Improved silica ceramic antenna window and its composite die molding method

Abstract

The application discloses an improved silica ceramic antenna window with a density of 1.8-1.9 g / cm 3 , a bending strength of 55-65 MPa, a tensile strength of 35-45 MPa, a thermal conductivity of 0.5-0.6 W / m.k, a dielectric constant of 3-3.8, and a loss tangent of 0.0004-0.0006. The composite die molding method of the improved silica ceramic antenna window comprises the following steps: preparing a premix, feeding, die molding, drying, high-temperature treatment, impregnation, post-impregnation heat treatment, and polishing and finishing. The silica ceramic antenna window obtained by the composite die molding method has a good surface quality, is free of pits, slag dropping, cracking and the like, and has the advantages of high apparent quality, high mechanical strength, high density and stable performance. The die molding method can quickly complete molding without mechanical processing, and has the advantages of simple process, high production efficiency, high product yield, stable product performance and low production cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramic materials, in particular to an improved silica ceramic antenna window and a composite die forming method thereof. BACKGROUND

[0002] Space products are often used in extreme environments such as high temperature, impact and vibration. In order to ensure the electromagnetic wave transmission efficiency of the antenna in the extreme environment, the heat-proof material at the antenna must be partially opened and replaced with a new material having heat-proof and wave-transparent effects, i.e. an antenna window. Quartz composite ceramic has the characteristics of low density, high strength and good wave-transparent performance, and is widely used in the field of aerospace. It has become a commonly used material system for products such as antenna covers and antenna windows.

[0003] The most commonly used forming method for quartz ceramic antenna windows at present is silicon sol impregnation composite forming based on sol-gel method. This method needs to obtain the final product by impregnation, drying, heat treatment and mechanical processing of the fiber woven body for multiple times. The production cycle is often long, and the cost of the woven body is high, which is not conducive to mass production. In addition, the fibers are prone to breakage and tearing during the processing, resulting in poor apparent quality and decreased local mechanical strength. Another die forming method breaks through the traditional processing mode and can quickly complete the forming. The antenna window produced by the die forming method does not need to use quartz fiber woven body, which can greatly reduce the production cost. The premixed material can be pressed into a nearly net size state through the mold, which saves the mechanical processing time and effectively shortens the production cycle. However, the antenna window product obtained by the existing die forming method has the problem of uneven product density, and most of the product internal has crystals and pores, which leads to unstable product performance. In addition, due to the generation of pores and crystals during production, the product is prone to cracking, resulting in a low yield.

[0004] Therefore, it is urgent to propose a new scheme to solve the problems of long production cycle, high cost, poor apparent quality and decreased local mechanical strength of the existing impregnation composite forming method, and to solve the problem of uneven internal density of the product of the existing die forming method. SUMMARY

[0005] In order to overcome the above technical deficiencies, the present application provides an improved silica ceramic antenna window and a composite die forming method thereof, which solves the problems of complex process and fiber easy to tear of the existing impregnation composite forming method and the problem of uneven internal density of the product of the existing die forming method, so as to obtain a product with high apparent quality, high mechanical strength, high density and stable performance, and to achieve the purposes of improving product quality, improving yield, shortening production cycle and reducing cost.

[0006] In order to achieve the above purposes, the technical scheme adopted by the present application is as follows:

[0007] An improved silica ceramic antenna window has a density of 1.8-1.9 g / cm 3 , a bending strength of 55-65 MPa, a tensile strength of 35-45 MPa, a thermal conductivity of 0.5-0.6 W / m·k, a dielectric constant of 3-3.8, and a loss tangent of 0.0004-0.0006.

