JP2012196620A - Gas decomposing element, method for production thereof, and ammonia decomposition method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas decomposing element which supplements the lack of contact area of a gas to be treated and a catalyst or insufficiency in temperature of the catalyst itself when the gas to be treated contacts the catalyst, prevents break of a linear or coiled catalyst when elevating temperature, and is excellent in decomposition efficiency, response and durability.SOLUTION: The gas decomposing element comprises a metal porous body having continuous pores. The metal porous body has an integrally continued three-dimensional network structure, and comprises an alloy containing at least Ni, and Cr whose percentage in the alloy is ≥25 wt.% but ≤32 wt.%.

Description

  The present invention relates to a gas decomposing element mainly used for decomposing ammonia, a method for producing the same, and an ammonia decomposing method.

  Environmental standards have been established for odorous gases and toxic gases such as ammonia gas discharged from semiconductor manufacturing plants and wastewater treatment facilities. By installing certain facilities, these harmful gases are removed to below the environmental standard value. Processing (detoxification processing) is performed. As the detoxification treatment, conventionally, a method of burning and decomposing ammonia gas using liquefied natural gas or the like, or a method of decomposing ammonia gas into nitrogen and oxygen by a catalyst has been performed.

  Speaking of the detoxification treatment with a catalyst, for example, Patent Document 1 is used in semiconductor manufacturing factories and chemical factories for the purpose of decomposing ammonia, hydrogen sulfide, trimethylamine, methyl mercaptan, etc., which are called four major malodors. The invention relating to the deodorizing apparatus is described. Specifically, the raw gas that includes a heat-resistant member having one or a plurality of pores through which the raw gas passes and a heating element that heats the inside of the pores of the heat-resistant member, and passes through the pores. Is oxidized without thermal oxidation. For example, linear or coiled nickel or chromium is used for the heating element.

Japanese Patent Laid-Open No. 10-263367

  However, sufficient decomposition characteristics cannot be obtained only by using a heating element as a linear or coiled catalyst as in Patent Document 1. That is, (i) when a high concentration of ammonia or the like (hereinafter referred to as a gas to be processed) is supplied at a high flow rate, (ii) when the concentration of the gas to be processed is rapidly switched from a low concentration to a high concentration, Or (iii) When the supply of the gas to be processed is continued for a long time, it is difficult to sufficiently decompose the gas to be processed. In other words, conventional detoxification equipment using a catalyst that performs gas decomposition is inferior in terms of (i) decomposition efficiency, (ii) response characteristics, and (iii) durability.

  As a result of the studies by the present inventors, the causes are a lack of contact area between the gas to be treated and the catalyst, a lack of temperature of the catalyst itself when the gas to be treated comes into contact with the catalyst, and a rise in temperature. It was found that this was due to the disconnection of the linear or coiled catalyst. The present invention has been made in view of the above problems, and the present invention provides a gas decomposition element that is excellent in terms of decomposition efficiency, response characteristics, and durability.

  As a result of the intensive investigations by the present inventors to solve the above problems, the above problems can be solved by the following means.

(1) The present invention is a gas decomposition element comprising a porous metal body having continuous pores, wherein the porous metal body has an integrally continuous three-dimensional network structure, and the porous metal body is at least It is made of an alloy containing Ni and Cr, and the ratio of Cr in the alloy is 25 wt% or more and 32 wt% or less.

  The photograph which observed the metal porous body with which the gas decomposition element by this invention is equipped with the electron microscope is shown in FIG. As can be understood from FIG. 1, the porous metal body 1 has a skeleton so as to form an integrally continuous three-dimensional network structure, and has continuous pores 10 having a substantially polygonal shape in the mesh gap. .

  In the present invention, since the gas decomposition element is a porous metal body having continuous pores, when the gas to be processed is circulated, the contact frequency between the gas to be processed and the metal porous body included in the gas decomposition element is linear. Or it is very large compared to that of a coil. As a result, the gas decomposing element of the present invention can efficiently decompose a large amount of gas to be processed and a gas having a high concentration. Therefore, the decomposition efficiency is excellent.

  In the gas decomposition element of the present invention, the metal porous body is made of an alloy containing at least Ni and Cr. Therefore, when the metal porous body is energized, the metal porous body itself generates heat. Therefore, the catalytic function of Ni contained in the alloy is enhanced.

