CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims the benefit of Provisional Patent Application No. 63/233,425, filed on August 16, 2021, the disclosure of which is incorporated by reference herein in its entirety.

FIELD OF THE DISCLOSURE

[0002] The present invention is directed to a device and method for producing an improved carbon foam electrically powered heating element from coal, and a method for producing a carbon foam composite tool from coal. The methods can be done at atmospheric pressure, above atmospheric pressure, or below atmospheric pressure.

BACKGROUND OF THE DISCLOSURE

[0003] It has been known for some time that when an electrical voltage is applied to carbon foam made from coal, it will heat up via resistive heating. This concept has been applied to carbon foam composite tools for carbon fiber part manufacture, where surface temperatures of over 300°F have been achieved. An example of such a tool is shown in Fig. 1. In this particular case, electrodes are attached to either side of the carbon foam just beneath the carbon fiber composite surface and heavy gauge wires are attached to the electrodes. Current is then passed through the foam and resistance heating causes the tool surface to increase in temperature. This concept is attractive to manufacturers of carbon fiber composite parts because a given part can be cured right on the surface of the tool without the need of an oven, which in turn then reduces the need for the capital and space required for an oven.

[0004] The downside of this concept is that the voltage and amperage required to suitably heat the carbon foam is atypical. To achieve the temperature needed to cure carbon fiber composite parts, the foam surface must carry roughly 80 amps of current at a low voltage of about 3 volts. These electrical parameters are not typical of most commercial electrical systems, therefore requiring complicated or costly electrical components to make it work, (e.g. custom transformer, large breaker, heavy gauge wire). [0005] This conundrum largely results from the relatively low resistivity of carbon foam when fired to the temperature at which it is commonly manufactured (about 1000°C); at this temperature, the resistivity of typical carbon foam having a density of 30 pounds per cubic foot is about 0.05 ohm-cm. In order to solve this problem and bring the voltage and amperage requirements for this concept to values more commonly utilized in commercial applications, we need to change the electrical properties of the carbon foam itself. In this way, this concept then can find more commercial opportunities.

BRIEF SUMMARY OF THE INVENTION

[0006] A method for producing an improved carbon foam electrically powered heating element from coal is disclosed. The method comprises the steps of: pulverizing coal into a fine coal powder, wherein the coal comprises a high-volatile bitumen, anthracite, lignite, and mixtures thereof comprising about 35% to about 45% by weight volatile matter; blending the fine coal powder and at least one additive to form a coal mixture; foaming the coal mixture by heating the coal mixture to a temperature between 250°C and 500°C under an inert gas; pyroprocessing the coal mixture to a temperature between 500°C and 1000°C under an inert gas to form a carbon foam heating element having a resistivity in the range of about 0.01 to about 100 ohm-cm; attaching electrically conductive connections to the carbon foam heating element, applying electrical power to the electrically conductive connections, thereby resistively heating the carbon foam heating element; and wherein the steps are performed at atmospheric pressure. A device produced by these steps is also disclosed.

[0007] Also disclosed is a method for producing and using a carbon foam composite tool from coal, comprising the steps of: pulverizing coal into a fine coal powder, wherein the coal comprises a high-volatile bitumen, anthracite, lignite, and mixtures thereof comprising about 35% to about 45% by weight volatile matter; blending the fine coal powder and at least one additive to form a coal mixture; foaming the coal mixture by heating the coal mixture to a temperature between 250°C and 500°C under an inert gas; pyroprocessing the coal mixture to a temperature between 500°C and 1000°C under an inert gas to form a carbon foam heating element having a resistivity in the range of about 0.01 to about 100 ohm-cm; cutting one or more carbon foam panels to the proper size; binding the carbon foam panels together to make a preformed billet; machining the preformed billet to near-final shape to make a profiled billet; applying a tooling surface to a portion of the profiled billet; machining the tooling surface to final shape to form a composite tool; laying up a composite structure in contact with the tooling surface; supplying a heat source to the composite tool; controlling the heat source to cure the composite structure outward from the tooling surface; and wherein the steps are performed at atmospheric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Fig. 1 illustrates a typical self-heated carbon foam composite heating element for carbon fiber part manufacture,

[0009] Fig. 2 is a plot showing resistivity of typical carbon foam heating element as a function of firing temperature,

[0010] Fig. 3 is an analysis of the resistivity and associated voltage and amperage required to generate 41 W,

[0011] Fig. 4 illustrates a typical test set-up,

[0012] Fig. 5 is a plot of temperature at the surface of the carbon foam heating element as a function of time,

[0013] Fig. 6 illustrates a typical carbon foam heating element showing electrical connections, conductive joints, and insulating joints,

[0014] Fig. 7 illustrates a self-heating tool setup with a controller and transformer.