[0008] A composite die molding method of an improved silica ceramic antenna window comprises the following steps:

[0009] 1) Preparation of premix:

[0010] Silica sol treatment: take silica sol, heat in a water bath at 60-80 ℃ until gel is formed, crush the gel, dry at 140-160 ℃ until constant weight, then grind into gel coarse powder, add 5-15% PVA aqueous solution based on the mass of the gel coarse powder, then grind, sieve, and obtain powder; the content of PVA in the PVA aqueous solution is 5-7 wt%;

[0011] Mixing: mix silica sol, silica short fibers with a fiber length of 2-4 mm, and the prepared powder in a mass ratio of 1:8-12:18-28, then seal and stand at room temperature for 4-6 h to obtain a premix;

[0012] 2) Feeding: heat the mold treated with a release agent to 40-50 ℃ and keep for 10-20 min, then evenly layer and fill the prepared premix into the mold; wherein the heating speed is 0.5-1 ℃ / min, the feeding time is controlled to be 6-10 min, and the feeding temperature is controlled to be 40-50 ℃;

[0013] 3) Die pressing treatment: after feeding is completed, close the mold and pressurize to 20-25 MPa and keep pressure, then heat treatment, then naturally cool to 15-25 ℃, and start natural pressure relief to normal pressure when naturally cooling to 60-50 ℃; during the heat treatment, first heat to 60-70 ℃ and keep for 100-120 min, then heat to 110-120 ℃ and keep for 100-120 min;

[0014] 4) Drying: demold the green body after die pressing, and put it into a drying box, heat to 140-150 ℃ and dry for 2-3 h to obtain a die pressed ceramic green body; wherein the heating speed is 1-3 ℃ / min;

[0015] 5) High temperature treatment: put the dried green body into a heating furnace, heat to 700-750 ℃ at a speed of 2-3 ℃ / min, keep for 100-120 min, then cool to 15-25 ℃ with the furnace and take out;

[0016] 6) Immersion: after high-temperature treatment, the blank is put into a container, vacuum is extracted to -0.07 to -0.09 MPa and pressure is maintained, and when pressure is maintained for 10 to 20 min, the blank is immersed by injecting silica sol, and after the silica sol is injected, the silica sol is heated to 80 to 90℃ at a speed of 1 to 3℃ / min, and the temperature is maintained until the silica sol becomes a gel;

[0017] 7) Post-Immersion Heat Treatment: After the immersion treatment, the blank is put into a heating furnace, first heated to 400 to 450℃ and maintained for 100 to 120 min, then heated to 900 to 950℃ and maintained for 100 to 120 min, and finally cooled to 15 to 25℃ with the furnace and taken out;

[0018] 8) Polishing and Finishing: according to the product size requirements, the edges and corners are polished and finished.

[0019] Preferably, in steps 1) and 6), the silica sol has a pH value of 2 to 5 and a solid content of 38 to 42% at 20℃.

[0020] Preferably, in step 1), the amount of PVA aqueous solution added is 8 to 10% of the mass of the gel powder.

[0021] Preferably, in step 1), the content of PVA in the PVA aqueous solution is 7wt%.

[0022] Preferably, in step 1), the mass ratio of silica sol: 2 to 4 mm silica short fibers: prepared powder in the premix is 1:10:20 to 25.

[0023] Preferably, in step 1), the silica short fibers and the powder are mixed first, and then the silica sol is added, and the silica sol is added uniformly by spraying during the mixing of the silica short fibers and the powder.

[0024] Preferably, in step 3), the temperature rising speed during the temperature rising process is controlled to be 0.5 to 1℃ / min.

[0025] Preferably, in step 7), the temperature rising speed during the temperature rising process is controlled to be 2 to 3℃ / min.

[0026] Compared with the prior art, the present application has the following advantages:

[0027] The improved silica ceramic antenna window designed in the present application has a density of 1.8 to 1.9 g / cm 3The silica ceramic antenna window has the advantages of high apparent quality, high mechanical strength, high density and stable performance.

[0028] The improved composite die forming method of the silica ceramic antenna window is characterized in that: a gel prepared by a sol-gel method is dried and ground into a powder with high reactivity; the uniformity of the premix is improved and the moisture in the premix is reduced by adding the powder, thereby providing a basis for obtaining a silica ceramic antenna window product with uniform density; the strength of the product is improved by adding a small amount of PVA as a binder; the mechanical properties of the product are improved by adding quartz short fibers; the silicon sol is added in a spraying mode during mixing, thereby playing a role in filling gaps and improving the density of the product, and meanwhile having a certain bonding effect, which can reduce the amount of PVA and avoid excessive pores; the premix after treatment is filled into a die forming mold, and the temperature is raised and the pressure is increased in sections, so that volatile components can be fully discharged; the green body is improved in density, apparent quality and structural strength by immersion and composite and heat treatment. DETAILED DESCRIPTION

[0029] In order to better explain the present application, the main content of the present application is further illustrated below in combination with specific examples, but the content of the present application is not limited to the following examples only.

