Rare earth oxide modified ceramic heatproof material and preparation method thereof

Abstract

The invention relates to a rare earth oxide modified ceramic heat-proof material and a preparation method thereof. The rare earth oxide modified ceramic heat-proof material comprises the following components in percentage by mass: 58-78% of ZrB2, 12-30% of rare earth oxide and 10-30% of silicon carbide, the zirconium diboride is modified by the rare earth oxide, so that the work function of the ceramic composite material is reduced; the sintering time and the sintering temperature are effectively reduced by adopting a spark plasma sintering technology, and abnormal growth of crystal grains is inhibited, so that the ceramic composite material has good mechanical properties. The rare earth oxide modified zirconium diboride superhigh-temperature ceramic composite material is a heat-proof material with high-temperature resistance and low work function performance, and can meet the requirements of a novel electronic transpiration cooling thermal protection technology on a material with heat resistance and low work function.

Description

Technical Field

[0001] This invention relates to the field of composite materials technology, and in particular to a rare earth oxide modified ceramic heat-resistant material. Background Technology

[0002] Electron evaporation cooling is a novel thermal protection technology developed based on the thermionic emission effect of electron-emitting materials. It increases energy dissipation on the surface of an aircraft, thereby reducing surface thermal load. By controlling the emission current density at high-temperature regions of hypersonic vehicles, the temperature reduction effect of electron evaporation cooling can be maximized under limited conditions. Richardson's law states that the work function of the electron-emitting material is a key parameter affecting the emission current density; electron-emitting materials with a lower work function can generate a higher emission current density, thus enabling electron evaporation cooling to achieve a stronger temperature reduction effect.

[0003] The foundation for achieving the ETC effect in hypersonic flight environments lies in finding a heat-resistant material that can simultaneously meet the requirements of high temperature resistance and low work function. Currently, ultra-high temperature ceramics are the most promising candidate heat-resistant materials, possessing excellent properties such as high melting point, high hardness, good thermal conductivity, chemical stability, good oxidation resistance, and thermal shock resistance. However, their work function is generally high, which is detrimental to their ability to utilize the thermionic emission effect to achieve temperature reduction in high-temperature parts of hypersonic vehicles. Currently, the work function of refractory metals such as molybdenum and tungsten has been reduced by introducing rare earth oxides, but these matrix materials are unsuitable for hypersonic vehicle heat protection materials due to their poor oxidation resistance. Therefore, improving the work function of zirconium diboride ceramic materials to enable their application in novel electron evaporation cooling heat protection technologies has become an urgent need in the field of zirconium diboride ultra-high temperature ceramic materials. Summary of the Invention

[0004] The technical problem to be solved by this invention is that the existing ultra-high temperature ceramic materials have poor work function performance and insignificant high temperature resistance. Therefore, this invention provides a rare earth oxide modified ceramic heat-resistant material and its preparation method.

[0005] To address the aforementioned technical problems, the present invention provides a rare earth oxide modified ceramic heat-resistant material, wherein the rare earth oxide modified ceramic heat-resistant material comprises the following components by volume percentage: ZrB2 of 58%~78% (e.g., 58%, 60%, 65%, 70%, 78%, etc.), rare earth oxides of 12%~30% (e.g., 12%, 15%, 20%, 25%, 30%, etc.), and silicon carbide of 10%~30% (e.g., 10%, 15%, 20%, 25%, 30%, etc.).

[0006] This invention provides a rare-earth oxide-modified ceramic heat-resistant material. For the first time, it modifies an ultra-high temperature ceramic composite material with a ZrB2 main phase by adding rare-earth oxides with a volume percentage of 12% to 30%, thereby reducing the work function of the matrix material and improving the generally high work function of ultra-high temperature ceramic composite materials. This enhances the temperature reduction effect of the material when applied to electron evaporation cooling heat protection technology. Furthermore, this invention reveals that the volume percentage of rare-earth oxides in the rare-earth oxide-modified zirconium diboride ultra-high temperature ceramic composite material is particularly important. Only when the content of rare-earth oxides exceeds 11% can the rare-earth oxide-modified zirconium diboride ultra-high temperature ceramic composite material guarantee excellent low work function performance. If the volume percentage of rare-earth oxides is too small, the effect of reducing the material's work function is not significant.