DETAILED DESCRIPTION OF THE INVENTION

[0015] Some embodiments of the present invention are described in this section in detail sufficient for one skilled in the art to practice the present invention without undue experimentation. It is to be understood, however, that the fact that a limited number of preferred embodiments are described does not in any way limit the scope of the present invention as set forth in the claims.

[0016] It is to be understood that whenever a range of values is described herein, i.e. whether in this section or any other part of this patent document, the range includes the end points and every point there between as if each and every such point had been expressly described. Unless otherwise stated, the words “about” and “substantially” as used herein are to be construed as meaning the normal measuring and/or fabrication limitations related to the value or condition which the word “about” or “substantially” modifies. Unless expressly stated otherwise, the term “embodiment” is used herein to mean an embodiment of the present invention. The term “mold”, as used herein is meant to define a mechanism for providing controlled dimensional forming of the expanding coal. Thus, any chamber into which the admixture is deposited prior to or during heating and which, upon the coal powder attaining the appropriate expansion temperature, contains and shapes the expanding porous coal to some predetermined configuration such as: a flat sheet; a curved sheet; a shaped object; a building block; a rod; tube or any other desired solid shape can be considered a “mold” for purposes of the instant invention.

[0017] The coal for one embodiment of the heating element may include bitumen, anthracite, or even lignite, or blends of these coals that exhibit a “free swell index” as determined by ASTM D720 of between about 3.5 and about 5.0, but are preferably bituminous, agglomerating coals that have been comminuted to an appropriate particle size, preferably to a fine powder below about -60 to -80 mesh. Additionally, according to further highly preferred embodiments of the present invention, the coals of the present invention possess all or at least some of the following characteristics: 1) a volatile matter content (dry, ash-free basis) of between about 35% and about 45% as defined by ASTM D3175, “Test Method for Volatile Matter in the Analysis of Coal and Coke”; 2) a fixed carbon (dry basis) between about 50% and about 60% as defined by ASTM D3172, “Practice for Proximate Analysis of Coal and Coke”; 3) a Gieseler initial softening temperature of between about 380°C and about 400°C as determined by ASTM D2639, Test Method for Plastic Properties of Coal by the Constant-Torque Gieseler Plastometer”; 4) a plastic temperature range above about 50°C as determined by ASTM D2639; 5) a maximum fluidity of at least 300 ddpm (dial divisions per minute) and preferably greater than about 2000 ddpm as determined by ASTM D2639; 6) expansion greater than about 20% and preferably greater than about 100% as determined by Arnu Dilatation; 7) vitrinite reflectance in the range of from about 0.80 to about 0.95 as determined by ASTM D2798, “Test Method for Microscopical Determination of the Reflectance of Vitrinite in Polished Specimens of Coal”; 8) less than about 30% inert maceral material such as semifusinite, micrinite, fusinite, and mineral matter as determined by ASTM D2798; and 9) no significant oxidation of the coal (0.0 vol % moderate or severe oxidation) as determined by ASTM D 2798 and non-maceral analysis. The low softening point (380-400°C) is important so that the material softens and is plastic before volatilization and coking occur. The large plastic working range or “plastic range” is important in that it allows the coal to flow plastically while losing mass due to volatilization and coking. Vitrinite reflectance, fixed carbon content and volatile matter content are important in classifying these coals as “high- volatile” bituminous coals that provide optimum results in the process of the present invention. [0018] An improved carbon foam heating element, made from a coal mixture, for use when an electrical voltage is applied is taught herein. This element might be used in residential, automotive, aeronautical, industrial, or military applications. The carbon foam manufacturing approach is particularly well-suited to producing foam that will operate well at the voltages and amperages commonly supplied to products in these applications (e g. 12 - 120 volts, 1 - 13 amps). In particular, the carbon foam manufacturing approach is well-suited to producing foam that can operate at relatively low amperage, avoiding the unsafe practice of operating at high amperage.

