JP5322055B2 - Porous heating device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a porous heating device using silicon carbide ceramics and a method for manufacturing the same. The porous heat generating device of the present invention can be used for a fluid heating device, a filter device, an exhaust gas purifying catalyst, and the like by utilizing the characteristic feature of the porous heat generating device.

  Silicon carbide ceramics (SiC) have small changes in bending strength and elastic modulus even at temperatures up to 1400 ° C, have excellent oxidation resistance and corrosion resistance, and have extremely low reactivity with metals. Therefore, the heater composed of the silicon carbide sintered body is not limited in usable atmosphere, and is excellent in rapid temperature rise / fall characteristics. Therefore, it is used as a heater for various heat treatments of semiconductor wafers.

  For joining the heater and the metal electrode, a screwing structure using an aluminum strap and a clamp (spring) is generally used as described in, for example, Japanese Patent Application Laid-Open No. 2003-308951. However, the screwing structure has a problem that loosening occurs because the thermal expansion difference between the silicon carbide sintered body and the metal member is large.

  Therefore, JP 2008-117556 A describes an electrode structure in which a pair of silicon carbide electrodes are fixed to a heating element made of a silicon carbide sintered body, and the tips of the electrodes are sandwiched between a pair of metal plate electrodes. Has been. However, this electrode structure is inefficient because it generates heat up to a pair of silicon carbide electrodes. There is also a problem that the number of parts is large and the number of mounting steps is large.

  On the other hand, Japanese Patent No. 3699992, Japanese Patent No. 4273195, and Japanese Patent No. 4110244 disclose a method for producing a silicon carbide porous structure material from a sponge-like organic porous structure. In this manufacturing method, for example, corrugated paper or urethane sponge is impregnated with a slurry containing a phenol resin and silicon powder, and fired in an inert atmosphere, whereby a carbonized silicon carbide is obtained by reactive sintering through a carbonaceous porous structure. A raw porous structural material is manufactured.

  The silicon carbide porous structural material obtained by the above production method has innumerable open cells from which the film is removed, and is excellent in gas diffusibility. Therefore, it has been recalled that this silicon carbide porous structure material is used as a heating element. However, this silicon carbide based porous structural material has a problem that the contact area with the electrode is small and the contact resistance is large because innumerable pores are opened on the surface. Therefore, a device for fixing the electrode while maintaining high conductivity is required.

  For example, as a method of forming a metal electrode, a method of forming a metal layer on the surface of a silicon carbide based porous structure material using metal spraying, electroless plating, etc., and fixing the metal electrode terminal through the metal layer is considered. It is done. However, metal and silicon carbide cannot be said to have sufficient adhesion, and may peel off due to vibration during use and differences in thermal expansion. Therefore, it is conceivable to reinforce by covering with a covering such as a heat-resistant felt, but the number of manufacturing steps increases and the number of parts increases.

JP 2003-308951 A JP 2008-117556 A Patent No. 3699992 Patent No. 4273195 Patent No. 4110244

  The present invention has been made in view of the above circumstances, and can be mounted on automobiles and the like by using a silicon carbide porous structure as a heating element and firmly fixing a highly conductive electrode to the heating element. It aims at making it a typical porous heat generating apparatus.

  A feature of the porous heat generating device of the present invention that solves the above-described problem is that a porous structure made of silicon carbide-based ceramics and a pair of electrode bodies fixed to the porous structure are interposed via the electrode body. A porous heating device that generates heat when energized. The electrode body is made of a carbon-based material, and is fixed integrally with the porous structure via a silicon carbide layer formed at the interface between the electrode body and the porous structure. There is in being.

  Further, the feature of the method for producing the porous heating device of the present invention is an impregnation step of impregnating an organic porous structure with a slurry containing a resin as a carbon source and a silicon powder or a slurry containing a silicon carbide powder in a slurry. A removal step of removing excess slurry from the organic porous structure to form a skeleton of the organic porous structure and a precursor having the slurry attached to the surface thereof, and a carbon material to a predetermined portion of the organic porous structure A temporary fixing step of temporarily fixing the electrode body, and a carbonaceous porous structure by heating the precursor in a vacuum or in a non-oxidizing atmosphere to carbonize the resin and thermally decomposing the organic porous structure; A carbonization step, and heating the carbonaceous porous structure in a vacuum or non-oxidizing atmosphere to react silicon and carbon to form a silicon carbide porous structure from the carbonaceous porous structure. Formation It lies in performing a firing step of binding together, the a and Rutotomoni electrode body and the silicon carbide porous structure.

  In the production method of the present invention, it is desirable to perform a melt impregnation step in which a silicon carbide porous structure is impregnated with molten silicon to form a metal silicon layer in a vacuum or in a non-oxidizing atmosphere after the firing step.

  According to the porous heat generating device of the present invention, since the electrode body made of the carbon-based material is used, the heat resistance is excellent, the conductivity of the electrode body itself is high, and feeding loss can be prevented. The electrode body is firmly fixed integrally with the porous structure via a silicon carbide layer formed at the interface between the electrode body and the porous structure. Therefore, there is no problem that the electrode body peels off or falls off from the porous structure during use.

  And according to the manufacturing method of the porous heating device of the present invention, the electrode body can be firmly fixed to the porous structure only by performing the firing step, so that the manufacturing man-hour can be greatly reduced, and Variations in the adhesion strength of the electrode body can also be suppressed.

