Apparatus and method for mass production of particulate materials

Abstract

An apparatus and method are provided that enable the mass production of particulate materials, such as graphene particles. The apparatus includes an ignition assembly that includes an easily replaceable electrode cassette and that can be configured for self-cleaning between combustion cycles in which the particulate material is produced. The method for producing the particulate material requires low energy to initiate a combustion reaction, which then continues self-sustaining until the reactants are depleted.

Description

[Technical Field]

[0001] Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 63 / 039,087, filed June 15, 2020, which is incorporated herein by reference in its entirety. [Background technology]

[0002] FIELD OF THE INVENTION The present invention is generally directed to an apparatus and method for mass-producing particulate materials, particularly carbon-containing particulate materials such as graphene. The particulate materials are produced in a combustion process in which chemical energy contained in reactants is sufficient to sustain a reaction to produce the particulate material. In one or more embodiments, the apparatus includes an ignition assembly including a pair of electrodes, each housed in a cassette removable from the ignition assembly. The ignition assembly may be configured for self-cleaning between reaction cycles.

[0003] Description of the Prior Art Graphene has a hexagonal crystal structure and is sp 2 Graphene is a two-dimensional monolayer of bonded carbon atoms. It possesses several exceptional physical properties, including excellent mechanical strength, high intrinsic carrier mobility at room temperature, and electrical and thermal conductivities comparable to those of graphite. Graphene is therefore of interest for use in numerous applications, including nanoelectronics and sensors, nanocomposites, batteries, supercapacitors, and hydrogen storage. However, a drawback that has prevented graphene from being widely adopted in these fields is the inability to produce commercial quantities of graphene in a cost-effective manner. Current graphene production methods are expensive, complex, energy-intensive, and often require corrosive chemicals and catalysts.

[0004] U.S. Pat. No. 9,440,857 (incorporated herein by reference in its entirety) is directed to a method for producing graphene particles in a simple, controlled detonation process in which a carbon-containing material and an oxidant are detonated in a reactor. The reactor is charged with a desired amount of reactants, and a spark is used to detonate the materials. An aerosol containing graphene particles is produced. However, while the above-mentioned apparatus is suitable for producing laboratory-scale quantities of graphene, it has not been efficient for producing commercial quantities of graphene particles and has suffered from fouling of the spark generator after repeated detonation cycles.

[0005] Luong et al. describe a method for producing graphene by flash synthesis: "Gram-scale bottom-up flash graphene synthesis" Nature 577, 647-651 (2020). In flash synthesis, graphene is produced from solid carbon sources, such as coal, petroleum coke, biochar, or carbon black, using high-voltage electricity discharged from a capacitor bank, which rapidly heats the carbon source to high temperatures. While gram-scale production of graphene particles has been reported, such methods are expected to be capital- and energy-intensive due to the use of capacitor banks to rapidly heat the carbon source.

[0006] Therefore, there is a need in the art for an apparatus and method for producing graphene that is economical and allows for the production of commercial quantities of graphene particles. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Patent No. 9,440,857 [Non-patent literature]

[0008] [Non-Patent Document 1] “Gram-scale bottom-up flash graphene synthesis” Nature 577, 647-651 (2020) Summary of the Invention [Means for solving the problem]

[0009] According to one embodiment of the present invention, an apparatus for producing particulate material by combustion of reactants is provided. The apparatus includes a reaction chamber, a vacuum source operably connected to the reaction chamber, and an ignition assembly. The reaction chamber is operably coupled to a source of carbon-containing material and a source of oxidizer. The vacuum source is operable to selectively evacuate (vacuum) at least a portion of the contents of the reaction chamber, particularly after production of the particulate material. The ignition assembly is configured to initiate combustion of a quantity of carbon-containing material and a quantity of oxidizer delivered to the reaction chamber from the respective sources. The ignition assembly includes a pair of electrodes operable to generate an ionized arc therebetween, each electrode housed in a respective cassette removably housed within the ignition assembly.

