JPH0412068A - Bonded material of ceramic and bonding - Google Patents

Abstract

PURPOSE:To increase mechanical bond strength at high temperature and to prevent leakage of gas, by providing the surface of ceramic to be bonded with a metal layer which melts at a temperature of use and is reacted with a gas in an atmosphere to form a stable compound and melting the metal layer. CONSTITUTION:A metal layer 3 which melts at a temperature of use and is reacted with a gas in an atmosphere to form a stable compound is laid on a bonding part of ceramics 2 and 4, melted and is reacted with the gas in the atmosphere to give a bonded material of ceramic. Various kinds of metals can be used as the metal for bonding and aluminum which melts at a relatively low temperature of 660 deg.C and is reacted with oxygen in air to form alumina, a stable ceramic material, is suitable. The above-mentioned material of ceramic is suitable as a constituent member of high-temperature type fuel cell especially useful as an electrolyte of solid oxide.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a ceramic bonded body and a bonding method, and particularly to a bonded body and bonded body used as constituent members of a high-temperature fuel cell using a solid oxide electrolyte. Regarding the method.

[Prior art] Fuel cells are capable of converting chemical energy directly into electrical energy with high efficiency, so they are being developed as a power generation method to replace the current power generation method using steam generated from the combustion of fossil fuels. .

Among these, fuel cells using solid electrolytes that do not contain liquid or molten electrolytes and operate as electrolytes at high temperatures are being developed as third-generation fuel cells.

High-temperature fuel cells using solid electrolytes use zirconium oxide, which acts as an oxygen ion conductive electrolyte at high temperatures, stabilized by adding yttrium oxide or calcium oxide. In addition, various fuels such as hydrogen, carbon oxide, and hydrocarbons can be used, and since the electrolyte is solid, evaporation of the electrolyte, which is unavoidable in fuel cells using liquid or molten salt as the electrolyte, can be avoided. There is no problem of corrosion caused by fuel cells, and the structure is similar to that of a fuel cell.

In addition, because the operating temperature is high, expensive catalysts such as platinum group metals are not required, and the exhaust heat is also high temperature, so the exhaust heat can be effectively used for gas turbine power generation or steam generation. It has extremely high energy efficiency and is expected to be the most energy-efficient fuel cell.

- The generated voltage of a fuel cell consisting of a pair of positive and negative electrodes is about 1.2 volts when open, and the output current is also limited by the efficiency of the cell, so it is difficult to use a fuel cell for power generation in large numbers. It is necessary to electrically connect several unit fuel cells in series and parallel. When stacking unit fuel cells, sealing the unit fuel cells is important.

If the stacked parts of the unit fuel cells of a fuel cell are not sufficiently sealed, gaps will occur and oxygen and fuel gas will leak. If a gas leak occurs, the supplied gas will not be used for the cell reaction, which will not only reduce the fuel utilization rate but also be dangerous if oxygen and fuel gas mix.

In the case of phosphoric acid type fuel cells, the operating temperature is around 200°C, so it is possible to use gaskets such as fluororesin, and in the case of molten carbonate type fuel cells, the operating temperature is around 600°C. In addition, the molten salt that acts as an electrolyte acts as a kind of liquid seal.

However, high-temperature fuel cells that use solid electrolytes have high operating temperatures of 850°C to 1000°C, and no effective sealing material or method has been found. This is one of the development issues.

[Problem to be solved by the invention] Ceramics can be joined using mechanical joining, adhesive joining, metallization method in which a metal layer is formed on the surface of ceramics and then brazed, soldering method, and solid state joining using atomic diffusion. There are legal welding methods such as laser or electron beam welding, but
There are inorganic adhesives, metal solder methods, oxide solder methods, etc. that can bond the solid electrolytes of high-temperature fuel cells that operate at high temperatures of 1000°C. In some cases, pores are always present due to dehydration, resulting in poor gas sealing properties. Also, in other bonding methods, the difference in linear expansion coefficient is generally 2xlO-'
If the temperature exceeds l/℃, the bonding will be difficult, so in order to alleviate the stress caused by the difference in thermal expansion, it is necessary to laminate multiple layers of materials with intermediate coefficients of thermal expansion, or to process the bonded members. Vacuum and high temperatures were required, and the processing steps were complicated.

[Means for Solving the Problems] As a result of intensive studies on bonding ceramics, the present inventors provided a metal layer that melts at the operating temperature on the surfaces of the ceramics to be bonded, and heated the ceramics in the atmosphere. It was discovered that a strong bonded body could be obtained even at high temperatures by melting the metal and then allowing the reaction with oxygen in the air to proceed to bond and seal the ceramics.

That is, the present invention has sufficient bonding strength even at high temperatures such as 850°C to 1000°C, which is the operating temperature of high-temperature solid electrolyte fuel cells, and can sufficiently withstand thermal stress at high temperatures and during cooling. In order to obtain a bonded body, a layer of metal such as aluminum that melts at the operating temperature is formed on the bonded part of the ceramic, and is heated and melted while in contact with the body to be bonded, as well as reacting with the gas in the atmosphere. be.

