Chromium niobate ceramic with low thermal conductivity and preparation method thereof
By using chromium trioxide and niobium pentoxide as raw materials, low-thermal conductivity chromium niobate ceramics are prepared, which solves the problem of difficulty in matching existing materials with refractory metals and high-entropy alloys, and realizes the preparation of high-performance ceramic materials, which is suitable for the field of thermal insulation and insulation.
Patent Information
- Application Number
- CN202510380859.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-28
- Publication Date
- 2025-07-01
AI Technical Summary
The existing low thermal conductivity insulation materials are difficult to match refractory metals and refractory high entropy alloys, and the thermal expansion coefficient does not match, affecting their application effect.
Chromium trioxide and niobium pentoxide are used as raw materials to prepare low-thermal conductivity chromium niobate ceramics through ball milling, drying, calcining and hot pressing sintering to ensure that their thermal conductivity is less than 1.2W·m-1·K-1, bending strength is higher than 180MPa, hardness is more than 10GPa, and the thermal expansion coefficient is matched with refractory metals and high-entropy alloys.
The prepared chromium niobate ceramics have the characteristics of high relative density, high melting point, high flexural strength, high hardness and low thermal conductivity. They can effectively match the thermal expansion coefficient of refractory metals and high entropy alloys and are suitable for the field of thermal insulation.
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of high-performance special ceramics, and particularly relates to a low-thermal-conductivity chromium niobate ceramic and a preparation method thereof. Background Art
[0002] In the aerospace field, ceramic matrix composites are used to manufacture the thermal protection systems and engine components of aircraft to withstand extreme working environments of high temperature and high pressure; in the electronics field, ceramic materials play a crucial role as packaging materials and heat dissipation substrates for electronic components; in the energy field, ceramic materials are applied to the linings of high-temperature furnaces and heat-insulating pipes, aiming to improve energy utilization efficiency and reduce heat loss. As a key performance index of ceramic materials, thermal conductivity has a decisive impact on their performance in practical applications. For application scenarios that require good heat insulation performance, ceramic materials with low thermal conductivity can effectively prevent heat transfer, reduce energy consumption, and thus improve the energy utilization efficiency of the system. Currently, the mainly used low-thermal-conductivity materials include zirconia, alumina, silica thin films, silica aerogels, mullite fibers, aluminosilicate fibers, etc. Especially for the heat insulation of high-entropy refractory alloy materials, new low-thermal-conductivity heat insulation ceramic materials with a matching coefficient of thermal expansion are needed.
[0003] The above-reported heat insulation materials all have certain deficiencies. Comparative document 1 (Scientific Reports, 2018, 8: 10537) reported that the thermal conductivity of the SiO2 thin film is only 0.86 W·m -1 ·K -1 , but the high-temperature resistance level is below 1000 °C and it is easy to absorb moisture; comparative document 2 (Nanostructured Materials, 1998, 10(6): 909-916), aluminosilicate fibers exhibit excellent thermal conductivity, only 0.15 - 0.17 W·m at room temperature -1 ·K -1 , but there is a problem of mismatched coefficient of thermal expansion as a heat insulation coating for refractory high-entropy alloys. Due to its flexible characteristics, it is more suitable to be used as fiber felts, cloths, etc. to meet engineering requirements. Comparative document 3 (Journal of American Ceramics Society 2008, 91: 2623–2629), the coefficient of thermal expansion of rare earth silicate γ-Y2Si2O7 is about 3.9×10 -6 / K, and the thermal conductivity at room temperature is about 4.94 W·m -1 ·K -1Higher than common low-thermal-conductivity materials, it cannot meet the heat insulation requirements, and there is a large difference in the coefficient of thermal expansion from refractory metals and their alloys, so it cannot be used as their coating. Comparing with Document 4 (Acta Materialia, 2007, 55: 2949–2957), rare earth zirconate La2Zr2O7 exhibits the characteristic of low thermal conductivity, but its coefficient of thermal expansion is 9×10 -6 / K, which is much higher than that of refractory metals and their alloys, so it cannot be used as the heat insulation coating of refractory metals and their alloys. Comparing with Document 5 (Journal of MaterialsScience&Technology, 2015, 31: 369-374), yttria-stabilized zirconia (YSZ) material is the most commonly used coating for nickel-based alloys at present, showing a relatively low thermal conductivity, about 2.2W·m -1 ·K -1 at room temperature, but the coefficient of thermal expansion of YSZ is large, much higher than that of refractory metals and their alloys.
