JPH0250983A - Heat-resistant parts - Google Patents

Abstract

PURPOSE:To produce the title heat-resistant parts having resistance to oxidation and reduction by forming a coating film of La, etc., on the surface of a base alloy contg. Cr, Co, Ni, Fe, and Mn. CONSTITUTION:The surface of a base alloy contg. Cr, Co, Ni, Fe, or Mn or those metals is coated with one kind selected from a group consisting of lanthanum, lanthanum oxide, lanthanum and an alkaline-earth metal, lanthanum oxide and an alkaline-earth metal, lanthanum and an alkaline-earth metal oxide, and lanthanum oxide and an alkaline-earth metal oxide. The thickness of the coating is preferably controlled to about 0.1-1mu, and the molar ratio of M1/La of the alkaline-earth metal M1 to lanthanum La to about 0-0.7. The coating film reacts with the metal in the base alloy to form a perovskite composite oxide La1-xM M<2>O3 (M<1> is an alkaline-earth metal, M<2> is Cr, Co, Ni, Fe, or Mn, and 0<=x<1). By this method, a heat-resistant high-conductivity metal parts useful for the bonding body, current collecting body, etc., of a high-temp. fuel cell is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to heat-resistant parts, and particularly to a cathode-anode assembly and a cathode aggregate of a high-temperature fuel cell. More specifically, the present invention relates to a heat-resistant component in which the surface of a heat-resistant metal base material is covered with a conductive film having oxidation resistance and reduction resistance. It is useful in all fields that require electrical conductivity at high temperatures, such as power generation applications.

[Prior art and problems to be solved by the invention] High-temperature fuel cells include molten salt type fuel cells used at 650°C and 800°C
There is a solid electrolyte type that can be used at 1000°C.

The basic structure of a solid electrolyte fuel cell is as shown in Figure 8.
A solid electrolyte (e.g. partially stabilized zirconia) is sandwiched between the cathode (e.g. perovskite type Lao, n5ro).
, MnO:+) 2 and anode (e.g. Nio/Zr
O, ) 3 is formed into a film, and oxygen or air is supplied to the cathode 2 side, and fuel, such as hydrogen, is supplied to the anode 3 side. Zirconia (ZrO□) is 0 at 1000℃
．． It exhibits an electrical conductivity of 5 Ω-'cm-', and this is due to ionic conduction, that is, the movement of 02-, but since zirconia is very brittle, it must be stabilized with calcilyl or yttrium. The reaction of a cell like this example is represented by cathode: 48-102→202 anode: 02- + H2- + Hzo + 2 e, where 072- is transported in zirconia.

Also, although this is the structure of a unit cell, in order to integrate unit cells and connect multiple unit cells in parallel (or in parallel), an interconnector is used between the electrodes of adjacent unit cells. Connect with. The actual structure of a fuel cell is determined by the way the unit cells are integrated, and several integrated structures have been proposed so far, and development for practical use is progressing.

By the way, it is said that it is preferable for such a fixed electrolyte fuel cell assembly to satisfy the following conditions.

1) Stable under oxidizing and reducing atmospheres at high temperatures.

2) Good electrical conductor in oxidizing and reducing atmospheres at high temperatures.

3) It has a coefficient of thermal expansion close to that of an oxide ion conductive solid, such as stabilized zirconia.

4) It has a thermal expansion coefficient close to that of the electrode material.

Further, the following conditions are required for the cathode current collector.

1) Stable in oxidizing atmosphere at high temperatures.

2) Good electrical conductor under oxidizing atmosphere at high temperature.

3) It has a coefficient of thermal expansion close to that of an oxide ion conductive solid, such as stabilized zirconia.

4) It has a thermal expansion coefficient close to that of the oxygen electrode material.

Conventionally, metals or conductive ceramics have been used as bonded bodies and current collectors. However, since metal is heated to 600°C
If used above, a surface oxidation layer will be formed, contact resistance will increase significantly, resistance loss of electric power will increase, and fuel cell characteristics will deteriorate. Further, as conductive ceramics, metal composite oxides such as Lal-XM', M2O3(M'
is Sr, Ca or Ba, M2 is Go, Fe, M
Perovsky type I oxides with 0≦x<1), in particular La1-x Sr, where n is Ni or Cr,
CrO3 has been proposed as meeting the above requirements. However, although such ceramics are conductive, their resistance cannot be ignored, and for example, in the thin film cylindrical fuel cell proposed by Westinghouse Corporation in the United States, which uses perovskite oxide as the cathode material, the cathode Resistance accounts for about 65% of the total cell resistance and is an obstacle to improving the energy efficiency of fuel cells.

On the other hand, in recent years, batteries with new structures have been proposed with the aim of developing higher performance fuel cells. Examples are shown in FIGS. 6 and 7. In Figure 6, a honeycomb structure 5 is made of a solid electrolyte such as partially stabilized zirconia, and fuel 6 and air (oxygen) 7 are supplied countercurrently to every other pore (cell) of the honeycomb structure. An anode is formed on the wall inside the pore that supplies air (oxygen) 7, and a cathode is formed on the wall inside the pore that supplies air (oxygen) 7. Figure 7 shows multiple solid electrolyte partition walls 1
Fuel 14 and air (oxygen) 15 are supplied perpendicularly to every other layered space 12 and 13 formed by the partition wall 11, and an anode 16 is formed on the fuel 14 side of the partition wall 11, and a cathode 17 is formed on the air (oxygen) side. This is what I did. These types of batteries can be expected to have extremely high energy density per unit volume, and are thought to be suitable for mass production as conventional ceramic technology can be applied. However, the biggest problem is the 6th
In the structure shown in the figure, it is a current collector, and in the structure shown in FIG. 5, it is a joined body.

The present invention has been made especially for the purpose of providing a heat-resistant conductive component suitable for such a current collector or a bonded body.

[Means to solve the problem]

The present invention solves the above problems by applying (I) lanthanum, (II) lanthanum and alkaline earth metal, (IIi) oxidation A heat-resistant component coated with any one of the group consisting of lanthanum and an alkaline earth metal, (iv) lanthanum and an alkaline earth metal oxide, and (V) lanthanum oxide and an alkaline earth metal oxide. Solved by providing.

This film reacts with chromium, cobalt, nickel, iron, or manganese in the base material in a high-temperature oxygen atmosphere to form a layer of La+-x
M'x M2O3 (M' is alkaline earth metal, M2
is chromium, cobalt, nickel, iron or manganese, 0≦
A perovskite-type composite oxide (X<1) is produced. In particular, this perovskite-type composite oxide is stable at high temperatures and has excellent electrical conductivity of 10 to 1000Ω.
It has a value of −1 cm−1. For this reason, whereas alloys or pure metals alone form an oxide film at high temperatures and insulate the surface, the parts according to the present invention have excellent surface electrical conductivity due to the formation of a composite oxide film, and the joined body, Perfect for gatherings. Furthermore, since the main body of the heat-resistant component is made of a heat-resistant alloy or pure metal, it is excellent in all aspects of rigidity, workability, and electrical conductivity, increasing the practicality of this heat-resistant component.

The base metal may be an alloy containing chromium, cobalt, nickel, iron, or manganese, or a pure metal of chromium or cobalt, but the alloy is preferably a so-called heat-resistant alloy containing 9 wt% or more of chromium, cobalt, nickel, iron, or manganese. . For example, Ni 10.0. Cr20.
0. W15.0. Fe 1.5 , Co remaining, or those having compositions as shown in Examples below are useful.

The composition ratio x/(I-x) of lanthanum oxide and alkaline earth oxide in the film is not particularly limited, but M
, /L, ratio (M,: alkaline earth metal) is O ~ in molar ratio
0.7, especially 0 to 0.5 is preferred. This is because electrical conductivity and oxidation resistance are excellent within this range.

The method of forming a film on an alloy or pure metal is not particularly limited, and coating methods include a coating method, a thermal spraying method, a spackle method, a vapor deposition method, a plasma CVD method, an MBE method, and an MBE method.
Although any film forming technique such as OCVD, CVD, ion blating, plasma spraying, etc. can be used, thermal spraying, sputtering, and ion blating are particularly preferred because of their excellent density and adhesion.

The thickness of the coating is preferably within the range of 0.1 to 17/II+. This is because if it is too thin than 0.1 tm, the surface protection effect will not be sufficient, while if it is too thick than 1uIIl, the conductivity will decrease.

The conditions for the film of the heat-resistant component of the present invention to become a perovskite-type composite oxide La+-x M'x M20z are L++ and M
The composition ratio with L, the composition of the base material (especially M2), the thickness of the coating,
Although it depends on the atmosphere etc., generally 100 (I'c, 1
It changes into a composite oxide by heat treatment for about an hour.