[0019] Fig. 1 illustrates a typical self-heated carbon foam composite heating element 10 for carbon fiber part manufacture. Electrically conductive connections 12 are made to the carbon foam heating element 10 so that electrical power can be applied through electrical wiring 14, thereby resistively heating the carbon foam heating element 10.

[0020] Fig. 2 plots the resistivity of one embodiment of a carbon foam heating element 10 as a function of temperature. This dependence arises from the loss of hydrogen from the carbon foam and a further densification of the vitreous carbon matrix as firing temperature is increased from about 500°C to 1000°C or more.

[0021] The improved method involves firing coal to a temperature where the hydrogen has been nearly eliminated from the material, but the vitreous carbon still has a resistivity that enables it to be used as an electrical heating element at more common voltage and amperage (e.g. 12 volts and < 10 amps). In many commercial cases, only a small temperature increase on the surface may be desired. Thus, for a first example, we targeted a small amount of power (41 watts) on a part having dimensions 2.9375 x 4.625 x 9”, where the width of the electrodes attached to the top surface of the carbon foam had a width of about 0.4” and length about 2.375”. [0022] Fig. 3 is an analysis of the resistivity and associated voltage and amperage required to generate 41 watts. Note how the required voltage increases and amperage decreases as the resistivity increases. Fig. 4 shows the test set-up for the heating element 44 with resultant data reported in Fig. 3. A small 12 V transformer 42 with maximum 10-amp rating was utilized to convert from 110-V AC. Fig. 5 is a plot of temperature at the surface of the carbon foam heating element 44 as a function of time.

[0023] According to Fig. 2, an estimated firing temperature of 700°C would produce a resistivity that would put us in the ballpark of 12 volts and < 10 amps (as shown in Fig. 3, a resistivity of 1.82 ohm-cm would require 12 volts and 3.4 amps to produce 41 watts). The test unit was activated, and the surface temperature tracked using an infrared thermometer gun. Fig. 5 shows the temperature increase at locations just next to the electrodes (left side, positive electrode and right side, negative electrode) and in the center of the surface. The temperature roughly stabilized after 20 minutes at the edges between about 100-115°F, and after about 45 minutes in the center at about 90°F. The temperature on the bottom of the carbon foam was also tracked, but it remained at room temperature throughout the experiment as it sat on the tabletop. With further refinements in resistivity, part geometry, and incorporation of other materials, we believe this concept could be further tuned to better meet specific heating requirements at more common voltage and amperage availability.

[0024] Referring again to Fig. 2, reported discovery of unexpected results in material resistivity ranging from about 0.01 to about 100 ohm-cm, when produced over the firing temperature range of 500°C to 800°C, led to the development of the improved carbon foam heating element methods and devices disclosed herein. As seen in Fig. 2, the carbon foam heating element resistivity experiences a drastic, step change (on the order of 8 orders of magnitude) in this rather narrow firing temperature range while being relatively stable outside of this range. This is likely due the loss of hydrogen from the carbon foam and a further densification of the vitreous carbon matrix in this firing temperature range, but the vitreous carbon still has a resistivity that enables it to be used as an electrical heating element at more common voltage and amperage.

[0025] In addition to the embodiments described above, suitable devices for the improved heating element include heating devices requiring 12- or 24-volt DC power or 110-volt AC power connections such as, air process heaters, cartridge heaters, coil and nozzle heaters, foil heaters, heat trace cable, heating jackets, immersion heaters, and tubular heaters. Suitable applications for the improved heating element include; asphalt and concrete, condensation prevention, diesel engine freeze prevention, enclosure heating, engine component heating, flow viscosity control, food and cosmetics processing, freeze protection, gas handling and processing, heating for comfort, hydraulic systems, injection molding, laboratory uses, pipelines, roof and gutter deicing, process temperature control, and water and wastewater treatment.

[0026] Typically, the cells in carbon foams are of a size that is readily visible to the unaided human eye. Also, the void volume of carbon foams is such that it typically occupies much greater than one-half of the carbon foam volume. The density of carbon foams typically is less than about 1.0 g/cm ³ and generally less than about 0.8 g/cm ³ . In some embodiments, the density for carbon foam may range from about 0.05 g/cm ³ to about 0.8 g/cm ³ . In some embodiments, carbon foams may exhibit compressive strengths ranging up to about 10,000 psi. In other embodiments, the compressive strength for carbon foam may range from about 100 psi to about 10,000 psi. In certain other embodiments, compressive strengths for carbon foam may range from about 400 psi to about 7,000 psi. The carbon foam incorporated in a tool body may be carbonized carbon foam. Alternatively, if desired, the carbon foam incorporated in a tool body may be graphitized carbon foam.

[0027] Carbon foams have been produced by a variety of methods. Some of these methods include producing carbon foams directly from particulate coal. For example, US Patent Nos. 6,749,652; 6,814,765; and 7,588,608 describe methods for producing carbon foam directly from particulate coal. To produce carbon foam from particulate coal, typically, a suitable swelling coal, such as bituminous coal, is heated in an essentially closed vessel. The particulate coal is placed in a mold and is heated in an inert atmosphere under process atmospheric pressures typically greater than ambient and can reach pressures of about 500 psi or greater. The particulate coal is heated to temperatures sufficient to cause the coal to become plastic and swell, forming a carbon foam. In many instances, heating the particulate coal to a temperature between about 300°C and about 500°C is sufficient to form a carbon foam material. The temperatures and pressure conditions will vary depending upon the characteristics of the particulate coal. The resultant carbon foam may subsequently be heated under an essentially inert, or otherwise non- reactive, atmosphere, to temperatures as great as about 3000°C. Heating of the carbon foam to such elevated temperatures has been found to improve certain properties of the foam. Such properties have included, but are not limited to, electrical resistance, thermal conductivity, thermal stability, and strength. The production of carbon foam from mesophase pitch follows a similar process. [0028] During heating, the particles begin to melt and evolve gases that cause the material to foam. The foaming step is done under high pressure to help regulate bubble formation. As oxygen, nitrogen, and hydrogen are eliminated from the precursor during heat up, the carbon continues to cross-link until only a glassy like carbon material remains at 1000°C. Where mesophase pitch is used, further heating induces nucleation and growth of graphite crystals.

[0029] Some embodiments can comprise a low-density carbon foam, made from a coal that can have a density from about 0.1 to about 0.8 g/cm ³ , preferably from about 0.2 to about 0.6 g/cm ³ and most preferably from about 0.3 to about 0.4 g/cm ³ . The coal may include bitumen, anthracite, or even lignite, or blends of these coals that exhibit a “free swell index” as determined by ASTM D720 of between about 3.5 and about 5.0, but are preferably bituminous, agglomerating coals that have been comminuted to an appropriate particle size, preferably to a fine powder below about -60 to -80 mesh. Additionally, according to further highly preferred embodiments of the present invention the coals of the present invention possess all or at least some of the following characteristics: 1) a volatile matter content (dry, ash-free basis) of between about 35% and about 45% as defined by ASTM D3175, “Test Method for Volatile Matter in the Analysis of Coal and Coke”; 2) a fixed carbon (dry basis) between about 50% and about 60% as defined by ASTM D3172, “Practice for Proximate Analysis of Coal and Coke”; 3) a Gieseler initial softening temperature of between about 380° C and about 400° C as determined by ASTM D2639, Test Method for Plastic Properties of Coal by the Constant-Torque Gieseler Plastometer”; 4) a plastic temperature range above about 50° C as determined by ASTM D2639; 5) a maximum fluidity of at least 300 ddpm (dial divisions per minute) and preferably greater than about 2000 ddpm as determined by ASTM D2639; 6) expansion greater than about 20% and preferably greater than about 100% as determined by Amu Dilatation; 7) vitrinite reflectance in the range of from about 0.80 to about 0.95 as determined by ASTM D2798, “Test Method for Microscopical Determination of the Reflectance of Vitrinite in Polished Specimens of Coal”; 8) less than about 30% inert maceral material such as semifusinite, micrinite, fusinite, and mineral matter as determined by ASTM D2798; and 9) no significant oxidation of the coal (0.0 vol % moderate or severe oxidation) as determined by ASTM D 2798 and non-maceral analysis. The low softening point (380-400°C) is important so that the material softens and is plastic before volatilization and coking occur. The large plastic working range, or “plastic range” is important in that it allows the coal to flow plastically while losing mass due to volatilization and coking. Vitrinite reflectance, fixed carbon content and volatile matter content are important in classifying these coals as “high-volatile” bituminous coals that provide optimum results in the process of the present invention and thus, carbon foam materials that exhibit an optimum combination of properties when prepared in accordance with the process described and claimed herein. The presence of oxidation tends to hinder fluidity and consequently, foam formation.

[0030] Thus, according to various embodiments of the present invention, a coal particulate characterized as a high-volatile bituminous coal containing from about 35% to about 45% by weight (dry, ash-free basis) volatile matter, as defined by ASTM D3175, is a basic requirement for obtaining optimum results in the form of optimum carbon foaming in accordance with the process of the present invention. The various parameters derived from the Gieseler plasticity evaluations form the second highly important set of characteristics of the coal if optimum results are to be obtained. Thus, a softening point in the range of from about 380°C and about 400°C, a plastic range of at least about 50°C and preferably between about 75 and 100°C, and a maximum fluidity of at least several hundred and preferably greater than 2000 ddpm (dial divisions per minute) are highly important to the successful optimized practice of the present invention.

Accordingly, in order to obtain the carbon foams exhibiting the superior properties described herein, it is important that the coal be a high volatile bituminous coal having a softening point as just described and a plastic range on the order of above about 50°C all with the indicated Gieseler fluidity values described. Exhibition of Arnu dilatation values greater than about 20% and preferably above about 100% when combined with the foregoing characteristics provide indications of a highly preferred high volatile bituminous coal.

[0031] The cellular coal -based products described herein are semi-crystalline or more accurately turbostratically-ordered and largely isotropic, i.e., demonstrating physical properties that are approximately equal in all directions. The cellular coal-based products typically exhibit pore sizes on the order of less than 300 pm, although pore sizes of up to 500 pm are possible within the operating parameters of the process described. The thermal conductivities of the cellular coal-based products are generally less than about 1.0 W/m-K. Typically, the cellular coal-based products of the present invention demonstrate compressive strengths on the order of from about 1500 to about 3000 psi at densities of from about 0.4 to about 0.5 g/cm ³ . The coal can exhibit the previously specified free swell index of between about 3.5 and about 5.0 and preferably between about 3.75 and about 4.5. Selection of coals within these parameters was determined by evaluating a large number of coals characterized as ranging from high to low volatiles. In general, it has been found that bituminous coals exhibiting free swell indexes within the previously specified ranges provided the best foam products in the form of the lowest calcined foam densities and the highest calcined foam specific strengths (compressive strength/density). Such bituminous coals that also possess the foregoing set of properties, high volatile content (35% to 45% by weight), large plastic range (at least about 50°C), etc. and are thus characterized as high volatile bituminous coals, form the preferred coals of the process of the present invention. Coals having free swell indices below the specified preferred ranges may not agglomerate properly leaving a powder mass or sinter, but not swell or foam, while coals exhibiting free swell indices above these preferred ranges may heave upon foaming and collapse upon themselves leaving a dense compact.

[0032] The production method for one embodiment of the present invention comprises: 1) heating a high volatile bituminous coal admixture of preferably small i.e., less than about 100- pm particle size in a “mold” and under a non-oxidizing atmosphere at a heat up rate of from about 1 to about 20°C to a temperature of between about 300 and about 700°C; 2) soaking at a temperature of between about 300 and 700°C for about 10 minutes up to about 12 hours to form a preform or finished product; and 3) controllably cooling the preform or finished product to a temperature below about 100°C. The non-oxidizing atmosphere may be provided by the introduction of inert or non-oxidizing gas into the “mold” at a pressure of from about 0 psi, i.e., free flowing gas, up to about 500 psi. The inert gas used may be any of the commonly used inert or non-oxidizing gases such as nitrogen, helium, argon, CO2, etc.

[0033] It is generally not desirable that the reaction chamber be vented or leak during the heating and soaking operation. The pressure of the chamber and the increasing volatile content therein tends to retard further volatilization while the cellular product sinters at the indicated elevated temperatures. If the furnace is vented or leaks during soaking, an insufficient amount of volatile matter may be present to permit inter-particle sintering of the coal particles, thus resulting in the formation of a sintered powder as opposed to the desired cellular product. Thus, according to a preferred embodiment of the present process, venting or leakage of non-oxidizing gas and generated volatiles is inhibited, consistent with the production of an acceptable cellular product. Additionally, more conventional blowing agents may be added to the particulate prior to expansion to enhance or otherwise modify the pore-forming operation. [0034] Cooling of the preform or product after soaking is not particularly critical except as it may result in cracking of the preform or product as the result of the development of undesirable thermal stresses. Cooling rates less than 10°C/min to a temperature of about 100°C are typically used to prevent cracking due to thermal shock. Somewhat higher, but carefully controlled cooling rates may however, be used to obtain a “sealed skin” on the open cell structure of the product as described below. The rate of cooling below 100°C does not influence the final product.

