JP2003173792A - CORROSION-RESISTANT Ni-GROUP ALLOY SEPARATOR BOARD FOR SOLID POLYMER FUEL CELL WITH ENOUGH STRENGTH TO ALLOW THINNING - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a corrosion-resistant Ni-group alloy separator board for a solid polymer fuel cell with enough strength to allow thinning. <P>SOLUTION: The separator board for a solid polymer fuel cell made by piling, pressure-welding and assembling a plurality of single generating modules of a structure in which a separator board with a fuel gas flow path formed in contact with, and in a state of pinching, an anode on one side face of a solid polymer electrolyte membrane is arranged and another with an oxidizing gas flow path formed in contact with, and in a state pinching, a cathode on the other side face is composed of a Ni-group alloy with a composition containing in mass percent Cr by 40 to 48%, Mo and/or W by 0.1 to 2%, B by 0.01 to 1%, and the rest being Ni and inevitable impurities as well as with a constitution of metal boride distributed in dispersion on a substrate of austenite. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a high strength,
Also, the present invention relates to a corrosion-resistant Ni-based alloy separator plate material of a polymer electrolyte fuel cell (hereinafter, simply referred to as a fuel cell) which is excellent in corrosion resistance and therefore enables thinning indispensable for weight reduction and size reduction of a fuel cell. . 2. Description of the Related Art Conventionally, in general, the above-mentioned fuel cell is shown in FIGS.
As shown in the above, a single power generation module called a single cell has a structure in which a plurality of single power generation modules are stacked and pressed and assembled, and the single cell is sandwiched on one side of a solid polymer electrolyte membrane with an anode (hydrogen electrode) interposed therebetween. A separator plate is in contact with the separator, and the other side of the solid polymer electrolyte membrane is also in contact with a separator plate across a cathode (an oxygen electrode or an air electrode). It is well known that a fuel gas passage is formed on the contact surface, and an oxidizing gas passage is formed on the contact surface with the cathode. In the above fuel cell, a hydrogen gas at about 80 ° C. normally flows through a fuel gas flow path formed on the anode side of the separator plate, and a reaction gas of the fuel cell at about 80 ° C. flows through the oxidizing gas flow path on the cathode side. It is also known that a power generation function is exhibited by flowing a mixed gas of steam, which is a product, and the atmosphere. Furthermore, as described above, the cathode contact surface of the fuel cell separator plate is
The cathode is exposed to an oxidizing gas flow of a mixed gas of steam and air at about 80 ° C. When an oxide film is formed on the cathode contact surface, the contact surface conductivity is significantly reduced, and the battery Various materials having excellent corrosion resistance are used for forming the separator plate material because it causes deterioration of the function. Among such materials, a material having excellent corrosion resistance is referred to as a mass% (hereinafter,% Indicates mass%), and C
r: 40 to 48%, Mo and / or W: 0.1 to 2
%, And the austenitic single-phase Ni-based alloy having a composition consisting of Ni and inevitable impurities is attracting attention, and a separator plate material for a fuel cell formed of this Ni-based alloy has been proposed. On the other hand, there has been a strong demand for lighter and smaller fuel cells in recent years, and with this, there has been a strong demand for thinner separator plates, which are structural members of the fuel cells. I have. However, as described above, the fuel cell is put into practical use in a state where it is clamped and pressed at a pressure of usually about 2 to 3 MPa for the purpose of lowering the contact resistance between the single cells, that is, ensuring good contact surface conduction. Therefore, in the case of the conventional Ni-based alloy separator plate having excellent corrosion resistance, if the thickness is reduced too much, plastic deformation occurs due to insufficient strength, and it is possible to achieve a sufficiently satisfactory thickness. It is not possible at present. [0004] Accordingly, the present inventors have proposed:
In view of the above, the above-mentioned conventional Ni-based alloy separator plate having particularly excellent corrosion resistance was focused on, and as a result of conducting research to improve the strength thereof, the Ni which constitutes the conventional Ni-based alloy separator plate was obtained. When B (boron) is contained as an alloy component in the base alloy, Cr: 40 to 48%, Mo
And / or W: 0.1 to 2%, B: 0.01 to 1
%, And the remainder is composed of a Ni-based alloy having a composition consisting of Ni and unavoidable impurities. The resulting Ni-based alloy separator plate has an Ni-based alloy made of austenite. Since the metal has a structure in which metal boride having a size of about 0.5 to 10 μm in a length direction is dispersed and distributed in the base material, the strength is remarkably improved by the distribution of the metal boride, and is added in practical use. It exhibits excellent plastic deformation resistance even under the tightening pressure of a single cell, and the metal boride exhibits remarkably excellent corrosion resistance in the above-mentioned oxidizing gas flow path atmosphere as compared with the base austenite. The research results show that the contact surface conduction can be ensured over a long period of time. The present invention has been made based on the above research results, and has a separator in which a fuel gas channel is formed on one side of a solid polymer electrolyte membrane with an anode interposed therebetween and in contact with the anode. The plate member is formed by laminating a plurality of single power generation modules each having a structure in which a separator plate member having an oxidizing gas passage formed in contact with the cathode material is sandwiched on the other side surface, and is pressed and assembled. In the fuel cell, the separator plate is made of Cr: 40 to 48%,
Mo and / or W: 0.1 to 2%, B: 0.01 to
1%, the balance consisting of Ni and unavoidable impurities, and a Ni-based alloy having a structure in which metal boride is dispersed and distributed in an austenitic base material, and has a high strength capable of thinning. The present invention is characterized by a corrosion-resistant Ni-based alloy separator plate of a fuel cell. Next, the reason why the composition of the Ni-base alloy constituting the separator plate of the present invention is determined as described above will be described. (A) Cr In the Cr component, a base austenite is formed together with Ni to improve the corrosion resistance of the base, and a metal boride having excellent corrosion resistance is formed to improve the strength and to be dispersed and distributed in the base. However, if the content is less than 40%, a desired improvement effect cannot be obtained in the above-mentioned action, while the content is 48%.
%, The workability sharply decreases, so the content was determined to be 40 to 48%. (B) Mo and / or W These components have a solid solution in the base austenite,
While it has the effect of improving the strength and forming a metal boride as described above to contribute to the improvement of the strength and the contact surface electrical conductivity, if the content is less than 0.1%, the above-mentioned effect is desired. No improvement effect can be obtained, while if the content exceeds 2%, the workability sharply decreases, so that the content is 0.1 to 2%, preferably 0.3 to 1.5. %
It was decided. (C) BB In the B component, a small part of the B component forms a solid solution in the base material and contributes to the improvement of the corrosion resistance of the base material, but most of the B component has a diameter of 0 in the length direction as described above. A metal boride dispersed and distributed in a size of 0.5 to 10 μm is formed to significantly improve the strength, and also suppress the temporal deterioration of the contact surface electrical conductivity due to its excellent corrosion resistance, which is excellent for a long time. Although it has the function of maintaining the power generation function, if its content is less than 0.01%, the formation of metal borides is insufficient and the above-mentioned effect cannot be obtained, while its content exceeds 1%. Since the formation of metal borides becomes too large and the workability rapidly decreases, the content is determined to be 0.01 to 1%, preferably 0.1 to 0.9%. Next, the separator plate of the present invention will be specifically described with reference to examples. As raw materials, high-purity Ni and Cr materials each having a purity of 99.9% or more,
Mo material, W material, and Ni-B mother alloy (B: 17
%), And melted with a vacuum high-frequency induction melting device to prepare a melt having a predetermined component composition, and cast it into a water-cooled copper mold to form a plate-shaped ingot having a thickness of 5 mm. The ingot was repeatedly subjected to hot rolling at a rolling start temperature of 1200 ° C. four times to obtain a hot-rolled sheet having a thickness of 2 mm. The hot-rolled sheet was held at 1200 ° C. for 10 minutes, and then subjected to a water-cooled solution treatment and 500 ° C. After holding at 10 ° C. for 10 minutes and performing air-cooling tempering, 10 types of plate materials were formed by cold working to reduce the thickness from 1 mm to 0.1 mm in increments of 0.1 mm to 0.1 mm. After being kept at 500 ° C. for 10 minutes, it was subjected to an air-cooled heat treatment, and was pickled, and then was heated to
A plate material of 0 mm is cut out, and a width corresponding to the fuel gas flow path and the oxidizing gas flow path is formed in the center of the plate material by pressing.
5 mm × depth: separator plates 1 to 27 of the present invention, each formed of a Ni-based alloy having a component composition shown in Tables 1 and 2 by forming four grooves of 3 mm in parallel at intervals of 5 mm, and Separator plate materials 1 to 21 were produced. The structures of the various separator plates obtained as a result were examined with a scanning electron microscope (1000
2), the separator plate material 1 of the present invention was observed.
Nos. 27 to 27 each show a structure in which a metal boride having a size of 0.5 to 10 μm in a length direction is dispersed and distributed on an austenitic base material.
Each showed a structure consisting of an austenitic single phase. Then, for the purpose of evaluating the strength of the above-mentioned various separator plates, the above-mentioned 10 types of separator plates having different thicknesses were each subjected to a plane dimension of 150 mm × 150 mm.
mm, thickness: 4 MPa corresponding to the pressure for assembling a single cell constituting a fuel cell from above in a state where the stainless steel plate is horizontally sandwiched between 3 mm stainless steel plates from above and below.
The sheet pressure was applied, and the sheet was taken out after holding for 1 minute, and the sheet thickness at which plastic deformation occurred in the press-formed groove of the separator sheet (plastic deformation occurrence sheet thickness) was measured. The measurement results are shown in Tables 1 and 2. For the purpose of evaluating the corrosion resistance of the above-mentioned various separator plates, a 30 mm × 30 mm test piece is cut out from the above-mentioned 1 mm-thick various separator plates, and this test piece is passed through the oxidizing gas flow path of the separator plate. The corrosion test was performed for 3000 hours in an atmosphere equivalent to the oxidizing atmosphere to be exposed, that is, in an atmosphere saturated with steam at 80 ° C.
The contact electric resistance before and after the corrosion test was measured. In addition, the contact electric resistance value was set as a set of the above test pieces: two pieces, and they were superposed on each other with a 0.3 mm thick carbon paper sandwiched therebetween. A DC current of 15 A was passed in a state where the test piece was pressurized at a pressure of 3 MPa, a potential difference between the test pieces was measured, and a contact electric resistance value was calculated from the measured potential difference. Table 1 shows the results.
2 is shown. In this case, the lower the contact electric resistance value indicates that the contact surface electrical conductivity after the corrosion test on the surface of the separator plate material is excellent, and conversely, the higher the contact electric resistance value after the corrosion test, the higher the contact electric resistance value becomes. This indicates that the contact surface conductivity is low. [Table 1] [Table 2] From the results shown in Tables 1 and 2, from the results shown in Tables 1 and 2, any of the separator plates 1 to 27 of the present invention undergoes plastic deformation even if the thickness is reduced due to the presence of a metal boride dispersed and distributed in an austenitic base. In addition to having high strength that is difficult to
Since the metal boride itself is excellent in corrosion resistance, even if the austenite of the base material is oxidized and the contact surface conductivity at this portion is reduced, good contact surface conductivity through the metal boride is obtained. On the other hand, in the conventional separator plates 1 to 21 having no formation of the metal boride, it is easy to plastically deform due to insufficient strength, and it is not possible to achieve a satisfactory thickness reduction. It is clear that the entire surface oxide film formed by the oxidation of the austenitic single phase lowers the contact surface conductivity and inevitably increases the contact electric resistance. As described above, the separator plate material of the present invention has high strength that enables thinning, and also has excellent contact surface electrical conductivity, and thus greatly contributes to weight reduction and size reduction of fuel cells. is there.

[Brief description of the drawings] FIG. 1 is a schematic perspective view of a fuel cell. FIG. 2 is a partially exploded perspective view of the fuel cell.

Claims (1)

Claims: 1. A separator plate having a fuel gas passage formed in contact with one side of an anode on one side of a solid polymer electrolyte membrane, and a cathode on the other side of the solid polymer electrolyte membrane. In a polymer electrolyte fuel cell, a plurality of single power generation modules each having a structure in which a separator plate member in which an oxidizing gas flow path is formed in contact with and sandwiching the same are superimposed and assembled by pressure welding. A composition comprising, by mass%, Cr: 40 to 48%, Mo and / or W: 0.1 to 2%, and B: 0.01 to 1%, with the balance being Ni and unavoidable impurities, And a corrosion-resistant Ni-based alloy separator for a high-strength polymer electrolyte fuel cell capable of thinning, comprising a Ni-based alloy having a structure in which metal borides are dispersed and distributed on an austenitic substrate. Wood.