  In addition, the gas decomposition element of the present invention is excellent not only in decomposition efficiency but also in response characteristics. That is, when heat is generated by energizing the porous metal body of the gas decomposition element, the time required to reach the required temperature is significantly shorter than that when, for example, the gas decomposition element is warmed from its surroundings. As a result, even if there is a situation where the concentration of the gas to be processed suddenly changes from a low concentration to a high concentration, the gas to be processed can be detoxified by detecting it and changing the energization current, Excellent response characteristics.

  Furthermore, since the gas decomposition element of the present invention is adjusted so that the ratio of Cr in the metal porous body alloy is 25 wt% or more and 32 wt% or less, the decomposition efficiency at the start of decomposition is also several The decomposition efficiency after decomposition for 10 hours is also excellent. That is, the gas decomposition element of the present invention is excellent in terms of decomposition efficiency and durability. The result is shown in the Example mentioned later.

(2) The gas decomposition element of the present invention is characterized in that the window diameter formed by the skeleton of the porous metal body is 0.2 mm or more and 1.6 mm or less.

  As in the present invention, when the window diameter formed by the skeleton of the metal porous body is 0.2 mm or more, the gas passing through the gas decomposition element can pass without pressure loss. As a result, the decomposition characteristics are excellent. On the other hand, when the window diameter formed by the skeleton of the porous metal body is 1.6 mm or less, the skeleton is less likely to be broken, so that the durability is increased. Furthermore, in the present invention, it is more preferable if the window diameter is 0.35 mm or more and 0.65 mm or less.

  Here, the window diameter referred to in the present invention refers to the value of the diameter of the inscribed circle when a virtual inscribed circle is assumed for each of the continuous pores having a polygonal shape. And in this invention, the average value when 20 holes are observed with an electron micrograph shall represent the window diameter which the frame | skeleton of the metal porous body comprises. In addition, the window diameter in the case of FIG. 1 is 0.45 mm.

(3) The gas decomposition element of the present invention is characterized in that a porous metal body provided in the gas decomposition element is produced through the following steps.
(A) Step of conducting conductive treatment on three-dimensional network resin (B) First plating step of applying Ni plating to three-dimensional network resin (C) First heat treatment step of removing three-dimensional network resin ( D) Second plating step of applying Cr plating on Ni layer (E) Second heat treatment step of alloying Ni layer and Cr layer

  As in the present invention, since Ni and Cr are produced by the plating process, the composition of Ni and Cr is uniform throughout the porous metal body. Therefore, when the metal porous body is energized in decomposing the gas to be processed, the entire metal porous body generates heat uniformly. As a result, it is difficult to cause a situation in which a part of the metal porous body is disconnected, and the durability of the gas decomposition element is improved.

(4) The gas decomposition element of the present invention is characterized in that a porous metal body provided in the gas decomposition element is produced through the following steps.
(A) Step of conducting conductive treatment on three-dimensional network resin (B) First plating step of applying Ni plating to three-dimensional network resin (C) First heat treatment step of removing three-dimensional network resin ( D) In a gas generated by heating a Ni porous body that has undergone the first heat treatment step at 950 to 1100 ° C. with a powder containing Cr or a Cr compound and NH ₄ X (X is I, F, Cl, or Br) Heat treatment process

  As in the present invention, since the method of applying Cr to the surface of the Ni porous body is based on the gas phase method using gas, the composition of Ni and Cr is uniform throughout the metal porous body. Therefore, when the metal porous body is energized in decomposing the gas to be processed, the entire metal porous body generates heat uniformly. As a result, it is difficult to cause a situation in which a part of the metal porous body is disconnected, and the durability of the gas decomposition element is improved.

(5) The present invention is characterized in that the porous metal body has a skeleton composed of an outer shell and a hollow core, or a skeleton composed of an outer shell and a conductive core.

  This feature will be described with reference to FIG. FIG. 2 is an enlarged view of the periphery of the nodule portion 11 of the metal porous body 1. A plurality of branch parts 12 (four branch parts 12 in the case of FIG. 2) are gathered in the nodule part 11. A three-dimensional network structure is integrally and continuously formed by these nodes 11 and branches 12. If the branch part 12 is seen in detail, the branch part is provided with the frame | skeleton which consists of the outer shell 12a and the core part 12b. The gap that is a part other than the skeleton is continuous pores 10.

