JP2010064924A - Porous material and method for producing porous material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous material which has through-holes of a submicrometer order, does not cause pressure loss when a medium is made to flow into the through-holes, is chemically inert as well, also has sufficient strength and can be stably used over a long period of time. <P>SOLUTION: The porous material has the through-holes almost parallel to the thickness direction and includes crystalline alumina. The porous material is obtained, e.g. by immersing an aluminum base material into an electrolytic solution, performing electrolytic treatment so as to form an amorphous anodized film on the surface of the aluminum base material, next peeling the anodized film from the aluminum base material, arranging the same between a pair of plate-like members, further constraining the same by a pair of the plate-like members, and subjecting the anodized film to heat treatment while being constrained by a pair of the plate-like members so as to be crystallized. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a porous material that can be suitably used as a filter, a heat insulating material, a sound absorbing material, an impact buffering material, and the like, and a method for producing the same.

  Porous materials with a structure containing a large number of voids inside are used in a wide range of applications such as filters for various fluids, heat insulating materials, sound-absorbing materials, shock-absorbing materials, regardless of their gas phase or liquid phase. ing. In addition to the above physical properties, the internal surface area is large, so that the catalyst support or porous material directly functions as a catalyst, and is used as a chemical reaction field.

  Since the characteristics of the porous material are determined by the structure such as the pore diameter, the pore diameter distribution, the pore shape, etc., in many applications, a porous body having a plurality of structures is used in combination. For example, in a filter for the purpose of separating foreign substances, it has been proposed to configure a plurality of porous bodies from a porous structure having a structure in which pores are stacked in descending order. Also, ceramic filters used for water purification purposes have a porous structure that includes a fine porous membrane with a pore size on the order of submicron and a porous substrate with a pore size on the order of several to several hundred microns. The body. In this example, since the multi-layer structure is all made of a ceramic-based homogeneous material, it can be sintered integrally.

  On the other hand, for the purpose of fine chemical use, drinking water production, and other industrial process water production, there are many occasions where fine particles need to be filtered. At this time, a filtration membrane having a pore size on the order of submicron is required. However, in this region, there is a problem that the resistance when the medium passes through the pores is large and the pressure loss in the filtration membrane is increased. In addition, filtration materials generally composed of organic membranes capture particles in the randomly arranged resin or fiber voids inside the filtration material, so that once captured particles are desorbed. Is difficult and tends to be contaminated (see, for example, Patent Documents 1 and 2).

JP 2000-70683 A JP-A-2005-319376

  In view of the above-described problems, attempts have been made to produce a porous material having through holes substantially parallel along the thickness direction by using an anodizing treatment of a metal material such as aluminum. In this case, since the through-holes constituting the porous material are linearly formed substantially parallel to the thickness direction, even if the through-hole has a submicron size, There is no increase in pressure loss when flowing through the pipe.

  The pore diameter can be controlled by conditions such as the composition of the electrolytic solution and the voltage, and a porous material having through-holes with uniform pore diameter distribution can be obtained.

  However, the porous material formed by anodizing treatment as described above is an amorphous aluminum oxide and has a drawback that it is hard but relatively brittle. Therefore, it is very difficult to handle with a thin film, and when it is practically used, there is a risk of occurrence of cracks and breakage due to stress during manufacture and use. It is chemically active and has the property of dissolving when contacted with water or chemicals.

  Furthermore, since the porous material contains the composition of water and the electrolyte solution used during electrolysis, these residual substances are eluted in water or contained in water or chemicals when in contact with water or chemicals. May react with ingredients. Due to these phenomena, the wall of the through-hole is dissolved, the film thickness is decreased, and the fine structure of the film is changed, and eventually the film may be damaged.

  Therefore, when using a porous material made of an anodized aluminum film as a filtration filter, even if it can be used for a short time with a medium at room temperature, the performance of the membrane such as long-term, flux, separation pore size, strength can be improved. It is difficult to maintain.

  The present invention has a through hole of submicron order, and does not cause a pressure loss when a medium is flowed into the through hole, has a chemically inert and sufficient strength, and has a long period of time. An object of the present invention is to provide a porous material that can be used stably over a long period of time.

