Method for producing silica glass body and heating device

Abstract

This method for producing a silica glass body is provided with: a step for preheating a porous silica glass body; and placing the preheated porous silica glass body in a resonator and heating the porous silica glass body with microwaves, the resonator resonating the microwaves having a frequency band of 1 GHz to 30 GHz (inclusive). An additive other than silicon and oxygen is added to at least a portion of the porous silica glass body. In the preheating step, the porous silica glass body is preheated so as to reach or exceed the glass transition temperature of the added portion of the porous silica glass to which the additive is added. In the step of heating with microwaves, the porous silica glass to which the additive has been added is heated with microwaves.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a silica glass body and a heating device.

[0002] This application claims the benefit of priority based on Japanese Application No. 2022-163737 filed on October 12, 2022, and all the contents described in the above Japanese Application are incorporated herein by reference. Background Art

[0003] Patent Document 1, Patent Document 2, Non-Patent Document 1 and Non-Patent Document 2 disclose methods of preheating a glass tube by flame heating and then heating it in a microwave resonator. Patent Document 3, Patent Document 4, Patent Document 5 and Patent Document 6 disclose methods of preheating a glass tube by microwave plasma and then heating it by microwave. Patent Document 7 and Patent Document 8 disclose methods of heating a glass soot body or an optical fiber by microwave.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 61-063535

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 62-113732

[0008] Patent Document 3: Japanese Patent Application Laid-Open No. 01-183432

[0009] Patent Document 4: Japanese Patent Application Laid-Open No. 01-183436

[0010] Patent Document 5: Japanese Patent Application Laid-Open No. 04-114926

[0011] Patent Document 6: Japanese Patent Application No. 2004-043224

[0012] Patent Document 7: Japanese Patent Application Laid-Open No. 01-183435

[0013] Patent Document 8: Japanese Patent Application Publication No. 2005-145735

[0014] Non-patent literature

[0015] Non-patent document 1: YNGVE HASSLER et al., "A Homogeneous Heating Technique in Preform Manufacturing", Journal of Lightwave Technology, Vol. 4, No. 10, p1567-1570, 1986

[0016] Non-patent document 2: Y.HASSLER and L.JOHANSEN, "MICROWAVE HEATING OF FUSEDQUARTZ TO HIGH TEMPERATURES IN THE FABRICATION PROCESS OF OPTICAL FIBERS", Material Research Soc.Symp.Proc.Vol.124, p273-278, 1988 Summary of the invention

[0017] The method for manufacturing a silica glass body according to one embodiment of the present disclosure comprises the following steps: preheating a porous silica glass body; placing the preheated porous silica glass body in a resonator and heating the porous silica glass body with microwaves, wherein the resonator resonates microwaves having a frequency band of 1 GHz or more and 30 GHz or less. Additives other than silicon and oxygen are added to at least a portion of the porous silica glass body. In the preheating step, the porous silica glass body is preheated to a temperature above the glass transition temperature of the portion of the porous silica glass to which the additive is added. In the heating step with microwaves, the porous silica glass to which the additive is added is heated with microwaves. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram showing an example of a heating device for heating a porous silica glass body.

[0019] Figure 2 This is a schematic diagram showing another example of a heating device for heating a porous silica glass body.

[0020] Figure 3 This is a schematic diagram showing an example of an apparatus for measuring absorption of microwaves in a porous silica glass body.

[0021] Figure 4 It is shown that the accompanying Figure 3 The graph shows the relationship between the frequency of the glass sample and the presence or absence of the measuring device.

[0022] Figure 5 This is a graph showing changes in microwave absorption for each added amount when a halogen element (fluorine) is added to a silica glass body.

[0023] Figure 6 This is a graph showing changes in microwave absorption for each addition amount when an oxide (germanium dioxide) is added to a silica glass body.

[0024] Figure 7 The following is an example showing changes in microwave absorption for each added amount when an alkali metal element (potassium) is added to a silica glass body. DETAILED DESCRIPTION

[0025] [Technical Problems to be Solved by the Present Disclosure]

[0026] In the methods described in Patent Document 1 and the like, microwave heating is performed after preheating the glass tube. However, in these methods, since the glass tube absorbs microwaves, the glass tube needs to be heated to, for example, about 1500° C. in preheating. Thus, in the conventional methods, a lot of energy is required for heating, and it is desired to improve energy efficiency.

[0027] [Effects of the present disclosure]

[0028] According to the present disclosure, it is possible to reduce heating energy in the manufacture of a silica glass body.

[0029] [Description of Embodiments of the Present Disclosure]

[0030] First, the contents of the embodiments of the present disclosure are listed and described.

[0031] [1] A method for manufacturing a silica glass body according to an embodiment of the present disclosure comprises the following steps: preheating a porous silica glass body; placing the preheated porous silica glass body in a resonator and heating the porous silica glass body with microwaves, wherein the resonator resonates microwaves having a frequency band of greater than 1 GHz and less than 30 GHz. Additives other than silicon and oxygen are added to at least a portion of the porous silica glass body. In the preheating step, the porous silica glass body is preheated to a temperature above the glass transition temperature of the portion of the porous silica glass to which the additive is added. In the microwave heating step, the porous silica glass to which the additive is added is heated with microwaves.

[0032] According to the knowledge of the inventors, by adding additives to a porous silica glass body, the temperature at which the degree of microwave absorption by the porous silica glass body begins to increase changes and decreases. It is believed that the reason is that by adding additives other than silicon and oxygen (various elements, etc.), the viscosity of the silica glass is reduced and becomes easy to flow, thereby promoting the absorption of microwaves. In addition, the microwave absorption effect caused by polarization caused by the combination of different types of elements and the polarization caused by silicon (Si) bonding defects (SiO:, Si:, etc.) is also considered to be the cause. Therefore, in the method for manufacturing the silica glass body, the porous silica glass body is preheated, and the porous silica glass body to which additives other than silicon and oxygen are added is heated with microwaves. Therefore, even if the temperature at which the porous silica glass is preheated is lower than before, since it can be heated with subsequent microwaves, the heating energy can be reduced. In addition, in the method for manufacturing the silica glass body, since the porous silica glass is heated by heating the temperature by absorbing the self-heating generated by the microwaves, the entire furnace does not need to be heated. Therefore, according to this manufacturing method, the heating energy can be further reduced and the energy efficiency can be improved. It should be noted that even when the additive is added to part of the porous silica glass instead of the whole, the heating area is expanded from the added part due to heat transfer in the silica glass body, so even if the additive is not added to the whole of the porous silica glass body, it is possible to heat in the same manner as when the additive is added to the whole of the porous silica glass body.

