Abstract:
Process and apparatus for functionalizing and/or separating graphene particles and other nanomaterials in which graphene and other nanoparticles are placed in a pile on one of two opposing conductive surfaces that are charged with a high D.C. voltage so that material of a certain character is attracted to the other conducting surface. This process takes place in an enclosed chamber that has been flooded with a designated gas at ambient pressure, with the material attracted to the second conducting surface passing through the designated gas. The high energy field creates a condition such that the material remaining on the first conductive surface takes on atoms of the designated gas and material the going to the second surface is further exposed to and characterized by the designated gas.

Description:
RELATED APPLICATIONS 
       [0001]    Provisional Application No. 61/788,999, filed Mar. 15, 2013, the priority of which is claimed. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of Invention 
         [0003]    This invention pertains generally to the manufacture of nanomaterials and, more particularly, to a process and apparatus for functionalizing and/or separating graphene particles and other nanomaterials. 
         [0004]    2. Related Art 
         [0005]    Functionalization by surface modification is an important step in imparting characteristics to graphene and other nanomaterials that enable, improve, and/or optimize the material for specific applications. 
         [0006]    Techniques heretofore employed in the functionalization of graphene and other carbon and non-carbon nanomaterials are typically carried out in a vacuum. The use of vacuum pumps and pressures inn processing nanoparticles having small facial dimensions, typically less than 100 nm, creates problems because of the difficulty of containing the particles. 
         [0007]    Another problem is that particles of this small size cannot be processed in the presence of air turbulence, which is present even in partial vacuums, because sub-100 nm scale particles will disperse like smoke in a gaseous environment and are very difficult to collect. 
       OBJECTS AND SUMMARY OF THE INVENTION 
       [0008]    It is, in general, an object of the invention to provide a new and improved process and apparatus for functionalizing graphene and other nanoparticles and/or separating such particles according to size. 
         [0009]    Another object of the invention is to provide a process and apparatus of the above character which do not require the use of a vacuum. 
         [0010]    These and other objects are achieved in accordance with the invention by providing a process and apparatus in which graphene and other nanoparticles are placed in a pile on one of two opposing conductive surfaces that are charged with a high D.C. voltage so that material of a certain character is attracted to the other conducting surface. This process takes place in an enclosed chamber that has been flooded with a designated gas at ambient pressure, with the material attracted to the second conducting surface passing through the designated gas. The high energy field creates a condition such that the material remaining on the first conductive surface takes on atoms of the designated gas and the material going to the second surface is further exposed to and characterized by the designated gas. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a block diagram of one embodiment of a system for functionalizing and separating graphene and other nanoparticles in accordance with the invention. 
           [0012]      FIG. 2  is an isometric view of the electrode plates in the embodiment of  FIG. 1 . 
           [0013]      FIG. 3  is a block diagram of another embodiment of a system for functionalizing and separating graphene and other nanoparticles in accordance with the invention. 
           [0014]      FIG. 4  is an isometric view of the electrode plates and screen in the embodiment of  FIG. 3 . 
           [0015]      FIG. 5  is an isometric view of a pair of inwardly convex electrode plates for use in the embodiment of  FIG. 1 . 
           [0016]      FIG. 6  is an isometric view of a pair of inwardly concave electrode plates with a screen between them for use in the embodiment of  FIG. 2 . 
           [0017]      FIG. 7  is an isometric view of a pair of inwardly concave electrode plates for use in the embodiment of  FIG. 1 . 
           [0018]      FIG. 8  is an isometric view of a pair of inwardly convex electrode plates with a screen between them for use in the embodiment of  FIG. 2 . 
           [0019]      FIG. 9  is an isometric view of a pair of rotating electrode plates for use in the embodiment of  FIG. 1 . 
           [0020]      FIG. 10  is an elevational view of the rotating electrode plates of  FIG. 9 . 
           [0021]      FIG. 11  is an isometric view of a pair of rotating electrode plates with a screen between them for use in the embodiment of  FIG. 2 . 
           [0022]      FIG. 12  is an elevational view of the rotating electrode plates and screen of  FIG. 11 . 
           [0023]      FIG. 13  is an isometric view of another pair of electrode plates for use in the embodiment of  FIG. 1 . 
           [0024]      FIG. 14  is an isometric view of another pair of electrode plates with a screen between them for use in the embodiment of  FIG. 2 . 
           [0025]      FIG. 15  is an isomeric view of another set of electrodes for use in the embodiment of  FIG. 1 . 
           [0026]      FIG. 16  is an isomeric view of another set of electrodes for use in the embodiment of  FIG. 2 . 
           [0027]      FIG. 17  is an isomeric view of another set of electrodes for use in the embodiment of  FIG. 1 . 
           [0028]      FIG. 18  is an isomeric view of another set of electrodes for use in the embodiment of  FIG. 2 . 
           [0029]      FIG. 19  is an isomeric view of another set of electrodes for use in the embodiment of  FIG. 1 . 
           [0030]      FIG. 20  is an isomeric view of another set of electrodes for use in the embodiment of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    As illustrated in  FIGS. 1 and 2 , the apparatus includes a pair of electrically conductive plates or electrodes  31 ,  32  spaced vertically apart within a housing  33 . A D.C. charging voltage is applied to the plates from a high voltage power supply  34 . In this particular embodiment, the positive terminal of the power supply is connected to the upper plate, and the negative terminal is connected to the lower plate via the system ground. However, the polarity is not critical and can be reversed, if desired, with the positive terminal being connected to the lower plate and the negative terminal connected to the upper plate. A capacitor  36  is connected between the plates. 
         [0032]    In one exemplary embodiment, the electrodes are 12 inch square flat copper plates which are ¼ inch thick and spaced 2 inches apart. In this example, the power supply is a variable supply that can apply up to 20 KV to the plates, and capacitor  36  has a capacitance of 0.1 μF and a voltage rating of 20 KV. 
         [0033]    The particles to be functionalized and/or separated are placed in a pile  37  on the upper surface of lower electrode plate  12 . The housing is closed, and the chamber within the housing is flooded with a suitable gas at ambient pressure. When the D.C. voltage is applied to the plates, some of the graphene particles are attracted and adhere to the lower surface of upper plate  11 , as indicated at  38 . The particles in the pile and the particles attracted to the upper plate take on atoms of elements in the gas, thereby imparting functional characteristics to the material. 
         [0034]    A particularly preferred process for producing graphene particles for functional ization and/or separation by the invention is described in detail in U.S. Pat. No. 8,420,042, the disclosure of which is incorporated herein by reference. In that process, magnesium and carbon dioxide are combusted together in a highly exothermic reaction to produce carbon and magnesium oxide (MgO) products which are then separated and purified to produce graphenes of very high purity and quality. The purified graphene particles are ground and screened to provide particles of a desired size ranging from about 120 mesh to about 400 mesh. 
         [0035]    The gas introduced into the chamber is selected in accordance with the characteristics to be imparted to the particles. If the particles are to be functionalized, a functionalizing gas is used, and if the particles are being separated without functionalization, a gas such as carbon dioxide (CO2) or nitrogen (N2) is utilized to prevent combustion of the graphene particles. Suitable gases for functionalizing the graphene include oxygen, nitrogen, water vapor, hydrogen peroxide, carbon dioxide, ammonia, ozone, carbon monoxide, silane, dimethysilane, trimethylsilane, tetraetoxysilane, hexamethyldisioxane, chloro-silanes, fluoro-silanes, ethylene diamine, maleic anhydride, arylamine, acetylene, methane, ethane , propane, butane, ethylene oxide, hydrogen, air, sulfur dioxide, hydrogen, sulfonyl precursors, argon, helium, alcohols, methanol, ethanol, propanol, carbon tetrafluoride, carbon tetrachloride, carbon tetrabromide, chlorine, fluorine, and bromine. 
         [0036]    With or without functionalizing gasses, the invention acts as a particle sorting tool by preferentially transferring smaller particles of graphene and other nanomaterials to the upper electrode plate and thereby separated from the general mass of graphene powder on the lower plate. These transferred particles have been found to be surprisingly small, with cross sectional dimensions less than one tenth those of the particles in the general mass. The high energy to which the particles are exposed may impart or alter the characteristics of the transferred particles. Thus, for example, when 320 mesh graphene particles with a cross sectional dimension on the order of 10 microns are processed in the high voltage system, the particles collected from the upper plate have a cross sectional dimension on the order of 1 micron. 
         [0037]    Also somewhat surprisingly, it has been observed that when additional material is piled on top of material that has already been processed, the yield increases from about 4 percent to about 50 percent. 
         [0038]    Raman spectroscopic analysis has shown that samples prepared from similar graphene materials that were functionalized in a nitrous oxide (N2O) atmosphere by the high voltage process of the invention and in an N2O atmosphere in a conventional vacuum plasma reactor have similar Raman spectra, indicating that both samples were the same type of sp2 bonded carbon. Thus, the invention has made it possible to functionalize graphene materials without expensive plasma equipment that operates in a vacuum. The Raman analysis also suggests that it may be possible to control the degree of functionalization by controlling the time the material is in the functionalizing gas. 
         [0039]    The embodiment illustrated in  FIGS. 3 and 4  is similar to the embodiment of  FIGS. 1 and 2 , with the addition of a conductive metal screen  39  between the electrode plates. In this embodiment, the positive side of the high voltage supply is connected to the two plates, and the negative side is connected to the screen. The capacitor is connected between the two plates and the screen. 
         [0040]    Operation and use of the embodiment of  FIGS. 3 and 4  is similar to that of  FIGS. 1 and 2 . The particles or powder to be functionalized and/or separated are placed in a pile on the upper surface of the lower plate, the housing is closed, the chamber is flooded with gas at ambient pressure. When the D.C. voltage is applied to the plates and the screen, the smaller particles are attracted to the lower surface of the upper plate, taking on the atoms in the gas that impart functional characteristics to the material. 
         [0041]    Instead of being flat or planar, the electrode plates can have other contours such as the inwardly convex plates  41 ,  42  shown in  FIGS. 5 and 6  and the inwardly concave plates  43 ,  44  shown in  FIGS. 7 and 8 . Power is applied to these plates in the same manner it is applied to plates  31 ,  32  in the embodiment of  FIG. 1 . The curvature of the plates allows focusing, affects the rate of collection, and reduces arcing to allow operation at higher current levels. Flat, electrically conductive metal screens  46 ,  47  are disposed midway between the plates in the embodiments of  FIGS. 6 and 8 , and power is applied to the plates and screens in the same manner that it is applied to the plates and screen in the embodiment of  FIG. 3 . 
         [0042]      FIGS. 9-12  illustrate embodiments in which the electrode plates are electrically conductive circular plates or disks  48 ,  49  which are spaced apart vertically and offset laterally for rotation about vertically extending axes  51 ,  52 , with portions of the disks overlapping between the axes. The embodiment of  FIGS. 11-12  also has a flat, electrically conductive screen  53  between the disks in the area where the disks overlap. 
         [0043]    The plates and screen in these embodiments are energized in the same manner as the plates and screens in the previous embodiments, with the power being applied to the two plates in the embodiment of  FIGS. 9-10  and between the plates and the screen in the embodiment of  FIGS. 11-12 . 
         [0044]    Operation and use of the embodiments of  FIGS. 9-12  is similar to that of the previous embodiments. The particles or powder to be functionalized and/or separated are placed in a pile on the upper surface of the lower disk, the housing is closed, and the chamber is flooded with gas at ambient pressure. When the D.C. voltage is applied to the disks or to the disks and screen, the smaller particles are attracted to the lower surface of the upper disk, taking on the atoms in the gas that impart functional characteristics to the material. 
         [0045]    Collecting the functionalized and/or separated particles on a rotating disk provides faster rates of collection than collecting them on a stationary plate, and having both disks rotate facilitates the loading of material onto the lower disk prior to exposure to the electrically charged environment and allows the process to operate in a continuous mode. If desired, one of the disks can remain stationary, although that may make it more difficult to carry out the process on a continuous basis. 
         [0046]    The embodiments shown in  FIGS. 13 and 14  are similar to the embodiments of  FIGS. 1-4  in that they have square, flat copper plate electrodes  56 ,  57  which are spaced apart vertically, with a flat, electrically conductive screen  59  between the plates in the embodiment of  FIG. 14 . Upper plate  56  is smaller in lateral dimension than lower plate  57  and is positioned above the central area of the lower plate. Power is applied to these plates and to screen  59  in the same manner that it is applied to the plates and screen in the embodiments of  FIGS. 1-4 , and the particles to be functionalized and/or separated are placed in the central area of the lower plate and processed in the same manner as in those embodiments. 
         [0047]    In the embodiments of  FIGS. 15 and 16 , the electrodes consist of an electrically conductive, cylindrical drum  61  mounted for rotation about a horizontally extending axis  62  above a flat, electrically conductive plate  63 , with a flat, electrically conductive screen  64  between the drum and the plate in the embodiment of  FIG. 16 . In the embodiment of  FIG. 15 , the high D.C. charging voltage is applied between the drum and plate with either polarity, and in the embodiment of  FIG. 16 , the positive side of the D.C. voltage is applied to the drum and plate, and the negative side is applied to the screen. 
         [0048]    Particles to be functionalized and/or separated are placed in a pile on the plate beneath the drum, and the functionalized and/or separated particles are collected on the surface of the rotating drum at a faster rate than would be on a stationary plate. 
         [0049]      FIGS. 17-20  illustrate embodiments having an upper electrode plate  66  mounted on rollers  67  for movement back and forth above a stationary lower plate  68 . The rollers have grooved surfaces  67   a,  and the upper plate has guides  66   a  along its outer edges which are received in the grooves. A scraper  69  and a collection trough  71  are mounted in a stationary position near one end of the lower plate for removing and collecting particles from the lower surface of the upper plate. In the embodiment of  FIGS. 17-18 , the positive charge is applied to the upper plate, and the negative charge is applied to the lower plate. In the embodiment of  FIGS. 19-20 , a flat, electrically conductive screen  73  is disposed midway between the plates, the positive charge is applied to the two plates, and the negative charge is applied to the screen. 
         [0050]    Particles to be functionalized and/or separated are placed in a pile on the upper surface of the lower plate, and the functionalized and/or separated particles attach to the lower surface of the upper plate. As the upper plate passes over the trough, the scraper engages the lower surface of that plate and scrapes the particles on it into the trough where they are collected. Here again, the moving plate is able to collect the processed particles at a faster rate than a stationary plate. 
         [0051]    The invention has a number of important features and advantages. It provides a process and apparatus for functionalizing and/or separating graphene particles and other nanoparticles in an ambient plasma environment without the use of vacuum or other expensive plasma equipment. 
         [0052]    It is apparent from the foregoing that a new and improved process and apparatus for functionalizing and/or separating graphene particles and other nanoparticles have been provided. While only certain presently preferred embodiments have been described in detail, as will be apparent to those familiar with the art, certain changes and modifications can be made without departing from the scope of the invention, as defined by the following claims.