JPH08932A - Production of ceramic filter - Google Patents

Abstract

PURPOSE:To easily produce a ceramic filter having a homogenous membrane. CONSTITUTION:The viscosity of a slurry having ceramic particles dispersed therein is adjusted to 2-5dPa-S and this slurry is applied to a porous ceramic base material by spray coating. The coated base material is dried and baked to obtain a ceramic filter having a homogenous membrane free from a pinhole or voids.

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 ceramic filter used for removing dust in high temperature air and for removing suspended particles in high temperature liquid or corrosive liquid.

[0002]

2. Description of the Related Art Ceramic filters are used for the above-mentioned applications by utilizing the heat resistance and corrosion resistance of ceramics. When the dust or suspended particles to be removed are fine, a multilayer structure in which one or two ceramic membranes having a pore size smaller than that of the substrate are provided on the porous ceramic substrate. A ceramic filter consisting of is used.

In order to produce such a multilayer ceramic filter, a suspension of ceramic particles in water is filtered through a ceramic substrate, left on the substrate and then calcined. There is known a method of fixing a ceramic film on a ceramic substrate. However, in this method, since a suspension is used at the time of applying the film, when the particle size of the ceramic particles is large or the specific gravity is large, the ceramic particles tend to settle in the liquid, and there is a problem that the film application cannot be performed uniformly. is there.

Further, when the pore diameter of the ceramic base material varies depending on the location, there is a problem that it is difficult to make the film thickness uniform because the filtration rate varies depending on the location. Furthermore, even if a binder is added to the suspension, it is difficult for the binder to remain on the film,
There is a problem that the adhesion of the film to the substrate is poor.

There is also a method of forming a ceramic film by spraying a slurry of ceramic particles onto a base material using a spray, but holes such as pinholes are generated on the surface of the film, and a ceramic having a uniform film is formed. There was a drawback that a filter could not be obtained.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and can provide a ceramic filter in which a uniform ceramic film is provided on a ceramic substrate without requiring a large-scale device. It is made to provide a method for manufacturing a ceramic filter.

[0007]

The method for producing a ceramic filter according to the present invention, which has been made to solve the above-mentioned problems, has a viscosity of a slurry in which ceramic particles are dispersed in a range of 2-5.
It is characterized in that it is adjusted to dPa-S, the slurry is spray-coated on a porous ceramic substrate, dried and then fired.

As the material of the ceramic particles used in the present invention, all ceramics that can be dispersed in water can be used, but they should be selected according to the use conditions of the filter. For example, for use in water, Al
₂ O ₃ , SiC, ZrO ₂ and TiO ₂ are preferred. For use in high temperature gas or high temperature high pressure water, SiC is preferred. Further, particles having a uniform particle size can be used as the ceramic particles, but powders of various different particle sizes may be blended and used in order to adhere to a substrate and obtain desired film strength.

As the material of the ceramic base material, all ceramics capable of producing a porous sintered body can be used, and if the difference in thermal expansion between the ceramic film and the ceramic base material is small, the ceramic base material is damaged by thermal stress. Because there is less risk of
It is preferable to use the same material for the ceramic particles and the ceramic base material or ceramics having a small difference in coefficient of thermal expansion.

In addition to the ceramic particles, various kinds of binders may be contained in the slurry in order to enhance the film strength after the film is applied. Usually, since a film is formed by spraying and then dried and baked for the purpose of enhancing the adhesion and bonding between the ceramic base material and the ceramic film, an organic binder that decomposes and volatilizes by baking is preferable as the binder.

In the present invention, the viscosity of the slurry in which the ceramic particles are dispersed is adjusted to 2 to 5 dPa-S before use. This is because when the viscosity of the slurry is smaller than 2 dPa-S, many holes such as voids and pinholes are generated on the surface of the film, and a uniform film cannot be obtained. This is because they are generated and a homogeneous film is not formed in either case. The void is defined as a hole with a diameter of 0.1 mm or more, and the pinhole is defined as a hole with a diameter of 0.1 mm or less.

For spray coating, various devices capable of atomizing the slurry can be used, but it is preferable to use a spray gun in practice. Further, the pressure of the spray gun is preferably in the range of 0.3 to 4.0 kg / cm ² .

Drying is carried out after the spray coating. However, if the drying is carried out rapidly, surface defects such as scratches and cracks are likely to occur, so the drying is carried out as slowly as possible. For example, it is preferable to dry the film in a dryer after the water content in the film is reduced to 10% or less by natural drying. Alternatively, drying may be performed while controlling the humidity using a humidity dryer. Baking is performed after drying. The firing temperature, time and atmosphere are appropriately selected according to the type of ceramic material. On the other hand, if the firing temperature is too high, the pore size may become too large due to evaporation of the ceramic component and coarsening of the ceramic particles. On the other hand, if it is too low, the sintering may be insufficient and the bonding strength between the film and the substrate may be reduced. Therefore, it is preferable to set the optimum firing conditions according to the type of ceramic material and the desired pore size.

