsequently formed graphitic films are themselves a new class of materials.

Note that the film obtained by simply spraying the HA-solvent solution onto the glass surface and drying the solvent does not have any strength (it is so brittle that you can break the film by simply touching it with your finger). . After heat treatment at temperatures above 100° C., these films fragment (break into a significant number of pieces). In contrast, oriented HA films (where all HA molecules or sheets are oriented and packed together), upon heat treatment at 150° C. for 1 hour, result in films of good structural integrity with tensile strengths exceeding 24 MPa.

Example 10 : Synthesis of polyacrylonitrile-grafted HA (HA-g-PAN)

Acrylonitrile (AN) was dried with calcium chloride for 48 hours, distilled under reduced pressure, and stored at -20°C. 2,2' Azobis(2-methylpropionitrile) (AIBN) and potassium persulfate (K2S2O8) were used after recrystallization twice.

To study an example of chemically functional HA, PAN was grafted onto HA sheets via an in situ free radical polymerization procedure. Typically, 100 mg of HA and 80 mL of dimethylformamide (DMF) were added to a 150 mL round bottom flask and sonicated in a 40 kHz ultrasonic bath for 10 minutes to obtain a well-dispersed solution. After addition of 10.6 g of AN (200 mmol) and 82 mg of AIBN initiator (0.5 mmol), the solution was purged with nitrogen for 40 minutes and then immersed in an oil bath at 65°C. After reacting for 48 hours under N2 protection and stirring, the reaction was terminated by exposure to air. The resulting mixture was precipitated in methanol, and the resulting gray precipitate was collected and redissolved in 200 mL of DMF. The solution was then centrifuged at 15,000 rpm (23,300 G) for 0.5 to 1 hour to remove free polymer not covalently bound to HA. The resulting cream-like fluid was washed thoroughly with DMF eight times until the upper layer appeared colorless. Afterwards, the obtained black colloidal product of HA-g-PAN was prepared for use by dispersing it in 50 mL of DMF.

Polymer-modified HA sheets were found to transition from an isotropic phase to a liquid-crystalline phase at higher critical volume fractions (Vc), which appears to be a slight disadvantage, although coating or casting can be achieved at significantly higher concentrations (e.g. Since it is performed as a dispersion of much more than 3 weight), this high Vc has no effect. However, this polymer component makes it easier to form thin films with good mechanical integrity and improved ease of handling, which are highly desirable properties. The HA-g-PAN dispersion is cast to form a wet film, which is dried and heat treated at 300°C for 5 hours, 1,000°C for 3 hours, and then at 2,500°C for 2 hours. The density of the HA-g-PAN liquid crystal-derived film is 2.13 g/cm3, which indicates a thermal conductivity of 1,566 W/mk.

For comparison, papers of HA-g-PAN were prepared by vacuum-assisted filtration of a DMF dispersion with a concentration of 5 mg/mL, followed by drying in vacuum at 50°C for 12 hours. The paper sheet was compressed and then subjected to the same heat treatment. The density of the HA-g-PAN paper-derived film is 1.70 g/cm3, which indicates a thermal conductivity of 805 W/mk.

In conclusion, the present inventors have presented an absolutely novel, novel, unexpected and clearly distinct class of highly conductive and high-strength materials, namely highly oriented humic acid films and highly conductive graphite films (HOGFs) derived therefrom, and their production processes. was successfully developed. The chemical composition (oxygen content), structure (crystal integrity, grain size, defect population, etc.), crystal orientation, morphology, production process, and properties of this new class of materials are similar to those of flexible graphite foil, polymer-induced pyrolysis graphite, and CVD. -Basically different and clearly distinct from derivatized HOPG, graphene-based thermal films, and catalytic CVD graphene thin films. The thermal conductivity, electrical conductivity, elastic modulus, and tensile strength exhibited by the materials of the present invention are those that could possibly be achieved by prior art flexible graphite sheets, papers of discrete graphene/GO/RGO platelets, or other graphitic materials. much higher than These HOGF materials have the best combination of excellent electrical conductivity, thermal conductivity, mechanical strength, and stiffness (modulus). These HOGF materials can be used in a wide variety of thermal management applications. For example, due to its excellent thermal conductivity, HOGF structures can be part of thermal management devices, such as heat dissipating films used in smartphones, tablet computers, flat panel TV displays, or other microelectronic or communication devices. .

