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Title:
METHOD FOR PRODUCTION OF SPIRAL-SHAPED CARBON COATED WITH NANO-CRYSTALLINE STRUCTURED CARBON LAYER AND INFRARED EMITTER COMPRISING SPIRAL-SHAPED CARBON
Document Type and Number:
WIPO Patent Application WO/2006/009331
Kind Code:
A1
Abstract:
The present invention relates to a method for making a spiral-shaped carbon material as a heating element used for an infrared emitter. An initial carbon material formed of carbon fibers is wound onto a mandrel in the form of spiral. The carbon material is saturated with resin solution. The carbon material is heated by applying an electric current via the electric contacts in an inert or reducing atmosphere. After finishing this first heating process, the carbon material is cooled and taken off the quartz tube. The strengthened spiral carbon material is re-heated by applying the electric current in gaseous hydrocarbon atmosphere. As a result, a coat of nano-crystalline structure carbon is formed on a surface of the carbon material . The spiral-shaped carbon material with nano-crystalline structured carbon coating layer shows low thermal inertness and maximal radiating ability in comparison with other type of heating elements, including the elements made of usual carbon fiber as well.

Inventors:
ALEKSANDR TSOI (KR)
Application Number:
PCT/KR2004/001813
Publication Date:
January 26, 2006
Filing Date:
July 21, 2004
Export Citation:
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Assignee:
NCT CO LTD (KR)
ALEKSANDR TSOI (KR)
International Classes:
B29C71/00; (IPC1-7): B29C71/00
Domestic Patent References:
WO1994028693A11994-12-08
Foreign References:
US6464918B12002-10-15
KR100394981B12003-08-19
JPH1055877A1998-02-24
Attorney, Agent or Firm:
Rhee, We Beg (Guweol-1Don, Namdong-Gu Incheon 405-832, KR)
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Description:
Description

METHOD FOR PRODUCTION OF SPIRAL-SHAPED CARBON COATED WITH NANO-CRYSTALLINE STRUCTURED CARBON LAYER AND INFRARED EMITTER COMPRISING SPIRAL-SHAPED CARBON [1] Technical Field [2] The present invention concerns to the method for production of a carbon heating element used for an infrared emitter, more specifically a spiral-shaped carbon coated with a nano-crystalline structured carbon layer by precipitation from gaseous phase. Furthermore, the present invention concerns to an infrared emitter comprising the spiral-shaped carbon as an infrared electro-heating element. [3] Background Art [4] It is known the method from USA Patent JN° 6,464,918 from 15 Oct. 2002. In this Patent the method for making spiral-shaped heating elements of carbon fiber is described. Carbon fiber heating element is saturated with thermo-plastic polymeric material. The method includes the following stages: heating an initial material up to softening temperature of strengthening compound; winding of heated initial material onto mandrel so as to make a spiral; and keeping the spiral shape by removing of strengthening compound wherein removing of strengthening compound includes annealing spiral at the temperature and in the atmosphere which transforms strengthening material into volatile material. [5] This method allows to obtain spiral-shaped carbon heating element having better radiating ability and low inertia of heating velocity because of large carbon spiral radiating surface. In this case the maximum surface density of electric energy can mount to 195KW/m . However, in the case of the increasing surface density of electric energy the carbon material overheating and its destruction take place. At maximum surface density of electric energy, the luminescence temperature mounls to 1,200 0C through 1,300 0C . These characteristics are better in comparison with metal heating elements such as nickel-chromium, tungsten, and other alloys, but not the best. [6] Meanwhile, it is known that nano-crystalline materials on the base of carbon and other elements have unique physical, electrical, mechanical and electronic properties. High mechanical strength and thermo-resistance in combination with their electro- conductivity give a good possibility to use them for production of resistive heating elements such as light sources, electrodes for electrochemical processes and so on. The pores in the nano-crystalline material have nano-size that gives possibility to obtain special optical characteristics: mixing of absorption and omission stripes; appearance of additional stripes; possibility of pore -resonance because nano-meter size is less than light wave length. It gives possibility to make, for example, heating resistive electric element in which visible light quantum transforms into infra-red radiation. Thus, it gives possibility to make high-temperature heater which completely converts electric energy into heat. When the pores of nano-crystalline material are filled up with kations of corresponding elements, for example, rare-earth ones, An inverse effect is possible where the heat photon transforms into visible light quantum, i.e. it gives possibility to make very high-effective light sources. [7] There are many methods for obtaining nano-crystalline material (A.V.Elelskiy, Carbon nano-tubes. Physical science progress, V.167. #9, pp.945-972.1997): thermal dispersion in electric arc; laser dispersion; electrolytic synthesis; catalytic acetylene cracking and so on. All methods can be conditionally divided into catalytic and non- catalytic ones. Catalytic methods give possibility to obtain nano-carbon material at low temperature (under 1,200 0C ) in the presence of catalyst, but only in powder form. Non-catalytic methods need higher temperature, but in this case process productivity is very low and final product is obtained in the form of fragile coat (thin coating) on cooled support. [8] Method of resistive heating is described in Japan Patent (JN°2000272913 from 25.03.2002), where carbon granules are used as dispersed material; electric current is passed through the granules and the temperature mounts up to 3,400 0C . Carbon granules are in the medium of inert gas. Carbon vapor precipitates onto rotating water- cooled support and the coat of nano-crystalline material forms on the support's surface at temperature of 2,500 0C . However, this method doesn't let to obtain thickness- uniformed coat with low adhesion to support. [9] On the other side, there are methods to bring pyrolytic coat onto carbon fiber with gas-phase process, for example, pyrolysis of hydrocarbons (methane, propane, butane, acetylene and so on). As a rule, the process is carried out in running furnace where hy¬ drocarbon gas is heated and it decomposes on to carbon and other components; the temperature is not over 1,300 0C . Pyrolytic carbon structure is close to graphite structure and has higher density and electro-conductivity in comparison with carbon fiber. [10] The goods of composition material on the base of carbon fiber are made for using at high temperatures in oxidizing mediums. Besides, composition materials on the base of carbon fiber have high electro-conductivity and can be used for producing heater and illuminator. It is known the method to obtain composition material on the base of carbon fiber and silicon-carbide (Russian Patent RU 205 8964 Cl on 27.04.1996), where carbon semi product is made from two layeis: the main layer has carbon fiber with low reactive ability to silicon and the surface layer has carbon fiber with high- limited reactive ability. Semi product can be made by dint of selection from carbon fiber with different densities or by making half-finished product surface layer from carbon fiber with barrier coating from pyro-carbon and/or silicon-carbide. At such conditions normal crystalline structure with higher density forms, but nano-crystalline structure doesn't form; the process velocity is very low and can't be used in industrial production. [11] Furthermore, there is the method from Russian Patent JN°2149215 Cl from 20.05.2000, where the method for obtaining pyro-carbon layeis is described. According to the Russian Patent, obtaining carbon material is carried out by pre¬ cipitation of pyrolytic carbon layer from gas phase onto various material surfaces. Pre¬ cipitated pyrolytic carbon layer has high crystalline structure regulation degree. Pre cipitation process is carried out onto heated surface under atmosphere pressure and temperature range of 950 0C through 1,350 0C from steam-gas mixture of carbon tetra¬ chloride and hydrogen in 1 : (5 through 50) ratio. This invention lets increase life-time of graphite goods on the base of carbon composition material and decrease their cost price. When basing the pyrolytic carbon precipitation process parameteis, it is indicated that increasing carbon tetra-chloride : hydrogen ratio more than 1 : 5 leads to homogeneous reaction, and as a result soot (carbon-black) sediment precipitates within reactor and on the reactor's walls. Decreasing carbon tetra-chloride : hydrogen ratio less than 1 : 50 leads to lowering obtained pyrolytic-carbon crystallization degree and precipitation process efficiency. When the precipitation process is carried out at temperature below 950 0C , pyro-carbon formation doesn't take place and the sediment has soot structure. Heating of the support up to temperature above 1,350 0C is also un¬ desirable because of decreasing structure regulation degree of pyro-carbon sediment and its density, and as well precipitation velocity decreasing. [12] Maximum pyro-carbon density, achieved in this method, is 2.21g/cm , and maximum pyro-carbon precipitation velocity is 1,250 m m/h at volume expenditure of steam-gas mixture 0.5m /h or 8.3L/min. This method can be used for brining protective coating the composition material, but can't be used for making composition material and goods, because precipitation velocity is very low and doesn't ensure coating uniformity on sediment thickness. In this method the structure is very close to pure graphite structure, but not is nano-crystalline. [13] Disclosure of the Invention [14] Therefore, the present invention has been made in view of the above problems. The purpose of the present invention is to provide the method for obtaining a carbon on the base of carbon fibeis with pyrolytic coat of nano-crystalline structured carbon in the form of spiral. According to the present invention, precipitation process productivity is at least in ten times more in comparison with known methods. [15] The invented method allows the production of a spiral-shaped carbon material coated with a nano-crystalline structured carbon layer, said method comprising the steps of: (a) winding a carbon material formed of a plurality of carbon fibeis onto a mandrel in the form of a spiral; (b) fitting both ends of the carbon material with contacts for electrical connection; (c) saturating the carbon material with resin solution; (d) heating the carbon material wound onto the mandrel by means of applying an electric current on the carbon material via the contacts thereof in an inert or reducing atmosphere; (e) taking the carbon material off the mandrel; and (f) re¬ heating the carbon material by means of applying an electric current on the carbon material via the contacts thereof in a medium of gaseous hydrocarbon. [16] According to the preferred method of the present invention, heating of the carbon material is carried out by means of a resistive heating wherein an electric current is applied on the carbon material. Especially, during the step of (d) of the present method, the carbon material is heated up to a temperature when resin pyrolysis starts and during time that is necessary for fixing a form of spiral. In this heating process, the temperature should be not more than the melting point of the mandrel. When a quartz tube is used as the mandrel, the electric current is applied on the carbon material so that a surface density of electric energy is not less than 20W/cm and not more than 2 50W/cm in re-count to surface area of the carbon material. [17] As far as the step of (f) is concerned, the carbon material is re-heated in a temperature range of 1,400 0C through 2,500 0C on a surface of the carbon material for the purpose of the stable formation of a nano-crystalline structured carbon coating, and the work efficiency. Accordingly, in the step of (f), the electric current is applied so that a surface density of electric energy is not less than 50W/cm and not more than 200W/cm in re-count to surface area of the carbon material. Furthermore, in the step of (f), the carbon material is heated in a furnace through which the gaseous hy- drocarbon is blown at gas expenditure of 0.015L/min- cm through 0.15L/min- cm . [18] Furthermore, the other purpose of the present invention is to provide the infrared emitter comprising the spiral-shaped carbon material coated with a nano-crystalline structured carbon layer as a heating element. The infrared emitter according to the present invention distinguishes its low heat inertia, and provides maximum limited radiating ability at any temperatures. [19] Brief Description of the Drawings [20] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: [21] Fig. 1 shows the X-ray diffraction diagram for the carbon material produced by the method according to the present invention; [22] Fig. 2 shows the X-ray diffraction diagram for initial carbon fibers; and [23] Fig. 3 shows the electronic-microscope picture of the surface of the carbon material coated with a nano-crystalline structured carbon layer. [24] Best Mode for Carrying Out the Invention [25] Now, preferred embodiment of a method for production of a spiral-shaped carbon material according to the present invention will be described in detail. [26] Fiist, as an initial material, it is prepared carbon fibeis of 4 parallel viscose threads with lOOtex linear density. Next, the carbon fibeis are wound onto a mandrel by a winding device. The mandrel is made of a quartz tube, and has a form of bar with 5mm diameter. The carbon fibeis are wound in the form of a spiral- shaped ribbon with step of 2 per lcm and length of 30cm. The material formed of the carbon fibeis has straight ends of twisted threads. The ends are fitted with contacts for electrical connection. The contacts are made of aluminum or copper sticking foil. [27] After preparing the carbon material for winding onto the mandrel in the form of spiral, the carbon material is saturated with polymer phenol -formaldehyde resin solution together with the mandrel . Although any resin solution is available, phenol- formaldehyde resin is preferable because it contains much carbon. After drying the carbon material, the electric contacts of the carbon material are fixed into a special carrier with electric terminals . [28] Next, the special carrier is placed into a reactor. The reactor is preferably