JPH075356B2 - Method of firing beta-alumina tube - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for firing a beta-alumina tube capable of imparting high mechanical strength and low electric resistance characteristics.

[0002]

2. Description of the Related Art For example, a beta-alumina tube used as a solid electrolyte tube of a sodium-sulfur battery is an important member that governs battery performance, and has high mechanical strength in order to maintain stable durability over a long period of time. And low electric resistance characteristics are required.

However, in order to obtain a high mechanical strength of the beta-alumina tube, it is necessary to suppress the abnormal growth of crystal grains acting as a fracture source to form a homogeneous crystal, and therefore, it is necessary to lower the sintering temperature. On the other hand, in order to obtain low electric resistance characteristics, it is necessary to increase the sintering temperature because it is necessary to make the size of the single crystal as large as possible. Therefore, it was difficult to set the firing conditions for the beta-alumina tube that sufficiently satisfies both characteristics. As a firing method that satisfies the above two conditions, a treatment means that repeats a plurality of heating and cooling cycles is Japanese Patent Publication No. 61-12869.
It is known from Japanese Patent Publication No. Gazette, etc., but when this method is used, a plurality of firing treatments are required, which complicates the work, and
When considering a continuous firing furnace on the premise of mass production, there was a problem that a cooling zone had to be provided on the way.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned conventional problems and is capable of simultaneously imparting two of high mechanical strength and low electric resistance characteristics, and heating and cooling once. The present invention has been completed for the purpose of providing a method for firing a beta-alumina tube, which enables simple and efficient firing work only by cycles.

[0005]

The method for calcination of the beta-alumina tube of the present invention made to solve the above-mentioned problems is as follows.
In the firing method of the beta-alumina tube, the beta-alumina particles are pressure-molded, and the beta-alumina molded body is heated to a predetermined maximum temperature range without being lowered in the middle, and then cooled and sintered without being raised in the middle . In the middle of the temperature rising process, the temperature is maintained for a predetermined time in a predetermined temperature range so as to suppress the growth of abnormal grain size, or the temperature is slowly raised at a rate of 50 ° C./hour or less for a predetermined time. While warming, hold in a predetermined temperature for a predetermined time so that the crystal grains of the matrix particles grow uniformly during the cooling process , or at a rate of 30 ° C./hour or less for a predetermined time.
Only and is characterized in that the slow cooling.

In the present invention, the beta-alumina particles are heated and cooled to a predetermined maximum temperature range so as to densify the beta-alumina compacts compacted under pressure, followed by cooling and sintering. The outline of the heat curve is as shown in FIG. 1, and basically , the temperature raising process without lowering the temperature in the middle , the holding process at the maximum temperature, and the middle
This is a single heating / cooling cycle consisting of three cooling processes that do not raise the temperature .

In the present invention, first, the temperature raising process (A to
In C), hold for a predetermined time in a predetermined temperature range before reaching the maximum temperature, or for a predetermined time at a speed of 50 ° C / hour or less
The temperature raising process (B in the figure) is performed slowly only during the period. By this treatment, the growth of abnormal crystal grains is suppressed, the growth of homogeneous matrix particles is promoted, and the mechanical strength is improved. The specified temperature range changes depending on the composition
However, the range of 1500 to 1540 ° C. is usually preferable,
If the treatment is carried out in a temperature range outside this range, abnormal crystal grains will be generated and the mechanical strength will decrease. Also, 50
Similarly, when the temperature is raised at a rate higher than ° C / hour, the mechanical strength also decreases. The treatment time at the predetermined temperature can be arbitrarily set in consideration of the furnace capacity and the like, but is preferably in the range of about 0.5 to 4 hours.

Holding process at maximum temperature (D in the figure)
Is performed within a temperature and time range sufficient to densify the beta-alumina compact, and conditions are within a range of 1600 to 1650 ° C. and 0.5 to 2 hours depending on the characteristics of the object to be sintered. Set. Excessively high temperature treatment and long-term treatment cause abnormal crystal grain growth and reduce mechanical strength.

On the other hand, in the middle of the cooling process (E to G in the figure) , the temperature is maintained in a predetermined temperature range for a predetermined time, or 3
The cooling process (F in the figure) is slowly performed for a predetermined time at a rate of 0 ° C./hour or less. Then, by this treatment, the crystal grains of the matrix grains are grown uniformly to the largest possible size and the electrical resistance characteristics are reduced. The above predetermined temperature range varies depending on the composition of the composition, but is usually 1550 to 1
The range of 400 ° C. is preferable, and if the treatment is performed in a temperature range outside this range, the crystal grains cannot be grown uniformly and the electrical resistance becomes high. In addition, the electric resistance also increases when cooled at a rate higher than 30 ° C./hour. The processing time can be arbitrarily set within the range of about 0.5 to 10 hours.

[0010]

EXAMPLE A beta-alumina molded body having an outer diameter of 68 mm, an inner diameter of 60 mm and a total length of 510 mm was sintered according to the firing conditions shown in Table 1 to produce a beta-alumina tube for a solid electrolyte tube of a sodium-sulfur battery. Both the mechanical strength and the electric resistance characteristics of the obtained beta alumina tube were satisfactory. As a comparative example, the characteristics of the beta-alumina tube when the same beta-alumina molded body as above was treated under different sintering conditions are shown in Table 2. As is clear from these results, the present invention can be obtained. It was confirmed that the characteristics of the beta-alumina tube were excellent.

[0011]

[Table 1] Note: The units in the table are strength (MPa) and resistance (Ωcm).

[0012]

[Table 2] Note: The units in the table are strength (MPa) and resistance (Ωcm).

[0013]

As is apparent from the above description, according to the present invention, both high mechanical strength and low electric resistance characteristics can be imparted at the same time, and the heating and cooling cycle can be performed simply and efficiently. There is also an advantage that the firing work can be carried out effectively, and that the firing furnace can be used as it is without making a great improvement to the conventional firing furnace. Therefore, the present invention is extremely large in that it contributes to the industrial development as a method for firing a beta-alumina tube that eliminates the conventional problems.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a heat curve of heating and cooling in the present invention.

Claims (3)

[Claims] 1. A beta-alumina obtained by heating a beta-alumina compact in which beta-alumina particles are pressure-molded to a predetermined maximum temperature range without lowering the temperature halfway and then cooling and sintering without raising the temperature midway. In the tube firing method, the temperature is maintained in a predetermined temperature range for a predetermined time so as to suppress the growth of an abnormal particle size during the temperature rising process , or the temperature is slowly raised at a rate of 50 ° C./hour or less for a predetermined time and cooling is performed. Way in the process
A method for calcination of a beta-alumina tube, characterized in that the matrix particles are held in a predetermined temperature range for a predetermined time so that the crystal grains of the matrix particles uniformly grow therein, or slowly cooled at a rate of 30 ° C./hour or less for a predetermined time . 2. The method for calcination of a beta-alumina tube according to claim 1, wherein the process for suppressing the growth of abnormal grain size in the temperature rising process is performed in a temperature range of 1500 to 1540 ° C. 3. The method for calcination of a beta-alumina tube according to claim 1, wherein the homogeneous growth treatment of the crystal grains of the matrix particles in the cooling process is performed in a temperature range of 1550 to 1400 ° C.