Claims (61)

An oriented humic acid film comprising a humic acid (HA) or a humic acid (CHA) sheet containing a functional group, the film having a thickness of 5 nm to 500 ㎛, a physical density of 1.3 g/cm3 or more, as measured by X-ray diffraction. has hexagonal carbon planes with a hexagonal carbon interplanar spacing (d002) of 0.4 nm to 1.3 nm, and a non-carbon element content or oxygen content of less than 5% by weight,
The functional groups are SO3H, COOH, NH2, OH, R'CHOH, CHO, CN, COCl, halide, COSH, SH, COOR', SR', SiR'3, Si(--OR'--)yR'3- y, Si(--O--SiR'2--)OR', R", Li, AlR'2, Hg--X, TlZ2 and Mg--X, where y is 3 is the following integer, where R' is hydrogen, alkyl, aryl, cycloalkyl, or aralkyl, cycloaryl, or poly(alkyl ether), and R" is fluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoro is aralkyl or cycloaryl, X is halide, and Z is carboxylate or trifluoroacetate, or a combination thereof. A highly conductive graphite film derived from the oriented humic acid film of claim 1 through heat treatment, wherein the graphite film has a hexagonal carbon interplanar spacing (d002) of less than 0.4 nm and an oxygen content or non-carbon element content of less than 2% by weight. Highly conductive graphite having a hexagonal carbon plane, a physical density greater than 1.6 g/cm3, an in-plane thermal conductivity greater than 600 W/mK, an in-plane electrical conductivity greater than 2,000 S/cm, and a tensile strength greater than 20 MPa. film. The method of claim 1, further comprising a graphene sheet or molecule parallel to the HA or CHA sheet, wherein the HA-to-graphene or CHA-to-graphene ratio is 1/100 to 100/1, Graphene in which graphene has 0% oxygen, graphene oxide, reduced graphene oxide, graphene fluoride, graphene bromide, graphene iodide, boron-doped graphene, nitrogen-doped graphene, or a combination thereof. A highly conductive graphite film derived from the oriented humic acid film of claim 3 through heat treatment, wherein the graphite film has a hexagonal carbon interplanar spacing (d002) of less than 0.4 nm and an oxygen content or non-carbon element content of less than 2% by weight. Highly conductive graphite having a hexagonal carbon plane, a physical density greater than 1.6 g/cm3, an in-plane thermal conductivity greater than 600 W/mK, an in-plane electrical conductivity greater than 2,000 S/cm, and a tensile strength greater than 20 MPa. film. The oriented humic acid film of claim 1 further comprising a polymer, wherein the HA or CHA sheets are dispersed in or bound by the polymer. The humic acid film according to claim 3, further comprising a polymer, wherein the HA or CHA sheet and the graphene sheet are dispersed in or bound to the polymer. delete The method of claim 3, wherein the graphene sheet is a polymer, SO ₃ H, COOH, NH ₂ , OH, R'CHOH, CHO, CN, COCl, halide, COSH, SH, COOR', SR', SiR' ₃ , Si(--OR'--) _y R' _3-y , Si(--O--SiR' ₂ --)OR', R", Li, AlR' ₂ , Hg--X, TlZ ₂ and Mg --Contains graphene containing a chemical functional group selected from ), R" is fluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl or cycloaryl, X is halide, Z is carboxylate or trifluoroacetate, or a combination thereof, Oriented humic acid film. The highly conductive graphite film of claim 2, wherein the graphite film has a thickness of 10 nm to 200 μm. 2. The method of claim 1, wherein the oriented humic acid film has an oxygen content of less than 2.0%, a hexagonal carbon interplanar spacing of less than 0.35 nm, a physical density of at least 1.6 g/cm3, a thermal conductivity of at least 800 W/mK, and 2,500 S/cm. An oriented humic acid film having an electrical conductivity of more than cm. 4. The method of claim 3, wherein the oriented humic acid film has an oxygen content of less than 2.0%, a hexagonal carbon interplanar spacing of less than 0.35 nm, a physical density of greater than 1.6 g/cm3, a thermal conductivity of at least 800 W/mK, and 2,500 S/cm. An oriented humic acid film having an electrical conductivity of more than cm. The highly conductive graphite of claim 2, wherein the graphite film has an oxygen content of less than 1.0%, a hexagonal carbon interplanar spacing of less than 0.345 nm, a thermal conductivity of at least 1,000 W/mK, and an electrical conductivity of at least 5,000 S/cm. film. 5. The highly conductive graphite of claim 4, wherein the graphite film has an oxygen content of less than 1.0%, a hexagonal carbon interplanar spacing of less than 0.345 nm, a thermal conductivity of at least 1,000 W/mK, and an electrical conductivity of at least 5,000 S/cm. film. 3. The method of claim 2, wherein the graphite film has an oxygen content of less than 0.1%, a hexagonal carbon interplanar spacing of less than 0.340 nm, a mosaic diffusion value of less than 0.7, a thermal conductivity of at least 1,300 W/mK, and an electrical conductivity of at least 8,000 S/cm. A highly conductive graphite film with electrical conductivity. 