  In order to achieve the above object, the present invention relates to a porous material having a through hole substantially parallel to the thickness direction and containing crystalline alumina.

  In view of the problems related to the prior art described above, the inventors of the present invention, for example, may have a porous material made of alumina formed by anodizing treatment having through-holes in the order of submicrons approximately parallel to the thickness direction. However, it was noted that the chemical activity is caused by the fact that the porous material is amorphous. From such a viewpoint, the porous material is attempted to be crystallized based on the manufacturing method as described below, and has a through-hole substantially parallel to the thickness direction as formed by anodizing treatment, and has a crystallinity. We succeeded in obtaining a porous material containing alumina.

  According to the porous material of the present invention, since the through hole is linearly formed substantially in parallel with the thickness direction, the inside of the through hole is formed even if the through hole has a submicron size. There is no increase in pressure loss when flowing. Further, since the porous material is made of crystalline alumina, it is chemically inert and does not dissolve even when contacted with water or chemicals.

  Furthermore, when the porous material contains the composition of water and an electrolytic solution used during electrolysis, these residual substances may be eluted in water or may react with components contained in water or chemicals. However, the porous material is not damaged without melting the pore walls of the through holes, reducing the thickness of the porous material, and changing the microstructure.

  Further, since the porous material is crystalline, the strength is high, and there is no risk of cracking or breaking due to stress during use.

  The porous material described above is basically manufactured through heat treatment for crystallization. On the other hand, from the viewpoint that a porous material having through-holes substantially parallel along the thickness direction can be easily produced, it is preferable to use an anodizing treatment of a metal material such as aluminum. However, in order to form a porous material made of crystalline alumina, it is necessary to heat at least 600 ° C. or higher, and 900 ° C. or higher or 1200 ° C. or higher depending on the purpose.

  Therefore, the alumina material (anodized film) is deformed during the heat treatment simply by using both the anodizing treatment and the heat treatment, and the hole diameters of the through holes on the front side and the back side of the obtained porous material Are different from each other, and a substantially parallel through hole cannot be formed along the thickness direction.

  From this point of view, in the present invention, an alumina material (anodized film) obtained by anodizing treatment is sandwiched and restrained by a pair of plate-like members, and is crystallized by heat treatment in this state.

  That is, an aluminum substrate is immersed in an electrolytic solution to perform an electrolytic treatment, an amorphous anodic oxide film is formed on the surface of the aluminum substrate, and the anodic oxide film is peeled off from the aluminum substrate. A step of being arranged between the plate-like members and being restrained by the pair of plate-like members; and a step of crystallizing the anodic oxide film by heat treatment in a state of being restrained by the pair of plate-like members. It manufactures based on the manufacturing method of the porous material characterized by this.

  According to this method, even when the alumina material (anodized film) obtained by the anodizing treatment is heat-treated at 600 ° C. or higher, deformation of the alumina material during the heat treatment can be suppressed, and in the thickness direction. A porous material containing crystalline alumina having through-holes substantially parallel therewith can be obtained.

  In addition, the said manufacturing method is an example to the last, Comprising: The porous material mentioned above can also be manufactured by another method. For example, by controlling the voltage application profile during the anodizing process, the initial electrolysis voltage is lowered (10 V), the electrolysis voltage is then increased (40 V), and then the electrolysis voltage is lowered (10 V to 5 V). It can also be produced by a method such as making the temperature rising rate extremely low.

  However, according to the manufacturing method described above, the above-described crystalline porous material of the present invention can be manufactured easily and reliably.

  Further, in the present invention, “substantially parallel in the through hole substantially parallel to the thickness direction of the porous material” is not limited to the case of being completely parallel to the thickness direction, and is −30 degrees to Including the case of tilting in the range of 30 degrees.

  As described above, according to the present invention, there is a through hole of submicron order, no pressure loss occurs when a medium is passed through the through hole, and it is chemically inert and sufficient. It is possible to provide a porous material that has strength and can be used stably over a long period of time.

  Hereinafter, details of the present invention, other features, and advantages will be described based on embodiments.

(Porous material)
First, an outline of the configuration of the porous material of the present invention will be described. FIG. 1 is a configuration diagram showing an example of the porous material of the present invention. FIG. 1 is a perspective view showing a part of the porous material cut out and enlarged.

  As shown in FIG. 1, the porous material 10 of this example includes cells 11 made of crystalline alumina, and each cell 11 has a through-hole substantially parallel to the thickness direction of the porous material 10. 12 is formed. Note that “substantially parallel” includes not only the case of being completely parallel but also the case of being inclined within a range of −30 degrees to 30 degrees.

  In the porous material 10 of this example, since the through-hole 12 is linearly formed substantially parallel to the thickness direction, even if the hole diameter of the through-hole 12 is a submicron size, There is no increase in pressure loss when flowing. Further, since the porous material 10 is made of crystalline alumina, it is chemically inert and does not dissolve even when contacted with water or chemicals.

  Further, when the porous material 10 contains a composition of water and an electrolytic solution used at the time of electrolysis, these residual substances are eluted in water or react with components contained in water or chemicals. However, the porous material 10 is not damaged without melting the hole wall of the through-hole 12, reducing the thickness of the porous material 10, and changing the microstructure.

  In addition, since the porous material 10 is crystalline, the strength is high, and there is no fear of occurrence of cracks or destruction due to stress during use.

In this example, the through hole 12 has a uniform hole diameter over the entire thickness direction of the porous material 10. In this case, the structure of the through holes 12 on both surfaces of the porous material 10 is the same, and the porosity in the vicinity of both surfaces is substantially the same. In general, volume shrinkage increases when the porosity is small, and volume shrinkage decreases when the porosity is large. However, in this example, since the porosity on both surfaces of the porous material 10 is substantially the same, deformation (warping) due to heat treatment during production, which will be described in detail below, can be suppressed. The pressure loss in the through hole 12 can be further reduced.

  However, according to the manufacturing method of the present invention described below, as described above, the porous material 10 does not have a uniform pore diameter in the entire thickness direction, and the porous material 10 penetrates on both sides. Even when the structure of the hole 12 is not the same and the porosity in the vicinity of both surfaces is not the same, deformation during heat treatment can be sufficiently suppressed. However, by adopting the above-described embodiment, it becomes possible to more effectively suppress deformation during heat treatment.

  Further, the thickness t of the porous material 10 is preferably 50 μm or more. If the thickness t of the porous material 10 is less than 50 μm, even if the porous material 10 is crystalline, the strength is not sufficient, and in some cases, it cannot be used as a self-supporting material.

  In addition, although the upper limit of the thickness t of the porous material 10 is not specifically limited, For example, it can be 200 micrometers. This is mainly due to the manufacturing method described in detail below. That is, an amorphous alumina material is produced by anodizing treatment prior to heat treatment, but when the porous material 10, that is, the alumina material is thicker than 200 μm, a voltage is applied to the whole in the anodizing treatment. This is because it may not be possible to perform uniform electrolytic treatment.

  The hole diameter of the through hole 12 can be 10 nm to 200 nm. This is preferably determined from a practical viewpoint when the medium is allowed to flow through the through-holes 12 of the porous material 10 and used as, for example, a filter.

  The porous material 10 can include alpha alumina. There are many types of crystalline alumina, including stable and metastable structures. Among them, α-alumina has the most stable structure that has been completely dehydrated, and is excellent in chemical stability. Other metastable aluminas exhibit some resistance to neutral water at room temperature, but are reactive to high-temperature water and low and high pH chemicals, and can be dissolved or modified. .

  On the other hand, α-alumina, which is a stable phase, is almost stable to high temperature water and chemicals and hardly changes in quality. Therefore, by increasing the content of α-alumina in the porous material 10 and ideally forming a film composed entirely of α-alumina, resistance to high-temperature water and chemical resistance can be improved. . Actually, when the porous material 10 made of α-alumina was stored in a state of being sealed in high-temperature water at 100 ° C. or higher, almost no change in appearance was observed, and almost no change was observed before and after the test.

  The porous material 10 can contain γ-alumina. Since this γ-alumina has catalytic activity, in this case, particles passing through the through holes 12 of the porous material 10 can be adsorbed separately from the pressure loss described above.

  FIG. 2 is a modification of the porous material 10 shown in FIG. Note that the same reference numerals are used for the same or similar components.

  In the example related to FIG. 1, the through-hole 12 has a uniform hole diameter throughout the thickness direction of the porous material 10, but in the example related to FIG. 2, the through-hole 12 of the porous material 10 Only the hole diameter on the front surface side and the hole diameter on the back surface side are substantially the same. Even in this case, the structure of the through-holes 12 on both surfaces of the porous material 10 is the same, and the porosity in the vicinity of both surfaces is substantially the same. Therefore, it is possible to suppress deformation (warping) due to heat treatment during manufacturing, which will be described in detail below.

  In addition, it is known that there is a correlation between the electrolytic voltage at the time of anodization and the hole diameter of the through hole, and it is possible to obtain an arbitrary hole diameter by changing the electrolytic voltage. Therefore, in order to form the through-hole 12 as shown in FIG. 2, in the anodizing process described in detail below, electrolysis is performed at a low voltage (for example, 10 V) at the initial stage of electrolysis, and then at a high voltage (for example, 40 V). After the electrolysis, the electrolysis is finally performed again at a low voltage (for example, 10 V to 5 V).

  Other features are the same as in the example shown in FIG.

(Method for producing porous material)
Next, the manufacturing method of the porous material of this invention is demonstrated. 3 to 6 are process diagrams relating to the method for producing a porous material of the present invention.

  First, as shown in FIG. 3, an aluminum substrate 110 is prepared and degreased by a method such as ultrasonic cleaning in acetone as necessary. Thereafter, the electrode 21 is disposed so as to face the aluminum base 110, and the electrode 21 and the aluminum base 110 are each connected to the power source 22. Further, the electrode 21 and the aluminum substrate 110 are immersed in a predetermined electrolytic solution. Thereafter, electrolysis is performed between the electrode 15 and the aluminum substrate 110, and the aluminum substrate 110 is anodized and made porous to obtain a porous intermediate body (anodized film) 121.

  In addition, as shown in FIG. 2, when only the hole diameter on the front surface side and the hole diameter on the back surface side of the target porous material are substantially the same, electrolysis is performed at a low voltage (for example, 10 V) at the initial stage of electrolysis, Thereafter, electrolysis is performed at a high voltage (for example, 40 V), and finally electrolysis is performed again at a low voltage (for example, 10 V to 5 V).

  The electrode 21 can be made of carbon, stainless steel, or the like. As the electrolytic solution, an electrolytic solution of an acid having an appropriate dissolving power such as sulfuric acid, phosphoric acid, and oxalic acid is used.

  As the electrolytic solution, it is particularly preferable to use a phosphoric acid electrolytic solution. The porous intermediate 121 formed using the phosphoric acid electrolytic solution has less residual moisture and anions than the porous intermediate 121 formed using the oxalic acid electrolytic solution, and changes in weight due to transformation. Is small. As a result, there is a feature that the change in dimensions is relatively small and there are few cracks and cracks during heat treatment.

  After producing the porous intermediate 121 as described above, the remaining aluminum substrate 110 is removed by mercury (II) chloride coating or dissolution treatment with acid or alkali, so that only the porous intermediate 121 is obtained. It becomes possible to separate and take out. The remaining aluminum base material 11 is also removed by gradually lowering the electrolysis voltage during electrolysis of anodization, and further by performing electrolysis under conditions of reverse polarity by gas pressure caused by hydrogen generation. Only the porous intermediate 121 can be separated and taken out (FIG. 4).

In the porous intermediate 121 separated from the remaining aluminum base 110, a layer called a barrier layer 121A that does not penetrate pores remains in the lower portion thereof. For example, the barrier layer 121A can be removed mechanically by polishing or the like, or can be removed using a mixed solution of chromic acid and phosphoric acid, a phosphoric acid solution, a NaOH solution, or a H ₂ SO ₄ solution. When using a solution, the solution is heated from room temperature to around 60 ° C., and the porous intermediate 121 is immersed in the solution in such a state for several minutes to several tens of minutes.

  At this stage, the porous intermediate 121 is amorphous alumina having through holes that are substantially parallel to the thickness direction.

  Next, as shown in FIG. 5, the porous intermediate body 121 is disposed between the pair of plate-like members 24, and both ends of the plate-like member 24 are sandwiched between the pair of fixing members 26 as shown in FIG. Fasten in the direction. As a result, the porous intermediate body 121 is restrained between the pair of plate-like members 24. Note that the thickness, weight, and the like of the plate-like member 24 are not particularly limited.

  The plate member 24 is preferably made of a ceramic material containing alumina. Among aluminas, α-alumina, which has a linear expansion coefficient equivalent to that of an anodic oxide film, is excellent in chemical stability, and is not altered by the current heat treatment, is particularly excellent. As components other than alumina, those containing components such as magnesia and silica can be applied. However, since the higher alumina content is advantageous in terms of matching the linear expansion coefficient with that of the anodized film, it is desirable to include approximately 90% or more of α-alumina.

  Next, the porous intermediate body 121 in the state shown in FIG. 6 is put in a heating furnace such as an electric furnace and heat-treated. At this time, since the porous intermediate body 121 is fastened and fixed in the vertical direction by the plate-like member 24, the porous intermediate body 121 can be crystallized as intended without being deformed by heat.

  In addition, the said heat processing temperature can be arbitrarily set according to the objective. For example, by setting the heat treatment to a temperature of 1200 ° C. or higher, the porous intermediate 121 can be made into a porous material 120 made of α-alumina. The characteristics of α-alumina are as described above. In this case, the upper limit of the heat treatment temperature can be 1400 ° C.

  The heat treatment can be performed at a temperature of 900 ° C. or higher and lower than 1200 ° C. In this case, the porous intermediate 121 can be a porous material 120 containing γ-alumina. In this case, other crystal phases are rarely included. The characteristics of γ-alumina are as described above.

  Furthermore, the heat treatment can be performed at a temperature of 600 ° C. or higher and lower than 900 ° C. In this case, the porous intermediate 121 is a mixed phase of γ alumina and an amorphous phase. Therefore, thermal deformation can be further suppressed due to the low heating temperature while exhibiting the characteristics of γ-alumina. That is, although the porous intermediate body 121 is constrained between the plate-like members 24, if the heat treatment temperature becomes too high, it may be thermally deformed to some extent. However, in this example, since heat treatment is performed at a relatively low temperature, thermal deformation can be further reduced as described above.

  FIG. 7 shows the relationship between the heat treatment temperature and the phase transformation. In FIG. 7, the peak appearing at about 900 ° C. is presumed to be the peak due to γ-alumina. FIG. 7 is a differential thermogravimetric curve obtained as a result of thermogravimetric analysis. Further, in the thermogravimetric analysis, no peak corresponding to α-alumina appears, so that X-ray diffraction was performed after the heat treatment was performed at around 1200 ° C. Thereby, a diffraction peak corresponding to α-alumina was obtained, and it was confirmed that the porous material 120 was made of α-alumina by heat treatment at a temperature of 1200 ° C. or higher.

  In this example, it is preferable that the rate of temperature increase during the heat treatment is 100 ° C./hour or less. Decreasing the rate of temperature increase and gradually increasing the temperature are effective in preventing cracks and cracks due to rapid temperature changes of the porous intermediate body 121 in the heat treatment process. The lower limit value of the heating rate can be set to, for example, 50 ° C./hour from a practical viewpoint.

  Further, in this example, in the temperature raising process of the heat treatment, after the temperature raising operation is interrupted in the temperature range of about 800 ° C. to 900 ° C. near the transformation temperature of alumina, the temperature raising operation is performed again to raise the temperature to the set temperature. can do. In this case, during the heat treatment of the anodic oxide film, moisture and anions remaining in the porous intermediate 121 during electrolysis are released at a temperature at which alumina undergoes transformation. In this temperature region, the weight change is large and a dimensional change also occurs.However, by keeping the temperature in the temperature region for a certain period of time, the release of the moisture and the anion can be performed gradually. By gradually advancing the dimensional change, it becomes an effective means for preventing cracks and cracks.

  Further, in this example, in the temperature raising process of the heat treatment, the temperature raising rate can be reduced to 50 ° C./hour or less near the transformation temperature of alumina, for example, 800 ° C. to 900 ° C. In this case as well, as described above, by holding for a certain period of time in the temperature range, moisture and anions remaining in the porous intermediate 121 are gradually released, and the change in weight and dimensions is gradually advanced, thereby causing cracks. This is an effective means for preventing cracks.

  The present invention has been described in detail based on the above specific examples. However, the present invention is not limited to the above specific examples, and various modifications and changes can be made without departing from the scope of the present invention.

It is a block diagram which shows an example of the porous material of this invention. It is a block diagram which shows the modification of the porous material shown in FIG. It is process drawing regarding the manufacturing method of the porous material of this invention. Similarly, it is process drawing regarding the manufacturing method of the porous material of the present invention. Similarly, it is process drawing regarding the manufacturing method of the porous material of the present invention. Similarly, it is process drawing regarding the manufacturing method of the porous material of the present invention. It is a graph which shows the relationship between the heat processing temperature of alumina, and a phase transformation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,120 Porous material 11 Alumina cell 12 Through-hole 21 Electrode 22 Power supply 24 Plate member 26 Fixing member 110 Aluminum base material 121 Porous intermediate body 121A Barrier layer

Claims (20)

  A porous material having a through hole substantially parallel to the thickness direction and containing crystalline alumina.   The porous material according to claim 1, wherein the alumina contains α-alumina.   The porous material according to claim 1, wherein the alumina includes γ-alumina.   The porous material according to any one of claims 1 to 3, wherein the thickness of the porous material is 50 µm or more.   The porous material according to any one of claims 1 to 4, wherein a hole diameter on the front surface side of the porous material and a hole diameter on the back surface side of the through hole are substantially the same.   The porous material according to any one of claims 1 to 5, wherein the through-hole has a uniform pore diameter throughout the thickness direction of the porous material.   The porous material according to claim 1, wherein a diameter of the through hole is 10 nm to 200 nm. Performing an electrolytic treatment by immersing the aluminum substrate in an electrolytic solution, and forming an amorphous anodic oxide film on the surface of the aluminum substrate;
Peeling the anodic oxide film from the aluminum substrate, disposing the anodic oxide film between a pair of plate-like members, and constraining the pair of plate-like members;
A step of crystallizing the anodic oxide film by heat treatment in a state constrained by the pair of plate-like members;
A method for producing a porous material, comprising:   The method for producing a porous material according to claim 8, wherein the electrolytic solution is a phosphoric acid electrolytic solution.   The method for producing a porous material according to claim 8 or 9, wherein the anodic oxide film is peeled off by dissolving and removing the aluminum base material.   The method for producing a porous material according to any one of claims 8 to 10, wherein the pair of plate-like members are made of a material containing alumina.   The method for producing a porous material according to claim 11, wherein the pair of plate-like members contain α-alumina at a ratio of 90 mol% or more.   The method for producing a porous material according to any one of claims 8 to 12, wherein the heat treatment is performed at a temperature of 1200 ° C or higher.   The method for producing a porous material according to any one of claims 8 to 12, wherein the heat treatment is performed at a temperature of 900 ° C or higher and lower than 1200 ° C.   The method for producing a porous material according to any one of claims 8 to 12, wherein the heat treatment is performed at a temperature of 600 ° C or higher and lower than 900 ° C.   The method for producing a porous material according to any one of claims 8 to 15, wherein a temperature increase rate during the heat treatment is 100 ° C / hour or less.   17. The heat treatment according to claim 8, wherein in the temperature raising process of the heat treatment, after the temperature raising operation is interrupted near the transformation temperature of alumina, the temperature raising operation is performed again to raise the temperature to a set temperature. The manufacturing method of the porous material as described in 2.   The method for producing a porous material according to claim 17, wherein the temperature raising operation is interrupted in a temperature range of 800 ° C to 900 ° C.   The method for producing a porous material according to any one of claims 1 to 8, wherein in the temperature raising process of the heat treatment, the temperature raising rate is reduced to 50 ° C / hour or less near the transformation temperature of alumina. .   The method for producing a porous material according to claim 19, wherein the temperature increase rate is lowered in a temperature range of 800C to 900C.

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