[0007] Unlike existing ZrB2-SiC-rare earth oxide multiphase ceramic materials with ZrB2 as the matrix material (main component), as disclosed in CN102976760A, this invention adds 0.1%~10% rare earth oxides by volume, utilizing their sintering aid properties to obtain a dense ceramic material and improve the material's mechanical properties, thermal conductivity, and oxidation ablation resistance. However, the low rare earth oxide content in this invention fails to provide excellent low work function performance.

[0008] Preferably, the rare earth oxide modified ceramic heat-resistant material comprises the following components by volume percentage: 63%~75% ZrB2, 12%~25% rare earth oxides, and 12%~20% silicon carbide.

[0009] Preferably, the rare earth oxide includes any one or a combination of at least two of La2O3, Gd2O3, Sc2O3 or Y2O3.

[0010] On the other hand, the present invention provides a method for preparing the rare earth oxide modified ceramic heat-resistant material as described above, the method comprising: mixing ZrB2 powder with rare earth oxide powder, and sintering to obtain the rare earth oxide modified ceramic heat-resistant material.

[0011] Preferably, the ZrB2 powder has an average particle size of 1-3 μm, and the rare earth oxide powder has an average particle size of 100-500 nm. In this invention, the smaller the particle size of the powder, the more thoroughly the two components can be mixed in the dried mixed powder.

[0012] Preferably, the mixing process is as follows: using zirconium dioxide balls and anhydrous ethanol, mixing ZrB2 powder and rare earth oxide powder, dispersing by ball milling, and then drying.

[0013] In this invention, zirconium diboride matrix powder and rare earth oxide powder are dispersed by ball milling using zirconium dioxide balls and anhydrous ethanol as the dispersion medium, thereby obtaining a composite slurry. The zirconium dioxide balls possess high hardness and good chemical stability, effectively preventing impurities from entering the ball mill. Furthermore, the composite slurry can be evaporated and dried in an evaporator, thus rapidly removing liquid from the slurry.

[0014] Preferably, the ball milling dispersion time is 12-14 hours. In this invention, the longer the wet milling time, the better the dispersibility of the raw materials.

[0015] Preferably, the sintering is spark plasma sintering.

[0016] Preferably, the temperature of the discharge plasma sintering is 1500~1700℃, for example, 1500℃, 1600℃ or 1700℃, preferably 1600℃; the pressure is 25~35MPa, for example, 25MPa, 28MPa, 30MPa, 32MPa or 35MPa, preferably 30MPa; the time is 5~15min, for example, 5min, 8min, 10min, 12min or 15min, preferably 10min.

[0017] This preferred process helps to ensure a denser rare-earth oxide-modified zirconium diboride ultra-high temperature ceramic composite material. This invention has found that if the temperature and pressure of the spark plasma sintering are too low, the obtained rare-earth oxide-modified ceramic-based heat-resistant material will become porous; if the temperature and pressure are too high, the mechanical properties of the material will deteriorate, the strength will decrease, and the work function of the material will be affected.

[0018] Implementing this invention has the following beneficial effects: This invention reduces the work function of the ceramic composite material by modifying zirconium diboride with rare earth oxides. The use of spark plasma sintering technology effectively reduces sintering time and temperature, and also inhibits abnormal grain growth, thus giving the ceramic composite material excellent mechanical properties. The rare earth oxide-modified zirconium diboride ultra-high temperature ceramic composite material of this invention is a heat-resistant material with high temperature resistance and low work function, meeting the requirements of novel electron evaporation cooling thermal protection technology for materials that combine heat protection and low work function. Attached Figure Description

[0019] Figure 1 This is the work function graph of the rare earth oxide modified ceramic heat-resistant material obtained in Embodiment 1 of the present invention.