  The metal porous body 1 of the present invention is formed so as to be integrally continuous by a skeleton composed of the outer shell 12a and the hollow core portion 12b, or a skeleton composed of the outer shell 12a and the conductive core portion 12b. Yes. For this reason, when resistance heating is performed by energizing the metal porous body, it is possible to generate heat uniformly over the entire metal porous body.

  The technique for forming such a skeleton is not limited. For example, after a plating layer or a metal coating layer is provided on the surface of a three-dimensional network resin, the skeleton is formed by eliminating the resin. In this case, the core of the skeleton is hollow or / and conductive.

  That is, when a skeleton is formed by removing the resin after providing a plating layer on the surface of the three-dimensional network resin, the resin disappears and becomes a hollow core 12b. In addition, when the conductive material is coated on the surface of the three-dimensional network resin to provide the plating layer and then the resin is lost, the conductive material remains in the hollow. By the subsequent heat treatment, the outer shell 12a contracts and the hollow portion disappears. In this case, the conductive core portion 12b is formed.

(6) Further, in the present invention, the three-dimensional network structure is formed by integrally forming a plurality of branches constituting the skeleton at a knot, and collecting at one knot. The thickness of the outer shell at the plurality of branch portions is substantially constant.

  This feature will be described with reference to FIG. When the metal porous body 1 is energized, the current from the plurality of branch portions 12 concentrates on the nodal portion 11. Therefore, if the electrical resistances of the plurality of branches 12 gathering in one node 11 are different from each other, an excessive current flows only in some branches 12 around the node 11. As a result, the temperature rises and the branches may melt or deteriorate. If it becomes like this, the gas decomposition element provided with the metal porous body 1 will not exhibit sufficient decomposition performance.

  However, as in the present invention, by adjusting the thickness of the outer shell 12a of the branch portion 12 that collects in the one nodule portion 11 to be substantially constant, the electric power of the branch portion 12 that gathers in the one nodule portion 11 is adjusted. There is no difference in resistance, and the fusing or deterioration of the branch portion 12 can be prevented. Thus, in order to make the thickness of the outer shell 12a substantially constant, it is preferable to use a manufacturing method as described in (3) or (4) above.

  Here, the thickness t of the outer shell 12a in the branch part 12 gathering at one nodule part 11 may be substantially constant. That is, it does not require that the thickness of the outer shell 12a is constant throughout the porous metal body 1. For example, depending on the manufacturing method or the like, it is conceivable that the thickness t of the outer shell 12a is different from the surface layer portion of the porous metal body 1 inside. In this case, the thickness of the outer shell 12a of each branch portion gathering at the knot portion 11 located on the surface layer portion may be different from the thickness of the outer shell 12a of the branch portion 12 gathering at the knot portion 11 located inside. However, if the thickness of the skeleton gathering at each nodule is substantially constant, an excessive current does not flow through some branches, so that the skeleton near the nodule is prevented from fusing.

(7) In the ammonia decomposing method of the present invention, the gas decomposing element according to the present invention is used, the temperature of the porous metal body provided in the gas decomposing element is set to 800 ° C. or more, and the gas to be treated containing ammonia is brought into contact with the gas decomposing element. It is characterized by making it.

By using the gas decomposition element according to the present invention and setting the temperature of the metal porous body to 800 ° C. or higher, when the gas to be treated containing ammonia comes into contact with the metal porous body, the ammonia is “2NH ₃ → N ₂ Thermal decomposition as in the chemical reaction formula of “+ 3H ₂ ”. Furthermore, if the temperature of the metal porous body is 880 ° C. or higher, the catalytic activity of nickel contained in the metal porous body is increased, and thermal decomposition is further promoted. Moreover, it is more preferable if the temperature of the porous metal body included in the gas decomposition element is 880 ° C. or more and 920 ° C. or less.

  As described above, as a method of setting the metal porous body to 800 ° C. or higher, there are a method of causing resistance heat generation by energization and a method of heating the gas decomposition element from the surroundings, which will be described in detail later.

(8) The ammonia decomposition method of the present invention is characterized in that the method of setting the temperature of the porous metal body to 800 ° C. or more is by energizing the porous metal body.

  In order to set the temperature of the porous metal body to 800 ° C. or more, it can be realized by energizing the porous metal body. Thereby, the metal porous body generates resistance heat. According to this method, the degree of heat generation can be controlled by the energization current. This method is easier in terms of temperature control than the method of heating a gas decomposition element including a metal porous body from the surroundings, and is advantageous in reducing heat loss. In addition, when the metal porous body itself is caused to generate resistance heat by energizing the metal porous body, the temperature exceeds the temperature range of 960 to 1100 ° C., although it depends on conditions such as the skeleton thickness and the window diameter of the metal porous body. From around, the metal porous body itself deteriorates and melts. Therefore, when the gas decomposition element is used with resistance heat generated by energization, the temperature is preferably controlled so as not to exceed a temperature range of 960 to 1100 ° C.

(9) The ammonia decomposition method of the present invention is characterized in that the gas to be treated is substantially composed only of ammonia.

  Conventionally, ammonia and oxygen are often mixed to form a gas to be treated. However, it is preferable to use only ammonia as in the present invention because nitrogen oxides are not generated.

  The phrase “substantially consisting only of ammonia” here means not only containing no gas other than ammonia, but also means containing an inevitable impurity gas. Specifically, for example, in a semiconductor manufacturing factory that manufactures a GaN substrate, an impurity gas derived from Ga may be contained in the ammonia gas that is discharged. The description “becomes” is not intended to exclude such a case.

  ADVANTAGE OF THE INVENTION According to this invention, it is an element which decomposes | disassembles the gas discharged | emitted, for example from a waste water treatment facility, a chemical factory, etc., Comprising: A thing excellent in decomposition | disassembly efficiency, a response characteristic, and durability can be provided.

It is an electron micrograph which shows the external appearance structure of the metal porous body which concerns on this invention. It is a schematic diagram regarding the cross-sectional structure of the vicinity of the knot part of the metal porous body which concerns on this invention. It is a schematic diagram which shows an example of the gas decomposition element which is this invention. It is a schematic diagram which shows an example of the conventional gas decomposition | disassembly element.

  Regarding the gas decomposition element according to the present invention, materials required in the production process, treatments and procedures using them will be described in order.

(Resin porous body)
As the three-dimensional network resin, a resin foam, a nonwoven fabric, a felt, a woven fabric, or the like is used, but these may be used in combination as necessary. Moreover, although it does not specifically limit as a raw material, The thing which can be removed by incineration after plating a metal is preferable. Further, in handling the porous resin body, in particular, a sheet-like material is preferably a flexible material because it breaks when the rigidity is high.

  In the present invention, it is preferable to use a resin foam as the three-dimensional network resin. The resin foam is not particularly limited as long as it is porous, and examples thereof include urethane foam, foamed styrene, and melamine foam. Among these, urethane foam is preferable from the viewpoint of particularly high porosity. The thickness, porosity, and average pore diameter of the foamed resin are not limited, and can be appropriately set according to the application.

(Conductive treatment)
The method for conducting the three-dimensional network resin is not particularly limited as long as the conductive coating layer can be provided on the surface of the resin porous body. Examples of the material forming the conductive coating layer include metals such as nickel, titanium, and stainless steel, amorphous carbon such as carbon black, and carbon powder such as graphite. Among these, carbon powder is particularly preferable, and carbon black is more preferable. In addition, when amorphous carbon other than a metal is used, the said conductive coating layer is also removed in the removal process of the resin porous body mentioned later.

  As specific examples of the conductive treatment, for example, when nickel is used, an electroless plating treatment, a sputtering treatment, and the like are preferable. In addition, when using a material such as titanium, stainless steel or the like, carbon black, graphite, or the like, it is preferable to apply a mixture obtained by adding a binder to the fine powder of these materials to the surface of the resin porous body. Can be mentioned.

  As the electroless plating treatment using nickel, for example, the resin porous body may be immersed in a known electroless nickel plating bath such as a nickel sulfate aqueous solution containing sodium hypophosphite as a reducing agent. If necessary, the resin porous body may be immersed in an activation liquid containing a trace amount of palladium ions (cleaning liquid manufactured by Kanigen Co., Ltd.) or the like before immersion in the plating bath.

  As a sputtering process using nickel, for example, a resin porous body is attached to a substrate holder, and then ionization is performed by applying a DC voltage between the holder and the target (nickel) while introducing an inert gas. The inert gas thus made may collide with nickel, and the blown-off nickel particles may be deposited on the surface of the resin porous body.

The conductive coating layer only needs to be continuously formed on the surface of the porous resin body, and the amount per unit area is not limited and is usually about 0.1 g / m ² or more and 20 g / m ² or less, preferably 0.5 g / m ^2. m ² may be set to or higher than 5 g / ^{m 2} or less.

(Nickel plating process)
The nickel plating step is not particularly limited as long as it is a step of performing nickel plating by a known plating method, but it is preferable to use an electroplating method. If the thickness of the plating film is increased by the above electroless plating process and / or sputtering process, the electroplating process is not necessary, but it is not preferable from the viewpoint of productivity and cost. For this reason, it is preferable to employ a method of forming a nickel plating layer by an electroplating method after first conducting the step of conducting the conductive treatment of the resin porous body as described above.

  The electro nickel plating process may be performed according to a conventional method. For example, a known or commercially available plating bath can be used, and examples thereof include a watt bath, a chloride bath, a sulfamic acid bath, and the like. A resin porous body having a conductive coating layer formed on the surface by electroless plating or sputtering is immersed in a plating bath, and the resin porous body is connected to the cathode, and the nickel counter electrode is connected to the anode, and direct current or pulse is intermittently connected. By applying an electric current, an electric nickel plating coating can be further formed on the conductive coating layer.

The electric nickel plating layer only needs to be formed on the conductive coating layer to such an extent that the conductive coating layer is not exposed. The basis weight is not limited, and is usually about 100 g / m ² or more and 600 g / m ² or less, preferably 200 g / ^{m 2} may be set to an extent more than 500 g / ^{m 2} or less.

(First heat treatment step for removing the three-dimensional network resin)
The first heat treatment condition for removing the three-dimensional network resin is preferably heat treatment at 600 ° C. or higher and 800 ° C. or lower in an oxidizing atmosphere such as air in a stainless steel muffle. If the heat treatment temperature is lower than 600 ° C., the three-dimensional network resin cannot be completely removed, and if it exceeds 800 ° C., it becomes brittle and the strength is greatly reduced, so that it cannot withstand practical use.

(Chrome plating process)
The chrome plating step is not particularly limited as long as it is a step of performing chrome plating by a known plating method, but it is preferable to use an electroplating method. If the thickness of the plating film is increased by sputtering, there is no need for electroplating, but it is not preferable from the viewpoint of productivity and cost.

The electrochrome plating process may be performed according to a conventional method. For example, a known or commercially available plating bath can be used, and examples thereof include a hexavalent chromium bath and a trivalent chromium bath. The nickel porous body is immersed in a chromium plating solution, connected to a cathode, a chromium counter electrode plate is connected to the anode, and direct current or pulsed intermittent current is applied to further form an electrochrome plating coating on the nickel layer. be able to. Basis weight of the electric chromium plating layer is not limited, usually 10 g / ^{m 2} or more 600 g / ^{m 2} degree or less, preferably may be set to the degree 50 g / ^{m 2} or more 300 g / ^{m 2} or less.

  In addition, after performing a conductive treatment on the three-dimensional network resin, it is preferable to perform plating in the order of nickel and chromium. If the chrome plating is first applied to the conductive three-dimensional network resin, the chrome plating layer cannot be formed to the inside of the skeleton. This is due to the fact that the conductivity of the three-dimensional network resin is only reduced to less than 1 S / m, and the uniform electrodeposition of chrome plating is extremely poor compared to nickel plating. . On the other hand, the conductivity of the three-dimensional network resin that has been subjected to the conductive treatment and the nickel plating is improved to 1 S / m or more, and then the chromium plating layer can be formed up to the inside of the skeleton by applying the chromium plating.

(Second heat treatment step for alloying nickel layer and chromium layer)
The order of steps after the conductive treatment is as follows: “First plating step for applying Ni plating, first heat treatment step for removing three-dimensional network resin, second plating step for applying Cr plating on Ni layer, Ni layer In the order of “second heat treatment step for alloying Cr layer and Cr layer”, the second heat treatment condition for alloying the nickel layer and the chromium layer is a reducing gas such as CO or H ₂ in the stainless steel muffle. Heat treatment is preferably performed at 800 ° C. to 1100 ° C. in an atmosphere. When the heat treatment temperature is less than 800 ° C., it takes a long time to reduce the nickel oxidized in the first heat treatment step and to alloy the nickel layer and the chromium layer. In the case of exceeding, the furnace body of the heat treatment furnace is damaged in a short period of time. Therefore, it is preferable to perform heat treatment in the above temperature range.

On the other hand, the order of the steps after the conductive treatment is “a first plating step for performing Ni plating, a second plating step for applying Cr plating on the Ni layer, a first heat treatment step for removing the three-dimensional network resin, In the order of “the second heat treatment step for alloying the Ni layer and the Cr layer”, the second heat treatment condition for alloying the nickel layer and the chromium layer is reduction of CO, H ₂ or the like in the carbon muffle. Heat treatment is preferably performed at 1000 ° C. or higher and 1500 ° C. or lower in a reactive gas atmosphere or an inert gas atmosphere such as N ₂ or Ar. This is because carbon is required to reduce chromium oxidized in the first heat treatment step, and when the heat treatment temperature is less than 1000 ° C., reduction of nickel and chromium oxidized in the first heat treatment step, and It takes a long time to alloy the nickel layer and the chromium layer, which is disadvantageous in cost. If the temperature exceeds 1500 ° C., the furnace body of the heat treatment furnace is damaged in a short period.

  By the above process, it is possible to produce a Ni—Cr alloy porous body having a small chromium concentration variation in the skeleton cross section and having high corrosion resistance even at the cut surface. This is because only a desired amount of Cr to be diffused into the nickel porous body is deposited by plating and then alloyed by heat treatment, so that variation in chromium concentration in the skeleton cross section is reduced.

(Filling process into module container)
The metal porous body that has undergone the second heat treatment step described above is filled into a module container. As the module container, various materials can be used as long as they can withstand the temperature reached by the porous metal body when the gas to be treated is decomposed. For example, silica, quartz glass, alumina, or the like is used as the material. Moreover, as the shape of the module container, a hollow pipe having a cylindrical shape or a quadrangular prism shape is used as appropriate.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to these Examples.

(Conductive treatment of 3D network resin)
Using a 1.5 mm thick polyurethane sheet as a three-dimensional network resin, 100 g of carbon black, which is amorphous carbon having a particle size of 0.01 to 0.2 μm, is added to 0.5 L of a 10% acrylate resin resin solution. An adhesive paint was prepared at this ratio. Next, the porous resin sheet was continuously dipped in the paint, squeezed with a roll, and then dried to conduct a conductive treatment, thereby forming a conductive coating layer on the surface of the three-dimensional network resin.

(Nickel plating process)
Nickel was attached to 300 g / m ² by electroplating on the conductive three-dimensional network resin to form an electroplating layer. As the plating solution, a nickel sulfamate plating solution was used.

(First heat treatment step for removing the three-dimensional network resin)
Next, in order to remove the three-dimensional network-like resin, heat treatment was performed at 700 ° C. in an atmospheric oxidation atmosphere in a stainless steel muffle to obtain a nickel porous body.

(Chrome plating process)
On the nickel porous body, 30 g / m ² , 60 g / m ² , 75 g / m ² , 96 g / m ² and 105 g / m ^{2 were further} deposited. The ratio of Cr corresponds to 10 wt%, 20 wt%, 25 wt%, 32 wt% and 35 wt%, respectively, when Ni and Cr are finally alloyed. A trivalent chromium plating solution was used as a plating solution for chromium plating.

(Second heat treatment step for alloying nickel layer and chromium layer)
Subsequently, heat treatment was performed in a stainless steel muffle at 1000 ° C. in an H ₂ gas atmosphere. Through the above-described steps, the Ni—Cr alloy porous body (hereinafter referred to as samples A-1, A-2, A-3, A-4, and A-5, respectively) to be included in the gas decomposition element of the present invention. Was called). In addition, the Ni-Cr alloy porous body of this invention has high corrosion resistance in the cut surface.

