Method for producing a porous glass filter

Abstract

A method of manufacturing a porous glass filter, the method comprising: Preparation of an alkali borosilicate glass by melting and cooling an alkali oxide (R2O), boron trioxide (B2O3) and silicon dioxide (SiO2); Heat-treating the alkali borosilicate glass at a glass transition temperature to phase separate the alkali borosilicate glass into an alkali borosilicate phase (R2O-B2O3) and a silicon dioxide phase (SiO2 phase); Heat-treating or acid-treating the phase-separated alkali borosilicate glass that has undergone phase separation to dissolve the alkali-boron phase (R2O-B2O3 phase), thereby creating micropores, wherein the processing of the alkali borosilicate glass comprises: Melting and cooling the alkali oxide (R2O), boron trioxide (B2O3) and silicon dioxide (SiO2) to produce a primary glass; Pulverizing the primary glass produced by processing the alkali borosilicate glass; and Melting the powdered primary glass in a graphite mold to remove air bubbles and then cooling the molten glass to produce the alkali borosilicate glass as a secondary glass, wherein the alkali borosilicate glass comprises 5 to 10 wt% of the alkali oxide (R2O), 35 to 50 wt% of boron trioxide (B2O3) and 40 to 55 wt% of silicon dioxide (SiO2).

Description

[0001] This application claims priority to Korean Patent Application No. 10-2021-0189526, filed on December 28, 2021, the contents of which are incorporated herein by reference in their entirety. Background of the invention 1. Field of the invention

[0002] The present disclosure relates to a porous glass filter for blocking siloxane or organic silicone, which reduces gas sensitivity in a gas sensor for detecting combustible and reducing gas, and a method thereof. More specifically, the present disclosure relates to a porous glass filter having excellent filtering efficiency due to its high porosity of 30% or more and its method of manufacturing, in which the porous glass filter has a micropore diameter of 1 nm, such that combustible and reducing gases such as hydrogen, methane, propane, and alcohols pass through and the siloxane or silicone gas is blocked, thereby preventing contamination of the gas sensor. 2. Description of the related field

[0003] Gas sensors are used not only in household kitchens and boiler rooms, but also in explosive environments where flammable gas may be generated, such as factories, oil fields, mines, and underground sewage pipes. Gas sensors are also used in motor vehicles, power plants, and ships that use propane, natural gas, and hydrogen fuel.

[0004] These gas sensors include a metal oxide semiconductor (MOS) type gas sensor and a contact combustion (pellistor) type gas sensor.

[0005] In metal oxide semiconductor sensors, when a sensor containing a noble metal catalyst such as platinum or palladium in a powder such as tin oxide (SnO2) adsorbs oxygen in the atmosphere, the sensor's free electron is trapped in the adsorbed oxygen, and the resistance increases. The metal oxide semiconductor sensor uses a resistance change, in which the resistance is reduced by reacting with oxygen adsorbed on a sensor when combustible or reducing gas is generated, oxygen is desorbed, and free electrons trapped by the oxygen are released. The sensor uses the principle that the greater the amount of gas, the more significant the resistance change becomes.

[0006] The pellistor gas sensor is formed by molding a ceramic powder containing platinum or a palladium catalyst into a bead shape in a coil-shaped heater made of platinum, which has a high temperature coefficient of resistance and high corrosion resistance, to form a detection bead or an activation bead. A balance bead (reference bead) is prepared by forming another bead shape using the same ceramic powder without platinum or a palladium catalyst. The detection element and the balance element are connected in series, and a voltage in the range of 2 to 5 V is applied thereto so that the surface temperature of the element becomes approximately 400°C, taking the resistance of the coil into account.When a combustible gas is present, oxidation or combustion occurs in the sensing element, causing the temperature of the sensing element to rise, and the resistance of the platinum coil in the sensing element to increase proportionally to the temperature. As the amount of gas increases, the resistance increases, allowing the gas concentration to be determined.