[0004] Therefore, developing a material with high temperature resistance, matching with refractory high-entropy alloys and low thermal conductivity has become a key problem to be solved urgently in the current field of ceramic materials. Based on this background, the present invention aims to provide an innovative low-thermal-conductivity ceramic material and its preparation method to meet the urgent needs of the refractory metal and refractory high-entropy alloy markets for high-performance ceramic materials. Summary of the Invention
[0005] The object of the present invention is to provide a low-thermal-conductivity chromium niobate ceramic and its preparation method to solve the problem that existing low-thermal-conductivity heat insulation materials are difficult to match with refractory metals and refractory high-entropy alloys.
[0006] To achieve the above object, the present invention adopts the following technical scheme: a low-thermal-conductivity chromium niobate ceramic, the raw materials for preparing the chromium niobate ceramic are chromium trioxide and niobium pentoxide, and the molar ratio of chromium trioxide to niobium pentoxide is 1.00~1.05: 0.98~1.00.
[0007] Furthermore, both the chromium trioxide and the niobium pentoxide are powders, the particle sizes of the chromium trioxide and the niobium pentoxide are both 1~3μm, and the purities are not less than 99.9%.
[0008] The preparation method of the low-thermal-conductivity chromium niobate ceramic includes the following steps:
[0009] S1. Mix chromium trioxide and niobium pentoxide evenly in a medium to obtain a well-mixed slurry;
[0010] S2. Filter, dry and sieve the slurry obtained in S1 to obtain a mixed powder;
[0011] S3. Calcinate and sinter the mixed powder obtained in S2 to obtain the chromium niobate ceramic of the present invention.
[0012] Further, in S1, chromium(III) oxide and niobium pentoxide are uniformly mixed in a ball mill tank. The ball milling medium is zirconia ceramic balls with a particle size of 5 - 10 mm; the mixing medium is anhydrous ethanol; the mass ratio of the raw material powder, zirconia ceramic balls, and anhydrous ethanol is 1:1 - 3:5 - 10; the ball milling speed is 60 - 180 r / min, and the ball milling time is 4 - 12 h.
[0013] Further, in S2, the drying temperature is 50 - 80 °C, and the drying time is 6 - 12 h; after drying, it is sieved through a 100 - 400 mesh sieve.
[0014] Further, in S3, the calcination temperature is 1000 - 1300 °C, and the calcination time is 1 - 4 h.
[0015] Further, in S3, the sintering temperature is 1300 - 1500 °C, and the sintering time is 0.5 - 2 h; the sintering atmosphere is vacuum, argon, or air; the sintering pressure is controlled at 20 - 40 MPa; the heating rate is 5 - 20 °C / min, and the cooling rate is 5 - 20 °C / min.
[0016] Further, it is characterized in that: in S3, the relative density of the obtained chromium niobate ceramic is not less than 95%, the flexural strength is not less than 180 MPa, the hardness is not less than 10 GPa, and the room temperature thermal conductivity is not higher than 1.2 W·m -1 ·K -1 .
[0017] Advantages of the present invention:
[0018] 1. The present invention uses chromium(III) oxide and niobium pentoxide as raw materials for the first time to obtain chromium niobate ceramic. Under vacuum conditions, chromium niobate ceramic with high relative density, high flexural strength, high hardness, and low thermal conductivity is obtained by hot - press sintering. Analysis shows that chromium niobate ceramic has the characteristics of high relative density, high melting point, high flexural strength, high hardness, and low thermal conductivity. The relative density is above 95%, the melting point is not less than 1750 °C, the flexural strength is above 180 MPa, the hardness is above 10 GPa, and the thermal conductivity is below 1.2 W·m -1 ·K -1 below;
[0019] 2. The process for preparing chromium niobate powder in the present invention is simple and rapid. High - purity chromium niobate ceramic powder is directly obtained from chromium(III) oxide and niobium pentoxide raw materials. The purity of chromium niobate powder is above 99%. Chromium niobate ceramic is obtained by hot - press sintering method, which is convenient for industrial application and has broad application prospects. Brief Description of the Drawings
[0020] Figure 1 is the X-ray diffraction pattern of the chromium niobate ceramic powder obtained in Example 1 of the present invention;
[0021] Figure 2 is the microstructural diagram of the chromium niobate ceramic bulk obtained in Example 2 of the present invention;
[0022] Figure 3 is the curve graph of the thermal conductivity of the chromium niobate ceramic bulk obtained in Example 3 of the present invention varying with temperature;
[0023] Figure 4 is the microstructural diagram of the hardness indentation of the chromium niobate ceramic obtained in Example 4 of the present invention. Detailed implementation manners
[0024] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention.
[0025] The raw material sources in the embodiments of the present invention are: Cr2O3 (Beijing Huawei Ruike Chemical Co., Ltd., purity 99.9%, particle size 1 - 3μm); Nb2O5 (Beijing Huawei Ruike Chemical Co., Ltd., purity 99.9%, particle size 1 - 3μm); high-temperature muffle furnace (Zhengzhou Kejing Electric Furnace Co., Ltd., KSL-1600X-A4); hot press sintering furnace (Shanghai Chenhua Technology Co., Ltd., ZT-25-20Y).
[0026] Example 1
[0027] Weigh Cr2O3 and Nb2O5 according to the molar ratio of Cr2O3:Nb2O5 = 1.02:1, and mix them in a ball milling tank. The ball milling medium is zirconia ceramic balls (particle size 5 - 10mm), and the mixing medium is anhydrous ethanol; the mass ratio of the raw material powder, anhydrous ethanol, and zirconia ceramic balls is 1:2:7; the ball milling speed is 120r / min, and the mixing time is 6h to obtain a uniformly mixed slurry.
[0028] Filter and dry the obtained uniformly mixed slurry. The drying temperature is 60°C, and the drying time is 10h; and pass through a 300-mesh sieve to obtain a mixture powder.
[0029] Put the mixture powder into a high-temperature furnace for calcination. The calcination temperature is 1150°C, and the calcination time is 2h to obtain chromium niobate ceramic powder.
[0030] The composition of the obtained chromium niobate ceramic powder is as shown in Figure 1 the X-ray diffraction pattern, indicating that chromium niobate ceramic powder with a purity of not less than 99wt% can be prepared when the high-temperature reaction temperature is 1150°C.
[0031] The chromium niobate ceramic powder is placed in a hot press sintering furnace for high-temperature sintering. The atmosphere is vacuum, the sintering temperature is 1350 °C, the sintering time is 2 h, the sintering pressure is controlled at 35 MPa, the heating rate is 5 °C / min, and the cooling rate is 5 °C / min to obtain a chromium niobate ceramic block.
[0032] The relative density of the chromium niobate ceramic block is 96%, the melting point is 1780 °C, the flexural strength is 200 MPa, the hardness is 10.2 GPa, and the thermal expansion coefficient is 5.61×10 -6 / K, and the room temperature thermal conductivity is 1.10 W·m -1 ·K -1 。
[0033] Example 2
[0034] Cr2O3 and Nb2O5 are weighed according to the molar ratio of Cr2O3:Nb2O5 = 1.02:0.99 and mixed in a ball milling tank. The ball milling medium is zirconia ceramic balls (particle size 5 - 10 mm), and the mixing medium is anhydrous ethanol; the mass ratio of the raw material powder, anhydrous ethanol, and zirconia ceramic balls is 1:2:7; the ball milling speed is 120 r / min, and the mixing time is 6 h to obtain a uniformly mixed slurry.
