JPH02103861A - Method for manufacturing electrodes for molten carbonate fuel cells - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing an anode for a molten carbonate fuel cell, and in particular to a method for manufacturing an anode made of a nickel-chromium alloy.

[Traditional techniques]

Traditionally, bath-fused carbonate fuel cells have been known to convert the energy of chemical reactions into electrical energy.
A cathode and an anode are arranged with a molten carbonate electrolyte sandwiched between them, and an oxidant gas is supplied to the cathode side, and a fuel gas is supplied to the anode side.

In order for the reaction between gas and carbonate to occur efficiently in the electrode portion, the electrode needs to have a porous structure, and up to now, sintered bodies of nickel powder have been mainly used.

In this case, the cathode on the oxidizing gas side is exposed to the oxidizing atmosphere during battery operation! 7. Since an oxide layer is formed on the coating, sinkling of the nickel particles does not proceed. However, during battery operation, the anode on the fuel gas side is exposed to a reducing atmosphere containing hydrogen, and the surface of the nickel particles maintains a metallic state. Therefore, the electrode tends to sink at a battery operating temperature of 600 to 700°C, and as sinkling progresses, the initial porosity decreases. Furthermore, the electrodes are always subject to clamping pressure when assembled into a battery.
This causes the anode to undergo creep deformation, reducing its initial porosity. Such a decrease in the porosity of the anode results in deterioration of battery performance.

As a method for preventing these, a method of using a material in which a second element is added to nickel is widely used for the anode, and it is known that addition of chromium is particularly effective.

When manufacturing this type of anode, the first method is to prepare an alloy powder of nickel and a second element, mold this powder, and sinter it. However, since these alloy powders are generally manufactured by an atomization method, the particles are not spherical, and when sintered, it is difficult to obtain particles with high porosity. In addition, since the commonly used nickel powder for electrode materials is produced by the carbonyl method, it is easy to obtain particles with an average particle size of several micrometers or less, whereas with the atomization method, coarse particles with an average particle size of several tens of micrometers or more are produced. The yield was poor to obtain powder of several micrometers or less.

The second method is to prepare a porous body such as nickel foam or sintered nickel powder in advance, impregnate it with a second element in the form of a metal salt, and then chemically treat it with reduction heat. The manufacturing process is complicated, and when a large amount of the second element is added, multiple impregnation treatments are required, resulting in poor industrial efficiency.

As a third method, the method of mixing the base nickel powder and the powder of the second element, molding and sintering this is the simplest and easiest method compared to the above two methods. However, in this method, segregation of the second element component is unavoidable, and there is a possibility that some parts do not contain the second element, and due to segregation, local alloying reaction progresses during sintering, and the sintering reaction The accompanying shrinkage became uneven, sometimes resulting in cracks and deformation. Furthermore, even if no structural defects occur, long-term heat treatment at high temperatures is required to reduce the segregation of the second element, and in this case, the porosity of the sintered body may decrease. I don't like it.

[Problem to be solved by the invention]

As mentioned above, conventional methods still have various problems and no satisfactory method has been found.

The present invention aims to solve the problems of the conventional method and to obtain a nickel-chromium alloy anode by a simple method.

[Means to solve the problem]

In order to achieve the above object, the inventors of the present invention have made extensive studies and found that in the production of nickel-chromium alloy anodes, ultrafine chromium particles are produced using chromium, which is the second element, in the form of a pure metal and by an evaporation method. The present invention was completed based on the discovery that by using the above-mentioned anode, it is possible to produce a uniformly dispersed anode without segregation.

That is, the present invention is characterized in that, in a method for manufacturing a nickel-chromium alloy anode for a molten carbonate fuel cell, nickel powder and ultrafine chromium particles manufactured by an evaporation method are mixed, molded, and sintered. This invention relates to a method for manufacturing a nickel-chromium alloy anode.

Next, the present invention will be explained in more detail.

In the present invention, chromium, which is the second element, is added in the form of a pure metal, and its feature is that ultrafine chromium particles produced by an evaporation method are used as the second element. By the way, the evaporation method heats the solid material to vaporize it, cools it in a refrigerant, and condenses it into ultrafine particles.In the case of chromium, particles with an average particle diameter of 50 OA are obtained. The ultrafine metal particles obtained here have a very small particle size, so they are not suitable as a sintering material alone, but they are effective as a material for adding a second element.

That is, since the obtained ultrafine chromium particles have a particle size two orders of magnitude smaller than the base nickel powder, they can easily be uniformly dispersed between the nickel powders and do not segregate to a large extent.

In addition, the ultrafine particles easily diffuse into nickel during sintering heat treatment, and most of the added amount is alloyed with nickel.
It is sufficient to add only an amount corresponding to the desired alloy composition.

In addition, in the case of the present invention, although a pure metal element is used as the second element additive, the dispersion effect is equivalent to that of metal salts, and moreover, the desired dispersion effect can be achieved by -degree sintering treatment. An alloy sintered body containing two element components can be obtained.

In order to further improve the diffusion, it is necessary to weigh and mix a predetermined amount of base nickel powder and chromium ultrafine particles at the raw material stage, and then preliminarily heat-treat the mixture at a temperature lower than the sintering temperature during electrode manufacturing. It is possible to better diffuse chromium into nickel. If a sintered body is produced using the powder after this preliminary heat treatment as a raw material, there is an advantage that the distribution of chromium in the sintered body can be made more uniform.

[For production]

The main driving force for the sintering reaction is the surface energy of the powder particles. Mass transfer occurs to reduce this energy,
Sintering proceeds such that the surface area of the powder particles is reduced. In the present invention, the material to be sintered is a mixture of two types of metal powders, and as the material transfers, alloying of the two metals progresses. That is, the base nickel powder forms a porous body structure that determines the physical properties of the porous body by mutual fusion, and at that time, it is alloyed with the ultrafine chromium particles dispersed in various parts. In this case, a similar reaction occurs even if micron-order chromium powder is used instead of ultrafine chromium particles, but ultrafine particles have a higher particle surface energy and are less dispersible among nickel powders. The sintering reaction progresses easily.

The method of the present invention is particularly effective as a method for producing porous alloy bodies such as electrodes for fuel cells. In other words, when simply producing a dense alloy sintered body, the sintering temperature must be increased,
Nickel and chromium can be easily alloyed by applying pressure during molding or sintering to bring the particles into close contact with each other, but when producing porous sintered bodies, it is necessary to apply high sintering temperatures and pressure. is undesirable because it reduces porosity. However, according to the present invention, nickel and chrome alloy can be formed without reducing the porosity.

〔Example〕

The present invention will be explained below based on Examples, but the present invention is not limited to these Examples.

Example 1 Ultrafine chromium particles (with an average particle size of 500 A) produced by evaporation in gas using nickel powder (Type 255 manufactured by INC0) with an average particle size of 2.2 to 2.8 μm as a base material and a 90f1 second element additive ( (manufactured by vacuum metallurgy) 1021
Polyvinyl butyral 'i8 F as an organic binder
, hydroxypurmethylcellulose 'e2 as plasticizer
F, 1:1 weight ratio of ethanol and trichlene as solvents
A slurry was prepared by weighing 802 pieces of mixed solutions and kneading them in a ball mill for 100 hours.

This slurry was coated onto a reinforcing nickel wire mesh (wire diameter o, 2 mm, 20 mesh) using a full doctor blade device and formed into a thin plate.The formed product after drying was heated to 950°C in a vacuum.
The anode was heated and held for 1 hour for sintering to obtain a 90 square anode with a thickness α81+1111. A test piece of about 1 f was taken from this electrode and its porosity including the reinforcing material was measured, and it showed a value of 64%.

Example 2 The same nickel powder and ultrafine chromium particles used in Example 1 were weighed so that their total weight was 90% by weight and 10% by weight, respectively. Ethanol corresponding to 50 parts by weight based on the total powder weight of 00 parts by weight and the above two yuzu metal powders were mixed in a ball mill for 100 hours. After drying the mixed slurry, it is placed in an aluminium crucible and subjected to preliminary heat treatment in a vacuum.
The mixture was heated and maintained at 650°C for 4 hours to diffuse chromium into the nickel. After crushing the powder after preliminary heat treatment in a mortar,
5. Use a second sieve to remove coarse particles.