It is a perspective view of the porous heat generating apparatus which concerns on one Example of this invention. It is a principal part expanded sectional view of the porous heat generating apparatus which concerns on one Example of this invention. It is a perspective view of the porous heat generating apparatus which concerns on the 2nd Example of this invention. It is a principal part expanded sectional view of the porous heat generating apparatus which concerns on the 2nd Example of this invention. It is a principal part expanded sectional view of the porous heat generating apparatus which concerns on the other aspect of the 2nd Example of this invention. It is a perspective view of the porous heat generating apparatus which concerns on the 3rd Example of this invention. It is a principal part expanded sectional view of the porous heat generating apparatus which concerns on the 3rd Example of this invention. It is a perspective view of the porous heat generating apparatus which concerns on the 4th, 5th Example of this invention. It is a principal part expanded sectional view of the porous heat generating apparatus which concerns on the 4th, 5th Example of this invention. It is a perspective view of the porous heat generating apparatus which concerns on the 6th Example of this invention.

  The porous heat generating device of the present invention includes a porous structure and an electrode body, and generates heat when energized through the electrode body. The porous structure is made of silicon carbide-based ceramics, and may be made of silicon carbide only. If silicon carbide is the main component, carbon, silicon, or as an aggregate or antioxidant Silicon nitride, zirconia, zircon, alumina, silica, mullite, molybdenum disilicide, boron carbide, boron powder, Mg, Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Metals such as W may be included. Moreover, if a silicon layer is provided on the surface of the porous skeleton, the strength is improved. Further, if the silicon layer is oxidized, the hydrophilicity is improved, so that a noble metal can be easily supported, and a catalyst capable of generating heat can be obtained.

  The electrode body can be made of a carbon-based material such as graphite, carbon fiber aggregate, carbon powder molded body such as black ink, and the shape is selected according to the purpose such as plate shape or rod shape. The This electrode body needs to have higher conductivity than a porous structure made of silicon carbide ceramics, and preferably contains at least 70% by mass of carbon. By doing so, the conductivity of the electrode body can be made sufficient, and loss during energization can be suppressed.

  A silicon carbide layer is formed at the interface between the electrode body and the porous structure. In this silicon carbide layer, carbon supplied from the electrode body and a resin component and organic porous structure in a slurry described later as a carbon source reacts with silicon in the slurry described later or silicon supplied from the outside. Is formed. Therefore, the electrode body and the porous structure are chemically bonded together through the silicon carbide layer, and the electrode body is firmly fixed integrally with the porous structure. The thickness of the silicon carbide layer is not particularly limited, and can be in a range from nano level to millimeter level.

The porous structure desirably contains silicon on the skeleton surface or in the pores. This improves the strength. In addition, if SiO ₂ is formed by oxidizing silicon, the hydrophilicity is remarkably improved, so that the catalytic metal can be directly supported on the porous structure using an aqueous solution in which the catalytic metal compound is dissolved. Therefore, it can be used as a catalyst for exhaust gas purification, and exhaust gas can be purified even at low temperatures such as at the time of start-up by energizing through the electrode body to generate heat.

  In order to further improve the fixing strength of the electrode body, the surface of the electrode body is covered with a plate-like covering member made of silicon carbide-based ceramics and fixed integrally, and the covering member is further fixed to the surface of the porous structure. It is preferable. In this case, the covering member plays a role of reinforcement, and the covering member also generates heat by energization through the electrode body. Moreover, if the carbon content and silicon amount of the covering member are set to be large and densified, the conductivity is improved, so that the covering member also functions as an electrode body.

  When the contact area between the electrode body and the porous structure is small, the power supply to the porous structure is not uniform, and the heat generation efficiency may be deteriorated. In such a case, it is preferable to use a covering member with a large carbon content and a large area, and the covering member covers 50% or more of the area of the end face of the porous structure to which the electrode body is fixed. It is desirable to do.

  In the porous heat generating device of the present invention, the surface of the porous structure may have a certain degree of conductivity, so a short circuit with surrounding members may occur during energization during use. In order to avoid this problem, it is desirable to form an insulating layer having heat resistance on the surface of the porous structure. As this insulating layer, a ceramic coating is desirable. In order to form such a ceramic coating, for example, a ceramic powder such as alumina cement, alumina or zirconia is slurried with an inorganic binder such as alumina sol or silica sol, and the slurry is washed on the surface of the porous structure and then fired. Therefore, it can be formed easily.

  In the method for manufacturing a porous heating device of the present invention, an impregnation step, a removal step, a temporary fixing step, a carbonization step, and a firing step are performed. In the impregnation step, the organic porous structure is impregnated with a slurry containing a resin as a carbon source and silicon powder or a slurry containing silicon carbide powder in the slurry. Here, as the organic porous structure, those having continuous pores such as urethane foam, foamed rubber, foamed polyolefin, and corrugated paper can be used. The shape, pore diameter, pore distribution, etc. are not particularly limited and can be variously selected according to the purpose.

  As the carbonaceous electrode body, graphite, carbon fiber aggregates, carbon powder molded bodies such as black ink, etc. can be used, and the shape is selected according to the purpose such as plate shape, rod shape, etc. .

  As the resin that is a carbon source, a resin that dissolves in a solvent to form a solution can be used, and examples thereof include phenol resins, furan resins, and organometallic polymers such as polycarbosilane. One kind selected from these may be used, or a plurality of kinds may be mixed and used. Carbon powder, graphite powder, carbon black may be added as additives, and silicon nitride, zirconia, zircon, alumina, silica, mullite, molybdenum disilicide, boron carbide, boron powder as aggregates and antioxidants Etc. can also be added.

