JP2001048638A - Production of translucent alumina in slurry casting using gypsum mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce translucent alumina in slurry casting using a gypsum mold. SOLUTION: When a molding produced by the casting of an alumina slurry using a gypsum mold is sintered to produce an alumina sintered body, the molding is freed of impurities derived from the gypsum mold by acid treatment to enhance the translucency of the alumina sintered body. An alumina slurry is poured into a gypsum mold to form a molding, this molding is dried, calcined and immersed in an acid to remove contaminants from the molding contaminated with gypsum components in casting and drying, and then the molding is dried and sintered to obtain the objective translucent alumina.

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 translucent alumina by slurry casting using a gypsum mold, and more particularly, to a method of forming a slurry after casting a slurry using a gypsum mold. The present invention relates to a method for improving the light-transmitting property of an alumina sintered body by removing a gypsum component mixed from a gypsum mold by acid treatment, and a method for producing the light-transmitting alumina.

[0002]

2. Description of the Related Art Conventionally, translucent alumina has been used, for example, as a high-pressure sodium arc tube. In molding ceramics, slip casting is a molding method in which a complicated shape is easily formed as compared with dry press molding and wet press molding. A gypsum mold used in slurry casting is cheaper and easier to form than a resin mold, a porous ceramics mold, and a porous mold. However, in the slip casting using a gypsum mold, the grain growth in the alumina sintered body during sintering has been abnormal due to contamination of the formed body with a gypsum component (calcium sulfate) dissolved from the gypsum mold. It is known that the alumina sintered body has a disadvantage in that the translucency is reduced due to the grain growth. Therefore, as a method of producing translucent alumina by slurry casting, there is a method of sintering a molded article free of impurity contamination produced by vacuum pressure casting using a synthetic resin mold, and a method of using a porous ceramic mold. A slurry casting method has been reported. However, as described above, the slurry cast molding using the resin mold and the porous ceramic mold is more expensive than the molding using gypsum, and has a problem that it is difficult to form a shape and is difficult to release.

[0003]

Under such circumstances, the present inventors, in view of the above prior art, have diligently studied a method of producing translucent alumina by slip casting using a gypsum mold. After conducting research, the gypsum component, which is a contaminant entering the molded body from the gypsum mold, was ionized and dissolved by treating it with an acid from the viewpoint of ionization tendency, and the contaminant could be removed from the molded body by washing with water. The present inventors have found that it is possible to prevent abnormal grain growth in the alumina sintered body during sintering and to significantly improve the translucency of the alumina sintered body, and have accomplished the present invention. That is, the present invention provides a method for removing a gypsum component mixed from a gypsum mold by performing acid treatment on a molded body after slurry casting using a gypsum mold, and improving the translucency of the alumina sintered body. The purpose is to: Further, the present invention provides a method for producing a light-transmitting alumina having high light-transmitting property by sintering a molded body produced by slurry casting using a gypsum mold by acid treatment. Aim.

[0004]

The present invention for solving the above-mentioned problems comprises the following technical means. (1) In a method of sintering a molded body produced by alumina slurry casting using a gypsum mold to produce an alumina sintered body, the molded body after the slurry cast molding using a gypsum mold is subjected to an acid treatment. And removing impurities mixed from the gypsum mold to improve the translucency of the alumina sintered body. (2) A molded body is prepared by pouring alumina slurry into a gypsum mold, dried and calcined. Then, the molded body is immersed in an acid to contaminate the molded body contaminated with the gypsum component during casting and drying. After drying, drying and sintering to obtain a translucent alumina. (3) The method for producing translucent alumina according to (2), wherein the molded body is immersed in an acid of 0.1N to 1N at a temperature of 15 to 50 ° C. (4) The method for producing a light-transmitting alumina according to (2), wherein after dipping the molded body in acid, the acid and the ionized gypsum component are washed away with water, sufficiently dried, and sintered.

[0005]

Next, the present invention will be described in more detail. As described above, the present invention removes a gypsum component mixed from a gypsum mold by performing an acid treatment on a molded body after slurry casting using a gypsum mold, and abnormal grain growth in an alumina sintered body during sintering. And improving the translucency of the alumina sintered body. In the present invention, a method for producing a molded body by alumina slurry casting using a gypsum mold, and sintering to produce an alumina sintered body, using a normal slurry casting and sintering method, What is necessary is just to implement. In the present invention, the molded body after the slip casting using a gypsum mold is treated with an acid, but the acid used in the present invention does not necessarily need to be hydrochloric acid,
As long as calcium sulfate, which is a gypsum component, is ionized and dissolved, an appropriate acid (for example, sulfuric acid, nitric acid, etc.) can be used, and the type is not limited.