5. The method of claim 4, wherein the graphite film has an oxygen content of less than 0.1%, a hexagonal carbon interplanar spacing of less than 0.340 nm, a mosaic diffusion value of less than 0.7, a thermal conductivity of at least 1,300 W/mK, and an electrical conductivity of at least 8,000 S/cm. A highly conductive graphite film with electrical conductivity. 3. The highly conductive film of claim 2, wherein the graphite film has an inter-graphene spacing of less than 0.336 nm, a mosaic diffusion value of less than or equal to 0.4, a thermal conductivity of greater than 1,600 W/mK, or an electrical conductivity of greater than 10,000 S/cm. Graphite film. 5. The method of claim 4, wherein the graphite film has a hexagonal carbon interplanar spacing of less than 0.336 nm, a mosaic diffusion value of less than or equal to 0.4, a thermal conductivity of greater than 1,600 W/mK, and an electrical conductivity of greater than 10,000 S/cm. Highly conductive graphite film. 3. The highly conductive graphite film of claim 2, having a physical density greater than 1.9 g/cm3, a tensile strength greater than 80 MPa, and an elastic modulus greater than 60 GPa. 5. The highly conductive graphite film of claim 4, having a physical density greater than 1.9 g/cm3, a tensile strength greater than 80 MPa, and an elastic modulus greater than 60 GPa. 3. The highly conductive graphite film of claim 2, having a physical density greater than 2.0 g/cm3, a tensile strength greater than 100 MPa, and an elastic modulus greater than 80 GPa. 5. The highly conductive graphite film of claim 4, having a physical density greater than 2.0 g/cm3, a tensile strength greater than 100 MPa, and an elastic modulus greater than 80 GPa. 3. The highly conductive graphite film of claim 2, having a physical density greater than 2.1 g/cm3, a tensile strength greater than 120 MPa, and an elastic modulus greater than 120 GPa. A microelectronic device containing the oriented humic acid film of claim 1 as a heat-dissipating or heat-spreading component. A microelectronic device containing the oriented humic acid film of claim 3 as a heat-dissipating or heat-spreading component. A microelectronic device containing the highly conductive graphite film of claim 2 as a heat-dissipating or heat-spreading component. A microelectronic device containing the highly conductive graphite film of claim 4 as a heat dissipating or heat spreading component. 24. The microelectronic device of claim 23, which is a smartphone, tablet computer, flat panel display, flexible display, pocket watch, wearable electronic device, TV, or microelectronic communication device. 25. The microelectronic device of claim 24, which is a smartphone, tablet computer, flat panel display, flexible display, pocket watch, wearable electronic device, TV, or microelectronic communication device. 26. The microelectronic device of claim 25, which is a smartphone, tablet computer, flat panel display, flexible display, pocket watch, wearable electronic device, TV, or microelectronic communication device. 27. The microelectronic device of claim 26, which is a smartphone, tablet computer, flat panel display, flexible display, pocket watch, wearable electronic device, TV, or microelectronic communication device. A method for producing an oriented humic acid film having a thickness of 5 nm to 500 μm and a physical density of 1.3 g/cm3 or more, comprising:
(a) preparing a dispersion of humic acid (HA) or humic acid (CHA) sheets containing functional groups dispersed in a liquid medium, wherein the HA sheets contain an oxygen content higher than 5% by weight, or the CHA sheets contains a non-carbon element content higher than 5% by weight;
(b) dispensing and depositing the HA or CHA dispersion on the surface of a support substrate to form a wet layer of HA or CHA, wherein the dispensing and deposition procedure involves subjecting the dispersion to orientation-induced stress. Steps comprising;
