Infrared optical transparent ceramic and preparation method thereof

Abstract

The invention belongs to the technical field of infrared optical transparent ceramics, and discloses an infrared optical transparent ceramic and a preparation method thereof. Sc2O3 with a negative thermo-optical coefficient is used as a matrix, and other components with positive thermo-optical coefficients are added as compensation components. Through compensation of the thermo-optical coefficients of all the components, the controllability of the thermo-optical coefficient of the transparent ceramic is achieved, meanwhile, a lens cone material matched with the linear thermal expansion coefficient of the transparent ceramic is selected, the focal length of an infrared optical system can not change within the range of-40 DEG C to + 60 DEG C, the environmental adaptability of the infrared optical system is improved, and the imaging quality is improved. The use of an extra electromechanical active device or a combination of a plurality of optical elements in the athermalization technology is avoided, the requirements of miniaturization and light weight of the infrared optical system design are met, and the method has a wide application prospect in the field of athermalization optical system design.

Description

Technical Field

[0001] The invention relates to the field of infrared optical transparent ceramics, and in particular to infrared optical transparent ceramics and a preparation method thereof. Background Art

[0002] In recent years, the continuous development and innovation of infrared optical systems have made them widely used in many fields, including photoelectric detection, remote sensing cameras, navigation thermal imagers, star sensors, etc. This requires the optical system to have all-weather, large observation space range, high precision, high sensitivity and other characteristics. However, in complex application environments, the imaging of optical systems is significantly affected by changes in the surrounding environment, and a particularly critical factor is temperature. Factors such as high-altitude flight, day and night temperature differences, and geographical location will cause temperature changes during the application process.

[0003] The influence of temperature on infrared optical systems is mainly reflected in two aspects. On the one hand, the refractive index-temperature coefficient (i.e., thermo-optic coefficient, dn / dT) of optical materials determines the sensitivity of the refractive index to temperature changes. At present, the thermo-optic coefficient of commonly used infrared materials is relatively large, as shown in Table 1. Under the influence of temperature, severe changes in the refractive index will directly affect the propagation path of light in the optical element, thereby causing the focus position of the imaging system to shift, resulting in blurred imaging and reduced contrast; on the other hand, the barrel material will also produce different degrees of thermal expansion and contraction due to temperature changes, resulting in thermal defocusing of the image plane of the optical lens, making it impossible for the imaging camera to obtain a clear target image. Especially in high-precision application scenarios, slight changes in imaging distance will cause defocusing at the lens image plane. To solve this problem, additional athermal compensation technology has to be used to achieve little or no change in the focal length of the optical system within the temperature range of -40℃ to +60℃.

[0004] Table 1 Thermo-optic coefficients of commonly used infrared materials

[0005]

[0006]

[0007] At present, athermal compensation technology is generally divided into mechanical passive, electromechanical active and optical passive athermal technologies. The working principle of both mechanical passive and active athermal methods is to move the components in the optical system to return the image plane position of the entire optical system that has changed due to temperature changes to its original position. The mechanical passive method utilizes the thermal expansion and contraction characteristics of mechanical materials, and often uses solid rods or shape memory alloys with high linear expansion coefficients to connect to the lens barrel. The mechanical active method configures a temperature sensor in the system, calculates the axial distance that the compensation element needs to move according to the temperature value, and then drives the motor to move the element in the system to the corresponding position. These two athermal compensation technologies introduce additional structures and devices, increase the weight and volume of the optical system, and make it difficult to ensure the sealing of the system. Optical passive compensation technology achieves mutual compensation of various influencing factors through the mutual matching of the thermo-optical coefficients of optical materials and the linear thermal expansion coefficients of optical and mechanical components, so as to ensure the focal length stability and imaging quality of the optical system when the temperature changes. For example, Chinese patent CN118859474A discloses a wide temperature range and wide working spectrum visible light athermalization optical system, including a front lens group and a rear lens group, and the two lens groups are respectively composed of multiple lenses of different materials and shapes. This complex material matching brings great difficulty to the structural design and assembly work, and also increases the volume and weight of the system.

