KR20060024244A - Sintering method for single cell materials of solid oxide fuel cell - Google Patents

Abstract

    The present invention relates to a sintering method of a solid oxide fuel cell composition, wherein a unit cell for a solid oxide fuel cell (SOFC) formed by a sequential combination of a cathode layer, an electrolyte layer, and an anode layer is molded according to a conventional ceramic manufacturing process. In the method of sintering and manufacturing into a sintered body,

The unit cell for the solid oxide fuel cell is positioned inside a reactor surrounded by zirconia or silicon carbide-based insulation, and microwaves are applied for a predetermined time in the reactor.

As described above, the present invention not only reduces the process time and reduces the energy cost, but also eliminates the risk of thermal shock that may occur in the molded body during sintering, and also due to the small particle size of the sintered compact, which is an effect of rapid sintering. There is an effect that can contribute to the improvement of physical properties.

    Solid oxide fuel cell, unit cell, rapid sintering, microwave

Description

Sintering Method for Single Cell Materials of Solid Oxide Fuel Cell}

1 is a schematic diagram of a device configuration for sintering a fuel cell composition of the present invention;

Figure 2 is a graph measuring the temperature rise process of the molded article when the microwave is applied to the apparatus of the present invention.

※ Explanation of symbols about main part of drawing ※

11 molded body 12 reactor

13: heat insulation

The present invention relates to a unit cell sintering method for a solid oxide fuel cell, and more particularly, a thermal shock and non-uniform sintering that can be applied to a specimen while rapidly raising the temperature efficiently when sintering a unit cell of a solid oxide fuel cell (SOFC). The purpose of the present invention is to provide a method for manufacturing a solid oxide fuel cell (SOFC) unit cell, which is more economical, by shortening the process time and reducing energy costs by eliminating the risk of the present invention.                         

The present invention relates to a sintering method of a negative electrode, an electrolyte, and a positive electrode composition constituting a unit cell of a solid oxide fuel cell (SOFC), and more specifically, to a fuel cell unit cell in an economical manner in a short time. It relates to a method for producing a sintered compact.

A fuel cell is a device that generates electricity by reacting fuel such as hydrogen or natural gas with oxygen, and is recognized as one of the main energy technologies of the future because of its high efficiency, pollution-free, and noise-free characteristics. There are many types of fuel cells, among which solid oxide fuel cells (SOFC) use zirconia ceramics (ZrO ₂ ), ceria (CeO ₂ ) or lanthanum-strontium-gadolinium-magnesium oxide (LSGM) as solid electrolytes. (The above solid oxides are usually yttria (Y ₂ O ₃ ), ceria (CeO ₂ ), Scandia (Sc ₂ O ₃ ) oxidation for the purpose of improving thermal stability and ionic conductivity at high temperature. It contains an appropriate amount of stabilizer such as gadolinium (Gd ₂ O ₃ ).) The unit cell of a solid oxide fuel cell (SOFC) has the above-mentioned solid electrolytes in the center and a cathode material on one side and an anode material on the other side. Made in attached form. As a conventional cathode material, a mixture of nickel oxide (NiO) and stabilized zirconia is used, and lanthanum-strontium-manganese oxide (LSM), lanthanum-strontium-cobalt-iron oxide (LSCF), or the like is used as the anode material.

In the conventional method of manufacturing a unit cell of a solid oxide fuel cell (SOFC), first, a dense electrolyte sintered body of a suitable thickness (about 200 μm) is manufactured by sintering in a conventional furnace, and then a cathode material is formed on one side and a cathode on the other side. There is also a method of manufacturing by coating and heat treatment of the positive electrode material. Another method is to first form the negative electrode material (mixture of NiO and zirconia powder) to a suitable thickness (about 1mm or so) according to a conventional ceramic molding process and to relatively low temperature. After primary sintering at (1300-1400 ℃ in total) to form a pre-sintered body, a thin oxide (about 5-20 µm) is coated on the electrolyte, which is a solid oxide, by a conventional ceramic coating method (such as slurry coating or spray coating). After sintering, the secondary sintering was carried out by raising the temperature at a slow rate of 10 ^o C or less per minute and maintaining it for 1 to 5 hours at a temperature range of 1400-1500 ^o C. In addition, a method of coating a cathode material (LSM, LSCF, etc.) on the upper surface of the electrolyte layer and performing a third sintering by a method similar to the above is known to produce a sintered body.

However, the method of manufacturing a sintered compact of a solid oxide fuel cell (SOFC) unit cell is not only subjected to three sintering processes but also takes a long time of at least 5 hours for each sintering process and a long heat treatment at a high temperature. It has the disadvantage of high energy cost.

In order to solve this problem, some researchers sinter the negative electrode material and the electrolyte at the same time in one sintering process and then sinter only the positive electrode material in a separate process, or after coating the negative electrode material, the electrolyte and the positive electrode material sequentially We are working on the development of co-firing process technology that sinters in one sintering process. (Academic Conference Presentation: 9th Asian Conference on Solid State Ionics, Jeju, Korea, 2004.6.6-11) The problem remains even in the simultaneous sintering process. Since the thickness of the fuel cell unit cell compositions is very thin, defects due to warpage or crushing due to breakage due to thermal shock or difference in sintering speed of each part of the unit cell (that is, uneven sintering) are prevented In order to reduce the temperature, the temperature increase rate should be slowed down to a maximum of 10 ° C / min (usually 3 ° C / min or less). The longer it takes at least five hours in the (usually over 10 hours) is a problem that will remain.

On the other hand, a method of rapid sintering is known in ceramics such as zirconia and alumina (Al ₂ O ₃ ). (E.g. J.Br.Ceram.Soc., Vol. 80, p147) Rapid sintering is used to sinter ceramic shaped bodies. When heated to a speed much faster than the usual heating rate (approximately 50 ^o C / min) and sintered at high temperature for a short time, the process time and energy cost are reduced. The reason why such rapid sintering is useful is that when sintering ceramic powder compacts, excessive grain growth occurs in a relatively low temperature region (for example, about 800-1200 ° C in the case of alumina and zirconia) during sintering, thereby reducing the sintering driving force. This is because the faster the temperature passes through the low temperature region, that is, the faster the temperature increase rate, the smaller the decrease in the sintering driving force.

In other words, the sintering driving time required to obtain a compact sintered body is also shorter because the sintering driving force is higher immediately after the final sintering temperature is reached than when the temperature is higher. It is also known that another advantage of the rapid sintering method is that a sintered compact having better physical properties (eg, mechanical strength) after sintering can be obtained due to less grain growth during sintering.

However, in order to apply the method of rapid sintering with the above advantages to the sintering of the fuel cell composition, an apparatus capable of raising the temperature quickly and efficiently is required. To this end, a method of conventionally using a tube furnace to raise the temperature of the furnace in advance and then rapidly inserting the specimen into the furnace has been used. In addition, there is a disadvantage that there is a risk of heat shock applied to the specimen when the specimen to be sintered into the furnace.

Therefore, the present invention has been invented to solve the above problems, while efficiently heating the unit cell of the solid oxide fuel cell (SOFC) while removing the risk of thermal shock and non-uniform sintering that may be applied to the specimen It is an object of the present invention to provide a method for manufacturing a solid oxide fuel cell (SOFC) unit cell which is more economical by shortening process time and reducing energy costs, and a unit cell manufactured by the method.

The unit cell sintering method for a solid oxide fuel cell of the present invention for achieving the above object is a conventional ceramics unit cell for a solid oxide fuel cell (SOFC) composed of a sequential combination of a cathode layer, an electrolyte layer, and an anode layer. In the method of forming, sintering and sintering a compact according to a manufacturing process, the unit cell for a solid oxide fuel cell is placed inside a reactor surrounded by zirconia or silicon carbide-based insulation, and microwaves are applied for a predetermined time in the reactor. It consists of

The wavelength of the microwave is 1-60 GHz, and the time for applying the microwave is within 1 hour.

In addition, the unit cell for a solid oxide fuel cell of the present invention is formed by sintering a unit cell for a solid oxide fuel cell (SOFC) formed by a sequential combination of a cathode layer, an electrolyte layer, and an anode layer according to a conventional ceramic manufacturing process Is placed inside the reactor surrounded by zirconia or silicon carbide-based insulation, and the microwave was added by a certain time.

On the other hand, the wavelength of the microwave is 1-60 GHz, the time to apply the microwave is within 1 hour.

Hereinafter, a method of manufacturing a unit cell for a solid oxide fuel cell and a unit cell manufactured by the method of the present invention having the above characteristics will be described in more detail.

First, commercially available nickel oxide (NiO) and stabilized zirconia powder (YSZ) as a negative electrode material are mixed in a conventional composition ratio (typically, the composition ratio is in the range of 4: 6 to 6: 4) and molded according to a conventional ceramic molding process. The molded body 11 is about 1 mm thick. At this time, the molded body may include a conventional organic binder (binder) to improve the molding strength, and may also be added to the pore forming agent carbon or starch to control the porosity after sintering.

On the prepared negative electrode material, an electrolyte layer having a thickness of about 5 to 20 μm is formed by using a conventional ceramic powder coating method, that is, slurry coating or spray coating. As the electrolyte material, conventional stabilized zirconia (YSZ), ceria, lanthanum-strontium-gadolinium-magnesium oxide (LSGM), or the like can be used.

As described above, the anode layer having a thickness of about 10 to 100 μm is formed on the upper surface of the dried electrolyte layer after the formation of the electrolyte layer by using the conventional ceramic powder coating method, and the anode material is a conventional lanthanum-strontium-manganese oxide. (LSM), lanthanum-strontium-cobalt-iron oxide (LSCF), or a mixed composition of lanthanum-strontium-manganese oxide and lanthanum-strontium-cobalt-iron oxide, and the like can be used.

Meanwhile, each of the layers of the molded body 11 may be manufactured in a multi-layered structure instead of a single layer in order to improve performance. For example, the cathode layer may have a two-layer structure according to particle size, or the anode layer may be lanthanum-strontium-manganese. An oxide or lanthanum-strontium-cobalt-iron oxide may be coated sequentially to have a multilayer structure.

The molded body 11 formed by the above method is made of a reaction chamber made of a zirconia-based heat insulating material (such as an insulating brick and a heat insulating plate containing zirconia powder or zirconia-based fiber) or silicon carbide-based heat insulating material 13 as shown in FIG. The reactor 12 is placed in a center of the interior of the reactor, and the entire reactor 12 is placed in a conventional microwave oven or similar device that is capable of applying microwaves.

At this time, under the reactor 12, a conventional low-temperature insulation 13 (general insulation without zirconia or silicon carbide) is placed so that heat from the reactor is not transferred to the bottom of the apparatus.

The sintering of the molded body 11 is completed in the reactor 12 positioned as described above by adding a microwave (frequency range 1-60 GHz), which is used for ordinary household and industrial purposes, within a period of one hour and then cooling. The specific reason is as follows.

In general, all ceramic materials have a polarity (dipole) to absorb the microwaves and generate heat. However, these characteristics are not usually shown at room temperature because the efficiency of ceramics absorbing microwaves (usually called loss factor) is very low at room temperature and increases with increasing temperature. Because.

On the other hand, commercially available zirconia-based and silicon carbide-based insulations are known to absorb microwaves even at room temperature to generate heat because the loss factor of the zirconia-based fibers and silicon carbide particles inside the insulation is very large. It is becoming.

Therefore, when the reactor 12 is constituted as in the present invention, the molded body 11 inside the reactor 12 initially absorbs microwaves, but the zirconia or silicon carbide system used as the heat insulator 13 is applied. Insulation material acts as a susceptor to absorb microwaves and generate heat.

At this time, the temperature of the heat insulator 13 does not rise so high, because the heat insulator 13 itself is not protected by other heat insulators, so the heat generated is continuously taken out. However, in the case of the molded body 11 inside the heat insulator 13, the temperature is continuously increased by receiving heat generated from the heat insulator 13.                     

When this condition continues for a certain time and the temperature of the molded body 11 is heated above the critical temperature (temperature of generating microwaves by absorbing microwaves well, it is known to be about 200 ° C in general ceramics). After this, the molded body 11 itself absorbs microwaves and generates heat directly, so that the temperature rises rapidly.

Figure 2 shows the temperature rise curve of the molded body when the microwave was applied to the reactor fabricated in the experiment of the present invention. (The measurement of the molded body temperature was measured by a pyrometer through a small hole in the insulation.) As described above, the microwave In the initial period (approximately 10 minutes), the temperature of the molded article rises very slowly, but once it reaches the critical temperature, it rises very rapidly and within 1 minute it is heated to 1400 ℃ or more suitable for the sintering temperature of the fuel cell composition. It can be seen.

The reason why the temperature rises at such high speed is that the loss factor (absorption efficiency of microwaves) of the ceramic molded body increases as the temperature increases, so that the temperature and the absorption efficiency exhibit mutually synergistic effects. On the other hand, once the direct heating of the molded body is started, the relatively low temperature (and thus low absorption efficiency) insulation material can not absorb any more microwaves and thus maintain a relatively low temperature.

In the fuel cell composition molded body sintered as described above, the relative density of the electrolyte layer is densified by 98% or more within approximately 1 hour regardless of the size, and the sintering is completed in a short time. Since not too dense is conducive to battery performance, porosity is usually controlled through the addition of pore formers or the use of coarse particles.)

The reason why the fuel cell composition molded body is rapidly densified regardless of its size is that, unlike the case of using a conventional furnace, in the present invention, the molded body itself generates heat by self-sintering, and for this reason, As a result, the possibility of non-homogeneous sintering due to the heat shock risk or the unevenness of the temperature distribution, which may occur when rapid sintering is performed in a conventional furnace, which is an indirect heating method, is naturally reduced.

On the other hand, the reason why the frequency range of the microwave used in the present invention is limited to 1 to 60 GHz is that the microwave absorption efficiency of the ceramic material is generally higher as the resonance frequency of the dipole inside the material increases. The resonant frequency of is known to be in the 10-60 GHz range. However, in the case of the fuel cell composition of the present invention, it is not very useful to design a specific frequency because it is a mixture of various materials, and it is inexpensive because the zirconia or silicon carbide susceptor is used to easily generate heat at low temperatures. It would be most desirable to use commercially available microwave oscillators (eg 2.45 GHz, 28 GHz, 60 GHz, etc.) at a price.

However, at frequencies below 1 GHz, zirconia or silicon carbide-based thermal insulation used as susceptors also has a very low reaction efficiency, so it may be desirable to use a frequency above 1 GHz.

Hereinafter, the present invention will be described through Examples.                     

(Example)

In the experiment of the present invention, PVB (organic binder) was used as an organic binder in a composition in which a commercially available NiO powder (Japanese high purity chemistry) and zirconia (YSZ) powder (TZ-8Y, Tosoh, Japan, TZ-8Y) were mixed at a ratio of 5: 5. Polyvinyl-butiral) was added 3%, and carbon black (Korean carbon) 10% was added as a pore-forming agent to prepare a 50 x 50 x 1 mm molded article according to a conventional ceramic molding process.

The zirconia powder was used on the molded body to form an electrolyte layer having a thickness of 10 μm by a conventional spraying process, and then, on the electrolyte layer, a lanthanum-strontium-manganese oxide (LSM) powder was used on a 20 μm by a conventional slurry coating method. A thick anode layer was formed.

The dried and calcined (binder burn-out) molded bodies were placed so as to be placed in the center in the reactor made of a cube-shaped so that each side is 10cm as shown in Figure 1 using a zirconia insulation board. The molded body and the reactor were sintered by applying a microwave at 2.45 GHz to a power of about 600 W for a predetermined time in a commercial microwave oven. The result of measuring the temperature rise curve of the molded body was shown in FIG. The results of measuring the sintered density of the electrolyte layer over time are shown in Table 1 below.

TABLE 1

Sintering time 20 minutes 30 minutes  40 minutes 50 minutes 60 minutes Sintered Density 93% 98% 99.1% 99.5% 99.7%

As shown in Table 1, when the solid oxide fuel cell unit cell composition is sintered by the method of the present invention, it can be seen that a compact sintered body having a sintered density of 98% or more is obtained in about 30 minutes. It was possible to obtain the effect of normal rapid sintering because it was possible to rapidly increase the temperature while avoiding the thermal shock under the microwave.

As described above, in the present invention, when sintering a unit cell of a solid oxide fuel cell (SOFC), the sintering is performed by adding a microwave in a zirconia or silicon carbide-based insulating material to a predetermined time, thereby reducing the process time and reducing the energy cost. Not only will it bring a risk of thermal shock that may occur in the molded body during sintering, but also has a side effect that can contribute to the improvement of various physical properties due to the small particle size of the sintered compact, which is an effect of rapid sintering.

Claims (6)

In the method for producing a solid oxide fuel cell (SOFC) unit cell formed by a sequential combination of the negative electrode layer, the electrolyte layer and the positive electrode layer according to a conventional ceramic manufacturing process and sintered to produce a sintered body, The unit cell sintering method for a solid oxide fuel cell, characterized in that the unit cell for the solid oxide fuel cell is located inside the reactor surrounded by zirconia or silicon carbide-based heat insulating material, and a microwave is added in the reactor for a predetermined time. The unit cell sintering method for a solid oxide fuel cell according to claim 1, wherein the microwave wavelength is 1-60 GHz. 2. The method of sintering a unit cell for a solid oxide fuel cell according to claim 1, wherein the microwave application time is within 1 hour. The solid oxide fuel cell (SOFC) unit cell formed by a sequential combination of a cathode layer, an electrolyte layer and an anode layer is molded and sintered according to a conventional ceramic manufacturing process to surround the sintered body with zirconia or silicon carbide-based insulation. A unit cell for a solid oxide fuel cell, wherein the unit cell is placed inside a reactor, and microwaves are added to the reactor for a predetermined time. The unit cell for a solid oxide fuel cell according to claim 4, wherein the microwave wavelength is 1-60 GHz. The unit cell for a solid oxide fuel cell according to claim 4, wherein the microwave is applied within 1 hour.

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