  The silicon powder is preferably a fine powder having an average particle size of 30 μm or less. Those having a large particle size are preferably used after being pulverized by a ball mill or the like. The silicon powder may be a pure silicon powder, or a silicon alloy powder containing a metal such as Mg, Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, W, Alternatively, a mixed powder of pure silicon powder and these metal powders can be used.

  The mixing ratio of the resin and silicon powder in the slurry is preferably in the range of Si / C = 0.05 to 5.00 in terms of atomic ratio. If the atomic ratio is less than 0.05, the amount of porous silicon carbide generated by reaction sintering is small, and it is not practical as a heating element. On the other hand, when the atomic ratio exceeds 5.00, the amount of silicon powder in the slurry increases, and precipitation tends to occur.

  A slurry obtained by further mixing silicon carbide powder with a slurry containing resin and silicon powder can also be used. In this case, the silicon carbide powder is preferably within a range of 3 times the weight of the silicon powder. If the silicon carbide powder exceeds 3 times the weight of the silicon powder, mixing may be insufficient.

  The solid content concentration in the slurry is not particularly limited as long as it is a viscosity capable of impregnating the organic porous structure with the slurry. The solvent used for the slurry is not particularly limited, but a solvent capable of dissolving the resin is used. In order to impregnate the organic porous structure with the slurry, it may be simply dipped and pulled up, or is preferably impregnated under reduced pressure.

  In the removing step, surplus slurry is removed from the organic porous structure to form a skeleton of the organic porous structure and a precursor having the slurry attached to the surface thereof. The reason why the excess slurry is removed from the organic porous structure is to remove the slurry filled in the continuous pores, such as centrifugation, a method of sucking the excess slurry from the organic porous structure, or the organic porous structure. For example, a method of squeezing the mass structure to remove excess slurry can be used. By removing the excess slurry, a precursor is formed in which the slurry adheres to the inside or the surface of the organic porous structure.

  In the temporary fixing step, an electrode body made of a carbon-based material is temporarily fixed to a predetermined portion of the organic porous structure. This temporary fixing step can be performed by sticking a pair of electrode bodies to the organic porous structure using the slurry. If a paste-like slurry having a higher concentration than that of the slurry used in the impregnation step is used, the adhesive strength is increased, so that the strength of temporary fixing is improved. For example, after impregnating the slurry into the organic porous structure, the electrode body may be stuck through the slurry, or after placing the electrode body at a predetermined portion of the organic porous structure, the slurry is impregnated to form the electrode body and the organic porous body. The electrode body can be adhered by allowing the slurry to enter the interface with the porous structure.

  After the removing step or the temporary fixing step, it is desirable to perform a drying step for drying the solvent in the slurry. The drying step can be performed in the atmosphere, and it is sufficient to hold at 70 ° C. for about 3 hours. Note that either the removal step or the temporary fixing step may be performed first or at the same time. The temporary fixing step can be performed after the carbonization step and before the firing step. Since the carbonaceous porous structure formed in the carbonization step has low strength, it is easy to process, and grooves and holes for temporarily fixing the electrode body can be easily formed.

  In the carbonization step, the precursor is heated in vacuum or in a non-oxidizing atmosphere to carbonize the resin, and the organic porous structure is pyrolyzed to obtain a carbonaceous porous structure. As the non-oxidizing atmosphere, an inert gas atmosphere such as argon gas is preferable. In the carbonization process by thermal decomposition of the resin, tar-like substances and vaporized substances are generated, so that it is not preferable to perform in a vacuum. Further, in a nitrogen gas atmosphere, silicon nitride may be generated, which is not preferable. The firing temperature in the carbonization step can be in the range of 900 to 1350 ° C. By heating in the range of 900 to 1350 ° C, the resin adhering to the skeleton surface of the organic porous structure is carbonized, and the organic porous structure is pyrolyzed and carbonized while maintaining its three-dimensional skeleton. Is done. Therefore, a carbonaceous porous structure that maintains the skeleton of the organic porous structure is formed.

  A baking process is performed after a carbonization process. In this firing step, the carbonaceous porous structure is heated in a vacuum or in a non-oxidizing atmosphere to cause silicon and carbon to react to form a silicon carbide porous structure from the carbonaceous porous structure. At the same time, the electrode body and the silicon carbide porous structure are bonded together. The firing atmosphere can be the same as in the carbonization step.

  The firing temperature can be 1350 ° C. or higher. By heating to 1350 ° C. or higher, carbon and silicon react to form a silicon carbide based porous structure mainly composed of silicon carbide. This reaction is a reaction in which the volume is reduced because silicon and carbon are present in the system, and when carbon is diffused and reacts with silicon, fine pores are formed in the interior simultaneously with the formation of silicon carbide. In the firing step, a silicon carbide layer is formed at the interface between the electrode body and the organic porous structure by the reaction between carbon supplied from both and carbon derived from the resin and silicon, and the electrode body and the silicon carbide porous body are formed. The structure and the structure are chemically bonded to each other through the silicon carbide layer.

  The carbonization step and the firing step may be performed separately, but it is desirable to perform the firing step continuously after the carbonization step. In this way, waste of heat energy can be prevented.

  Further, in the temporary fixing step, the temporarily fixed portion between the electrode body and the organic porous structure is covered with an organic porous plate such as paper or nonwoven fabric, and pasted on the electrode body and the organic porous structure with the slurry described above. It is preferable. If it does in this way, in the baking process after a carbonization process, an organic porous board will turn into a silicon carbide porous board, and will adhere to an electrode body and a silicon carbide porous structure integrally. Therefore, the fixing strength between the electrode body and the silicon carbide porous structure is further improved.

