JPH10237504A - Metallic porous body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a metallic porous body easy to be produced as compared to the case of metallic fiber, capable of using inexpensive metal powder and excellent in permeability by forming it into metal flat fine powder in which the average value of the flattening degree is regulated to a specified range. SOLUTION: An assembled body of metal flat fine powder in which the average value of the flattening degree (the thickness of the flat part in the flat powder/the maximum length of the flat powder) lies in the range of 0.05 to 0.5 is formed. In this way, the porosity of the metallic porous body is improved, so that the permeability of the metallic porous body can be improved. In the case the average value of the flattening degree exceeds 0.5, the porosity reduces to drastically deteriorate its permeability. Furthermore, in the case the average value of the flattening degree is <=0.05, good permeability can be obtd., but, there is a limitation on flattening working to the metal fine powder, and furthermore, the working cost is made drastically high. Moreover, the average grain size of the metal flat fine powder is regulated to the range of 3 to 20μm. By using this metallic porous body for a filter for gas in particular, fine impurity grains can be removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal porous body used for a filter, a catalyst, a molding die for plastics, and more particularly to a metal porous body used for a gas filter member. is there.

[0002]

2. Description of the Related Art Porous metal bodies include filters, catalyst bodies,
Used in plastic molds and the like. The filter is used for filtering and purifying various fluids, and has a filtration pore size of 2 to 100 μm. Filters include
In addition to the metal porous body, a metal fiber composite, a polymer material (for example, polypropylene), a ceramic porous body, and the like are used.

[0003] A filter used in a semiconductor manufacturing process will be described. In the semiconductor manufacturing process,
The degree of integration of integrated elements has been rapidly increasing, and the pattern width of integrated elements has become a sub-micron interval.
For this reason, the process gas (A
r, N ₂ , H ₂ , HCl, HF, etc.) by using a high-performance filtration filter to reduce the pattern width of the integrated device to 1/1.
It is indispensable to remove impurity particles having a diameter of 0 or more (for example, particles having a size of about 0.01 μm or more) to prevent a short circuit of a wiring. In addition, due to the demand for ultra-high purity of the process gas, a baking process is required to heat the filter to 300 ° C or higher in order to remove harmful moisture and impurity gas adsorbed on the filter before operation. It is.

[0004] For this reason, filters used in the semiconductor manufacturing process are not suitable for filters made of a polymer material or the like which have been conventionally used for filters because of their heat resistance.
Metallic material filters have come into use.
In order to remove fine impurity particles, it is necessary to reduce the pore size of the filter, and a metal porous body using a metal powder with a small particle size and a metal fiber composite using a metal fiber with a small fiber diameter are required. Has been developed.

[0005] In order to trap the above-mentioned particles of about 0.01 µm or more from gas using a filter made of a porous metal body,
For example, it is necessary to use micron-order metal powder. However, the metal powder often has a spherical shape, and in particular, the metal alloy powder has a spherical shape because it is produced by an atomizing method. For this reason, the porosity of the metal porous body becomes extremely small, the pressure loss becomes so large that it cannot withstand use, and there is a problem that the air permeability is significantly reduced.

Therefore, in order to remove fine impurity particles, a metal fiber composite filter is often used. For example, a metal fiber composite filter disclosed in Japanese Patent Application Laid-Open No. 5-27712 is used. This means that the diameter is 0.5-10 μm and the aspect ratio is 2-20.
Is a metal fiber composite obtained by sintering short metal fibers having a columnar shape in the range of (1).

[0007] Applications other than the filter of the porous metal body include a catalyst body and a molding die for plastic. As a catalyst, a porous catalyst is used in a purifier that oxidizes NOx in exhaust gas of an automobile to make it harmless. Further, in an application example to a plastic mold, a metal porous body is used to fill the plastic to the end of the mold at the time of injection molding. At the time of injection molding, the gas pressure becomes high at the tip of the mold, so that filling may not be possible. Therefore, a mold having air permeability has been developed for degassing.

[0008]

However, the metal fibers, which are the raw materials of the metal fiber composite, are more expensive than the metal powder, and it may be difficult to produce metal fibers having the required shape. In particular, metal short fibers having a small fiber diameter are more expensive, and sometimes cannot be produced. For example, Japanese Patent Publication No. 63-63645 discloses a method for obtaining short metal fibers having a fine diameter, which involves cutting a stainless steel fiber by grain boundary selective corrosion because the cutting method is expensive. However, even this method is expensive, and many metal fibers cannot use the grain boundary selective corrosion method. In addition, since the metal fiber composite is likely to be entangled with fibers, uniform filling is often difficult, and it may be difficult to obtain a uniform pore distribution as a filter.

On the other hand, metal powder can easily obtain a metal having a required composition and particle size by an atomizing method, and is less expensive than metal fibers. Furthermore, since uniform filling is easy, it is possible to obtain a porous metal body having a uniform void distribution. However, as described above, a porous metal body using fine metal powder has a problem that air permeability is significantly reduced.

[0010] In addition, the catalyst body is required to have increased air permeability and contact area, but there has been a problem that satisfactory properties have not been obtained with conventional porous metal bodies. As for the metal mold for plastic, the air permeability is not sufficient with the conventional porous metal body. Regarding the mold, a mold made of a porous metal body is being developed due to problems such as air permeability, strength, and ease of production.

It is an object of the present invention to provide a porous metal body which is easy to produce as compared to metal fibers and has excellent air permeability using inexpensive metal powder. Especially,
It is an object of the present invention to provide a metal porous body used for a gas filter capable of removing fine impurity particles.

[0012]

Means for Solving the Problems In order to solve the above-mentioned problems in the prior art, the present inventors have intensively studied the factors affecting the air permeability of a porous metal body. As a result, the aggregate filled with the flat fine powder has a high porosity,
This aggregate was found to have excellent air permeability. It was also found that the flattening treatment reduced the substantial particle size of the flat fine powder, and reduced the pore size of the obtained aggregate. . Further, the specific surface area of the flat fine powder is increased, the trapping rate of the impurity particles is improved, and the life can be improved.

According to the present invention, a porous body having fine pores formed by partitioning a space by a wall structure made of metal flat fine powder is excellent in air permeability, enables capture of fine impurity particles, and provides a longer life. The present invention has been completed based on the finding that the present invention can be performed.

In the metal porous body according to the first aspect of the present invention, the average value of the flatness (the thickness of the flat portion of the flat powder / the maximum length of the flat powder) is 0.05 to 0.1. An aggregate formed of the metal flat fine powder having a range of 5 and having air-permeable pores.
By forming an aggregate of metal flat fine powder having an average value of flatness (thickness of flat portion of flat powder / maximum length of flat powder) in the range of 0.05 to 0.5, the metal porous material The porosity is improved, and as a result, the air permeability of the porous metal body is improved.
If the average value of the flatness exceeds 0.5, the porosity decreases and the air permeability deteriorates remarkably. Further, the average value of the flatness is 0.
If it is 5 or less, good air permeability can be obtained, but the flattening of the metal fine powder is limited and the processing cost becomes extremely high. Therefore, the average value of the flatness is preferably 0.05 or more.

According to a second aspect of the present invention, in addition to the configuration of the first aspect, the average particle diameter of the metal flat fine powder is in a range of 3 to 20 μm. By setting the average particle diameter of the metal flat fine powder in the range of 3 to 20 μm, fine impurity particles can be captured. At this time,
The volume particle diameter is used as the average particle diameter of the metal flat fine powder. The volume particle diameter is a value obtained by assuming that a particle having a certain volume is spherical, the particle diameter corresponding to this volume. If the average particle diameter of the metal flat fine powder is less than 3 μm, the filling property is remarkably reduced, and the ratio of the closed voids of the porous body is increased, whereby the air permeability is significantly reduced. On the other hand, when the average particle diameter of the metal flat fine powder exceeds 20 μm, the specific surface area decreases, and the capture rate of fine impurity particles decreases.

According to a third aspect of the present invention, in addition to the configuration of the first or second aspect, the average porosity of the porous metal body is in the range of 40 to 55%. When the average porosity of the metal porous body is in the range of 40 to 55%, the pore size distribution becomes uniform throughout the metal porous body, and the dispersion of the capture of the impurity particles is reduced, which contributes to stabilization of quality. Further, a stable air permeability can be obtained, and the trapping rate of the impurity particles can be increased.

