JP7425400B2 - 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, large specific surface area, heat resistance, and organic solvent resistance, so it has been used for a wide range of applications such as separation membranes, air diffusers, electrode materials, and catalyst supports. It is being considered. Generally, porous glass is produced by heat-treating a glass base material made of alkali borosilicate glass to separate it into two phases, a silica-rich phase and a boron oxide-rich phase, and removing the boron oxide-rich phase with acid ( For example, see Patent Document 1).

Japanese Unexamined Patent Publication No. 48-101409

Some of the above-mentioned uses of porous glass include use in alkaline environments, and when such applications are taken into consideration, porous glass is required to have alkali resistance. However, conventional porous glass has a problem of poor alkali resistance.

In view of the above, an object of the present invention is to provide a method for producing a porous glass member that can produce a porous glass member having excellent alkali resistance.

As a result of extensive studies, the inventors of the present invention have found that the above technical problem can be solved by strictly regulating the composition of the base material of the porous glass member.

That is, the method for producing a porous glass member of the present invention includes, in mol%, SiO ₂ 40-80%, B ₂ O _30-40 %, Li ₂ O 0-20%, Na ₂ O 0-20%. , K ₂ O more than 0 to 20%, ZrO ₂ more than 0 to 20%, Al ₂ O ₃ 0 to 10%, and RO (R is at least one selected from Mg, Ca, Sr, and Ba) 0 to a step of heat-treating a glass base material containing 20% and having a molar ratio of K ₂ O/(Li ₂ O + Na ₂ O + K ₂ O) of 0.1 to 0.5 to separate into two phases; The method is characterized by including a step of removing the phase with an acid.

In addition, in this specification, "x+y+..." means the total amount of each component of x, y... Moreover, "x/y" means the value obtained by dividing the content of x by the content of y.

In the method for producing a porous glass member of the present invention, the glass base material preferably has an aspect ratio of 2 to 1000. Note that the aspect ratio is calculated using 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°C.

The glass base material for porous glass members of the present invention contains, in mol%, SiO ₂ 40 to 80%, B ₂ O ₃ more than 0 to 40%, Li ₂ O 0 to 20%, Na ₂ O 0 to 20%, K ₂ O more than 0 to 20%, ZrO ₂ more than 0 to 20%, Al ₂ O ₃ 0 to 10%, and RO (R is at least one selected from Mg, Ca, Sr, and Ba) 0 to 20 %, and the molar ratio of K ₂ O/(Li ₂ O+Na ₂ O+K ₂ O) is 0.1 to 0.5.

According to the present invention, it is possible to provide a method for manufacturing a porous glass member that can produce a porous glass member having excellent alkali resistance.

The method for producing a porous glass member of the present invention includes, in mol%, SiO ₂ 40 to 80%, B ₂ O ₃ more than 0 to 40%, Li ₂ O 0 to 20%, Na ₂ O 0 to 20%, K ₂ O more than 0 to 20%, ZrO ₂ more than 0 to 20%, Al ₂ O ₃ 0 to 10%, and RO (R is at least one selected from Mg, Ca, Sr, and Ba) 0 to 20% a step of heat-treating a glass base material containing the following and having a molar ratio of K ₂ O/(Li ₂ O+Na ₂ O+K ₂ O) of 0.1 to 0.5 to separate into two phases; The method is characterized in that it includes a step of removing with an acid.

The reason why the content of each component in the glass base material was specified as described above will be explained below. In addition, unless otherwise specified, "%" means "mol%" in the following description of component content.

SiO ₂ is a component that forms a glass network. The content of SiO ₂ is 40-80%, preferably 45-75%, 47-60%, particularly 50-65%. If the content of SiO ₂ is too small, the weather resistance and mechanical strength of the porous glass member tend to decrease. Additionally, in the manufacturing process, the amount of expansion due to hydration of silica gel tends to be smaller than the amount of contraction due to the elution of alkaline components such as Na ₂ O from the silica-rich phase, making it easier for cracks to occur in the porous glass member. . On the other hand, if the content of SiO ₂ is too large, 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%, particularly 15 to 25%. If the content of B ₂ O ₃ is too low, it will be difficult to obtain the above effects. On the other hand, if the content of B ₂ O ₃ is too large, the weather resistance of the glass base material tends to decrease.

Li ₂ O is a component that lowers the melting temperature and improves meltability, as well as a component that promotes phase separation. The content of Li ₂ O is 0 to 20%, preferably 0.3 to 15%, particularly 0.6 to 10%. If the content of Li ₂ O is too large, on the contrary, phase separation becomes difficult.

Na ₂ O is a component that lowers the melting temperature and improves meltability, and is also a component that promotes phase separation. The content of Na ₂ O is 0 to 20%, preferably more than 0 to 15%, particularly 4 to 10%. If the content of Na ₂ O is too low, it will be difficult to obtain the above effects. On the other hand, if the content of Na ₂ O is too large, it becomes difficult to cause phase separation.

K ₂ O is a component that lowers the melting temperature and improves meltability, as well as a component that promotes phase separation. It is also a component that increases the ZrO ₂ content in the silica-rich phase. Therefore, by including K ₂ O, the ZrO ₂ content in the obtained porous glass member increases, and the alkali resistance can be improved. The content of K ₂ O is preferably more than 0 to 20%, 0.3 to 5%, particularly 0.8 to 3%. If the content of K ₂ O is too small, it will be difficult to obtain the above effects. On the other hand, if the content of K ₂ O is too large, phase separation becomes difficult.

The content of Li ₂ O + Na ₂ O + K ₂ O is preferably more than 0 to 20%, 2 to 15%, 4 to 12%, particularly 5 to 10%. If the content of Li ₂ O + Na ₂ O + K ₂ O is too small, the melting temperature may become high and the meltability may decrease. Also, phase separation becomes difficult. If the content of Li ₂ O + Na ₂ O + K ₂ O is too large, on the contrary, phase separation becomes difficult.

K ₂ O/(Li ₂ O+Na ₂ O+K ₂ O) is 0.1 to 0.5, preferably 0.13 to 0.45, particularly 0.15 to 0.4. If K ₂ O/(Li ₂ O+Na ₂ O+K ₂ O) is too small, it becomes difficult to obtain the effect of increasing the ZrO ₂ content in the silica-rich phase. On the other hand, if K ₂ O/(Li ₂ O+Na ₂ O+K ₂ O) is too large, the phase separation state changes from spinodal phase separation to binodal phase separation, or phase separation does not occur. As a result, it becomes difficult to obtain a porous glass member having desired communicating pores.

Na ₂ O/B ₂ O ₃ is preferably 0.1 to 0.5, 0.15 to 0.45, particularly 0.2 to 0.4. In this way, in the manufacturing process, the amount of expansion due to hydration of the silica gel and the amount of contraction due to elution of Na ₂ O from the silica-rich phase can be balanced, making it difficult for cracks to occur in the porous glass member. .

(Li ₂ O + Na ₂ O + K ₂ O)/B ₂ O ₃ should be 0.2 to 0.5, 0.29 to 0.45, 0.31 to 0.42, especially 0.33 to 0.42. is preferred. In this way, in the manufacturing process, the amount of expansion due to hydration of the silica gel and the amount of contraction due to elution of alkaline components from the silica-rich phase are balanced, and cracks are less likely to occur in the porous glass member.

ZrO ₂ is a component that improves the weather resistance of the glass base material and the alkali resistance of the porous glass member. The content of ZrO ₂ is more than 0 to 20%, preferably 2 to 15%, particularly 2.5 to 12%. 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 large, devitrification tends to occur and phase separation becomes difficult.

Al ₂ O ₃ is a component that improves the weather resistance and mechanical strength of the porous glass member. The content of Al ₂ O ₃ is 0 to 10%, preferably 0.1 to 7%, particularly 1 to 5%. If the content of Al ₂ O ₃ is too large, the melting temperature will increase and the meltability will tend to decrease.

RO (R is at least one selected from Mg, Ca, Sr, and Ba) is a component that increases the ZrO ₂ content in the silica-rich phase. Therefore, by including RO, the ZrO ₂ content in the obtained porous glass member increases, and the alkali resistance can be improved. Further, RO is a component that improves the weather resistance of the porous glass member. The content of RO (total amount of MgO, CaO, SrO and BaO) is 0 to 20%, 1 to 17%, 3 to 15%, 4 to 13%, 5 to 12%, especially 6.5 to 12%. It is preferable that If the content of RO is too large, phase separation becomes difficult. Note that the content of MgO, CaO, SrO and BaO is preferably 0 to 20%, 1 to 17%, 3 to 15%, 4 to 13%, 5 to 12%, particularly 6.5 to 12%. . Furthermore, when at least two components selected from MgO, CaO, SrO and BaO are contained, the total amount is 0 to 20%, 1 to 17%, 3 to 15%, 4 to 13%, 5 to 12%. %, particularly preferably from 6.5 to 12. Among ROs, it is preferable to use CaO because it has a particularly large effect of improving the alkali resistance of the porous glass member.

The glass base material can contain the following components in addition to the above components.

ZnO is a component that increases the ZrO ₂ content in the silica-rich phase. It also has the effect of improving the weather resistance of the porous glass member. The content of ZnO is preferably 0 to 20%, 0 to 10%, particularly 0 to less than 3%. If the ZnO content is too large, phase separation becomes difficult.

P ₂ O ₅ is a component that promotes phase separation. The content of P ₂ O ₅ is preferably 0 to 10%, 0.01 to 5%, particularly 0.05 to 2%. If the content of P ₂ O ₅ is too large, there is a risk of crystallization.

Also, TiO ₂ , La ₂ O ₃ , Ta ₂ O ₅ , TeO ₂ , Nb ₂ O ₅ , Gd ₂ O ₃ , Y 2 O 3 , Eu ₂ O ₃ , Sb _{2 O 3} , SnO ₂ and Bi _{2 O 3} etc. may be contained in a range of 15% or less each, 10% or less each, particularly 5% or less each, and 30% or less in total.

Note that since PbO is an environmentally hazardous substance, it is preferable that it is substantially not contained. Here, "substantially not containing" means not intentionally containing it as a raw material, and objectively refers to a case where the content is less than 0.1%.

A glass batch prepared to have the above glass composition is melted, for example, at 1300 to 1600° C. for 4 to 12 hours. Next, after shaping the molten glass, it is slowly cooled, for example, at 400 to 600° C. for 10 minutes to 10 hours, thereby obtaining a glass base material. Although the shape of the obtained glass base material is not particularly limited, it is preferably a plate with a rectangular or circular planar shape. Note that in order to give the obtained glass base material a desired shape, processing such as cutting or polishing may be performed.

The obtained glass base material preferably has an aspect ratio of 2 to 1000, particularly 5 to 500. If the aspect ratio is too small, there will be a large difference in the etching rate between the surface and the inside of the glass base material during the process of removing (etching) the boron oxide rich phase with acid, which will cause stress to occur inside the porous glass member. It becomes easy to crack and cracks occur easily. On the other hand, if the aspect ratio is too large, it becomes difficult to handle.

Note that the bottom area and thickness of the obtained glass base material may be adjusted as appropriate so as to have the above aspect ratio. For example, the base area is preferably 1 to 1000 mm ² , particularly 5 to 500 mm ² , and the thickness is preferably 0.1 to 1 mm, particularly 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 (spinodal phase separation). The heat treatment temperature is preferably 500 to 800°C, particularly 600 to 750°C. If the heat treatment temperature is too high, the glass base material will soften, making it difficult to obtain the desired shape. On the other hand, if the heat treatment temperature is too low, it will be difficult to phase separate the glass base material. The heat treatment time is preferably 1 minute or more, 10 minutes or more, particularly 30 minutes or more. If the heat treatment time is too short, it will be 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 realistically 180 hours or less because phase separation does not proceed beyond a certain point even if heat treatment is performed for a long time.