[0008] In most cases, the refractive index of a material increases with increasing temperature, and such materials have a positive thermo-optic coefficient. However, some special materials exhibit the opposite behavior, that is, an increase in temperature causes a decrease in the refractive index, which is the so-called negative thermo-optic coefficient. In optical systems, the use of materials with negative thermo-optic coefficients can design equipment that automatically compensates for the effects of temperature changes and maintains the stability and accuracy of the system. At present, materials with negative thermo-optic coefficients are widely used in applications such as fiber-optic communications, lasers, optical sensors, and optical filters. In 2017, U.S. Patent US9709699B2 first disclosed a nano / nano composite ceramic optical lens, which achieves athermal material design by matching positive and negative thermo-optic coefficients in complex phase materials. This design simplifies the design of optical components, but fluorides with negative thermo-optic coefficients have disadvantages such as poor chemical stability, low mechanical strength, easy decomposition at high temperatures, and difficult preparation.

[0009] Therefore, the present invention proposes an infrared optical transparent ceramic with adjustable thermo-optic coefficient, which uses Sc2O3 with a negative thermo-optic coefficient as a matrix and adds other components with positive thermo-optic coefficients as compensation components. By compensating the thermo-optic coefficients of each component, the adjustability of the thermo-optic coefficient of the transparent ceramic is achieved. At the same time, by selecting a lens barrel material that matches its linear thermal expansion coefficient, the focal length of the optical system can remain unchanged within the range of -40°C to +60°C, thereby improving its environmental adaptability and imaging quality. Avoiding the use of additional electromechanical active devices or a combination of multiple optical elements in the athermal technology meets the requirements of miniaturization and lightweight design of the optical system, and has broad application prospects in the field of athermal optical system design. Summary of the invention

[0010] 1. Technical issues to be resolved

[0011] The present invention provides an infrared optical transparent ceramic to address a series of problems such as high thermo-optical coefficient of existing infrared optical materials and complex athermal compensation technology, which lead to limited application scenarios of optical systems.

[0012] (II) Technical solution

[0013] In order to achieve the above object, the technical solution of the present invention is as follows:

[0014] An infrared optical transparent ceramic is a composite material composed of Sc2O3 and alkali metal oxides, the thermo-optic coefficients of which compensate each other, wherein the volume ratio of Sc2O3 to alkali metal oxides is 1:1.

[0015] Furthermore, one or more of the rare earth oxides Ln2O3, Al2O3, ZrO2, and ZnO are added to adjust the thermo-optical coefficient of the infrared optically transparent ceramic.

[0016] The rare earth oxide Ln2O3 is one or more of Y2O3, La2O3, Gd2O3, Lu2O3, and Yb2O3.

[0017] The alkali metal oxide is one or more of BeO, MgO, CaO, SrO and BaO.

[0018] When rare earth oxide Ln2O3 is added and the molar ratio with Sc2O3 is in the range of 1:0 to 1:0.25, rare earth oxide Ln2O3 forms a solid solution with Sc2O3 and no new phase is formed; when the molar ratio of rare earth oxide Ln2O3 to Sc2O3 is in the range of 1:2.5 to 1:1.5, the two react in a solid phase to generate a new phase; when ZrO2 is added, it forms a solid solution with Sc2O3, where the molar ratio of Sc2O3 to ZrO2 is in the range of 1:0 to 1:0.05; when ZnO is added and the molar ratio to alkali metal oxide is in the range of 1:0 to 1:0.33, ZnO and alkali metal oxide form a solid solution and no new phase is formed; when the molar ratio of ZnO to alkali metal oxide is greater than 1:0.33, ZnO cannot be completely dissolved into the alkali metal oxide, and a ZnO phase appears; when Al2O3 is added, it reacts with Sc2O3 and alkali metal oxide in a solid phase, respectively, and the reaction product is controlled by the amount of Al2O3 added.

