JPS63171803A - Production of porous laminated and sintered body - Google Patents

Abstract

PURPOSE:To produce the titled sintered body consisting of double-layered structure having high strength and different pore characteristics by mixing metal powder with the fibers which are consumedly heating and having different sizes to form a sheet-shaped mixture, laminating the mixtures and subjecting the laminate to a heating treatment to consume the fibers and to sinter the metal powder. CONSTITUTION:The sheet-shaped mixture is formed by mixing the metal powder and/or metallic fibers with the consumable fibers (natural fibers, carbon fibers, etc.) which are consumed by heating. (1) The metal powder and/or metallic fibers having different physical properties or sizes are used, or (2) the consumable fibers or different sizes are used, or (3) the materials having different compounding ratios of the consumable fibers and the metal powder and/or metallic fibers are used at this time. Plural sheets of such sheet-shaped mixtures are laminated and are subjected to the heating treatment by which the consumable fibers are consumed and the metal powder and metallic fibers are sintered. The porous laminated and sintered body having the uniform quality, high porosity and excellent strength is thereby produced with high productivity at one time of the heating treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a porous laminated sintered body that exhibits excellent performance as a catalyst, a filter, an electrode for a fuel cell, and the like.

[Prior Art] Porous sintered bodies applied to the above-mentioned uses are manufactured using fine metal powder as a raw material by a pressureless sintering method, a slurry molding method, a roll molding method, or the like.

The pressureless sintering method involves filling a mold with fine metal powder, smoothing the surface, and then sintering it to join the fine metal powders together with appropriate gaps left. For example, if fine powder such as nickel powder or iron powder obtained by the carbonyl method is used, a highly porous metal sintered body with a porosity exceeding O, a can be easily obtained. In this case, when sintering is performed in an oxidizing atmosphere, the metal fine powder is oxidized and then sintered, resulting in a porous metal oxide sintered body. However, this method has the problem that productivity cannot be increased because each process is a batch method, and it is difficult to obtain shapes other than flat plates (for example, cylindrical shapes), which severely limits the field of use. .

Next, the slurry molding method involves blending fine metal powder with a small amount of binder (polyvinyl alcohol, methyl cellulose, etc.), and then adding condensate or other solvents with auxiliary agents such as antifoaming agents as necessary to form a slurry. This is a method in which the solvent is volatilized and removed after forming into a tape shape with a doctor blade, the binder etc. is removed by pre-firing, and the partial fusion of fine metal powders or oxides is partially fused together by main baking, and continuous production is possible. Since the system can be adopted, productivity is high and products of stable quality can be obtained. However, this method has the disadvantage that the metal fine powders begin to adhere to each other as early as the forming process, resulting in a decrease in porosity, which is at most 0.6 in the sintered state.
In order to compensate for the lack of porosity, which is only a moderate degree of porosity, fine powders (carbon, plastics, cellulose, etc.) and fibers that disappear during heat treatment during sintering are mixed into the raw material slurry. Although methods have also been proposed,
Even if this method is adopted, it is not possible to obtain the high porosity that is the difference in pressureless sintering properties, but rather, the strength of the sintered body deteriorates significantly due to excessive addition, leading to problems such as cracking.

The roll forming method is basically the same as the slurry forming method mentioned above, and although it has the advantage of being able to perform continuous production, the adhesion between fine metal powders or their oxides is more difficult than in the slurry forming method. Further, the porosity cannot be sufficiently increased.

By the way, the above porous sintered body has almost uniform pore characteristics when viewed in the cross-sectional direction, but for the following reasons,
A sintered body having a structure in which a plurality of porous layers having different pore characteristics are stacked is sometimes required.

For example, when used as a catalyst, its carrier, or a filter, the idea is to combine a sintered layer with relatively low strength due to high porosity and a sintered layer with relatively high strength due to low porosity. When a laminated structure is adopted, the latter sintered layer serves to strengthen the former sintered layer, and as a whole, it is possible to exhibit sufficient strength for practical use. In addition, in the case of nickel-based porous sintered bodies used as electrodes for molten carbonate fuel cells, it is necessary to appropriately balance gas diffusion and molten carbonate penetration to ensure sufficient contact between gas and liquid. However, in order to ensure sufficient gas diffusion, pores with relatively large diameters are preferable, while pores with small diameters are advantageous for the penetration of molten carbonate due to the capillary principle. In order to satisfy both of these requirements, a sintered body with a laminated structure combining materials with different pore characteristics is advantageous.

However, when trying to manufacture a porous sintered body with such a laminated structure using conventional methods, no matter which method is used, ■
First, a plurality of porous sintered bodies with different pore characteristics are manufactured separately, and then these sintered bodies are stacked and sintered again to join them together, or After producing the sintered body, one of the methods of laminating the sintering raw materials on the sintered body using the method described above and sintering must be adopted, and the sintering process must be divided into at least two stages. It makes productivity even lower because it has to be done.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a multilayer structure with high strength and high porosity, and different pore characteristics. The present invention aims to provide a method capable of manufacturing porous laminated sintered bodies with good productivity.

[Means for Solving the Problems] The structure of the method of the present invention that has achieved the above-mentioned object is that a thin plate-like material obtained by inserting metal powder and/or metal fibers into fugitive fibers that can be dissipated by heating. It is a mixed material, and ■ using metal powder and/or metal fibers with different physical properties or sizes, ■ using fugitive fibers with different sizes, or ■ fugitive fibers and metal powder and/or metal fibers. A plurality of sheets of the thin plate shape obtained by either using materials with different blending ratios of
``The gist is that the mixed paper sheets are laminated, the laminated body is then heat-treated to eliminate the fugitive fibers, and the metal powder and/or metal fibers or their oxides are sintered with each other. be.

[Function] In the present invention, metal powder is added together with a coagulating fixing agent such as polyacrylamide into an aqueous dispersion of fugitive fibers that can be dissipated by heating, such as organic fibers such as bulbs, natural fibers, and synthetic fibers, or carbon fibers. In addition, paper is made with the metal powder adsorbed to fugitive fibers to obtain a mixed paper, or metal fibers and fugitive fibers are mixed to obtain a mixed paper, and these mixed paper is laminated and heated. By processing, the fugitive fibers are eliminated and the metal powder and/or metal fibers mixed with the fugitive fibers are sintered and integrated, or the metal powder and/or metal fibers are oxidized and sintered and integrated. At the same time, the laminated interfaces are also sintered and joined to integrate, leaving the portion where the fugitive fibers were present as voids, thereby obtaining a porous metal (or metal oxide) laminated sintered body.

In this case, the porosity and pore characteristics of each layer of the sintered body to be laminated and formed are determined by the physical properties of the metal powder and/or metal fibers (especially melting point, specific surface area, etc.) It can be freely adjusted by changing the size (diameter and length), (1) the size of the fugitive fiber, or (2) the blending ratio of the fugitive fiber and the metal powder and/or metal fiber.

Therefore, by adjusting the conditions ① to ② above in the paper mixing process, a mixed paper material that provides porosity and pore characteristics according to the purpose is produced, and if these are laminated and heat treated, the porosity and pore characteristics A porous metal (or metal oxide) laminated sintered body in which two or more porous layers with different
It can be obtained by multiple heat treatments. Moreover, since each porous layer is obtained by eliminating fugitive fibers from the respective mixed paper sheets in a uniform mixed paper state, each layer has uniform porosity and pore characteristics, and metal powder and Or the metal fibers are bonded to each other three-dimensionally by sintering, resulting in extremely high strength. If the sintering is performed in a reducing atmosphere, a porous metal laminate sintered body can be obtained, and if the sintering is performed in an oxidizing atmosphere, a porous metal oxide laminated sintered body can be obtained.

The fugitive fibers used in the present invention are not limited to any type as long as they can be burnt out by heat treatment as described above, including various natural fibers such as cotton, linen, and wool, regenerated cellulose fibers, nylon, Various synthetic fibers such as polyester, carbon fibers, and even bulbs can all be used, but vegetable natural fibers and bulbs are most preferred for efficiently fixing metal powder and metal fibers.

