CN1300275C - Seal agent of medium-temperature solid oxide fuel cell - Google Patents

Abstract

The present invention relates to a glass and ceramic sealing agent, particularly to a sealing agent of medium-temperature solid oxide fuel cells, which comprises glass powder and a binding agent, wherein the binding agent is a binding agent usually used in the prior art. The present invention is characterized in that the glass powder has a formula: 30 to 60 wt% of SiO2, 0 to 10 wt% of Al2O3, 10 to 40 wt% of B2O3, 5 to 10 wt% of Na2O and 5 to 10 wt% of CaO. In the glass powder of the present invention, high SiO2 content can ensure thermal shock resistance; the addition of the Al2O3 and the CaO enhances the mechanical performance of the sealing agent; high B2O3 content and a small amount of Na2O can greatly reduce the melting temperature of the sealing agent, and the softening temperature is about 700 DEG C; thus, the present invention is especially suitable for being used at medium temperature; meanwhile, owing to low Na2O content in the present invention, favorable electric insulation of the sealing agent can be guaranteed during cell operation; a small amount of free Al2O3 is added to form the glass and ceramic sealing agent, and thus, the resistance is further increased; as a result, the present invention has an insulating effect. The sealing agent has the advantages of simple raw materials, convenient manufacture and low cost is suitable for the sealing use of medium-temperature solid oxide fuel cell groups.

Description

Sealants for Intermediate Temperature Solid Oxide Fuel Cells

technical field

The invention relates to a glass ceramic sealant, in particular to a sealant for a medium temperature solid oxide fuel cell.

Background technique

A solid oxide fuel cell (SOFC) is an all-solid-state fuel cell, usually composed of two porous ceramic electrodes and a solid oxide electrolyte between the electrodes. Oxygen obtains electrons at the cathode to form oxygen ions, diffuses to the anode through the electrolyte, and reacts with the fuel to generate electrons, H ₂ O and CO ₂ , and the electrons return to the cathode through an external circuit. The fuel of the solid oxide fuel cell is usually hydrogen, methane, natural gas, etc., the oxidant is air, and the fuel and air flow in their respective channels. Electrochemical conversion occurs near the three-phase region, where fuel and air electrochemically react to produce DC power output. In the actual application of single cells and battery stacks, in order to prevent direct contact between oxygen and fuel gas to reduce the efficiency of the cell and even cause the risk of explosion, the fuel gas and oxidizing gas (air) must be completely isolated. That is, the individual cells or different parts of the stack must be sealed. Sealing methods in the prior art mainly include compression seals and sealants. Compression sealing is prone to stress concentration, which limits the height and number of layers of the battery stack, so most of the current sealants are used to achieve sealing. The sealant should generally have a suitable softening temperature and melting temperature. According to different operating temperatures, fuel cells can be divided into low-temperature, medium-temperature and high-temperature fuel cells. This requires the softening temperature and melting temperature of the sealant to be compatible with it. For intermediate temperature solid oxide fuel cells with an operating temperature in the range of 600-800°C, the sealant must have good thermal and chemical stability and good electrical insulation when used at operating temperature and room temperature; At the same time, it is required to have good thermal expansion matching with each part of the battery, and the general thermal expansion coefficient is 9-15×10 ^-6 /°C.

Chinese patent application 91101165 discloses a sealing glass composition, which includes 18-70wt% lead oxide, 18-60wt% vanadium oxide, 1-10wt% phosphorus oxide, 0-30wt% bismuth oxide, 1-15wt% at least one An oxide selected from antimony oxide and selenium oxide and 0.5-5 wt% niobium oxide. The sealant can only achieve satisfactory bond strength at a sintering temperature lower than 400°C, because its service temperature is too low to be suitable for intermediate temperature solid oxide fuel cells. Disclosed in Chinese patent application 96115217 is a kind of ceramic high-temperature sealing bonding method, and it adopts weight ratio (0.1-0.3) K ₂ O: (0.1-0.3) Na ₂ O: (0.2-0.5) PbO ₂ : (0.2- 0.5) CaO: (0.2-0.5) Al ₂ O ₃ : (2.0-2.3) SiO ₂ The glaze prepared by the ratio is fired at a temperature of 800-1300 ° C and an atmosphere of 4-25% oxygen to make the ceramic , Porous ceramics or bonding between combinations. It is suitable for use in high temperature solid oxide fuel cells. Bonding between ceramics or combinations. It is suitable for use in high temperature solid oxide fuel cells.

Disclosed in EP0982274A2 is a glass sealant for intermediate temperature solid oxide fuel cells, and its two groups of formulations are as follows: (1) 55-65wt% SiO ₂ , 0-3wt% Al ₂ O ₃ , 0-4wt% Li2O, 6 -12wt% _K2O , 2-8wt% _Na2O , _0-5wt % BaO, 0-6wt% ZrO2, 15-20wt% ZnO, 0-5wt% TiO2; (2 ₎ 50-70wt% _SiO2 , 0-5wt% Al ₂ O ₃ , 0-6wt% Li ₂ O, 5-15wt% K ₂ O, 2-10wt% Na ₂ O, 0-10wt% BaO, 0-10wt% ZrO ₂ , 10-25wt %ZnO, 0-5 wt% _TiO2 . From the perspective of their formula, they mainly use zinc-silicon alkali glass compound with high yield point or high expansion coefficient. Since it contains a large amount of alkali metal oxide, it cannot guarantee good electrical insulation during battery operation.

Also disclosed in US6271158 is a sealant for medium temperature solid oxide fuel cells, which is made of 40-90wt% glass frit as a matrix, and the filler in the sealant is selected from metal materials and ceramic materials, accounting for 10-60wt%. The agent can seal the gap of 3mm. The glass transition temperature is 500-800°C, and the thermal expansion coefficient is 8-13×10 ^-6 /°C. The main components of glass frit are: 50-70wt% SiO ₂ , 10-25wt% ZnO, 5-20wt% K ₂ O, 0-15wt% Na ₂ O, 0-8wt% Li ₂ O, 0-8wt% BaO, 0 - 5 wt% _ZrO2 , 0-3 wt% CaO, 0-2 wt% MgO. The main components of the filler are: 12-77wt% Ni, 3-65wt% Fe, 16-23wt% Cr, 0-15wt% W, 0-6wt% Co, 0-5wt% Al and the like. The sealant also contains a large amount of alkali metal oxide, and the filler is also an all-metal material, so it will also produce electronic conductivity when used, and cannot be completely electrically insulated.

Contents of the invention

The object of the present invention is to provide a sealant for medium temperature solid oxide fuel cells with high resistivity and good insulation effect, aiming at the deficiencies of the prior art.

The purpose of the present invention is achieved in the following ways.

The sealant for intermediate temperature solid oxide fuel cells of the present invention includes glass powder and a binder, the binder is a commonly used binder in the prior art, such as water or Na ₂ SiO ₃ ·9H ₂ O (0-10wt%) or (0-10wt%) Al ₂ O ₃ , etc., characterized in that the formula of the glass powder is: 30-60wt% SiO ₂ , 0-10wt% Al ₂ O ₃ , 10-40wt% B ₂ O ₃ , 5-10 wt% _Na2O , 5-10 wt% CaO.

The preparation process of the glass powder is as follows: Weigh the raw materials according to the ratio of the above-mentioned glass components, mix the materials by ball milling, put them into a stainless steel crucible and put them in a muffle furnace, keep them warm at 1000°C (or 900°C) for 2 hours, and then water Tempered into glass, dried, crushed and ground into glass powder.

The sealing process using this sealant is: (1) component processing. Grind the stainless steel parts to be sealed with sandpaper, scrub with alcohol cotton balls, and scrub the ceramic surface; (2) Take a certain amount of glass powder, add a binder, mix and grind it, and make it into a paste, and choose different according to different usage occasions The amount of binder used to obtain the desired consistency of the paste, said binder is water or Na ₂ SiO ₃ .9H ₂ O (0-10wt%) or (0-10wt%) Al ₂ O ₃ etc.; (3 )Apply the paste sealant evenly on the seal, make it tight and dry in the shade for 24 hours. (4) Raise the sealing part from room temperature at 0.5°C/min to 180°C and keep it warm for 30 minutes; raise it at 1°C/min to above the glass melting point and keep it warm for 30 minutes; then lower it to 50°C below the glass softening temperature at 1°C/min Left and right, constant temperature use.

Compared with the sealant of the existing solid oxide fuel cell, in the glass powder of the sealant of the present invention, a large amount of SiO ₂ can ensure good thermal shock resistance; the addition of Al ₂ O ₃ and CaO can improve its mechanical properties ; There is a large content of B ₂ O ₃ and a small amount of Na ₂ O, which can greatly _reduce the melting temperature of the sealant, making its softening temperature around 700°C, which is especially suitable for use at medium temperatures; Low, to ensure that the resistance of the sealant is large enough during battery operation; and a small amount of Al ₂ O ₃ powder can be added to form a glass-ceramic seal, which further increases the resistance and achieves a high insulation effect.

In actual use, the sealant of the present invention can also adjust _the softening temperature and melting temperature of the sealant by adjusting the amount of _B2O3 and _SiO2 .

The sealing agent of the present invention adopts simple raw materials, simple manufacturing process and low cost, and is suitable for battery stacks.

Detailed ways

Example 1

(1) Weigh each component with the ratio of 30wt% SiO ₂ , 10wt% Al ₂ O ₃ , 40wt% B ₂ O ₃ , 10wt% Na ₂ O, and 10wt% CaO, put them in a ball mill and mix them into Ball milled in a ball mill for 24 hours.

(2) Put it into a stainless steel crucible and put it in a muffle furnace, keep it warm at 1000°C (or 900°C) for 2 hours, then water quench it into glass, dry it, crush it and grind it into glass powder.

(3) After adding water to make a paste, it is used to seal stainless steel tubes and YSZ ceramic sheets. After operating according to the sealing process, rise from room temperature to 180°C at 0.5°C/min and keep warm for 30min; After testing, the sealant melted completely, flowed, and evenly distributed, and bonded well with stainless steel and YSZ, and the airtightness was measured to be very good. When used to seal the YSZ electrolyte single cell, the open circuit voltage of the battery measured at 450°C is 1.12v, which is close to the theoretical value, which shows that its sealing effect and electrical insulation effect are good.

Example 2.

(1) Weigh each component with the ratio of 45wt% SiO ₂ , 1wt% Al ₂ O ₃ , 38wt% B ₂ O ₃ , 8wt% Na ₂ O, 8wt% CaO, put them in a ball mill and mix them in Ball milled in a ball mill for 24 hours.

(2) Put it into a stainless steel crucible and put it in a muffle furnace, keep it warm at 1000°C (or 900°C) for 2 hours, then water quench it into glass, dry it, crush it and grind it into glass powder.

(3) After adding binder water to make a paste, it is used to seal stainless steel pipes and YSZ ceramic sheets. After operating according to the sealing process, rise from room temperature at 0.5°C/min to 180°C and hold for 30 minutes; rise to 750°C at 1°C/min and hold for 30 minutes; then drop to 700°C at 1°C/min and hold for 120 minutes. After testing , The sealant melts completely, flows, distributes evenly, and bonds well with stainless steel and YSZ. When it is used to seal YSZ cells, the open circuit voltage measured at 450°C is 1.16v, which is close to the theoretical value, which shows that its sealing effect and electrical insulation effect are good.

Example 3.

(1) Weigh each component with the ratio of 60wt% SiO ₂ , 8wt% Al ₂ O ₃ , 12wt% B ₂ O ₃ , 10wt% Na ₂ O, 10wt% CaO, put them in a ball mill and mix them in Ball milled in a ball mill for 24 hours.

(2) Put it into a stainless steel crucible and put it in a muffle furnace, keep it warm at 1000°C (or 900°C) for 2 hours, then water quench it into glass, dry it, crush it and grind it into glass powder.

(3) After adding binder water to make a paste, it is used to seal stainless steel pipes and YSZ ceramic sheets. After operating according to the sealing process, rise from room temperature at 0.5°C/min to 180°C and hold for 30 minutes; rise to 800°C at 1°C/min and hold for 30 minutes; then drop to 700°C at 1°C/min and hold for 120 minutes. After testing , The sealant melts completely, flows, distributes evenly, and bonds well with stainless steel and YSZ. When it is used to seal YSZ cells, the open circuit voltage measured at 450°C is 1.07v, which shows that its sealing effect and electrical insulation effect are good.

Example 4.

(1) Weigh each component with the ratio of 52wt% SiO ₂ , 5wt% Al ₂ O ₃ , 28wt% B ₂ O ₃ , 5wt% Na ₂ O, and 10wt% CaO, put them in a ball mill and mix them into Ball milled in a ball mill for 24 hours.

(2) Put it into a stainless steel crucible and put it in a muffle furnace, keep it warm at 1000°C (or 900°C) for 2 hours, then water quench it into glass, dry it, crush it and grind it into glass powder.

(3) After adding binder water to make a paste, it is used to seal stainless steel pipes and YSZ ceramic sheets. After operating according to the sealing process, rise from room temperature at 0.5°C/min to 180°C and hold for 30 minutes; rise to 750°C at 1°C/min and hold for 30 minutes; then drop to 700°C at 1°C/min and hold for 120 minutes. After testing , The sealant melts completely, flows, distributes evenly, and bonds well with stainless steel and YSZ. When used to seal the YSZ single cell, the open circuit voltage measured at 450°C is 1.11v, which shows that its sealing effect and electrical insulation effect are good.

Example 5.

(1) Weigh each component with the ratio of 42wt% SiO ₂ , 8wt% Al ₂ O ₃ , 37wt% B ₂ O ₃ -, 8wt% Na ₂ O, 5wt% CaO, put them in a ball mill and mix them Enter the ball mill in the ball mill for 24 hours.

(2) Put it into a stainless steel crucible and put it in a muffle furnace, keep it warm at 1000°C (or 900°C) for 2 hours, then water quench it into glass, dry it, crush it and grind it into glass powder.

(3) After adding binder water to make a paste, it is used to seal stainless steel pipes and YSZ ceramic sheets. After operating according to the sealing process, rise from room temperature at 0.5°C/min to 180°C and hold for 30 minutes; rise to 750°C at 1°C/min and hold for 30 minutes; then drop to 700°C at 1°C/min and hold for 120 minutes. After testing , The sealant melts completely, flows, distributes evenly, and bonds well with stainless steel and YSZ. When it is used to seal YSZ single cell, the open circuit voltage measured at 450°C is 1.17v, which is close to the theoretical value, which shows that its sealing effect and electrical insulation effect are good.

Claims (1)

1. A sealant for a medium temperature solid oxide fuel cell, comprising glass powder and a binder, the binder is a commonly used binder in the prior art, characterized in that the formula of the glass powder is: 30-60wt% SiO ₂ , 0-10 wt% Al ₂ O ₃ , 10-40 wt% B ₂ O ₃ , 5-10 wt% Na ₂ O, 5-10 wt% CaO.