(Lamination of porous Ni-Cr metal)
About each of the Ni-Cr alloy porous body of sample A-1, A-2, A-3, A-4, and A-5, thickness was adjusted to 1.1 mm with the roller press. Thereafter, four sheets of 120 mm length × 7 mm width, two sheets of 120 mm length × 6 mm width, and two sheets of 120 mm length × 4 mm width were cut into rectangular sheets. These sheets were laminated in order. The stacking order was 4 mm width-6 mm width-7 mm width-7 mm width-7 mm width-7 mm width-6 mm width-4 mm width in order.

(Create connection part)
Subsequently, two Ni porous bodies having a length of 100 mm and a width of 6 mm were prepared. Two pieces of the sample A-1 were sandwiched with respect to a 10 mm portion at one end, and the sandwiched portion was further crimped. Further, the same was applied to the opposite end of the sample A-1. As described above, connection portions for supplying a current were provided to both ends of the sample A-1. And the nickel ribbon was spot-welded to those connection parts. Similarly, for A-2, A-3, A-4, and A-5, a connection portion was provided and a nickel ribbon was spot welded.

(Insertion into quartz tube)
The laminate of the Ni—Cr porous metal body with the connection portion was inserted into a quartz tube (length: 700 mm) having an outer diameter of 10 mm and an inner diameter of 8 mm. At this time, the nickel ribbon was led out of the quartz tube as a lead terminal. The nickel ribbon functions as a terminal for energization. FIG. 3 shows a state in which the Ni—Cr alloy porous body is inserted into the quartz tube. As shown in FIG. 3, the connection portion is provided at the left end of the laminate of the Ni—Cr metal porous body 14, and the whole is inserted into the quartz tube 14. The nickel ribbon is not shown. The Ni—Cr alloy porous body 14 according to the present invention is inserted into the quartz tube 13, and this Ni—Cr alloy porous body 14 becomes an element for decomposing ammonia.

(Comparative example)
In order to compare with the gas decomposition element of the present invention, a conventional coiled Ni—Cr alloy wire was prepared. The ratio of Cr in the Ni—Cr alloy was adjusted to 25 wt%. This was cut out in a coil shape. In this case, the coil length of the Ni—Cr alloy of the comparative example was adjusted so as to be the same as the weight of the sample A-3. For the coiled Ni—Cr alloy body (sample name: B-1) obtained as described above, lead terminals were welded to both ends and inserted into a quartz tube by the same method as A-1 to A-5. The inserted state is shown in FIG. 4 (the nickel ribbon is not shown). As shown in FIG. 4, a conventional coiled Ni—Cr alloy wire 15 is inserted into the quartz tube 13, and this coiled Ni—Cr alloy wire 15 becomes an element for decomposing ammonia.

<Evaluation>
(Evaluation of decomposition characteristics of ammonia gas)
The decomposition characteristics of the gas to be treated were evaluated for each of the Ni—Cr alloy porous body and the coiled Ni—Cr alloy wire. In the evaluation, a mixed gas of 20 vol% ammonia and 80 vol% nitrogen was used as the gas to be treated, and the flow rate was 0.5 L / min. Therefore, when calculated from the inner diameter of the quartz tube 13, the flow velocity is about 16 cm / second.

(Evaluation method 1)
For each Ni—Cr alloy porous body and coiled Ni—Cr alloy wire, the applied voltage was set to 12 V, and the current passed so that the equilibrium temperature was 900 ° C. was adjusted. Next, the above-mentioned mixed gas was circulated, and the concentration of ammonia discharged from the outlet side of the quartz tube was measured. The result of this measurement was used as the initial characteristic. Next, after maintaining this state for 60 hours, the concentration of ammonia discharged from the outlet side of the quartz tube was measured. This was defined as a 60-hour durability characteristic. The results are shown in Table 1.

  As shown in Table 1, in Sample B-1, before the 60-hour durability characteristics were evaluated, the coiled Ni—Cr alloy wire was melted and could not be measured. In comparison, all of Samples A-1 to A-5 were excellent in the initial characteristics and 60-hour durability characteristics because the ammonia concentration on the outlet side could be 30 ppm or less. However, in Samples A-1, A-2, and A-3, the value of the current passed through the gas decomposition element exceeds 30 A, so that the energy loss is extremely large.