[0033] [2] In the method for manufacturing a silica glass body of [1] above, the additive may be a halogen element. In this case, the glass network formed by Si-O is broken by the pre-addition of the halogen element, and the viscosity of the glass is reduced. As a result, the viscous flow of the silica glass causes a decrease in the microwave absorption starting temperature. Furthermore, the expansion of the far-infrared absorption of the Si-X (X: halogen (F, Cl, Br, I)) combination may also contribute to the absorption characteristics in the microwave region.

[0034] [3] In the method for manufacturing a silica glass body of [2], a halogen element may be added as an additive to the porous silica glass body during the preheating step. In this case, since the halogen element is added to the porous silica glass body by utilizing the heat during the preheating, it is not necessary to add the halogen to the porous silica glass body in advance, and the microwave absorption effect is brought about in the glass heating process, so that the glass manufacturing process can be made more efficient.

[0035] [4] In the method for producing a silica glass body of [2] or [3], in the preheating step and the microwave heating step, a halogen compound gas may be supplied into a furnace core tube including a resonator, thereby adding a halogen element as an additive to the porous silica glass body. In this case, since the halogen is added to the porous silica glass body using the compound gas, the method of adding can be simplified.

[0036] [5] In the method for producing a silica glass body of [1], the additive may be an oxide of an element selected from the group consisting of germanium, aluminum, boron, phosphorus, and titanium. As a result, the viscosity of the glass is reduced. In addition, the viscous flow of the silica glass produces an effect of reducing the microwave absorption starting temperature. Furthermore, these oxides are prone to have combined defects, and the expansion of far-infrared absorption caused by the polarization of the defects may also contribute to the absorption characteristics in the microwave region.

[0037] [6] In the method for producing a silica glass body of [1], an oxide of an element selected from the group consisting of germanium, aluminum, boron, phosphorus, and titanium and a halogen element may be added as an additive to the porous silica glass body in the preheating step. In this case, the microwave absorption starting temperature can be further lowered by superimposing the microwave absorption effects brought about by the halogen element and the oxide.

[0038] [7] In the method for producing a silica glass body of [1], the additive may be at least one alkali element selected from alkali metals and alkaline earth metals. In this case, the viscosity can be reduced by adding the alkali element, and the polarization in the microwave band can be facilitated by the isolated ionization of the alkali element in the glass.

[0039] [8] In the method for producing a silica glass body of [1], at least one of the halogen elements and at least one of the alkali metals and alkaline earth metals may be added as additives to the porous silica glass body in the preheating step. In this case, the microwave absorption starting temperature can be further lowered by superimposing the microwave absorption effects of the halogen elements and the alkali elements.

[0040] [9] In the method for producing a silica glass body according to any one of [1] to [8], the glass transition temperature may be 700° C. or higher and lower than 1100° C. In this case, the temperature during preheating can be lower than that in the past, and the heating energy can be reduced more reliably.

[0041]

[10] The method for producing a silica glass body according to any one of [1] to [9] may further include a step of adding an additive to the porous silica glass body before the preheating step. In this case, the additive can be added to the porous silica glass more reliably.

[0042]

[11] A heating device according to one embodiment of the present disclosure is a heating device used in the method for producing a silica glass body according to any one of [1] to

[10] . The heating device comprises: a furnace core tube capable of accommodating a porous silica glass body; a preheating mechanism configured to preheat the porous silica glass body; and a resonant heating mechanism configured to heat the porous silica glass body preheated by the preheating mechanism by resonating microwaves. According to this device, as described above, the heating energy can be reduced.

[0043]

[12] The heating device of

[11] may further include a gas introduction portion capable of introducing a gas containing an additive into the furnace core tube. In this case, the additive can be more reliably added to the porous silica glass in the heating device.

[0044]

[13] In the heating device of

[11] or

[12] , the preheating mechanism and the resonance heating mechanism may be arranged in sequence along the direction in which the porous silica glass body moves in the furnace core tube, thereby enabling the preheated porous silica glass body to be smoothly transferred to microwave heating.

[0045]

[14] In the heating device of any one of

[11] to

[13] above, the preheating mechanism may be configured to heat the porous silica glass body at a temperature of 700° C. or higher and less than 1100° C. In this case, the heating temperature in the preheating mechanism can be lowered compared to the conventional method, and the heating energy can be reduced more reliably. In addition, the range of choices of the heating method and the material of the heater used for resistance heating is expanded, and a more economical option can be selected.

[0046] [Details of the embodiments of the present disclosure]

[0047] Hereinafter, with reference to the accompanying drawings, a specific example of a method for manufacturing a silica glass body and a heating device according to an embodiment of the present disclosure is described. In the following description, the same reference numerals are used for the same elements or elements having the same functions, and repeated descriptions are omitted. It should be noted that the present invention is not limited to these examples, but is shown by the claims, and is intended to include all changes within the meaning and scope equivalent to the claims.

[0048] First, refer to Figure 1 , a heating device for manufacturing a silica glass body is described. Figure 1Schematic diagram showing an example of a heating device for heating a porous silica glass body. Figure 1 As shown, the heating device 1 includes a furnace core tube 10 , a resistance heating heater 20 (preheating mechanism), a resonance heating mechanism 30 , and a gas introduction unit 40 .

[0049] The furnace core tube 10 is a component for accommodating the porous silica glass body P inside and heating it, and is, for example, cylindrical in shape. From the perspective of suppressing deformation during heating and transmitting microwaves, the furnace core tube 10 may be made of, for example, high-purity alumina (Al 2 O 3 ) or low OH silica glass, etc. A rod not shown in the figure is provided on the heating device 1. The porous silica glass body P supported by the seed rod 11 is connected to the rod and inserted into the furnace core tube 10 from the top of the furnace core tube 10. The rod can be moved along the length direction of the furnace core tube 10, and can also rotate around the central axis. The porous silica glass body P held on the rod can move from top to bottom, or can also reciprocate along the length direction of the furnace core tube 10, so that it is heated by the resonant heating mechanism 30 after being heated by the resistance heating heater 20. It should be noted that since the gas is introduced from the gas inlet 40, the furnace core tube 10 is made airtight.

[0050] The resistance heating heater 20 is a preheating mechanism for preheating the porous silica glass body P. The resistance heating heater 20 is arranged so as to surround the outer periphery of the furnace core tube 10 and is arranged at a position further upstream than the resonance heating mechanism 30 for performing the main heating ( Figure 1 , which is above the resonant heating mechanism 30). In the method for manufacturing a silica glass body according to the present embodiment, the resistance heating heater 20 can suppress the heating temperature to be lower than the conventional temperature (e.g., 1500°C), so it can be set to heat the porous silica glass body P at a temperature of 700°C or higher and less than 1100°C, for example. The set heating temperature is a temperature above the glass transition temperature Tg of the added portion obtained by adding an additive (e.g., fluorine as an alkyl halide element) to the porous silica glass body P described below, and is adjusted according to the type and amount of the additive. It should be noted that various conventional resistance heaters can be used as the resistance heating heater 20, so a detailed description is omitted.

[0051] The resonant heating mechanism 30 includes a microwave generator 31, a waveguide 32, and a resonator 33. The microwave generator 31 is a device that includes a magnetron and generates microwaves having a frequency band of 1 GHz or more and 30 GHz or less. The microwave generator 31 is configured to generate microwaves in a frequency band of 2.45 GHz, 10 GHz, or 24 GHz, for example. The microwave generator 31 is connected to one end of the waveguide 32, and introduces microwaves of a predetermined frequency into the waveguide 32. The waveguide 32 is composed of a conductive material including a metal such as stainless steel (SUS) or copper, for example. The resonator 33 is connected to the other end of the waveguide 32. The microwaves generated by the microwave generator 31 are introduced into the resonator 33 through the waveguide 32.

[0052] The resonator 33 of the resonant heating mechanism 30 is in the shape of a hollow cylinder. The resonator 33 is arranged so as to surround the outer periphery of the furnace core tube 10 and is located at a position ( Figure 1 The resonator 33 is configured separately from the resistance heating heater 20 in the middle. The resonator 33 can also be composed of a heat-resistant metal or a conductive carbon material. The resonator 33 can also adopt a structure that is not easily changed by high-temperature radiation from the heated object (for example, water cooling). The resonator 33 limits the introduced microwaves within the resonator 33 to heat the porous silica glass body P located in the resonator 33. The structure of the resonator 33 can adjust the power distribution of the microwaves to match the porous silica glass body P as the object of heat treatment. As the distribution within the resonator 33, the cavity structure can also be adjusted to a structure with an LP0n (HE1n) mode having a power peak in the central part and an LPm1 (TEm+11, etc.) mode having a peak in the peripheral part. The resonator 33 can also be adjusted to a mixed existence of multiple modes. In the resonator 33, it is also possible to have a structure in which the power of the microwaves in the furnace core tube 10 is reduced. As a result, the effect of suppressing the heating of the furnace core tube 10 can be expected.

[0053] The gas introduction part 40 is a part for introducing various gases into the furnace core tube 10. Inert gas (for example, nitrogen (N 2 ) or helium (He)), halogen-based gas (gas containing halogen elements), gas containing oxidizing compounds, vapor containing alkali metals or alkaline earth metals, etc. The additives contained in the introduced gas, etc. are added to the porous silica glass body P. It should be noted that the gas introduced into the furnace core tube 10 from the gas introduction part 40 is discharged to the outside of the furnace core tube 10 through an exhaust system (not shown) when the addition to the porous silica glass body P is completed.

[0054] Examples of halogen elements contained in the halogen-based gas include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). Of these, fluorine or chlorine is particularly added. This causes the glass network formed by Si-O to break, thereby reducing the viscosity of the glass. As such a halogen-based gas, for example, chlorine (Cl) can be used. 2 ), silicon tetrachloride gas (SiCl 4 ), Silicon tetrafluoride gas (SiF 4 ), carbon tetrafluoride gas (CF 4 )wait.

[0055] Examples of the oxidizing compound contained in the oxidizing compound gas include germanium dioxide (GeO 2 ), boron oxide (B 2 O 3 ), aluminum oxide (Al 2 O 3 ), phosphorus pentoxide (P 2 O 5 ). Among them, GeO 2 Therefore, it can be expected that GeO 2 Microwave absorption effect caused by oxygen vacancies.

[0056] As alkali metals, sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs) can be exemplified. As alkaline earth metals, magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba) can be exemplified. Among alkali metals and alkaline earth metals, alkali metals are preferred. When alkali metals are used, a significant reduction in viscosity can be expected, and in particular, even when added in a low concentration range of less than 1 mol%, a reduction in the microwave absorption starting temperature due to the reduction in viscosity can be expected.

[0057] Here, refer to Figure 2 Modifications of the heating device 1 will be described. Figure 2 FIG. 1 is a schematic diagram showing another example of a heating device for heating a porous silica glass body. Figure 2 As shown in FIG. 1 , the heating device 1A includes a furnace core tube 10, an infrared heater 20A (preheating mechanism), a resonance heating mechanism 30, and a gas introduction unit 40. The heating device 1A according to the modified example has the same Figure 1The heating device 1 shown in the figure has the same structure, but is different in that the preheating mechanism is an infrared heater that heats by irradiating infrared rays. Such a heating device 1A can also be used to manufacture the silica glass body involved in this embodiment. It should be noted that the preheating mechanism used in the heating devices 1 and 1A is not limited to the above-mentioned resistance heating heater 20 or infrared heater 20A, and an induction resistance furnace or a movable microwave absorbing heating element (such as a Si / SiC resistance element) can also be used. They can be used for preheating.

[0058] Next, a method for producing a silica glass body using the above-mentioned heating device 1 will be described. The same applies to the case of using the heating device 1A. The method for producing a silica glass body according to the present embodiment includes the following steps (a), (b), and (c).

[0059] (a) Step of preparing porous silica glass body P

[0060] (b) Step of preheating the porous silica glass body P

[0061] (c) Step of Mainly Heating the Porous Silica Glass Body P with Microwaves

[0062] [Step (a)]

[0063] In the step (a) of preparing the porous silica glass body P, the porous silica glass body P is prepared by a known method such as VAD (Vapor-phase Axial Deposition) or OVD (Outside Vapor Deposition). The porous silica glass body P is, for example, a silicon compound gas (SiCl 4 The structure obtained by depositing glass particles with a particle size of 0.1μm to 1μm on a specified target through flame hydrolysis reaction and oxidation reaction of porous silica glass (such as siloxane, etc.) is also generally called soot. In step (a) of preparing the porous silica glass body P, additives other than silicon and oxygen (such as fluorine as a halogen element, germanium oxide or phosphorus pentoxide as an oxide other than silicic acid) may be added to the porous silica glass body or a part thereof to be described below. The method of adding additives in the stage of preparing the porous silica glass body P can use the method of mixing compound gas and silica glass raw material gas when synthesizing the above-mentioned porous silica glass body, so the detailed description is omitted.

[0064] [Step (b)]

[0065] In the step (b) of preheating the porous silica glass body P, first, the porous silica glass body P formed on the lower part of the seed rod 11 prepared in the step (a) is installed on the Figure 1 The heating device 1 is placed on a rod of the heating device 1 shown in the figure and arranged in the furnace core tube 10. Then, while introducing a predetermined gas from the gas introduction part 40, the porous silica glass body P arranged in the furnace core tube 10 is heated to a predetermined temperature by the resistance heating heater 20. The temperature here refers to the surface temperature of the porous silica glass body P. The introduced gas is an inert gas (e.g., nitrogen (N 2 ) or helium (He)), halogen gas (gas containing halogen elements), gas containing oxidizing compounds, vapor containing alkali metals or alkaline earth metals, etc. The inert gas may contain halogen gas, gas containing oxidizing compounds, vapor of alkali metals, etc., or may contain two or more gases. As an example, it is also possible to add a predetermined amount of SiCl 4 or SiF 4 Nitrogen gas (a type of halogen gas) is introduced from the gas inlet portion 40 into the atmosphere in the furnace core tube 10 for preheating. By introducing the gas containing the additive while heating it in this way, a predetermined additive (for example, chlorine, fluorine, germanium dioxide or potassium) is added to the porous silica glass body P. In addition, the temperature during preheating in step (b) is, for example, 700°C or more and less than 1100°C, which is set to a temperature lower than the previous heating temperature of 1500°C. The heating temperature is a temperature above the glass transition temperature Tg of the added part (the entire porous silica glass body P or a part thereof) obtained by adding the additive (for example, chlorine or fluorine as a halogen element) to the porous silica glass body P. The heating temperature is adjusted according to the type and amount of the additive. Details of the additive will be described below.

[0066] [Step (c)]

[0067] In the step (c) of formally heating the porous silica glass body P with microwaves, the porous silica glass body P with the specified additives added thereto is kept heated by preheating, and formal heating is performed by a resonant heating mechanism 30 using microwaves. In the porous silica glass body P with the additives added thereto, as will be described below, the viscosity decreases and becomes easy to flow, and accordingly, even if the temperature of the glass body is lower than before, the absorption of microwaves will be promoted. In the step (c), the microwaves used by the resonant heating mechanism 30 are microwaves having a frequency band of 1 GHz or more and 30 GHz or less, for example, microwaves of 2.45 GHz band, 10 GHz band or 24 GHz band. In addition, the maximum output of the microwaves in the resonant heating mechanism 30 is, for example, 1 kW or more and 30 kW or less. As an example, the maximum output of the microwaves is 10 kW. In step (c), specifically, microwaves are introduced from a microwave generator 31 into a 2.45 GHz cavity resonator 33 having a maximum microwave output of 10 kW, for example, in an atmosphere filled with (100%) helium, with respect to the porous silica glass body P to which a predetermined additive has been added and which has been preheated. Then, the surface temperature of the porous silica glass body P is detected by a thermometer (not shown) while the microwave output is adjusted. When the surface temperature of the porous silica glass body P reaches 1450° C., the porous silica glass body P is moved at a predetermined speed (at a speed of 100° C.). Figure 1 The silica glass body is produced by the above process.

[0068] Here, by adding a halogen element, an oxidizing compound, an alkali metal, an alkaline earth metal, etc. to the porous silica glass body P in step (b) or step (a), the heating temperature in the preheating (step (b)) before the microwave heating (main heating) in step (c) can be reduced. The reason for this is shown in the following formula (1) and Figures 3 to 7 Provide explanation. Figure 3 This is a schematic diagram showing an example of an apparatus for measuring absorption of microwaves in a porous silica glass body. Figure 4 It is shown that the accompanying Figure 3 The graph shows the relationship between the frequency of the glass sample and the presence or absence of the measuring device. Figure 5 This is a graph showing changes in microwave absorption for each added amount when a halogen element (fluorine) is added to a silica glass body. Figure 6 This is a graph showing changes in microwave absorption for each addition amount when an oxide (germanium dioxide) is added to a silica glass body. Figure 7 The following is an example showing changes in microwave absorption for each added amount when an alkali metal element (potassium) is added to a silica glass body.

[0069] Microwave-based heating is a method of heating by absorbing the microwave band caused by the flow of the material through the electrode. The response of electromagnetic waves to the material can be expressed by the propagation speed and absorption coefficient at a specified frequency in the material. The index representing the propagation speed of the former is the relative dielectric constant ε', and the index representing the absorption coefficient of the latter is the relative dielectric loss factor ε". As a loss index, the dielectric loss tangent tanσ≈ε" / ε', which represents the response delay of the electromagnetic wave, is usually used.

[0070] The microwave energy absorption rate of a substance is expressed by, for example, the following formula (1).

[0071] [Mathematical formula 1]

[0072] P=πfεtanδ∫E 2 dv···(1)

[0073] Here, P is the absorbed energy, f is the frequency, ε is the relative dielectric constant, tanσ is the dielectric loss tangent, and E is the electric field strength.

[0074] According to the above formula (1), since the absorption of a substance is proportional to the frequency and dielectric loss tangent, it is effective to increase tanσ and frequency in order to efficiently absorb microwaves. However, for electromagnetic waves in the microwave band between 0.1 GHz and 30 GHz, the tanσ of silica glass at room temperature is 1×10 -4 The absorption efficiency of silica glass is relatively small. Therefore, silica glass cannot be efficiently heated by microwaves. For the technical problem of low absorption efficiency, for example, in Patent Document 1, microwave heating is achieved by applying preheating to microwave heating of silica glass. However, the current situation is that in this existing method, if the preheating does not heat the glass body to about 1500°C, microwave absorption will not occur.

[0075] To this end, the inventors of the present invention use Figure 3 The test device 50 shown in the figure measured the temperature dependence of microwave band absorption of glass G, and found that the temperature range in which microwave absorption begins to increase varies depending on the additive composition. It should be noted that the test device 50 includes a microwave oscillator 51, a waveguide 52, a resonator 53, and an output monitor 54, thereby being able to monitor the frequency dependence of the resonator output. In addition, Figure 4 Graphs 1 and 2 show changes in the resonance frequency when the glass G as a sample is placed in the test device 50 and when the glass G is not placed.

[0076] The following summarizes the changes brought about by the types of elements added in this experiment. In this experiment, the relative dielectric constant (ε') is calculated based on the change in the resonant frequency when a rod-shaped sample (glass G) heated to a specified temperature is inserted into the resonator 53 of the cavity, and the relative dielectric loss factor (ε") is calculated based on the change in the peak value. Then, the dielectric loss tangent (tan(σ) = ε" / ε') is derived from the relative dielectric constant (ε') and the relative dielectric loss factor (ε"). However, this value is not a quantitative value, but a relative value relative to the reference sample (low OH silica glass). The following will expand on the results centered on the temperature characteristics of tan(σ).

[0077] (0) Reference sample: Silica glass with low OH (less than 50 ppm) (impurity elements other than OH are within the detection limit of 10 ppm)

[0078] The reference sample is heated to about 1300°C and tan(σ) is calculated. Figures 5 to 7 As shown in FIG. 1 , the calculated tan(σ) is also less than 0.01 at around 1300°C.

[0079] (1) Samples with halogen added: Silica glass obtained by adding fluorine to the above-mentioned reference sample

[0080] like Figure 5 As shown in Figure 1, in this sample, the amount of fluorine added was changed to 0.5 mol%, 3.5 mol%, and 7 mol%, and the sample was heated to around 1300°C, and tan(σ) in the sample with each addition amount was calculated. The calculated tan(σ) began to increase to more than 0.01 in the range of 800°C to 1000°C. It is also estimated that tan(σ) of other halogen elements (such as chlorine) also began to increase to more than 0.01 in the range of 800°C to 1000°C.

[0081] (2) Samples with added oxides: Germanium dioxide (GeO) was added to the above-mentioned reference sample. 2 ) and the silica glass obtained

[0082] like Figure 6 As shown in Figure 1, in this sample, the amount of germanium dioxide added was changed to 5 mol%, 10 mol%, and 15 mol%, and the sample was heated to around 1300°C, and tan(σ) in the sample with each addition amount was calculated. The calculated tan(σ) began to increase to above 0.01 in the range of 800°C to 1000°C. For other oxides (such as B 2 O 3 、Al 2 O 3 , P 2 O 5It is also estimated that tan(σ) starts to increase to above 0.01 in the range of 800°C to 1000°C.

[0083] (3) Samples with added alkali metals: Silica glass obtained by adding potassium to the above-mentioned reference sample

[0084] like Figure 7 As shown in Figure 1, in this sample, the amount of potassium added was changed to 0.001 mol%, 0.005 mol%, and 0.1 mol%, and the sample was heated to around 1300°C, and tan(σ) in the sample with each addition amount was calculated. The calculated tan(σ) began to increase to more than 0.01 in the range of 700°C to 900°C. It is estimated that tan(σ) of other alkali metals (such as Na, Rb, Cs, etc.) or alkaline earth metals (Mg, Ca, Sr, Ba) also began to increase to more than 0.01 in the range of 700°C to 900°C.

[0085] Based on the above experimental results, it can be confirmed that SiO added to silica glass 2 Although the effects of additives other than the components vary, they all have the effect of shifting the temperature dependence of microwave absorption to the low temperature side. It can be seen from this that by introducing additives into the glass, the microwave absorption temperature can be lowered. In other words, it can be seen that the heating temperature in the preheating (the above-mentioned step (b)) before heating with microwaves can be lowered compared to the past. Moreover, it can be seen that even if preheating is performed at such a low temperature, self-heating will be generated due to the absorption of microwaves. By heating treatment under this self-heating, the porous silica glass body can be made transparent and vitrified even if the entire furnace is not heated, and it can be seen that the heating energy can be greatly reduced.

[0086] Thus, according to the knowledge of the inventors of the present invention, by adding additives to the porous silica glass body P, the temperature at which the degree of microwave absorption by the porous silica glass body P begins to increase is lowered. The reason is believed to be that by adding additives (various elements, etc.) other than silicon (Si) and oxygen (O), the viscosity of the silica glass is reduced and it becomes easy to flow, thereby promoting the absorption of microwaves. In addition, the microwave absorption effect caused by polarization caused by the combination of different types of elements and the polarization caused by silicon (Si) bonding defects (SiO:, Si:, etc.) is also considered to be the cause. In the method for manufacturing a silica glass body involved in the present embodiment, the porous silica glass body P is preheated, and the porous silica glass body P to which additives other than silicon and oxygen are added is heated by microwaves. Therefore, even if the temperature for preheating the porous silica glass is greatly reduced compared with the past (for example, about 1500°C), since it can be heated by microwaves later, the heating energy can be reduced. Moreover, in the method for manufacturing the silica glass body, since the porous silica glass body P is heated by absorbing the self-heating generated by the microwaves to increase the temperature, the entire furnace does not need to be heated. Therefore, according to the manufacturing method, the heating energy can be further reduced, and the energy efficiency can be greatly improved. It should be noted that even in the case where the additive is added to a part of the porous silica glass instead of the whole, the heating area is expanded from the added part due to the heat transfer in the silica glass body, so even if the additive is not added to the whole of the porous silica glass body, it can be heated in the same way as when the additive is added to the whole of the porous silica glass body.

[0087] In the method for manufacturing the silica glass body according to the present embodiment, the additive may be a halogen element. In this case, the glass network formed by Si-O is broken by the halogen element added in advance, and the viscosity of the glass is reduced. As a result, the microwave absorption starting temperature is reduced due to the viscous flow of the silica glass. Furthermore, the expansion of the far-infrared absorption of the Si-X (X: halogen (F, Cl, Br, I)) combination may also contribute to the absorption characteristics in the microwave region.

[0088] In the method for producing a silica glass body according to the present embodiment, a halogen element may be added as an additive to the porous silica glass body P in the preheating step (b). In this case, since the halogen element is added to the porous silica glass body P by utilizing the heat during preheating, it is not necessary to add the halogen to the porous silica glass body in advance, and the microwave absorption effect is introduced in the glass heating process, so that the glass manufacturing process can be made more efficient.

[0089] In the method for producing a silica glass body according to the present embodiment, in the preheating step (b) and the microwave heating step (c), a halogen compound gas may be supplied into the furnace core tube 10, thereby adding a halogen element as an additive to the porous silica glass body P. In this case, since the halogen is added to the porous silica glass body by using a compound gas, the method of adding can be simplified.

[0090] In the method for manufacturing the silica glass body according to the present embodiment, the additive may be an oxide of an element selected from the group consisting of germanium, aluminum, boron, phosphorus, and titanium. As a result, the viscosity of the glass is reduced. In addition, the effect of reducing the microwave absorption starting temperature caused by the viscous flow of the silica glass is produced. Furthermore, these oxides are prone to have combined defects, and the expansion of far-infrared absorption caused by the polarization of the defects may also contribute to the absorption characteristics in the microwave region.

[0091] In the method for producing a silica glass body according to the present embodiment, in the preheating step (b), an oxide of an element selected from the group consisting of germanium, aluminum, boron, phosphorus, and titanium and a halogen element may be added as an additive to the porous silica glass body. In this case, the microwave absorption starting temperature can be further reduced by superimposing the microwave absorption effects brought about by the halogen element and the oxide.

[0092] In the method for manufacturing the silica glass body according to the present embodiment, the additive may be at least one alkali element among alkali metals and alkaline earth metals. In this case, the viscosity can be reduced by adding the alkali element, and the polarization in the microwave band can be facilitated by the isolated ionization of the alkali element in the glass.

[0093] In the method for producing a silica glass body according to the present embodiment, at least one of the halogen elements and at least one of the alkali elements of the alkali metal and the alkaline earth metal may be added as an additive to the porous silica glass body in the preheating step (b). In this case, the microwave absorption starting temperature can be further reduced by superimposing the microwave absorption effects brought about by the halogen elements and the alkali elements.

[0094] In the method for producing a silica glass body according to the present embodiment, the glass transition temperature may be 700° C. or higher and lower than 1100° C. In this case, the temperature during preheating can be lowered compared to conventional methods, and the heating energy can be reduced more reliably.

[0095] The method for producing a silica glass body according to the present embodiment may further include a step of adding an additive to the porous silica glass body before the preheating step. In this case, the additive can be added to the porous silica glass more reliably.

[0096] The heating device 1, 1A according to the present embodiment is a heating device used in the method for producing the silica glass body. The heating device 1, 1A comprises: a furnace core tube 10 capable of accommodating the porous silica glass body P; a preheating mechanism (resistance heating heater 20, infrared heater 20A) configured to preheat the porous silica glass body P; and a resonant heating mechanism 30 configured to heat the porous silica glass body preheated by the preheating mechanism by resonating microwaves. According to this device, as described above, the heating energy can be reduced.

[0097] The heating apparatus 1, 1A according to the present embodiment further includes a gas introduction portion 40 capable of introducing a gas containing an additive into the furnace core tube 10. In this case, in the heating apparatus 1, 1A, the additive can be more reliably added to the porous silica glass.

[0098] In the heating apparatus 1, 1A according to the present embodiment, the preheating mechanism and the resonance heating mechanism 30 are sequentially arranged along the direction in which the porous silica glass body moves in the furnace core tube. Thus, the preheated porous silica glass body P can be smoothly transferred to microwave heating.

[0099] In the heating device 1, 1A according to the present embodiment, the preheating mechanism may be configured to heat the porous silica glass body at a temperature of 700°C or higher and less than 1100°C. In this case, the heating temperature in the preheating mechanism can be lowered compared to the conventional method, and the heating energy can be reduced more reliably. In addition, the range of choices of the heating method and the material of the heater used for resistance heating is expanded, and a more economical option can be selected.

[0100] Example

[0101] Hereinafter, the present disclosure will be described in further detail by way of examples, but the present invention is not limited to the following examples.

[0102] [Experimental Example 1]

[0103] As Experimental Example 1, first, as shown in the above step (a), a porous silica glass body containing silica glass was prepared by the VAD method. The outer diameter of the prepared porous silica glass body was 180 mm, and the relative density to the transparent glass was 0.15.

[0104] Next, prepare Figure 1The heating device 1 shown in the figure, as shown in the above step (b), accommodates the produced porous silica glass body in the furnace core tube 10. Then, the resistance heating heater 20 is heated to preheat the porous silica glass body to 950° C. During the preheating, a gas containing 2% by volume of SiCl2 in a nitrogen atmosphere is introduced from the gas inlet 40. 4 The gas was added to the entire porous silica glass body P. The addition rate of chlorine was 1.0 mol%.

[0105] Next, helium gas is introduced from the gas inlet 40 into the furnace core tube 10, and the furnace core tube 10 contains a porous silica glass body P in a state where chlorine is added and heated to about 950°C by preheating. As a result, the porous silica glass body P is in an atmosphere of 100% helium in the furnace core tube 10. In this state, the microwave generated by the microwave generator 31 is introduced into the resonator 33, and the porous silica glass body P is heated by the resonance heating mechanism 30. The maximum value of the microwave output in the resonance heating mechanism 30 is 10 kW, and the frequency band of the introduced microwave is 2.45 GHz. When the microwave is introduced, the resonance heating mechanism 30 monitors the surface temperature of the porous silica glass body P and adjusts the output of the introduced microwave so that the specified surface temperature is reached. When the surface temperature of the porous silica glass body P reaches 1450°C, the porous silica glass body P is moved (descended) at 10 mm / min in the resonator 33. The porous silica glass body P is transformed into transparent vitrification by microwave heating by the resonance heating mechanism 30. It should be noted that the microwave output at this time is in the range of 4 kW to 5 kW.

[0106] The chlorine concentration in the silica glass obtained by the above-mentioned experimental example 1 is 0.8 mol%. Through the above-mentioned manufacturing method, the silica glass is transparently vitrified in the entire length direction. In the case of making an equivalent glass body by a resistance heating method without microwave heating, the resistance heating output needs to be 22 kW to 24 kW. In contrast, according to the manufacturing method involved in this embodiment, the required energy is 1 / 4 to 1 / 6 of the previous heating output. In this way, it can be confirmed that according to the manufacturing method of this experimental example, even if the preheating temperature is lowered, microwaves can be used for heating treatment to improve energy efficiency.

[0107] [Experimental Example 2]

[0108] As Experimental Example 2, first, as shown in the above step (a), a VAD method was used to prepare a glass film containing silica glass and 5 mol % GeO 2 The porous silica glass body produced had an outer diameter of 140 mm and a relative density of 0.12 to the transparent glass.

[0109] Next, prepare Figure 1 The heating device 1 shown in the figure, as shown in the above step (b), accommodates the produced porous silica glass body in the furnace core tube 10. Then, the resistance heating heater 20 is heated to preheat the porous silica glass body to 950° C. During the preheating, a gas containing 5 volume % of Cl mixed in a nitrogen atmosphere is introduced from the gas inlet 40. 2 The gas was added to the entire porous silica glass body P. The addition rate of chlorine was 0.2 mol%.

[0110] Next, helium gas is introduced from the gas inlet 40 into the furnace core tube 10, and the furnace core tube 10 contains a porous silica glass body P in a state where chlorine is added and heated to about 950°C by preheating. As a result, the porous silica glass body P is in an atmosphere of 100% helium in the furnace core tube 10. In this state, the microwave generated by the microwave generator 31 is introduced into the resonator 33, and the porous silica glass body P is heated by the resonance heating mechanism 30. The maximum value of the microwave output in the resonance heating mechanism 30 is 10 kW, and the frequency band of the introduced microwave is 2.45 GHz. When the microwave is introduced, the resonance heating mechanism 30 monitors the surface temperature of the porous silica glass body P and adjusts the output of the introduced microwave so that the specified surface temperature is reached. When the surface temperature of the porous silica glass body P reaches 1450°C, the porous silica glass body P is moved (descended) at 10 mm / min in the resonator 33. The porous silica glass body P is transformed into transparent vitrification by microwave heating by the resonance heating mechanism 30. It should be noted that the microwave output at this time is in the range of 3 kW to 4 kW.

[0111] The chlorine concentration in the silica glass obtained by the above-mentioned Experimental Example 2 is 0.6 mol%. By the above-mentioned manufacturing method, the silica glass is transparently vitrified in the entire length direction. In the case of making an equivalent glass body by a resistance heating method without microwave heating, the resistance heating output needs to be 22 kW to 24 kW. In contrast, according to the manufacturing method involved in this embodiment, the required energy is 1 / 5 to 1 / 8 of the previous heating output. In this way, it can be confirmed that according to the manufacturing method of this experimental example, even if the preheating temperature is lowered, microwaves can be used for heating treatment to improve energy efficiency.

[0112] [Experimental Example 3]

[0113] As Experimental Example 3, first, as shown in the above step (a), a porous silica glass body containing silica glass was prepared by the VAD method. The outer diameter of the prepared porous silica glass body was 180 mm, and the relative density to the transparent glass was 0.15.

[0114] Next, prepare Figure 1 The heating device 1 shown in the figure, as shown in the above step (b), accommodates the produced porous silica glass body in the furnace core tube 10. Then, the resistance heating heater 20 is heated to preheat the porous silica glass body to 950° C. During the preheating, a gas containing 10% by volume of SiF mixed in a nitrogen atmosphere is introduced from the gas inlet 40. 4 The gas was added to add fluorine to the entire porous silica glass body P. The addition rate of fluorine was 1.0 mol%.

[0115] Next, nitrogen gas and 5 volume % SiF 4 The furnace core tube 10 contains a porous silica glass body P which is heated to about 950° C. by preheating and to which fluorine is added. Thus, the porous silica glass body P is in a nitrogen and SiF 4 In an atmosphere of a mixed gas. In this state, the microwaves generated by the microwave generating device 31 are introduced into the resonator 33, and the porous silica glass body P is heated by the resonant heating mechanism 30. The maximum value of the microwave output in the resonant heating mechanism 30 is 10 kW, and the frequency band of the introduced microwaves is 2.45 GHz. When the microwaves are introduced, the resonant heating mechanism 30 monitors the surface temperature of the porous silica glass body P, and adjusts the output of the introduced microwaves so that the specified surface temperature is reached. When the surface temperature of the porous silica glass body P reaches 1250°C, the porous silica glass body P is moved (descended) at 5 mm / min in the resonator 33. Through the microwave heating performed by the resonant heating mechanism 30, fluorine is further added to the porous silica glass body P. It should be noted that the microwave output at this time is in the range of 2 kW to 3 kW.

[0116] Furthermore, helium gas and 5 volume % SiF 4 The furnace core tube 10 contains a porous silica glass body P which is heated to about 950° C. by preheating and to which fluorine is added. Thus, the porous silica glass body P is in a state of helium and SiF 4atmosphere. In this state, the microwaves generated by the microwave generating device 31 are introduced into the resonator 33, and the porous silica glass body P is heated by the resonant heating mechanism 30. The maximum value of the microwave output in the resonant heating mechanism 30 is 10 kW, and the frequency band of the introduced microwaves is 2.45 GHz. When the microwaves are introduced, the resonant heating mechanism 30 monitors the surface temperature of the porous silica glass body P and adjusts the output of the introduced microwaves so that the specified surface temperature is reached. When the surface temperature of the porous silica glass body P reaches 1400°C, the porous silica glass body P is moved (descended) at 10 mm / min in the resonator 33. The porous silica glass body P is transparently vitrified by the microwave heating performed by the resonant heating mechanism 30. It should be noted that the microwave output at this time is in the range of 3 kW to 4 kW.

[0117] The fluorine concentration in the silica glass obtained by the above-mentioned Experimental Example 3 is 1.2 mol%. By the above-mentioned manufacturing method, the silica glass is transparently vitrified in the entire length direction. In the case of making an equivalent glass body by a resistance heating method without microwave heating, the resistance heating output needs to be 16 kW to 20 kW. In contrast, according to the manufacturing method involved in this embodiment, the required energy is 1 / 4 to 1 / 6 of the previous heating output. In this way, it can be confirmed that according to the manufacturing method of this experimental example, even if the preheating temperature is lowered, microwaves can be used for heating treatment to improve energy efficiency.

[0118] Description of Reference Numerals

[0119] 1. 1A heating device

[0120] 10 furnace core tube

[0121] 11 kinds of sticks

[0122] 20. Resistance Heating Heater

[0123] 20A infrared heater

[0124] 30 Resonance Heating Mechanism

[0125] 31. Microwave generating device

[0126] 32 Waveguide

[0127] 33 Resonator

[0128] 40 Gas inlet

[0129] 50 Test equipment

[0130] 51 Microwave Oscillator

[0131] 52 Waveguide

[0132] 53 Resonator

[0133] 54 Output Monitor

[0134] G Glass

[0135] P Porous silica glass.

Claims

1. A method for producing a silica glass body, comprising the following steps: preheating the porous silica glass body; and The preheated porous silica glass body is placed in a resonator, and the porous silica glass body is heated by microwaves, wherein the resonator resonates the microwaves, and the microwaves have a frequency band of 1 GHz or more and 30 GHz or less, An additive other than silicon and oxygen is added to at least a portion of the porous silica glass body. In the preheating step, the porous silica glass body is preheated to a temperature equal to or higher than the glass transition temperature of the portion of the porous silica glass to which the additive is added. In the step of heating with microwaves, the porous silica glass to which the additive is added is heated with the microwaves.

2. The method for producing a silica glass body according to claim 1, wherein: The additive is a halogen element.

3. The method for producing a silica glass body according to claim 2, wherein: In the preheating step, the halogen element is added as the additive to the porous silica glass body.

4. The method for producing a silica glass body according to claim 2, wherein: In the preheating step and the microwave heating step, the halogen compound gas is supplied into the furnace core tube including the resonator, thereby adding the halogen element as the additive to the porous silica glass body.

5. The method for producing a silica glass body according to claim 1, wherein: The additive is an oxide of an element selected from the group consisting of germanium, aluminum, boron, phosphorus, and titanium.

6. The method for producing a silica glass body according to claim 1, wherein: In the preheating step, oxides of elements selected from the group consisting of germanium, aluminum, boron, phosphorus, and titanium, and halogen elements are added as the additives to the porous silica glass body.

7. The method for producing a silica glass body according to claim 1, wherein: The additive is at least one alkali element selected from alkali metals and alkaline earth metals.

8. The method for producing a silica glass body according to claim 1, wherein: In the preheating step, at least one of halogen elements and at least one of alkali metals and alkaline earth metals are added as the additive to the porous silica glass body.

9. The method for producing a silica glass body according to any one of claims 1 to 8, wherein: The glass transition temperature is 700°C or higher and lower than 1100°C.

10. The method for producing a silica glass body according to any one of claims 1 to 8, wherein: The method for producing a silica glass body further comprises a step of adding the additive to the porous silica glass body before the preheating step.

11. A heating device for use in the method for producing a silica glass body according to any one of claims 1 to 8, the heating device comprising: A furnace core tube capable of accommodating the porous silica glass body; a preheating mechanism configured to preheat the porous silica glass body; and The resonance heating mechanism is configured to heat the porous silica glass body preheated by the preheating mechanism by causing microwaves to resonate.

12. The heating device according to claim 11, wherein: The heating device further includes a gas introduction portion capable of introducing the gas containing the additive into the furnace core tube.

13. The heating device according to claim 11, wherein: The preheating mechanism and the resonance heating mechanism are sequentially arranged along a direction in which the porous silica glass body moves in the furnace core tube.

14. The heating device according to claim 11, wherein The preheating mechanism is configured to heat the porous silica glass body at a temperature of 700° C. or higher and lower than 1100° C.

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