[0020] Figure 2This is the work function graph of the rare earth oxide modified ceramic heat-resistant material obtained in Comparative Example 1 of this invention.

[0021] Figure 3 These are the XRD spectra of the rare earth oxide modified ceramic heat-resistant materials obtained in Embodiment 1 and Comparative Example 1 of the present invention.

[0022] Figure 4 These are UPS test curves of rare earth oxide modified ceramic heat-resistant materials obtained in Embodiments 1, 2, and 3 and Comparative Example 1 of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 A low work function rare earth oxide modified ceramic-based heat-insulating material is composed of 70% ZrB2, 15% SiC, and 15% Gd2O3 by volume percentage. Only when prepared according to the stated proportions can a significant reduction in work function be detected in the prepared low work function rare earth oxide modified ceramic-based heat-exothermic material, with a work function reduction of 13.82% compared to the control group (Comparative Example 1).

[0025] The preparation of rare earth oxide modified ceramic matrix heat-resistant materials is as follows: First, ZrB2, SiC, and Gd2O3 powders were mixed in a volume ratio of 7:2:1 using a wet ball milling process for 12 hours to obtain a homogeneous powder. The mixed powder was then subjected to spark plasma sintering (SPCS) at a sintering pressure of less than 10 Pa, a sintering temperature of 1700℃, a sintering pressure of 30 MPa, a holding time of 10 minutes, a heating rate of 200℃ / min from room temperature to 1400℃, and a heating rate of 100℃ / min from 1400℃ to 1700℃. The mixture was then cooled in the furnace to obtain a dense rare-earth oxide modified ceramic-based heat-resistant material (70 vol% ZrB2 - 15 vol% SiC - 15 vol% Gd2O3 material).

[0026] This invention utilizes ultraviolet photoelectron spectroscopy to characterize the surface work function of the rare-earth oxide modified ceramic-based heat-resistant material in this embodiment. The 70 vol% ZrB2-15 vol% SiC-15 vol% Gd2O3 material in this embodiment was calibrated with Ag, and the calculated work function values ​​are as follows: Figure 1As shown, the intersection of the tangent of the secondary electron cutoff edge and the baseline corresponds to an abscissa value of 17.54 eV, a photon energy of 21.22 eV, and a work function of 3.68 eV.

[0027] Example 2 A low work function rare earth oxide modified ceramic-based heat-insulating material is composed of 70% ZrB2, 18% SiC, and 12% Gd2O3 by volume percentage. Only when prepared according to the stated proportions can a significant reduction in work function be detected in the prepared low work function rare earth oxide modified ceramic-based heat-exothermic material, with a work function reduction of 11.24% compared to the control group (Comparative Example 1).

[0028] The rare earth oxide modified ceramic-based heat-resistant material is prepared as follows: First, ZrB2, SiC, and Gd2O3 powders were mixed in a volume ratio of 15:4:1 using a wet ball milling process for 12 hours to obtain a uniformly mixed powder. The mixed powder was then subjected to spark plasma sintering at a sintering pressure of less than 10 Pa, a sintering temperature of 1700℃, a sintering pressure of 30 MPa, a holding time of 10 minutes, a heating rate of 200℃ / min from room temperature to 1400℃, and a heating rate of 100℃ / min from 1400℃ to 1700℃. The mixture was then cooled in the furnace to obtain a dense rare-earth oxide modified ceramic-based heat-resistant material (70 vol% ZrB2 - 18 vol% SiC - 12 vol% Gd2O3 material).

[0029] Example 3 A low work function rare earth oxide modified ceramic-based heat-insulating material is composed of 65% ZrB2, 15% SiC, and 20% La2O3 by volume percentage. Only when prepared according to the stated proportions can a significant reduction in work function be detected in the prepared low work function rare earth oxide modified ceramic-based heat-exothermic material, with a work function reduction of 14.75% compared to the control group (Comparative Example 1).