[0014]

According to the method of manufacturing the ceramic filter of the present invention, the viscosity of the slurry in which the ceramic particles are dispersed is adjusted to 2 to
Since it is adjusted to 5 dPa-S and the slurry is spray-coated on a porous ceramic substrate, there are no holes such as voids and pinholes, and no vomit is formed on the surface of the film. It is possible to obtain a ceramic filter having

[0015]

【Example】

Example 1 Outer diameter 60 × inner diameter 40 having pore diameter of about 30 μm
× # 400, # 800, # 2000, # 4000, 1.5 μm for forming a film of SiC on a 100 mm long SiC substrate
200 g of each of the SiC powders having the above five kinds of particle diameters were weighed, mixed with 40 g of isoban as a binder, and water was added so as to have the viscosity shown in Table 1 to prepare a slurry. The viscosity was measured using a rotational viscometer.

[0016]

[Table 1]

The prepared slurry was put in a spray gun,
It was sprayed onto the ceramic substrate with 1.5 kg / cm ² of air. With the comparative product 1 having a slurry viscosity outside the range of the present invention, fluttering occurred and spray coating was substantially impossible. Other spray coats that were possible were spray-dried and then naturally dried at room temperature for one day to adjust the water content in the film to 0.5%, and then baked in Ar gas at 2050 ° C. for 3 hours. The surface condition of the film of the fired ceramic filter was visually observed and shown in Table 1.

The products 1 to 6 of the present invention showed a uniform appearance visually. On the other hand, in the case of the comparative product 2 having a slurry viscosity other than that of the present invention, pores were observed everywhere and the appearance was non-uniform. Three points of 15 mm, 50 mm, and 85 mm from the upper end in the axial direction were selected on the outer surfaces of the samples of the present invention products 1 to 6 and the comparative product 2, and three points of the same height on the opposite side of the shaft were selected. For these 6 points in total, the number of pinholes (smaller than 0.1 mm in diameter) and voids (0.1 mm or larger in diameter) were measured within a field of view of 3 mm in diameter using a magnifying glass with a magnification of 40, and the average per unit area was measured. The number (pieces / mm ² ) was calculated and is also shown in Table 1. As shown in Table 1, in the case where the slurry viscosity was within the range of the present invention (invention products 1 to 6), the pinhole density and the void density showed small values of 1.1 and 0.8 or less, respectively.

[Example 2] In order to compare the characteristics of the films obtained by the spray coating method and the filtration method, the same SiC substrate as in Example 1 was used to prepare a sample by the filtration method and the spray coating method. In the spray coating method, Example 1
Using a slurry having a viscosity of 3.5 dPa-S prepared in the same manner as in (3), the SiC substrate was sprayed to form a film having a thickness of 80 μm and dried. After drying, it was baked in Ar at 2000 ° C. for 2 hours. As a result of measuring the pore diameter of the obtained membrane, it was found that the pore diameter was 3 μm. The surface pinhole and void densities were evaluated in the same manner as in Example 1, and as a result, both were found to be 0.
It was less than 1 piece / mm ² .

In the filtration method, in order to form a film on the above-mentioned ceramic substrate, Si having the same particle size composition as in Example 1 was used.
A slurry having C powder and a binder dispersed in water was prepared. Add 2 kg / c of slurry so that the film thickness is 80 μm.
It was filtered at a pressure of m ² for 6 hours. When the sample was pulled up from the suspension after filtration, a part of the membrane part was seen to fall off. After drying
Using the same method as in Example 1, pinhole surface portion other than the dropout portion, a result of the density of voids was measured, 21 / mm ^2, a density of 5.5 pieces / mm ² in the voids resulting in pinhole However, only a heterogeneous film was obtained as compared with the spray coating.

[0021]

As described above, according to the method for producing a ceramic filter of the present invention, the viscosity of the slurry in which the ceramic particles are dispersed is adjusted to 2 to 5 dPa-S, and spray coating is performed on the porous ceramic substrate. By adopting the method, there is an advantage that a ceramic filter having a homogeneous membrane can be easily manufactured without using a large-scale device.

Claims (2)

[Claims] 1. A ceramic filter characterized in that the viscosity of a slurry in which ceramic particles are dispersed is adjusted to 2 to 5 dPa-S, the slurry is spray-coated on a porous ceramic substrate, dried and then fired. Production method. 2. The ceramic particles and the ceramic substrate are
The method of manufacturing a ceramic filter according to claim 1, which is made of SiC.