Composite silica glass material

Abstract

To provide a composite silica glass material that is resistant to breakage during fire processing or handling and has high reflectivity. [Solution] A composite silica glass material is provided, which is formed by bonding at least an opaque silica glass layer and at least a transparent silica glass layer, has a bonding interface between the opaque silica glass layer and the transparent silica glass layer, and has a birefringence of 20 to 4000 nm / cm at a wavelength of 520 nm. The density difference between the opaque silica glass layer and the transparent silica glass layer is 0.05 to 1.0 g / cm. 3 It is preferable that:

Description

[Technical Field]

[0001] The present invention relates to a composite silica glass material, and more particularly to a composite silica glass material that is resistant to breakage. [Background technology]

[0002] There is a known method for producing composite silica glass, which is a silica glass laminate, by stacking and heating silica glass plates of different or the same type. Conventional methods for producing composite silica glass include, for example, Patent Documents 1 to 4. However, the silica glass laminate produced by the known method has a problem of being weak and easily broken during handling, such as processing and cleaning. Demands for the performance of such composite silica glass have been increasing year by year, and a composite silica glass material that is resistant to breakage has been eagerly awaited. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 51-061522 [Patent Document 2] Patent Publication No. 63-201026 [Patent Document 3] Patent Publication No. 2004-067456 [Patent Document 4] Patent Publication No. 2004-091314 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a composite silica glass material that is resistant to breakage during fire processing or handling and has high reflectivity. [Means for solving the problem]

[0005] In order to solve the above problems, the composite silica glass material of the present invention is a composite silica glass material which is formed by bonding at least an opaque silica glass layer and at least a transparent silica glass layer, has a bonding interface between the opaque silica glass layer and the transparent silica glass layer, and has a birefringence of 20 to 4000 nm / cm at a wavelength of 520 nm.

[0006] The density difference between the opaque silica glass layer and the transparent silica glass layer is 0.05 to 1.0 g / cm 3 It is preferable that:

[0007] The composite silica glass material preferably has an average reflectance of 30% or more in the wavelength range of 1000 nm to 2500 nm.

[0008] It is preferable that the composite silica glass material has a total thickness of 2 to 10 mm, the transparent silica glass layers have a total thickness of 1 to 7 mm, and the opaque silica glass layers have a total thickness of 1 to 5 mm.

[0009] It is preferable that the difference between the maximum fictive temperature and the minimum fictive temperature of the transparent silica glass layer is within 150°C.

[0010] It is preferable that the optical fiber includes at least a first transparent silica glass layer, an opaque silica glass layer formed on the first transparent silica glass layer, and a second transparent silica glass layer formed on the opaque silica glass layer, and that the birefringence of the first transparent silica glass layer and the second transparent silica glass layer at a wavelength of 520 nm is 20 to 4000 nm / cm. [Effects of the Invention]

[0011] The present invention has the remarkable effect of providing a composite silica glass material that is resistant to breakage during fire processing or handling, has high reflectivity, and is breakage-resistant. [Brief explanation of the drawings]

[0012] [Figure 1]1 is a schematic diagram showing a method for measuring birefringence in a first embodiment of the composite silica glass material of the present invention. FIG. [Figure 2] FIG. 2 is a schematic diagram showing a method for measuring birefringence in a second embodiment of the composite silica glass material of the present invention. [Figure 3] FIG. 4 is a schematic diagram showing a method for measuring birefringence in a third embodiment of the composite silica glass material of the present invention. [Figure 4] FIG. 2 is a schematic diagram illustrating a measurement method for evaluating heat-shielding properties. [Figure 5] 1 is a schematic diagram showing heating by a burner in a method for producing a composite silica glass material according to the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following describes embodiments of the present invention, but these embodiments are shown by way of example only, and it goes without saying that various modifications are possible without departing from the technical spirit of the present invention. In the drawings, the same members are designated by the same reference numerals.

[0014] 1 to 3 are schematic diagrams showing methods for measuring birefringence in the first to third embodiments of the composite silica glass material of the present invention, in which (a) is a diagram showing a birefringence measurement sample 20 cut out from the composite silica glass material 10a, 10b, or 10c of the present invention, and (b) is a diagram showing the measurement of birefringence using the measurement sample 20.

