JP2018087106A - Porous member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous member having excellent filter performance and mechanical strength in combination.SOLUTION: A porous member of the present invention is made of alumina-based ceramic of which main phase is alumina crystal and has the porosity of 16% or larger and 27% or smaller, in which the alumina crystal has an average crystal grain diameter of 0.30 μm or larger and 0.42 μm or smaller. By satisfying the structure like this, the porous member has not only excellent filter performance such as deodorizing or moisture uptake but also strong mechanical strength. As a result, the porous member of the present invention has excellent filter performance and the mechanical strength in combination.SELECTED DRAWING: None

Description

  The present disclosure relates to a porous member.

  In recent years, porous members made of ceramics have attracted attention as members used for various filters such as deodorization and moisture absorption.

  For example, Patent Document 1 discloses a particulate adsorbent for a vacuum device, and alumina has been proposed as a moisture adsorbent used for the particulate adsorbent.

JP2015-104704A

  The porous member made of ceramics has a lower mechanical strength than the dense ceramics although it has better filter performance such as deodorization and moisture absorption. Therefore, in recent years, there is a demand for a porous member that has not only excellent filter performance but also excellent mechanical strength.

  The present disclosure has been devised to satisfy the above requirements, and an object of the present disclosure is to provide a porous member having both excellent filter performance and mechanical strength.

  The porous member of the present disclosure is made of an alumina ceramic whose main phase is alumina crystals, has a porosity of 16% or more and 27% or less, and an average crystal grain size of the alumina crystals is 0.30 μm or more and 0.42 μm or less. It is.

  The porous member of the present disclosure has excellent filter performance and mechanical strength.

The porous member of the present disclosure is made of alumina ceramics whose main phase is alumina crystals. Here, the aluminum oxide ceramics are those in which alumina accounts for 90% by mass or more out of 100% by mass of all components constituting the ceramics. And whether it is alumina ceramics can be confirmed by the following method. First, measurement is performed using an X-ray diffractometer (XRD), and the presence of alumina is confirmed by identifying the obtained 2θ (2θ is a diffraction angle) using a JCPDS card. Next, quantitative analysis of aluminum (Al) is performed using an ICP emission spectroscopic analyzer (ICP). Then, the content in terms of alumina (Al 2 _{O 3)} from the aluminum content was determined by ICP is not more 90 wt% or more, and alumina ceramics.

  Since the porous member of the present disclosure has a high content of alumina, it is preferable to measure the content of components other than alumina and subtract the content of components other than alumina from 100% by mass. The content of alumina can be calculated with high accuracy.

  The porous member of the present disclosure has a porosity of 16% or more and 27% or less, and an average crystal grain size of alumina crystals is 0.30 μm or more and 0.42 μm or less.

  Since the porous member of the present disclosure satisfies such a configuration, it has excellent filter performance and mechanical strength. Here, the excellent mechanical strength is that the value of the three-point bending strength based on JIS R 1601-2008 is 150 MPa or more.

  On the other hand, if the porosity is less than 16%, since there are few pores for deodorizing or absorbing moisture, the filter performance is not excellent. On the other hand, if the porosity is higher than 27%, since there are many pores as starting points of cracks, the mechanical strength is not excellent.

  Further, if the average crystal grain size of the alumina crystal is less than 0.30 μm, the alumina crystal is likely to fall off, so that it does not have excellent mechanical strength. On the other hand, if the average crystal grain size of the alumina crystal is larger than 0.42 μm, the surface area of the alumina crystal that deodorizes and absorbs moisture is reduced as a whole, so that it does not have excellent filter performance.

  Here, the porosity may be obtained by a mercury intrusion method. Specifically, first, 2 g or more of the porous member of the present disclosure is prepared and used as a sample. Next, mercury is injected into pores existing on the surface of the sample using a mercury intrusion porosimeter. Then, the porosity may be calculated from the relationship between the pressure applied to mercury and the volume of mercury that has entered the pores.

  Moreover, what is necessary is just to measure the average crystal grain diameter of an alumina crystal with the following method. First, the surface of the porous member of the present disclosure is used as an observation surface, and a photograph with a magnification of about 10,000 times to 20,000 times is taken using a scanning electron microscope (SEM). Next, using the photograph taken, the average value of the crystal grain size of the alumina crystal is calculated by the code method. Specifically, for the photograph taken, the crystal grain size of the alumina crystals is measured from the number of alumina crystals on a straight line of a certain length, and this is performed at least at three places, and the average value may be obtained.

  In the porous member of the present disclosure, the maximum value of the crystal grain size of the alumina crystal may be 1.0 μm or less. If such a configuration is satisfied, the surface area of the alumina crystal on which deodorization and moisture absorption are performed as a whole increases, and the porous member of the present disclosure is further excellent in filter performance.

  Here, the maximum value of the crystal grain size of the alumina crystal may be obtained by the following method. First, in the photograph obtained by photographing the observation surface described above, at least five alumina crystals that are considered to have the largest crystal grain size with the naked eye are selected. Then, the longest length of each of the selected alumina crystals is measured, and the maximum value among them may be regarded as the maximum value of the crystal grain size of the alumina crystals.

  Further, the porous member of the present disclosure may have a central pore diameter of 0.097 μm or more and 0.111 μm or less. Here, the central pore diameter is the value of the diameter of the pore located in the center when the pore diameters obtained by the mercury intrusion method are arranged in ascending order.

  If such a configuration is satisfied, since the pores are generally small while maintaining the filter performance, the mechanical strength is further improved.

  Next, an example of the manufacturing method of the porous member of this indication is explained.

First, an alumina powder as a main raw material and a sintering aid are prepared. Here, when the average particle diameter of the alumina powder is small, the firing activity is high, and the crystal grain diameter of the alumina crystal after firing tends to be large. On the other hand, when the average particle size of the alumina powder is large, the firing activity is low, and the crystal grain size of the alumina crystal after firing is difficult to increase. Therefore, alumina powder having an average particle diameter of 0.2 to 0.3 μm is used in order to control the crystal grain diameter of the alumina crystals after firing at the density and firing temperature of the compact to be described later.

  In addition, as a sintering aid, a combination of magnesium oxide powder, calcium oxide powder, and silicon oxide powder may be used.

  Then, the alumina powder and the sintering aid are weighed out so that 90% by mass or more of the total amount of components constituting the alumina ceramic is 90% by mass in terms of alumina and the balance becomes the sintering aid.

  Next, 2 parts by mass or more and 10 parts by mass or less of a binder such as a water-soluble acrylic resin and 100 parts by mass of a solvent are mixed in an agitator with respect to 100 parts by mass of the alumina powder and the sintering aid. Stir to obtain a slurry.

Next, the granulated powder obtained by spray-drying the slurry is placed in a mold having an arbitrary shape, and a powder press molding is performed to obtain a compact. Here, by adjusting the molding pressure and performing powder press molding, the density of the molded body is set to 2.30 to 2.40 g / cm ³ .

  Next, the porous member of the present disclosure is obtained by firing at a maximum temperature of 1240 to 1350 ° C. in an air atmosphere and holding time at the maximum temperature of 1.5 to 4.0 hours.

  In order to set the maximum value of the crystal grain size of the alumina crystal to 1.0 μm or less, the holding time at the maximum temperature may be set to 3.0 hours or less.

  Examples of the present disclosure will be specifically described below, but the present disclosure is not limited to these examples.

  Samples having different porosity and average crystal grain size of alumina crystals were prepared, and three-point bending strength and water absorption were evaluated.

First, an alumina powder having an average particle size of 0.24 μm, which is a main raw material, and a sintering aid were prepared. Here, as the sintering aid, magnesium oxide powder, calcium oxide powder, and silicon oxide powder are used, and the values converted into MgO, CaO, and SiO ₂ in each sample after firing are 2: 3: 5. Weighed out.

  Then, the alumina powder and the sintering aid powder were weighed out of 100% by mass of the total components constituting the alumina ceramic so that 99.5% by mass in terms of alumina and the balance became the sintering aid.

  Next, 4 parts by mass of a water-soluble acrylic resin binder and 100 parts by mass of a solvent are mixed in and stirred in a stirrer with respect to a total of 100 parts by mass of the alumina powder and the sintering aid. It was.

  And the granulated powder which spray-dried this slurry was put into the metal mold | die, and the molded object was obtained by performing powder press molding. In this powder press molding, the molding pressure was adjusted so that the density of the molded body was the value shown in Table 1.

  Next, each sample was obtained by baking the maximum temperature in the air atmosphere with the value shown in Table 1 and the holding time at this maximum temperature being 2.5 hours. In each sample, a three-point bending strength measurement sample having a width of 4 mm, a thickness of 3 mm, and a length of 30 mm and a cylindrical water absorption measurement sample having a diameter of 2 cm were obtained.

  Next, the porosity of each sample was determined by a mercury intrusion method. Furthermore, the average crystal grain size of alumina crystals of each sample was measured by the following method. First, the surface of each sample was used as an observation surface, and a photograph with a magnification of about 15,000 times was taken using an SEM. Next, the average value of the crystal grain size of the alumina crystal was calculated by the code method using the photographed photo. Specifically, for the photograph taken, the crystal grain size of the alumina crystal was measured from the number of alumina crystals on a straight line of a certain length, and this was performed at three places to determine the average value.

  Next, the three-point bending strength was determined for the three-point bending strength measurement sample in accordance with JIS R 1601-2008.

  Next, the water absorption rate was measured for each sample by Archimedes method in accordance with JIS A 1509-3. Then, the samples were ranked in order from the highest water absorption rate. That is, the sample with the highest water absorption was ranked first and the sample with the lowest water absorption was ranked lowest. In addition, if the water absorption rate is excellent, it can be said that the filter performance is excellent.

  The results are shown in Table 1.

  As shown in Table 1, sample no. 1-15, sample Nо. Although 1-3 were excellent in the water absorption rate, the mechanical strength was low. Sample No. Although 12-15 was excellent in mechanical strength, the water absorption was low. In contrast, sample no. 4 to 11 are samples Nо. No. 1 to 3 have higher mechanical strength. The water absorption was higher than 12-15. Therefore, it was found that when the porosity is 16% or more and 27% or less and the average crystal grain size of the alumina crystal is 0.30 μm or more and 0.42 μm or less, it has excellent filter performance and mechanical strength. .

  Next, samples having different maximum crystal grain sizes of alumina crystals were prepared, and three-point bending strength and water absorption were evaluated.

In addition, as a manufacturing method, the sample No. 1 in Example 1 except that the holding time at the maximum temperature during firing was set to the value shown in Table 2. 6 was the same as the manufacturing method. Sample No. 18
Is the sample No. of Example 1. Same as 6.

  And the maximum value of the crystal grain diameter of the alumina crystal in each sample was calculated | required with the following method. First, the surface of each sample was used as an observation surface, and a photograph with a magnification of about 15,000 times was taken using an SEM. Next, in the photograph taken, five alumina crystals that were considered to have the largest crystal grain size with the naked eye were selected. Then, the crystal grain size of the selected alumina crystal was actually measured, and the crystal grain size value of the largest alumina crystal was set as the maximum crystal grain size of the alumina crystal.

  Further, in the same manner as in Example 1, the three-point bending strength and water absorption were measured.

  The results are shown in Table 2. In addition, the ranking of the water absorption rate is given by comparing only the samples shown in Table 2.

  As shown in Table 2, sample no. Compared to sample No. 20, sample no. The water absorption of 16-19 was high. From this result, it was found that the filter performance is improved when the maximum value of the crystal grain size of the alumina crystal is 1.0 μm or less.

Claims (2)

  A porous member comprising alumina ceramics in which an alumina crystal is a main phase, a porosity of 16% or more and 27% or less, and an average crystal grain size of the alumina crystal of 0.30 μm or more and 0.42 μm or less.   The porous member according to claim 1, wherein a maximum value of a crystal grain size of the alumina crystal is 1.0 μm or less.