(c) Partial or total removal of the liquid medium from the wetting layer of HA or CHA to dry hexagonal carbon planes and a hexagonal carbon interplanar spacing (d002) of 0.4 nm to 1.3 nm as measured by X-ray diffraction. forming a HA or CHA layer; and
(d) said oriented humic acid containing inter-connected, merged or thermally reduced HA or CHA sheets parallel to each other at a first heat treatment temperature of said dried HA or CHA layer greater than 80° C. Including heat treating to produce a film,
The functional group is SO ₃ H, COOH, NH ₂ , OH, R'CHOH, CHO, CN, COCl, halide, COSH, SH, COOR', SR', SiR'3, Si(--OR'--)yR '3-y, Si(--O--SiR'2--)OR', R", Li, AlR'2, Hg--X, TlZ2 and Mg--X, wherein: y is an integer of 3 or less, R' is hydrogen, alkyl, aryl, cycloalkyl, or aralkyl, cycloaryl, or poly(alkylether), and R" is fluoroalkyl, fluoroaryl, fluorocycloalkyl , fluoroaralkyl or cycloaryl, X is halide, and Z is carboxylate or trifluoroacetate, or a combination thereof. 32. The method of claim 31, wherein (e) the humic acid film of fused or reduced HA or CHA has a hexagonal carbon interplanar spacing (d002) of less than 0.4 nm and a hexagonal carbon interplanar spacing (d002) of less than 5% by weight at a second heat treatment temperature greater than the first heat treatment temperature. further heat treating to produce a graphite film having an oxygen content or non-carbon element content of and (f) compressing the graphite film to produce a highly conductive graphite film having a physical density of at least 1.6 g/cm3. 32. The method of claim 31, further comprising compressing the humic acid film of fused or reduced HA or CHA after step (d). 32. The method of claim 31, wherein the HA or CHA dispersion further contains graphene sheets or molecules dispersed therein, and the HA-to-graphene or CHA-to-graphene ratio is from 1/100 to 100/ 1, wherein the graphene has 0% oxygen, graphene oxide, reduced graphene oxide, graphene fluoride, graphene bromide, graphene iodide, boron-doped graphene, nitrogen-doped A method selected from graphene, or a combination thereof. 35. The method of claim 34, wherein (e) the humic acid film of fused or reduced HA or CHA has a hexagonal carbon interplanar spacing (d002) of less than 0.4 nm and a hexagonal carbon interplanar spacing (d002) of less than 5% by weight at a second heat treatment temperature greater than the first heat treatment temperature. further heat treating to produce a graphite film having an oxygen content or non-carbon element content of and (f) compressing the graphite film to produce a highly conductive graphite film having a physical density of at least 1.6 g/cm3. delete 32. The method of claim 31, wherein the dispersion contains a first volume fraction of HA or CHA dispersed in the liquid medium, exceeding the critical volume fraction (Vc) for liquid crystalline phase formation, and wherein the dispersion is HA or CHA. Concentrated to reach a second volume fraction of HA or CHA, which is greater than the first volume fraction, to improve sheet orientation. 36. The method of claim 35, wherein the first volume fraction is equivalent to a weight fraction of 0.05% to 3.0% by weight of HA or CHA in the dispersion. 32. The method of claim 31, wherein the dispersion is concentrated to contain greater than 3.0% and less than 15% by weight of HA or CHA dispersed in the liquid medium prior to step (b). 32. The method of claim 31, wherein the dispersion further contains a polymer dissolved in the liquid medium or attached to the HA or CHA. delete 35. The method of claim 34, wherein the graphene sheet is a polymer, SO ₃ H, COOH, NH ₂ , OH, R'CHOH, CHO, CN, COCl, halide, COSH, SH, COOR', SR', SiR' ₃ , Si(--OR'--) _y R' _3-y , Si(--O--SiR' ₂ --)OR', R", Li, AlR' ₂ , Hg--X, TlZ ₂ and Mg --Contains graphene containing a chemical functional group selected from , R" is fluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl, or cycloaryl, X is halide, and Z is carboxylate or trifluoroacetate, or a combination thereof. 33. The method of claim 32, wherein the second heat treatment temperature is greater than 1,500° C. to reduce the hexagonal carbon interplanar spacing (d002) to a value of less than 0.36 nm and the oxygen content or non-carbon element content to less than 0.1 weight percent. High, way. 32. The method of claim 31, wherein the liquid medium consists of water or alcohol. 32. The method of claim 31, wherein the liquid medium is selected from polyethylene glycol, ethylene glycol, propylene glycol, alcohol, sugar alcohol, polyglycerol, glycol ether, amine-based solvent, amide-based solvent, alkylene carbonate, organic acid, or inorganic acid. A method comprising a non-aqueous solvent. 