[0007] Such a gas sensor becomes contaminated with siloxane or silicone, and the catalytic function of the gas sensor disappears, thereby degrading the sensor's sensitivity. In particular, the pellistor gas sensor loses its function as a gas sensor because even a small amount of silicone reduces its gas sensitivity. Silicone is commonly found in all areas of our lives, such as silicone adhesives in glass windows of buildings, kitchens, and bathrooms; siloxane in cosmetics; silicone oil; silicone rubber; and the like. As a result, the performance of the gas sensor deteriorates, leading to the gas detector malfunctioning or its service life being shortened.

[0008] In particular, motor vehicles contain a significant amount of rubber or interior materials that contain silicone. In hydrogen fuel cell vehicles that use hydrogen as fuel, a gas sensor is essential for detecting hydrogen gas leaks, and a decrease in gas sensitivity due to silicone is a serious risk factor.

[0009] In the meantime, various methods of using filters have been invented to prevent silicone contamination.

[0010] In Japanese patent JP 3901602 B2, a disc containing a silicate powder containing a platinum powder between porous fibers was manufactured and used as a filter, and in addition, a filter using zeolite, activated alumina and activated carbon was also invented.

[0011] Such a powder is used for molecular sieves, etc., has many pores, has a micropore diameter in the range of several Å to 10 Å, and has a very large specific surface area, such that it is used as an adsorbent.

[0012] Since the size of the gas is about 2.4 Å for hydrogen, 2.8 Å for oxygen, 4.0 Å for methane, 4.9 Å for propane, 6.7 Å for benzene and 7.4 Å for ortho-xylene, each gas can be filtered using a molecular sieve with a suitable micropore diameter.

[0013] These powders have a large particle size, but have a structure with numerous micropores distributed throughout the particles. When this powder is placed in a porous fabric and placed in a gas pipeline, and the gas is then passed through, only gases of a size that can enter the micropores are trapped, while larger gases pass between the powder particles. If only the gases trapped in the micropores are separated, only a specific gas can be filtered out.

[0014] Originally, gas sensors were used to adsorb alcohol using the adsorption performance of these powders to prevent malfunction due to alcohol, but gas sensors were also developed to adsorb siloxane.

[0015] To manufacture these powders as filters, the powders are enclosed between porous meshes or formed into a disc shape and heat-treated. The resulting filter is installed in the section where the gas enters.

[0016] The gap between the powder particles is a few tens of nm to a few micrometers. Therefore, when applied to a gas sensor, a large gas such as siloxane is not trapped in the micropores of zeolite or activated alumina and escapes between the particles, thus making contact with the sensor detection device. Therefore, when applied to a gas sensor, there is little effect of preventing silicon from adsorbing. Instead, the gas to be detected is adsorbed onto zeolite or activated alumina, which reduces gas sensitivity or slows down the response rate and reduces accuracy.

[0017] Japanese Patent Application Laid-Open No. JP 2018-176084 A is characterized in that activated carbon with a micropore diameter in the range of 1.5 to 3.0 nm is used to increase the adsorption of siloxane.

[0018] This is to trap and adsorb the siloxane in these micropores using a micropore diameter larger than that of general activated carbon because the molecular size of siloxane is relatively large.

[0019] In this case, this has the effect of adsorbing more siloxane, but does not prevent siloxane from entering between the activated carbon powder particles.

[0020] Since the sensitivity of the semiconductor gas sensor or the pellistor gas sensor is seriously reduced with only a few tens of ppm of siloxane, it has the effect of delaying siloxane contamination but does not prevent silicone contamination.

[0021] In particular, in motor vehicles, a lot of silicone rubber is used and the temperature is high, so that silicone is produced in large quantities, so that this is insufficient to prevent silicone contamination.

[0022] Since there is a limit to the adsorption amount of activated carbon, its effectiveness is lost when a certain amount or more accumulates, and it becomes useless. The same applies to activated alumina and zeolite.

[0023] JP 6 642 563 B2 discloses a glass substrate for observing minute substances, which is made of porous glass and is capable of separating and capturing a minute substance with an average particle diameter of 10 to 500 nm contained in a solution or suspension.It comprises a porous glass substrate having a plurality of pores, wherein the plurality of pores have an average pore diameter in the range of 30 to 110% of the average particle diameter of the minute substance, each of the plurality of pores has a surface pore diameter on an uppermost surface of the glass substrate, a standard deviation of the surface pore diameter is 60% or less of the average particle diameter of the minute substance, and a pore having a pore diameter in the range of 60 to 140% of a pore diameter at the peak tip in a pore diameter distribution of the plurality of pores occupies 90% or more of the total pore volume.

[0024] EP 0 220 764 A1 discloses a chemically resistant porous glass whose skeleton consists mainly of SiO2-ZrO2 system glass with a ZrO2 content of 2 or more wt.%, and a process for producing such a glass. Summary of the invention

[0025] The present disclosure was invented to solve the problems of the related field. An object of the present disclosure is to provide a porous glass filter that can quickly and accurately detect combustible and reducing gases. The porous glass filter has a micropore size of 10 Å (1 nm), blocks siloxane and silicone, which cause contamination, without reducing sensitivity, and has a porosity of more than 30%.

[0026] The object of the present invention is solved by means of the subject matter of the independent patent claim.

[0027] The porous glass filter according to the present disclosure is obtained by heat-treating an alkali borosilicate glass containing an alkali oxide (R2O), boron trioxide (B2O3), and silicon dioxide (SiO2) as a composition at a glass transition temperature to subject the alkali borosilicate glass to phase separation into an alkali boron phase (R2O-B2O3 phase) and a silicon dioxide phase (SiO2 phase), and by heat-treating or acid-treating the alkali borosilicate glass subjected to phase separation to dissolve an alkali boron phase (R2O-B2O3 phase).

[0028] The alkali borosilicate glass has a weight ratio of 5% to 10% of alkali oxide (R2O), 35% to 50% boron trioxide (B2O3) and 40% to 55% silicon dioxide (SiO2).

[0029] The manufacturing method of the porous glass filter according to the present disclosure may include:

[0030] Preparation of an alkali borosilicate glass by melting and cooling an alkali oxide (R2O), boron trioxide (B2O3) and silicon dioxide (SiO2);

[0031] Heat-treating the alkali borosilicate glass at a glass transition temperature to phase separate the alkali borosilicate glass into an alkali borosilicate phase (R2O-B2O3 phase) and a silicon dioxide phase (SiO2 phase);

[0032] Heat treatment or acid treatment of the phase-separated alkali borosilicate glass that has undergone phase separation to dissolve the alkali-boron phase (R2O-B2O3 phase), thereby generating micropores.

[0033] The processing of alkali borosilicate glass includes the following:

[0034] Melting and cooling the alkali oxide (R2O), boron trioxide (B2O3) and silicon dioxide (SiO2) to produce a primary glass;

[0035] Pulverizing the primary glass produced by processing the alkali borosilicate glass;

[0036] Melting the powdered primary glass in a graphite mold to remove air bubbles and then cooling the molten glass to produce the alkali borosilicate glass.

[0037] The porous glass filter according to the present disclosure has a pore diameter of 10 Å (1 nm) and a porosity of 30% or higher, allowing combustible and reducing gases to pass smoothly without clogging, allowing the gas sensor to detect the gas quickly and accurately. The present disclosure relates to a porous glass filter that prevents the sensitivity of a gas sensor from deteriorating by blocking siloxane and silicone contamination, and a method therefor, which is inexpensive and suitable for mass production and is highly useful for industrial development. Brief description of the drawings Fig. 1 is a flowchart of a manufacturing method of a porous glass filter according to the present disclosure; Fig. 2 is a schematic diagram intuitively expressing a manufacturing method of a porous glass filter according to the present disclosure; Fig. 3 is a measuring circuit diagram for measuring the sensitivity of a gas sensor; Fig. 4 is a graph of a sensitivity change of the gas sensor according to the concentration of methane in the gas sensor according to the presence or absence of a filter and its type; Fig. 5 is a graph of a sensitivity change of the gas sensor over time in the gas sensor according to the presence and type of a filter; Fig. 6 is a graph of a sensitivity change of the gas sensor according to the concentration of further methane in the gas sensor according to the presence or absence of a filter and its type. Description of the preferred embodiments

[0038] Hereinafter, the porous glass filter and the manufacturing method thereof according to the present disclosure will be described in greater detail with reference to the drawings.

