JP2936331B2 - Support tube for solid electrolyte fuel cell - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a calcia-stabilized zirconia sintered body used as a support tube for a solid oxide fuel cell.

[Prior art] Conventionally, there is a nuclear power generation using the fuel together with a thermal power generation using coal, oil, natural gas or the like as an electric power supply source. The fuel is fissioned and converted into thermal energy, which is converted into electrical energy via mechanical energy. The thermal efficiency of converting the thermal energy into electrical energy is almost limited to about 40%. In addition, the power supply source has environmental problems such as emission of air pollutants, generation of noise, and necessity of a large amount of cooling water, and has a problem that the location is extremely restricted.

Therefore, a so-called direct power generation method, in which thermal energy is directly converted into electric energy without passing through mechanical energy in order to solve the problems of the thermal power generation and nuclear power generation as the conventional power supply sources, for example, MHD power generation (Magneto-
Hydro-Dynamic Generation), EFD power generation (Electro-Flui)
d-Dynamic Generation), thermoelectric power generation or thermionic power generation have been proposed.
It is low, about 10-205, and is not practical.

Furthermore, as a high-efficiency power generation system that directly converts chemical energy of fuel into electric energy without passing through the heat energy, for example, a substance serving as a source of an electromotive reaction, that is, a reducing agent and an oxidizing agent are continuously used. It has been proposed to generate electricity by means of fuel cells, which supply and extract in the form of direct power the energy released when they react.

The fuel cell includes a low-temperature fuel cell and a high-temperature fuel cell.

As a low-temperature fuel cell, for example, an acidic electrolytic solution composed of a phosphoric acid solution is used as an electrolyte, air can be used as an oxidizing agent, and reformed hydrogen from fossil fuels such as coal, oil, and natural gas is used as a fuel. There is an acidic electrolyte fuel cell. However, in the low-temperature fuel cell that operates at about 300 ° C. or lower, a high current density cannot be obtained at a high voltage unless an expensive platinum catalyst is used to promote the cell reaction, and finally hydrogen is used as a fuel. There was a restriction that it must be a metamorphic one.

In addition, as a high-temperature fuel cell, a molten solution of an alkali carbon salt is used as an electrolyte, air is used as an oxidizing agent, and petroleum gas, natural gas, methanol, etc. are used as fuel in addition to reformed hydrogen,
There is a molten salt electrolyte fuel operated at a temperature of about 600 ° C. However, the molten salt electrolyte fuel cell has a problem in that the electrolyte deteriorates due to a temporal change of the electrolyte due to a high temperature, so that the reaction speed of the battery is reduced and furthermore, corrosion is generated. .

In order to solve such problems, in addition to coal, which is hard to operate at low temperatures of about 300 ° C using air as an oxidant, reformed hydrogen, hydrogen monoxide, hydrocarbons, etc., through a solid electrolyte composed of an oxide solid solution Can also be used as fuel, about 1000 ℃
There has been proposed a high-temperature type solid electrolyte fuel cell which can obtain good cell efficiency and a high current density on the electrode surface by operating at a high temperature.

Therefore, a high-temperature solid electrolyte fuel cell will be described with reference to FIG.

The support tube 1 is made of stabilized zirconia stabilized by calcia, and is made of a porous material having an open porosity of about 40%, which allows the passage of an appropriate gas with heat resistance and maximizes the partition wall function. An electrode and a solid electrolyte are formed on the outer surface of the support tube 1. That is, an anode 2 made of, for example, a complex oxide of lanthanum and manganese (LaMnO ₃ ) doped with calcium, a solid electrolyte 3 made of porous calcia-stabilized zirconia, and a nickel oxide are formed on the outer surface of the support tube 1. The cathode 4 made of a mixture of zirconia has a structure in which the cathodes 4 are sequentially laminated, and a cutout 4a of the cathode 4 is formed with an interconnector 5 for connecting unit batteries in series. Air 6 is supplied to the inside of the support tube 1 and fuel 7 is supplied to the outside of the battery, and the energy when these react via the support tube 1, the anode 2 and the cathode 4, and the solid electrolyte 3 is directly supplied to the electric power. In the form of

[Problems of the prior art]

Since the output of the fuel cell in the basic unit is as low as about 10 W, it is necessary to increase the output by connecting a large number of the cells in the basic unit in series in order to realize commercial power generation. However, the support tube 1 made of the calcia-stabilized zirconia-based sintered body has a problem in that the battery is slightly deformed by high-temperature heating when the electrodes 2, 4 and the solid electrolyte 3 are formed on the outer surface of the support tube 1. It becomes difficult to connect a large amount, and the support tube 1 is deformed during the operation at a high temperature of 1000 to 1200 ° C., and the electrodes 2, 4 and the solid electrolyte 3 are separated from the support tube 1. Alternatively, there has been a problem that the fuel cell may fall off, and eventually, the support tube 1 itself may be damaged, leading to the destruction of the fuel cell.

Therefore, conventionally, SiO ₂ , Al ₂ O ₃ , F mixed from zirconia powder in a calcia-stabilized zirconia sintered body
Since unavoidable impurities such as e ₂ O ₃ form a low-melting glassy phase at the grain boundaries in the sintered body, reducing these impurities will improve the chemical and mechanical stability of the sintered body. Keeping was done.

However, the reduction of these impurities has limitations in themselves and is insufficient in effect, and is not practical.

The present applicant has already proposed that the amount of thermal deformation of a sintered body can be reduced by reducing the amount of magnesia in impurities in a calcia-stabilized zirconia sintered body (Japanese Patent Application Laid-Open No. 64-33853). Gazette). However, even in this case, the deformation rate per unit length after heat treatment at 1400 ° C. was about 1.25%, and did not reach the level of the deformation rate of 0.25% or less required for the solid oxide fuel cell support tube.

[Object of the invention]

The present invention has a main object to solve the above problems, specifically, to reduce thermal deformation of a porous support tube,
Provided is a support tube for a solid electrolyte fuel cell which is excellent in heat resistance without any peeling or falling off of electrodes and solid electrolyte formed on the outer surface of the support tube and which does not hinder the function as a fuel cell. It is intended to do so.

[Means for solving the problem]

The present invention provides a support tube for a fixed electrolyte fuel cell made of a porous calcia-stabilized zirconia sintered body, wherein the amounts of magnesia and alumina in the calcia-stabilized zirconia sintered body are each 2.5 wt. % Or less and 5.0% by weight or less.

In the present invention, the amounts of magnesia and alumina in the calcia-stabilized zirconia sintered body were determined by ICP emission spectroscopy. Also, from the results of analysis by an X-ray microanalyzer, these magnesia and alumina usually form a main component of a low melting point glassy phase by crystallizing at crystal grain boundaries, and the glassy phase causes slip of the grain boundaries. It is thought that it wakes up and leads to deformation. Therefore, the present invention aims to prevent the deformation of the support tube due to the vitreous phase grain boundary sliding by preferentially reducing magnesia and alumina.

In the present invention, the ratio of magnesia and alumina to the total additive is set to 2.5% by weight or less and 5.0% by weight or less, respectively, because an electrode and a solid electrolyte are closely formed on the outer surface of the support tube, This is because the deformation rate per unit length required for forming a high-power fuel cell by connecting to the above is within the range of 0.25% or less.

The term “all additives” used herein includes not only additives such as sintering aids but also impurities in calcia powder and zirconia powder as raw material powders, and impurities mixed in the manufacturing process. It means the total amount of other components except calcia and zirconia which are the main components of the consolidation. In addition, the total amount of additives in the sintered body is desirably 10% by weight or less,
If the amount is too small, the sinterability deteriorates, so that the total amount of additives is about 8% by weight.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

A calcia-stabilized zirconia raw material powder containing 15 mol% of calcia, the total amount of additives being set to approximately 8% by weight, and varying the amounts of magnesia and alumina in all the additives as shown in Table 1 was prepared. did. Dispersants such as ceramisol, plasticizers such as glycerin, and PVA
In addition to such a binder, fibrous cellulose or the like was added so that the open porosity in the sintered body was about 38%, and mixed using a mixing stirrer. While kneading the thus obtained mixed material under reduced pressure using a vacuum kneader, the kneaded material was extruded from a die portion to obtain a hollow cylindrical molded body. Next, the cylindrical molded body is set up and stored in a firing furnace using a jig such as mullite, and fired in the atmosphere at a temperature of 1500 to 1600 ° C. for 2 to 6 hours, and the inner diameter is 10 mm, the outer diameter is 12 mm, and the length is longer. A cylindrical sintered body made of calcia-stabilized zirconia having a thickness of 200 mm was obtained.

Next, a sample for analysis was cut out from one end of each cylindrical sintered body, and the amounts of magnesia and alumina were measured by ICP emission spectroscopy. The straightness of the side surface of each cylindrical sintered body was measured by a straightness measuring device.

Further, a supporting jig made of mullite or the like is placed in a heating furnace for 15 minutes.
The cylindrical sintered body was placed horizontally on the support jig, and subjected to a heat treatment at a temperature of 1450 ° C. in the atmosphere for 2 hours. Thereafter, the straightness was measured by a straightness measuring device, and a difference between the straightness before and after the heat treatment was defined as a maximum deformation amount, and a value obtained by dividing the maximum deformation amount by the distance between the support jigs was defined as a deformation ratio.

Magnesia of each cylindrical sintered body with respect to the total amount of additives,
The ratio of alumina and the deformation ratio after heat treatment are as shown in Table 1. Since the deformation rate required for the support tube for a solid electrolyte fuel cell was 0.25% or less, it was judged whether the condition was satisfied or not.

From Table 1, it is understood that all of the cylindrical sintered bodies of Nos. 1 to 12 have the same total additive amount and porosity, but have different deformation rates after heat treatment depending on the amounts of magnesia and alumina. The ratio of magnesia and alumina to all additives is
In Nos. 3, 6, 9, 10, 11, and 12 exceeding 2.5% by weight and 5.0% by weight, the deformation ratio was larger than 0.25%. On the other hand, when the ratio of magnesia and alumina to all additives is 2.5% by weight or less and 5.0% by weight or less, the deformation ratio is 0.25% or less.
% Or less, which is within the required range.

In addition, in addition to the above-mentioned magnesia and alumina, silica and titania occupied most of the additives of the calcia-stabilized zirconia sintered body in this example. Also,
In order to reduce magnesia in the additive, the purity of the calcia raw material powder is increased, and a high-purity material may be used.
On the other hand, in order to reduce the amount of alumina, it is only necessary to prevent the mixing of alumina during the manufacturing process, for example, by changing the grinding balls at the time of grinding the raw materials from those made of alumina to those made of zirconia.

〔The invention's effect〕

As described above, in the present invention, the contents of magnesia and alumina in the calcia-stabilized zirconia sintered body forming the support tube for the solid oxide fuel cell are respectively 2.5% by weight or less and 5.0% by weight with respect to the total additive amount. By adopting the following conditions, thermal deformation of the support tube is remarkably reduced, and a highly reliable and high-quality support tube for a solid electrolyte fuel cell with improved heat resistance can be obtained.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view of a high-temperature type solid electrolyte fuel cell for illustrating a support tube for a solid oxide fuel cell of the present invention. DESCRIPTION OF SYMBOLS 1 ... Support tube 2 ... Anode 3 ... Solid electrolyte 4 ... Cathode

Claims (1)

(57) [Claims] 1. A solid electrolyte fuel cell support tube comprising a porous calcia-stabilized zirconia sintered body, wherein all additives except for zirconia and calcia which are main components of the calcia-stabilized zirconia sintered body are provided. The solids are characterized in that the ratio of magnesia and alumina to the total additive in the above is 2.5% by weight or less and 5.0% by weight or less, respectively, so that the deformation rate after heat treatment at 1450 ° C for 2 hours is 0.25% or less. Support tube for electrolyte fuel cells.