Ceramic sintered body and telescope

Abstract

A ceramic sintered body contains a cordierite crystal and a spinel crystal. The total of the content of cordierite crystals and the content of spinel crystals is 95 mass% or more. In addition, the content of spinel crystals is from 0.1% by mass to 17% by mass (inclusive).

Description

Technical Field

[0001] Embodiments of the invention relate to a ceramic sintered body and a telescope. Background Art

[0002] In recent years, ceramic components with low thermal expansion have been used in equipment in various fields. As such low thermal expansion ceramics, cordierite ceramics have recently attracted attention (for example, see Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-204198 Summary of the Invention

[0006] A ceramic sintered body according to one embodiment includes cordierite crystals and spinel crystals. Furthermore, the total content of the cordierite crystals and the spinel crystals is 95% by mass or greater. Furthermore, the content of the spinel crystals is 0.1% by mass or greater and 17% by mass or less. DETAILED DESCRIPTION

[0007] Hereinafter, embodiments of the ceramic sintered body and telescope of the present invention will be described. However, the present invention is not limited to the embodiments described below.

[0008] In recent years, ceramic components with low thermal expansion have been used in equipment in various fields. As such low thermal expansion ceramics, cordierite ceramics have attracted attention in recent years.

[0009] However, in the above-mentioned prior art, there is room for further improvement in the application of cordierite ceramics in various fields. Therefore, it is desired to solve the above-mentioned problems and realize a ceramic sintered body that can be applied in various fields.

[0010] The temperature dependence of the thermal expansion coefficient of cordierite ceramics is known to be expressed as a linear line from below -100°C to near room temperature. Conventional cordierite ceramics have a zero-crossing temperature of the thermal expansion coefficient near room temperature, for example, around 22°C. In the present invention, the zero-crossing temperature of the thermal expansion coefficient is also referred to as "ZCT."

[0011] Cordierite ceramics have been used in optical components such as semiconductor exposure equipment and telescope mirrors, where dimensional changes due to temperature are a concern. For example, low thermal expansion glass is used for these components.

[0012] However, the Young's modulus of low expansion glass is as low as 100 GPa or less, and the value obtained by dividing the Young's modulus by the specific gravity is as low as 30 GPa / g / cm 3 Therefore, if the thickness of the glass is reduced when used in a reflector for a satellite, for example, it may be damaged by the impact during launch. In addition, if the thickness of the glass is increased to ensure strength, the weight during launch will increase.

[0013] To address this issue, cordierite ceramics have a Young's modulus of approximately 140 GPa and a specific stiffness of 55 GPa / g / cm. 3 Therefore, compared with low-expansion glass, it is possible to reduce the thickness of components and make the device lighter. For equipment launched into space, it has the significant advantage of reducing launch costs, and has therefore attracted attention in recent years.

[0014] On the other hand, cordierite ceramics have a larger temperature dependence of the thermal expansion coefficient than low-expansion glass, and therefore, when utilizing the zero expansion property, it is necessary to use it at a temperature near the ZCT.

[0015] Therefore, for example, when cordierite ceramics are used in components mounted on artificial satellites, temperature regulation within the device is required to maintain the component temperature around 22°C, which is the ZCT. This requires particularly strict temperature management near the components.

[0016] Therefore, using cordierite ceramics in multiple components requires temperature control for each component, complicating equipment design. This leads to increased manufacturing costs, weight due to the addition of additional equipment, and increased power consumption in spacecraft, where power supply is limited.

[0017] To address this issue, it is conceivable to control the ZCT of cordierite ceramics according to the operating temperature of the equipment to solve the above problem.

[0018] Here, the ceramic sintered body of the embodiment may contain cordierite crystals and spinel crystals. In addition, the total content of the cordierite crystals and the spinel crystals may be 95% by mass or more. In addition, the content of the spinel crystals may be 0.1% by mass or more and 17% by mass or less.

[0019] With this configuration, the ZCT of cordierite ceramics can be controlled within the range of -120°C to 45°C. Therefore, according to the embodiment, cordierite ceramics can be used in various fields, including the aerospace field. Furthermore, cordierite ceramics having the desired ZCT can be provided.

[0020] In the ceramic sintered body of the embodiment, the content of spinel crystals may be 5% by mass or less. If the amount of spinel crystals having a higher dielectric constant than cordierite crystals is 5% by mass or less, a cordierite ceramic having a low dielectric constant can be provided.

[0021] In the ceramic sintered body of the embodiment, the content of cordierite crystals may be 90% by mass or greater. If the amount of cordierite crystals, which have a lower dielectric constant than spinel crystals, is 90% by mass or greater, a cordierite ceramic having a low dielectric constant can be provided.

[0022] In addition, in the ceramic sintered body of the embodiment, when crystals other than cordierite crystals and spinel crystals are detected in the Rietveld analysis of the X-ray diffraction pattern, the total amount of such other crystals may be 3% by mass or less.

[0023] When the amount of crystalline phases other than cordierite and spinel precipitated is 3% by mass or less, the sintering temperature dependence of ZCT is relatively low, making it easy to produce a desired ZCT sintered body. In particular, in the case of large-sized sintered bodies, the amount of crystalline phases other than cordierite and spinel precipitated is preferably 3% by mass or less, because a temperature difference occurs between the periphery and the center of the sintered body during sintering.

[0024] Furthermore, the ceramic sintered body of the embodiment can have a thermal expansion coefficient within 0±1 ppb / K within the temperature range of ZCT-1K to ZCT+1K. This reduces dimensional changes in the ceramic sintered body near the ZCT.

[0025] Furthermore, the ceramic sintered body of the embodiment may have a ZCT of not less than -100° C. and not more than 35° C. Thus, the ceramic sintered body can be used in various fields including the space field.

[0026] Furthermore, the ceramic sintered body of the embodiment may have a relative dielectric constant of 4 to 5 at a measurement frequency of 10 GHz. With such a configuration, for example, when the ceramic sintered body of the present invention is used as a substrate for a high-frequency circuit, signal delay can be reduced.

[0027] In addition, the ceramic sintered body of the embodiment may have a specific gravity of 2.8 g / cm 3 Therefore, when cordierite ceramics are used in the space field, launch costs can be reduced.

[0028] In addition, the ceramic sintered body of the embodiment can have a specific rigidity of 50 GPa / g / cm 3 Therefore, when cordierite ceramics are used in the space field, launch costs can be reduced.

[0029] Furthermore, the ceramic sintered body of the embodiment may contain substantially no mullite crystals, thereby reducing the surface roughness after processing, making it suitable for optical components such as reflective mirror components.

[0030] In addition, the ceramic sintered body of the embodiment can be a dense substance. If it has such a structure, it becomes a ceramic sintered body with excellent strength. In addition, in the embodiment, the water absorption rate of the ceramic sintered body can be 0.05% or less. If it has such a structure, it can form a surface with few bumps when the surface is processed into a mirror surface.

[0031] Furthermore, in the ceramic sintered bodies of the embodiments, it is important to ensure homogeneity within the sintered body. This means that variations in the CTE (coefficient of thermal expansion) and ZCT within the sintered body are minimal. For example, homogeneity can be achieved such that variations in CTE within ±20 ppb / K and variations in ZCT within ±1°C are achieved in reflective mirror components used in astronomy and space applications.

[0032] Furthermore, the telescope of the embodiment may include the ceramic sintered body described above as a reflector component. Furthermore, the telescope of the embodiment may include the ceramic sintered body described above as a support member that directly or indirectly supports the reflector component. Furthermore, the telescope of the embodiment may include the ceramic sintered body described above as a reflector component and a support member that directly or indirectly supports the reflector component.

[0033] This reduces inertial vibrations in astronomical telescopes, even when the optical axis adjustment speed is increased. Therefore, according to the embodiment, optical axis adjustment can be accelerated. Furthermore, vibration damping is improved across the entire device. Furthermore, due to its high mechanical strength, it offers excellent long-term reliability. Furthermore, its light weight and high rigidity reduce launch costs.

[0034] Example

[0035] Next, the cordierite ceramic of this embodiment was specifically produced and its properties were evaluated. First, powders of magnesium hydroxide (Mg(OH) 2 ), aluminum oxide, and silicon dioxide were prepared as raw material powders of Mg, Al, and Si.

[0036] In addition, as raw material powder, Mg2Al4Si5O 18 The prepared powder of synthetic cordierite raw material was prepared together with calcium carbonate powder. The purity of the prepared magnesium hydroxide powder was 99.3%, the purity of the aluminum oxide powder was 99.9%, the purity of the silicon dioxide powder was 99.5%, and the purity of the calcium carbonate powder was 99.5%.

[0037] Next, magnesium hydroxide powder, aluminum oxide powder, and silicon dioxide powder were mixed in various ratios ranging from 2:2.4:5 to 3:2.4:5 in terms of the molar ratio of MgO:Al2O3:SiO2 to prepare various base raw material mixed powders.

[0038] Next, the synthetic cordierite raw material powder and the raw material mixed powder were mixed at a mass ratio of 70:30. 0.892 mass % of calcium carbonate was added externally, and a binder such as paraffin was added to prepare various granulated powders.

[0039] Next, the various granulated powders prepared were pressed into cylindrical compacts with a diameter of 150 mm and a height of 100 mm. These compacts were then fired in air to produce cordierite ceramic samples Nos. 1 to 39. Each sample was fired at a temperature of 1375°C and held at this temperature for 7 hours.

[0040] Furthermore, when the compositions of the prepared samples were determined by ICP emission spectrometry, all samples had compositions consistent with the prepared compositions.

[0041] Next, the following evaluations were performed on the prepared samples Nos. 1 to 39. Crystalline phase identification and crystallization phase ratio measurement were performed by powder X-ray diffraction and the Reitveld method. One sample was used for each of the measurements.

[0042] Thermal expansion characteristics were measured using an optical heterodyne interferometer over a temperature range of -100°C to 50°C, with dimensions at 22°C as the reference. The temperature dependence of the thermal expansion coefficient was calculated from the measured data, and the temperature at which the thermal expansion coefficient reached zero was defined as the ZCT.

[0043] Furthermore, the ZCT of each sample obtained by the above method was used as the reference temperature. The thermal expansion coefficient of each sample was measured in the temperature range from the reference temperature -1K to the reference temperature +1K. The obtained thermal expansion coefficient was used as the thermal expansion coefficient of each sample in the ZCT neighborhood (CTE at ZCT).

[0044] The bulk density and water absorption were measured using the Archimedean method. The water absorption was 0.0% for all samples. Young's modulus was measured using the ultrasonic resonance method. The sample dimensions used for the measurement were 10 mm in diameter and 5 mm in height. The specific stiffness was calculated by dividing the Young's modulus by the bulk density.

[0045] Thermal conductivity was measured using the laser flash method. Flexural strength was determined by processing test pieces specified in JIS R 1601 from each sample to obtain four-point bending strength. Fracture toughness was measured using the indenter penetration method specified in JIS R 1607-1995.

[0046] Porosity was measured using the following procedures. First, each sample was cut and the cross section was mirror-polished. Next, the ratio of the area occupied by pore openings within the measured region of the cross section was calculated (area %). This ratio was then used as the porosity (volume %) to determine the porosity of each sample.

[0047] The relative dielectric constant was measured at a measurement frequency of 10 GHz using the dielectric cylindrical resonator method (international standard IEC 61338-1-3 (1999)).

[0048] Tables 1 and 2 show the measurement results for Samples Nos. 1 to 39, including the total cordierite and spinel crystal contents, cordierite and spinel crystal contents, ZCT, thermal expansion coefficient of the ZCT neighborhood, bulk density, Young's modulus, specific stiffness, thermal conductivity, flexural strength, fracture toughness, porosity, and relative dielectric constant. The mass percentage of "other crystals" in Tables 1 and 2 refers only to the mass percentage of crystals other than cordierite and spinel crystals, excluding the mass of glassy materials. Examples of such other crystals include enstatite and forsterite.

[0049]

Table 1

[0050]

[0051]

Table 2

[0052]

[0053] As shown in Tables 1 and 2, when the total content of cordierite crystals and spinel crystals is 95% by mass or more and the spinel crystal content is 0.1% by mass or more and 17% by mass or less, the ZCT can be controlled within the range of -120°C to 45°C. Therefore, in the embodiment, the above-mentioned problems can be solved.

[0054] Furthermore, as shown in Tables 1 and 2, when the total content of cordierite crystals and spinel crystals is 95% by mass or greater, and the spinel crystal content is 0.1% by mass or greater and 9% by mass or less, the ZCT can be controlled within the range of -30°C to 45°C. Therefore, in the embodiment, the above-mentioned problems can be solved.

[0055] In addition, as shown in Tables 1 and 2, the specific stiffness is all above 55 GPa / g / cm 3 The above-mentioned samples can reduce the thickness of components and the weight of devices compared to low-expansion glass.

[0056] The ZCT values ​​of the samples shown in Tables 1 and 2 were measured. These values ​​are recorded in the ZCT (1) column of Table 3 below. Furthermore, the ZCT values ​​of the samples fired at a temperature 50°C higher than the firing temperature were measured. This temperature is indicated as ZCT (2) in Table 3. Furthermore, the difference between ZCT (1) and ZCT (2) is shown in Table 3. The smaller this difference, the smaller the change in ZCT due to the firing temperature.

[0057]

Table 3

[0058]

[0059] As mentioned above, although each embodiment of the present invention was described, the present invention is not limited to the above-mentioned each embodiment, and various changes can be made without departing from the spirit of the present invention.

[0060] It should be understood that the embodiments of the present invention are illustrative in all respects and are not restrictive. In fact, the above-mentioned embodiments can be implemented in a variety of ways. In addition, the above-mentioned embodiments can be omitted, replaced, or modified in various ways without departing from the scope and purpose of the invention.

[0061] Furthermore, the present technology may also adopt the following structure.

[0062] (1) A ceramic sintered body, wherein:

[0063] Contains cordierite crystals and spinel crystals,

[0064] The total content of the cordierite crystals and the spinel crystals is 95% by mass or more,

[0065] The content of the spinel crystals is 0.1% by mass or more and 17% by mass or less.

[0066] (2) The ceramic sintered body according to (1) above, wherein the content of the spinel crystals is 5% by mass or less.

[0067] (3) The ceramic sintered body according to (1) or (2) above, wherein the cordierite crystal content is 90% by mass or more.

[0068] (4) The ceramic sintered body according to any one of (1) to (3), wherein when crystals other than the cordierite crystals and the spinel crystals are detected in a Rietveld analysis of an X-ray diffraction pattern, the total amount of the other crystals is 3% by mass or less.

[0069] (5) The ceramic sintered body according to any one of (1) to (4), wherein the thermal expansion coefficient is within 0±1 ppb / K in the temperature range of the reference temperature -1 K to the reference temperature +1 K, when the zero-cross temperature of the thermal expansion coefficient is used as the reference temperature.

[0070] (6) The ceramic sintered body according to any one of (1) to (5), wherein the zero-cross temperature of the thermal expansion coefficient is not less than -100°C and not more than 35°C.

[0071] (7) The ceramic sintered body according to any one of (1) to (6), wherein the relative dielectric constant at a measurement frequency of 10 GHz is 4 or more and 5 or less.

[0072] (8) The ceramic sintered body according to any one of (1) to (7), wherein the specific gravity is 2.8 g / cm 3 the following.

[0073] (9) The ceramic sintered body according to any one of (1) to (8), wherein the specific rigidity is 50 GPa / g / cm 3 above.

[0074] (10) A telescope comprising the ceramic sintered body according to any one of (1) to (9) as a reflector component.

[0075] (11) A telescope comprising the ceramic sintered body according to any one of (1) to (9) as a support member that directly or indirectly supports a reflector component.

[0076] (12) A telescope comprising the ceramic sintered body according to any one of (1) to (9) as a reflector component and a support member that directly or indirectly supports the reflector component.

Claims

1. A ceramic sintered body comprising cordierite crystals and spinel crystals, The total content of the cordierite crystals and the spinel crystals is 95% by mass or more, The content of the spinel crystals is 0.1% by mass or more and 17% by mass or less.

2. The ceramic sintered body according to claim 1, wherein The content of the spinel crystals is 5% by mass or less.

3. The ceramic sintered body according to claim 1 or 2, wherein The content of the cordierite crystals is 90% by mass or more.

4. The ceramic sintered body according to any one of claims 1 to 3, wherein When crystals other than the cordierite crystal and the spinel crystal are detected in the Rietveld analysis of an X-ray diffraction pattern, the total amount of the other crystals is 3% by mass or less. The ceramic sintered body according to any one of claims 1 to 4, wherein the thermal expansion coefficient of the ceramic sintered body is within 0±1 ppb / K in a temperature range from the reference temperature -1K to the reference temperature +1K, when the zero-crossing temperature of the thermal expansion coefficient is used as the reference temperature. 6 . The ceramic sintered body according to claim 1 , wherein the zero-cross temperature of the thermal expansion coefficient is not less than −100° C. and not more than 35° C. 7 . The ceramic sintered body according to claim 1 , wherein the relative dielectric constant thereof at a measurement frequency of 10 GHz is 4 or more and 5 or less.

8. The ceramic sintered body according to any one of claims 1 to 7, which has a specific gravity of 2.8 g / cm 3 the following.

9. The ceramic sintered body according to any one of claims 1 to 8, which has a specific rigidity of 50 GPa / g / cm 3 above. 10 . A telescope comprising the ceramic sintered body according to claim 1 as a reflecting mirror component. 11 . A telescope comprising the ceramic sintered body according to claim 1 as a support member that directly or indirectly supports a reflector component. 12 . A telescope comprising the ceramic sintered body according to claim 1 as a reflector component and a support member that directly or indirectly supports the reflector component.

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