JP7280547B2 - Method for manufacturing porous glass member - Google Patents

Description

The present invention relates to a method for manufacturing a porous glass member.

In recent years, porous glass has a sharp pore distribution, a large specific surface area, heat resistance, and resistance to organic solvents. being considered. Some of these are used in an alkaline environment, and the porous glass is required to have alkali resistance in consideration of its application. Alkali-resistant porous glass is produced by heat-treating a glass base material made of alkali borosilicate glass containing zirconia to separate it into two phases, a silica-rich phase and a boron oxide-rich phase, and removing the boron oxide-rich phase with an acid. (See Patent Document 1, for example).

Patent No. 4951799

However, in the method for producing an alkali-resistant porous glass described in Patent Document 1, cracks may occur in the porous glass member during production, making it difficult to produce a member having a desired shape. .

In view of the above, an object of the present invention is to provide a method for manufacturing a porous glass member in which cracks are less likely to occur in the porous glass member.

As a result of repeating various experiments, the inventors of the present invention have found that the above technical problems can be solved by strictly controlling the glass composition of the glass base material.

That is, in the method for producing a porous glass member of the present invention, SiO ₂ is 40 to 80%, B ₂ O ₃ is more than 0 to 40%, Na ₂ O is more than 0 to 20%, and ZrO ₂ is more than 3 to 10% by mass. %, Al ₂ O ₃ 2 to 5%, RO (R is at least one selected from Mg, Ca, Sr and Ba) 0.5 to 20%, and the mass ratio is Na ₂ O/B ₂ O It is characterized by including a step of heat-treating a glass base material in which ₃ is 0.25 to 0.5 to separate into two phases, and a step of removing one of the phases with an acid. In addition, " _Na2O / _B2O3 " _refers to the value _obtained by dividing the content of _Na2O by the content of _B2O3 .

The cause of the cracks is the volume change that occurs in the process of removing the boron oxide-rich phase with acid, and the cause of the volume change is the expansion due to hydration of the silica gel remaining in the pores of the porous glass, the silica-rich This is contraction due to elution of Na ₂ O from the phase. As a result of investigation, it was found that the Na ₂ O/B ₂ O ₃ ratio in the glass base material affects expansion and contraction. Specifically, when the Na ₂ O/B ₂ O ₃ ratio is 0.25 to 0.5, the amount of expansion and the amount of contraction are about the same, volume change is less likely to occur, and cracks occur in the porous glass member. I found it difficult to do.

In the method for producing a porous glass member of the present invention, the glass base material preferably has a mass ratio of B ₂ O ₃ /SiO ₂ of 0.3 to 0.5.

In the method for producing a porous glass member of the present invention, the glass base material preferably has an aspect ratio of 2-1000. Incidentally, the aspect ratio is calculated by the following formula.

Aspect ratio = (bottom area of glass base material) ^1/2 /thickness of glass base material

In the method for producing a porous glass member of the present invention, the heat treatment temperature is preferably 500 to 800.degree.

The glass base material for a porous glass member of the present invention contains, in % by mass, SiO ₂ 40 to 80%, B ₂ O ₃ more than 0 to 40%, Na ₂ O more than 0 to 20%, and ZrO ₂ more than 3 to 10%. , Al ₂ O ₃ 2 to 5%, RO (R is at least one selected from Mg, Ca, Sr and Ba) 0.5 to 20%, and the mass ratio is Na ₂ O/B ₂ O ₃ is 0.25 to 0.5.

The glass base material for porous glass members of the present invention preferably has a B ₂ O ₃ /SiO ₂ mass ratio of 0.3 to 0.5.

The porous glass member of the present invention is characterized by containing 85 to 98% by mass of SiO ₂ , 1 to 10% by mass of Al ₂ O ₃ and 1 to 10% by mass of ZrO ₂ .

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the manufacturing method of the porous-glass member which a crack does not generate|occur|produce in a porous-glass member easily.

A method for manufacturing the porous glass member of the present invention will be described.

First, a glass base material for a porous glass member is prepared as follows. In % by mass, SiO ₂ 40-80%, B ₂ O ₃ 0-40%, Na ₂ O 0-20%, ZrO _3-10 %, Al _{2 O} 2-5%, RO(R is at least one selected from Mg, Ca, Sr and Ba) 0.5 to 20%, and the glass composition has a Na ₂ O/B ₂ O ₃ mass ratio of 0.25 to 0.5 Mix the glass raw materials as follows. The reasons for specifying the content of each component as described above will be described below. In addition, unless otherwise specified, "%" means "% by mass" in the following descriptions of component contents.