  Further, the organic porous plate desirably has a carbon element concentration of 50% by mass or more, more preferably 70% by mass or more. By using such an organic porous plate, the density of the silicon carbide porous plate produced in the firing process is increased and the conductivity is increased, so that the power supply from the electrode plate to the silicon carbide porous structure is uniform when energized. Can be achieved. In this sense, it is desirable that the organic porous plate be adhered to the organic porous structure over a wide area so as to cover 50% or more of the area of the end face of the organic porous structure to which the electrode body is fixed. It is desirable to stick to.

  In the reaction in the firing step, if the composition of silicon and carbon is Si / C <1 by atomic ratio, silicon carbide and unreacted carbon remain, and if Si / C> 1, silicon carbide and unreacted metal silicon Remains. If unreacted carbon remains, the strength of the silicon carbide porous structure may not be sufficient. In this case, it is desirable to perform a melt impregnation step in which a silicon carbide porous structure is impregnated with molten silicon to form a metal silicon layer in a vacuum or in a non-oxidizing atmosphere after the firing step. The silicon carbide porous structure is reinforced by the formed metal silicon layer.

  The melt impregnation step may be performed by heating metal silicon to a melting point (about 1410 ° C.) or higher to form molten silicon and impregnating the silicon carbide porous structure, and it is particularly preferably performed in a vacuum. The melt-impregnating silicon may be in the form of powder, granules, or lumps.

  In the melt impregnation process, since silicon carbide has good wettability to molten silicon, the molten silicon penetrates into fine pores formed in the three-dimensional skeleton during the firing process and reacts with the remaining carbon to carbonize. Silicon is formed. This reaction is a reaction in which the volume increases because silicon is added from outside the system, and fine pores formed inside the three-dimensional skeleton are filled with silicon or silicon carbide. Therefore, the strength of the three-dimensional skeleton portion is improved, and the adhesion strength between the metal silicon layer and the three-dimensional skeleton portion is remarkably increased by the anchoring effect.

  In the melt impregnation step, since the exposed carbon is exposed to a high temperature of 1410 ° C. in a vacuum or non-oxidizing atmosphere, most of the remaining carbon is silicon carbide. The melt impregnation step can be performed simultaneously with the firing step or continuously after the firing step. That is, after the carbonization process, silicon for melt impregnation is added, and silicon is melted and impregnated at a temperature equal to or higher than the melting point of silicon (about 1410 ° C.) in a vacuum or non-oxidizing atmosphere to react unreacted carbon with silicon. . Excess silicon remains as silicon.

When the silicon carbide based porous structure contains silicon, it is also preferable to perform an oxidation process in which at least part of the contained silicon is oxidized to form SiO ₂ . Silanol group easily generated hydrophilicity is enhanced in the SiO _2. Therefore, it is possible to absorb a large amount of an aqueous solution of the catalyst metal compound, and by firing it, a catalyst carrying a highly dispersed catalyst metal such as platinum can be formed. This catalyst can be used as an exhaust gas purifying catalyst, and generates heat when energized. Therefore, harmful components can be purified from low-temperature exhaust gas at the start.

In this oxidation step, the silicon carbide porous structure containing silicon may be heated in an oxidizing atmosphere such as the air. It has been clarified that the higher the heating temperature, the larger the amount of SiO2 generated relative to the total amount of silicon, and it is desirable to heat at 400 ° C. or higher. It is sufficient to keep the heating time for about 10 minutes. The amount of SiO ₂ formed can be adjusted by the heating temperature, and the higher the heating temperature, the more SiO ₂ can be formed. Therefore, it is only necessary to select a heating temperature at which the catalyst metal such as Pt can be supported in a highly dispersed state with a sufficient amount of support.

  FIG. 1 shows a porous heating device of the present embodiment, and FIG. This porous heat generating device includes a porous structure 1 made of silicon carbide-based ceramics, and a pair of electrode bodies 2 formed integrally with the porous structure 1. The porous structure 1 has a cylindrical shape and has a large number of continuous pores. The pair of electrode bodies 2 has a rod shape made of graphite, each having one end inserted into the center of both end faces of the porous structure 1 and fixed integrally with the porous structure 1 via the silicon carbide layer 3. ing.

  Hereinafter, a method for manufacturing the porous heating device will be described, and the detailed description of the configuration will be substituted.

  The mixing ratio of phenol resin and silicon powder with an average particle size of about 20μm is set to a ratio where the carbon / silicon atomic ratio by carbonization of phenol resin is Si / C = 0.6, which is about 2.4 times the weight of silicon powder. Dissolve phenol resin with heavy ethyl alcohol to prepare slurry, mix with ball mill for 1 day to reduce the particle size of silicon powder, and further add silicon carbide powder with an average particle size of about 3 μm to 0.5 times that of silicon powder. By weight addition, a dispersion slurry was prepared.

<Impregnation process / removal process>
Prepare a # 13 (13 cells per inch) cylindrical polyurethane sponge, fully impregnated with the above dispersion slurry, squeeze the dispersion slurry so that it does not block the continuous pores, and dry it at 70 ° C. for 3 hours. It was.

<Carbonization process / temporary fixing process>
The sponge with the dispersed slurry adhered thereto was carbonized by heating to 1000 ° C. under an argon gas atmosphere. At this time, the sponge was thermally decomposed and the phenol resin was carbonized to form a carbonaceous porous body having a three-dimensional skeleton equivalent to the sponge used.

  Since the carbonaceous porous body is easy to process, a concave portion extending in the axial direction is formed at the center of both end faces. On the other hand, a pair of electrode bodies 2 formed in advance from graphite is prepared, a high-viscosity paste prepared by increasing the solid content concentration of the dispersion slurry is applied to one end, and one end where the paste is applied The parts were inserted into the recesses at both ends. This was dried at 70 ° C. for 3 hours, and the pair of electrode bodies 2 were each temporarily fixed to the carbonaceous porous body. Subsequently, this carbonaceous porous body was baked at 1000 ° C. for 1 hour in an argon gas to carbonize the paste.

<Baking process and melt impregnation process>
Next, an appropriate amount of silicon granules was placed on the surface of the carbonaceous porous body, and fired at 1450 ° C. for 1 hour in a vacuum. In this firing, first, carbon reacts with silicon powder at a temperature lower than the melting point of silicon (about 1410 ° C.) to form a porous structure 1 having a sponge skeleton composed of silicon carbide and unreacted carbon. . Further, at the interface between the electrode body 2 and the carbonaceous porous body, the carbon and silicon powder contained in the electrode body 2 and the carbonaceous porous body react to form a silicon carbide layer 3, whereby the electrode body 2 is carbonized. It was integrally fixed to the porous structure 1 via the silicon layer 3.

  Furthermore, silicon granules are melt-impregnated into the porous structure 1 at a temperature equal to or higher than the melting point of silicon to react with unreacted carbon to produce silicon carbide, and the porous structure is reinforced with excess metal silicon to form an electrode. The fixing strength of the body 2 is further improved.

  In the obtained porous heating device, the pair of electrode bodies 2 were fixed integrally with the silicon carbide porous structure 1, and the pair of electrode bodies 2 had sufficient strength to withstand use.

  However, in the porous heat generating device of Example 1, the fixing part of the electrode body 2 is local, and the contact area between the electrode body 2 and the porous structure 1 through the silicon carbide layer 3 is small. Therefore, the current density at the time of energization through the pair of electrode bodies 2 may vary, and the heat generation of the porous structure 1 may become non-uniform.

  Therefore, as shown in FIGS. 3 and 4, the porous heat generating device of this example includes a rectangular parallelepiped porous structure 1 and a pair of electrode bodies 2 integrally joined to both end faces in the longitudinal direction, Consists of. The pair of electrode bodies 2 has a plate shape made of graphite, and are fixed integrally with the porous structure 1 via the silicon carbide layer 3. A metal silicon layer 10 is formed on the skeleton surface of the porous structure 1. Hereinafter, the manufacturing method of this porous heat generating device will be described and replaced with a detailed description of the structure.

  The mixing ratio of phenol resin and silicon powder with an average particle size of about 20μm is set to a ratio where the carbon / silicon atomic ratio by carbonization of phenol resin is Si / C = 0.6, which is about 2.4 times the weight of silicon powder. Dissolve phenol resin with heavy ethyl alcohol to prepare slurry, mix with ball mill for 1 day to reduce the particle size of silicon powder, and further add silicon carbide powder with an average particle size of about 3 μm to 0.5 times that of silicon powder. A dispersion slurry was prepared by weight addition.

<Temporary fixing process / impregnation process / removal process>
# 13 (13 cells per inch) rectangular polyurethane foam was prepared. This sponge was sufficiently impregnated with the above dispersion slurry, squeezed to such an extent that the dispersion slurry did not block the continuous pores, and then dried at 70 ° C. for 3 hours. Next, a high-viscosity paste prepared by increasing the solid content concentration of the dispersion slurry was used, and graphite electrode bodies 2 were adhered to both ends in the longitudinal direction of the polyurethane sponge. This was dried at 70 ° C. for 3 hours to temporarily fix the electrode body 2.

<Carbonization process>
The sponge on which the electrode body 2 was temporarily fixed was heated and carbonized at 1000 ° C. in an argon gas atmosphere. At this time, the sponge was thermally decomposed and the phenol resin was carbonized to form a carbonaceous porous body having a three-dimensional skeleton equivalent to the sponge used.

<Baking process and melt impregnation process>
Subsequently, an appropriate amount of silicon granules was placed on the surface of the carbonaceous porous body and baked in vacuum at 1450 ° C. for 1 hour. In this firing, first, carbon reacts with the silicon powder at a temperature not higher than the melting point of silicon (about 1410 ° C.) to form a porous structure 1 composed of sponge skeleton silicon carbide and unreacted carbon. In addition, at the interface between the electrode body 2 and the carbonaceous porous body, the carbon contained in the electrode body 2 and the carbonaceous porous body reacts with the silicon powder to form a silicon carbide layer 3. The layer 3 was fixed integrally to the porous structure 1.

  In this calcination, when the temperature is higher than the melting point of silicon, silicon granules are melted and impregnated into the porous structure 1 to react with the remaining carbon, and finally the porous structure 1 having the metal silicon layer 10 is obtained.

  In the obtained porous heating device, the pair of electrode bodies 2 were fixed integrally with the porous structure 1 and had sufficient strength to withstand use. Further, the contact area between the electrode body 2 and the porous structure 1 through the silicon carbide layer 3 is sufficiently large to be 50% or more of the area of the end face of the porous structure 1, so that the porous structure 1 is energized. Sometimes evenly generates heat.

  In this porous heat generating device, most of the surface of the porous structure 1 is exposed, and the surface of the electrode body 2 is exposed except for the part necessary for power feeding. Therefore, a short circuit with other members may occur during actual use. In order to prevent such a problem, it is desirable to form the insulating layer 4 on the surface that is not desired to be exposed, as shown in FIG.

  The insulating layer 4 can be formed to a thickness of about 50 μm on the entire surface of the porous structure 1 excluding the tip of the electrode body 2. For example, the insulating layer 4 is prepared by preparing a slurry made of alumina cement and water, and wash-coating the entire surface of the porous heat generating device 1 manufactured as described above except for the tip of the electrode body 2 and applying it to the atmosphere. It can be formed by baking at a temperature of 1000 ° C.

  In Example 2 above, the plate-like electrode body 2 is fixed to both end faces in the longitudinal direction of the porous structure 1, but as shown in FIG. There is a case where it is desired to form a pair of electrode bodies 2. In this case, when the electrode body 2 having the same shape as that of the second embodiment is used, the ratio of the contact area of the electrode body 2 to the area of the end face in the short direction of the porous structure 1 is reduced. In some cases, the current density at the time of energization through 2 varies, and the heat generation of the porous structure 1 may become uneven.

  Therefore, in this embodiment, as shown in FIGS. 6 and 7, a plate-shaped covering member 5 having conductivity is arranged on the surface of the electrode body 2, and the covering member 5 is in the short direction of the porous structure 1. It is configured to cover most of the end face (about 80%). The covering member 5 is integrally fixed to the surface of the electrode body 2 and the surface of the porous structure 1. Therefore, since current flows from the electrode body 2 to the porous structure 1 through the covering member 5 when energized, the porous structure 1 generates heat uniformly when energized. Further, the covering member 5 more reliably prevents the electrode body 2 from falling off, and the porous structure 1 is also reinforced.

  A method for manufacturing this porous heating device will be described below.

<Temporary fixing process / impregnation process / removal process>
A # 13 (13 cells per inch) rectangular parallelepiped polyurethane sponge (the same as in Example 2) was prepared. The sponge was sufficiently impregnated with the same dispersed slurry as in Example 2, and after the slurry was squeezed to such an extent that the continuous slurry did not block the continuous pores, it was dried at 70 ° C. for 3 hours. Next, a high-viscosity paste prepared by increasing the solid content concentration of the dispersion slurry was used, and graphite electrode bodies 2 were attached to both ends in the lateral direction. On the other hand, a 0.3 mm thick paperboard (corrugated paperboard) containing 70% by mass of activated carbon is prepared, impregnated with the dispersion slurry, and then dispersed on the surface of the electrode body 2 and the end face of the sponge in the short direction. It stuck using the slurry. This was dried at 70 ° C. for 3 hours to temporarily fix the electrode body 2 and the paperboard.

<Carbonization process>
The sponge on which the electrode body 2 and the paperboard were temporarily fixed was carbonized by heating to 1000 ° C. in an argon gas atmosphere. At this time, the sponge and paperboard were thermally decomposed, and the phenol resin was carbonized, and a carbonaceous porous body in which the carbon plate body in which the paperboard was carbonized and the electrode body 2 was temporarily fixed was formed.

<Baking process and melt impregnation process>
Next, an appropriate amount of silicon granules was placed on the surface of the carbonaceous porous body, and fired at 1450 ° C. for 1 hour in a vacuum. In this firing, first, carbon reacts with the silicon powder at a temperature lower than the melting point of silicon (about 1410 ° C.), and is adhered to the porous structure 1 composed of silicon carbide having a sponge skeleton and unreacted carbon. A silicon carbide coating member 5 is formed in the form of a paperboard. Further, a silicon carbide layer 3 is formed at each interface of the electrode body 2, the covering member 5, and the porous structure 1, whereby the electrode body 2 and the covering member 5 are formed on the porous structure 1 via the silicon carbide layer 3. It was fixed together.

  When the temperature is equal to or higher than the melting point of silicon, the silicon granules melt and impregnate the porous structure 1 and the covering member 5 and react with the remaining carbon. A metal silicon layer is formed on the surface of the skeleton of the porous structure 1 due to excess silicon. The covering member 5 has a dense structure made of silicon carbide and silicon.

  In the obtained porous heat generating device, the pair of electrode bodies 2 are integrally fixed to the porous structure 1 and covered with the covering member 5. Since this covering member 5 is made of silicon carbide and silicon and has a dense structure, it has high conductivity. Therefore, since the current flows from the electrode body 2 to the porous structure 1 through the covering member 5, even if the contact area between the electrode body 2 and the porous structure 1 through the silicon carbide layer 3 is small, the porous structure body 1 generates heat uniformly when energized.

The porous heat generating apparatus of the present embodiment can be used as an exhaust gas purifying catalyst as follows, for example. That is, the porous heat generating device manufactured above is first heated to about 600 ° C. in the atmosphere to oxidize the metal silicon layer to form a SiO ₂ layer. Next, the porous structure 1 having a SiO ₂ layer is immersed in an aqueous solution of dinitrodiamine platinum nitric acid solution, pulled up, dried, and baked at, for example, 300 ° C. for 1 hour.

  The exhaust gas-purifying catalyst thus obtained can carry about 3 g of platinum per 1 L of the apparent volume of the porous structure 1. Since the supported amount of platinum in the automobile three-way catalyst is 1 to 2 g per 1 L of the apparent volume of the honeycomb substrate, this exhaust gas purification catalyst carries 1.5 to 3 times as much platinum as a general three-way catalyst. Will be.