[0030] The rare earth oxide modified ceramic-based heat-resistant material is prepared as follows: First, ZrB2, SiC, and La2O3 powders were mixed in a volume ratio of 7:2:1 using a wet ball milling process for 12 hours to obtain a uniformly mixed powder. The mixed powder was then subjected to spark plasma sintering at a sintering pressure of less than 10 Pa, a sintering temperature of 1700℃, a sintering pressure of 30 MPa, a holding time of 10 minutes, a heating rate of 200℃ / min from room temperature to 1400℃, and a heating rate of 100℃ / min from 1400℃ to 1700℃. The mixture was then cooled in the furnace to obtain a dense rare-earth oxide modified ceramic-based heat-resistant material (65 vol% ZrB2 - 15 vol% SiC - 20 vol% La2O3 material).

[0031] Example 4 A low work function rare earth oxide modified ceramic-based heat-insulating material is composed of 70% ZrB2, 12% SiC, and 18% Gd2O3 by volume percentage. Only when prepared according to the stated proportions can a significant reduction in work function be detected in the prepared low work function rare earth oxide modified ceramic-based heat-exothermic material, with a work function reduction of 14.52% compared to the control group (Comparative Example 1).

[0032] The preparation of rare earth oxide modified ceramic matrix heat-resistant materials is as follows: First, ZrB2, SiC, and Gd2O3 powders were mixed in a volume ratio of 7:2:1 using a wet ball milling process for 12 hours to obtain a homogeneous powder. The mixed powder was then subjected to spark plasma sintering (SPCS) at a sintering pressure of less than 10 Pa, a sintering temperature of 1700℃, a sintering pressure of 30 MPa, a holding time of 10 minutes, a heating rate of 200℃ / min from room temperature to 1400℃, and a heating rate of 100℃ / min from 1400℃ to 1700℃. The mixture was then cooled in the furnace to obtain a dense rare-earth oxide modified ceramic-based heat-resistant material (70 vol% ZrB2 - 12 vol% SiC - 18 vol% Gd2O3 material).

[0033] Example 5 A low work function rare earth oxide modified ceramic-based heat-insulating material is composed of 75% ZrB2, 12% SiC, and 13% Gd2O3 by volume percentage. Only when prepared according to the stated proportions can a significant reduction in work function be detected in the prepared low work function rare earth oxide modified ceramic-based heat-exothermic material, with a work function reduction of 13.34% compared to the control group (Comparative Example 1).

[0034] The preparation of rare earth oxide modified ceramic matrix heat-resistant materials is as follows: First, ZrB2, SiC, and Gd2O3 powders were mixed in a volume ratio of 7:2:1 using a wet ball milling process for 12 hours to obtain a homogeneous powder. The mixed powder was then subjected to spark plasma sintering at a sintering pressure of less than 10 Pa, a sintering temperature of 1700℃, a sintering pressure of 30 MPa, a holding time of 10 minutes, a heating rate of 200℃ / min from room temperature to 1400℃, and a heating rate of 100℃ / min from 1400℃ to 1700℃. The mixture was then cooled in the furnace to obtain a dense rare-earth oxide modified ceramic-based heat-resistant material (75 vol% ZrB2 - 12 vol% SiC - 13 vol% Gd2O3 material).

[0035] Example 6 A low work function rare earth oxide modified ceramic-based heat-insulating material is composed of 71% ZrB2, 15% SiC, and 14% Gd2O3 by volume percentage. Only when prepared according to the stated proportions can a significant reduction in work function be detected in the prepared low work function rare earth oxide modified ceramic-based heat-exothermic material, with a work function reduction of 12.18% compared to the control group (Comparative Example 1).

[0036] The preparation of rare earth oxide modified ceramic matrix heat-resistant materials is as follows: First, ZrB2, SiC, and Gd2O3 powders were mixed in a volume ratio of 7:2:1 using a wet ball milling process for 12 hours to obtain a homogeneous powder. The mixed powder was then subjected to spark plasma sintering (SPCS) at a sintering pressure of less than 10 Pa, a sintering temperature of 1700℃, a sintering pressure of 30 MPa, a holding time of 10 minutes, a heating rate of 200℃ / min from room temperature to 1400℃, and a heating rate of 100℃ / min from 1400℃ to 1700℃. The mixture was then cooled in the furnace to obtain a dense rare-earth oxide modified ceramic-based heat-resistant material (71 vol% ZrB2 - 15 vol% SiC - 14 vol% Gd2O3 material).

[0037] Comparative Example 1 A ceramic-based heat-resistant material is composed of 80% ZrB2 and 20% SiC by volume percentage.

[0038] The ceramic-based heat-resistant material is prepared as follows: First, ZrB2 and SiC powders were mixed at a volume ratio of 4:1 using a wet ball milling process for 12 hours to obtain a homogeneous powder. The mixed powder was then subjected to spark plasma sintering (SPCS) at a sintering pressure of less than 10 Pa, a sintering temperature of 1700℃, a sintering pressure of 30 MPa, a holding time of 10 minutes, a heating rate of 200℃ / min from room temperature to 1400℃, and a heating rate of 100℃ / min from 1400℃ to 1700℃. The mixture was then cooled in the furnace to obtain a ceramic-based heat-resistant material (80 vol% ZrB2 - 20 vol% SiC).

[0039] This comparative example uses the same method as in Example 1 to characterize the surface work function of the 80 vol% ZrB2-20 vol% SiC material. The results show that the work function value of the 80 vol% ZrB2-20 vol% SiC material in this comparative example, calibrated with Ag, is calculated as follows: Figure 2As shown, the intersection of the tangent of the secondary electron cutoff edge and the baseline corresponds to an abscissa value of 16.95 eV, a photon energy of 21.22 eV, and a work function of 4.27 eV, which is significantly higher than the work function of the 70 vol% ZrB2-20 vol% SiC-10 vol% Gd2O3 material in Example 1.

[0040] Comparative Example 2 A low work function rare earth oxide modified ceramic-based heat-insulating material is composed of 80% ZrB2, 17% SiC, and 3% Gd2O3 by volume percentage. Only when prepared according to the stated proportions can a significant reduction in work function be detected in the prepared low work function rare earth oxide modified ceramic-based heat-exothermic material, with a work function reduction of 2.81% compared to the control group (Comparative Example 1).

[0041] The preparation of rare earth oxide modified ceramic matrix heat-resistant materials is as follows: First, ZrB2, SiC, and Gd2O3 powders were mixed in a volume ratio of 7:2:1 using a wet ball milling process for 12 hours to obtain a homogeneous powder. The mixed powder was then subjected to spark plasma sintering (SPCS) at a sintering pressure of less than 10 Pa, a sintering temperature of 1700℃, a sintering pressure of 30 MPa, a holding time of 10 minutes, a heating rate of 200℃ / min from room temperature to 1400℃, and a heating rate of 100℃ / min from 1400℃ to 1700℃. The mixture was then cooled in the furnace to obtain a dense rare-earth oxide modified ceramic-based heat-resistant material (80 vol% ZrB2 - 17 vol% SiC - 3 vol% Gd2O3 material).

[0042] Comparative Example 3 A low work function rare earth oxide modified ceramic-based heat-insulating material is composed of 75% ZrB2, 17% SiC, and 8% Gd2O3 by volume percentage. Only when prepared according to the stated proportions can a significant reduction in work function be detected in the prepared low work function rare earth oxide modified ceramic-based heat-exothermic material, with a work function reduction of 4.45% compared to the control group (Comparative Example 1).