[0010] According to another embodiment of the present invention, an electrical ignition assembly operable to initiate a combustion reaction within a reaction chamber is provided. The electrical ignition assembly includes a housing having an inlet port configured to fluidly connect to one or more sources of gaseous reactant material and an outlet port configured to fluidly connect to the reaction chamber. The inlet and outlet ports are connected by a passageway. The ignition assembly further includes a pair of electrodes, each having an electrode tip extending toward the passageway. Each electrode is housed in a respective cassette that is removably housed within the housing.

[0011] According to yet another embodiment of the present invention, there is provided a method for producing graphene particles. The method includes introducing a mixture containing a carbon-containing material and an oxidizer into a reaction chamber. The carbon-containing material and the oxidizer are introduced into the reaction chamber through an ignition assembly including a pair of electrodes. An ionized arc is generated between the pair of electrodes in the ignition assembly, causing the carbon-containing material and the oxidizer to combust and generating a temperature of at least 3000 K in the reaction chamber to produce an aerosol containing graphene particles. The aerosol is evacuated from the reaction chamber using a vacuum source operably connected to the reaction chamber. The graphene particles are recovered as graphene powder from the aerosol evacuated from the reaction chamber. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of an apparatus for producing particulate material by combustion of reactants, in accordance with one or more embodiments of the present invention. [Figure 2] FIG. 1 illustrates an example of a reaction chamber and ignition assembly according to one or more embodiments of the present invention. [Figure 3] FIG. 3 is a perspective view of the ignition assembly of FIG. 2. [Figure 4] FIG. 4 is a cross-sectional view of the ignition assembly of FIG. 3. [Figure 5] 4 is a cross-sectional view of the ignition assembly of FIG. 3 showing a pair of electrodes held in the ignition assembly. [Figure 6] FIG. 6 is an exploded view of the electrode of FIG. 5. [Figure 7] 4 is a cross-sectional view of the ignition assembly of FIG. 3 showing a pair of venturis that direct the flow of liquid introduced into the ignition assembly around the electrodes. The drawings do not necessarily represent the exact dimensions and tolerances of the parts and structures shown, but are intended to illustrate the relationships between parts of the structures depicted in the drawings to scale. DETAILED DESCRIPTION OF THE INVENTION

[0013] Referring to FIG. 1, an apparatus 10 for producing particulate material according to one or more embodiments of the present invention is shown. The apparatus 10 generally includes a reaction chamber 12, a vacuum system 14, a particle collector 20, and an ignition assembly 22. The vacuum system 14 includes a vacuum pump 16 and a vacuum ballast tank 18. A source of carbon-containing material 24 and a source of oxidizer 26 are operably connected to the reaction chamber 12 via a gas manifold 28. In some embodiments, a source of flushing gas 30, such as air, may be connected to the reaction chamber 12 via the manifold 28. However, it is within the scope of the present invention to use the oxidizer source 26 as a flushing gas rather than requiring a separate flushing gas source. The inlet of the vacuum pump 16 is connected to a three-way valve 38b, which is also connected to the manifold 28 and the vacuum ballast tank 18. In this manner, the vacuum pump 16 can be configured to evacuate the reaction chamber 12 in preparation for loading the reaction chamber with reactants, or to evacuate the ballast tank 18 to facilitate vacuum recovery during a reaction and recovery cycle. A filter 32a, such as a HEPA filter, can be positioned between the pump 16 and the valve 38b to prevent particulates from being drawn into the pump. A filter 32b, also a HEPA filter, can be positioned upstream of the ballast tank to capture particles that may be entrained in the gas flow from the particle collector 20. In another embodiment, a second vacuum pump (not shown) can be used to continuously evacuate the ballast tank 18.

[0014] The masses of carbon-containing material and oxidant introduced into manifold 28 can be measured by mass meters 34, 36. It is understood that multiple mass meters operably connected to other reactant sources can be provided to give apparatus 10 the capability to react more complex mixtures of reactants than the simple binary mixture shown. Additionally, the flow of reactants and flushing gas into and out of manifold 28 can be controlled by multiple control valves 38a-e. Operation of valves 38 can be controlled by a central electronic controller (not shown). The central controller can also include various sensors (not shown) located throughout apparatus 10 to monitor and record data on critical process parameters to provide quality control, traceability, documentation, and mean time between failures (MTBF) monitoring.