[0015] As shown in FIG. 1(a), the composite silica glass material 10a of the present invention is a composite silica glass material formed by bonding at least an opaque silica glass layer 12 and at least transparent silica glass layers 14a, 14b, and has a bonding interface 16 between the opaque silica glass layer 12 and the transparent silica glass layers 14a, 14b, and the birefringence of the transparent silica glass layers 14a, 14b at a wavelength of 520 nm is 20 to 4000 nm / cm. Since the composite silica glass material 10a of the present invention has an opaque silica glass layer, it can be a composite silica glass material that is resistant to breakage even if the birefringence of the transparent silica glass layer is large. In particular, in a composite silica glass material having a bonding interface 16 between the opaque silica glass layer 12 and the transparent silica glass layers 14a, 14b, by setting the birefringence at a wavelength of 520 nm of the transparent silica glass layers 14a, 14b within the above range, it is possible to obtain a composite silica glass material that is resistant to breakage during fire processing or handling, has high reflectivity, and is resistant to breakage.

[0016] The birefringence of the transparent silica glass layers 14a and 14b can be measured using a known two-dimensional birefringence evaluation device. In Fig. 1(a), reference numeral 22 denotes a birefringence measurement area. As shown in Fig. 1, a measurement sample 20 is cut out from the composite silica glass material 10a, and when the direction perpendicular to the plate thickness direction A is defined as the top and bottom, it is preferable to measure the birefringence from the top and bottom directions of the measurement sample 20. The lower limit of the birefringence of the transparent silica glass layers 14a, 14b at a wavelength of 520 nm is 20 nm / cm or more, preferably 50 nm / cm or more, and more preferably 100 nm / cm or more. Setting the birefringence below 20 nm / cm requires a very long process, resulting in poor productivity and high costs. Furthermore, since compressive stress manifests as birefringence, a certain degree of birefringence is desirable. Setting the birefringence to 20 nm / cm or more makes the surface more susceptible to compressive stress, making it less susceptible to breakage. The upper limit of the birefringence of the transparent silica glass layers 14a and 14b at a wavelength of 520 nm is 4000 nm / cm or less, preferably 3000 nm / cm or less, and more preferably 1000 nm / cm or less. If the birefringence exceeds 4000 nm / cm, the layer becomes easily broken and insufficient strength can be obtained.

[0017] In the composite silica glass material of the present invention, the number of opaque silica glass layers and transparent silica glass layers may be one or more, and there is no particular limitation thereon. However, as shown in FIG. 1, it is preferable that the composite silica glass material includes at least a first transparent silica glass layer 14b, an opaque silica glass layer 12 formed on the first transparent silica glass layer 14b, and a second transparent silica glass layer 14a formed on the opaque silica glass layer 12. Fig. 2 shows an example of a composite silica glass material 10b of the present invention, which is formed by bonding one opaque silica glass layer 12 and one transparent silica glass layer 14 together, and has one bonding interface 16 between the opaque silica glass layer 12 and the transparent silica glass layer 14. Fig. 3 shows an example of a composite silica glass material 10c of the present invention, which is formed by alternately bonding two opaque silica glass layers 12a, 12b and two transparent silica glass layers 14a, 14b together, and has three bonding interfaces 16 between the opaque silica glass layers 12a, 12b and the transparent silica glass layers 14a, 14b.

[0018] The density difference between the opaque silica glass layer and the transparent silica glass layer is 0.05 to 1.0 g / cm 3 It is preferable that the density is 0.2 to 0.6 g / cm 3 When there is a certain difference between the density of the opaque silica glass layer and the density of the transparent silica glass layer, the opaque silica glass layer contracts and compressive stress is applied to the bonding interface between the opaque silica glass layer and the transparent silica glass layer, so that the strength is increased and the fracture strength can be increased. In particular, when the density difference between the opaque silica glass layer and the transparent silica glass layer is 0.05 g / cm 3 By making the density difference 1.0 g / cm or more, compressive stress is easily applied to the surface, making it difficult to crack. 3 If the density difference exceeds 1.0 g / cm, the strength will tend to decrease. 3 The following is preferred:

[0019] There is no particular limitation on the thickness of the opaque silica glass layer, but the thickness of each layer is preferably 1 mm or more, more preferably 1.2 mm or more, and is preferably 4 mm or less, more preferably 2 mm or less. The method for forming the opaque silica glass layer is not particularly limited, and a method using silica slurry or an opaque silica glass material such as an opaque silica glass plate can be used.

[0020] There is no particular limitation on the thickness of the transparent silica glass layer, but the thickness of each layer is preferably 0.8 mm or more, more preferably 1.0 mm or more, and is preferably 3 mm or less, more preferably 2 mm or less. The method for forming the transparent silica glass layer is not particularly limited, but a transparent silica glass material such as a transparent silica glass plate is preferably used.

[0021] There is no particular restriction on the total thickness of the composite silica glass material, but it is preferable that the total thickness of all layers is 2 mm or more and 10 mm or less, the total thickness of the transparent silica glass layers is 1 to 7 mm, and the total thickness of the opaque silica glass layers is 1 to 5 mm. The ratio of the total thickness of the transparent silica glass layers to the total thickness of the opaque silica glass layers is preferably 1:0.5 to 1.5, more preferably 1:0.7 to 1.2, and by setting the ratio within this range, a composite silica glass material with higher strength can be obtained.

[0022] The composite silica glass material preferably has an average reflectance of 30% or more, more preferably 35% or more, in the wavelength range of 1000 nm to 2500 nm. By making the reflectance 30% or more, the heat reflective effect of the opaque silica glass layer can be improved, and if the reflectance is 35% or more, more sufficient heat shielding properties can be obtained.

[0023] The difference between the maximum fictive temperature and the minimum fictive temperature of the transparent silica glass layer is preferably within 150° C. By keeping the fictive temperature difference of the transparent silica glass layer within 150° C., the mechanical strength can be increased.

[0024] The composite silica glass material of the present invention is resistant to breakage during fire processing or handling, has high reflectivity, and is suitable for use in applications such as improving the heat insulation properties of semiconductor manufacturing equipment and saving energy. [Example]

[0025] The present invention will be explained in more detail below by way of examples, but it goes without saying that these examples are given for illustrative purposes and should not be construed as limiting.

[0026] Example 1 The composite silica glass material 10a shown in FIG. 1 was produced by the following method. Silica powder, silicon nitride powder, and pure water were mixed to prepare a silica slurry. The silica concentration was adjusted to 70 wt% of the total weight, and the silicon nitride concentration relative to the silica weight was adjusted to 200 ppm. The silica powder used had an average particle size of 70 μm, and the silicon nitride powder had an average particle size of 1 μm. The silica slurry prepared above was applied to a transparent silica glass substrate of 350 mm square and 1 mm thick by scraping to a thickness of 1.5 mm. The silica glass substrate coated with the silica slurry was placed in a dryer at 40° C. for 5 hours to dry the silica slurry, thereby obtaining a silica glass substrate with a dried body. A transparent silica glass substrate measuring 350 mm square and 1 mm thick was placed on the resulting dried silica glass substrate with the dried body to prepare a pre-heated composite silica glass material. The unheated composite silica glass material was subjected to double-sided heating using a burner by the following method. As shown in Fig. 5, after heating the surface of one of the silica glass substrates using a burner 18 (single-sided heating), the unheated composite silica glass material was flipped over and the surface of the other silica glass substrate was again heated using a burner, thereby obtaining a composite silica glass material 10a of the present invention, which is formed by bonding an opaque silica glass layer 12 and transparent silica glass layers 14a, 14b, and has a bonding interface 16 between the opaque silica glass layer 12 and the transparent silica glass layers 14a, 14b. In Example 1, a line-type burner having multiple burners arranged in a row and a distance between the farthest burners on both ends of 400 mm (hereinafter abbreviated as 400L) was used as the burner.

[0027] <Evaluation method> The composite silica glass material obtained was evaluated by the following measurement methods, and the results are shown in Table 1. 1.Measuring method for birefringence of transparent silica glass layer As shown in Fig. 1, six rectangular samples were cut out from a 350 mm square composite silica glass material 10a, and the top and bottom surfaces were polished to prepare measurement samples 20, with the direction perpendicular to the plate thickness direction A being the top and bottom. At this time, the thickness in this direction was 1 mm. Measurements were taken from the top and bottom of this sample using a two-dimensional birefringence evaluation system (PA-micro) manufactured by Photonic Lattice (see Figure 1). Using Photonic Lattice's PA-view software, the average birefringence value of the transparent silica glass layer of the cut-out strip-shaped measurement sample 20 was measured at a wavelength of 520 nm. The measurement area 22 was an area of ​​1.5 mm width x 1 mm height (direction A) (thickness of the transparent silica glass layer). Similar measurements were taken for six strip-shaped measurement samples, and the average value was used as the measured birefringence value.

