JPH08293321A - Manufacture of beta-alumina tube - Google Patents

Abstract

PURPOSE: To uniform the scattering of Na2 O from a β-alumina compact at baking and improve the dimensional precision by putting the bottomed cylindrical β-alumina compact in a specified cylindrical fire resisting vessel with the opening end side down followed by baking. CONSTITUTION: A pelleted powder obtained by adding a binder, as occasion demands, to an electromelting MgO powder having a MgO purity of 99.5wt.% or more and a maximum particle size 100μm or less followed by wet mixing, and atomizing and drying the resulting mixture is press molded followed by baking to provide a cylindrical fire resisting vessel 21 having a roundness of inner wall surface <=1.03 and a straightness <=0.2%. A bottomed cylindrical β-alumina compact 25 is set in the space formed of the vessel 21, and an upper lid 22 and a lower lid 23 of the same material with the opening end side down, and baked.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a β-alumina tube capable of firing a β-alumina tube used as a solid electrolyte tube for a Na-S battery with high dimensional accuracy. .

[0002]

2. Description of the Related Art As a firing method for a bottomed cylindrical β-alumina tube, Na ₂ O contained in a β-alumina compact being fired is used.
The following firing methods have been proposed in order to prevent the decrease in ionic conductivity of the β-alumina tube due to the scattering of carbon dioxide and the decrease in its mechanical strength. For example, a platinum metal container,
Refractory container with platinum-based metal coated on the inner wall, MgO
The β-alumina molded body is stored in a refractory container such as Na
It is a method of preventing ₂ O from scattering and heating and firing in the air. Is an expensive container, and eliminates its drawbacks, but it is not always satisfactory because the platinum-based metal and the refractory container cause peeling of the platinum-based metal coating due to the difference in thermal expansion, etc. . The MgO-based refractory container described above does not have these drawbacks, and is attracting attention as a firing container for β-alumina tubes that prevents the above-mentioned problems caused by the scattering of Na ₂ O.

By the way, the bottomed cylindrical β-alumina tube is
When used in an aS battery, high dimensional accuracy is required. In order to meet the demand, a means has been taken to increase the dimensional accuracy of the molded body itself by performing cutting processing with a lathe or the like when manufacturing the molded body. On the other hand, even when the β-alumina molded body is housed in the MgO-based refractory container, if there is a variation in the distance between the inner wall surface of the container and the molded body, Na ₂ from the β-alumina molded body during firing is changed. There is a possibility that the amount of scattered O will partially vary, the growth of β-alumina particles will be partially heterogeneous, and the β-alumina tube will be deformed. At the same time, the uniform ionic conductivity and uniform mechanical strength of the β-alumina tube may be impaired. Therefore, a structure for positioning is provided in the MgO-based refractory container so that the space between the inner wall surface of the container and the molded body is kept constant (Japanese Patent Application Laid-Open No. Hei 3 (1999) -312058).
-88278), and a raw setter using a material having the same firing cracking ratio as that of the formed body as a setter of the β-alumina formed body installed upside down (JP-A-5-58511). There is. However, even if these methods are adopted, if the dimensional accuracy of the cylindrical refractory container itself is low, the interval between the inner wall surface of the container and the molded body cannot be kept constant.

[0004]

DISCLOSURE OF THE INVENTION According to the present invention, when a bottomed cylindrical β-alumina molded body is fired by inverting the open end side in a cylindrical refractory container and inverting it, By reducing the variation in the distance between the wall surface and the bottomed cylindrical β-alumina formed body, the amount of Na ₂ O scattered from the β-alumina formed body is made uniform during firing, and the roundness and straightness can be improved. It is an object of the present invention to provide a method for producing a β-alumina tube having excellent dimensional accuracy.

[0005]

Means for Solving the Problems The present invention for achieving the above-mentioned object is to bake a bottomed cylindrical β-alumina formed body in a cylindrical refractory container with its open end side facing down and inverted. The inner wall surface of the cylindrical refractory container has a circularity of ≦ 1.0.
3. The method of manufacturing a β-alumina tube is characterized in that the straightness is ≦ 0.2%.