[0015] In certain embodiments, the carbon-containing material may be in the form of a carbon-rich precursor, gas, gas mixture, powder, aerosol, or the like, but is not limited to these. In preferred embodiments, the carbon-containing mixture comprises a hydrocarbon compound, preferably a saturated or unsaturated hydrocarbon compound having 1 to 12 carbon atoms. In certain embodiments, acetylene is a particularly preferred hydrocarbon material. The carbon-containing material may be a single substance or compound, or may be a mixture of carbon-containing compounds. For example, acetylene may be the only carbon-containing compound present in the reaction mixture, or the reaction mixture may comprise a mixture of hydrocarbon compounds. Furthermore, the carbon-containing material need not be supplied as a gas. The carbon-containing mixture may comprise a solid or liquid that can be finely dispersed in the reaction vessel (e.g., an aerosol containing solid particles such as coal dust or petroleum coke and / or liquid droplets such as liquid hydrocarbons). In certain embodiments, the carbon-containing material should have as large a surface area as possible so that the combustion reaction can proceed rapidly and generate the heat necessary to achieve the desired reaction temperature.

[0016] The oxidizer can be any material capable of oxidizing a carbon-containing material in a combustion reaction. In one or more embodiments, the oxidizer includes oxygen in elemental form or in combination with other elements. In certain embodiments, the oxidizer is selected from the group consisting of O2, NO, NO, and mixtures thereof. When the oxidizer includes O2, the O2 may be provided in a nearly pure form (i.e., 99% or greater), as air, or with other inert materials. The ratio of oxidant to carbon-containing material in the reaction vessel prior to combustion contributes to the characteristics of the graphene particles formed upon combustion of the reaction mixture. In some embodiments, the molar ratio of oxidant to carbon-containing material is about 1.5 or less. In particular embodiments, the ratio of oxidant to carbon-containing material is about 0.1 to about 1.5, about 0.2 to about 1.2, about 0.4 to about 1.0, or about 0.6 to about 0.8.

[0017] 2 illustrates an exemplary reaction chamber 12 connected to an exemplary ignition assembly 22 with pipe nipples 39, 40 and a pipe union 42. In some embodiments, the ignition assembly 22 may be integral with the reaction chamber 12 rather than being separate from the reaction chamber 12. As shown, the reaction chamber 12 is generally cylindrical and includes an inlet port 44 configured to introduce reactants into the reaction chamber 12 and an outlet port 46 through which particulate material produced in the reaction chamber 12 is removed and transported to the particle collector 20. In some embodiments, the reaction chamber 12 is configured to withstand the high temperatures generated by the combustion of the reactants and the resulting shock waves. Additionally, the reaction chamber 12 may contain a catalyst or a consumable feedstock.

[0018] 3-7 detail one embodiment of the ignition assembly 22 and its components. As shown, the ignition assembly 22 includes a housing 48 having an inlet 50 and an outlet 52. However, again, it is within the scope of the present invention for the ignition assembly 22 to be integral with the reaction chamber 12 rather than being provided as a separate module. A pipe nipple 54 threads into the inlet 50, connecting the inlet to the gas manifold 28. A pipe nipple 39 threads into the outlet 52. The inlet 50 and outlet 52 are connected by a passage 56 extending through the housing 48. At least one pair of electrode cassettes 58 are removably received within a port 60 extending through a surrounding housing sidewall 62. Preferably, the cassettes 58 are positioned opposite each other and include electrode tips 64 extending into the passage 56. The distance between the electrode tips 64 is referred to as the arc gap. Also disposed within the housing are one or more fluid diverter cartridges 66 housed within ports 68 that also extend through the sidewall 62. In the illustrated embodiment, the assembly 22 includes two opposing fluid diverter cartridges 66 positioned approximately 90° from each electrode cassette 58.