[0035] After expanding the high volatile bituminous admixture as just described, the porous or foamed coal product is an open celled material. Several techniques have been developed for “sealing” the surface of the open celled structure to improve its adhesive capabilities for further fabrication and assembly of several parts. For example, a layer of a commercially available graphitic adhesive can be coated onto the surface and cured at elevated temperature or allowed to cure at room temperature to provide an adherent skin. Alternatively, the expansion operation can be modified by cooling the expanded coal product or preform rapidly, e g. at a rate of 10°C/min or faster after expansion. It has been discovered that this process modification results in the formation of a more dense skin on the preform or product which presents a closed pore surface to the outside of the preform or product. At these cooling rates, care must be exercised to avoid cracking of the preform or product.

[0036] After expanding, the porous coal-based preform or product, i.e. carbon foam in accordance with the present invention, is readily machineable, sawable and otherwise readily fabricated using conventional fabrication techniques.

[0037] Subsequent to production of the preform or product as just described, the preform or product may be subjected to carbonization and/or graphitization according to conventional processes to obtain particular properties desirable for specific applications of the type described hereinafter. Ozonation may also be performed, if activation of the coal-based expanded product would be useful in a final product application such as in filtering of air. Additionally, a variety of additives and structural reinforcers may be added to the coal based preforms or products either before or after expansion to enhance specific mechanical properties such as fracture strain, fracture toughness, and impact resistance. For example, particles, whiskers, fibers, plates, etc. of appropriate carbonaceous or ceramic composition can be incorporated into the porous coal-based preform or product to enhance its mechanical properties. [0038] The open celled, coal-based preforms or products, i.e. carbon foams, of the present invention can additionally be impregnated with an additive, for example, petroleum pitch, epoxy resins or other polymers, an organic material, and/or an inert particulate, using a vacuum assisted resin transfer type of process. The incorporation of such additives provides load transfer advantages similar to those demonstrated in carbon composite materials. In effect a 3-D composite is produced that demonstrates enhanced impact resistance and load transfer properties. [0039] The cooling step in the expansion process results in some relatively minimal shrinkage on the order of less than about 5% and generally in the range of from about 2% to about 3%. This shrinkage must be accounted for in the production of near net shape preforms or final products of specific dimensions and is readily determinable through trial and error with the particular coal being used. The shrinkage may be further minimized by the addition of some inert solid material such as coke particles, ceramic particles, ground waste from the coal expansion process etc. as is common practice in ceramic fabrication.

[0040] Carbonization, sometimes referred to as calcining, is conventionally performed by heating the preform or product under an appropriate inert gas at a heat-up rate of less than about 5°C per minute to a temperature between about 1000°C and about 1200°C and soaking for from about 1 hour to about three or more hours. Appropriate inert gases are those described above that are tolerant of these high temperatures. The inert atmosphere is supplied at a pressure from about 0 psi up to a few atmospheres. The carbonization/calcination process serves to remove all of the non-carbon elements present in the preform or product such as sulfur, oxygen, hydrogen, etc. [0041] Graphitization, commonly involves heating the preform or product either before or after carbonization at heat-up rate of less than about 10°C per minute, preferably from about 1°C to about 5°C per minute, to a temperature of between about 1700°C and about 3000°C in an atmosphere of helium or argon and soaking for a period of less than about one hour. Again, the inert gas may be supplied at a pressure ranging from about 0 psi up to a few atmospheres.

[0042] The porous coal-based preforms or products resulting from processing in accordance with the foregoing procedures can be used in a broad variety of product applications, some, but not all, of which will now be broadly described.