According to a fourth aspect of the present invention, in addition to the configuration of the first or second or third aspect, the flat portion of the metal flat fine powder is moved from one surface through which the gas of the metal porous body passes. It has a parallel layer arranged in parallel to the direction leading to the other surface. By passing the gas from one surface to the other surface along the parallel layer, finer impurity particles can be captured, and the air permeability can be further improved.

According to a fifth aspect of the present invention, in addition to the constitution of the first aspect of the present invention, the metal flat fine powder contains a short metal fiber having an aspect ratio (length / diameter) in the range of 2 to 20 by mass. 5 to 30% by weight. The air permeability can be improved by adding short metal fibers. The amount of the short metal fiber to be added is preferably 5 to 30%. 5%
If it is less than 30%, there is no effect on improving the air permeability, and if it exceeds 30%, the pore size becomes large, and the trapping rate of fine impurity particles decreases. Further, the diameter of the short metal fiber is preferably in the range of 0.5 to 10 μm. By using short metal fibers having a fine diameter in the range of 0.5 to 10 μm, the capture rate of fine impurity particles can be improved. The diameter of the short metal fiber is preferably as small as possible, but it is difficult or expensive to produce a short metal fiber having a diameter of less than 0.5 μm. Therefore, the diameter of the short metal fiber used is preferably 0.5 μm or more.

According to a sixth aspect of the present invention, there is provided a gas filter member used for the metal porous body according to any one of the first to fifth aspects. By using the metal porous body of the present invention for a gas filter member, air permeability is improved,
Fine impurity particles can be trapped, and durability can be improved.

[0020]

Next, a first embodiment of the present invention will be described. The test material of this example was manufactured by the atomizing method,
Fine powder of stainless steel (S) having an average particle diameter of 11 μm (volume diameter)
US316L) from the raw materials. In order to change the flatness of the stainless steel fine powder, the stainless steel fine powder is charged into a ball mill, and dry mixing is performed using stainless steel balls in an N ₂ atmosphere to prevent oxidation, and flattening is performed. Was. By changing the processing time in the ball mill, as shown in Table 1, the flatness was 0.03 to 0.8.
A stainless steel flat fine powder changed to 1 was obtained. Table 1 shows the measurement results of the flatness, porosity, average pore diameter, and filtration pressure difference of the test material. The stainless steel fine powder having a flatness of 0.81 is a raw material powder that has not been subjected to flattening treatment.

[0021]

[Table 1]

In the flattening process, not only a ball mill process but also other ball type mixers (for example, an attritor) can be used. Not only stainless steel balls but also other commercially available steel balls and hard metal balls can be used. In this embodiment, stainless steel balls having a composition close to that of the stainless steel fine powder were used in order to prevent the stainless steel fine powder from being contaminated by ball wear during the flattening process. The flattening treatment by mixing in the ball mixer may be not only dry but also wet mixing using an organic solvent. Further, the flattening treatment can also be performed by rolling the powder.

The flatness was measured by taking a photograph of the flattened stainless steel fine powder with a scanning electron microscope, and based on this photograph, for 100 particles of each fine powder, the thickness and flatness of the flat part of the flat fine powder were measured. By measuring the maximum length of the fine powder, these average flatness (thickness of flat portion of flat fine powder /
The maximum length of the flat fine powder) was obtained. At this time, it was also observed that the specific surface area of the stainless steel fine powder was increased by increasing the flatness of the stainless steel fine powder.

Next, a stainless steel flat fine powder having a different degree of flatness was filled in a mold to produce an aggregate of stainless steel flat fine powder. The shape of this assembly is 40 mm long and 20 m outside diameter
m, 18 mm in inner diameter. After pre-sintering the assembly as filled in the mold in an N ₂ atmosphere,
The aggregate of stainless steel flat fine powder was released from the mold. This aggregate was sintered in vacuum (1100 ° C. for 2 hours) to produce a porous metal body. At this time, stainless steel (SUS304) was used for the mold, but other heat-resistant metal materials, ceramics, and the like can be used. As the sintering atmosphere, not only a vacuum but also a non-oxidizing atmosphere, an inert atmosphere, or a reducing atmosphere may be used.

The porosity, average pore size, and flow rate characteristics of these porous metal bodies were measured as filtration differential pressures.
And FIG. 1 and FIG. The porosity is obtained by measuring the size and weight of the porous metal body and calculating from the volume and weight obtained from the size. The average pore size was determined by a mercury intrusion method. The filtration pressure difference was determined from the filtration pressure difference between the inside and outside of the cylinder of the cylindrical assembly. FIG. 1 shows the effect of flatness on the porosity, average particle diameter and filtration pressure difference, and FIG. 2 shows the relationship between gas flow rate and filtration pressure difference. Incidentally, filtration differential pressure of 1 within the filtration pressure difference of FIG. 2, N ₂ flow rate of 2 Nl / c
This shows the case of m ² · min.

FIG. 1 shows the measurement results of the flatness of the porous metal body on the horizontal axis and the porosity, average pore diameter and filtration pressure difference on the vertical axis. The porosity of the porous metal body increases as the flatness decreases, and changes little when the porosity is 0.1 or less. On the other hand, the average pore diameter decreases as the flatness decreases.
By reducing the average pore diameter, the size of the impurity particles that can be captured is reduced. The filtration pressure difference of a porous metal body, which is a measure of air permeability, decreases significantly with the decrease in flatness. When the flatness is 0.5 or less, the filtration pressure difference is 0.35 × 1.
0 ⁵ Pa or less, which proved to exhibit excellent air permeability.

Next, a second embodiment of the present invention will be described with reference to Table 2. Table 2 shows the manufacturing conditions, flatness, porosity, average pore size, and measurement results of the filtration pressure difference of the test materials. In this embodiment, flattened stainless steel flat fine powder C (flatness: 0.1
1) and stainless steel fine powder F as raw material (flatness: 0.81)
Were dry-mixed in a ratio shown in Table 2 with a V-type mixer. The weighted average flatness at that time was 0.3 for the mixed powder G (flat fine powder C: 70% by mass, fine powder F: 30% by mass).
2. Mixed powder H (flat fine powder C: 30% by mass, fine powder F: 70)
Mass%) was 0.60.

[0028]

[Table 2]

From these mixed powders, a porous metal body was manufactured under the same manufacturing conditions as in the first embodiment. As shown in Table 2, although the filtration differential pressure of the porous metal body using the mixed powder G having the flatness of 0.32 is 0.31 × 10 ⁵ Pa, which has excellent air permeability,
The filtration differential pressure of the porous metal body using the mixed powder H having a flatness of 0.60 was 0.49 × 10 ⁵ Pa. in this way,
Even in mixed powders of metal fine powders having different degrees of flatness, the average value of the degrees of flatness obtained by the weighted average of the mixed powder is 0.05 to
It was found that the aggregate of the metal flat fine powder having a range of 0.5 had excellent air permeability.

Further, a third embodiment in which the filling condition of the flat fine powder into the mold is changed will be described with reference to Table 3. Table 3 shows the manufacturing conditions, flatness, porosity, average pore size, and measurement results of the filtration pressure difference of the test materials. After the mold used in the first example was set in an ultrasonic vibration device, the stainless steel flat fine powder C (flatness: 0.11) used in the first example was filled in the mold. Thereafter, the ultrasonic vibrator was operated to apply vibration to the mold, and at the same time, the flat fine powder C was further charged into the mold, thereby increasing the packing density of the aggregate of the flat fine powder C. At this time, the vibration was activated for 20 seconds and 60 seconds.

[0031]

[Table 3]

These assemblies were vacuum-sintered under the same conditions as in the first embodiment to produce a porous metal body. Table 3 shows the measurement results of the porosity, average pore diameter, and filtration pressure difference of these metal porous bodies. The porosity and the average pore diameter of the metal porous body I manufactured by giving vibration for 20 seconds at the time of filling were smaller than those of the metal porous body C not given vibration at the time of filling.
However, it was found that the porous metal body I had excellent air permeability at a value lower than the filtration pressure difference of the porous metal body C, despite the reduced porosity. This is due to the vibration of the flat powder filling the mold, parallel to the bottom of the mold,
That is, a parallel layer in which the flat portions of the metal flat fine powder are arranged in the radial direction with respect to the central axis of the cylindrical assembly and parallel to the gas flow from the inside to the outside of the cylindrical assembly is formed. It is because of that.

Further, the metal porous body J whose vibration time is increased to 60 seconds at the time of filling has a further smaller porosity,
As a result, the filtration pressure difference increased significantly.

Finally, a fourth embodiment of a fiber composite metal porous body produced by mixing short metal fibers with flat fine powder will be described with reference to Table 4. Table 4 shows the production conditions, flatness, porosity, average pore size, and measurement results of the filtration pressure difference of the test materials. The short metal fibers used are stainless steel (SUS316L) short fibers having a diameter of 2 μm and a length of 30 μm. This short metal fiber and stainless steel flat fine powder C (flatness: 0.11) were mixed by a V-type mixer under the conditions shown in Table 4, and the mixed powder and fine powder were given while applying ultrasonic vibration to the same mold as in the first embodiment. Each of the metal short fibers was filled, and thereafter, a fiber composite metal porous body and a metal fiber composite were manufactured by vacuum sintering as in the first example. Table 1 shows the measurement results of the porosity, the average pore diameter, and the filtration pressure difference of these metal porous bodies. The reason why the filling was performed while applying the ultrasonic vibration was that the filling property of the short metal fibers was poor.

[0035]

[Table 4]

Both the porosity and the average pore diameter of the fiber composite metal porous body containing short metal fibers increased. When the blending amount of the fiber was 30% by mass, the increase in the average pore diameter was small, but when the blending amount of the fiber was 70% by mass, the average pore size increased remarkably, and there was a problem in capturing fine impurity particles. It has been found.

The porous metal body of the present invention can be produced by other methods without being limited to this embodiment. For example, the metal porous body of the present invention can be manufactured by a sintering method such as slip casting, injection molding, and pressure molding into a mold. Further, the metal porous body may be manufactured by a method other than the sintering method. For example, a metal porous body can be made by bonding metal powders with a resin. Further, the composition of the metal powder is not limited to this embodiment, but can be changed depending on the application. For example, in applications requiring corrosion resistance, not only the stainless steel powder of this embodiment, but also Ti powder,
Ni powder or the like can be used.

[0038]

As described above, according to the present invention, it is possible to obtain a metal porous body which is easier to manufacture than metal fibers, enables use of inexpensive metal powder, and has excellent air permeability. It is possible. In particular, by using the metal porous body of the present invention for a gas filter, fine impurity particles can be removed. This is because the porous metal body of the present invention has fine pores formed by partitioning a space by a wall structure made of metal flat fine powder, thereby improving air permeability, an improvement in the capture rate of fine impurity particles, and a long life. It is possible.

[Brief description of the drawings]

FIG. 1 shows a porosity of a porous metal body according to a first embodiment of the present invention;
FIG. 3 is a diagram showing the influence of flatness on average particle diameter and filtration differential pressure.

FIG. 2 is a diagram showing a relationship between a gas flow rate of a porous metal body and a filtration pressure difference in an example of the present invention.

Claims (6)

[Claims] An aggregate formed of metal flat fine powder having an average value of flatness (thickness of flat portion of flat powder / maximum length of flat powder) of 0.05 to 0.5. Metal porous body having pores with air permeability 2. An average particle diameter of the metal flat fine powder is 3 to 2.
2. The metal porous body according to claim 1, which is in a range of 0 μm. 3. The porosity of the porous metal body is 40 to 55.
% Of the metal porous body according to claim 1 or 2 in the range of 4. The flat portion of claim 1, wherein the flat portion of the metal flat fine powder is provided with a parallel layer arranged in parallel to a direction from one surface of the porous body to the other surface. Metal porous body 5. A short metal fiber having an aspect ratio (length / diameter) in the range of 2 to 20 is added to the metal flat fine powder in a mass ratio of 5 to 5.
2. The metal porous body according to claim 1, which is added by 30%. 6. The metal porous body according to claim 1, which is used for a gas filter member.