33. The method of claim 32, wherein the second heat treatment temperature is 1,500°C to 3,200°C. 32. The method of claim 31, wherein the highly conductive graphite film has a thickness of 10 nm to 200 μm. 32. The method of claim 31, wherein step (b) feeds a sheet of solid substrate material from a roller into a deposition zone and deposits a layer of the HA or CHA dispersion on the surface of the sheet of solid substrate material to form a layer of HA or CHA thereon. forming a wet layer of dispersion, drying the HA or CHA dispersion to form a dried HA or CHA layer deposited on the substrate surface, and collecting the HA or CHA layer-deposited substrate sheet on a roller. method, including that. 32. The method of claim 31, wherein the first heat treatment temperature is in the range of 100° C. to 1,500° C., and the oriented humic acid film has an oxygen content of less than 2.0%, a hexagonal carbon interplanar spacing of less than 0.35 nm, and a physical weight of more than 1.6 g/cm3. A method having a density, a thermal conductivity of at least 800 W/mK, and an electrical conductivity of at least 2,500 S/cm. 32. The method of claim 31, wherein the first heat treatment temperature is in the range of 1,500° C. to 2,100° C., and the oriented humic acid film has an oxygen content of less than 1.0%, an interplanar spacing of less than 0.345 nm, and a thermal conductivity of at least 1,000 W/mK. , and having an electrical conductivity of at least 5,000 S/cm. 33. The method of claim 32, wherein the first heat treatment temperature or the second heat treatment temperature is greater than 2,100° C., and the highly conductive graphite film has an oxygen content of less than 0.1%, a hexagonal carbon interplanar spacing of less than 0.7 nm, and a hexagonal carbon interplanar spacing of less than 0.7 nm. A method having a mosaic diffusion value, a thermal conductivity of at least 1,300 W/mK, and an electrical conductivity of at least 8,000 S/cm. 33. The method of claim 32, wherein the second heat treatment temperature is at least 2,500° C., and the highly conductive graphite film has a hexagonal carbon interplanar spacing of less than 0.336 nm, a mosaic diffusion value of less than 0.4, and a thermal conductivity greater than 1,600 W/mK. and having an electrical conductivity greater than 10,000 S/cm. 32. The method of claim 31, wherein the oriented humic acid film exhibits a degree of graphitization of at least 80% and a mosaic diffusion value of less than 0.4. 32. The method of claim 31, wherein the oriented humic acid film contains hexagonal carbon planes that are parallel to each other. 32. The method of claim 31, wherein the HA or CHA sheets have a length and the oriented humic acid film contains HA or CHA sheets having a length greater than the length of the HA or CHA sheets. 33. The method of claim 32, wherein the highly conductive graphite film is a polycrystalline graphene structure having a crystalline orientation as measured by the X-ray diffraction method. The method of claim 34, wherein the heat treatment step (e) induces fusion or chemical bonding of the HA or CHA sheet with another HA or CHA sheet, or reorganization of the graphite structure. The method of claim 35, wherein the heat treating step (e) induces fusion or chemical bonding of the HA or CHA sheet with another HA or CHA sheet or with a graphene sheet, or reorganization of the graphite structure. 33. The method of claim 32, wherein the highly conductive graphite film has an electrical conductivity greater than 5,000 S/cm, a thermal conductivity greater than 800 W/mK, a physical density greater than 1.9 g/cm, a tensile strength greater than 80 MPa, and having an elastic modulus greater than 60 GPa. 33. The method of claim 32, wherein the highly conductive graphite film has an electrical conductivity greater than 8,000 S/cm, a thermal conductivity greater than 1,200 W/mK, a physical density greater than 2.0 g/cm, a tensile strength greater than 100 MPa, and having an elastic modulus greater than 80 GPa. 33. The method of claim 32, wherein the highly conductive graphite film has an electrical conductivity greater than 12,000 S/cm, a thermal conductivity greater than 1,500 W/mK, a physical density greater than 2.1 g/cm, a tensile strength greater than 120 MPa, and having an elastic modulus greater than 120 GPa.

Images