[0028] 2. Density measurement of opaque silica glass layer The transparent silica glass layer of the composite silica glass material was ground to leave only the opaque silica glass layer, and then the density was calculated using the Archimedes method. The density of the transparent silica glass part was 2.2 g / cm 3 It was decided.

[0029] 3. Reflectance measurement method The surface of the transparent silica glass layer of the obtained composite silica glass material was mirror-polished, and the reflectance was measured using an integrating sphere attached to a LAMDA950 (manufactured by PerkinElmer). Spectralon reflector (manufactured by Labsphere) was used as the standard reflector for the reflectance measurement. The measurement wavelength was 1000 nm to 2500 nm, and the reflectance measured at 2 nm intervals in that wavelength range was averaged to obtain the average reflectance.

[0030] 4.Measuring method for the total thickness of composite silica glass material Measurements were made at five points on the surface of the composite silica glass material using a dial gauge.

[0031] 5.Method for measuring the thickness of transparent and opaque silica glass layers The composite silica glass material was divided and the cross section was observed under a microscope to measure the thickness of each layer.

[0032] 6. Three-point bending fracture strength measurement method The composite silica glass material was cut into strips of 50 mm x 10 mm, and a three-point bending test was performed using Shimadzu Corporation's AGS-5KNX in accordance with JIS R1607, except for the size.

[0033] 7. How to measure fictive temperature The measurement was carried out by Raman scattering spectrophotometry as described in AEGEISSBERGER and FLGALEENER, Raman studies of vitreous SiO2 versus fictive temperature, Physical Review B, Vol. 28, No. 6, pp. 3266-3271.

[0034] 8.Measuring method for evaluating heat insulation performance The measurement method for evaluating the heat insulation performance is shown in Figure 4. 1) The composite silica glass material was cut into a 50 mm square piece, and as shown in Figure 4, an incandescent lamp 34 (Olympus Optical, light source device MODEL TGHM), composite silica glass material 10, heat absorber 30 (50 mm square × 2 mm thick SUS steel material coated with black paint), and thermo viewer 32 (FLIR ThemaCAM SC640) were placed in this order. The temperature of the room in which the measurement was performed was 25°C, the distance between the composite silica glass material 10 and the heat ray absorber 30 was 8 mm, the distance between the composite silica glass material 10 and the incandescent lamp 34 was 40 mm, and the distance between the heat ray absorber 30 and the thermoviewer 32 was 200 mm. 2) The surface temperature of the heat absorber was measured using a thermoviewer. The temperature at this point was designated as T0. 3) Turn on the incandescent lamp and set the knob to maximum output. After 30 minutes, measure the surface temperature of the heat absorber with a thermo viewer. This temperature was designated as T1. 4) The temperature rise was calculated by T1-T0, and the thermal insulation properties were evaluated based on the temperature rise.

[0035] 9. Overall rating The results of the three-point bending fracture strength and heat shielding property evaluation were evaluated on a five-point scale of A to E, with E being considered unsatisfactory. The fracture strength in the three-point bending test was evaluated based on the bending strength of silica glass, which is 105 MPa. The results are shown in Table 1. A: Breaking strength of 74 MPa or more (strength exceeding 73.5 MPa, which is 70% of 105 MPa), and temperature rise of 18°C ​​or less. B: Breaking strength of 69 MPa or more (strength exceeding 68.25 MPa, which is equivalent to 65% of 105 MPa), and temperature rise of 23°C or less (excluding those included in rating A). C: Breaking strength of 63 MPa (60% of 105 MPa) or more and temperature rise of 26°C or less (excluding those included in ratings A and B). D: Breaking strength of 58 MPa or more (strength exceeding 57.75 MPa, which is equivalent to 55% of 105 MPa) and temperature rise of 28°C or less (excluding those included in evaluations A to C). E: Breaking strength less than 58 MPa and / or temperature rise exceeding 28°C.

[0036] [Table 1] In the table, the transparent layer means a transparent silica glass layer, the opaque layer means an opaque silica glass layer, and the composite material means a composite silica glass material.

[0037] Example 2 A composite silica glass material was obtained in the same manner as in Example 1, except that the unheated composite silica glass material was heated in a heating furnace at 1300°C for 5 hours instead of using a burner. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0038] Example 3 A composite silica glass material was obtained in the same manner as in Example 1, except that the silicon nitride concentration relative to the weight of silica in the silica slurry was 100 ppm. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0039] Example 4 A composite silica glass material was obtained in the same manner as in Example 1, except that the particle size of the silicon nitride used in the silica slurry was changed to an average particle size of 10 μm. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0040] Example 5 A composite silica glass material was obtained in the same manner as in Example 1, except that the heating of the unheated composite silica glass material with a burner was changed to single-sided heating. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0041] Example 6 A composite silica glass material was obtained in the same manner as in Example 1, except that the thickness of the slurry applied to a transparent silica glass substrate measuring 350 mm square and 3 mm thick was changed to 4 mm, and the thickness of the transparent silica glass substrate placed on top was changed to 3 mm. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0042] Example 7 A composite silica glass material was obtained in the same manner as in Example 1, except that the thickness of the slurry applied to a transparent silica glass substrate measuring 350 mm square and 0.5 mm thick was 1 mm, and the thickness of the transparent silica glass substrate placed on top was changed to 0.5 mm. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0043] Example 8 A composite silica glass material was obtained in the same manner as in Example 1, except that the heating of the pre-heated composite silica glass material with a burner was changed to a process of heating the surface with a round burner having a diameter of 50 mm. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0044] Example 9 The composite silica glass material 10b shown in FIG. 2 was produced by the following method. A composite silica glass material was obtained in the same manner as in Example 1, except that the 350 mm square x 1 mm thick transparent silica glass substrate was not placed on the silica glass substrate with the dried body. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0045] Example 10 Two silica glass substrates with dried bodies were prepared, and the surfaces of the dried bodies coated with silica slurry were placed together and heated in a 400 L line burner. A composite silica glass material was obtained in the same manner as in Example 1. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0046] Example 11 The composite silica glass material 10c shown in FIG. 3 was produced by the following method. Two silica glass substrates with dried bodies were prepared, the surface of the dried body of one of the silica glass substrates with dried bodies was coated with silica slurry, and the silica slurry-coated surface was placed on the silica glass substrate surface of the other silica glass substrate with dried body, and heated using a 400 L line burner. A composite silica glass material was obtained in the same manner as in Example 1. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0047] Example 12 The composite silica glass material 10a shown in FIG. 1 was produced by the following method. One opaque silica glass sheet measuring 350 mm square and 6 mm thick and two transparent silica glass sheets measuring 350 mm square and 3 mm thick were stacked in the order of transparent silica glass, opaque silica glass, and transparent silica glass and fixed with tape to obtain a pre-heated composite silica glass material. A silica glass scaffolding rod was attached to the upper and lower clamping parts of a composite silica glass material manufacturing device having clamps that move up and down, and the scaffolding rod and the unheated composite silica glass material were welded with an oxyhydrogen flame. While heating the pre-heated composite silica glass material from below with a propane-oxygen burner, the upper clamp's feed rate was set at 3 mm / min and the lower clamp's pull rate was set at 9 mm / min. The upper and lower clamps were moved downward to elongate the pre-heated composite silica glass material, thereby obtaining a composite silica glass material. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0048] Example 13 A composite silica glass material was obtained in the same manner as in Example 1, except that the heating of the pre-heated composite silica glass material with a burner was changed to a treatment in which the in-plane heating was performed with a round burner having a diameter of 150 mm. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0049] Example 14 A composite silica glass material was obtained in the same manner as in Example 1, except that the heating of the pre-heated composite silica glass material with a burner was changed to a process of heating the surface with a round burner having a diameter of 200 mm. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0050] Example 15 A composite silica glass material was obtained in the same manner as in Example 1, except that the silicon nitride concentration relative to the weight of silica in the silica slurry was changed to 50 ppm. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0051] Example 16 A composite silica glass material was obtained in the same manner as in Example 1, except that the silicon nitride concentration relative to the weight of silica in the silica slurry was changed to 500 ppm. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 1.

[0052] (Comparative Example 1) A composite silica glass material was obtained in the same manner as in Example 1, except that the thickness of the slurry applied to a transparent silica glass substrate measuring 350 mm square and 4 mm thick was changed to 6 mm, and the thickness of the transparent silica glass substrate placed on top was changed to 4 mm. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 2.

[0053] [Table 2]

[0054] (Comparative Example 2) A composite silica glass material was obtained in the same manner as in Example 1, except that instead of heating the pre-heated composite silica glass material using a burner, it was held in a heating furnace at 1300°C for 5 hours, then at 1150°C for 50 hours, and then slowly cooled to 50°C at 10°C / h. The same measurements as in Example 1 were carried out on the obtained composite silica glass material. The results are shown in Table 2.

[0055] (Comparative Example 3) A composite silica glass material was obtained in the same manner as in Example 1, except that the heating of the pre-heated composite silica glass material with a burner was changed to a process of heating the surface with a round burner having a diameter of 30 mm. The obtained composite silica glass material was subjected to the same measurements as in Example 1. The results are shown in Table 2.

[0056] As shown in Table 1, in Examples 1 to 16, in which the birefringence of the transparent silica glass layer at a wavelength of 520 nm was 20 to 4000 nm / cm, composite silica glass materials were obtained that had high fracture strength, were resistant to breakage during fire processing or handling, had high reflectivity, and were breakage-resistant. In Examples 8, 13, and 14, in which in-plane heating treatment was performed using a round burner, more distortion was generated by heating and high birefringence was observed, but composite silica glass materials were obtained that had high fracture strength and were breakage-resistant. Therefore, according to the composite silica glass material of the present invention, a composite silica glass material that has high fracture strength and is breakage-resistant can be obtained, even when heated under strong conditions during processing. On the other hand, Comparative Examples 1 and 3, in which the birefringence of the transparent silica glass layer at a wavelength of 520 nm exceeded 4000 nm / cm, exhibited low fracture strength and strength problems. Furthermore, Comparative Example 2, in which the birefringence of the transparent silica glass layer at a wavelength of 520 nm was less than 20 nm / cm, required an additional process of heating and slow cooling over a long period of time in addition to the process used in Example 2, which utilized a heating furnace, resulting in poor productivity and high manufacturing costs. Furthermore, the three-point bending fracture strength was also inferior to, for example, Example 1. Therefore, the composite silica glass material of Comparative Example 2 had the problem of being unsuitable for industrial products. [Explanation of symbols]

[0057] 10, 10a, 10b, 10c: composite silica glass material, 12, 12a, 12b: opaque silica glass layer, 14, 14a, 14b: transparent silica glass layer, 16: bonding interface, 18: burner, 20: measurement sample, 22: measurement area, 30: heat absorber, 32: thermoviewer, 34: incandescent lamp, A: plate thickness direction.

Claims

1. At least an opaque silica glass layer and at least a transparent silica glass layer are bonded together, a bonding interface between the opaque silica glass layer and the transparent silica glass layer; The composite silica glass material has a birefringence of 20 to 4000 nm / cm at a wavelength of 520 nm of the transparent silica glass layer.

2. The density difference between the opaque silica glass layer and the transparent silica glass layer is 0.05 to 1.0 g / cm ３ 2. The composite silica glass material according to claim 1, wherein:

3. 2. The composite silica glass material according to claim 1, wherein the composite silica glass material has an average reflectance of 30% or more in the wavelength range of 1000 nm to 2500 nm.

4. The total thickness of the composite silica glass material is 2 to 10 mm, the total thickness of the transparent silica glass layer is 1 to 7 mm; 2. The composite silica glass material according to claim 1, wherein the total thickness of the opaque silica glass layers is 1 to 5 mm.

5. 2. The composite silica glass material according to claim 1, wherein the difference between the maximum fictive temperature and the minimum fictive temperature of the transparent silica glass layer is within 150°C.

6. The optical fiber substrate includes at least a first transparent silica glass layer, an opaque silica glass layer formed on the first transparent silica glass layer, and a second transparent silica glass layer formed on the opaque silica glass layer, 2. The composite silica glass material according to claim 1, wherein the first transparent silica glass layer and the second transparent silica glass layer have birefringence of 20 to 4000 nm / cm at a wavelength of 520 nm.

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