JP3412223B2 - Ceramic filter and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic filter having excellent thermal shock resistance, a small pore size and a high porosity, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, there has been an increasing need for various filters and catalyst carriers having high heat resistance, high strength and excellent thermal shock resistance. For example, a filter or a catalyst carrier for removing CO ₂ , nitrogen oxides, and black smoke contained in automobile exhaust gas is required to have a heat resistance higher than 1000 ° C. The same applies to a desulfurization filter for exhaust gas in a thermal power plant or a chemical plant and a slag removal filter for molten metal.

In response to such demands, filters and catalyst carriers made of porous ceramics have been studied. Usually, the structure of the filter made of porous ceramics is
It has a multi-layer structure in which a porous ceramics film having a controlled pore diameter is laminated on the porous ceramics substrate required for maintaining strength by changing the filling rate of the green compact and the sintering conditions. However, since such a filter is manufactured by sintering raw material powder, the porosity is only about 40% by volume at the maximum.

Further, the most important transmission performance as a filter is Hagen-Poisiuiie shown in the following formula 1.
It is basically determined from the formula (1) depending on the pore size and porosity of the filter. That is, the larger the pore diameter and the smaller the film thickness of the filter, the larger the permeation flow rate as the filter, that is, the smaller the pressure loss.

[0005]

## EQU1 ## dQ / dt = nπr ⁴ ΔP / 8ηl (where Q: flow rate, t: time, n: number of pores, r: pore radius, ΔP: differential pressure, η: fluid viscosity, l : Film thickness)

However, in the filter having the above-mentioned ordinary multi-layer structure, since the base material portion has a large pore diameter, the pressure loss during filtration is small even if the porosity is small, but the membrane portion has a small pore diameter. Therefore, there is a drawback that the pressure loss rapidly increases, that is, the permeation performance as a filter is poor. Moreover, since the porosity is as small as about 40% by volume at the maximum, it is difficult to remove even when the filtered matter attached to the filter is loaded by applying a back pressure, and there is a drawback that the regeneration function of the filter is low.

Therefore, as a ceramics filter having an improved porosity, there has been reported a structure in which continuous fibers of oxide ceramics such as alumina are crossed and wound in multiple layers on the outer periphery of a mesh-shaped metal cylindrical base material. (Eg, M. A. Barriset al., SAE Rep.
ort, 920139, 1992).

However, when a continuous fiber of spun ceramics is wound, a large tensile stress remains in the fiber due to the tension applied during winding. Therefore, when this filter is used at high temperature, the fiber is broken or cracked by thermal shock. There was a big drawback. Further, since the metal cylindrical base material on the inner side has a larger thermal expansion than the ceramic fiber, a larger tensile stress is generated on the fiber wound on the outer side, and the breakage or cracking of the fiber becomes more remarkable. Such fractures and cracks are remarkable in oxide ceramic fibers having poor thermal shock resistance, but fractures and cracks also occur in other ceramic fibers for the same reason.

Furthermore, in order to apply tension to the outer periphery of the cylindrical substrate and wind it, the diameter of the spun ceramic continuous fiber must be 10 μm or more. Therefore, the porosity of the fiber layer portion around which the fiber is wound is reduced. When it is 50% by volume or more, the pore diameter of that portion becomes at least 10 μm or more. On the other hand, if it is attempted to form pores having a pore diameter of 10 μm or less, a decrease in the porosity of the fiber layer portion cannot be avoided due to its structure, and only a small porosity that is the same as that of a normal ceramics filter can be obtained.

[0010]

In view of the above conventional circumstances, the present invention has a small pore size and a large porosity so as to have an excellent permeation performance and a collection rate as a filter, and further has a thermal shock resistance. The object is to provide a ceramic filter excellent in

[0011]

In order to achieve the above object, a ceramics filter provided by the present invention comprises a base material made of porous ceramics having continuous air holes, and formed and fixed on the base material by vapor phase synthesis. length 100μ, which is
m silicon nitride fiber with a thickness of 10 μm or more
It is characterized in that it comprises a non-oriented reticulated aggregate that is intertwined with each other .

Another ceramic filter of the present invention is a substrate made of ceramics having a large number of through holes having a diameter of 1 to 10 mm, and vapor phase synthesis in the through holes of the substrate.
The silicon nitride fibers with a length of 100 μm or more formed and filled and fixed by entanglement with a thickness of 10 μm or more
And a non-oriented reticulated aggregate.

The above-mentioned base material may be a porous ceramic having continuous ventilation holes, and a large number of through holes having a diameter of 1 to 10 mm may be formed separately from the continuous ventilation holes. A filter can be formed by fixing non-oriented reticulated aggregates of silicon nitride fibers each having a thickness of 10 μm or more in the pores.

In such a ceramics filter of the present invention, a base material made of porous ceramics having continuous ventilation holes or a base material made of ceramics having a large number of through holes having a diameter of 1 to 10 mm is placed in a reaction furnace to obtain titanium oxide powder. Amorphous silicon nitride powder mixed with 1 in a nitrogen gas atmosphere
400-1600 ° C temperature and 300-1200 Tor
A non-oriented reticulated aggregate in which silicon nitride fibers having a length of 100 μm or more are entangled with each other and having a thickness of 10 μm on the base material and / or in the through holes of the base material by heating at a furnace pressure of r to cause a gas phase reaction. It is manufactured by the method of depositing and fixing as described above.

[0015]

The ceramic filter of the present invention is composed of a ceramic base material and a non-oriented reticulated aggregate of silicon nitride fibers, so that it has a smaller coefficient of thermal expansion than metal, excellent chemical stability, and heat resistance. It is also possible to obtain a filter having excellent thermal shock resistance. In particular, silicon nitride (Si ₃ N ₄ ) that constitutes a non-oriented reticulated aggregate has a thermal expansion coefficient of about 3.2 × 10 ⁻⁶ K ⁻¹ , which is the smallest of all ceramics, and has excellent thermal shock resistance and oxidation resistance. Are better.

The performance of the ceramics filter as a filter, such as the transmission performance, is determined by the non-oriented reticulated aggregate of Si ₃ N ₄ fibers, and the substrate only supports the non-oriented reticulated aggregate of the fibers. However, if silicon nitride or silicon carbide (SiC) is used as the base material, it is possible to construct a filter that can be used even at high temperatures, which cannot be used with the oxide-based ceramic base material.

The structure of the ceramics filter of the present invention is roughly classified into two. One of them is a base material 1a made of porous ceramics having continuous ventilation holes as shown in FIG.
S having a thickness of 10 μm or more, which is fixed in a film shape on the base material 1a.
and an unoriented reticulated aggregate 2a of i ₃ N ₄ fibers.
The non-oriented network assembly 2a of film-like Si ₃ N ₄ fibers is usually one layer, but as shown in FIG. 2, it may be composed of two or more layers having different pore diameters and porosities.

Porous ceramics having continuous ventilation holes are already known and are used as a filtering material, a carrier, a sensor and the like. Originally, since the ceramics sintered body is obtained by sintering powder, there are a large number of pores having a diameter of about several μm. However, the pore diameter is controlled by the filling rate of the green compact, the sintering conditions, etc. The porous ceramics are those that have been formed. However, in the present invention, since it is necessary as a filter, it is assumed that the pores are continuous ventilation holes.

Another structure has a diameter of 1 to 1 as shown in FIG.
A base material 1b made of ceramics having a large number of 0 mm through holes, and a non-oriented reticulated aggregate 2b of Si ₃ N ₄ fibers having a thickness of 10 μm or more filled and fixed in the through holes 3 of the base material 1b. . The reason why the diameter of the through-hole 3 is 1 to 10 mm is that if the diameter is less than 1 mm, it is difficult to fill the fiber, and if the diameter exceeds 10 mm, it becomes difficult to fill the entire through-hole without any gap, and the filled fiber is filtered. It is because the pressure at the time makes it easy to peel off.

In the filter having the structure shown in FIG. 3, since filtration is performed through the through hole and there is almost no pressure loss in the base material portion, the filter having a better permeation performance than the filters shown in FIGS. Further, the ceramic base material 1b having the through holes 3 formed therein is preferably ceramics having almost no pores or closed pores. When porous ceramics is used as the substrate, it is necessary to form a non-oriented network assembly of Si ₃ N ₄ fibers not only in the through holes but also on the substrate surface as in FIGS. 1 and 2. .

The non-oriented reticulated aggregate of Si ₃ N ₄ fibers formed on the substrate or in the through holes of the substrate is composed of relatively thin and long silicon nitride fibers vapor-phase synthesized by the following method . As shown in FIG. 7 , the fibers have a structure in which they are entwined with each other in a non-oriented state in which they are not oriented in a fixed direction and are gathered in a net shape, and further, they are fixed to the surface of the base material or the through holes of the base material. Therefore, the non-oriented reticulated aggregate of Si ₃ N ₄ fibers has a small pore size and a high porosity, has excellent permeability as a filter, and has no tensile stress in the fiber, so that it may be broken. There is no danger.

Specifically, the length of the fiber is 100 μm or more, and its non-oriented reticulated state in order to obtain sufficient entanglement between the obtained Si ₃ N ₄ fibers and to obtain sufficient fixation to the substrate. It is necessary that the thickness of the aggregate is 10 μm or more in both cases of forming a film on the surface of the base material and filling the through holes of the base material. or,
It is preferable that the diameter of the Si ₃ N ₄ fiber is mainly in the range of 0.01 to 5 μm, and as a result, the pore size of the non-oriented reticulated aggregate of the Si ₃ N ₄ fiber is 10 μm or less,
Moreover, a porosity of 80% by volume or more is obtained.

Next, a method for forming a non-oriented network assembly of Si ₃ N ₄ fibers will be described. As a method for synthesizing the ceramic fiber, there is a thermal carbon reduction method for synthesizing a fiber made of Si ₃ N ₄ or SiC by reducing a mixed powder of oxide ceramic powder containing silicon as a main component and carbon in a nitrogen gas. It is well known that the ceramic fibers synthesized by this method are short fibers or whiskers and the length of the fibers is short, so there is little entanglement with each other, the fibers fall off, and the fibers with the base material Can not be obtained.

Therefore, the present inventors pay attention to the ease of decomposing amorphous Si ₃ N ₄ at high temperature, and promote the decomposition to produce a large amount of thin and long Si ₃ N ₄ fibers. It was found that they were synthesized and formed into a net-like aggregate that was intertwined with each other in a non-oriented manner. That is, amorphous S
Although i ₃ N ₄ is more likely to evaporate at a higher temperature than a crystalline material, the amount of evaporation of i ₃ N ₄ is still insufficient, and a thin and long fiber cannot be sufficiently produced.

However, when titanium oxide (TiO ₂ ) is added to amorphous Si ₃ N ₄ , the amount of evaporation rapidly increases, and the evaporated Si ₃ N ₄ becomes long S on the substrate due to the gas phase reaction.
It was found that a large amount of i ₃ N ₄ fibers were produced to obtain a non-oriented reticulated aggregate entangled with each other. The vaporization of amorphous Si ₃ N ₄ is activated, and the vapor phase reaction causes Si ₃ N ₄
It was also found that in order to obtain a non-oriented reticulated aggregate in which fibers are entangled with each other, it is necessary to add TiO _{2 in} an amount of 5% by weight or more with respect to amorphous Si ₃ N ₄ .

The generation principle of Si ₃ N ₄ fiber is considered as follows. In order for the Si ₃ N ₄ fiber to be formed on the substrate, firstly it is necessary that the amount of evaporation of the amorphous Si ₃ N ₄ is large, and secondly, the generated Si ₃ N ₄ vapor is the basis. It is necessary to grow into fibers by vapor phase reaction on the material.

Regarding the first requirement, when TiO ₂ is added, TiO ₂ reacts with nitrogen in amorphous Si ₃ N ₄ to form TiN, and N in amorphous Si ₃ N ₄ is generated. The decrease in the number of atoms makes the structure of amorphous Si ₃ N ₄ thermally unstable. Therefore, it is considered that the evaporation of the amorphous Si ₃ N ₄ is activated, and at the same time, part of TiO ₂ is released as TiO gas.

With respect to the second requirement, the generated TiO gas reacts with nitrogen on the substrate to form fine TiN nuclei,
Amorphous Si ₃ N ₄ vapor reacts with nitrogen on TiN nuclei to produce Si
₃ N ₄ is deposited. It is considered that the reason why the precipitation form is not powdery but fiber-like is that the growth of Si ₃ N ₄ grows only in the crystal plane in a certain direction due to the interaction with the TiN nucleus.

As an additive that makes the structure of amorphous Si ₃ N ₄ unstable other than TiO ₂ , as a result of experiments, Fe, Cr, M
Each oxide of n, etc. could be confirmed. These additives are Ti
The case of O ₂ in the opposite, by reacting with Si atoms in the amorphous Si ₃ N _4, is believed to destabilize the structure of amorphous Si ₃ N _4. However, these additives did not produce Si ₃ N ₄ fibers. In this case S
It is considered that the i ₃ N ₄ fiber is not generated because TiN nuclei are not generated.

Even if metallic Ti, TiN or TiC is used in place of TiO ₂ , Si ₃ N ₄ fibers are produced, but the production amount is very small and a non-oriented reticulated aggregate in which Si ₃ N ₄ fibers are entangled with each other is obtained. I couldn't do that. When Ti or its non-oxide is used as an additive, Si ₃ N ₄ fibers are produced as shown in the schematic diagrams of FIGS. 4 to 6.
Oxygen of surface oxide film SiO ₂ of amorphous Si ₃ N ₄ and Ti, T
The reaction with iN or TiC produces Ti ₃ O ₅ , and this T
i ₃ O ₅ acts in the same manner as TiO ₂ described above, and amorphous Si ₃ N
It is considered that ₄ is destabilized, the evaporation is activated, and TiO gas is released at the same time. In this case, it is considered that the amount of produced fiber is small because the amount of produced Ti ₃ O ₅ is small.

In order to obtain a non-oriented reticulated aggregate in which Si ₃ N ₄ fibers are entangled with each other by the above-mentioned gas phase reaction, a mixed powder of amorphous Si ₃ N ₄ and TiO ₂ is contained in a nitrogen gas atmosphere at 1400 to 400. 1600 ° C temperature and 300-1200To
It heats with the furnace pressure of rr. The reason is that the reaction temperature is 1
This is because if the temperature is lower than 400 ° C., the evaporation of the amorphous Si ₃ N ₄ is insufficient, and if the temperature exceeds 1600 ° C., the obtained Si ₃ N ₄ fiber becomes short whiskers. Further, when the pressure in the reaction furnace is less than 300 Torr, vapor phase reaction between evaporated Si and N does not occur, and when it exceeds 1200 Torr, amorphous S
Evaporation of i ₃ N ₄ is less likely to occur.

The non-oriented reticulated aggregate of Si ₃ N ₄ fibers obtained by the above-mentioned gas phase reaction is such that the fibers are simply entangled with each other and are not joined to each other, but on the base material and / or the penetration of the base material. The non-oriented reticulated aggregate of fibers deposited in the pores is further heated in the atmosphere at 800 to 1500 ° C.
Heat treatment at a temperature of 170 ° C., then 170
By firing at a temperature of 0 to 1900 ° C, each Si ₃
It is possible to form a skeletal structure in which N ₄ fibers are joined together.

By heat-treating in the air at a temperature of 800 to 1500 ° C., a SiO ₂ layer having an appropriate thickness is formed on the surface of the Si ₃ N ₄ fiber, which is again in a nitrogen gas atmosphere at 1700 to 1900 ° C. By firing at the temperature of, the surface SiO ₂ layer forms a liquid phase and sintering proceeds,
As a result, a skeleton structure in which the Si ₃ N ₄ fibers are joined to each other is obtained. It should be noted that a nitrogen pressure of 1 atm or more is required so that Si ₃ N ₄ does not evaporate during firing.