Such heat treatment may be specially performed to convert the film into the desired composite oxide before putting the heat-resistant parts of the present invention into practical use, or may be performed to improve the practical use of the heat-resistant parts of the present invention when the heat-resistant parts of the present invention are put into practical use. It may also be carried out under high temperature conditions.

Moreover, the layer L obtained by heat-treating the film of the heat-resistant component of the present invention may also be used.
a+-x M'XM2O3 perovskite type composite oxide has high conductivity at high temperatures (I00-10010
00S') and its coefficient of thermal expansion (9×10-
6/”C) is that of the base material (generally 16~19X10-6
/°C), and has the characteristic and advantage that it reacts with chromium, cobalt, nickel, iron, or manganese contained in the base material during heat treatment to form an extremely dense film. Furthermore, the coefficient of thermal expansion of this composite oxide is relatively close to that of the solid electrolyte (I0x 10-6/''c), making the heat-resistant component of the present invention more suitable for application to solid electrolyte fuel cells. Although the heat-resistant component of the present invention is particularly intended for application to current collectors and assemblies of solid electrolyte fuel cells, its usefulness is not limited thereto.
For example, it can be widely used in fields where heat resistance is required, such as gas turbines and MHD power generation parts.

〔Example〕

Cobalt-based alloy plate on apex base (I01 irises x 10mII x 1■■, composition: W14.57%, Co 52.51%, Cr 19
．． 69%, Ni 9.39%, C0.10%, Si0.
La20.48%, Mn1.51%) by Rf sputtering according to a conventional method. -5rO(SrO/Laz
The molar ratio of Oz was 2:1) and the mixture was applied to both sides to a thickness of about 1. The Rf sputtering method was performed at a margon gas ratio of 2 to 5 mTorr and a power of 100 to 200 W for 1 hour. This sample was heated in air at 1000°C for 24 hours.

After heating, the product was slowly cooled to room temperature and the reaction product on the surface was identified using an X-ray diffraction device.
(X=0.1-0.5).

(M2 became Cr and Co was not confirmed because
(This is thought to be because the reactivity of Cr is higher than that of Co.) Figure 1 shows the weight change and surface resistance change with respect to time when the above sample was heated in air at 1000°C.

The surface resistance was measured by the four-probe method according to a conventional method. For comparison, the weight change of the same type of alloy without the La203-8rOT'J film on the surface is also shown.

In the case of only the alloy, the weight increase reached its maximum after about 100 hours of heating and decreased thereafter. This weight loss is due to the exfoliation of oxides, mainly chromium oxide and cobalt oxide, formed on the alloy surface. Note that the surface resistance of the alloy-only sample showed a value close to that of an insulator when heated at 1000° C. for 24 hours, but this was due to the formation of chromium oxide and cobalt oxide on the surface. Note that under a reducing atmosphere of 1000° C. (10% water, 90% argon), no change in the surface or increase in resistance was observed in this cobalt-based alloy.

Next 1 "Shishi process i" In the same manner as in Example 2, La20: +-3
A mixture of rCOz (La203/SrCO3 molar ratio 3:1) was coated on both sides to a thickness of about 1 yuan, and heated at 1000°C in air.
It was heated for 24 hours.

As a result of X-ray diffraction analysis of the reaction products on the alloy surface, it was confirmed that the products shown in Table 2 were produced.

La2O2-3rCO: + sample after deposition in air 100%
Figure 2 shows the weight change when heated at 0°C. For comparison, FIG. 3 shows the weight change due to similar heating of an alloy without LazO+-3rCO3 deposited on the surface.

Further, Table 2 shows the electrical resistance of the surface of the coated alloy and the bare alloy after the heating.

Table 1: Heat treatment at 1000°C in the air A cobalt pure metal plate (I0mXI) was prepared in the same way as in Example 1.
Metal lanthanum was sputter-deposited on both sides of the QmmXlm) to a thickness of 2 to 3 μm using the Rf sputtering method. It was then heat treated in air at 1000''c for 5 hours.

After heating, it was slowly cooled to room temperature, and the reaction product on the surface was analyzed by X-ray diffraction, and it was confirmed that it was LaCoO3.

When this sample was heated in air at 1000'C for 5 hours,
It showed an electrical conductivity of 363 cm-', which was a very good result. No change over time was observed even after 168 hours, and no peeling of the film was observed even after the temperature was lowered.

FIG. 4 shows the air conductivity of the coating thus investigated with respect to the measured temperature.

FIG. 5 shows a developed diagram of the stacked structure of a solid oxide fuel cell to which the heat-resistant component of the present invention is applied. In the figure, 21 is a sheet of solid electrolyte (e.g., Ca-stabilized zirconia) with an anode (e.g., Lao, qSro, 1Mn0:+) on the top surface.
22, a cathode (eg, NiO/ZrO□ cermet) 23 is formed on the lower surface. 24 is a joined body, which is a heat-resistant component of the present invention (e.g., La2 on the cobalt-based alloy of the above example).
0. , -3rO coating). 25 is a heat-resistant component like 24, but is used as an external output terminal.

As seen in FIG. 5, the joined body 24 constitutes a flow path for the air 26 and the fuel (eg, hydrogen) 27 by the grooves formed therein, and serves as a separator for separating the air 26 and the fuel 27, and also serves as a separator for separating the air 26 and the fuel 27. It also plays the role of electrically connecting the cathode 23 and anode 22 of the unit cell.

The external output terminal 25 is a member that forms a flow path for air 26 and fuel 29 at both ends of the integrated unit cell, and is also a member that electrically connects with the cathode 23 or anode 22, and is also a heat-resistant component of the present invention. Configure. Further, although FIG. 5 shows a fuel cell in which two unit cells are integrated, it is also possible to integrate three or more unit cells, and in that case, the assembly 24 is inserted between each unit cell.

When such a fuel cell is used by supplying air and fuel (hydrogen) at a high temperature of 1000°C, the coating (La20+5rO) of the heat-resistant parts of the assembly 24 and the external output terminal 25 immediately turns into a composite oxide (La+5rO) after use. -x Srx CrO:
+), the resistance decreases, and power is generated stably for a long time thereafter.

Furthermore, the heat-resistant component of the present invention is extremely useful as a current collector and an assembly for the fuel cells shown in FIGS. 6 and 7.

〔Effect of the invention〕

According to the present invention, there is provided a heat-resistant, highly conductive metal component coated with a highly conductive coating that can withstand oxidizing and reducing atmospheres at high temperatures. Useful in all areas that require sexual contact. For example, a heat-resistant component made of a highly conductive heat-resistant metal material having a protective coating that can withstand a redox atmosphere at a high temperature of 1000° C. or higher and has an electrical conductivity of 10 to 10003 cm −′ is provided.

By using the redox-resistant metal conductor (heat-resistant parts) of the present invention, it is possible to create a high-temperature solid electrolyte fuel cell with an integrated structure that is expected to have significantly superior performance compared to conventional high-temperature solid electrolyte fuel cells. Become.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the weight change and resistance change of the coated material of the example in 1000°C air, and Figs. 2 and 3 are graphs showing the weight change and resistance change of the coated material of the example and the uncoated alloy in 1000°C air. A graph showing the weight change, FIG. 4 is a graph showing the temperature change in the electrical conductivity of the coating of the example, and FIG. A schematic development diagram, FIGS. 6 and 7 are schematic diagrams of a high-temperature solid electrolyte fuel cell, and FIG. 8 is a schematic diagram showing a W-tree structure of a solid electrolyte fuel cell. ■...Solid electrolyte, 2...Cathode, 3...
・Anode, 6...Fuel, 7...Air,
11... Solid electrolyte, 14... Fuel, 15... Air, 16... Anode,
17... Cathode, 21... Solid electrolyte,
22... Anode, 23... Cathode, 2
4... Joined body, 25... External output terminal, 26...
・Air, 27...Fuel. Plaker type solid electrolyte fuel cell (two-stage series type) Fig. 5 26... Air Fig. 15... Air

Claims (1)

[Claims] 1. On the surface of the base material of chromium, cobalt, nickel, iron or manganese, or alloys containing these metals, (I) lanthanum, (II) lanthanum oxide, (III) lanthanum and alkaline earth metals, (IV) lanthanum oxide and alkaline earth metal, (V) lanthanum and alkaline earth metal oxide, and (V
I) A heat-resistant component coated with any one of the group consisting of lanthanum oxide and alkaline earth metal oxide.