[0039] Before explaining in greater detail the porous glass filter and its manufacturing method according to the present disclosure, it is intended that the present disclosure be described in detail in the text of the embodiment (aspect or example) and may be applied to various modifications and take various forms. However, this is not intended to limit the present disclosure to the specific form disclosed; it should be understood to include all modifications, equivalents, and substitutions included within the spirit and scope of the present disclosure.

[0040] In each drawing, the same reference symbols, in particular the tens digit and the units digit, or the tens digit, the units digit, and the same reference symbols in the alphabet, indicate elements that have the same or similar functions. Unless specifically indicated, the elements designated by each reference symbol in the drawing can be considered as elements that meet these criteria.

[0041] In addition, in each drawing, components having an exaggeratedly large (or thick) or small (thin) size or thickness are expressed or simplified in consideration of convenience for understanding, etc., but the scope of the present disclosure should not be interpreted as being limited.

[0042] The terminology used herein is used only to describe a specific embodiment (a specific aspect or example) and is not intended to limit the present disclosure. The singular term includes the plural term unless the context clearly indicates otherwise. Throughout the present application, terms such as includes or consists of are intended to mean the presence of the features, numbers, steps, acts, components, ingredients, or combinations thereof described in the specification and do not preclude the presence or addition of one or more other features or numbers, steps, acts, components, or combinations thereof.

[0043] Unless otherwise defined, all terms used herein that contain technical or scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Terms such as those defined in a commonly used dictionary should be interpreted to have a meaning consistent with the meaning in the context of the related field and should not be interpreted in an ideal or overly formalized sense unless expressly defined in the present application.

[0044] As in Fig. 1, the manufacturing method of a porous glass filter according to the present disclosure can be roughly divided into a glass forming step S10, a processing step S20, a phase separation step S30, and a micropore forming step S40.

[0045] In the glass forming step S10, the raw material powders of an alkali oxide (R2O), boron trioxide (B2O3) and silicon dioxide (SiO2) are mixed, melted at a high temperature and rapidly cooled to produce an alkali borosilicate glass.

[0046] Here, the alkali metal (R) of the alkali oxide (R2O) contains Na, Li, K and the like.

[0047] After mixing the raw material powder of alkali oxide (R2O), boron trioxide (B2O3) and silicon dioxide (SiO2), it is put into a platinum crucible and the platinum crucible is heated in an electric furnace at 1300 °C for 2 hours to melt the raw material powder, and the molten solution is poured into a graphite mold made of graphite with a hole with a diameter of 12 mm and cooled to prepare a rod-shaped alkali borosilicate glass with a diameter of 12 mm.

[0048] The process of pouring a molten solution at a high temperature of 1300 °C into a narrow 12 mm diameter hole in a graphite mold is highly hazardous. To reduce this risk, the glass formation step S10 can consist of a primary glass formation step S11, a pulverization step S13, and a secondary glass formation step S15.

[0049] In the primary glass forming step S11, the raw material powders of an alkali oxide (R2O), boron trioxide (B2O3) and silicon dioxide (SiO2) are mixed, placed in a platinum crucible and melted by heating at 1300 °C in an electric furnace for 2 hours, and then cast into a stainless steel plate and quenched to produce an alkali borosilicate glass.

[0050] In the pulverization step S13, the alkali borosilicate glass produced by the primary glass forming step S11 is pulverized into a glass powder having a size in the range of 1 to 3 mm.

[0051] In the secondary glass forming step S15, the pulverized glass powder is filled into a graphite mold having a hole with a diameter of 12 mm, and the graphite mold is heated in an electric furnace at 1000 °C to remelt the glass powder to remove air bubbles and cooled to produce a rod-shaped alkali borosilicate glass.

[0052] When making glass from the raw material powder, a high temperature of 1300 °C or higher is required, but once the glass is made, the pulverized glass powder melts sufficiently even at 1000 °C and enters a molten state without bubbles.

[0053] In processing step S20, the alkali borosilicate glass produced in glass formation step S10 is processed into a shape that is easy to mount on a gas sensor. Generally, the processed shape is a thin disc and is processed into a circular or polygonal shape.

[0054] A glass sheet with a thickness of 1 mm is prepared by cutting the rod-shaped alkali borosilicate glass produced in the glass forming step S10.

[0055] In the phase separation step S30, the glass sheet is heat-treated for 8 hours at 550 °C, which is the glass transition temperature of the alkali oxide (R2O), boron trioxide (B2O3) and silicon dioxide (Si2O), to form a separate alkali-boron phase (R2O-B2O3 phase) and silicon dioxide phase (SiO2 phase).

[0056] In the micropore generation step S40, the phase-separated glass sheet is heat-treated or acid-treated to elute the phase-separated boron trioxide (B2O3) from the glass sheet, thereby forming micropores.

[0057] As a heat treatment process, the glass sheet can be hydrothermally treated in a water bath at 95 °C for 3 hours and then dried at 110 °C for 1 hour.

[0058] When the glass sheet is heat-treated or acid-treated in this way, most of the alkali-boron phase (R2O-B2O3 phase) is eluted, leaving only about 2% to 3%.

[0059] By eluting such an alkali-boron phase (R2O-B2O3 phase), micropores are formed. The micropores have a diameter in the range of 10 Å and a pore volume of 30% or more. The micropores are open on both sides, and flammable gases can pass through these micropores. However, siloxanes or silicones larger than this size cannot pass through.

[0060] Fig. 2 is a view intuitively showing a manufacturing method of a porous glass filter according to the present disclosure.

[0061] [A] of Fig. 2 is a cross-sectional view of the alkali borosilicate glass 10 produced by the glass-forming step S10, and [B] is a cross-sectional view of the alkali borosilicate glass phase separated into the alkali boron phase 11 and the silicon dioxide phase 13 by the phase-separation step S30. [C] is a cross-sectional view of the alkali borosilicate glass subjected to phase separation on the silicon dioxide 13, and [C] is a cross-sectional view of the porous glass filter in which pores 15 were formed by eluting the phase-separated alkali 11 through the micropore-forming step S40.

[0062] The following [Table 1] refers to the composition and weight ratio of the porous glass filter according to the present disclosure using sodium (Na) as an alkali metal. [Table 1] Symbol Na2O (%) B2O3 (%) SiO2 (%) Al2O3 (%) B 35 You 55 10 35 55 0 B 40 You 50 10 40 50 0 B 45 You 45 10 45 45 0 B 50 You 40 10 50 40 0 B 44 To 45 Al5 10 45 45 7,5 B 50 Yes 50 A5 10 50 40 7,5

[0063] Six kinds of porous glass filters having a disc structure with a thickness of 1 mm were prepared for the composition having a weight ratio as shown in Table 1 above through a glass forming step S10, a processing step S20, a phase separation step S30, and a micropore forming step S40.

[0064] The produced porous glass filter is placed on the gas sensor and the gas sensor with the porous glass filter and the gas sensor without a filter are placed in an environment with a gas mixture containing 2.5% CH4 and 25 ppm HMDS and the sensitivity change with respect to methane CH4 was measured using the method described in Fig. 3 shown measuring circuit. In Fig. 3, 'S' is a sensing element, 'C' is a compensating element, 'Vin' is an input voltage and 'Vout' is an output voltage indicating the sensor sensitivity.

[0065] Fig. 4 shows the sensitivity change according to the methane concentration and Fig. Figure 5 shows the sensitivity change over time.