[0043] Products that could be fabricated using the coal -based porous preforms or products of the present invention are various lightweight sheet products useful in the construction industry. Such products may involve the lamination of various facing materials to the surface of a planar sheet of the preform material using an appropriate adhesive. For example, a very light and relatively inexpensive wall board would simply have paper laminated to its opposing planar surfaces, while a more sophisticated curtain wall product might have aluminum sheet, polymer or fiber-reinforced polymer sheets or even stainless steel sheet laminated thereto. A wide variety of such products that have lightweight, low cost and adequate strength can easily be envisioned for wallboard, structural wallboard, bulkheads, etc. The materials of the present invention exhibit sound insulation and vibration resistance due to excellent sound and vibration damping properties, good thermal insulating properties (less than about 1 watt per meter K thermal conductivity).

[0044] Laminates of these materials may even be used to produce heating element incorporating members, since a graphitized core could serve as an electrical heating element when connected to an appropriate source of electrical energy.

[0045] Similar surface laminated porous preform core-based products could also find use in the transportation industry where lighter and, especially fire retardant walls, bulkheads, containers, etc. are in constant demand. Such products would of course require that the expanded coal-based porous core be carbonized as described hereinabove prior to application of the exterior skins, if fire resistance or retardancy is desired.

[0046] Yet other product applications for the carbon foam materials of the present invention reside in the field of heat exchangers. In this application, the heat transfer properties of a graphitized porous coal-based material can be exploited to produce a heat exchanger capable of extracting heat from or adding heat to a fluid (gas or liquid) flowing through porous coal pores. In this case, the coal-based porous product is joined to an appropriate heat transfer mechanism such as an aluminum skin.

[0047] Similar relatively minor process modifications can be envisioned to fabricate the carbon foams of the present invention in injection molding, casting and other similar conventional material fabrication processes.

[0048] Another embodiment of the invention can be a self-heated composite tool for manufacturing various composite structures and shapes out-of-autoclave. Self-heated composite tooling can improve throughput, reduce energy costs, eliminate temperature limitations for autoclaves and kilns and reduce the shop space necessary to produce composite parts. [0049] CFOAM® carbon foam can currently be manufactured at densities between about 17 and 65 lbs. per cubic foot. For reference, standard CFOAM® 20 has a compressive strength of about 876 psi and an electrical resistivity of 0.07 ohm-centimeters; standard CFOAM® 30 has a compressive strength of about 2300 psi and an electrical resistivity of 0.05 ohm-centimeters. CFOAM® carbon foam can be used in air at temperatures up to around 700° Fahrenheit or 370° Celsius. Because CFOAM® carbon foam can be used at high temperature, it provides a platform to design and build a suite of self-heated tooling solutions using heated oils (similar to injection molding) or embedded wires (resistance heating) as a heating source.

[0050] Most composite tools made from CFOAM® carbon foam are manufactured by cutting panels of CFOAM® to the proper size, gluing the panels together to make a preformed billet, machining the preformed billet to just shy of the final surface to make a profiled billet, applying a tooling surface to the profiled billet, and then performing a final machine to the tooling surface to achieve a high tolerance. The tooling surface can be paint, a polymer, a composite surface and combinations thereof.

[0051] To build composite tooling, two kinds of gluedjoints for the CFOAM® are required; one that conducts electricity well, for example using a conductive adhesive, and one which electrically insulates or isolates. When using an insulating adhesive, the rough surfaces of the CFOAM® often penetrate through the adhesive layer. Lightly sanding the CFOAM® rough surfaces to knock down sharp points that might penetrate through the adhesive layer helped make a satisfactory insulating adhesive joint. A very thin layer of non-conducting fiberglass was also found to work well for insulating joints.

[0052] As shown in Fig. 6, the carbon foam composite tool 62 there are two electrically conductive joints 64 that permit electric current to flow from one conductor 68 to the other conductor 69, through the conductive joints 64. The horizontal joint in the middle, extending from one conductor 68 to the other 69, is an electrically non-conductive joint 66 (insulating joint). The temperature is sufficiently uniform across the entire surface of the composite tool 62. The two vertical joints (conductive joints 64) are electrically conductive and again the temperature uniformity is across the conductive joint 64 is acceptable. A thermal image of the performance of the tool showed uniform temperature across the surface except where there are heat losses on the side, which can be improved by thermally insulating the outer edges of the tool to reduce heat loss. [0053] Fig. 7 illustrates a self-heating tool 72 setup with a controller 74 and transformer 76. This self-heating tool 72 can be used to cure flat composite panels from "pre-impregnated" fibers and a partially cured polymer matrix, such as epoxy or phenolic resin, or even thermoplastic mixed with liquid rubbers or resins.