[0030] Example 1:

[0031] 1) The silicon sol with a pH value (20℃) of 3 and a solid content of 38% (the same type of silicon sol is used in the following of this example) is heated to gel in a water bath at 60℃, the gel is crushed and dried at 140℃ to constant weight, and then ground into coarse powder, 8% PVA aqueous solution of the mass of the coarse powder is added, ground, and sieved through a 60-mesh sieve to obtain powder; the PVA content in the PVA aqueous solution is 7wt%.

[0032] Another silicon sol is prepared, and the silicon sol: 2mm silica short fibers: the powder prepared in step 1) are mixed in a mass ratio of 1:10:20 to obtain a premix, the silica short fibers and the powder are first mixed, and the silicon sol is added uniformly in a spraying mode during mixing. After mixing uniformly, the premix is sealed and left to stand at room temperature for 4-6h.

[0033] 2) The demolding agent treated pressurized mold is heated to 40℃ at a rate of 0.5℃ / min and kept at 40℃ for 10min.

[0034] The premix is evenly layered and filled into the mold, and the feeding time is controlled within 6min, and the mold temperature is maintained at 40℃ during the feeding process.

[0035] 3) clamp pressure to 20 MPa and keep pressure, then heat to 60°C at a heating rate of 0.5°C / min, keep temperature for 100 min, then heat to 110°C at a heating rate of 0.5°C / min, keep temperature for 100 min, and finally naturally cool to 15-25°C, and start natural pressure relief when cooling to 60°C.

[0036] 4) remove the blank, and put the removed blank into an electrically heated air drying oven, heat to 140°C at a heating rate of 1°C / min, and dry for 2 h to obtain a pressed ceramic body.

[0037] 5) put the body into a muffle furnace, heat to 700°C at a heating rate of 2°C / min, keep temperature for 100 min, and then take out after the furnace is cooled to 15-25°C.

[0038] 6) put the body into a container, vacuumize to -0.07 MPa and keep pressure for 10 min, then inject silica sol to immerse the body, the silica sol is injected to be more than 6 cm above the body, heat the silica sol to 80°C at a heating rate of 1°C / min to improve the impregnation efficiency, keep temperature and pressure until the silica sol becomes a gel, which can repair the small pits on the surface of the body and improve the apparent quality of the product.

[0039] 7) put the blank into a muffle furnace, first heat to 400°C at a heating rate of 2°C / min, keep temperature for 100 min, then heat to 900°C at a heating rate of 2°C / min, keep temperature for 100 min, and then take out after the furnace is cooled to 15-25°C, and polish and trim the edge and corner parts according to the product size requirements.

[0040] The pressed part prepared in this example has good surface quality, no pits, no slag, etc., uniform internal density, and a yield rate of 98%. The performance test results of the pressed part processing sample are shown in Table 1.

[0041] Table 1 Performance test results

[0042]

[0043] Example 2:

[0044] 1) the silica sol with a pH value (20°C) of 4 and a solid content of 40% (the same type of silica sol is used in the following of this example) is heated to gel in a water bath at 70°C, the gel is crushed and dried to constant weight at 150°C, then ground into coarse powder, 9% PVA aqueous solution is added to the coarse powder, and the powder is ground through a 60 mesh sieve; the PVA content in the PVA aqueous solution is 7 wt%.

[0045] Another silica sol was taken and mixed with the silica sol: 3 mm silica short fiber: powder prepared in step 1) at a mass ratio of 1:10:22 to obtain a premix. The silica short fiber and the powder were first mixed, and the silica sol was added uniformly by spraying during the mixing process. After uniform mixing, the premix was sealed and left to stand at room temperature for 5 h.

[0046] 2) The release agent treated pressurized mold was heated to 45°C at a rate of 0.7°C / min and kept for 15 min.

[0047] The premix was uniformly layered and filled into the mold, and the feeding time was controlled at 8 min. The mold temperature was maintained at 45°C during the feeding process.

