JPH0643273B2 - Method for producing microporous ceramic body - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in a method for producing a microporous ceramic body. More specifically, the present invention has a high porosity and a fine pore size that can be suitably used as, for example, a filter, an electrode for a fuel cell, an electrolyte holding material, a catalyst carrier, etc. The present invention relates to a method for producing a porous ceramic body that is free from deformation and cracks with high productivity by a simple operation.

2. Description of the Related Art In recent years, the demand for porous ceramics having fine pores has rapidly increased, for example, for filters, electrodes for fuel cells, electrolyte holding materials, catalyst carriers, and the like.

Such a ceramic porous body is usually manufactured by molding a mixture of ceramic powder and a combustible substance and firing the mixture.

However, in such a method, it is possible to obtain a porous body having a normal porosity having a porosity of about 80%, but for those having fine pores, the upper limit of the porosity is 65%. It is a degree, and it is not possible to obtain a porosity higher than that. This is because it is necessary to add fine organic powder in order to form fine pores, but if this amount exceeds a certain limit, the molded body is inevitably collapsed by firing. Further, in the method using such an organic powder, it is difficult to form the organic powder in a size of several μm or less, and thus it is difficult to form pores having a diameter of a few μm or less. Since it has elasticity, there is a problem that it expands and cracks easily when the pressure is returned after molding.

It is also known that in this method, a polyurethane foam is used as a base material instead of the organic powder, the partition walls of the foam are removed, and then a ceramic raw material is coated to obtain a porous body having continuous ventilation holes. Has been. However, in this case, the porosity of the porous body is 8
Although it is 5 to 90%, the pore diameter is large and about 1 to 4 mm, and it is not possible to obtain a fine porous body ("Industrial Materials", Vol. 26, No. 7, pp. 56-61).

On the other hand, as a method for producing a dense sintered body having fine pores, by adding a small amount of 10% by weight or less of water or an aqueous binder solution to the raw material ceramic powder, press-molding the material, and then firing it, the porosity can be reduced. It is known that a sintered body having low but fine pores can be obtained. In this case, when the amount of water is increased to 18 to 22% by weight, extrusion molding becomes possible, but the porosity of the green molded body is 40%.
It is -50%, and a porous body having a porosity of 50% or more cannot be obtained. Further, when the amount of water is increased to 20 to 30% by weight, the raw material-water system mixture becomes a slurry and slip casting can be performed, but the porosity of the green molded body is still about 40 to 50%, A molded product having a porosity of 50% or more cannot be obtained.

As described above, according to the conventional method for producing a porous ceramic body, it is not possible to obtain a high quality ceramic porous body having a high porosity and fine pores.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention overcomes the drawbacks of the conventional method for producing a porous ceramic body, has a high porosity and a fine pore diameter,
Moreover, the object of the present invention is to provide a method capable of manufacturing a ceramic porous body which is homogeneous and is free from deformation and cracks and which is excellent in quality by a simple operation with high productivity.

Means for Solving the Problems As a result of various researches conducted to develop a microporous ceramics porous body having excellent quality, the present inventors have found that a specific organic liquid is used as a medium for molding ceramic ultrafine powder. If a substance is used, a homogenous powder in a wet state is obtained, and this press-molded body has high mechanical strength despite containing a large amount of molding medium. It was found that a ceramics porous body having high quality and fine pores and excellent quality can be easily obtained, and the present invention has been completed based on this finding.

That is, according to the present invention, when a kneaded product of ceramics ultrafine powder is pressure-molded and then fired to produce a microporous ceramics porous body, the molding medium has a viscosity of 2 to 100 centistokes and an average molecular weight of 70. The present invention provides a method for producing a microporous ceramics porous body, characterized in that a lubricious organic liquid substance of ~ 700 is used.

The inventors have noticed that the ceramic powder increases the surface area as the particle diameter decreases, and as a result of examining the relationship between the particle diameter of the powder and the amount of liquid that the powder can adsorb, the particle diameter is When it is larger than about 0.1 μm, the amount of liquid adsorbed on the powder is such that it fills the particle gaps (20 to 30% by volume), but when the particle size is smaller than 0.1 μm,
The amount of liquid adsorbed on the powder increases significantly, and the particle size is 0.
We have found that the adsorption amount of ultrafine powder of 01μm reaches up to 4 times the true volume of the powder. In addition, the mixture of ultrafine powder and liquid has no fluidity, and the adsorbed liquid is hardly lost by external force such as squeezing. It became clear that it was rich in formality. In this case, depending on the type of liquid used, there was a significant difference in the amount adsorbed to the ultrafine powder and the shape retention of the molded body, and also in the presence or absence of cracks when firing the molded body.

By the way, water, which has been most commonly used as a molding medium for ceramic powders, is soft and poor in shape retention when added to ceramics ultrafine powder in an amount of about 40% by volume, and also has a low dry strength. In addition, since it gives a molded body which is prone to cracking during firing, it is unsuitable as a medium for producing a microporous ceramic body.

Therefore, in the method of the present invention, the molding medium has a viscosity of 2 to 100 centistokes and an average molecular weight of 70 to 7
It is necessary to use 00 lubricious organic liquid substances. Examples of such organic liquid substances include aliphatic, alicyclic or aromatic hydrocarbons, alcohols, esters, silicones and the like. These may be natural products or synthetic products. Further, they may be used as a single body or as a mixture of two or more kinds.

These are suitable as a medium for molding fine ceramic powders because they have a lower evaporation rate at room temperature than water, do not react with ceramics, and have low toxicity.

The reason why a low evaporation rate is desirable for the molding medium is as follows. As described above, since the porosity of the molded body is determined by the amount of the molding medium added to the raw material, if the molding medium is lost by evaporation after being added, the porosity of the I cannot hope for improvement. Conventionally, water that has been used as a molding medium has an evaporation rate of 8.4 × 10 _-1 g / h (35 ° C., humidity 50%, opening area 14.4 cm ² ). , It is often difficult to keep the water constant. On the other hand, the organic liquid substance used in the present invention is 1/9 of the evaporation rate of water (α olefin oligomer, viscosity 2.6 cS
t), 2/100 (liquid paraffin, viscosity 8 cSt) or less (liquid paraffin, viscosity 16 cSt),
The loss of the liquid medium due to evaporation is small, which is advantageous for controlling the porosity.

These organic liquid substances need to have a viscosity in the range of 2 to 100 centistokes at 37 ° C., and need to have a viscosity lower than this, and a viscosity lower than this is sufficient for maintaining. Formability cannot be obtained, and higher viscosities result in insufficient wettability.

Next, the amount of these used is usually appropriate in the range of 65 to 330% by weight based on the weight of the ultrafine ceramic powder. The amount used depends on the particle size of the ultrafine powder and the size of the specific surface area.
This corresponds to a range of 0.014 to 0.07 g / m ² .

Generally, in the production of a porous body, it is important to control the porosity, but in the present invention, the pretreatment of the raw material ceramic ultrafine powder and the combination of the molding medium, the firing temperature, the particle size of the raw material, etc. The porosity can be controlled by selecting

For example, ultrafine alumina without pretreatment (particle size 0.002μ
m), α olefin oligomer is added and molded
The porosity was 88% when fired at 1000 ° C., and the porosity was 70% when the ultrafine alumina powder pretreated with water was similarly shaped and fired. Also, liquid paraffin was added to ultrafine alumina treated with water and molded in the same manner as above.
The porosities when fired at 1000 ° C. and 1350 ° C. were 78% and 66%, respectively. On the other hand, liquid paraffin was added to finely powdered alumina (particle diameter 0.4 μm) and molded 1
The porosity when fired at 350 ° C. was 24%. In general, the pore size or pore size distribution of a porous body is determined depending on its use. Therefore, in manufacturing the porous body,
Those controls are needed.

In the present invention, similarly to the case of controlling the porosity, the pore diameter can be controlled by combining the pretreatment of the ceramic ultrafine powder and the molding medium, and selecting the firing temperature and the like.

For example, a sharp peak is observed at 0.03 μm in the pore diameter distribution when liquid paraffin is added to ultrafine alumina pretreated with water, shaped and baked at 1000 ° C. In addition, when the α-olefin oligomer is added to the ultrafine-powder alumina treated in the same manner, and the mixture is molded and fired at 1100 ° C. and 1350 ° C., sharp peaks are observed at 0.2 and 0.4 μm, respectively.

According to the method of the present invention, the porosity and the pore diameter can be controlled over a wide range in this way.

In the method of the present invention, the kind of ceramics used as a raw material is not particularly limited, and any one can be selected from those conventionally used as a raw material for a ceramic molded body. For example, at least one selected from oxide-based ceramics such as alumina, silica, zirconia, magnesia, and titania, and non-oxide-based ceramics such as silicon carbide, silicon nitride, and boron nitride.
A variety of ceramics can be used.

In the present invention, the ceramic is used in the form of an ultrafine powder, preferably one having an average particle size in the range of 0.005 to 2.5 μm. If the particle size exceeds 2.5 μm, the amount of the molding medium added cannot be increased,
It is difficult to obtain high porosity. The lower limit of the particle size is not particularly limited, but those smaller than 0.005 μm are practically difficult to obtain and are difficult to handle.
There is no special merit. In particular, from the viewpoints of economy, porosity, pore diameter, quality, etc., those having a particle diameter of 0.10 to 0.005 μm are preferable. Those having a particle size in such a range usually have a bulk specific gravity in the range of about 0.005 to 0.15,
Moreover, the specific surface area is in the range of approximately 50 to 500 m ² / g. The purity of the ceramic ultrafine powder is not particularly limited, and commercially available ones can be used.

In adding the molding medium, depending on the type, pretreatment of the raw ceramics ultrafine powder may be preferable,
Regardless of whether pretreatment is necessary or not, a good ceramic porous body can be obtained by adding a predetermined molding medium to the raw material powder.

In the method of the present invention, the kneaded product in a wet state prepared by adding the molding medium to the raw material ceramic ultrafine powder in this manner is pressure-molded to form a molded body having a desired shape, Bake. As the pressure molding method, a uniaxial press molding method, a hydrostatic press molding method, or the like can be used. The molding pressure may be a pressure sufficient to maintain the shape and give strength not inconvenient to handle, but a pressure of 30 kg / cm ² or more is usually used.
Generally, when the molding pressure is increased, the density of the green compact is increased, and the porosity of the resulting sintered compact is decreased. For example, when the molding pressure is increased from 50 kg / cm ² to 300 kg / cm ² , the porosity of the alumina porous body obtained by firing at a temperature of 1350 ° C. is reduced by about 1%. In addition, when the molding medium is added in an optimum amount or more and molded, the molding medium leaches out and plays a role as a wetting agent that facilitates release of the molded body from the mold.

In the method of the present invention, when the fine ceramic powder is kneaded, additives commonly used in the sintering of ceramics, such as binders and wetting agents, can be added as desired.

The strength of the green molded body thus obtained is relatively high, even though it contains a large amount of molding medium. However, when the particle size of the raw material ultrafine powder exceeds 1 μm, the strength of the obtained molded body is insufficient, which is inconvenient for handling.

In the method of the present invention, by firing the molded body obtained as described above, the molding medium contained in the molded body is gasified and burned to obtain a ceramic porous body. The firing temperature is appropriately selected depending on the type of ceramics used, but is generally selected in the range of 500 to 1400 ° C.

The porosity of the thus obtained porous ceramics sintered body depends on the particle size of the raw material ceramic powder, the molding pressure, etc., but if the proper conditions are selected, the average porosity of 60
It is possible to obtain a porous ceramics sintered body of up to 90%.

The pores of the porous ceramics sintered body are usually 12
It is extremely fine and has a pore diameter of 0.05 μm or less and an average of 0.05 μm, and about 90% of the pores are continuous air holes.

EFFECTS OF THE INVENTION According to the method for producing a ceramic porous body of the present invention, by using an organic liquid substance having a viscosity of 2 to 10 setstokes and an average molecular weight of 70 to 700 as a molding medium, a conventional method can be used. In comparison with the above, it is possible to manufacture a porous ceramics sintered body having high porosity, a fine pore diameter, a single pore diameter distribution and sharpness, and other excellent quality with high productivity.

The porous ceramics sintered body obtained in the present invention is suitably used for filters, electrodes for fuel cells, electrolyte holding materials, catalyst carriers, and the like.

EXAMPLES Next, the present invention will be described in more detail with reference to Examples.
The invention is in no way limited by these examples.

Example 1 Alumina powder 10 having a bulk specific gravity of 0.4 obtained by treating an alumina fine powder having an average particle diameter of 0.02 μm with a 0.1% by weight aqueous solution of Triton and pulverizing the dried product with a vacuum electric dryer.
8 cc of liquid paraffin with a viscosity of 15 centipoise was added to g and kneaded, and then molded at a pressure of 300 kg / cm ² ,
A molded body was obtained. Then, the molded body is placed in an electric furnace,
From room temperature to 450 ° C, the heating rate is 9.3 ° C / hr, and from 450 ° C to 1370 ° C, the heating rate is 52 ° C / hr.
The temperature was maintained for 5 hours and firing was performed to obtain a sintered body having a linear shrinkage rate of 12% and an average porosity of 66%.

Examples 2 to 9 Under the conditions shown in the attached table, porous ceramic sintered bodies were prepared in the same manner as in Example 1.

The linear shrinkage rate and average porosity of these sintered bodies are shown in Table 1 together with Examples.

Example 10 Alumina fine powder having an average particle diameter of 0.02 μm was mixed with 3% by weight of PVA.
In addition to the aqueous solution, after obtaining a slurry having a viscosity of 350 centipoise, spray drying with a disc spray dryer,
Alumina powder having an average particle size of 90 μm was obtained.

To 10 g of this alumina powder, 8 cc of liquid paraffin was added and kneaded, and then treated in the same manner as in Example 3 to obtain a sintered body having a linear shrinkage of 10% and an average porosity of 64%.

Example 11 7 g of silica powder having a bulk specific gravity of 0.3 obtained by treating fine silica powder having an average particle diameter of 0.012 μm in the same manner as in Example 1
7 cc of liquid paraffin with a viscosity of 63 centipoise and a viscosity of 1
4 cc of 00 Setch Poise silicone oil was added and kneaded, and this was molded at a pressure of 300 kg / cm ² to obtain a molded body.

Next, this molded body is heated from room temperature to 400 ° C. at a temperature rising rate of 9 ° C./hr and from 400 ° C. to 920 ° C. at a temperature rising rate of 68 ° C./hr, and held at 920 ° C. for 10 hours. Firing was performed to prepare a sintered body having a linear shrinkage rate of 4% and an average porosity of 79%.

Example 12 Fine silica powder having an average particle diameter of 0.012 μm was treated in the same manner as in Example 10 using an aqueous solution of 0.5% by weight of PVA to give an average particle diameter of 8
0 μm silica powder was obtained. After adding 8.4 cc of liquid paraffin to 7 g of this silica powder and kneading, Example 11
In the same manner as described above, a sintered body having a linear shrinkage of 7% and an average porosity of 77% was obtained.

Example 13 7.5 g of liquid paraffin was added to 10 g of titanium oxide having an average particle diameter of 0.030 μm, mixed, and molded at a pressure of 200 kg per 1 cm ² to obtain a molded body having a uniform structure, which was placed in an electric furnace. Place at room temperature up to 300 ° C per hour for 93
C., 450.degree. C. to 850.degree. C. were heated at a temperature rising rate of 72.degree. C. per hour and kept at 850.degree. C. for 10 hours. As a result, a fired body having a linear shrinkage of 31.6% and an average porosity of 30.6% was obtained.

Example 14 Granulating ultrafine magnesia having an average particle diameter of 0.010 μm,
The bulk specific gravity is 0.3, and 11.5cc of liquid paraffin is added to 10g.
Was added and mixed, and then molded at a pressure of 100 kg per 1 cm ² to obtain a molded body, which was placed in an electric furnace and
The temperature was raised at the same rate as in 2, and the temperature was maintained at 1000 ° C. for 5 hours for firing. As a result, the linear shrinkage rate was 17.4% and the average porosity was 68.8.
A fired body of 1% was obtained.

Example 15 16.4 g of α-olefin oligomer (viscosity 17 cSt / 37.8 ° C.) directly on 5 g of silica fine powder having an average particle diameter of 0.012 μm
After adding and kneading, pour this into the mold, 200kg
A molded body was obtained by molding at a pressure of / cm ² . Next, this molded body was placed in an electric furnace and fired. Upon firing, the temperature was raised from room temperature to 300 ° C. at a rate of 10 ° C./hr, 300 ° C. or more was raised at a rate of 70 ° C./hr, and kept at 850 ° C. for 12 hours. As a result, a highly porous multi-pore body having a porosity of 90% and an average pore diameter of 0.04 μm was obtained.

Example 16 10 g of alumina ultrafine powder having an average particle diameter of 0.020 μm was directly added to an α-olefin oligomer (viscosity 17 cSt / 37.8 ° C.) 1
After adding 9.6g, the same procedure as in Example 15 was repeated at 1000 ° C.
After firing for 5 hours, a fine porous body having a porosity of 88% and an average pore diameter of 0.04 μm was obtained.

Examples 17 to 26 Porous ceramics sintered bodies were prepared in the same manner as in Example 16 under the conditions shown in the attached table. The linear shrinkage rate and average porosity of these fired bodies are shown in Table 2 together with Example 16.

Example 27 10 g of magnesia ultrafine powder having an average particle size of 0.010 μm was directly added to α-olefin oligomer (viscosity 13 cSt / 37.8 ° C.) 1
After adding 8.9 g, the same procedure as in Example 1 was conducted at 600 ° C.
After firing for 5 hours, a fine porous body having a porosity of 88% and a shrinkage rate of 4% was obtained.

Example 28 9.9 g of α-olefin oligomer (viscosity 3 cSt / 37.8 ° C.) directly on 10 g of titania ultrafine powder having an average particle size of 0.021 μm
Was added, and the mixture was baked at 600 ° C. for 15 hours in the same manner as in Example 1 to obtain a fine porous body having a porosity of 74% and a shrinkage rate of 11%.

Claims (1)

[Claims] 1. A kneaded product of ceramics ultrafine powder is pressure-molded and then fired to produce a microporous ceramics porous body having a viscosity of 2 to 100 centistokes and an average molecular weight of 70 to 700 as a molding medium. A method for producing a microporous ceramics porous body, which comprises using the above-mentioned lubricious organic liquid substance.