[0043] The preparation of rare earth oxide modified ceramic matrix heat-resistant materials is as follows: First, ZrB2, SiC, and Gd2O3 powders were mixed in a volume ratio of 7:2:1 using a wet ball milling process for 12 hours to obtain a uniformly mixed powder. The mixed powder was then subjected to spark plasma sintering (SPCS) at a sintering pressure of less than 10 Pa, a sintering temperature of 1700℃, a sintering pressure of 30 MPa, a holding time of 10 minutes, a heating rate of 200℃ / min from room temperature to 1400℃, and a heating rate of 100℃ / min from 1400℃ to 1700℃. The mixture was then cooled in the furnace to obtain a dense rare-earth oxide modified ceramic-based heat-resistant material (75 vol% ZrB2 - 17 vol% SiC - 8 vol% Gd2O3 material).

[0044] The XRD patterns of the materials obtained in Example 1 and Comparative Example 1 are as follows: Figure 3 As shown.

[0045] The material performance parameters of Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 1 below.

[0046] Table 1 The materials from Examples 1, 2, 3 and Comparative Example 1 were subjected to UPS (ultraviolet photoelectron spectroscopy) tests.

[0047] Figure 4 The image shows the photoelectron spectra of four materials, SPS-ZS, SPS-ZSGO5, SPS-ZSGO10, and SPS-ZSLO10, measured by UPS. Based on the photoelectron spectra of the Ag standard, the Fermi edges of the four materials are marked at the binding energy of 0 eV. SPS-ZS has the lowest secondary electron cutoff edge at 16.95 eV. Considering that the incident photon energy is provided by He I (21.22 eV), the work function of SPS-ZS is calculated to be 4.27 eV. The secondary electron cutoff edges of SPSZSGO5, SPS-ZSGO10, and SPS-ZSLO10 are 17.25 eV, 17.54 eV, and 17.42 eV, respectively, meaning that the work functions of the three materials are 3.97 eV, 3.68 eV, and 3.80 eV, respectively. Compared to SPS-ZS, the work functions of all three materials doped with rare earth oxides decreased, and the work function decreased further as the Gd2O3 doping content increased from 5 vol.% to 10 vol.%. Compared to SPS-ZS, the work function of SPSZSGO10 decreased by 0.59 eV, a reduction of 13.8%.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A rare earth oxide modified ceramic heat-resistant material, characterized in that, The rare earth oxide modified ceramic heat-resistant material comprises the following components by volume percentage: ZrB2 58%~78%, rare earth oxides 12%~30%, and silicon carbide 10%~30%.

2. The rare earth oxide modified ceramic heat-resistant material according to claim 1, characterized in that, The rare earth oxide modified ceramic heat-resistant material comprises the following components by volume percentage: ZrB2 63%~75%, rare earth oxides 12%~25%, and silicon carbide 12%~20%.

3. The rare earth oxide modified ceramic heat-resistant material according to claim 1, characterized in that, The rare earth oxides include any one or a combination of at least two of La2O3, Gd2O3, Sc2O3, or Y2O3.

4. The method for preparing rare earth oxide modified ceramic heat-resistant material according to any one of claims 1 to 3, characterized in that, The preparation method includes: mixing ZrB2 powder with rare earth oxide powder and sintering to obtain the rare earth oxide modified ceramic heat-resistant material.

5. The preparation method according to claim 4, characterized in that, The ZrB2 powder has an average particle size of 1~3μm, and the rare earth oxide powder has an average particle size of 100~500nm.

6. The preparation method according to claim 4, characterized in that, The mixing process is as follows: using zirconium dioxide balls and anhydrous ethanol, ZrB2 powder and rare earth oxide powder are mixed, dispersed by ball milling, and then dried.

7. The preparation method according to claim 6, characterized in that, The ball milling dispersion time is 12-14 hours.

8. The preparation method according to claim 4, characterized in that, The sintering is spark plasma sintering.

9. The preparation method according to claim 8, characterized in that, The discharge plasma sintering temperature is 1500~1700℃, the pressure is 25~35MPa, and the time is 5~15min.

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