[0019] FIG. 6 illustrates the structure of an exemplary cassette 58 made in accordance with the present invention. Each cassette 58 includes an electrical terminal 70 that may be connected to a power source (not shown) capable of providing the voltage necessary to generate an ionized arc between the electrode tips 64. The electrode tips 64 include the ends of elongated electrodes 72 that are received within bores 74 in a body 76. Preferably, the electrodes 72 are filaments or wires formed from a metal or metal alloy, such as copper, gold, silver, aluminum, nickel, iron, platinum, brass, or steel. The body 76 includes an insulating material that electrically insulates the electrodes 72 from other portions of the cassette 58. In one or more embodiments, the body 76 is also relatively non-porous and may comprise, for example, glass or a glazed ceramic. As discussed below, the non-porous nature of the body 76 helps to retard or prevent the infiltration of graphene particles into the interior of the cassette 58, which could cause short circuits within the cassette given the high electrical conductivity of graphene. In certain embodiments, the insulating material forming the body 76 and insulating the electrode 72 may have a porosity of less than 0.1, less than 0.01, or less than 0.001 as measured by any of the accepted methods for measuring the porosity of a material, such as the direct volume method, the optical method, the imbibition method, or the gas expansion method.

[0020] The body 76 is received within the holder 78 with the body tubular portion 80 protruding through the orifice 82. A plurality of washers or spacers 84 (collectively) are disposed around the tubular portion 80 and within the holder 78. A sleeve 86 also surrounds a portion of the body 76 and is itself received within the holder 78. An O-ring 88 provides a seal between the sleeve 86 and the body 76. A washer 90 and nut 92 are threaded onto the long electrode 72 to maintain sealing pressure and positional security of the O-ring 94 and tip 64 against the body 76. The O-ring 94 provides a seal between the electrode tip 64 and the body 76. O-rings 96, 98 provide a seal between the holder 78 and the housing 48.

[0021] A ferrule 100 surrounds the distal end of the electrode 72 and is housed within a collar 102 configured to abut the sleeve 86. Preferably, the ferrule 100 includes an electrical insulator, which may be the same as or different from that of the body 76. The collar 102 is threaded onto the holder 78 to provide positional security for the components of the electrode assembly. In particular, the collar 102 holds the electrode tip 64 in a fixed position within the passageway 56. A setscrew 104 may be used to secure the collar 102 to the holder 78. A nut 106 secures the ferrule 100 within the collar 102. The terminal 70 is connected to the distal end of the electrode 72. A bearing 108 and bushing 110 surround portions of the holder 78, and a setscrew 112 may be used to secure the bushing 110 within the port 60.

[0022] The electrode cassettes 58 are also adjustable within each port 60 so that the desired arc gap can be set and maintained when the ignition assembly 22 is serviced and cassettes are replaced.

[0023] In certain embodiments, the electrode 72 is configured to be movable within the ignition assembly. As described in more detail below, the ability to move the electrode 72 without completely removing it from the ignition assembly 22 facilitates cleaning of the electrode tip 64. In one or more embodiments, the electrode 72 is rotatable by connecting an actuator (not shown), such as a servo motor or pneumatic piston, to the electrode itself or to the cassette 58. The actuator can operate to rotate or intermittently drive the electrode for each combustion reaction or for a predetermined number of combustion reactions. In other embodiments, the electrode 72 may extend and / or rotate within the ignition assembly 22 to allow for cleaning or symmetrical wear of the electrode.

[0024] In one or more embodiments, as shown, the ignition assembly 22 includes one or more, preferably two, fluid diverter cartridges 66. As shown in FIG. 7 , the fluid diverter cartridge 66 includes a venturi structure 114 that extends into the passageway 56. The venturi structure 114 includes an angled surface 116 that is configured to direct fluid flowing through the passageway 56 toward the entire face of the electrode tip 64 opposite the direction of fluid flow through the ignition assembly (i.e., toward the face of the electrode tip 64 facing the outlet 52). In this manner, the venturi structure 114 allows flushing gas flowing through the passageway 56 to contact substantially the entire face of the electrode tip 64, ensuring removal of particles, particularly carbonaceous deposits, that have accumulated thereon.

[0025] In certain embodiments, the cassette 58 and / or diverter cartridge 66 are configured to be easily removed from the ignition assembly 22 so that another cassette and / or diverter cartridge can be easily installed in its place. Thus, servicing of the ignition assembly 22 can be performed with minimal downtime of the apparatus 10. The self-cleaning operation of the ignition assembly 22 and the rapid replacement of the cassette 58 and / or cartridge 66 contributes significantly to the ability of the apparatus 10 to produce commercial-scale quantities of particulate material.

[0026] As described above, the apparatus 10 can be used to produce particulate materials, particularly graphene particles, through a combustion reaction. The carbon-containing material and oxidizer are loaded into the reaction chamber 12 through the manifold 28 and the ignition assembly 22. The carbon-containing material and oxidizer may be mixed upstream of or within the manifold 28 before being delivered to the reaction chamber 12. The pressure of the reaction mixture within the reaction chamber 12 may be altered prior to combustion to control the reaction conditions and / or reaction products. In some embodiments, the initial pressure of the reaction mixture within the reaction chamber 12 may be about 0.1 to about 3 atm, about 0.5 to about 2 atm, or about 1 atm. A vacuum system 14 can be employed to assist in loading the reactants into the reaction chamber 12. The vacuum system 14 can be used to evacuate the reaction chamber 12 prior to introducing the reactants. In some embodiments, the reaction chamber is evacuated to an absolute pressure of less than 0.2 atm, less than 0.1 atm, or less than 0.05 atm. This evacuation creates a pure environment for the reaction and aids in drawing the reactants into the reaction chamber without the need to evacuate the reaction chamber upon reactant introduction.

[0027] Once the desired amount of carbon-containing material and oxidizer has been loaded into the reaction chamber 12, an ionized arc is struck between a pair of electrodes 72 within the ignition assembly 22 to initiate combustion of the carbon-containing material and oxidizer. Once initiated, the combustion reaction continues self-sustaining until the reactants within the reaction chamber 12 are exhausted. In a preferred embodiment, the combustion reaction is a detonation reaction. However, it is within the scope of the present invention for the combustion reaction to be a deflagration or firing reaction. As used herein, "detonation" is distinguished from the mere "deflagration" or "firing" of carbon-containing material. Detonation generally refers to a supersonic heat front accelerating through a medium, which ultimately drives a shock wave front that propagates directly ahead of the detonation. Deflagration is generally described as subsonic combustion propagating through heat transfer. A detonation reaction is also generally characterized by the production of high temperatures in the reactants and reaction products.

[0028] In one or more embodiments, the combustion reaction occurs at a temperature of at least 3000 K, at least 3500 K, or at least 4000 K. In certain embodiments, the combustion reaction occurs at a temperature of about 3000 K to about 5000 K, about 3500 K to about 4500 K, or about 4000 K. Combustion of the carbon-containing material and oxidizer at these temperatures favors the formation of highly ordered graphene particles, as opposed to graphite soot. If desired, the reaction mixture charged to the reaction vessel can include an inert gas such as helium, neon, argon, or nitrogen to assist in temperature control during combustion. Additionally, in some embodiments, particularly those in which the combustion reaction is a detonation, combustion of the reaction mixture proceeds extremely rapidly. In certain embodiments, combustion lasts for about 5 to about 100 milliseconds, about 10 to about 75 milliseconds, or about 20 to about 50 milliseconds.

[0029] In some embodiments, particulate material (e.g., graphene particles) produced in the combustion reaction is dispersed in aerosol form within the reaction chamber 12. Once formed, the particulate material may tend to aggregate, resulting in particles with an average particle size of about 35 to about 250 nm, about 50 to about 200 nm, or about 75 to about 150 nm. In some embodiments, if particle aggregation is allowed to continue under quiescent conditions, the particles will coalesce to form a gel. The conditions and requirements for particulate material to aggregate into a solid aerosol gel are described in U.S. Pat. No. 7,691,909, the entire contents of which are incorporated herein by reference. To form a gel, the particles typically must remain in the reaction chamber, substantially undisturbed, for a significant period of time. In one or more embodiments, it is desirable to remove the particles from the reaction vessel before they have sufficiently aggregated to form an aerosol gel. Thus, in some embodiments of the present invention, the particles are removed from the reaction vessel while they remain dispersed as an aerosol, avoiding gel formation.

[0030] Particulate material produced during the reaction is typically very fine and can easily form coatings on the surfaces of the device, particularly on the electrodes 72, potentially leading to fouling. However, in one or more embodiments, the electrode cassette 58 is configured to withstand the pressures generated within the device 10 during the combustion reaction and to prevent particulates from entering, thereby maintaining an electrically isolated system. As noted above, embedding the electrodes 72 in a non-porous material prevents particles from entering the cassette 58 and causing a short circuit. The electrodes 72 can also be configured to repel pressure-coated graphene.

[0031] As shown in Figure 1, a vacuum system 14 may be used to evacuate the aerosol from the reaction chamber 12 to a particle collector 20. In one or more embodiments, the particle collector 20 may be a conventional device for removing particulates from a gas stream. For example, the particle collector 20 may include any dust collection device, such as an inertial dust collector (e.g., a settling chamber, sedimentation chamber, or centrifugal collector such as a cyclone), a fibrous filter device such as a baghouse, a wet scrubber, or an electrostatic precipitator. The particulate material, particularly graphene particles, may then be removed from the particle collector as a powder.

[0032] It is within the scope of the present invention for particle collector 20 to be operatively connected to multiple reaction chambers 12 arranged in parallel. To ensure continuous production of particulate materials and continuous collection of those materials in particle collector 20, the reaction cycles within each reaction chamber 12 can be staggered.

[0033] While the aerosol is being evacuated from reaction chamber 12, a cleaning or flushing operation is performed to remove carbon deposits from the interior surfaces of ignition assembly 22, particularly from electrode tip 64. The flow of carbon-containing material from source 24 and oxidizer from source 26 into manifold 28 is stopped, and a flushing gas begins to flow from source 30. Alternatively, in embodiments where a separate flushing gas is not provided, the flow of carbon-containing material from source 24 is stopped, while the flow of oxidizer continues, now functioning as a flushing gas.

[0034] The flushing gas passes through manifold 28 to ignition assembly 22 and reaction chamber 12. As the flushing gas passes through the ignition assembly, it functions to remove carbonaceous particles, particularly graphene particles, that have adhered to the surface of electrode tip 64 due to the generation of graphene aerosol in reaction chamber 12 and passageway 56. The flushing gas resuspends the deposited particles and transports them through reaction chamber 12 to particle collector 20. In one embodiment, a vacuum is maintained within reaction chamber 12 by vacuum system 14 to draw the suspended graphene particles from ignition assembly 22 and into particle collector 20.

[0035] 7 , the fluid diverter cartridge 66 redirects the flow of flushing gas through the passageway 56 so that the flushing gas flows across the face of the electrode tip 64 opposite the positive direction of fluid flow through the ignition assembly 22. In this embodiment, if the diverter cartridge 66 were not present, the face of the electrode tip 64 facing the positive direction of fluid flow through the ignition assembly 22 would effectively protect the opposite face from dead spaces where graphene particles could accumulate and remain unaffected. However, the angled surface 116 of the venturi structure 114 directs the flushing gas across these potential dead spaces and across the face of the electrode tip 64 facing the ignition assembly outlet 52.

[0036] As also mentioned above, instead of or in conjunction with the diverter cartridge 66, the electrode cassette 58 may be configured to rotate so that the side of the electrode tip 64 facing the outlet 52 is periodically changed, thereby significantly reducing deposition of graphene particles on any portion of the surface of the electrode tip 64.

[0037] In some embodiments, an ionized arc may be struck between the pair of electrode tips 64 while the flushing gas is passing through the ignition assembly 22. Striking an arc or series of arcs in the presence of the flushing gas and resuspended carbonaceous material can vaporize the carbonaceous material and further ensure its transport away from the ignition assembly 22. Additionally, one or more sensors can monitor the occurrence of one or more ionized arcs during the electrode cleaning process. Detecting an arc during this process provides high confidence in the success of subsequent particle-generating reactions when the reaction chamber 12 is recharged with carbon-containing material and oxidizer.

[0038] After the cleaning operation in which the flushing gas is passed through the ignition assembly 22, the reaction chamber 12 is isolated from the vacuum system 14, and additional carbon-containing material and oxidizer are introduced into the reaction chamber 12. The reaction chamber is now filled with reactants and is ready for the ignition assembly 22 to begin combustion of the reactants to produce additional quantities of particulate material, particularly graphene particles. This process can be repeated multiple times. Note that in some embodiments, the cleaning operation described above need not be performed after every combustion reaction that occurs within the reaction chamber 12. In such embodiments, a predetermined number of combustion and aerosol extraction cycles may be performed before initiating a cleaning cycle with the flushing gas.

[0039] The following is an example of one mode of operation of the apparatus 10. At t=0, the pressure in the gas manifold 28 and reaction chamber 12 is 1 atm, and the particle collector 20 and vacuum ballast tank 18 are evacuated to a pressure of approximately 0.1 atm. Valves 38c and 38e are opened, and valve 38b is set to pull a vacuum on the reaction chamber 12. Due to the large vacuum reservoir of the vacuum ballast system, opening valve 38e rapidly evacuates the pressure in the gas manifold 28 and reaction chamber 12 to approximately 1 / 3 atm, which causes valve 38e to close. The reaction chamber 12 and gas manifold 28 continue to depressurize through valves 38b and 38c until they reach approximately 0.1 atm. At t=0.5-5 seconds, valve 38b switches to evacuating the ballast tank 18, and mass meters 34 and 36 begin to precisely deliver reactant materials to the reaction chamber 12 at the programmed rate and concentration. The delivery volume is calculated so that the reaction chamber returns to 1 atm and fills, typically within 15 to 50 seconds. Once all reactants have been delivered, valves 38a and 38c close, while valve 38d opens as a safety pressure relief. The control system can then wait a programmed delay, typically 1 second, before initiating the reaction with the ignition assembly 22. Once the control system detects a successful reaction, and after an optional programmed delay (typically 0 seconds, but sometimes 1 or 2 seconds), valve 38e opens, initiating the collection process by rapidly returning the reaction chamber to approximately 1 / 3 atm. Shortly thereafter, valve 38c opens, venting the reaction chamber 12 to 1 atm through the already-open valve 38d. This introduces a high-velocity airflow through the gas manifold 28 and into the reaction chamber 12. This airflow pushes the graphene aerosol from the reaction chamber 12 into the particle collector 20, where it is collected in a specially modified industrial bag filter. At the same time, the high velocity airflow impinges on and flows against the ignition system electrode 72 (and electrode tip 64), which, in combination with a special spark sequence, effectively cleans the electrode and prepares it for the next reaction.This programmable sampling / cleaning period typically lasts 5-20 seconds, after which ignition assembly 22 switches off, valve 38d closes, valve 38a opens, valve 38b switches vacuum pump 16 to manifold 28, and reaction chamber 12 is rapidly evacuated to about 1 / 3 atm with valve 38c open and valve 38d closed, and the cycle repeats. In certain embodiments, the time required to complete a cycle is less than 120 seconds, preferably about 20 to about 100 seconds, about 30 to about 90 seconds, or about 35 to about 75 seconds.

Claims

1. 1. An apparatus for producing a particulate material by combustion of reactants, comprising: a reaction chamber operably connected to a source of carbon-containing material and a source of oxidant; a vacuum source operably connected to the reaction chamber and operable to selectively evacuate at least a portion of the contents of the reaction chamber; an ignition assembly configured to initiate combustion of the quantity of the carbon-containing material and the quantity of the oxidizer delivered from each source to the reaction chamber; the ignition assembly includes a pair of electrodes operable to generate an ionized arc therebetween, each electrode housed in a respective cassette removably housed within the ignition assembly; The apparatus further includes one or more fluid diverters configured to direct or disrupt at least a portion of the fluid flowing within the ignition assembly across a face of the electrode that does not face a direction of fluid flow into the ignition assembly.

2. 10. The apparatus of claim 1, wherein the ignition assembly includes a housing having an inlet port configured to fluidly connect to the source of carbon-containing material and the source of oxidizer, the housing also having an outlet port configured to fluidly connect to the reaction chamber, the inlet port and the outlet port connected by a passageway through the housing.