is provided with a quartz tube having a large inside diameter. The special carrier where the carbon ribbon is fixed into is placed inside of the reactor. And then, an electric current such as an alternating or direct current is applied on the carbon material via the electric contacts thereof. Furthermore, applying the electric current is performed in an inert or reducing atmosphere. Preferably, any gaseous hydrocarbon containing carbon and hydrogen, such as methane and acetylene, is blown through the inside of the reactor during applying the electric current on the carbon material. In this case, for safety, the gas is burnt on the outlet of the reactor. [29] While applying the electric current on the carbon material in this manner, the carbon material warms up and a pyrolysis reaction of the phenol-formaldehyde resin takes place on a surface of the carbon material. As a result of the pyrolysis reaction, the carbon coating is formed on the surface of the carbon material. Preferably, heating of the carbon material is performed up to temperature when the phenol-formaldehyde resin pyrolysis reaction starls and is kept during time that is necessary for fixing the form of spiral by pyrolytic carbon. [30] In this heating process (hereinafter, referred to 'first heating process'), when the electric current is applied on the carbon material, the surface density of electric energy must be not less than 20W/cm on the surface of the carbon material. The area of the carbon material can be calculated from the thread length and the thread width on the mandrel. In case the thread length is 126cm and the thread width is 3mm, the area is to be 38cm . Initial resistance is 158 ohm. At 380 voltages, the surface density of electric 2 energy is 24W/cm and the initial power is 920W. After phenol-formaldehyde de¬ composition, the conductivity increases and current grows correspondingly from 2.5A to 3.0A. Further, because of methane pyrolysis, the current increases gradually up to 5.0A that corresponds to 50W/cm in re-count on the surface density of electric energy. [31] In this fiist heating process, the surface density of electric energy must be not less 2 2 than 20W/cm and not more than 50W/cm . If the surface density of electric energy is less than 20W/cm , the pyrolytic carbon is not enough for keeping the spiral form. Moreover, because carbon fibeis of the initial material contain the amorphous graphite-like componenls as well as the graphite-crystalline components, it is necessary to transform the amorphous componenls into the graphite-crystalline componenls. Accordingly, the carbon material should be heated up to at least the temperature necessary for crystallization of the amorphous componenls. However, when the surface density of electric energy is less than 20W/cm , the temperature on the surface of the carbon material would not go up to the temperature necessary for crystallization of the amorphous componenls. Furthermore, if the surface density of electric energy is more than 50W/cm , the mandrel made of quartz tube starls to melt (i.e. in this case the temperature exceeds 1,300 0C that is a soften temperature for quartz glass). [32] By means of the fiist heating process, it is formed into the strengthened spiral of the carbon material. After cooling the reactor with the strengthened spiral of the carbon material, the carbon material is taken out from pyrolysis zone and taken off the mandrel. And t hen , the spiral -shaped carbon material is fixed into another special carrier with the electric terminals and placed again into the reactor. [33] The spiral-shaped carbon material without the mandrel is heated by means of applying the electric current on the carbon material via the contacts thereof and the carrier. Further, any gaseous hydrocarbon such as methane is passed through the reactor. Hereinafter, this heating process is referred to second heating process. This second heating process is performed at 380 voltages and fiist current of 4.8 A (that 2 corresponds to 48W/cm of the surface density of electric energy) up to 6.5 A (that 2 corresponds to 65W/cm of the surface density of electric energy). In this period, the temperature is above 2,200 0C . During the second heating process, the pyrolysis reaction takes place again . [34] The specific expenditure of the gaseous hydrocarbon plays a large role in the pyrolysis process. When gas expenditure is less than 0.015 L/min-cm (gas amount per minute and unit area of the surface of the carbon material), the pyrolysis process proceeds irregularly along the length of the spiral- shaped carbon material and a carbon coating is not identical on thickness. On the other hand, when gas expenditure is more than 0.15 L/min-cm , one of ends of the carbon material cools thus forming non- identical nano-crystalline carbon coat on the spiral-shaped carbon material. [35] During the second heating process, the given surface density of electric energy 