[0048] 3) The mold was closed and pressurized to 22 MPa and kept, then heated to 65°C at a rate of 0.7°C / min and kept for 110 min, heated to 115°C at a rate of 0.7°C / min and kept for 110 min, and naturally cooled to 15-25°C. When the temperature dropped to 55°C, the pressure was naturally released.

[0049] 4) The blank was demolded, and the demolded blank was placed in an electrically heated air drying oven and heated to 145°C at a rate of 2°C / min and dried for 2.5 h to obtain a pressed ceramic body.

[0050] 5) The above body was placed in a muffle furnace and heated to 725°C at a rate of 2.5°C / min, kept for 110 min, then cooled to 15-25°C with the furnace and taken out.

[0051] 6) The body was vacuumed in a container to -0.08 MPa and kept for 15 min, and silica sol was injected to immerse the body by 8 cm above the body height, then the silica sol was heated to 85°C at a rate of 2°C / min to improve the impregnation efficiency. The temperature was kept and the pressure was kept until the silica sol became a gel, which could repair the small pits on the surface of the body and improve the apparent quality of the product.

[0052] 7) The blank was placed in a muffle furnace, first heated to 425°C at a rate of 2.5°C / min and kept for 110 min, then heated to 925°C at a rate of 2.5°C / min with the furnace, kept for 110 min, then cooled to 15-25°C with the furnace and taken out. The edges and corners were polished and trimmed according to the product size requirements.

[0053] The pressed part prepared in this example has good surface quality, no pits, no slag, etc., uniform internal density, and a yield of 99%. The performance test results of the pressed part processing sample are shown in Table 2.

[0054] Table 2 Performance test results

[0055]

[0056] Example 3

[0057] 1) The silica sol with pH value (20℃) 5 and solid content 42% (the same silica sol was used in the following examples) was heated in water bath at 80℃ until gelling. The gelled product was crushed and dried at 160℃ until constant weight, then ground into coarse powder. The powder was mixed with PVA aqueous solution (10% of the mass of the powder) and ground through a 60 mesh sieve. The PVA content in the PVA aqueous solution was 7wt%.

[0058] Another silica sol was prepared and mixed with the silica short fibers and the powder prepared in step 1) at a mass ratio of 1:10:25 to obtain a premix. The silica short fibers were first mixed with the powder, and the silica sol was added by spraying during the mixing process. After mixing, the premix was sealed and left to stand at room temperature for 6h.

[0059] 2) The pressurized mold treated with the release agent was heated to 50℃ at a rate of 1℃ / min and kept at this temperature for 20min.

[0060] The premix was evenly layered and filled into the mold. The filling time was controlled at 10min, and the temperature of the mold was maintained at 50℃ during the filling process.

[0061] 3) The mold was closed and pressurized to 25MPa and kept at this pressure, then heated to 70℃ at a rate of 1℃ / min and kept at this temperature for 120min, then heated to 120℃ at a rate of 1℃ / min and kept at this temperature for 120min, then naturally cooled to 15-25℃, and naturally depressurized when the temperature dropped to 50℃.

[0062] 4) The green body was demolded, and the demolded green body was placed in an electrically heated air drying oven and heated to 150℃ at a rate of 3℃ / min and dried for 3h to obtain a pressed ceramic green body.

[0063] 5) The green body was placed in a muffle furnace and heated to 750℃ at a rate of 3℃ / min and kept at this temperature for 120min, then the furnace was cooled to 15-25℃ and the green body was taken out.

[0064] 6) The green body was placed in a container and vacuumized to -0.09MPa and kept at this pressure for 20min. Silica sol was injected to immerse the green body by 10cm above the green body. The silica sol was heated to 90℃ at a rate of 3℃ / min to improve the impregnation efficiency. The silica sol was kept at this temperature and pressure until it became a gel, which could repair the small pits on the surface of the green body and improve the apparent quality of the product.

[0065] 7) The green body was placed in a muffle furnace and heated to 450℃ at a rate of 3℃ / min and kept at this temperature for 120min, then the furnace was heated to 950℃ at a rate of 3℃ / min and kept at this temperature for 120min, then the furnace was cooled to 15-25℃ and the green body was taken out. The edges and corners of the green body were polished and trimmed according to the product size requirements.

