JP2565380B2 - Method of manufacturing porous porcelain - Google Patents

Description

TECHNICAL FIELD The present invention relates to a porous porcelain widely used for filters, aerators and the like in the food industry, chemical industry, medical care, environmental conservation business and the like.

"Prior Art" This type of porous porcelain is widely known to be obtained by sintering ceramic particles such as coarse alumina produced by a flame melting method, but the above-mentioned coarse ceramic particles are produced at a high melting temperature. Therefore, there is a drawback that extremely high temperature is required for firing a molded product using this.

The applicant has previously used ceramic powder having an average particle size of 1 μm or less as a starting material, and has an average particle size of 5 μm by spray drying or the like.
After granulating the above granules, calcining them at 1000 ° C or higher, making them semi-sintered, molding them with an organic molding aid, and sintering at a temperature 400 ° C or higher higher than the above-mentioned calcination temperature This has solved the above-mentioned drawbacks and found that an excellent porous material having a high mechanical strength can be obtained by firing at a relatively low temperature, and proposed this (Japanese Patent Application No. 63-57177).

“Problems to be solved by the invention” The porous porcelain manufactured in this manner has a higher mechanical strength than the porous porcelain obtained by using the coarse alumina particles produced by the above-mentioned fire melting method. Along with
Although the porosity and the pore diameter are also increased, the calcination temperature is required to be high because it needs to satisfy the mechanical strength of the granules, and this high temperature calcination reduces the sintering activity of the granules on the one hand. Therefore, in order to satisfy both characteristics at the same time, it is necessary to strictly control the calcination temperature, which leaves a problem in terms of mass productivity.

"Means for Solving Problems" The present invention provides a suspension obtained by blending a ceramic powder having an average particle diameter of 0.1 to 1 µm with a colloid or a soluble substance composed of fine ceramic particles having an average particle diameter of 0.01 µm or less. Granules made of ceramic powder whose surface is coated with the above colloid or soluble substance are granulated by spray-drying the suspension, and after mechanical strength is given by calcination, the granules are molded into a desired shape and then fired. It is characterized by

"Operation" When granulating the above suspension by spray drying, etc., the colloid or soluble substance consisting of finer particles than the main ceramic powder is suspended due to its high fluidity due to its liquidity. The granules granulated because they move to the surface of the liquid droplets have a shape in which a large number of fine particles are coated on the outer peripheral surface of a large number of ceramic powders. With a low calcination temperature, strength that can withstand raw material preparation such as kneading and molding operations is obtained.
A high intergranular bond can be obtained by firing at a relatively low temperature due to the remaining sintering activity during the main firing after molding.

Here, the average particle size of the main ceramic powder is 0.1
The reason for specifying to 1 μm is that if it is less than 0.1 μm, the accumulation phenomenon of fine particles of the ceramic that coats these surroundings is unlikely to occur during granulation, and conversely if it exceeds 1 μm, it is difficult to obtain satisfactory sinterability. Because. On the other hand, the average particle size of the ceramic fine particles distributed in the ceramic powder is 0.01
When the particle size is more than μm, the above-mentioned accumulation phenomenon becomes difficult. Therefore, it is preferable that the particles are as fine as possible, but the raw material price rises. Therefore, the particle size is determined to be 0.01 μm or less in accordance with the required characteristics.

Next, when the amount of fine particles mixed with the main ceramic powder is less than 3% by weight, it is difficult to obtain a sufficient effect.
The above range is preferable because the material is almost saturated in the vicinity and the raw material price becomes high.

"Example" 3 kg of alumina powder (commercial item) with an average particle size of 0.2 µm and a purity of 99.99%, 3 kg of alumina sol (commercial item) with an average particle size of 0.005 µm and a concentration of 10%, polyvinyl alcohol 30 g and water 300 g in an internal volume of 5 The mixture was placed in an alumina porcelain ball mill and mixed for 24 hours to obtain a suspension.

This suspension was granulated into granules having an average particle size of 20 μm under the condition of a gas temperature of 160 ° C. using a rotary disk type spray dryer of 12,000 rpm.

Next, granulate the granules at 900 ℃, 1000 ℃ and 1100 ℃ each 1
When the calcination temperature was 900 ℃, the strength of the granules was insufficient, and at 1000 ℃, satisfactory molding strength was obtained, so for 1 Kg of the granules calcinated at 1000 ℃ Methyl cellulose (50 g) and water (150 g) were added and kneaded for 30 minutes to extrude a tubular body having an outer diameter of 20 mm, an inner diameter of 18 mm and a length of 600 mm, and baked in an electric furnace at various temperatures (holding for 1 hour). Table 1 shows the average values of the porosity, the pore diameter, and the crush strength due to a load perpendicular to the radial direction for each of the five porous tubes according to the present invention. In the table, alumina sol is not used as a starting material, and 3 Kg of water is used to compensate the moisture of the alumina sol.
Under the same conditions as in this example except that the amount was increased to
A tubular body manufactured by satisfying the requirements of No. 7 is shown as a comparative example.

"Effects of the Invention" As is clear from Table 1, the product of the present invention has almost no difference in porosity as compared with the comparative example, but the small pore size means that the fine burning is small. The binding granules lead to much higher mechanical strength and smoothness of the surface. In particular, the smoothness of the surface adds the effect of sintering fine particles of the surface of the sintered granules, thus reducing the fluid friction. Increase.

Although the examples have been described with respect to spray-drying granulation, granulation of granules is not limited to these, and an aqueous slurry W in which ceramic powder having an average particle size of 0.1 to 1 μm is dispersed is used.
Ceramic fine particles of 0.01 μm or less are subjected to a lipophilic treatment and poured into an oil-based slurry O dispersed in an organic solvent that is incompatible with water together with an emulsifier that emulsifies water. Granules obtained by freeze-drying the W / O emulsion disclosed in Japanese Examined Patent Publication No. Sho 63-19470 prepared by dispersing an aqueous slurry W in the form of particles can be used.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuyuki Mizushima 14-18 Takatsuji-cho, Mizuho-ku, Nagoya, Aichi Japan Special Ceramics Co., Ltd. (56) Reference JP-A-62-278175 (JP, A)

Claims (1)

(57) [Claims] 1. A suspension obtained by blending a ceramic powder having an average particle diameter of 0.1 to 1 μm with a colloid or a soluble substance composed of fine ceramic particles having an average particle diameter of 0.01 μm or less is sprayed to form a suspension. Granules consisting of ceramic powder coated with the above colloid or soluble substance are granulated, imparted with mechanical strength by calcination, shaped into a desired shape, and then fired. Production method.