3. The apparatus of claim 2 , wherein the one or more fluid diverters include one or more venturis having an angled surface projecting toward the passageway.

4. 10. The apparatus of claim 1, wherein the apparatus is operably coupled to a source of flushing gas and configured to direct the flushing gas through the ignition assembly to remove carbon and / or carbon-containing compounds deposited on the electrode by combustion of the carbon-containing material and the oxidizer.

5. 5. The apparatus of claim 4, wherein said source of said flushing gas is the same as said source of said oxidizer.

6. The apparatus of claim 4 , wherein the flushing gas comprises air.

7. The apparatus of claim 1 , wherein the oxidant comprises oxygen.

8. The apparatus of claim 1 , wherein the carbon-containing material comprises one or more hydrocarbon compounds.

9. The apparatus of claim 1 , wherein the electrode is selectively rotatable within the ignition assembly.

10. 10. The device of claim 1, wherein the electrode includes a non-porous material surrounding a conductor, the conductor including an electrode tip that protrudes through the non-porous material toward a passageway within the ignition assembly.

11. The device of claim 10 , wherein the non-porous material comprises glass or glazed ceramic.

12. The apparatus of claim 1 , wherein the vacuum source comprises a vacuum pump and a ballast tank.

13. an electrical ignition assembly operable to initiate a combustion reaction within the reaction chamber, a housing having an inlet port configured to fluidly connect to a source of gaseous reactant material and an outlet port configured to fluidly connect to the reaction chamber, the inlet port and the outlet port being connected by a passageway; a pair of electrodes each having an electrode tip extending toward the passageway, one electrode housed in a respective cassette removably housed within the housing; 1. An electrical ignition assembly, wherein the ignition assembly further includes one or more fluid diverters configured to direct at least a portion of fluid flowing within the ignition assembly across a face of the electrode that does not face a direction of fluid flow into the ignition assembly.

14. 14. The electrical ignition assembly of claim 13, wherein the one or more fluid diverters include one or more venturis having an angled surface projecting toward the passage.

15. 14. The electrical ignition assembly of claim 13, wherein the electrodes are selectively rotatable within the ignition assembly.

16. 14. The electrical ignition assembly of claim 13, wherein the electrode includes a non-porous material surrounding a conductor, the conductor including an electrode tip that protrudes through the non-porous material toward a passageway within the ignition assembly.

17. 17. The electrical ignition assembly of claim 16, wherein the non-porous material comprises glass or glazed ceramic.

18. 1. A method for producing graphene particles, comprising: introducing a mixture including a carbon-containing material and an oxidizer into a reaction chamber, the carbon-containing material and the oxidizer being introduced into the reaction chamber through an ignition assembly including a pair of electrodes; generating an ionized arc between the pair of electrodes in the ignition assembly to combust the carbon-containing material and the oxidizer and generate a temperature of at least 3000 K in the reaction chamber to generate an aerosol comprising graphene particles; evacuating the aerosol from the reaction chamber using a vacuum source operably connected to the reaction chamber; and recovering the graphene particles as graphene powder from the aerosol pumped out of the reaction chamber; further comprising passing a flushing gas through the ignition assembly while maintaining a vacuum in the reaction chamber; wherein passing a flushing gas through the ignition assembly includes causing at least a portion of the flushing gas flowing through the ignition assembly to flow across a surface of one or both of the electrodes opposite a direction of flow of the carbon-containing material and the oxidizer through the ignition assembly to remove graphene particles deposited on the surface.

19. 20. The method of claim 18, wherein the flushing gas is of the same composition as the oxidizer.

20. 20. The method of claim 18, further comprising the step of generating an ionized arc between the pair of electrodes within the ignition assembly while the flushing gas is passing through the ignition assembly.

21. 20. The method of claim 18, further comprising isolating the reaction chamber from the vacuum source and introducing additional carbon-containing material and oxidizer into the reaction chamber after passing the flushing gas through the ignition assembly.

22. 20. The method of claim 18, wherein the step of combusting the carbon-containing material and the oxidizer is a detonation reaction.

23. 20. The method of claim 18, wherein the step of combusting the carbon-containing material and the oxidizer is a deflagration reaction.

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