[0006] Next, alumina slurry is preferably prepared by adding water to alumina so that the powder concentration becomes 80% by weight, and adding a polycarboxylic acid-based dispersant to 2.6% by weight. In addition, after adjustment, it is pulverized by a ball mill for 8 to 24 hours to produce. The blending of these raw materials can be appropriately adjusted, and is not limited to the above blending. In the examples described below,
Alumina is a high-purity commercially available Daimei Chemical TM
DAR was used, water was distilled water, and the dispersant used was Alon A6114, a commercially available polycarboxylic acid-based dispersant manufactured by Toagosei Co., Ltd. Appropriate ones can be used as well.

In the present invention, the translucent alumina is prepared by pouring alumina slurry into a gypsum mold, draining the slurry, and drying the slurry.
Calcined at 0 ° C to 800 ° C and immersed in a 0.1N to 1N acid at a temperature of 15 to 50 ° C for a time of 30 to 60 minutes, preferably at room temperature to about 40 ° C for 30 minutes to 1 hour; It is produced by removing the contaminant component from the molded body contaminated with the gypsum component during casting and drying. In this case, in the acid treatment, it is important that the acid is introduced to the inside of the molded article in order to remove the gypsum component (calcium sulfate) that has entered the surface of the molded article and the inside of the molded article from the molded article. The conditions of the acid treatment are set in consideration of these. Thereafter, the acid and the ionized gypsum component are washed away with water,
After sufficiently drying and sintering, the desired translucent alumina is obtained. The sintering condition is, for example, preferably sintering at 1350 ° C. for 2 hours under vacuum, but is not limited to this, and any condition having the same effect as the sintering condition can be appropriately adopted.

[0008] The microstructure of the translucent alumina obtained in this way, as shown in the examples described later, compared with the microstructure of the alumina sintered body not subjected to the acid treatment, abnormal grain growth occurred. And clearly show high translucency. According to the method of the present invention, the gypsum component (calcium sulfate) that has entered the molded body by the above-described acid treatment is ionized and dissolved by the reaction with an acid such as hydrochloric acid, and is removed from the molded body. Abnormal grain growth in the sintered body is prevented, and the translucency of the alumina sintered body can be improved. The method for producing a light-transmitting alumina of the present invention can use inexpensive gypsum that can be easily formed into a complex shape as a molding die, and furthermore, acid treatment, since high effects can be obtained by a simple and inexpensive method of washing with water, It is an industrially suitable and advantageous method.

[0009]

Next, the present invention will be described in more detail with reference to the following examples. The following examples show preferred examples of the present invention, and the present invention is not limited by the examples. Not something. Example (1) Production of Translucent Alumina Water and a polycarboxylic acid dispersant were added to alumina, the powder concentration was adjusted, and the mixture was pulverized by a ball mill for 8 to 24 hours to produce alumina slurry. In this embodiment, the powder concentration is 8
Water was added to alumina so as to be 0% by weight, and 2.6% by weight of a dispersant was added to adjust the powder concentration. Next, the alumina slurry was poured into a gypsum mold, drained, and then dried. After drying, remove the molded body from the gypsum mold,
Calcination was performed. The molded body was immersed in about 1N hydrochloric acid for about 1 hour to ionize and dissolve the gypsum component that had entered the molded body during casting and drying. It was thoroughly washed with water, and the ionized and dissolved gypsum component was removed from the molded body. Next, after the molded body is sufficiently dried, 13
Vacuum sintering was performed at 50 ° C. to obtain a desired translucent alumina.

(2) Results The microstructure of the translucent alumina obtained as described above is compared with the microstructure of the alumina sintered body not subjected to the acid treatment.
It was found that abnormal grain growth did not occur. This means
Both were confirmed by electron microscopic observation. FIG. 1 shows an electron micrograph (× 15000) of the translucent alumina produced according to the present invention and an alumina sintered body produced without performing the acid treatment. In the figure, (a) shows the microstructure of the translucent alumina, and (b) shows the microstructure of the alumina sintered body not subjected to the acid treatment.
Also, when comparing the sample of the translucent alumina prepared according to the method of the present invention with the sample of the alumina sintered body not subjected to the acid treatment, it is apparent that the alumina sintered body subjected to the acid treatment according to the method of the present invention has a high translucency. (No. 2
Figure). When the transmissive alumina (a) thus obtained and the alumina sintered body (b) not subjected to the acid treatment were measured for transmittance in the visible region (sample thickness 1 mm), it was produced according to the present invention. The translucent alumina thus obtained is clearly more transparent than the alumina sintered body (sample thickness 1 mm) that was not acid-treated.
It was found that the transmittance was improved (FIG. 3).