[0035] The obtained uniformly mixed slurry is filtered and dried. The drying temperature is 60 °C, and the drying time is 10 h; and it is sieved through a 300-mesh sieve to obtain a mixture powder.
[0036] The mixture powder is placed in a high-temperature furnace for calcination. The calcination temperature is 1200 °C, and the calcination time is 2 h to obtain chromium niobate ceramic powder.
[0037] The chromium niobate ceramic powder is placed in a hot press sintering furnace for high-temperature sintering. The atmosphere is air, the sintering temperature is 1450 °C, the sintering time is 1 h, the sintering pressure is controlled at 30 MPa, the heating rate is 10 °C / min, and the cooling rate is 10 °C / min to obtain a chromium niobate ceramic block.
[0038] The fracture microstructure of the obtained chromium niobate ceramic block is as Figure 2 shown; the relative density of the chromium niobate ceramic block is 97%, the melting point is 1770 °C, the flexural strength is 208 MPa, the hardness is 10.2 GPa; the thermal expansion coefficient is 5.73×10 -6 / K, and the room temperature thermal conductivity is 1.08 W·m -1 ·K -1 。
[0039] Example 3
[0040] Weigh Cr2O3 and Nb2O5 according to the molar ratio of Cr2O3:Nb2O5 = 1:0.9, mix them in a ball milling tank, with zirconia ceramic balls (particle size 5 - 10 mm) as the ball milling medium and absolute ethanol as the mixing medium; the mass ratio of the raw material powder, absolute ethanol and zirconia ceramic balls is 1:2:7; the ball milling speed is 120 r / min and the mixing time is 6 h to obtain a uniformly mixed slurry.
[0041] Filter and dry the obtained uniformly mixed slurry, with the drying temperature at 60 °C and the drying time at 10 h; and pass through a 300 - mesh sieve to obtain a mixture powder.
[0042] Put the mixture powder into a high - temperature furnace for calcination, with the calcination temperature at 1300 °C and the calcination time at 1 h to obtain chromium niobate ceramic powder.
[0043] Put the chromium niobate ceramic powder into a hot - pressing sintering furnace for high - temperature sintering, with the atmosphere being argon, the sintering temperature at 1400 °C, the sintering time at 1 h, the sintering pressure controlled at 25 MPa, the heating rate at 10 °C / min and the cooling rate at 10 °C / min to obtain a chromium niobate ceramic block.
[0044] The relative density of the obtained chromium niobate ceramic block is 95%, the melting point is 1770 °C, the flexural strength is 189 MPa, and the hardness is 10.1 GPa; the thermal expansion coefficient is 5.52×10 -6 / K, and the thermal conductivity of chromium niobate ceramic changes with temperature as Figure 3 shown. The room - temperature thermal conductivity is 1.13 W·m -1 ·K -1 , and as the temperature increases, the thermal conductivity gradually decreases, and at 1200 °C it is only 0.51 W·m -1 ·K -1 .
[0045] Example 4
[0046] Weigh Cr2O3 and Nb2O5 according to the molar ratio of Cr2O3:Nb2O5 = 1.02:1, mix them in a ball milling tank, with zirconia ceramic balls (particle size 5 - 10 mm) as the ball milling medium and absolute ethanol as the mixing medium; the mass ratio of the raw material powder, absolute ethanol and zirconia ceramic balls is 1:2:7; the ball milling speed is 120 r / min and the mixing time is 6 h to obtain a uniformly mixed slurry.
[0047] Filter and dry the obtained uniformly mixed slurry, with the drying temperature at 60 °C and the drying time at 10 h; and pass through a 300 - mesh sieve to obtain a mixture powder.
[0048] Put the mixture powder into a high - temperature furnace for calcination, with the calcination temperature at 1150 °C and the calcination time at 2 h to obtain chromium niobate ceramic powder.
