KR20010016867A - Metod for manufacturing γ-LiAlO2 matrix for Molten Carbonate Fuel Cell - Google Patents

Abstract

PURPOSE: An economical and environment-friendly hydrous tape casting process is provided to reduce the drying time of the process shorter than a time required for drying an alcoholic solvent by using protein as a binder. CONSTITUTION: HSA-10 100g, LSA-50 50g and Al(OH)3 39g are mixed into distilled water 100ml and the first ball milling is performed for three days. Glycerine 15ml and deaerator 1ml are mixed into two kinds of slurry where gelatine 9g and ovalbumin 16g are added, and the second ball milling is performed for six hours. A vacuum pump is used to eliminate bubbles while maintaining the first slurry containing ovalbumin at a room temperature and the second slurry containing gelatine at a temperature of 70 to 90°C. The first slurry is tape cast with a blade height of 1mm and a blade velocity of 4mm/s to produce a green sheet. The green sheet is cured. The second slurry is made into a green sheet(2) and left at a room temperature to be gelled. The green sheets are heat treated to produce gamma-LIAlO2 matrix.

Description

Method for manufacturing gamma-lithium aluminate matrix for molten carbonate fuel cell using aqueous slurry {Metod for manufacturing γ-LiAlO2 matrix for Molten Carbonate Fuel Cell}

The present invention relates to a method for preparing a γ-LiAlO2 matrix, which is an electrolyte support of a molten carbonate fuel cell (hereinafter referred to as MCFC), and in particular, an aqueous γ-LiAlO2 particle slurry using water as a dispersion medium. It relates to a method for producing a γ-LiAlO 2 matrix using.

The MCFC electrolyte matrix serves as an electrical non-conductor to prevent shorts between the two electrodes, and serves as a passage for moving carbonate ions from the cathode to the anode, while preventing cross-over between fuel gas and oxidizing gas. Play a role.

In order to fulfill this role, the material of the matrix should be chemically inert with the constituents of the cell, in particular the molten carbonate electrolyte material in the cell operating temperature range of 650 ° C, and the porosity or pore size should be small during operation.

That is, the sintering phenomenon by Oswald ripening or the diffusion phenomenon along the surface or volume of the material should not occur.

In addition, since the matrix for MCFC must continue to contain the electrolyte during the operation of the cell, the pore size of the matrix should be less than 0.5㎛ less than the pore of the electrode.

That is, the pore size of the matrix must be smaller than the pore size of the electrode so that the electrolyte contained in the pores of the matrix does not overflow toward the electrode, and the porosity of 50 to 70% must be maintained for the matrix to be practically used.

In addition, the thickness of the matrix has a significant effect on the cell performance. The thinner the thickness, the lower the ohmic loss, and the easier the gas crossover, it is important to set the optimum thickness.

γ-LiAlO2 is a material widely used as a matrix material for MCFC because it satisfies the above conditions well. Among the γ-LiAlO2 powders, a material having a specific surface area of 10 m2 / g is most suitable for the preparation of the matrix. Known.

However, the use of commercially available submicron-sized γ-LiAlO2 together with large particle size γ-LiAlO2 is required to enhance mechanical strength because it is less resistant to crack formation and propagation during thermal cycling. It is common to add.

It is known that γ-LiAlO 2 having a large particle size deflects the direction of crack propagation and suppresses crack formation.

Methods for producing γ-LiAlO2 matrices include hot pressing, cold pressing, paper making methods, electrophoretic deposition, tape casting, and the like. have.

Among these, tape casting is the most widely used method for manufacturing matrices for MCFC due to its advantages such as being easy to manufacture a thin thickness matrix, relatively easy to control porosity, and mass producing a large area matrix.

However, the γ-LiAlO2 matrix manufacturing process for MCFC, which is currently mainly used, uses a highly toxic dispersion medium such as toluene, dibutyl phthalate (DBP), polyvinyl butyral (PVB), and organic additives to prepare the slurry. In the case of large-scale production facilities, not only the working environment but also the environmental pollution problem is serious, so it is urgent to develop an environment-friendly manufacturing process to solve this problem.

In order to solve this problem, a process of preparing γ-LiAlO2 matrix using water as a dispersion medium instead of a toxic solvent is preferable. However, when γ-LiAlO2 reacts with water, it causes severe coagulation like dough, which makes tape casting impossible. Γ-LiAlO2 matrix manufacturing process using slurry has not been developed yet.