_SiO2 is a component that forms a glass network. The content of SiO ₂ is 40-80%, preferably 45-75%, 50-70%, especially 52-65%. If the _SiO2 content is too low, weather resistance and mechanical strength tend to decrease. On the other hand, if the content of _SiO2 is too high, phase separation becomes difficult.

B ₂ O ₃ is a component that forms a glass network and promotes phase separation. The content of B ₂ O ₃ is more than 0 to 40%, preferably 10 to 30%, especially 20 to 25%. If B ₂ O ₃ is not contained, the above effects are difficult to obtain. On the other hand, if the B ₂ O ₃ content is too high, the weather resistance tends to decrease.

B ₂ O ₃ /SiO ₂ is preferably 0.3-0.5, 0.35-0.48, 0.38-0.46, especially 0.4-0.45. If the ratio of B ₂ O ₃ /SiO ₂ is too small, internal stress is likely to occur in the step of removing the SiO ₂ colloid with an alkaline aqueous solution, which will be described later, and cracks are likely to occur in the porous glass member. On the other hand, if the ratio of B ₂ O ₃ /SiO ₂ is too large, the mechanical strength tends to decrease in the step of removing the SiO ₂ colloid with an alkaline aqueous solution, which will be described later, and cracks tend to occur in the porous glass member. In addition, " _B2O3 / _SiO2 " refers to _{the value obtained by dividing the content of B2O3 by the} content of _SiO2 .

Na ₂ O is a component that lowers the melting temperature to improve meltability and promotes phase separation. The content of Na ₂ O is more than 0 to 20%, preferably 3 to 10%, especially 4 to 8%. If Na ₂ O is not contained, the above effects are difficult to obtain. On the other hand, when the content of Na ₂ O is too high, phase separation becomes difficult.

Na ₂ O/B ₂ O ₃ is 0.25-0.5, preferably 0.28-0.4, especially 0.3-0.35. If the Na ₂ O/B ₂ O ₃ ratio is too small, it becomes difficult to remove the boron oxide-rich phase in the step of removing the boron oxide-rich phase with an acid, which will be described later. On the other hand, if the ratio of Na ₂ O/B ₂ O ₃ is too large, the amount of swelling due to hydration of silica gel tends to be smaller than the amount of shrinkage due to elution of Na ₂ O from the silica-rich phase, and the porous glass member cracks. becomes more likely to occur.

_ZrO2 is a component that improves weather resistance. The content of ZrO ₂ is more than 3-10%, preferably 4-8%, especially 5-7%. If the content of ZrO ₂ is too small, it is difficult to obtain the above effects. On the other hand, if the content of ZrO ₂ is too high, devitrification tends to occur and phase separation becomes difficult.

Al ₂ O ₃ is a component that improves weather resistance and mechanical strength. The content of Al ₂ O ₃ is 2-5%, preferably 3-4%. If the content of Al ₂ O ₃ is too small, it will be difficult to obtain the above effects. If the content of Al ₂ O ₃ is too large, phase separation becomes difficult.

RO (R is at least one selected from Mg, Ca, Sr and Ba) is a component that increases the _ZrO2 content of the silica-rich phase and improves weather resistance. The content of RO (total amount of MgO, CaO, SrO and BaO) is 0.5 to 20%, preferably 1 to 17%, 3 to 15%, 4 to 13%, and particularly 5 to 10%. preferable. If the content of RO is too small, the above effects are difficult to obtain. On the other hand, when the content of RO is too high, phase separation becomes difficult. The contents of MgO, CaO, SrO and BaO are preferably 0 to 20%, 1 to 17%, 3 to 15%, 4 to 13%, particularly 5 to 10%, respectively. Among them, it is preferable to use CaO because the effect of improving the weather resistance is particularly large.

The glass base material for a porous glass member of the present invention can contain the following components in addition to the components described above.

K ₂ O is a component that lowers the melting temperature to improve meltability and promotes phase separation. The content of K ₂ O is preferably 0-20%, 3-10%, especially 4-8%. If the K ₂ O content is too high, phase separation becomes difficult.

ZnO is a component that increases the _ZrO2 content of the silica-rich phase and improves weather resistance. The content of ZnO is preferably 0-20%, 0-10%, especially 0-3%. If the ZnO content is too high, phase separation will be difficult.

In addition to the above components, various components can be contained within a range that does not impair the effects of the present invention. For example, _{TiO2 , La2O3 , Ta2O5 , TeO2} , _{Nb2O5 , Gd2O3 , Y2O3} , _{Eu2O3 , Sb2O3 , SnO2 , P2O5} and Bi ₂ O ₃ and the like may be contained in a range of 15% or less, further 10% or less, particularly 5% or less, and a total amount of 30% or less.

The prepared glass batch is then melted at 1300-1500° C. for 4-12 hours. Next, after forming the molten glass into a plate, it is slowly cooled at 400 to 600° C. for 10 minutes to 10 hours to obtain a glass base material. The shape of the obtained glass base material is not particularly limited, but the surface shape is preferably rectangular or circular plate-like. In order to form the obtained glass base material into a desired shape, processing such as cutting and polishing may be performed. Continuous production using a refractory furnace may also be used. The method of melting and forming the glass is not limited to the methods described above.

The obtained glass base material preferably has an aspect ratio of 2 to 1,000, particularly 5 to 500. If the aspect ratio is too small, in the step of removing the boron oxide-rich phase with an acid, there will be a large difference in the removal rate of the boron oxide-rich phase between the surface and the inside of the glass base material, so stress will easily occur and the glass will become porous. The glass member becomes easily broken. On the other hand, if the aspect ratio is too large, it becomes difficult to handle.

The bottom area and thickness of the obtained glass base material may be appropriately adjusted so as to achieve the above aspect ratio. For example, the base area is preferably 1 to 1000 mm ² , especially 5 to 500 mm ² , and the thickness is preferably 0.1 to 1 mm, especially 0.2 to 0.5 mm.

Next, the obtained glass base material is heat-treated to separate into two phases, a silica-rich phase and a boron oxide-rich phase. The heat treatment temperature is preferably 500 to 800°C, particularly 600 to 700°C. If the heat treatment temperature is too high, the glass base material will soften, making it difficult to obtain a desired shape. On the other hand, if the heat treatment temperature is too low, it becomes difficult to separate the phases of the glass base material. The heat treatment time is preferably 10 minutes or more, 1 hour or more, particularly 3 hours or more. If the heat treatment time is too short, it becomes difficult to separate the phases of the glass base material. Although the upper limit of the heat treatment time is not particularly limited, it is practically 180 hours or less because the phase separation does not progress beyond a certain level even if the heat treatment is performed for a long time.

Next, the glass base material phase-separated into two phases is immersed in acid to remove the boron oxide-rich phase, thereby obtaining a porous glass member. Hydrochloric acid and nitric acid can be used as the acid. In addition, you may mix and use these acids. The concentration of the acid is preferably 0.1 to 5N, more preferably 0.5 to 3N. The acid immersion time is preferably 1 hour or more, 10 hours or more, particularly 20 hours or more. If the immersion time is too short, it becomes difficult to obtain a porous glass member. Although the upper limit of the immersion time is not particularly limited, it is practically 100 hours or less. The immersion temperature is preferably 20° C. or higher, 25° C. or higher, particularly 30° C. or higher. If the immersion temperature is too low, it becomes difficult to obtain a porous glass member. Although the upper limit of the immersion temperature is not particularly limited, it is practically 95° C. or less.

In the step of heat-treating the glass base material and separating it into two phases, a silica-rich phase and a boron oxide-rich phase, a silica-containing layer (a layer containing approximately 80% by mass or more of silica) is formed on the outermost surface of the glass base material. tend to be formed. Since the silica-containing layer is difficult to remove with an acid, when the silica-containing layer is formed, the phase-separated glass base material is cut and polished, and after the silica-containing layer is removed, it is immersed in an acid. Easier to remove the phase.

Furthermore, it is preferable to remove ZrO ₂ colloids and SiO ₂ colloids remaining in the pores of the obtained porous glass. Methods for removing ZrO ₂ colloids and SiO ₂ colloids are described below, but are not limited to these methods.

ZrO ₂ colloids can be removed, for example, with sulfuric acid. The concentration of sulfuric acid is preferably 0.1 to 5N, more preferably 1 to 5N. The immersion time in sulfuric acid is preferably 1 hour or more, particularly 10 hours or more. If the immersion time is too short, it will be difficult to remove the _ZrO2 colloid. Although the upper limit of the immersion time is not particularly limited, it is practically 100 hours or less. The immersion temperature is preferably 20° C. or higher, 25° C. or higher, particularly 30° C. or higher. If the soaking temperature is too low, it will be difficult to remove the _ZrO2 colloid. Although the upper limit of the immersion temperature is not particularly limited, it is practically 95° C. or less.

_SiO2 colloids can be removed, for example, with an aqueous alkaline solution. Sodium hydroxide, potassium hydroxide, or the like can be used as the alkali. In addition, you may mix and use these alkalis. The immersion time in the alkaline aqueous solution is preferably 10 minutes or more, particularly 30 minutes or more. If the immersion time is too short, it will be difficult to remove the _SiO2 colloid. Although the upper limit of the immersion time is not particularly limited, it is practically 100 hours or less. The immersion temperature is preferably 15° C. or higher, particularly 20° C. or higher. If the immersion temperature is too low, it will be difficult to remove the _SiO2 colloid. Although the upper limit of the immersion temperature is not particularly limited, it is practically 95° C. or less.

The resulting porous glass member contains SiO ₂ 85-98%, Al ₂ O ₃ 1-10%, and ZrO ₂ 1-10% by mass. In addition, since the porous glass member contains a large amount of SiO ₂ , Al ₂ O ₃ and ZrO ₂ , it has excellent alkali resistance.

The median diameter of the pore distribution of the porous glass member is preferably 1 µm or less, 200 nm or less, 150 nm or less, 120 nm or less, 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, and particularly preferably 50 nm or less. Although the lower limit of the median diameter of the pore distribution is not particularly limited, it is practically 1 nm or more, 2 nm or more, and further 5 nm or more. Moreover, the hole has various shapes such as a spherical shape, a substantially ellipsoidal shape, and a tubular shape. The thickness and aspect ratio of the porous glass member are the same as those of the glass base material.

EXAMPLES The present invention will be described below based on examples, but the present invention is not limited to these examples.

Tables 1 to 3 show examples of the present invention (Sample Nos. 1 to 14, 16 to 24) and Comparative Example (Sample No. 15).

Raw materials prepared so as to have the respective compositions in the table were placed in a platinum crucible and then melted at 1400° C. for 6 hours. When the glass batch was melted, it was homogenized by stirring using a platinum stirrer. Next, the molten glass was poured onto a carbon plate, formed into a plate shape, and then gradually cooled at 500° C. for 30 minutes to obtain a glass base material.

The resulting glass base material was heat-treated in an electric furnace at 675° C. for 24 hours to separate the phases. The glass base material after phase separation was cut and polished to a size of 5 mm×5 mm×0.5 mm (thickness). Then, after being immersed in 1N nitric acid (90° C.) for 48 hours, it was washed with deionized water to obtain a porous glass member.

When the surfaces of the obtained porous glass members were observed with an FE-SEM (SU-8220 manufactured by Hitachi, Ltd.), each glass had a skeleton structure based on spinodal decomposition. Also, the composition, the median diameter of the pore distribution, and the cracks of the obtained porous glass member were evaluated.

The composition was measured by an energy dispersive X-ray analyzer (EX-250 manufactured by Horiba, Ltd.).

The median value of the pore size distribution was measured with a pore size distribution measuring device (QUADRASORB SI manufactured by Quantachrome).

Cracks were evaluated as "O" when no cracks were observed in the porous glass member, and as "X" when cracks were confirmed.

The composition of the porous glass member was SiO ₂ 93%, ZrO ₂ 4%, and Al ₂ O ₃ 3% by mass for all glasses.

No. 4, which is an embodiment of the present invention. No cracks were observed in samples 1 to 14 and 16 to 24. On the other hand, no. Fifteen samples were confirmed to have cracks.

Furthermore, No. In order to remove the SiO ₂ colloid remaining in the pores of the samples Nos. 1 to 14 and 16 to 24, crack generation was evaluated when they were immersed in an aqueous sodium hydroxide solution (90° C.) for 6 hours. Although not shown in the _{table ,} no _. No cracks were observed in samples 1, 2, 5 to 8, and 16 to 24. On the _{other hand} , _no . Cracks were confirmed in samples 3, 4, and 9 to 14.

INDUSTRIAL APPLICABILITY The production method of the present invention is suitable as a method for producing porous glass members that are used in a wide range of applications such as separation membranes, air diffusers, electrode materials, and catalyst supports.

Claims (4)

% by mass, SiO ₂ 40-70 %, B ₂ O ₃ 10-30 %, Na ₂ O 3-15 %, ZrO ₂ 3-10 %, Al ₂ O ₃ 2-5%, RO (R is Mg , Ca, Sr and Ba) containing 8 to 20%, CaO 8 to 20%, and a Na ₂ O/B ₂ O ₃ mass ratio of 0.3 to 0.5 A method for producing a porous glass member, comprising the steps of heat-treating a base material to separate it into two phases, and removing one of the phases with an acid. 2. The method for producing a porous glass member according to claim 1 , wherein the glass base material has an aspect ratio of 2-1,000. 3. The method for producing a porous glass member according to claim 1, wherein the heat treatment temperature is 500 to 800.degree. % by mass, SiO ₂ 40-70 %, B ₂ O ₃ 10-30 %, Na ₂ O 3-15 %, ZrO ₂ 3-10 %, Al ₂ O ₃ 2-5%, RO (R is Mg , Ca, Sr and Ba) 8 to 20%, CaO 8 to 20%, and a Na ₂ O/B ₂ O ₃ mass ratio of 0.3 to 0.5 A glass base material for a porous glass member, characterized by: