JP2012193067A - Borosilicate glass, porous glass, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide borosilicate glass causing phase separation even though the containing ratio of silicon oxide is high and capable of producing porous glass with high strength; and to provide a method for producing the porous glass using the same.SOLUTION: The borosilicate glass contains 60 wt.% or more and 72 wt.% or less of silicon oxide, 18 wt.% or more and 30 wt.% or less of boron oxide, 9.5 wt.% or more and 15 wt.% or less of sodium oxide, and 0.1 wt.% or more and 5.0 wt.% or less of cerium oxide. The method for producing the porous glass includes: a step for separating phases into a silica-rich phase and a non-silica rich phase by carrying out phase separating processing by heating the borosilicate glass; and a step for dissolving out the silica-rich phase by etching with solution.

Description

  The present invention relates to borosilicate glass, a method for producing porous glass using the borosilicate glass, and porous glass.

  There is a method using a phase separation phenomenon as a relatively easy manufacturing method of porous glass. As a base glass of a porous glass utilizing a phase separation phenomenon, borosilicate glass containing silicon oxide (silica), boron oxide, and alkali metal oxide as a constituent element is generally used. The borosilicate glass produced by the melting method, etc. is caused to undergo phase separation by heat treatment that is maintained at a constant temperature (hereinafter referred to as phase separation treatment), and the non-silica rich phase is eluted by selective etching with an acid solution to be porous. Manufacture glass.

  It is mainly silicon oxide that constitutes the skeleton of the porous glass. When the skeleton diameter, the pore diameter, and the porosity are similar, the strength increases as the proportion of silicon oxide constituting the skeleton increases. The ratio of silicon oxide constituting the skeleton increases as the silicon oxide component of the base material borosilicate glass increases. For this reason, borosilicate glass with many silicon oxide components is desirable for increasing the strength of the porous glass.

  In addition, since the structure of the porous glass, such as the skeleton diameter, pore diameter, and porosity, affects various properties, it is necessary to control the formation of the structure over a wide range. In order to obtain porous glass having porous structures of various sizes, it is desired to cause phase separation in a wide composition region of borosilicate glass. From the above, it is necessary to induce phase separation with a borosilicate glass rich in silicon oxide.

  However, phase separation occurs only in a specific composition range in a borosilicate glass containing only silicon oxide, boron oxide and sodium oxide. Therefore, it is necessary to control the appearance of phase separation in the borosilicate glass in the composition region with a lot of silicon oxide by adding other components.

  For example, in Non-Patent Document 1, aluminum oxide is added to borosilicate glass as a constituent element, which acts to suppress phase separation.

  Patent Document 1 discloses a porous glass containing a heavy metal or a rare earth element, but is a borosilicate glass having a silicon oxide component of 60% by weight or less. Moreover, although it is a borosilicate glass containing a heavy metal or a rare earth element as an additive, the additive does not exert an effect of promoting phase separation.

JP-A-2005-060679

John Wiley & Sons, “Introduction to Ceramics”, second edition, Chapter 8, 1960.

  However, in the conventional technology, in a borosilicate glass whose components are composed of silicon oxide, boron oxide, sodium oxide and containing 60% by weight or more of silicon oxide, the phase separation is promoted by adding an additive, and the porous material is porous. There are no reports of obtaining glass.

  Thus, in order to obtain a porous glass having high strength and various porous structures, a borosilicate glass having a high content of silicon oxide, causing phase separation, and resisting etching after phase separation treatment. Was needed.

  The present invention has been made in view of such a problem, and provides a borosilicate glass capable of producing a porous glass having high strength, causing phase separation even when the content of silicon oxide is large. To do.

  In addition, the present invention provides a method for producing porous glass having high strength using borosilicate glass that causes phase separation even when the content ratio of silicon oxide is large.

  Moreover, this invention provides the porous glass obtained by the manufacturing method of said porous glass.

  The borosilicate glass according to the present invention is composed of silicon oxide 60 wt% or more and 72 wt% or less, boron oxide 18 wt% or more and 30 wt% or less, sodium oxide 9.5 wt% or more and 15 wt% or less, cerium oxide 0.1 It is characterized by containing from 5% by weight to 5.0% by weight.

  The method for producing a porous glass according to the present invention includes a step of subjecting the borosilicate glass to a phase separation treatment by heating to phase-separate it into a silica-rich phase and a non-silica-rich phase, and etching the non-silica-rich phase with a solution. And a step of elution.

  The porous glass according to the present invention is a porous glass having a skeleton containing silicon oxide as a main component, obtained by the method for producing a porous glass.

  ADVANTAGE OF THE INVENTION According to this invention, even if there is much content rate of a silicon oxide, phase separation will be caused and the borosilicate glass which can manufacture the porous glass with high intensity | strength can be provided.

  Moreover, according to this invention, the manufacturing method of porous glass with high intensity | strength can be provided using the borosilicate glass which raise | generates a phase separation even if there are many content rates of a silicon oxide.

  Moreover, according to this invention, the porous glass obtained by the manufacturing method of said porous glass can be provided.

2 is a scanning electron micrograph of the surface of a porous glass prepared in Example 1. FIG. 2 is a scanning electron micrograph of the surface of a porous glass produced in Comparative Example 1.

  Hereinafter, embodiments of the present invention will be described in detail.

The borosilicate glass according to the present invention comprises silicon oxide (SiO ₂ ) 60 wt% or more and 72 wt% or less, boron oxide (B ₂ O ₃ ) 18 wt% or more and 30 wt% or less, sodium oxide (Na ₂ O) 9 0.5 wt% or more and 15 wt% or less, and cerium oxide (CeO ₂ ) 0.1 wt% or more and 5.0 wt% or less.

The borosilicate glass will be described below. In particular, the borosilicate glass according to the present invention is characterized by containing cerium oxide (CeO ₂ ).

  Borosilicate glass is a glass that undergoes phase separation to obtain porous glass. Borosilicate glass is generally amorphous with silicon oxide, boron oxide, alkali metal oxide, especially sodium oxide as a constituent element. The composition of this borosilicate glass is expressed by a weight ratio in terms of silicon oxide, boron oxide, and sodium oxide.

  First, glass materials are mixed and melted to obtain a glass body. A glass body is manufactured by preparing a raw material so that it may become a desired composition, heat-melting the prepared raw material, and shape | molding in a desired form as needed. The heating temperature in the case of heating and melting may be appropriately set depending on the raw material composition or the like, but it is usually preferably in the range of 1300 to 1500 ° C, particularly 1350 to 1450 ° C.

  For example, sodium carbonate, boric acid and silicon oxide may be mixed uniformly as raw materials and heated and melted at 1350 to 1450 ° C. In this case, any raw material may be used as long as a borosilicate glass having a desired composition is obtained.

  In addition, the shape of the porous glass may be any shape such as tubular, plate-like, spherical, and film-like, and accordingly the shape of the glass body is also tubular, plate-like, spherical, membrane-like, etc. Any shape is acceptable. When the glass body has a tubular shape, a plate shape, a spherical shape, a film shape, or the like, the glass raw material is mixed and melted and then molded into various shapes at approximately 700 to 1000 ° C. For example, after melting the raw material, it is possible to suitably employ a method of molding in a state where the temperature is lowered from the melting temperature and maintained at 700 to 1000 ° C.

  A borosilicate glass having a specific composition is phase-separated into a silica-rich phase mainly composed of silicon oxide and a non-silica-rich phase mainly composed of boron oxide and an alkali metal oxide by phase separation treatment. Usually, phase separation occurs in the range of 500 to 700 ° C. In order to obtain a porous glass, it is desirable that the phase separation occurs in a spinodal type, and the composition of the borosilicate glass that is phase-separated in this way has the main three components within a specific ratio range. In particular, borosilicate glass having a large content of silicon oxide hardly causes desired phase separation.

  Subsequently, by performing an etching process for eluting the non-silica rich phase with the solution from the phase-separated borosilicate glass, the porous glass is obtained with the silica rich phase remaining as a skeleton.

  The skeleton constituting the porous glass is mainly silicon oxide. When the skeleton diameter, the pore diameter, and the porosity are similar, the strength increases as the proportion of silicon oxide constituting the skeleton increases. Moreover, when there are few silicon oxide components which comprise frame | skeleton, a crack may generate | occur | produce at the time of an etching process. The ratio of silicon oxide constituting the skeleton increases as the silicon oxide component of the base material borosilicate glass increases. For this reason, in order to raise the intensity | strength of porous glass, it is desirable that base material glass is borosilicate glass with many silicon oxide components.

  In addition, the structure of the porous glass, such as the skeleton diameter, the pore diameter, and the porosity, affects various properties, and thus needs to be controlled over a wide range. In order to change the porous structure, it is possible to change the composition of the borosilicate glass serving as the base material, and to change the profile such as the temperature and time of the phase separation treatment. It is desirable to change the composition of borosilicate glass in order to change the porous size in various ways and increase the degree of freedom of structure formation. In addition, it is desirable that phase separation treatment can be performed in a wide composition range of borosilicate glass. It is.

  From the above, the borosilicate glass of the present invention is a borosilicate glass that causes phase separation while being a composition region having a relatively large amount of silicon oxide.

[Embodiment of composition of borosilicate glass (1)]
A preferred embodiment (1) of the composition of the borosilicate glass of the present invention is the following composition.
The borosilicate glass of the present invention comprises silicon oxide (SiO ₂ ) 60 wt% or more and 72 wt% or less, boron oxide (B ₂ O ₃ ) 18 wt% or more and 30 wt% or less, sodium oxide (Na ₂ O) 9. 5 to 15% by weight and cerium oxide (CeO ₂ ) 0.1 to 5.0% by weight are contained.

[Embodiment (2) of composition of borosilicate glass]
A preferred embodiment (2) of the composition of the borosilicate glass of the present invention is the following composition.

  The borosilicate glass of the present invention is composed of silicon oxide 63 wt% to 68 wt%, boron oxide 18 wt% to 21 wt%, sodium oxide 9.5 wt% to 11 wt%, cerium oxide 0.1 wt%. It is desirable that it comprises a composition containing from 0.5% to 5.0% by weight.

[Embodiment of composition of borosilicate glass (3)]
A more preferred embodiment (3) of the composition of the borosilicate glass of the present invention is the following composition.

  The borosilicate glass of the present invention comprises silicon oxide 68 wt% or more and 72 wt% or less, boron oxide 18 wt% or more and 19 wt% or less, sodium oxide 9.5 wt% or more and 10 wt% or less, cerium oxide 0.1 wt%. It is desirable to consist of a composition containing no less than 3.0% and no more than 3.0% by weight.

In the present invention, the atomic ratio of cerium atoms to silicon atoms (Ce / Si) in silicon oxide (SiO ₂ ) and cerium oxide (CeO ₂ ) is 0.01 ≦ Ce / Si ≦ 0.13, preferably 0.02 ≦ It is desirable that Ce / Si ≦ 0.13.

The phase-separated base glass of the present invention may contain other components other than silicon oxide, boron oxide, sodium oxide, and cerium oxide. For example, the impurity component contained in a raw material and the impurity component contained in a manufacturing process are mentioned. Examples of other components include calcium, magnesium, barium, and zinc oxides. The content of other components is preferably 2% by weight or less, particularly preferably 1% by weight or less, based on the total of each component of SiO ₂ B ₂ O ₃ Na ₂ O and CeO ₂

  In the present invention, cerium oxide is added to the component to facilitate phase separation in borosilicate glass with a high proportion of silicon oxide. Although this mechanism is not clear, the following hypothesis can be considered. The addition of another compound to the component changes the free energy, and the stable state when the temperature is raised as in the phase separation process. Cerium oxide is added to a borosilicate glass having a composition ratio that does not cause sufficient phase separation, particularly spinodal phase separation, with the main three components (silicon oxide, boron oxide, sodium oxide). As a result, the free energy of the borosilicate glass changes and the state where spinodal phase separation is caused when the temperature of the phase separation treatment is applied becomes the most stable, so that spinodal type phase separation is manifested.

  On the other hand, if the proportion of cerium oxide increases too much, the change in free energy increases. Therefore, the most stable state at the time of temperature application in the phase separation process also changes, and spinodal type phase separation does not occur. Even if spinodal type phase separation occurs, the content ratio of cerium oxide in the skeleton increases, and the strength of the porous body decreases. Therefore, cracks occur during etching, and porous glass cannot be obtained.

  In the borosilicate glass of the present invention, the content of cerium oxide is 0.1 wt% or more and 5.0 wt% or less, preferably 2.0 wt% or more and 5.0 wt% or less.

  Next, the manufacturing method of the porous glass of this invention is demonstrated.

  The method for producing a porous glass according to the present invention includes a step of subjecting the borosilicate glass to a phase separation treatment by heating to phase-separate it into a silica-rich phase and a non-silica-rich phase, and etching the non-silica-rich phase with a solution. And a step of elution.

  The glass phase separation phenomenon is manifested by forming a spinodal structure or a binodal structure by a phase separation treatment in which a borosilicate glass is generally held at around 500 to 700 ° C. for several hours to several tens of hours. A spinodal structure is desirable for the porous structure. The step in the phase separation process may be held at a constant temperature, or may be a heat application process that maintains a constant temperature increase rate or temperature decrease rate. The time of the phase separation process is 1 minute or more, more preferably 5 minutes or more. The appearance of phase separation can be confirmed by an observation method such as a scanning electric microscope (SEM) or a transmission electron microscope (TEM).

  In the phase separation treatment, the higher the temperature in the phase separation temperature region and the longer the holding time, the larger the porous skeleton diameter and pore diameter, and at the same time, the porosity tends to increase. Although the mechanism of this phenomenon is not clear, the following hypothesis can be considered. It takes several hundred hours to reach the equilibrium state of phase separation at a certain temperature. It is considered that the longer the time is in the time domain of the phase separation treatment from several hours to several tens of hours, the closer to the equilibrium state of phase separation and the more remarkable phase separation, that is, the larger the skeleton diameter and pore diameter. In addition, the effect of increasing the reaction rate appears as the temperature rises, and the higher the temperature, the more the state of phase separation becomes prominent by approaching the equilibrium state of phase separation in the same treatment time, that is, the skeleton diameter and pore diameter become larger. Become. In addition, as the temperature increases, the composition of the phases in the equilibrium state of phase separation approaches. Since the content of silicon oxide in the non-silica rich phase is increased, the portion removed by acid etching is also relatively increased, and the porosity is considered to be increased.

  In the phase separated borosilicate glass, the non-silica rich phase is soluble in solutions such as acids, alkalis and water. Accordingly, the soluble phase is eluted by the treatment with the solution, and only the phase mainly formed from silicon oxide remains as a skeleton, and a porous structure is formed. The means for bringing the solution into contact with the glass is generally a means for immersing the glass in the solution. However, the means is not limited as long as it is a means for bringing the solution into contact with the glass, such as placing the solution on the glass. As the solution, any existing solution capable of eluting a soluble phase, such as an acid solution, an alkaline solution, or water, can be used. Moreover, you may select multiple types of processes made to contact these solutions according to a use.

  In general etching of glass that has undergone phase separation, acid treatment is preferably used from the viewpoint of a small load on the insoluble phase and the degree of selective etching. By contacting with a solution containing an acid, the non-silica rich phase, which is an acid-soluble component, is eluted and removed, while the erosion of the silica-rich phase, which is an insoluble phase, is relatively small, achieving high selective etching properties. Is possible.

  As the aqueous solution containing an acid, for example, inorganic acids such as hydrochloric acid, sulfuric acid, phosphoric acid and nitric acid can be preferably used. The solution containing an acid can be suitably used in the form of an aqueous solution usually using water as a solvent. What is necessary is just to set the density | concentration of the solution containing an acid suitably in the range of 0.1 mol / L to 2.0 mol / L (0.1 to 2 normal) normally.

  In this step, the temperature of the aqueous solution may be in the range of room temperature to 100 ° C., and the treatment time may be about 1 to 100 hours.

  Depending on the glass composition, a silica-rich layer that inhibits etching may occur on the glass surface after the phase separation treatment on the order of several hundred nanometers. This surface silica-rich layer can also be removed by polishing or alkali treatment.

  Depending on the glass composition, gel silica may be deposited on the skeleton during etching. If necessary, a method of etching in multiple stages using acid solutions or alkali solutions having different acidity and alkalinity can be used. Etching can also be performed at room temperature to 95 ° C. as an etching temperature. If necessary, ultrasonic waves can be applied during the etching process.

  After the immersion treatment with a solution, rinsing with water is generally performed for the purpose of removing the solution adhering in the porous glass and the soluble layer remaining without elution.

  The state of the porous structure of the glass obtained after the etching is completed can be confirmed by an observation method such as a scanning electric microscope (SEM).

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

Base glass was prepared for Examples and Comparative Examples of the present invention. As raw material compounds, silicon oxide powder (SiO ₂ ), boron oxide (B ₂ O ₃ ), sodium carbonate (Na ₂ CO ₃ ), and cerium oxide (CeO ₂ ) were used. The content composition of the borosilicate glass used in Examples and Comparative Examples is shown in Table 1 in terms of weight percent in each metal element oxide, that is, silicon oxide, boron oxide, sodium oxide, and cerium oxide.

  The powder mixed with the raw metal compound was placed in a platinum crucible and melted at 1500 ° C. for 24 hours to obtain glass. Thereafter, the glass was lowered to 1300 ° C. and then poured into a graphite mold. Borosilicate glass was obtained by cooling in air for 20 minutes. The obtained block of borosilicate glass was cut so as to be 40 mm × 30 mm × 1 mm, and double-side polishing was performed to a mirror surface.

(Examples 1 to 3)
15 mm × 15 mm × 1 mm was cut out from each base glass described in Table 1, and subjected to phase separation treatment at 600 ° C. for 50 hours.

  The glass sample after phase separation was etched with an acid solution. As the acid solution, 50 g of 1 mol / L nitric acid was used. Nitric acid was placed in a polypropylene container and preheated to 80 ° C. in an oven. The glass was hung with a platinum wire so as to come to the center in the solution. The polypropylene container was covered and allowed to stand for 24 hours while being kept at 80 ° C. The glass after the treatment with nitric acid was placed in water at 80 ° C. and rinsed.

  By observation with a scanning electron microscope (SEM), it was confirmed to be a porous glass. All of the porous glasses had a spinodal structure. A scanning electron microscope (SEM) image of the porous glass obtained in Example 1 is shown in FIG.

  Composition analysis of the obtained porous glass by fluorescent X-ray analysis (XRF) showed that silicon oxide was 90% by weight or more in terms of oxide, and the silicon oxide content was confirmed.

(Comparative Example 1)
Based on the composition used in Example 1, cerium oxide was not used, and samples having the compositions described in Table 1 were used for the ratio of the other three components. 15 mm × 15 mm × 1 mm was cut out and subjected to phase separation treatment at 600 ° C. for 50 hours.

  When the glass sample after the phase separation treatment was observed by SEM, it was not in a spinodal structure.

  When the glass sample was etched with an acid solution in the same manner as in Example 1, cracks occurred and porous glass was not obtained. The SEM image of the glass after etching is shown in FIG.

(Comparative Example 2)
15 mm × 15 mm × 1 mm of the composition sample described in Table 1 was cut out and subjected to phase separation treatment at 600 ° C. for 50 hours.

  A spinodal structure was observed when the glass sample after the phase separation treatment was observed with an SEM.

  When the glass sample was etched with an acid solution in the same manner as in Example 1, cracks occurred and porous glass was not obtained.

(Note 1) The (Ce / Si) atomic ratio of cerium atoms to silicon atoms is calculated by calculating the molar amount of silicon atoms and cerium atoms from silicon oxide (SiO ₂ ) and cerium oxide (CeO ₂ ) at the time of preparation. The Ce / Si atomic ratio was calculated.
(Note 2) Spinodalization (circle) shows the sample by which spinodal was confirmed by SEM observation after phase separation.
X indicates a sample in which spinodal was not confirmed by SEM observation after phase separation.
(Note 3) Acid treatment resistance ○ indicates a sample made porous by etching with an acid solution.
X indicates a sample in which breakage such as cracking occurred by etching with an acid solution.

  Since the borosilicate glass of the present invention causes phase separation even when the content ratio of silicon oxide is large, the borosilicate glass has high strength and can be widely applied to porous glass having various porous structures.

Claims (5)

  60% to 72% by weight of silicon oxide, 18% to 30% by weight of boron oxide, 9.5% to 15% by weight of sodium oxide, 0.1% to 5.0% by weight of cerium oxide Borosilicate glass characterized by containing.   The borosilicate glass according to claim 1, wherein the content of the cerium oxide is 2.0 wt% or more and 5.0 wt% or less.   The borosilicate according to claim 1 or 2, wherein an atomic ratio (Ce / Si) of cerium atoms to silicon atoms in the silicon oxide and cerium oxide is 0.01≤Ce / Si≤0.13. Glass.   A step of subjecting the borosilicate glass according to any one of claims 1 to 3 to phase separation by heating to phase-separate into a silica-rich phase and a non-silica-rich phase, and eluting the non-silica-rich phase by etching with a solution. The manufacturing method of the porous glass characterized by having a process.   A porous glass having a skeleton composed mainly of silicon oxide, obtained by the method for producing a porous glass according to claim 4.

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