The metal formed on the joint surface is not limited to aluminum, but also metals such as magnesium, cerium, bismuth, tin, indium, silver, lead, strontium, etc., and alloys such as aluminum-magnesium, aluminum-silicon, and aluminum-zinc, which are melted below the operating temperature. Many metals can be used, but metals that form compounds with high vapor pressure in high-temperature usage environments and substances that cause decomposition reactions at usage temperatures may evaporate during use or This is very unfortunate because the strength of the bonded body decreases and the bond itself breaks.

[Function] A metal layer that melts at the operating temperature and reacts with the gas in the atmosphere to form a stable compound on the surface of the ceramics to be bonded, and the ceramics are bonded by melting and reacting with the gas in the atmosphere. This increases mechanical bonding strength and prevents gas leakage at high temperatures.

[Examples] Examples of the present invention will be shown below to explain the present invention in more detail.

FIG. 1 shows a cross-sectional view of a ceramic bonded body 1 of the present invention, in which a metal layer 3 is formed on the bonding surface of at least one ceramic 2, and a ceramic 4 to be bonded is placed on the metal surface. Heat.

By heating, the metal melts and reacts with the gas in the atmosphere to obtain a bonded body.

Is it possible to use various metals for the metal layer used for bonding?Alumina, which is a stable ceramic material, can be formed by melting at a relatively low temperature of 660℃ and reacting with oxygen in the air. Aluminum or suitable to produce. Silicon oxide has excellent properties as a material for ceramics.
Alternatively, while zirconia has a high melting point, it reacts with oxygen at a relatively low temperature. In particular, zirconium has a melting point of 1900° C., but reacts violently with oxygen at low temperatures in air. Therefore, it is extremely difficult to obtain a bonded body of these substances by forming an oxide from the metal in a molten state.

It is also possible to obtain a bonded body by forming a compound layer such as a metal Alcolade on the surface of the ceramic instead of a metal layer, and forming oxides on the bonding surface by thermal decomposition in an oxygen-containing atmosphere. However, the airtightness of the joint is poor due to the gas generated during the production of metal oxides, so it cannot be applied to applications where airtightness is a problem.

The metal layer formed on the joint surface can be in the form of a metal plate, foil, powder, paste, etc., and the thickness of the metal layer is 0.005 mm-0, 5 mTl1.
Preferably it is in the range of OO1 to 005 mm. If the surface condition of the ceramics to be bonded is rough, a relatively thick metal layer is necessary, but if the surface condition is dense, a thin metal layer is sufficient.

Further, the present invention can be used not only for joining ceramics to ceramics, but also for joining metals to ceramics.

Example 1 A bonding experiment was conducted using small pieces of aluminum zirconia and lanthanum chromite, each measuring 3 mm x 10 mm x 50 mm, as ceramics.

These materials have linear expansion coefficients shown in Table 1.

These ceramics were laminated with an aluminum foil having a thickness of 015 mm sandwiched between them, and heated to 1000° C. in the atmosphere to obtain a bonded body.

Both bonded bodies have sufficient strength even at high temperatures, and although the ceramics used for bonding have a difference in linear expansion coefficient of 4X10-81/'C, thermal stress caused by the difference in linear expansion coefficient A durable zygote was obtained.

It was also confirmed that alumina was generated at the joint.

Example 2 A tube made of the same material as in Example 1 with a diameter of 30 mm and a thickness of 5+ nm was molded into a dense alumina tube with an outer diameter of 25 mm, an inner diameter of 23 mm, and a length of 150 mm. A foil was provided and bonded. When we tested the gas sealing properties by evacuating the inside of this tube with an oil rotary pump at room temperature and setting the outside of the tube to atmospheric pressure, we found that it was possible to evacuate to a pressure of 10-3 torr or less for any type of ceramic material. , gas sealing properties were good.

A similar sealing test was also conducted at 1000°C, and the same results as at room temperature were obtained, and the sealing performance at high temperatures was also good.

[Effects of the Invention] The present invention provides a metal layer that melts at the working temperature and reacts with the gas in the atmosphere to form a stable compound on the joint surfaces of the ceramics to be joined, and causes the metal layer to melt and react with the gas in the atmosphere. A ceramic bonded body with high bonding strength and excellent gas sealing properties can be obtained using a simple bonding method.It maintains its strength and gas sealing properties even at high temperatures, so it operates at temperatures around 1000℃. It is also suitable for bonding and sealing high-temperature fuel cells using solid electrolytes.

[Brief explanation of the drawing]

Claims (6)

[Claims] (1) A ceramic bonded body having a bonding layer made of a compound obtained by melting a metal layer formed at a bonding portion and then reacting with an atmospheric gas. (2) The ceramic bonded body according to claim 1, wherein the metal layer is aluminum. (3) A method for joining ceramics, which comprises providing a metal layer on the joint portion that melts at the operating temperature and reacts with atmospheric gas to form a stable compound, which is then melted and reacted with atmospheric gas. (4) The method for joining ceramics according to claim 3, wherein the metal layer is aluminum. (5) The ceramic bonded body according to claim 1 or 2, wherein the ceramic is a component of a fuel cell. (6) The method for joining ceramics according to claim 3 or 4, wherein the ceramic is a component of a fuel cell.