Next, the glass base material separated into two phases is immersed in acid to remove the boron oxide rich phase to obtain a porous glass member. As the acid, hydrochloric acid or nitric acid can be used. Note that a mixture of these acids may be used. The acid concentration is preferably 0.1 to 5N, particularly 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, etching will be insufficient and it will be difficult to obtain a porous glass member with desired continuous pores. Although the upper limit of the immersion time is not particularly limited, it is realistically 100 hours or less. The immersion temperature is preferably 20°C or higher, 25°C or higher, particularly 30°C or higher. If the dipping temperature is too low, etching will be insufficient and it will be difficult to obtain a porous glass member with desired continuous pores. The upper limit of the immersion temperature is not particularly limited, but realistically it is 95°C or lower.

In addition, in the step of phase-separating the glass base material, a silica-containing layer (a layer containing approximately 80 mol % or more of silica) may be formed on the outermost surface of the glass base material. The silica-containing layer is difficult to remove with acid, so when the silica-containing layer is formed, cutting or polishing the phase-separated glass base material, removing the silica-containing layer, and then immersing it in acid will result in boron oxide-rich Phases are easier to remove. Further, in order to remove the silica-containing layer, the glass base material after phase separation may be immersed in hydrofluoric acid for a short time.

Furthermore, it is preferable to remove ZrO ₂ colloid and SiO ₂ colloid remaining in the pores of the obtained porous glass.

The ZrO ₂ colloid can be removed, for example, by immersing the glass base material in sulfuric acid. The concentration of sulfuric acid is preferably 0.1 to 5N, particularly 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 realistically 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 realistically 95°C or lower.

The SiO ₂ colloid can be removed, for example, by immersing the glass base material in an alkaline aqueous solution. As the alkaline aqueous solution, a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, etc. can be used. Note that a mixture of these alkaline aqueous solutions may be used. 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 realistically 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 realistically 95°C or lower.

The obtained porous glass member contains SiO ₂ 75 to 99% (furthermore, 80 to 95%), Na ₂ O 0 to 15% (furthermore, 0 to 10%), and K ₂ O 0 in mass %. ~5% (furthermore, 0 to 3%), ZrO ₂ 4 to 20% (furthermore, 4.5 to 15%), Al ₂ O ₃ 0 to 5% (furthermore, more than 0 to 4%), It is also preferable to contain 0 to 5% (more preferably 0 to 3%) of RO (R is at least one selected from Mg, Ca, Sr, and Ba). When the porous glass member contains a predetermined amount of SiO ₂ and ZrO ₂ in this way, excellent alkali resistance can be achieved.

The median value 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, particularly 70 nm or less. The lower limit of the median value of the pore distribution is not particularly limited, but realistically it is 1 nm or more, 2 nm or more, and even 4 nm or more. In addition, examples of the shape of the holes include a continuous body of spherical or substantially elliptical holes, a tube shape, and the like. Note that dimensions such as aspect ratio, bottom area, and thickness of the porous glass member are the same as those of the glass base material.

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

Table 1 shows Examples (Samples Nos. 1 to 8) of the present invention and Comparative Examples (Samples Nos. 9 and 10).

Raw materials prepared to have the respective compositions shown in the table were placed in a platinum crucible and melted at 1400°C to 1500°C for 4 hours. When melting the raw materials, they were stirred using a platinum stirrer to achieve homogenization. Next, the molten glass was poured onto a metal plate and formed into a plate shape, and then slowly cooled at 580°C to 540°C for 30 minutes to obtain a glass base material.