[0019] A method for preparing infrared optical transparent ceramics comprises synthesizing uniform nano powder according to material composition, and performing green body molding and ceramic sintering to enable the ceramics to obtain a microstructure in which each phase is evenly distributed.

[0020] The ceramic sintering temperature is 1200-1350° C., and the sintering pressure is above 40 MPa.

[0021] When the number of phases in the infrared optically transparent ceramic is greater than two phases, the sintering pressure is greater than 100 MPa.

[0022] When the physical phases in the infrared optically transparent ceramics are greater than three phases, the sintering pressure is greater than 200 MPa.

[0023] The crystal size of the nano powder is less than 10 nm, and the particle size of the nano powder is D 50 <100nm, the particle size distribution range of nano powder is 30~150nm, and the specific surface area of ​​nano powder is>60m 2 / g.

[0024] Furthermore, the preparation method also includes a post-treatment step of the infrared optically transparent ceramic, wherein the obtained infrared optically transparent ceramic is annealed in a temperature range of 1000 to 1200° C. for 10 to 48 hours.

[0025] The relative density of the prepared infrared optical transparent ceramic is above 99.9%, the grain size of the infrared optical transparent ceramic is below 250nm, and the optical transmittance of the infrared optical transparent ceramic in the wavelength range of 3 to 5μm is above 80%.

[0026] Compared with the prior art, this application has the following beneficial effects:

[0027] The optically transparent ceramics in this application are composed of oxides. Compared with fluorides, oxide transparent ceramics not only have excellent optical transparency and can maintain high transmittance in a wide wavelength range, but also show good chemical stability, thermal stability and mechanical strength. In addition, oxide transparent ceramics can be prepared or processed into complex shapes and structures by a variety of methods to meet various application requirements.

[0028] The present application discloses an infrared optical transparent ceramic with adjustable thermo-optic coefficient, which uses Sc2O3 with negative thermo-optic coefficient as the matrix and adds other components with positive thermo-optic coefficient as compensation components. By compensating the thermo-optic coefficients of each component, the thermo-optic coefficient of the transparent ceramic can be adjusted. At the same time, by selecting a lens barrel material that matches its linear thermal expansion coefficient, the focal length of the optical system can remain unchanged within the range of -40°C to +60°C, thereby improving its environmental adaptability and imaging quality. It avoids the use of additional electromechanical active devices or a combination of multiple optical elements in the athermal technology, meets the requirements of miniaturization and lightweight design of the optical system, and has broad application prospects in the field of athermal optical system design. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the infrared transmittance spectrum of the ceramic prepared in Example 1.

[0030] Figure 2 The XRD diffraction patterns of the ceramics prepared in Example 1 and Example 3 are shown.

[0031] Figure 3 This is a SEM microstructure photograph of the ceramic prepared in Example 1. DETAILED DESCRIPTION

[0032] The following non-limiting embodiments may enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way.

[0033] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0034] [Example 1]

[0035] The ceramics were prepared by sol-gel method and hot pressing sintering technology according to the volume ratio of Sc2O3 and MgO of 1:1:

[0036] According to the above ratio, the inorganic salt solution containing various metal ions is dissolved and mixed, and the citric acid solution is added as a chelating agent. The molar ratio of the chelating agent to the total metal ions is 1:1. The mixed solution is stirred and heated in a water bath at 80°C for 2.5 hours to obtain a light yellow transparent wet gel. The beaker containing the wet gel is transferred to an oven at 200°C for drying for 2 hours. After the dried gel is ground, it is calcined in a muffle furnace at 600°C for 20 hours to obtain a nanopowder. The powder is dry-pressed into a green body under a pressure of 50MPa, and then the sintering mold containing the green body is placed in a hot pressing sintering furnace. Under the protection of an argon atmosphere, the temperature is raised to 1300°C at a rate of 20°C / min, and the pressure is gradually increased to 40MPa. The temperature and pressure are kept for 30 minutes, and then cooled with the furnace. The sintered ceramic is annealed in an air atmosphere at 1150°C in a muffle furnace for 24 hours, and the density of the obtained ceramic is 99.9% and the average grain size is 220nm. In this embodiment, the prepared ceramic is mainly composed of two phases of Sc2O3 and MgO.

[0037] [Comparative Example 1]

[0038] The ceramics were prepared by sol-gel method and hot pressing sintering technology according to the volume ratio of Sc2O3 and MgO of 1:1.5:

[0039] According to the above ratio, the inorganic salt solution containing various metal ions is dissolved and mixed, and the citric acid solution is added as a chelating agent. The molar ratio of the chelating agent to the total metal ions is 1:1.5. The mixed solution is stirred and heated in an 80°C water bath for 2.5 hours to obtain a light yellow transparent wet gel. The beaker containing the wet gel is transferred to a 200°C oven and dried for 2 hours. After the dried gel is ground, it is calcined in a muffle furnace at 600°C for 20 hours to obtain a nanopowder. The powder is dry-pressed into a green body under a pressure of 50MPa, and then the sintering mold containing the green body is placed in a hot pressing sintering furnace. Under the protection of an argon atmosphere, the temperature is raised to 1300°C at a rate of 20°C / min, and the pressure is gradually increased to 40MPa. The temperature and pressure are maintained for 30 minutes, and then cooled with the furnace. The sintered ceramics are annealed in an air atmosphere at 1150°C in a muffle furnace for 24 hours, and the density of the obtained ceramics is only 97.9%, and the average grain size is 210nm. In this embodiment, the prepared ceramic is mainly composed of two phases of Sc2O3 and MgO.

[0040] [Example 2]

[0041] The ceramics were prepared by spray pyrolysis and spark plasma sintering technology with a volume ratio of Sc2O3 to MgO of 1:1 and a molar ratio of Sc2O3 to Y2O3 of 1:0.25:

[0042] According to the above ratio, the inorganic salt solution containing various metal ions is dissolved and mixed, and 1L / min nitrogen is used as a carrier gas. The precursor droplets after ultrasonic atomization are successively subjected to evaporation heat treatment at 200°C, drying heat treatment at 500°C, and decomposition heat treatment at 750°C to obtain nano powder. The powder is dry pressed into a green body under a pressure of 50MPa, and the sintering mold equipped with the green body is placed in a spark plasma sintering furnace. Under the protection of argon atmosphere, the temperature is raised to 1200°C at a heating rate of 100°C / min, the pressure is increased to 80MPa, and the heat and pressure are maintained for 30min, and then cooled with the furnace. The sintered ceramic is annealed in a muffle furnace at 1150°C air atmosphere for 24h, and the density of the obtained ceramic is 99.9% and the average grain size is 190nm. In this embodiment, Y2O3 is dissolved in the Sc2O3 and MgO lattices, and the prepared ceramic is mainly composed of Sc2O3 and MgO two phases.

[0043] [Example 3]

[0044] The volume ratio of Sc2O3 to MgO is 1:1, and the molar ratio of Sc2O3 to Y2O3 is 1:0.5. The ceramics are prepared by spray pyrolysis and spark plasma sintering technology:

[0045] According to the above ratio, the inorganic salt solution containing various metal ions is dissolved and mixed, and 1L / min nitrogen is used as a carrier gas. The precursor droplets after ultrasonic atomization are successively subjected to evaporation heat treatment at 200°C, drying heat treatment at 500°C, and decomposition heat treatment at 750°C to obtain nano powder. The powder is dry pressed into a green body under a pressure of 50MPa, and the sintering mold equipped with the green body is placed in a spark plasma sintering furnace. Under the protection of argon atmosphere, the temperature is raised to 1200°C at a heating rate of 100°C / min, the pressure is increased to 100MPa, and the heat and pressure are maintained for 30min, and then cooled with the furnace. The sintered ceramic is annealed in a muffle furnace at 1150°C air atmosphere for 24h, and the density of the obtained ceramic is 99.9% and the average grain size is 230nm. In this embodiment, part of Y2O3 is dissolved in the Sc2O3 lattice, and the prepared ceramic is mainly composed of Sc2O3, MgO and ScYO3.

[0046] [Comparative Example 2]

[0047] The ceramics were prepared by spray pyrolysis and spark plasma sintering technology with a volume ratio of Sc2O3 to MgO of 1:1 and a molar ratio of Sc2O3 to Y2O3 of 1:0.5:

[0048] According to the above ratio, the inorganic salt solution containing various metal ions is dissolved and mixed, and 1L / min nitrogen is used as the carrier gas. The precursor droplets after ultrasonic atomization are successively subjected to evaporation heat treatment at 200°C, drying heat treatment at 500°C, and decomposition heat treatment at 750°C to obtain nano powder. The powder is dry pressed into a green body under a pressure of 50MPa, and the sintering mold equipped with the green body is placed in a spark plasma sintering furnace. Under the protection of argon atmosphere, the temperature is raised to 1200°C at a heating rate of 100°C / min, the pressure is increased to 80MPa, and the heat and pressure are maintained for 30min, and then cooled with the furnace. The sintered ceramic is annealed in a muffle furnace at 1150°C air atmosphere for 24h, and the density of the obtained ceramic is only 98%, and the grain size is 280nm. In this embodiment, part of Y2O3 is dissolved in the Sc2O3 lattice, and the prepared ceramic is mainly composed of Sc2O3, MgO and ScYO3 three phases.

[0049] [Example 4]

[0050] The ceramics were prepared by spray pyrolysis and spark plasma sintering technology according to the volume ratio of Sc2O3 to MgO of 1:1, the molar ratio of Sc2O3 to Y2O3 of 1:0.2, the molar ratio of Sc2O3 to ZrO2 of 1:0.03, and the molar ratio of MgO to ZnO of 1:0.1:

[0051] According to the above ratio, the inorganic salt solution containing various metal ions is dissolved and mixed, and 1L / min nitrogen is used as the carrier gas. The precursor droplets after ultrasonic atomization are sequentially subjected to evaporation heat treatment at 200°C, drying heat treatment at 500°C, and decomposition heat treatment at 750°C to obtain nanopowders. The powder is dry-pressed into a green body under a pressure of 50MPa, and the sintering mold containing the green body is placed in a spark plasma sintering furnace. Under the protection of an argon atmosphere, the temperature is raised to 1200°C at a heating rate of 100°C / min, the pressure is increased to 100MPa, and the heat and pressure are maintained for 30min, and then cooled with the furnace. The sintered ceramic is annealed in a muffle furnace at 1150°C in an air atmosphere for 24h to obtain an infrared transparent ceramic with a density of 99.9% and an average grain size of 195nm. In this embodiment, Y2O3 and ZnO are respectively dissolved in the Sc2O3 and MgO lattices, and the prepared ceramic is mainly composed of Sc2O3 and MgO phases.