If the heat treatment temperature in the atmosphere is less than 800 ° C., the SiO ₂ layer is not sufficiently formed on the fiber surface, and
When the temperature exceeds 500 ° C, oxidation rapidly progresses, and Si reaches the inside.
It is not preferable because it becomes O ₂ . Moreover, the firing temperature in a nitrogen gas atmosphere SiO ₂ in the liquid phase of the skeletal structure is not formed by sintering of fiber cross for not proceed below 1700 ° C., the evaporation the Si ₃ N ₄ exceeds 1900 ° C. This is not preferable because it is necessary to apply an excessive nitrogen pressure to suppress it.

When the skeleton structure is formed in this way, S
Since the strength of the non-oriented reticulated aggregate of i ₃ N ₄ fibers itself and the adhesion strength to the substrate are further improved, the filter can be used under a larger differential pressure. Further, the amount of SiO ₂ produced can be adjusted by changing the heat treatment temperature, and the degree of progress of sintering can be controlled by the firing temperature. Therefore, the pore diameter of the non-oriented reticulated aggregate of Si ₃ N ₄ fibers can be increased by these adjustments. It can be controlled by direction.

The shape of the ceramic filter of the present invention is not particularly limited, and may be, for example, a flat plate shape or a cylindrical shape, and it goes without saying that it can be appropriately selected depending on the application of the filter.

[0037]

Example 1 As shown in FIG. 8, a substrate 1a made of porous Si ₃ N ₄ having an average pore diameter of 10 μm and a porosity of 40% by volume and having a diameter of 25 mm and a thickness of 0.5 mm was formed by a CVD apparatus. It was installed in the reaction furnace 4. In the reaction furnace 4 below the substrate 1a, amorphous Si
A raw powder compact 5 was formed by molding a mixed powder obtained by adding 10% by weight of TiO ₂ powder to ₃ N ₄ powder into 25 × 25 × 10 mm.

N ₂ gas as a carrier gas was flowed in the reaction furnace 4 at a flow rate of 0.5 liter / min, the reaction temperature in the furnace was changed in the range of 1350 to 1650 ° C. by the heater 6, and the pressure in the furnace was changed. The vapor phase synthesis was carried out for 2 hours while changing the range of 300 to 700 Torr. With respect to the sample of the present invention, a non-oriented reticulated aggregate of Si ₃ N ₄ fibers having a thickness of 10 μm or more was formed on the surface of the substrate 1, and an optical micrograph (× 500) thereof is shown in FIG. 7. This S
The diameter of the i ₃ N ₄ fiber is about 0.5 to 1.0 μm,
The length was about 1 mm or more.

Next, for each of the obtained samples, Si ₃
The porosity of the non-oriented reticulated aggregate of N ₄ fibers was determined.
Further, the pore size distribution of the substrate and the filter was measured, and the pore size distribution of the non-oriented reticulated aggregate of Si ₃ N ₄ fibers was determined from the difference between them. However, not only the sample in which the Si ₃ N ₄ fiber was not formed, but also the sample in which the Si ₃ N ₄ whiskers were formed, in which the aggregate of the whiskers fell off during the measurement, could not be measured. The results are shown in Table 1.

The pore size distribution is measured by ASTM F-
316, the air flow rate (Fdry) was measured by changing the air pressure (P) for the dried substrate and the filter using a pore size distribution measuring instrument by the air flow method, and then the substrate wetted with isopropyl alcohol Similarly, the air pressure (P) was changed for the filter and the air flow rate (Fwet) was measured, and the pore size distribution of the non-oriented reticulated aggregate was determined from the difference between the respective pore size distributions Q = Fwet / Fdry.

[0041]

[Table 1] Reaction temperature Furnace pressure Average pore size Porosity Sample (° C) (Torr) Product (μm) (Volume%) 1 * 1350 300 Not generated Not measurable Not measurable 2 * 1350 700 Not generated Not measurable Not measurable 3 1400 300 Fiber 0.12 88 4 1500 500 Fiber 0.25 83 5 1550 500 Fiber 0.88 82 6 1600 700 Fiber 2.25 81 7 * 1650 300 Whisker not measurable Not measurable 8 * 1650 700 Whisker measurable Not measurable (Note) Samples marked with * are comparative examples (the same applies hereinafter).

From the results shown in Table 1, in the sample in which the reaction temperature and the pressure in the furnace are within the range of the present invention, a non-oriented reticulated aggregate in which elongated Si ₃ N ₄ fibers are entangled with each other is formed. It has a large pore diameter of 10 μm or less and a large porosity of 80% by volume or more, and it can be seen that it is optimum as a filter.

Example 2 Sample 4 prepared in Example 1 and having an average pore size of 0.25 μm
The filter (reaction temperature 1500 ° C., furnace pressure 500 Torr) was further heat-treated in the air at 800 to 1500 ° C. for 2 hours, and subsequently fired at 1600 to 1950 ° C. in a N ₂ gas atmosphere of 10 atm. For each of the obtained samples, the average pore diameter of the non-oriented reticulated aggregate of Si ₃ N ₄ fibers was determined in the same manner as in Example 1, and the results are shown in Table 2.

[0044]

[Table 2]

As can be seen from the results in Table 2, by controlling the heat treatment temperature in the air and the firing temperature in the N ₂ gas atmosphere of the unoriented reticulated aggregate of Si ₃ N ₄ fibers,
It is possible to change the pore size.

Example 3 Porous Si ₃ having an average pore diameter of 10 μm and a porosity of 40% by volume
And it filters the sample 10 of Example 2 in which a non-oriented mesh aggregates the Si ₃ N ₄ fibers to about 83 volume% porosity with an average pore diameter 0.55μm on the N ₄ base material, the same porous Si ₃ N _Four
Average pore size of 1.00 μm on the substrate with porosity of about 83% by volume
The filter of the sample 16 of Example 2 provided with the non-oriented reticulated aggregate of Si ₃ N ₄ fibers was prepared. These Si
The thickness of the non-oriented reticulated aggregate of ₃ N ₄ fibers is 20 μm.
m.

On the other hand, as a comparative example, an Al ₂ O ₃ layer having an average pore diameter of 3.0 μm and a thickness of 50 μm and an average pore diameter were formed on a porous Al ₂ O ₃ substrate having an average pore diameter of 10 μm and a porosity of 40% by volume. A commercially available filter (Sample a) in which a porous Al ₂ O ₃ layer having a thickness of 0.5 μm and a thickness of 30 μm was sequentially formed, and the same porous A
50 μm thickness with average pore size of 5.0 μm on l ₂ O ₃ substrate
Commercially available filters the Al ₂ O ₃ layer and an average porous the Al ₂ O ₃ layer with a thickness of 30μm in pore diameter 1.0μm are successively formed (Sample b) was prepared.

Using these filter samples, AST
In accordance with MF-316, a permeation flow rate measuring device was used to measure the pressure difference of 0.95 kg / cm ² with isopropyl alcohol (IP
A) and air were vacuum filtered. Table 3 shows the permeation flow rates of the obtained filters.

[0049]

[Table 3]

From Table 3, the filters of the present invention of Samples 10 and 16 have a thickness of 1/4 and a porosity approximately double that of the commercially available filters of Samples a and b which are comparative examples. Therefore, it can be seen that it has an excellent transmission performance of 3 to 4 times.

Example 4 Each filter of Example 3 was held in a furnace (atmosphere atmosphere) heated to a temperature of 1400 ° C. for 10 minutes and then rapidly cooled to room temperature. The diameter of the polyethylene latex dispersed in IPA was 0.7μ using each filter after cooling.
m and each uniform particle having a diameter of 1.3 μm were filtered and the collection rate was measured. The results are shown in Table 4.

[0052]

[Table 4]

The samples a and b of the commercially available filters made of Al ₂ O ₃ had cracks due to thermal shock in the base material and the film portion after heating, and thus the collection rate was lowered. Since the filters of Samples 10 and 16 were made of Si ₃ N ₄ , they exhibited excellent thermal shock resistance, and did not crack even when heated, and maintained a high collection rate.

Example 5 An inner diameter of 25 mm made of dense SiC having a relative density of 99%,
A cylindrical base material having a thickness of 0.5 mm and a length of 20 mm is prepared, and a large number of through holes 3 having a constant diameter are formed at equal intervals on the side wall of the cylinder. 5-15m
The porosity of the side wall is all 50% by volume while changing within the range of m.
Was adjusted so that

Next, as shown in FIG. 9, a cylindrical substrate 1
The portions other than the through holes 3 on the side wall of b were masked and placed in the reaction furnace 4 of the CVD apparatus. On the other hand, in the reaction furnace 4 below the base material 1b, a mixed powder obtained by adding 10% by weight of TiO ₂ powder to amorphous Si ₃ N ₄ powder was prepared as 25 × 25 × 10 mm.
The raw material powder compact 5 molded into the above was placed.

N ₂ gas as a carrier gas was flowed in the reaction furnace 4 at a flow rate of 0.5 liter / min to obtain a reaction temperature of 1500.
The vapor phase synthesis is carried out at a temperature of 700 ° C. and a furnace pressure of 700 Torr, and Si _{3 is} filled so as to fill the through holes 3 formed in the side wall of the base material 1b.
An unoriented reticulated aggregate of N ₄ fibers was formed. After that, heat treatment was performed at 800 ° C. for 2 hours in the air, and further, firing was performed at 1700 ° C. for 2 hours in a N ₂ gas atmosphere of 10 atm. The obtained non-oriented reticulated aggregate of Si ₃ N ₄ fibers had an average pore diameter of 0.5 μm and a porosity of about 83% by volume in each of Samples 19 to 23.

For reference, a cylindrical base material (without through-holes) having the same size as described above and made of porous SiC having an average pore diameter of 10 μm and a porosity of 50% by volume was used. A non-oriented reticulated aggregate of Si ₃ N ₄ fibers having the same average pore diameter and porosity as each of the above samples was formed on the entire inner peripheral surface of the cylinder to a thickness of 20 μm (Sample 24).

Using each of these filter samples, AST
In compliance with M F-316, isopropyl alcohol (IP differential pressure 1.0 kg / cm ² by the sample permeate flow meter
A) and air were vacuum filtered and the permeation flow rate was measured. or,
For each filter sample, uniform particles of 0.7 μm in diameter made of polyethylene latex dispersed in IPA were filtered, and the collection rate was measured. The results are shown in Table 5.

[0059]

[Table 5] Substrate side wall through hole Same porosity Permeation flow rate (ml / min · cm ² ) Collection rate Sample hole diameter (mm) (volume%) IPA Air (%) 19 * 0.5 50 211 302 69 20 1.0 50 233 311 98 21 5.0 50 266 344 98 22 9.0 50 341 398 98 23 * 15 50 399 425 60 24 No through hole 50 194 288 98

Sample 20 in which a non-oriented network assembly of Si ₃ N ₄ fibers was filled and fixed in a through hole having a hole diameter of 1 to 9 mm
It can be seen that each of the filters of No. 22 exhibits superior permeation performance to the filter of Sample 24 in which the same non-oriented reticulated aggregate is formed on the surface of the porous SiC substrate having no through holes. or,
Each of the filters of Samples 19 and 23 having a through hole diameter of 0.5 mm and 15 mm has excellent transmission performance,
In the former case, it was difficult to fill the Si ₃ N ₄ fibers in the through holes, and in the latter case, the thickness of the non-oriented reticulated aggregate of fibers in the central portion of the through hole was thin, so that the collection rate of fine particles was significantly reduced.

[0061]

According to the present invention, a ceramic base material is provided with a non-oriented reticulated aggregate of Si ₃ N ₄ fibers having a small average pore diameter and a large porosity. It is possible to provide a ceramics filter having excellent chemical property. Since this ceramics filter has extremely excellent permeation performance and collection rate, it is effective as a collection filter for bacteria and fine particles in liquid or gas, and can also be used as a catalyst carrier.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a specific example of a ceramics filter of the present invention.

FIG. 2 is a schematic cross-sectional view showing another specific example of the ceramics filter of the present invention.

FIG. 3 is a schematic cross-sectional view showing another specific example of the ceramics filter of the present invention.

FIG. 4 is a schematic diagram for explaining an initial reaction process between amorphous Si ₃ N ₄ and TiN when TiN is added.

FIG. 5 is a schematic diagram for explaining the next reaction process in which generation of Ti ₃ O ₅ and generation of TiO gas occur when TiN is added to amorphous Si ₃ N ₄ .

6 is a schematic diagram for explaining the end of the reaction process in which the evaporation of the amorphous Si ₃ amorphous Si in case of adding TiN to N _{4 3} N ₄ occurs.

FIG. 7 is a micrograph (× 500) showing the shape of a non-oriented network assembly of Si ₃ N ₄ fibers in the present invention.

FIG. 8 is a schematic cross-sectional view of an apparatus for forming an unoriented reticulated aggregate of Si ₃ N ₄ fibers on a flat substrate in the present invention.

FIG. 9 is a schematic sectional view of an apparatus for forming a non-oriented reticulated aggregate of Si ₃ N ₄ fibers on a cylindrical substrate in the present invention.

[Explanation of symbols]

1a, 1b Substrate 2a, 2b Non-oriented reticulated aggregate of Si ₃ N ₄ fiber 3 Through hole 4 Reactor 5 Raw material powder compact 6 Heater

Continuation of the front page (56) References JP-A-1-176285 (JP, A) JP-A-59-142820 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B01D 39 / 00-39/20

Claims (9)

(57) [Claims] 1. A base material made of porous ceramics having continuous ventilation holes, and formed and fixed on the base material by vapor phase synthesis.
A ceramics filter comprising a non-oriented reticulated aggregate in which silicon nitride fibers having a length of 100 μm or more are entangled with a thickness of 10 μm or more. 2. A base material made of ceramics having a large number of through holes having a diameter of 1 to 10 mm, and a length 10 formed by gas phase synthesis and filled and fixed in the through holes of the base material.
A ceramics filter comprising a non-oriented reticulated aggregate in which silicon nitride fibers having a thickness of 0 μm or more are entangled with a thickness of 10 μm or more. 3. The ceramic filter according to claim 1, wherein the silicon nitride fiber has a diameter of 0.01 to 5 μm. 4. The non-oriented reticulated aggregate of silicon nitride fibers has a skeleton structure in which entangled silicon nitride fibers are joined to each other.
The ceramic filter according to any one of 1 to 3. 5. The non-oriented reticulated aggregate of silicon nitride fibers has a pore size of 10 μm or less and a porosity of 80% by volume.
It is above, The ceramics filter in any one of Claims 1-4 characterized by the above-mentioned. 6. The ceramic filter according to claim 1, wherein the base material is made of silicon nitride or silicon carbide. 7. An amorphous material in which a base material made of porous ceramics having continuous ventilation holes or a base material made of ceramics having a large number of through holes having a diameter of 1 to 10 mm is placed in a reaction furnace and mixed with titanium oxide powder. The silicon nitride powder is placed in a nitrogen gas atmosphere at a temperature of 1400 to 1600 ° C. and 300 to 12
100 μm in length on the base material and / or in the through-holes of the base material by heating at a furnace pressure of 00 Torr to cause a gas phase reaction.
A method for producing a ceramics filter, comprising depositing and fixing a non-oriented reticulated aggregate in which silicon nitride fibers of m or more are entangled with each other to a thickness of 10 μm or more. 8. The method for producing a ceramics filter according to claim 7, wherein the amount of titanium oxide added is 5% by weight or more with respect to the amorphous silicon nitride. 9. A non-oriented reticulated aggregate of silicon nitride fibers is deposited and fixed on the base material and / or in the through holes of the base material, and then heat-treated at a temperature of 800 to 1500 ° C. in the atmosphere. , Then 1700 to 1 in a nitrogen gas atmosphere
The method for producing a ceramics filter according to claim 7, wherein a skeleton structure in which the silicon nitride fibers are bonded to each other is formed by firing at a temperature of 900 ° C.