The obtained glass base material was cut and polished to a size of 5 mm x 5 mm x 0.5 mm. Thereafter, it was heat-treated in an electric furnace at 650° C. to 750° C. for 30 minutes to 24 hours to cause phase separation. After phase separation, the glass base material was immersed in 1N nitric acid (95°C) for 48 hours, washed with ion-exchanged water, and then immersed in 3N sulfuric acid (95°C) for 48 hours. It was washed with ion-exchanged water, further immersed in a 0.5N aqueous sodium hydroxide solution (room temperature) for 3 to 5 hours, and then washed with ion-exchanged water. In this way, a porous glass member was obtained.

When the cross sections of the obtained porous glass members were observed using FE-SEM (SU-8220 manufactured by Hitachi, Ltd.), all glasses had a skeleton structure based on spinodal phase separation.

Next, the composition of the porous glass member was measured by analyzing the porous glass member using EDX (EX-370X-Max ^N 150 manufactured by Horiba, Ltd.). The analysis was conducted at three points in the center of the cross section of the porous glass member, and the average value was used.

In addition, the alkali resistance of the porous glass member was evaluated as follows. The porous glass member was immersed for 20 minutes in a 0.5N aqueous sodium hydroxide solution maintained at 80°C. Those whose weight loss per specific surface area before and after immersion was less than 3 mg/m ² were evaluated as "○", and those that were 3 mg/m ² or more were evaluated as "x". Note that the specific surface area was measured using QUADRASORB SI manufactured by Quantachrome.

No. 1, which is an embodiment of the present invention. In Nos. 1 to 8, the content of ZrO ₂ in the porous glass member was as high as 4.8 to 8.2% by mass, and the alkali resistance was excellent. On the other hand, the comparative example No. In Nos. 9 and 10, the ZrO ₂ content was as low as 3.5% by mass or less, and the alkali resistance was poor.

The porous glass member produced by the method of the present invention is suitable for uses such as separation membranes, air diffusers, electrode materials, catalyst supports, and the like.

Claims (6)

In mol%, SiO ₂ 40-80%, B ₂ O ₃ >0-40%, Li ₂ O 0-20%, Na ₂ O 0-20%, K ₂ O 1.25-20 %, ZrO ₂ 0 Contains >20%, Al ₂ O ₃ 0-10%, and RO (R is at least one selected from Mg, Ca, Sr, and Ba) 0-20%, with a molar ratio of K ₂ O/ A glass base material in which (Li ₂ O + Na ₂ O + K ₂ O) is 0.1 to 0.5 and (Li ₂ O + Na ₂ O + K ₂ O)/B ₂ O ₃ is 0.35 to 0.5 is heat-treated to obtain 2 A method for manufacturing a porous glass member, comprising the steps of separating the phases into phases, and removing one of the phases with an acid. The method for producing a porous glass member according to claim 1, wherein the glass base material has an aspect ratio of 2 to 1,000. The method for producing a porous glass member according to claim 1 or 2, wherein the heat treatment temperature is 500 to 800°C. The method for producing a porous glass member according to any one of claims 1 to 3, wherein the glass base material has a molar ratio of Na ₂ O/B ₂ O ₃ of 0.1 to 0.5. . In mol%, SiO ₂ 40-80%, B ₂ O ₃ >0-40%, Li ₂ O 0-20%, Na ₂ O 0-20%, K ₂ O 1.25-20 %, ZrO ₂ 0 Contains >20%, Al ₂ O ₃ 0-10%, and RO (R is at least one selected from Mg, Ca, Sr, and Ba) 0-20%, with a molar ratio of K ₂ O/ Porous glass characterized in that (Li ₂ O + Na ₂ O + K ₂ O) is 0.1 to 0.5 and (Li ₂ O + Na ₂ O + K ₂ O)/B ₂ O ₃ is 0.35 to 0.5 Glass base material for parts. The glass base material for a porous glass member according to claim 5, characterized in that the molar ratio of Na ₂ O/B ₂ O ₃ is 0.1 to 0.5.