The powder 1001 after the preliminary heat treatment prepared in this way was added with the same type and amount of organic binder as in Example 1, 0]' plasticizer,
A solvent was added, and the mixture was mixed and molded under the same conditions as in Example 1.

The dried molded body was heated and held at 1020° C. for 1 hour in a vacuum to sinter it to obtain an anode having the same shape as in Example 1. In addition, when the porosity was measured in the same manner as in Example 1, it was found that 6
It showed a porosity of 5%.

As a comparative example base material, 90t of the same nickel powder as used in the example was used.
1 Carom powder (manufactured by Fuchiyo Metal Office) 102 with an average particle size of 2 μm prepared by a pulverization method as a second element additive, the same type and the same amount of organic binder, plasticizer, and solvent as in the example. It was mixed and molded under certain conditions.

The dried molded body was heated and held at 1080° C. for 1 hour in a vacuum to sinter it to obtain an anode having the same shape as in the example. In addition, when the porosity was measured in the same manner as in the example, it was found to be 59%.
showed a porosity of

2 and [Comparison of Example 1 and Comparative Example] Δ Fig. 1-A, Fig. 2-A, and Fig. 3-A are the artificial fracture surfaces of the 0-electrode for Examples 1 and 2 and Comparative Example, respectively. These are scanning electron micrographs showing the particle structures of A characteristic X-ray photograph of nickel and chromium of the part is shown.

As can be seen from these drawings, Comparative Example 1 has approximately 20μ
In contrast, in Examples 1 and 2, chromium is generally uniformly distributed, although some segregation is observed.

Further, the segregation of chromium is smaller in Example 2 than in Example 1.

Of the artificially fractured surfaces of each electrode shown in the drawings, a quantitative analysis of chromium was performed using EPMA on a portion where chromium was thought to be uniformly distributed without segregation. The results are shown in Table 1. In addition, the above-mentioned sintering temperature and porosity are also listed in the table for reference.

The chromium concentration is higher in the order of Example 2, Example 1, and Comparative Example,
In the case of Example 2, the chromium concentration was equivalent to 90% of the added amount.

In the case of Comparative Example 1, the sintering temperature was the highest among the three examples in order to promote alloying of chromium and nickel, but the chromium concentration was the lowest. Furthermore, due to the high sintering temperature, the porosity was the lowest at 60% or less.

As described above, according to the present invention, an anode for a molten carbonate fuel cell made of a porous nickel-chromium alloy can be easily manufactured.

Furthermore, the method of the present invention can be applied to the production of porous bodies made of alloys other than nickel-chromium alloys.

〔Effect of the invention〕

According to the method for manufacturing a nickel-chromium alloy anode of the present invention, ultrafine chromium particles are uniformly dispersed in nickel powder without segregation, and the manufacturing process is also different from sintering nickel powder alone. A nickel-chromium alloy porous body of any composition can be easily manufactured using a similar process.

[Brief explanation of the drawing]

Figure 1-A, Figure 2-A, and Figure 5-A are, respectively,
These are electron micrographs showing the particle structures on the artificially fractured surfaces of the electrodes of Example 1.2 and Comparative Example.
The -mouth view and the 5th -mouth view are N1 characteristic X-ray photographs of the respective A view portions, and the 1st-No. view and the 2nd-No.
Figure 5-C shows the characteristic X of Cr in the part shown in Figure A, respectively.
It is a line photograph.

Claims (1)

[Claims] 1. A method for producing a nickel-chromium alloy anode for a molten carbonate fuel cell, which includes mixing nickel powder and ultrafine chromium particles produced by an evaporation method, and then molding and sintering the mixture. A method for producing a nickel-chromium alloy anode characterized by: 2. The mixture of the nickel powder and ultrafine chromium particles,
2. The method for producing a nickel-chromium alloy anode according to claim 1, wherein the anode is heat-treated at a temperature lower than the sintering temperature of the electrode, and then shaped and sintered.