2 2 must be not less than 50W/cm and not more than 200W/cm . When the energy density is less than 50W/cm , the precipitation velocity is very low. Moreover, in order to form a nano-crystalline structured carbon, the temperature on the surface of the carbon sh ould be not less than 1,400 0C that approximately corresponds to the surface density of 2 electric energy of 50W/cm . On the other hand, when the energy density is more than 200W/cm , the pyrolysis hydrocarbon decomposition it takes place not only on the carbon material but also within the furnace made of quartz tube around the carbon ribbon. When the pyrolysis hydrocarbon decomposition takes place far from the carbon material, the amount of hydrocarbon around the carbon material may be decreased. As a result, the efficiency of forming a nano-crystalline structured carbon coat may be deteriorated. [36] Substantiation of selected parameteis for the second heating process is shown in Table 1. Herein, 'density' means the density of the nano-crystalline structured carbon coat formed by the method according to the present invention. [37] Table 1 [38]

[39] By means of the second heating process, the nano-crystalline structured carbon coating layer is formed on the surface of the carbon material. To prove the formation of the nano-crystalline structured carbon coating layer, we adduce the next data: radio¬ graphic diagram for the carbon material produced by the method according to the present invention as shown in Fig. 1; radio-graphic diagram for initial carbon fiber as shown in Fig. 2 ; and electronic-microscope picture of the surface of the carbon material coated with a nano-crystalline structured carbon layer as shown in Fig. 3. [40] As known, graphite crystals are endless nels of hexagonal rings. The atoms in the nels are connected with each otheis by covalent bonds; the shortest distance between atoms is 1.42 A ; the number of nearest neighbors in the net is three ( 3 ) . The nels dispose themselves flaky one under other and the distance between layers is 3.35 A . Thus, the most characteristic inter-layer distance for graphite is d=3.35 A or 0.345nm. Characteristic inter-layer distance for nano-crystalline structure d (002) =0.340 through 0.350nm. Diamond structure can be presented as two HCC(hexahedron center cubic) lattices with displacement on 1/4 of body diagonal. The most strong reflection from layer family (111) is at d=0.357nm. Thus, nano- structure as is in the middle between diamond and graphite. [41] Fig. 1 and 2 show two radio-graphic diagrams in comparison. As seen from diagrams shown in Fig. 1 , the initial carbon fiber has exceptionally graphite structure with low crystallization degree and inter-plane distance for 002 plane is 0.335nm; whereas for the carbon material obtained with the method according to the present invention , as shown in Fig. 2, inter-plane distance for 002 plane is 0.348 through 0.350nm. It proves the aforesaid. [42] Fig. 3 shows an electronic-microscope picture of the surface of the carbon material obtained from the method according to the present invention . As seen from Fig. 3 , formed carbon coat has roll structure, i.e. rolled many-layeis coat around carbon filament . Coat's surface is scaly structure of irregular polygons. After oxidation such polygons have turned up borders. Polygons' size is within some nano-meteis. [43] Electro-conductivity calculations showed that nano-crystalline coat conductivity was in 5 through 7 times higher than for carbon fiber in re-calculation for identical density. [44] The present method gives possibility to make spiral heating elements with a coat of nano-crystalline structured carbon. Thanks to such nano- crystalline structure , the thermo-radiating characteristics of heating element grow up to maxim um possibly. For proof , Table 2 where the test resulls for various electric heateis placed into water is shown. [45] For comparison , we used the following heateis: metal nickel-chromium heater is soldered into U-quartz tube under vacuum; halogen heater; standard carbon heater; and carbon heater with nano-crystalline structure. Size, shape and electric capacity for all radiators are the same. Electric capacity is 1 , 00OW, water volume is 31iter, first water temperature is 17 0C and the finish temperature is 70 0C . Theoretical calculation shows that in the ideal case for 100% transformation of electric energy into heat it is necessary to spend 1.24W for heating 1 liter of water per 1 degree. [46] Table 2 [47]

[48] Thus, nano-crystalline carbon heater has maximal caloric ability in comparison with another kind of electric heateis. It is important to note that during work the nano- crystalline carbon heater absolutely doesn't radiate luminescence, while the otheis do. [49] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, these skilled in the art will appreciate that various modi¬ fications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.