[0049] The niobium chromate ceramic powder is put into a hot-pressing sintering furnace for high-temperature sintering. The atmosphere is vacuum, the sintering temperature is 1400 °C, the sintering time is 40 min, the sintering pressure is controlled at 35 MPa, the heating rate is 10 °C / min, and the cooling rate is 10 °C / min to obtain a niobium chromate ceramic block.
[0050] The relative density of the obtained niobium chromate ceramic block is 97%, the melting point is 1800 °C, the flexural strength is 205 MPa, the hardness is 10.2 GPa, and the thermal expansion coefficient is 5.72×10 -6 / K, and the room-temperature thermal conductivity is 1.09 W·m -1 ·K -1 . The indentation under a 0.98 N load for the hardness is as Figure 4 shown.
[0051] As can be seen from the above embodiments, the melting point of the low-thermal-conductivity niobium chromate ceramic prepared by the present invention is higher than 1750 °C, the room-temperature thermal conductivity is lower than 1.2 W·m -1 ·K -1 , the flexural strength is higher than 180 MPa, and the hardness is above 10 GPa; it has low thermal conductivity and high flexural strength and can be widely used in the field of heat insulation and heat preservation.
[0052] The present invention is not limited to the above best embodiment. Any person can obtain various other forms of products under the inspiration of the present invention. However, no matter what changes are made in its shape or structure, as long as it has a technical solution identical or similar to the present application, it falls within the protection scope of the present invention.
Claims
1. A low thermal conductivity chromium niobate ceramic, characterized in that: The raw materials for preparing the chromium niobate ceramic are chromium trioxide and niobium pentoxide, and the molar ratio of chromium trioxide to niobium pentoxide is 1.00-1.05:0.98-1.
00.
2. The low thermal conductivity chromium niobate ceramic according to claim 1, characterized in that: The chromium trioxide and niobium pentoxide are both powders, the particle sizes of the chromium trioxide and niobium pentoxide are both 1-3 μm, and the purity is not less than 99.9%.
3. The method for preparing the low thermal conductivity chromium niobate ceramic according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1. Evenly mix chromium trioxide and niobium pentoxide in a medium to obtain a mixed slurry; S2, filtering, drying and sieving the slurry obtained in S1 to obtain a mixed powder; S3, calcining and sintering the S2 mixed powder to obtain the chromium niobate ceramic of the present invention.
4. The method for preparing a low thermal conductivity chromium niobate ceramic according to claim 1, characterized in that: In the S1, chromium trioxide and niobium pentoxide are uniformly mixed in a ball mill, the ball milling medium is zirconium oxide ceramic balls with a particle size of 5 to 10 mm; the mixing medium is anhydrous ethanol; the mass ratio of raw material powder, zirconium oxide ceramic balls and anhydrous ethanol is 1:1 to 3:5 to 10; the ball milling speed is 60 to 180 r / min, and the ball milling time is 4 to 12 hours.
5. The method for preparing a low thermal conductivity chromium niobate ceramic according to claim 4, characterized in that: In the above-mentioned S2, the drying temperature is 50-80°C, the drying time is 6-12h; and after drying, the product is sieved through a 100-400 mesh sieve.
6. The method for preparing a low thermal conductivity chromium niobate ceramic according to claim 4, characterized in that: In the above-mentioned S3, the calcination temperature is 1000-1300° C., and the calcination time is 1-4 hours.
7. The method for preparing a low thermal conductivity chromium niobate ceramic according to claim 4, characterized in that: In the S3, the sintering temperature is 1300-1500°C, the sintering time is 0.5-2h; the sintering atmosphere is vacuum, argon or air; the sintering pressure is controlled to be 20-40MPa; the heating rate is 5-20°C / min, and the cooling rate is 5-20°C / min.
8. A method for preparing a low thermal conductivity chromium niobate ceramic according to any one of claims 3 to 7, characterized in that: In the above-mentioned S3, the relative density of the obtained chromium niobate ceramic is not less than 95%, the melting point is not less than 1750°C, the bending strength is not less than 180MPa, the hardness is not less than 10GPa, and the room temperature thermal conductivity is not higher than 1.2W·m -1 ·K -1 .