Therefore, the porous heat generating device of the present embodiment can support platinum at a high concentration on the SiO ₂ layer of the porous structure 1 and can be used as an exhaust gas purifying catalyst. Moreover, since the porous structure 1 is porous, it is excellent in gas diffusibility and fully exhibits the catalytic action of the supported platinum. In the case of a general exhaust gas purifying catalyst, when it is cold such as at the time of start-up, it is difficult to purify exhaust gas because platinum has not reached the activation temperature. Since the porous structure 1 can be heated in this manner, discharge of harmful substances can be prevented even when cold.

  The porous heat generating apparatus according to this example is shown in FIGS. This porous heat generating device includes a silicon carbide honeycomb substrate 6 having a large number of cell passages 60, an electrode body 2 that is integrally fixed to outer wall surfaces parallel to each other, an electrode body 2, and a honeycomb substrate 6. And a conductive covering member 7 covering the surface. The honeycomb substrate 6 is formed by alternately laminating a silicon carbide porous flat plate 61 and a silicon carbide porous corrugated plate 62, and a cell passage between the porous flat plate 61 and the porous corrugated plate 62. 60 is formed. Hereinafter, a method for manufacturing the porous heating device will be described, and the detailed description of the configuration will be substituted.

<Impregnation process / removal process / temporary fixing process>
A single-sided corrugated cardboard containing 70% by mass of activated carbon (“activated carbon mixed sheet” manufactured by Chiyoda Container Co., Ltd.) was laminated using a paper adhesive to form a honeycomb body having a large number of cell passages. A paperboard containing 70% by mass of activated carbon (single-sided cardboard paperboard) was joined to the last corrugated board.

  On the other hand, the mixing amount of the phenol resin and silicon powder having an average particle diameter of about 20 μm is set so that the atomic ratio between carbon and silicon by carbonization of the phenol resin is Si / C = 3, and the weight of silicon powder is about 0.8 A slurry is prepared by dissolving phenol resin with double weight of ethyl alcohol, and ball mill mixing for 1 day to reduce the particle size of the silicon powder. Further, silicon carbide powder having an average particle size of about 3 μm is added to 0.33 of the silicon powder. Double weight was added to prepare a dispersion slurry.

  The honeycomb body was impregnated with the dispersion slurry, and excess dispersion slurry was blown off and dried at 70 ° C. for 3 hours. Then, a high-viscosity paste prepared by increasing the solid content concentration of the dispersed slurry was used, and the graphite electrode bodies 2 were bonded to the porous flat plates 61 constituting the front and back surfaces parallel to each other. On the other hand, a 0.3 mm-thick paperboard (single-sided cardboard paperboard) containing 70% by mass of activated carbon was prepared, impregnated with the dispersion slurry, and then adhered to the surface of the electrode body 2 and the surface of the honeycomb body. This was dried at 70 ° C. for 3 hours, and the electrode body 2 and the paperboard were temporarily fixed to the honeycomb body.

<Carbonization process / firing process>
The honeycomb body on which the electrode body 2 and the paperboard were temporarily fixed was heated to 1000 ° C. in an argon gas atmosphere to be carbonized. At this time, the honeycomb body and the paperboard were thermally decomposed, and the phenol resin was carbonized, and a carbonaceous honeycomb body in which the carbon plate body in which the paperboard was carbonized and the electrode body 2 were temporarily fixed was formed.

  Next, this carbonaceous honeycomb body was fired in a vacuum. In this firing, carbon reacts with the silicon powder at a temperature not higher than the melting point of silicon (about 1410 ° C.), the silicon carbide honeycomb substrate 6, and the bonded paperboard-shaped silicon carbide coating member 7. Is formed. Further, at each interface of the electrode body 2, the covering member 7 and the honeycomb substrate 6, the contained carbon reacts with the silicon powder to form a silicon carbide layer 3, whereby the electrode body 2 and the covering member 7 are made of silicon carbide. It was fixed to the honeycomb substrate 6 integrally through the layer 3.

  In the obtained porous heating device, the pair of electrode bodies 2 are fixed integrally with the honeycomb substrate 6 and are covered with the covering member 7. Since an electric current flows from the electrode body 2 to the honeycomb base material 6 through the covering member 7, even if the contact area between the electrode body 2 and the honeycomb base material 6 through the silicon carbide layer 3 is small, the honeycomb base material 6 is not energized. Generates heat uniformly.

  Since this example is the same as Example 4 except that the firing step and the melt impregnation step are performed after the carbonization step, the figure is shared with FIGS. Description of is omitted.

<Baking process and melt impregnation process>
An appropriate amount of the silicon granules was placed on the surface of the carbonaceous honeycomb body on which the carbon plate with the paperboard carbonized and the electrode body 2 were temporarily fixed, and fired at 1450 ° C. for 1 hour in a vacuum. In this firing, first, carbon reacts with the silicon powder at a temperature below the melting point of silicon (about 1410 ° C.) to form a silicon carbide honeycomb substrate 6 and a bonded paperboard-shaped silicon carbide coating member. 7 are formed. Further, at each interface of the electrode body 2, the covering member 7 and the honeycomb substrate 6, the contained carbon reacts with the silicon powder to form a silicon carbide layer 3, whereby the electrode body 2 and the covering member 7 are made of silicon carbide. It was fixed to the honeycomb substrate 6 integrally through the layer 3.