Of course, when firing the β-alumina molded body in a cylindrical refractory container with the open end side facing down,
In order to maintain the firing atmosphere, it is necessary to seal the top and bottom of the cylindrical refractory container. Therefore, an upper lid and a lower lid made of the same material as the cylindrical refractory container are prepared, and these and the cylindrical refractory container form a closed space. Further, the distance between the inner wall surface of the upper lid and the bottom of the β-alumina molded body is preferably close to the distance between the inner wall surface of the cylindrical refractory container and the β-alumina molded body. As a material for the cylindrical refractory container, the upper lid and the lower lid, it is preferable to use a dense ceramic body made of MgO or MgO-Al ₂ O ₃ .

The circularity referred to here is a value represented by (maximum diameter / minimum diameter) of the inner wall surface in a cross section perpendicular to the central axis of the cylindrical body. The straightness represents the magnitude of distortion between the central axis of the cylindrical body and the actual central axis of the inner wall surface when the one end surface of the cylindrical body is used as the reference surface. However, here, for simple evaluation, one end face of the cylindrical body is placed on the reference plane, and a mapping is made by projecting the inner wall cross section at any position in the longitudinal direction of the cylindrical body vertically on the reference plane over the entire length. And the maximum deviation of the one end face from the inner wall surface is d, and the total length of the cylindrical body is L, which is expressed as a percentage of d / L.

[0008]

When the bottomed cylindrical β-alumina molded article is fired in a cylindrical refractory container with its open end facing down, the inner wall surface of the cylindrical refractory container has a circularity of ≦ 1.03. ,
By setting the straightness ≦ 0.2%, it is possible to reduce the variation in the interval between the inner wall surface of the cylindrical refractory container and the bottomed cylindrical β-alumina molded body, and to reduce the firing atmosphere of the entire molded body and Na. It is possible to eliminate the non-uniformity of the characteristics of the sintered body due to the variation in the amount of ₂ O scattered.

[0009]

EXAMPLES Examples within the scope of the present invention and those outside the scope of the present invention will be described below as comparative examples. As the material of the cylindrical refractory container, one having a MgO purity of 99.5% by weight or more is used. This is an electro-fused MgO powder having a maximum particle size of 100 μm or less, a binder is added if necessary, wet-mixed, and spray-dried to form a granulated powder, which is press-molded into a cylindrical compact of a desired size. It can be obtained by firing. In this example, the total length was 505 mm × outside diameter 70 mmφ × inside diameter 60 mmφ. The roundness and straightness of the inner wall surface of the obtained MgO-based cylindrical fireproof container were evaluated as follows, and as shown in Table 1, they were classified according to the roundness and straightness.

[0010]

[Table 1]

The roundness is 100 mm, 200 mm, 300 mm, 400 mm from the upper end of the cylindrical refractory container.
And the inner diameter variation at the lower end for measuring inner diameter
Roundness was calculated from the maximum diameter and the minimum diameter at each position, and the maximum value was defined as the roundness of the container.

As for straightness, as shown in FIG. 1, the cylindrical refractory container (11) is set on a horizontal plane A and the cylindrical refractory container (1
The maximum gap (S) formed between the outer wall surface and the plane B which is in contact with at least one point on the outer wall surface of 1) and is perpendicular to the horizontal plane A is measured. Next, the wall thickness (T _X ) of the cylindrical refractory container (11) where the maximum gap is formed and the wall thickness (T _Y ) at the point of contact with the plane B are measured, and the wall thickness is corrected.
The deviation (d) of the inner wall cross section is determined by the maximum gap (S).
And the wall thickness (T _X , T _Y ) are used to obtain d = S + T _X −T _Y , and the value (d / L) obtained by dividing this by the total length (L) of the cylindrical refractory container is the straightness. did.

On the other hand, a β-alumina compact to be fired was prepared as follows. Charged weight composition is Al ₂ O ₃ , Na ₂
90.25%, 9.0% in terms of O and Li ₂ O,
Α-alumina, sodium carbonate, so as to be 0.75%
A lithium aluminate compound was weighed, a binder was added, and the mixture was wet-mixed to obtain a slurry. The slurry was spray-dried to give a granulated powder, which was then molded into a bottomed cylindrical body by CIP (cold isostatic pressing) of 1.5 × 10 ³ Kg / cm ² . Further, by cutting the outer surface of the molded body with a lathe, the outer surface has a roundness of 1.0005 or less and a straightness of 0.
05% or less, total length 490 mm × outer diameter 55 mm φ ×
A bottomed cylindrical molded body having an inner diameter of 47 mmφ was prepared.

Example 1 As shown in FIG. 2, a cylindrical refractory container (21) having a roundness of 1.000 or more and 1.015 or less and a straightness of 0.1% or less was prepared. The upper lid (22) and the lower lid (23) made of the same material as the cylindrical refractory container (21).
The bottomed cylindrical molded body (25) was placed upside down with the open end side facing down in a space consisting of the and the cylindrical refractory container (21). In addition, in this example, the concave portion is made of the same material as that of the cylindrical refractory container (21), and the concave portion is formed so that the interval between the bottomed cylindrical molded body (25) and the cylindrical refractory container (21) becomes constant. The setter (24) provided was prepared, and the bottomed cylindrical molded body (25) was placed in the recess. 15 in an electric furnace
Calcination by heat treatment at 70 ° C for 1 hour
An alumina tube was obtained.

The dimensional accuracy of the β-alumina tube was evaluated by the roundness and straightness of its outer surface. The roundness is 100 mm, 200 m in the length direction from the opening end and the opening end.
It was measured at the positions of m and 300 mm, and the maximum value was defined as the roundness of the β-alumina tube. As for the straightness, the maximum gap was measured in the same manner as the straightness of the cylindrical refractory container, and the value without thickness correction was taken as the straightness of the β-alumina tube. The roundness of the β-alumina tube was less than 1.005, and the roundness was 1.005 or more. Also, the straightness of less than 0.4% passes,
Those with 0.4% or more were rejected. And roundness,
Those that passed both straightness were regarded as comprehensive passes. When such an evaluation was performed on 10 β-alumina tubes, 10 roundness passes, 9 straight passes, and 9 total passes.

Example 2 Example 2 is a cylindrical refractory container having a circularity of 1.00.
In this example, 0 or more and 1.015 or less and a straightness of more than 0.1% and 0.2% or less were prepared, and the other conditions were evaluated in the same manner as in Example 1. The 10 baked β-alumina tubes had 9 roundness passes, 9 straightness passes, and 8 overall passes.

Example 3 Example 3 is a cylindrical refractory container having a circularity of 1.01.
5 and 1.030 or less, and straightness is 0.1
% Is prepared, and the others are the same as in Example 1. The 10 baked β-alumina tubes had 9 roundness passes and 9 straightness passes,
The total passing was eight.

Example 4 Example 4 is a cylindrical refractory container having a roundness of 1.01.
5 and 1.030 or less, and straightness is 0.1
% And 0.2% or less are prepared, and the others are the same as in Example 1. Baked β
-The ten alumina tubes had 9 roundness passes, 8 straightness passes, and 7 overall passes.

Comparative Examples 1 to 12 In Comparative Examples 1 to 12, at least one of the roundness and straightness of the cylindrical refractory container is outside the scope of the present invention as shown in Table 1, and these are Example 1 except that a baking container was used
This is an example of evaluation performed in the same manner as. The total number of fired β-alumina tubes was 6 or less, and the dimensional accuracy was low.

[0020]

As described above, when the bottomed cylindrical β-alumina molded body is fired by inverting it in the cylindrical refractory container with its open end side facing down, the inner wall surface of the cylindrical refractory container is By setting the roundness ≦ 1.03 and the straightness ≦ 0.2%, it is possible to reduce the variation in the distance between the inner wall surface of the cylindrical refractory container and the cylindrical β-alumina compact with a bottom, and β at the time of firing. −
The amount of Na ₂ O scattered from the alumina compact is made uniform,
It is possible to manufacture a β-alumina tube having excellent dimensional accuracy represented by roundness, straightness, and the like.

[Brief description of drawings]

FIG. 1 is a schematic view showing a method for measuring the straightness of a cylindrical refractory container.

FIG. 2 is a cross-sectional view illustrating the manufacturing method of the present invention.

[Explanation of symbols]

 11, 21: Cylindrical refractory container 22: Upper lid 23: Lower lid 24: Setter-25: Bottomed cylindrical molded body

Claims (1)

[Claims] 1. When firing a bottomed cylindrical β-alumina molded body in a cylindrical refractory container with its open end side facing down and inverting it, the inner wall surface of the cylindrical refractory container has a circularity of ≦ 1. .0
3. Straightness ≦ 0.2% A method for producing a β-alumina tube.