[0011]

As described above in detail, the present invention relates to a method for producing an alumina sintered body by sintering a molded body produced by alumina slurry casting using a gypsum mold. The molded body after the slurry cast molding is subjected to an acid treatment to remove impurities mixed from the gypsum mold, and to improve the translucency of the alumina sintered body.
1) The gypsum component (calcium sulfate) that has entered the molded body can be ionized and dissolved by the reaction with acid and removed from the molded body. 2) Suppress abnormal grain growth in the alumina sintered body observed during sintering. 3) enables translucent alumina to be produced by slurry casting using a gypsum mold; 4) translucent having high translucency by a simple and inexpensive method of acid treatment and washing with water. An extraordinary effect, such as the ability to produce photo-alumina, which is not available in the conventional method can be obtained.

[Brief description of the drawings]

FIG. 1 shows translucent alumina (a) produced according to the present invention;
4 shows an electron micrograph of an alumina sintered body (b) produced without performing acid treatment.

FIG. 2 shows translucent alumina (a) produced according to the present invention;
The difference in translucency of the alumina sintered body (b) produced without performing the acid treatment is shown.

FIG. 3 shows translucent alumina (a) produced according to the present invention;
And the transmittance in the visible region of the alumina sintered body (b) manufactured without performing the acid treatment.

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[Procedure amendment]

[Submission date] July 14, 2000 (2007.1.
4)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction contents]

[0004]

The present invention for solving the above-mentioned problems comprises the following technical means. (1) In a method of producing an alumina sintered body by sintering a molded body produced by alumina slurry casting using a gypsum mold , abnormal grain growth in the alumina sintered body during sintering
In order to improve the light transmittance of the alumina sintered body
There was a mold made by slip casting using a gypsum mold.
The form is dried and calcined at 500-800 ° C.
Immerse the molded body in 0.1N to 1N acid, cast and
The gypsum component that has entered the surface and inside of the compact during drying
After had dividing taken ionized, dried, row sintered under vacuum
There, to prevent abnormal grain growth in alumina sintered body, different of the alumina sintered body, characterized in that to improve the translucency of their
Prevention and translucent improved method of its normally grain growth. (2) Produced by alumina slurry casting using a gypsum mold
Sintering of the compacted body causes abnormal grain growth in the alumina sintered body
A method for producing a translucent alumina sintered body in which
Te, alumina mud to form a compact poured into a plaster mold, dried and then calcined at 800 ° C. from 500 ° C., and immersed the molded article from 0.1N to acid 1N, during casting and drying Gypsum components entering the surface and inside of the molded body
After the removal ionized, dried, translucent alumina is characterized by obtaining a translucent alumina sintered body abnormal grain growth of the alumina sintered body was sintered is prevented under vacuum
A method for manufacturing a sintered body . (3) The translucent alumina firing according to (2), wherein the molded body is immersed in a 0.1N to 1N acid at a temperature of 15 to 50 ° C.
The method of manufacturing the aggregate . (4) The method for producing a translucent alumina sintered body according to the above (2), wherein after dipping the molded body in an acid, the acid and the ionized gypsum component are washed away with water, sufficiently dried, and sintered.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Saburo Sano 3-3, 2- 302 Kita Chikusa, Chigusa-ku, Nagoya, Aichi Prefecture (72) Inventor Takumi 2-109 Yatsushiro-cho, Kita-ku, Nagoya-shi, Aichi 103 Yatsushiro Accommodation 103 Room F term (reference) 4G030 AA36 BA15 GA16 GA20 GA36

Claims (4)

[Claims] 1. A method for sintering a molded body produced by alumina slurry casting using a gypsum mold to produce an alumina sintered body, comprising: A method for improving the translucency of an alumina sintered body, comprising removing impurities mixed from a gypsum mold by performing treatment to improve the translucency of the alumina sintered body. 2. A molded body is prepared by pouring alumina slurry into a gypsum mold, dried and calcined. The molded body is immersed in an acid to remove a molded body contaminated by a gypsum component during casting and drying. A method for producing a translucent alumina, comprising removing a contaminant component, drying and sintering to obtain a translucent alumina. 3. The molded product is treated with 0.1N to 1N acid in 15 to 15%.
The method for producing translucent alumina according to claim 2, wherein the immersion is performed at a temperature of 50 ° C. 4. The method for producing a translucent alumina according to claim 2, wherein after the molded body is immersed in an acid, the acid and the ionized gypsum component are washed away with water, dried sufficiently, and sintered.