1 shows a casting apparatus of an aqueous γ-LiAlO 2 slurry comprising a gelatin binder.

FIG. 2 shows a casting apparatus of an aqueous γ-LiAlO 2 slurry comprising an ovalbumin binder.

Figure 3 is an X-ray Diffiraction diagram of commercial γ-LiAlO2 and synthesized aqueous γ-LiAlO2.

4 is a pore size distribution of an aqueous γ-LiAlO 2 matrix.

5 is a SEM image of the surface of an aqueous γ-LiAlO 2 matrix.

Figure 6 is a SEM image of the fracture surface of the aqueous γ-LiAlO2 matrix.

<Description of the code | symbol about the principal part of drawing>

1: Water-based γ-LiAlO 2 slurry containing gelatin binder

1 ': Aqueous γ-LiAlO2 slurry containing an ovalbumin binder

2, 2 ': Green Sheet

3, 3 ': carrier film

4, 4 ': blade

5: heating wire

Therefore, the present inventors prevent the reaction between γ-LiAlO2 particles and water molecules, while drying the time of drying the volatile alcohol solvent using protein as a binder to shorten the drying time which is a problem in general aqueous slurry casting process. Invented an economical and environmentally friendly water based tape casting process that can be lowered below.

Addition of a dispersant is necessary to make a stable slurry in the tape casting process, and a binder and a plasticizer are required in order to give adequate strength and flexibility to the manufactured green sheet.

Among these additives, the binder forms crosslinks between the organic matter and strong adsorption after the solvent evaporates, thereby facilitating the workability and integrity of the green sheet.

Therefore, the physical properties of the binder ① act as a lubricant between the particles, ② must not interfere with the removal of the volatilization of the solvent or bubbles, ③ must also be effective in a small amount, ④ high to give strength to the green sheet Must have a molecular weight.

As a water-based binder that satisfies these conditions, polyvinyl alcohol (PVA), methylcellulose, acrylic acid, and synthetic latex are used in the present invention. A process using inexpensive protein was introduced.

Proteins that can be used as binders in water based tape casting processes include water-soluble proteins such as ovalbumin, gelatin and oryzenin.

Such proteins can be classified into hard gels by heating these aqueous solutions, such as ovalbumin, depending on their physical properties, and by forming elastic gels when the aqueous solution is left at room temperature below the boiling point of water, such as gelatin.

When the protein is used as a binder, one of the problems of water-based tape casting, which is a long drying time, can be compensated for, and the water-soluble proteins have the advantage of not having to add a separate dispersant by improving the dispersibility of the slurry. .

In order to efficiently manufacture the γ-LiAlO2 matrix for MCFC by tape casting with an aqueous γ-LiAlO2 particle slurry as in the present invention, the following conditions are preferable.

First, it is necessary to prevent excessive aggregation such as kneading due to the reaction between γ-LiAlO2 and water. Therefore, LiOH · H2O and Al (OH) 3 should be added to prevent agglomeration of the slurry and at the same time, LiOH · H2O and Al (OH) 3 added during the heat treatment should be reacted and transferred to the γ-LiAlO2 phase.

Second, the drying conditions should be appropriately selected according to the type of protein used to prevent cracking of the green sheet.

In other words, the heating temperature and time of the protein that causes curing by heating should be controlled, and the temperature of leaving the gelling protein should be lower than the gelling temperature.

The present invention as described above can be applied to the production of γ-LiAlO2 matrix by the tape casting apparatus as shown in Figures 1 and 2, in particular, because it uses a material that is not toxic at all, optimal in terms of pleasant working environment composition and environmental pollution prevention It can be said that the process of.

Hereinafter, the present invention will be described based on the following examples. The following examples are provided to illustrate the present invention more specifically, but the present invention is not limited thereto. In particular, the following examples are described for example ovalbumin and gelatin among various available proteins, and other water-soluble proteins, starch and the like can also be obtained.

For the preparation of the slurry for tape casting, firstly, 100 g of HSA-10 (average particle size: 2 µm, specific surface area: 10 m 2 / g) and commercially available γ-LiAlO2 powder (from Cyprus Foote Mineral Co.) Particle size: 50 μm, specific surface area 0.1 m 2 / g) To prevent the reaction of γ-LiAlO 2 with water at 50 g, 21 g of LiOH H2O (from Yakuri Pure Chemicals Co.) and Al (OH) 3 (from Fluka Chemical Co.) After mixing 39g in 100ml of distilled water, the first ball milling was performed for 3 days. To give strength and flexibility to the green sheet, two kinds of slurries containing 9 g and 16 g of gelatin and ovalbumin, which are proteins of different properties as binders, were mixed with 15 ml of glycerin and 1 ml of defoamer for 2 hours for 6 hours. Ball milling was performed.

Depending on the type of binder added, the slurry containing ovalbumin was maintained at room temperature, and the slurry containing gelatin was maintained at about 70-90 ° C., bubbles were removed by a vacuum pump, and adjusted to a viscosity suitable for a tape casting process.

The green sheet (2 ') produced by tape casting the slurry added with ovarianbumin as a binder at a blade (4') height of 1 mm and a blade (4 ') moving speed of 4 mm / s was kept at about 60 ° C to cure. Caused.

The slurry to which the gelatin was added was made to produce a green sheet 2 using the apparatus of FIG. 1 and then left at room temperature to cause gelation.

The green sheets (2, 2 '), which were dried within a few minutes, were heat-treated at 650 ° C., which is an operating temperature of MCFC, for 48 hours to prepare a γ-LiAlO 2 matrix.

Physical properties of the final γ-LiAlO 2 matrix were measured according to the following measurement methods.

① Component analysis: It was confirmed that the total amount of γ-LiAlO2 was synthesized by reacting LiOH.H2O and Al (OH) 3 present in the matrix prepared by X-ray diffraction.

② Microstructure: The surface and fracture surface of the matrix were observed by SEM.

③ Porosity: Mercury Porosimeter which is generally used for measuring porosity of γ-LiAlO2 matrix for MCFC was used.

④ Strength: The strength of the matrix prepared by the 3-point bending test was measured. As in the present invention, the three-point bending strength when the matrix has a rectangular shape is obtained by the following equation.

Where P is the applied load (kgf), L is the length of the specimen (cm), b is the width of the specimen (mm), and d is the thickness of the specimen.

As a result of analyzing the γ-LiAlO2 matrix thus prepared by X-ray, as shown in FIG. 3, the same pattern as the commercially available γ-LiAlO2 powder was subjected to the same heat treatment conditions.

In other words, it can be seen that LiOH.H 2 O and Al (OH) 3 added to prevent the reaction between the γ-LiAlO 2 particles and water were synthesized in the total amount of γ-LiAlO 2.

5A and 5B are SEM photographs of the surface of the aqueous γ-LiAlO 2 matrix, and FIGS. 6A and 6B are SEM photographs of the fracture surface of the aqueous γ-LiAlO 2 matrix.

In Figure 6 (a) it can be seen that the rod-like γ-LiAlO2 secondary phase is known to be effective for increasing the strength of the matrix.

In the present invention, since the γ-LiAlO2 rod-shaped particles produced-dispersed in the matrix do not have the orientation of the reinforcing material which appears when the slurry prepared by adding the reinforcing material such as rod-shaped particles or fibers to the initial combination does not exist, the strength of the matrix is enhanced. More effective.

As a result of measuring the porosity and strength after heat-treating the γ-LiAlO2 matrix prepared in the present invention at 650 ° C. for 24 hours, the pore size was about 0.1 μm and the porosity was about 55 to 65%, and the bending strength was 160 It was found that it was suitable as a matrix for MCFC at ˜200 gf / mm ² .

Although the present invention has been described above with reference to specific embodiments, the present invention is not limited thereto.

Those skilled in the art will be able to easily conceive various modifications from the above embodiments, and all such modifications and variations should be construed as being included in the scope of the present invention.

Claims (3)

In the method for producing a γ-LiAlO2 matrix for molten carbonate fuel cell, A method of producing a gamma -LiAlO2 matrix for a molten carbonate fuel cell using an aqueous gamma -LiAlO2 slurry containing gamma -LiAlO2 and water and a Li / Al additive. The method of claim 1, wherein the Li / Al-based dispersant is selected from the group consisting of LiOH, LiOH n (H 2 O), Al (OH) 3, and γ-AlOOH, wherein the matrix is produced by a tape casting method Method for producing a γ-LiAlO2 matrix for molten carbonate fuel cell characterized in that. The method of manufacturing a γ-LiAlO2 matrix for molten carbonate fuel cell according to claim 1 or 2, further comprising a water-soluble protein as an additive of the aqueous γ-LiAlO2 slurry.