  When the temperature is equal to or higher than the melting point of silicon, the silicon granules melt and impregnate into the honeycomb base material 6 and the covering member 7 and react if there is residual carbon, filling small pores existing in the honeycomb base material 6 and the covering member 7. Moreover, a metal silicon layer is formed on the surface of the skeleton of the honeycomb substrate 6 or the surface of the covering member 7 due to the excess silicon. Thereby, compared with Example 4, the strength of the honeycomb substrate 6 is improved and the fixing strength of the electrode body 2 is also improved.

  In the obtained porous heating device, the pair of electrode bodies 2 are fixed integrally with the honeycomb substrate 6 and are covered with the covering member 7. The covering member 7 has a metal silicon layer formed on the surface and is dense and has high conductivity. Therefore, current flows from the electrode body 2 to the honeycomb substrate 6 through the covering member 7, so that the honeycomb substrate 6 is energized even if the contact area between the electrode body 2 and the honeycomb substrate 6 through the silicon carbide layer 3 is small. Sometimes evenly generates heat.

  FIG. 10 shows a porous heating device according to this example. This porous heat generating device includes a cylindrical silicon carbide honeycomb substrate 6, a pair of graphite electrode bodies 2 integrally fixed to the outer peripheral surface thereof, the surface of the electrode body 2, and the honeycomb substrate 6. And a silicon carbide-based covering member 7 covering the surface of about ¼ circumference. The pair of electrode bodies 2 extend parallel to the axis of the honeycomb substrate 6 and are arranged symmetrically with respect to the axis so as to face each other. The pair of electrode bodies 2 and the covering member 7 are integrally fixed to the outer peripheral surface of the honeycomb substrate 6 through a silicon carbide layer (not shown).

  In order to manufacture this porous heating device, first, a single-sided cardboard containing activated carbon similar to that in Example 4 is used, and a large number of cell passages 60 are formed by winding in a roll shape so that the porous flat plate 61 is on the outside. Forming a honeycomb body. Then, the same dispersion slurry as in Example 4 was impregnated, the excess dispersion slurry was blown off, dried at 70 ° C. for 3 hours, and then the high viscosity paste prepared by increasing the solid content concentration of the dispersion slurry was used. A pair of electrode bodies 2 are temporarily fixed to the outer peripheral surface. Further, a paperboard containing activated carbon (corrugated cardboard paperboard) or the like is prepared, impregnated with the dispersed slurry, and then wound and pasted so as to cover the surface of the electrode body 2 and the surface of the honeycomb body. This is dried, and the electrode body 2 and the paperboard are temporarily fixed to the honeycomb body.

  Then, the porous heat generating apparatus of a present Example can be manufactured by performing a carbonization process and a baking process similarly to Example 4. FIG. Thus, if it is set as the cylindrical honeycomb base material 6, it can be mounted in the catalyst converter of a general motor vehicle, and its practicality is high.

  The porous heating device of the present invention can be used not only for various heaters but also for exhaust gas purification catalysts, diesel particulate filters (DPFs), and the like.

1: Porous structure 2: Electrode body 3: Silicon carbide layer
10: Metallic silicon layer

Claims (9)

A porous heating device comprising a porous structure made of silicon carbide-based ceramics and a pair of electrode bodies fixed to the porous structure, and generating heat by energization through the electrode body,
The electrode body is formed of a carbon-based material, and is fixed integrally with the porous structure through a silicon carbide layer formed at an interface between the electrode body and the porous structure. Porous heating device.   The porous heating device according to claim 1, wherein the surface of the electrode body and the surface of the porous structure are integrally covered with a plate-shaped covering member made of silicon carbide ceramics.   The porous heating device according to claim 2, wherein the electrode body is fixed to an end surface of the porous structure, and the covering member covers 50% or more of the area of the end surface to which the electrode body is fixed.   The porous heating device according to claim 1, wherein the electrode body contains 70% by mass or more of carbon.   The porous heat generating apparatus according to claim 1, wherein the porous structure includes silicon at least partially. An impregnation step of impregnating an organic porous structure with a slurry containing a resin as a carbon source and silicon powder or a slurry further containing silicon carbide powder in the slurry;
Removing the surplus slurry from the organic porous structure to form a skeleton of the organic porous structure and a precursor having the slurry attached to the surface thereof;
A temporary fixing step of temporarily fixing an electrode body made of a carbon-based material to a predetermined portion of the organic porous structure;
A carbonization step of heating the precursor in vacuum or in a non-oxidizing atmosphere to carbonize the resin and thermally decomposing the organic porous structure to form a carbonaceous porous structure;
The carbonaceous porous structure is heated in vacuum or in a non-oxidizing atmosphere to cause silicon and carbon to react to form a silicon carbide porous structure from the carbonaceous porous structure. A method for producing a porous heating device, comprising performing a firing step of integrally bonding an electrode body and the silicon carbide porous structure.   In the temporary fixing step, the electrode body is arranged on the surface of the organic porous structure, and the surface of the electrode body and the organic porous structure is covered with a paper-like organic porous board and the organic porous board is also covered. The slurry is impregnated, and the firing step forms a silicon carbide coating member from the organic porous plate, and the coating member is integrally bonded to the electrode body and the silicon carbide porous structure. The manufacturing method of the porous heat generating apparatus of description.   The method for manufacturing a porous heating device according to claim 7, wherein the concentration of the carbon element contained in the organic porous plate is 50% by mass or more.   9. The melt impregnation step of forming a metal silicon layer by impregnating the silicon carbide based porous structure with molten silicon in a vacuum or in a non-oxidizing atmosphere is performed after the firing step. Method for producing a porous heating device.

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