(Evaluation method 2)
About each Ni-Cr alloy porous body, the electric current of 12V / 22.5A was sent, and resistance heat_generation | fever was produced. This state was maintained for 30 minutes to allow the temperature to equilibrate. Next, the above-mentioned mixed gas was circulated, and the concentration of ammonia discharged from the outlet side of the quartz tube was measured. The result of this measurement was used as the initial characteristic. Next, after maintaining this state for 60 hours, the concentration of ammonia discharged from the outlet side of the quartz tube was measured. This was defined as a 60-hour durability characteristic. The results are shown in Table 2.

  As shown in Table 2, since the equilibrium temperature did not become sufficiently high in Sample A-1, the gas decomposition characteristics were not excellent. In Sample B-1, since the shape was coiled, the contact between the ammonia gas and the Ni—Cr alloy was insufficient, so the gas decomposition characteristics were not excellent.

  When Samples A-2 to A-5 were compared with each other, Sample A-3 and Sample A-4 were able to reduce the ammonia concentration to 300 ppm or less in both the initial characteristics and the 60-hour durability characteristics. It was. In Sample A-5, since the Cr content is high, the resistance of the Ni—Cr alloy porous body is high, and the equilibrium temperature reaches 963 ° C. Therefore, in the 60-hour endurance characteristics, it seems that the porous structure of the Ni—Cr metal porous body of the gas decomposition element deteriorates with the passage of time, and sufficient gas decomposition characteristics cannot be obtained. When the sample A-5 was disassembled and investigated, a part of the porous structure was damaged in the central portion of the Ni—Cr alloy porous body. From the above, the proportion of Cr in the Ni—Cr alloy porous body is preferably 25 wt% or more and 32 wt% or less.

  The gas decomposing element of the present invention can decompose a gas to be processed, such as ammonia, which is discharged from a semiconductor manufacturing factory, waste water treatment facility, or the like. The characteristics are excellent in any of decomposition efficiency, response characteristics, and durability. Therefore, the present invention can be used industrially and has great technical significance to the industry.

DESCRIPTION OF SYMBOLS 1 Metal porous body 10 Continuous pore 11 Node part 12 Branch part 12a Outer shell 12b Core part 13 Quartz tube 14 Ni-Cr alloy porous body 15 Coiled Ni-Cr alloy wire

Claims (7)

A gas decomposition element comprising a porous metal body having continuous pores,
The metal porous body has an integrally continuous three-dimensional network structure,
The porous metal body is made of an alloy containing at least Ni and Cr,
A gas decomposition element, wherein a ratio of Cr in the alloy is 25 wt% or more and 32 wt% or less. The gas decomposition element according to claim 1,
A gas decomposition element, wherein a window diameter formed by the skeleton of the metal porous body is 0.2 mm or more and 1.6 mm or less. Using the gas decomposition element according to claim 1 or 2,
The temperature of the porous metal body provided in the gas decomposition element is 800 ° C. or higher,
A method for decomposing ammonia, wherein a gas to be treated containing ammonia is brought into contact with the gas decomposing element. The ammonia decomposing method according to claim 3,
A method for decomposing ammonia, wherein the method of setting the temperature of the porous metal body to 800 ° C. or more is by energizing the porous metal body. The ammonia decomposing method according to claim 3 or 4,
The ammonia decomposition method, wherein the gas to be treated consists essentially of ammonia. It is a manufacturing method of the gas decomposition element according to claim 1 or 2, and the manufacturing method is at least,
(A) a step of conducting a conductive treatment on the three-dimensional network resin;
(B) a first plating step of applying Ni plating to the three-dimensional network resin;
(C) a first heat treatment step for removing the three-dimensional network resin;
(D) a second plating step of applying Cr plating on the Ni layer;
(E) a second heat treatment step of alloying the Ni layer and the Cr layer;
The manufacturing method of the gas decomposition element characterized by including this. It is a manufacturing method of the gas decomposition element according to claim 1 or 2, and the manufacturing method is at least,
(A) a step of conducting a conductive treatment on the three-dimensional network resin;
(B) a first plating step of applying Ni plating to the three-dimensional network resin;
(C) a first heat treatment step for removing the three-dimensional network resin;
(D) Gas generated by heating a Ni porous body that has undergone the first heat treatment step at 950 to 1100 ° C. with a powder containing Cr or a Cr compound and NH ₄ X (X is I, F, Cl, or Br) Heat-treating in,
The manufacturing method of the gas decomposition element characterized by including this.

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