[0054] These tools can be made precise in temperature uniformity using a few different approaches: 1) insulate cool areas, for example on the edges of the tool; 2) cool areas can be made hotter by making the CFOAM® cross sectional area smaller in that area or drilling small holes in the back making the cross sectional area somewhat smaller generating more heat locally; and/or 3) using graphite “shunts” to effectively shorten the distance across the tool which sees the same voltage drop to raise the temperature of this section of the tool.

[0055] This example out-of-autoclave self-heating tool operated at 3 volts and 80 amps and heated to a surface temperature of 359°F or 177°C using only 240 Watts. Comparing that to taking a tool to a walk-in oven for thermal processing which uses about 96,000 watts of power, or about 400 times more energy than the self-heating tool. Electrically self-heated tooling can substantially reduce power costs and reduce time, motion and manufacturing floor space required for oven (autoclave) processing. Through utilization of the technology described, carbon foam can be tuned to achieve an optimum voltage and amperage for heating, as well as a lower and safer operational amperage.

[0056] Oven-cured composite structures can be cured using the pressure of a vacuum bag (> 1 bar). In this kind of application, it is possible to cure the part on a self-heated tool that is located on the shop floor or sitting on a shelf out of the way. There are several advantages to this approach. You do not need to buy an oven to cure the part and saving the cost of this capital equipment is significant. You also gain flexibility, as you are not limited in the size of your part relative to the size of your oven. Also, oven size often determines how many parts can be cured in a batch. When each tool can be used as soon as the part is bagged and ready for cure, there is no need to wait to cure it along with other similar parts. It can be cured on its own, improving cycle time throughput, tool utilization and overheads.

[0057] Curing a composite part using a self-heating heating tool improves the cure dynamics of the part by reducing or eliminating voids. Voids are bubbles that get trapped in the resin as it hardens during cure. [0058] During composite part curing, as the resin heats, it becomes thinner (less viscous and more water-like). A breather is used to help remove the voids from the resin when this happens. With conventional composite part manufacturing, the tool prevents the bottom of the part from heating so that the part heats from the bag surface. This causes the top to "gel" before the viscosity of the resin at the tool surface begins to get thinner and flow, which traps the voids and prevents them from escaping because the thicker resin acts as a barrier between the laminate and the breather.

[0059] When heating from the self-heating tool surface, the opposite happens. The material at the tooling surface gets thinner first, allowing the voids the best opportunity to escape to the breather where they can be pulled away. So, the best opportunity to eliminate voids in a composite comes when we heat from the tool surface, a condition that always happens when using a self-heated tool.

[0060] Autoclave-cured composite structures can be cured using pressurized air and a vacuum bag (> 6.8 bar). In this kind of application, it is possible to cure the part on a self-heated tool located in the autoclave and use only the pressure needed to cure the part, without heating the air in the autoclave. During the pressurization of the autoclave, there will be some extra addition of heat generated from the compression of the air. This will assist with heating the part and reduce the need for additional heat input to the tool.

[0061 ] Electrical wiring (high temperature insulation) must be fed through the wall of the autoclave to transmit the current needed to heat the self-heated tool. The standard thermocouple ports will suffice for embedded thermocouple(s) used to communicate the tool temperature to the controller.

[0062] The reduction of cycle time pays big dividends when working with the operating expenses of the autoclave. There will be a reduction in both heating and cooling the tool. The cost of operation will be reduced by the amount of money saved by not having to heat the volume of air in the autoclave. However, the reduction in cycle time will also add capacity to the autoclave, enabling it to run many more cycles in the course of a year. This is important because the autoclave can easily become a bottleneck in a production environment. This reduces the demand to add autoclaves (a significant capital investment) in order to increase production volumes. [0063] Self-heated tools can be more expensive to build because they require a controller. One controller can only run one tool at a time, so a large production facility would require several controllers to manage the throughput requirements. However, a controller can be used interchangeably with any of the tools. An oven-cured part can begin curing as soon as it is ready for cure. Elimination of batch-size requirements is the most efficient way to manufacture and improve throughput.

[0064] The foregoing explanations, descriptions, illustrations, examples, and discussions have been set forth to assist the reader with understanding this invention and further to demonstrate the utility and novelty of it and are by no means restrictive of the scope of the invention. It is the following claims, including all equivalents, which are intended to define the scope of this invention.