[0066] The surface quality of the molded parts prepared in this example is good, without pits, slag drop, etc. The internal density is uniform, and the yield reaches 99.5%. The performance of the samples processed from the molded parts is tested, and the results are shown in Table 3.

[0067] Table 3 Performance test results

[0068]

[0069] The other parts not described belong to the prior art.

Claims

1. An improved composite die molding method for silicon oxide ceramic antenna windows, characterized by: The method comprises the following steps: 1) Preparation of premix: Silica sol treatment: Take silica sol, heat in water bath at 60-80℃ until gel is formed, crush the gel, dry at 140-160℃ until constant weight, then grind into coarse gel powder, add 5-15% PVA aqueous solution based on the mass of the coarse gel powder, then grind, sieve, and obtain powder; the content of PVA in the PVA aqueous solution is 5-7wt%; Mixing: mix silica sol, silica short fibers with a fiber length of 2-4mm, and the prepared powder in a mass ratio of 1:8-12:18-28, then seal and stand at room temperature for 4-6h to obtain a premix; in the mixing process, first mix the silica short fibers and the powder, then add the other silica sol, and the silica sol is added uniformly in the mixing process of the silica short fibers and the powder in a spraying manner; 2) Feeding: heat the mold treated with a release agent to 40-50℃ and keep for 10-20min, then evenly layer and fill the prepared premix into the mold; wherein the heating speed is 0.5-1℃ / min, the feeding time is controlled to be 6-10min, and the feeding temperature is controlled to be 40-50℃; 3) Molding treatment: after feeding is completed, close the mold and pressurize to 20-25MPa and keep pressure, then heat treatment, then naturally cool to 15-25℃, and start natural pressure relief to normal pressure when naturally cooling to 60-50℃; in the heating treatment process, first heat to 60-70℃ and keep for 100-120min, then heat to 110-120℃ and keep for 100-120min; 4) Drying: demold the blank after molding treatment, and put it into a drying box, heat to 140-150℃ and dry for 2-3h to obtain a molded ceramic body; wherein the heating speed is 1-3℃ / min; 5) High temperature treatment: put the dried blank into a heating furnace, heat to 700-750℃ at a speed of 2-3℃ / min, keep for 100-120min, then cool to 15-25℃ with the furnace and take out; 6) Impregnation: put the blank after high temperature treatment into a container, vacuumize to-0.07--0.09MPa and keep pressure, inject silica sol to impregnate the blank when keeping pressure for 10-20min, after injecting silica sol, heat the silica sol to 80-90℃ at a speed of 1-3℃ / min, keep pressure until the silica sol becomes gel; 7) Heat treatment after impregnation: put the blank after impregnation into a heating furnace, first heat to 400-450℃ and keep for 100-120min, then heat to 900-950℃ and keep for 100-120min, finally cool to 15-25℃ with the furnace and take out; 8) Polishing and trimming: polish and trim the edge and corner parts according to the product size requirement.

2. The improved composite die press molding method of a silica ceramic antenna window according to claim 1, characterized in that: In steps 1) and 6), the silica sol is a silica sol with a pH value of 2-5 and a solid content of 38-42% at 20℃.

3. The improved composite die press molding method of a silica ceramic antenna window according to claim 1, characterized in that: In step 1), the addition amount of the PVA aqueous solution is 8-10% based on the mass of the coarse gel powder.

4. The improved composite die press molding method of a silica ceramic antenna window according to claim 1, characterized in that: In step 1), the content of PVA in the PVA aqueous solution is 7wt%.

5. The improved composite die press molding method of a silica ceramic antenna window according to claim 1, characterized in that: In the step 1), the mass ratio of the silicon sol in the premix: 2-4 mm short silica fiber: the prepared powder is 1:10:20-25.

6. The improved composite die press molding method of a silica ceramic antenna window according to claim 1, characterized by: In the step 3), the temperature increasing speed of the temperature increasing process is controlled to be 0.5-1 ℃ / min.

7. The improved composite die press molding method of a silica ceramic antenna window according to claim 1, characterized in that: In the step 7), the temperature increasing speed of the temperature increasing process is controlled to be 2-3 ℃ / min.

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