[0066] As in Fig. As shown in Figure 4, the rate of change in sensitivity according to methane concentration is maintained constant in the gas sensor without a filter and in the gas sensor equipped with each type of filter.

[0067] However, as in Fig. 5, the rate of change in sensitivity change with time is constant for the gas sensor equipped with each type of filter, and the sensitivity gradually decreases with time, but for the gas sensor not equipped with the filter, the rate of change is rapidly increased for the gas sensor without the filter, and after a predetermined time has elapsed, the sensitivity has decreased to a level at which gas detection is meaningless.

[0068] The following [Table 2] refers to the composition and weight ratio of the porous glass filter according to the present disclosure using lithium (Li) as an alkali metal.

[0069] Because the Li2O type has a wider phase separation range than the Na2O type and a lower glass transition temperature, the pore size becomes larger when preparing the porous glass. Therefore, 7.5% to 10% Al2O3 is added to suppress phase separation and reduce the pore size. [Table 2] Symbol Li2O (%) B2O3 (%) SiO2 (%) Al2O3 (%) Yeah 55 To the 7.5 10 35 55 7,5 Yeah 50 To the 7.5 10 40 50 7,5 Yeah 45 To the 10 10 45 45 10 Yeah 40 To the 10 10 50 40 10

[0070] After mixing the raw material powder with the composition shown in Table 2, the mixture was melted and quenched at 1300 °C to produce glass. After pulverization, the powdered glass was added to a graphite mold, melted at 1000 °C, cooled from 1000 °C, the glass rod was cut to a thickness of 1 mm, heat-treated at 480 °C for 10 hours, and the Li2O-B2O3 phase was dissolved at 95 °C for 3 hours to prepare a porous glass filter.

[0071] The prepared porous glass filter is placed on the gas sensor and the gas sensor with the porous glass filter and the gas sensor without a filter are placed in an environment with a gas mixture containing 2.5% CH4 and 25 ppm HMDS and the sensitivity change with respect to methane CH4 was measured using the method described in Fig. 3 shown measuring circuit.

[0072] Fig.Figure 6 shows the sensitivity change over time. For the gas sensor equipped with each type of filter, the rate of change is fairly constant, and the sensitivity gradually decreases over time. However, for the gas sensor without a filter, the rate of change increases rapidly, and after a specified time has elapsed, the sensitivity decreases to a level where gas detection is meaningless.

[0073] In the above description of the present disclosure with reference to the accompanying drawings, a porous glass filter having a specific shape, structure, and procedure, and a method for manufacturing the same, have been described. However, the present disclosure is susceptible to various modifications and changes by those skilled in the art. Such changes should be considered as falling within the scope of the present disclosure.

Claims

[1] A method of manufacturing a porous glass filter, the method comprising: Preparation of an alkali borosilicate glass by melting and cooling an alkali oxide (R2O), boron trioxide (B2O3) and silicon dioxide (SiO2); Heat-treating the alkali borosilicate glass at a glass transition temperature to phase separate the alkali borosilicate glass into an alkali borosilicate phase (R2O-B2O3) and a silicon dioxide phase (SiO2 phase); Heat-treating or acid-treating the phase-separated alkali borosilicate glass that has undergone phase separation to dissolve the alkali-boron phase (R2O-B2O3 phase), thereby creating micropores, wherein the processing of the alkali borosilicate glass comprises: Melting and cooling the alkali oxide (R2O), boron trioxide (B2O3) and silicon dioxide (SiO2) to produce a primary glass; Pulverizing the primary glass produced by processing the alkali borosilicate glass; and Melting the powdered primary glass in a graphite mold to remove air bubbles and then cooling the molten glass to produce the alkali borosilicate glass as a secondary glass, wherein the alkali borosilicate glass comprises 5 to 10 wt% of the alkali oxide (R2O), 35 to 50 wt% of boron trioxide (B2O3) and 40 to 55 wt% of silicon dioxide (SiO2).

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