Stock material or miscellaneous articles – Self-sustaining carbon mass or layer with impregnant or...
Reexamination Certificate
2002-12-10
2004-09-07
Turner, Archene (Department: 1775)
Stock material or miscellaneous articles
Self-sustaining carbon mass or layer with impregnant or...
C428S364000, C428S367000, C428S402000, C423S44500R, C423S448000, C423S449100, C502S416000, C502S042000, C264S604000, C264S640000, C264S641000, C264S667000
Reexamination Certificate
active
06787235
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a new carbon based material, its manufacture and use. More particularly, the invention relates to a carbon based material produced from the consolidation of amorphous carbon under elevated temperature compression leaving a broad range of applications, such as for example, as electrode material and as structural material.
BACKGROUND OF THE INVENTION
Carbon is a solid element that exists in many forms. Solid carbon can have a tetrahedral crystalline array (diamond) or hexagonal graphine planes. If the graphine planes are arranged in planar formations, the resulting solid is known as graphite. If the graphine planes are more randomly arranged, the resulting form of carbon is known as amorphous carbon. Activated carbon, carbon black and charcoal are examples of amorphous carbon. With respect to crystallinity, graphite has short range and long range order, while amorphous carbon has only short range order in the graphine planes. This difference is manifested in their surface properties with amorphous carbon being more reactive than graphite. The difference is also manifested in the spectral patterns generated when the material is tested by x-ray diffraction—graphite spectra show ordered crystal patterns, while the amorphous material pattern has no discernible pattern.
One form of amorphous carbon, activated carbon, is manufactured from an organic source material. Typically, activated carbon is made through carbonization of organic materials, such as wood, coal, pitch, coconut shells, petroleum, animal bones, etc., followed by an activation process. During the activation process, some of the surface platelets are burned out leaving behind many pores with different shapes and sizes, hence activated carbon with an increased surface area and porosity is generated. In general, the pore size plays a role in determining the properties of the activated carbon for various applications. According to IUPAC definitions, pores can be characterized as macropores with pore diameters above 50 nm, mesopores with pore diameters between 2-50 nm, and micropores with pore diameters below 2 nm. In addition to its porosity, activated carbon is conductive and usually inert in many aqueous and organic systems.
Because of its porosity, activated carbon has been widely used in various industries as an adsorbent. The most commonly seen applications include deodorizing, decoloring of gas or liquid phase substances, and removing of toxic organics/inorganics from air and water. The mining industry uses activated carbon for the recovery of precious metals like gold from leaching solutions. Typically, activated carbon is packed into a column through which the gas or liquid to be treated is percolated continuously. The adsorption process takes place at the interface between the carbon phase and the fluid phase.
Its large specific surface area, porosity, conductivity and inert nature make it suited for use as an electrode in electrochemical applications such as energy storage devices and water deionization/desalination devices. The underlying principles of these electrochemical electrodes are rooted in the way that dissolved ions in water behave next to charged solids. Salt dissolves in water forming an electrolyte solution which has no net charge, that is, the net cationic charge will exactly equal the net anionic charge. When a charged solid (i.e., a particle, plate, etc.) is placed in such a solution, the ions of the electrolyte distribute in a manner that will minimize the charge density through a layer known as the electric double layer. Counter ions will be more concentrated within layers nearest the charged surface, but the concentration will gradually decay to equal ion charge in the bulk. A capacitor is formed between the charged surface and the net zero potential of the bulk. A typical value for this capacitance is on the order of 10 &mgr;F/cm
2
of surface area.
If two electrodes are placed in all electrolyte solution with an applied potential, the ions will partition so that the cations will migrate to the cathode to fill one double layer, and the anions will migrate to the anode and fill the other double layer. The separation of the cationic and anionic species in this manner is a means to store energy (ultracapacitors) or a means to desalinate water (capacitive deionization). Ultracapacitors have been studied as a potential storage mechanism in applications that require large energy storage devices capable of rapid energy discharge. The primary interest of these devices has been in electric automobiles and electronic devices. Capacitive deionization technology is recently being used in treating brackish water and seawater.
The basic operating principles of carbon electrodes are readily understood, but the manufacturing techniques for producing activated carbon electrode material have been limited. Three processes are currently used, identified by the types of materials they employ as feedstock: granular activated carbon, carbonization of polymers, and carbon aerogels.
Early in the 1950′s, researchers started to use granular activated carbon to make electrodes for electrochemical studies. Because carbon particles cannot consolidate under normal conditions, it is thought necessary to either apply high pressure or some kind of binder to keep the carbon particles in contact in order to form an electrode. It is difficult to make such an electrode that is maintained under constant high pressure, the system would be unacceptably bulky and dangerous. Thus, most studies have been carried out on carbon electrodes with an organic or polymeric binder mixed together with the carbon powders. The binders can be organic polymers, clays, or inorganic chemicals. Disadvantages exist with the use of binders to form the electrodes. Binders block a large portion of carbon surfaces, causing some pores to be blinded, and occlusion therefore is inevitable, thus lowering the available surface area of the carbon. Binders also deteriorate the conductivity of the electrodes because most binders are themselves nonconductive. The contamination from the binders also hinders their uses in electroanalytical applications.
Modern carbon electrodes are manufactured from phenolic resins or other types of resins by a process in which the resin is preformed to a certain shape then subjected to high temperatures for extended periods of time until complete carbonization occurs. The resulting carbon has relatively large surface area, but the manufacturing technique requires the use of toxic and environmentally dangerous chemicals. Often, organic solvents and aromatic compounds, such as benzene and toluene, are evolved during the manufacturing process. The volume of carbon formed is considerably smaller than the original resin size which leads to low product yield. This is a significant problem if specific geometric shapes or sizes are required. This manufacturing technique also has the disadvantages of high material cost and weak material strength due to the “shrinking” of the precursor carbon at high carbonization temperatures.
Some specific carbon electrodes are manufactured from aerogel compounds with sol-gel technology by similarly carbonizing organic compounds. Resorcinol-formaldehyde, for instance, can be infiltrated into a conductive substrate or formed into a solid. Solvents may be rinsed through the material prior to pyrolization in an inert atmosphere, such as in argon or nitrogen. The pyrolysis process produces a vitreous carbon material which has a high surface area and high electrical conductivity.
However, this manufacturing technique includes extremely high manufacturing costs and leads to the release of organic solvents such as acetone, formaldehyde and aromatic compounds as the substrate is thermally changed to carbon. These can pose serious health hazards to workers near the furnaces. The final shape of the carbon materials is much smaller than the feed material. Additional processing would be required to produce a specific geometric shape.
Thus, there exists a need for a
Nesbitt Carl C.
Sun Xiaowei
Boss Wendy
Michael & Best & Friedrich LLP
Reticle, Inc.
Turner Archene
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