[0052] [Example 5]

[0053] According to the volume ratio of Sc2O3 and MgO of 1:1, 0.01 mol Al2O3 powder was added and the ceramics were prepared by ball milling and hot isostatic pressing technology:

[0054] According to the above ratio, the powders of each component are mixed. The mixed powder is ball-milled for 24 hours using ZrO2 microspheres as grinding balls and anhydrous ethanol as ball-milling media. Among them, the mass ratio of grinding balls, anhydrous ethanol and powder is 6:7:1. The slurry after ball milling is dried at 100°C to obtain well-dispersed nanopowder. The powder is dry-pressed into a green body under a pressure of 50MPa. The green body is pre-sintered for 1 hour under air conditions at 1400°C, and then hot isostatically pressed for 1 hour under argon atmosphere at 1350°C and 200MPa. The sintered ceramic is annealed in a muffle furnace at 1000°C in an air atmosphere for 24 hours to obtain an infrared transparent ceramic with a density of 99.9% and an average grain size of 200nm. In this embodiment, the prepared ceramic is mainly composed of four phases of Sc2O3, MgO, MgAl2O4 and ScAlO3.

[0055] Table 2 Phase composition and effects of different embodiments

[0056] Phase composition Density Average grain size 3~5μm transmittance Example 1 <![CDATA[Sc2O3、MgO]]> 99.9％ 220nm 81.4％ Comparative Example 1 <![CDATA[Sc2O3、MgO]]> 97.9％ 210nm 78.2％ Example 2 <![CDATA[Sc2O3、MgO]]> 99.9％ 190nm 83.6％ Example 3 <![CDATA[Sc2O3、MgO、ScYO3]]> 99.9 230nm 81.2％ Comparative Example 2 <![CDATA[Sc2O3、MgO、ScYO3]]> 98％ 280nm 50.8％ Example 4 <![CDATA[Sc2O3、MgO]]> 99.9％ 195nm 83.5％ Example 5 <![CDATA[Sc2O3、MgO、MgAl2O4、ScAlO3]]> 99.9％ 200nm 80.7％

Claims

1. An infrared optically transparent ceramic, characterized in that: The composite material is composed of Sc2O3 and alkali metal oxides, the thermo-optic coefficients of the two compensate each other, and the volume ratio of Sc2O3 to alkali metal oxides is 1:

1.

2. The infrared optical transparent ceramic according to claim 1, characterized in that: One or more of the rare earth oxides Ln2O3, Al2O3, ZrO2, and ZnO are also added to adjust the thermo-optical coefficient of the infrared optically transparent ceramic.

3. The infrared optical transparent ceramic according to claim 2, characterized in that: The rare earth oxide Ln2O3 is one or more of Y2O3, La2O3, Gd2O3, Lu2O3, and Yb2O3; the alkali metal oxide is one or more of BeO, MgO, CaO, SrO, and BaO.

4. The infrared optical transparent ceramic according to claim 2, characterized in that: When ZrO2 is added, it forms a solid solution with Sc2O3, wherein the molar ratio of Sc2O3 to ZrO2 ranges from 1:0 to 1:0.

05.

5. A method for preparing the infrared optically transparent ceramic according to any one of claims 1 to 4, characterized in that: According to the material composition, uniform nanopowder is synthesized, and green body forming and ceramic sintering are carried out to make the ceramic obtain a microstructure with uniform distribution of various phases.

6. The preparation method according to claim 5, characterized in that: The ceramic sintering temperature is 1200-1350° C., and the sintering pressure is above 40 MPa.

7. The preparation method according to claim 6, characterized in that: When the physical phases in the infrared optically transparent ceramics are greater than two phases, the sintering pressure is greater than 100 MPa.

8. The preparation method according to claim 6, characterized in that: When the physical phases in the infrared optically transparent ceramics are greater than three phases, the sintering pressure is above 200 MPa.

9. The preparation method according to claim 5, characterized in that: The crystal size of the nano powder is less than 10 nm, and the particle size of the nano powder is D 50 <100nm, the particle size distribution range of nano powder is 30~150nm, and the specific surface area of ​​nano powder is>60m 2 / g.

10. The preparation method according to claim 5, characterized in that: The method also includes a post-processing step of the infrared optical transparent ceramic, wherein the obtained infrared optical transparent ceramic is annealed in a temperature range of 1000 to 1200° C. for 10 to 48 hours.

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