The production of mixed paper does not require any particularly special technology, and can be carried out in accordance with conventionally commonly used manufacturing methods for paper, fiber boards, etc. In this case, metal powder is used as the raw material. In some cases, it is desirable to use a polymer fixing agent such as polyacrylamide in combination to increase the fixation rate on fugitive fibers.

In the present invention, the two types or 311 or more mixed paper sheets obtained in this way are individually dried to remove moisture, and then stacked or piled up and dried simultaneously, and then heat-treated to eliminate the The method of heat treatment is the most common method, although it does not limit the present invention. An example is as follows.

■ A method in which the mixed volume footwear is heated in an oxidizing gas atmosphere to burn and eliminate fugitive fibers, and then the treatment atmosphere is switched to a reducing gas to reduce and sinter the metal oxides produced in the combustion process.

This method is particularly effective when producing a porous metal laminate sintered body using a metal whose oxide is easily reduced by a reducing gas such as hydrogen (e.g., nickel).

In this case, if the heat treatment atmosphere for sintering is kept oxidizing, a porous metal oxide laminated sintered body can be obtained.

■The mixed paper counterfeit is heated in a CO gas atmosphere or in a gas atmosphere containing CO to thermally decompose the fugitive fibers and remove the remaining carbon by the reaction (C+ CO2→2CO), and then remove the atmospheric gas. A method of switching to a reducing gas (mainly hydrogen) and sintering while reducing trace amounts of metal oxides generated during the disappearance process of fugitive fibers.

Compared to method (2) above, this method is less likely to cause oxidation of the metal during the process of disappearance of the fugitive fibers, so it is suitable for obtaining a metallic porous laminated sintered body using easily oxidized metal powder or metal fibers. This is a suitable method.

In carrying out the method (2) above, heat treatment is performed in a hydrogen atmosphere to thermally decompose the fugitive fibers and [C+ 2 Hz
It seems possible to proceed with the removal of residual carbon using the reaction [-C)I4], but in this method, the carbon generated from the thermal decomposition remains in a skeleton shape, resulting in metal powder and Or, since the sintering of the metal fibers is inhibited, the sintered body becomes extremely brittle and becomes impractical.

Also, by supplying water vapor into the heating atmosphere [C+H20=
It is possible to remove residual carbon and reduce metal oxides at the same time by causing a reaction of [CO + H2], but in reality, the removal of residual carbon is insufficient and the sintered body becomes brittle. becomes. For the same purpose, the heating atmosphere is [CO2 + H2] (7) mixed gas, and CO2
A method of simultaneously exerting the decarburization effect and the reduction effect by H2 was also attempted, but the residual carbon was still insufficiently removed, making sintering difficult, and the strength requirements could not be met.

The reason for this is that when using water vapor [C+H20=CO
+H2], when using a mixed gas of CO2 and H2 (7) [C02+ H2-4CO+ H20] 17) The CO produced by each reaction is decarburized by CO2 [C+C
It is thought that this is because it inhibits the progress of [O2, -2CO].

However, when a mixed gas containing CO3 and a small amount of water vapor is used, the decarburization reaction proceeds efficiently and a sintered body with excellent strength can be obtained.

In the case of manufacturing a metal oxide-based porous laminated sintered body, there is no need to suppress metal oxidation in the process of eliminating fugitive fibers, so there is no need to pay special consideration to the atmospheric gas. , it is sufficient to supply an oxidizing gas (usually air) throughout the entire process from dissipation to sintering.

The temperature for vanishing and sintering varies depending on the type of metal powder and/or metal fiber (especially melting point, etc.), or whether the desired sintered body is a metal or a metal oxide. Although it cannot be specified uniformly, for example, when nickel is used as the metal, the temperature when the fugitive fiber disappears is 400 to aOO℃, and the preferable temperature during sintering is 800 to 800℃ when obtaining a porous metal laminate molded body. 1000°C, when obtaining a porous metal oxide laminate molded product: 1000 to 12
It is 00℃. Note that if the temperature during sintering is low, sintering will be insufficient and sufficient strength will not be obtained, while if the sintering temperature is too high, oversintering will occur and the porosity will decrease, making the features of the present invention effective. It becomes impossible to make use of it.

Further, during sintering, in order to increase the adhesion of the laminated interface and to prevent the laminated product from warping, it is preferable to sandwich it between high-melting point porous ceramic plates or the like and press it lightly.

Various metal powders and metal fibers are used in the present invention depending on the purpose, but for catalysts or catalyst supports, nickel, nickel-chromium alloy, stainless steel, iron-chromium alloy, etc. Examples of materials for metal filters include stainless steel, and materials for fuel cell electrodes (or substrates) include nickel, nickel-chromium alloys, nickel-cobalt alloys, and the like.

Moreover, this sintered body can not only be made into any shape or size such as a flat plate, curved plate, or cylinder by devising the papermaking method or the lamination method, but also can be cut or sized before or after sintering. It can be changed freely through deformation processing.

[Examples] Example 1 The following two types of nickel powder-bulb mixed paper sheets (all having a wall thickness of approximately 1.0 mm) were prepared.

(a) Fine nickel powder (manufactured by Inco, Carbonyl Ni-255) with an average particle diameter of about 3 μm and wood bulbs with a diameter of 10 to 20 μm were mixed and dried in a weight ratio of 7 to 3.

(b) Nickel powder with an average particle size of 15 μm and a diameter of 10-2
0 μm wood bulbs were mixed and dried at a weight ratio of 765 for the former and 2.5 for the latter.

Layer the above two sheets of mixed paper and press (20 g/
cm') L/After being held between porous ceramic plates,
Set this in a tube furnace and supply CO2 gas.
After raising the temperature to 000° C. (required time: 3 hours), the supply gas was changed to hydrogen, and the same temperature was maintained for 30 minutes.

In the obtained sintered body, the porosity of the part made from the mixed paper material 1 (a) was 0.72 and the average pore diameter was 4.9 μm, while the porosity of the part made from the mixed paper material (b) was 0.72 and the average pore diameter was 4.9 μm. degree is 0
．． 64, and the average pore diameter was 8.8 μm.

The porosity of the laminated sintered body as a whole was 0.67, and the average pore diameter was 6.0 μm, which were approximately average values.

When we observed the layer boundaries of this layered sintered body using a scanning electron microscope, we found that not only were the layers sintered successfully leaving a three-dimensional space, but the layer interfaces were also strongly bonded and integrated. It was confirmed that there is. In addition, the strength of this laminated sintered body was extremely good and had no practical problems.

[Effects of the Invention] The present invention is configured as described above, and a porous laminated sintered body that is homogeneous, has high porosity, and has excellent strength can be manufactured with high productivity by only one heat treatment. became. This laminated sintered body exhibits its excellent performance to the fullest when used in the following applications.

■As a catalyst or its carrier.

It is known that porous metal (or metal oxide) sintered bodies can be used as catalysts in gas phase reactions or as catalyst carriers, but the laminated sintered bodies of the present invention have high porosity. Not only can it exhibit a high level of catalytic activity, but it also has extremely high mechanical strength because it is reinforced by stacking porous layers with different porosity.

■As a filter.

The porosity and pore diameter can be adjusted freely by changing the size of the raw material for paper mixing, and it can be applied to a wide range of applications as a furnace material. Moreover, since it is reinforced with a multi-layer structure, it can be used for vacuum filtration with a high degree of vacuum without any problems.

■For example, when used as an electrode for a molten carbonate fuel cell, the side in contact with the molten carbonate should have a pore layer that is advantageous for salt penetration, and the side in contact with the gas should have larger pores that are advantageous for gas diffusion. layer, which significantly contributes to improving the performance of fuel cells. Furthermore, as the strength of the electrode is improved, the life of the battery can also be extended.

Claims (1)

[Claims] A thin plate-like mixed paper product obtained by incorporating metal powder and/or metal fibers into fugitive fibers that can be burnt out by heating, comprising: (1) metal powders and metal powders having different physical properties or sizes; (2) Use fugitive fibers of different sizes; (3) Use materials with different blending ratios of fugitive fibers and metal powder and/or metal fibers. A plurality of the obtained thin plate-like mixed paper sheets are laminated, and then the laminated body is heat-treated to eliminate the fugitive fibers, and the metal powder and/or metal fibers or their oxides are sintered with each other. A method for producing a porous laminate molded article, characterized in that: