JPH02160678A - Production of porous ceramic structure - Google Patents

Abstract

PURPOSE:To obtain a high-purity porous ceramic structure in high yield in production of the porous ceramic structure by the method of attaching a ceramic slurry to a base material comprising a resin structure to be consumed by fire, by adding a colloidal ceramic precursor to the slurry. CONSTITUTION:A base material comprising a resin structure such as urethane foam is prepared. On the other hand, a ceramic raw material such as alumina is mixed with a solvent such as water, a binder of organic polymer and a surfactant and further blended with a ceramic precursor in a sol state to be characterized by ultrafine ceramic particles or inorganic polymer to give a ceramic slurry. The slurry is impregnated to the surface of the base material, stuck, dried and calcined. In the operation, the precursor is gelatinized by treatment such as drying to show dry strength, polycondensation takes place between sol gelatinized at the initial age of calcination, bonding between the ceramic raw material and the gel or bonding between the gels occurs to secure strength. Consequently, a high-purity product is obtained without reduction in yield caused by collapse of ceramic part.

Description

DETAILED DESCRIPTION OF THE INVENTION (Prior Art) Conventionally, two-dimensional or three-dimensional organic structures have been produced using organic foams having a three-dimensional skeleton, such as urethane foam, and woven or nonwoven fabrics made of organic fibers. A method of manufacturing a porous ceramic structure having a two-dimensional or three-dimensional network structure by impregnating and adhering a ceramic slurry to the surface, drying, and firing is known.

(Issues to be Solved by the Invention) When attempting to obtain a high-purity porous ceramic body, in the above conventional method, a solvent such as water is added to the ceramic raw material, and an organic polymer is added as a binder to fix the ceramic and maintain its shape. This is carried out by attaching a ceramic slurry obtained by adding molecules and various surfactants for improving moldability to the surface of the organic structure, and drying and firing the slurry. In the early stages of drying and firing, the ceramic part tends to shrink due to the volatilization of the solvent, while the organic structure of the skeleton experiences thermal expansion and gas generation due to thermal decomposition, causing tensile stress on the ceramic surface. As a result, the ceramic structure is placed in a state where cracks are likely to occur. For this reason, the weak parts of the skeleton resulting from non-uniform adhesion tend to collapse, making it difficult to obtain a sufficient product yield.

In order to improve the yield, porous ceramic structures have been manufactured by increasing the dry strength by adding clay minerals and inorganic binders such as aluminum phosphate, and by ensuring strength during the firing stage. However, since the purity is lower than that produced using only ceramic raw materials, the resulting porous ceramic structure is inferior in terms of heat resistance and corrosion resistance.

(Means for Solving the Problems) The present invention contains a colloidal ceramic precursor in a ceramic slurry, and takes advantage of the fact that the colloidal particles cause a sol-gel reaction to form a ceramic slurry from drying to the initial stage of firing. This paper shows a method for improving the strength of a structure in which a high-purity porous ceramic structure can be obtained in high yield.

In the present invention, the base made of a resin structure may be composed of a continuous organic foam having a three-dimensional network structure such as urethane foam, or may be composed of a two-dimensional or three-dimensional synthetic fiber such as nylon fiber. It may be composed of a material woven into a shape.

In the present invention, any necessary colloidal ceramic precursor can be used depending on the composition of the ceramic to be manufactured. That is, for oxide ceramics, oxide sols such as silica sol, alumina sol, zirconia sol, titania sol, iron oxide sol, and tin oxide sol, or mixtures thereof can be used, and for non-oxide ceramics, polysilazane Inorganic polymers such as , polycarbosilane, and polyborazene can be used.

(Function) The present invention adds a sol-like ceramic precursor characterized by fine ceramic particles or inorganic polymers to a ceramic slurry, and gels it by drying or other processing to generate dry strength. In addition, in the early stage of firing, condensation polymerization occurs between the gelled sol and bonds are formed between the ceramic raw material and the gel or between the gels, thereby suppressing the decrease in strength of the structure. This method takes advantage of the phenomenon of moreover,
The added gel not only plays the role of strength fiber during firing, but also has the effect of a high-purity sintering aid that lowers the sintering temperature of the ceramic because it has a large specific surface area and is highly reactive.

(Example) Examples and comparative examples based on the present invention are shown below.

The present invention is not limited to the following examples unless it exceeds the gist thereof.

Aluminum oxide powder (manufactured by Showa Denko:
Purity 99.7%; average particle size 2 μm) 25 parts silica sol (Nissan Chemical Co., Ltd.; 20% aqueous solution) as a colloidal ceramic precursor, peptizer (Chukyo Yushi Co., Ltd.; polycarboxylic acid) Ammonium salt: non-volatile content 50%
) and 0.5 parts of an antifoaming agent (manufactured by Dai-Kogyo Seiyaku; mineral oil) to prepare a ceramic slurry. Comparative Example 1: 100 parts of aluminum oxide powder, 30 parts of water, 5 parts of organic binder (PVA), 2 parts of deflocculant, and 0.5 parts of antifoaming agent.
% to prepare a ceramic slurry free of oxide sol. As Comparative Example 2, 45 parts of aluminum phosphate (manufactured by Tamoto Chemical; 30% aqueous solution) was added to 100 parts of aluminum oxide powder to prepare a ceramic slurry with excellent moldability. The viscosities of the three slurries are comparable.

Next, these slurries were impregnated as a three-dimensional network structure organic material into a fully open type soft urethane foam with a cell density of 8 cells/inch in size of 5Q x 50 x 10 m, and the amount of slurry attached was adjusted to the desired amount. Dry thoroughly at approximately 100°C using a dryer. The obtained structure was fired at a heating rate of 200°C/hr, a holding temperature of 1500°C, and a holding time of 2 hours. Among the 10 samples, all 10 sintered bodies having the composition of Example were obtained without any cracks as in Comparative Example 2 containing aluminum phosphate, but Comparative Example 1 without sol was obtained. However, only three complete porous ceramic structures were obtained, some of which were partially collapsed or cracked.

In addition, when these slurries were wet-formed into a plate shape, fired at a holding temperature of 1400 to 1550°C, and the bulk density was measured, it was found that the increase in bulk density of the sintered body with the composition of the example was almost saturated at 1500°C. It was found that the addition of sol was effective as a sintering aid at temperatures of 50°C or higher. JIS-R
When a bending strength test was conducted in accordance with 1601, Comparative Example 1, which did not contain sol, had an average strength of 150 MPa, Comparative Example 2, which contained aluminum phosphate, had an average strength of around 20 MPa, whereas the Example showed an average strength of 230 MPa, It has been found that the present invention is also effective in improving strength.

(Effects of the Invention) As detailed above, the method of the present invention does not cause a decrease in yield due to the collapse of the ceramic part during the drying and firing stages, and is lower than the conventional method that does not include a ceramic precursor. At the firing temperature, a highly pure porous ceramic structure is obtained.

Claims (1)

[Claims] A method of manufacturing a porous ceramic structure by adhering a ceramic slurry to a base made of a resin structure that is burnt out by firing, drying and firing, characterized in that a colloidal ceramic precursor is contained in the ceramic slurry. A method for manufacturing a porous ceramic structure.