Calcium stannate discoloring material and preparation method thereof

Abstract

The present application belongs to the technical field of luminescent materials, and particularly relates to a calcium stannate color-changing material and a preparation method thereof. 2.015‑ x Ho 0.005 SnO4:xYb 3+ wherein x is 0-0.07. The calcium stannate color-changing material provided by the present application has more obvious color-changing effect, higher color-changing rate and light intensity control rate, and has up-conversion luminescence intensity control and down-conversion luminescence intensity control performance at the same time, as compared with the color-changing ceramic obtained by doping a calcium stannate matrix with Al 3+ or Eu 3+ .

Description

Technical Field

[0001] The present invention belongs to the technical field of luminescent materials, and in particular relates to a calcium stannate color-changing material and a preparation method thereof. Background Art

[0002] Calcium stannate (Ca2SnO4) has a stable crystal structure and good physicochemical stability, making it a common material for luminescent substrates. Doping with appropriate rare earth ions not only imparts excellent luminescence properties but also enhances the substrate's photochromic properties. Specifically, the material's luminescence intensity is quenched as photochromism progresses. This change in fluorescence intensity during the photochromic process is known as fluorescence modulation. Calculating the fluorescence intensity modulation rate allows for quantification of optical data storage, making this material a promising candidate for future optical data storage applications.

[0003] The luminous intensity modulation caused by the photochromic effect is considered to be the easiest storage and reading method to implement because of its high resolution and fast response speed. If the material itself has a high luminous intensity modulation capability, the detection can be made more sensitive, which helps to reduce the bit error rate during information reading and improve the signal-to-noise ratio of information storage. At present, in the research on the photochromic and light intensity control properties of calcium stannate, ion doping is mainly used to improve the photochromic and light intensity control properties of the material. The choice of doping ion is to dope with non-rare earth ions, such as Al 3+ . The advantages of non-rare earth ion doping are relatively low cost and a wide range of doping ions to choose from. However, its disadvantages are limited improvement in the color-changing performance of the material, and most non-rare earth ions cannot serve as luminescence centers and do not have luminescence capabilities. Therefore, non-rare earth ion doped calcium stannate (Ca2SnO4) color-changing materials generally do not have light intensity control properties. Another choice of doping ions is rare earth ions. Rare earth ions have rich luminescence properties due to their unique 4f-4f energy levels. The selection of appropriate rare earth ion doping will improve the photochromic ability of calcium stannate materials while having light intensity control properties. For example, the selection of Eu 3+ or Al 3+ After doping, the material changes from light brown to gray, with a 35% change in reflectivity and a 40.5% luminescence modulation ratio under 240nm excitation. Compared to other photochromic materials with light intensity control capabilities, the light intensity control ratio of rare earth ion-doped calcium stannate remains to be improved. Furthermore, the current doping method uses only a single rare earth ion, which allows the material to only regulate the intensity of the down-conversion luminescence, resulting in a relatively single control mode. Achieving multi-mode light intensity control would help increase information storage capacity.

[0004] CN103923650A discloses a hollow structure calcium stannate luminescent material doped with metal particles and a preparation method thereof. The general structural formula of the luminescent material is Ca2-x SnO4: Tb x @M y , wherein M is a doped metal nanoparticle, M is selected from at least one of Ag, Au, Pt, Pd, Cu, @ represents coating, M is the core, Ca 2-x SnO4: Tb x is the shell. The hollow structure calcium stannate luminescent material provided by the application adopts dispersed carbon small spheres as a template to obtain spherical hollow structure calcium stannate, and then doped with metal nanoparticles to enhance the luminescent intensity of the fluorescent powder, so that the Ca 2-x SnO4: Tb x @M y The luminescent efficiency of the luminescent material under the same excitation condition is greatly improved, and the wavelength of the emitted light does not change.

[0005] CN111100638A discloses a samarium-zirconium co-doped calcium stannate white fluorescent powder and a soft chemical preparation method thereof. The white fluorescent powder has the following general formula: Ca2SnO4: xSm 3+ , yZr 4+ , x is 0.01-0.5, and y is 0-2. The soft chemical preparation method comprises the following steps: weighing raw materials SnCl4·5H2O, Sm2O3, CaCl2·2H2O, K2C2O4·H2O and ZrO(NO3)2·xH2O; dissolving the raw materials in water or acid to prepare a solution; mixing, adjusting the pH value to neutral; stirring and precipitating, then standing and washing; drying the slurry, grinding the dry powder, adding a fluxing agent to sinter, and grinding to obtain a samarium-zirconium co-doped calcium stannate fluorescent powder. Detection shows that the samarium-zirconium co-doped calcium stannate fluorescent powder prepared by the soft chemical method has uniform phase composition, good particle dispersity, easy control of particle size and morphology, uniform particle size, and good photoluminescence performance.

[0006] However, the above-mentioned calcium stannate material still cannot realize multi-mode light intensity control.

[0007] Therefore, the present application is proposed. SUMMARY

[0008] In view of the low light intensity control rate of rare earth ion doped calcium stannate material and the single light intensity control mode caused by single rare earth ion doping, the present application provides a calcium stannate photochromic material and a preparation method thereof. The calcium stannate photochromic material is selected from a holmium (Ho 3+ ) and ytterbium (Yb 3+ ) co-doped calcium stannate matrix material, and a dual-mode light intensity control photochromic material with high light intensity control rate (up to 95.03%) and both up-conversion luminescent intensity control and down-conversion luminescent intensity control is obtained.

[0009] To achieve the purpose of the present invention, the present invention adopts the following technical solutions:

[0010] A calcium stannate color-changing material, wherein the calcium stannate color-changing material has the following chemical formula: Ca 2.015- x Ho 0.005 SnO4:xYb 3+ , where x is 0 to 0.07.

[0011] In the above general formula, Ca2SnO4 is the matrix material; Ho 3+ As an activator, it is the luminescence center of the material; Yb 3+ It is a sensitizer used to absorb 980nm excitation photon energy and transfer it to the activator, contributing to the enhancement of upconversion luminescence.

[0012] As a preferred embodiment, in the above general chemical formula, 0<x≤0.07.

[0013] Currently, the existing Al 3+ or Eu 3+ The color-changing ceramics obtained by doping the calcium stannate matrix do not change significantly, the color change rate can only reach 35%, and it does not have the up-conversion luminescence intensity regulation performance, and the down-conversion luminescence intensity regulation performance can only reach 40.5%.

[0014] Experiments show that when the above preferred scheme is adopted, the calcium stannate color-changing material provided by the present invention has a more obvious color-changing effect, a higher color-changing rate and light intensity control rate, and has both up-conversion luminescence intensity regulation and down-conversion luminescence intensity regulation performance.

[0015] As a most preferred solution, x in the above chemical formula is 0.005.

[0016] The present invention also provides a method for preparing the calcium stannate color-changing material, comprising the following steps:

[0017] 1) First, pour CaCO3(AR), SnO2, Ho2O3 and Yb2O3 into a nylon jar filled with agate balls, add appropriate amount of alcohol, ball mill, and dry and grind into powder;

[0018] 2) Use a metal mold to press the powder into a disc, and then place it in a cold isostatic press for a period of time;

[0019] 3) Finally, the isostatically pressed disc is placed in an alumina crucible, placed in a silicon-molybdenum rod ultrahigh temperature electric furnace, heated and kept warm, and then naturally cooled to room temperature to obtain the calcium stannate color-changing material.

[0020] In the present invention, the CaCO3 is an analytically pure (AR) reagent, the SnO2 is a chemically pure reagent with a chemical purity of 99.9%, and the Ho2O3 and Yb2O3 are both chemically pure reagents with a chemical purity of 99.99%.

[0021] Furthermore, in step 1), the molar ratio of CaCO3(AR), SnO2(99.9%), Ho2O3(99.99%), and Yb2O3(99.99%) is (1.945-2.015):1:0.005:(0-0.07), preferably 2.01:1:0.005:0.005.

[0022] Furthermore, in step 3), the temperature is raised to 1300-1500° C. and kept warm for 3-5 hours, preferably raised to 1400° C. and kept warm for 4 hours.

[0023] Furthermore, the heating rate is 5 to 10° C. / min, preferably 7° C. / min.

[0024] Furthermore, in step 1), the ball milling time is 5 to 10 hours, preferably 8 hours.

[0025] Furthermore, in step 2), the product is placed in a cold isostatic press and maintained at a pressure of 230 to 280 MPa for 1 to 3 minutes, preferably at a pressure of 250 MPa for 2 minutes.

[0026] Furthermore, in step 2), the powder is pressed into round tablets with a diameter of 10 to 15 mm, preferably 13 mm.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] (1) Compared with the current Al 3+ or Eu 3+ Compared with the color-changing ceramics obtained by doping with calcium stannate matrix, the calcium stannate color-changing material provided by the present invention has more obvious color-changing effect and higher color-changing rate;

[0029] (2) Compared with the current Al 3+ 、Eu 3+ 、Ho 3+ Compared with the color-changing ceramics obtained by doping a single calcium stannate matrix, the light intensity control rate of the calcium stannate color-changing material provided by the present invention is higher;

[0030] (3) The calcium stannate color-changing material provided by the present invention has both up-conversion luminescence intensity regulation and down-conversion luminescence intensity regulation performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The reflectivity and color change diagram before and after color change;

[0032] Figure 2 is the down-conversion emission spectrum before and after color change;

[0033] Figure 3 Upconversion emission spectra before and after color change. DETAILED DESCRIPTION

[0034] The following are specific embodiments of the present invention. The examples are intended to further describe the present invention rather than to limit the present invention.

[0035] Example 1

[0036] This embodiment provides a holmium and ytterbium co-doped calcium stannate color-changing material having the following chemical formula: 2.015- x Ho 0.005 SnO4:xYb 3+ , wherein x is 0.005. The preparation method comprises the following steps:

[0037] 1) First, CaCO3 (AR), SnO2 (99.9%), Ho2O3 (99.99%), and Yb2O3 (99.99%) were poured into a nylon jar containing agate balls at a molar ratio of 2.01:1:0.005:0.005, and then ball-milled for 8 h with appropriate amount of alcohol, and then dried and ground into powder;

[0038] 2) Use a metal mold to press the powder into a disc with a diameter of 13 mm, and then place it in a cold isostatic press at a pressure of 250 MPa for 2 minutes;

[0039] 3) Finally, the isostatically pressed wafer was placed in an alumina crucible and placed in a silicon-molybdenum rod ultrahigh temperature electric furnace, heated to 1400°C at 7°C / min and kept at this temperature for 4 hours, and then naturally cooled to room temperature to obtain Ca2O3 co-doped with holmium and ytterbium. 2.01 Ho 0.005 SnO4:0.005Yb 3+ Calcium stannate color-changing material.

[0040] Example 2

[0041] This embodiment provides a holmium and ytterbium co-doped calcium stannate color-changing material having the following chemical formula: 2.015- x Ho 0.005 SnO4:xYb 3+ , wherein x is 0.001. The preparation method comprises the following steps:

[0042] 1) First, CaCO3(AR), SnO2(99.9%), Ho2O3(99.99%) and Yb2O3(99.99%) are poured into a nylon jar with agate balls in a molar ratio of 2.014:1:0.005:0.001, and a proper amount of alcohol is added for ball milling for 5h, and then dried and ground into powder;

[0043] 2) The powder is pressed into a disc with a diameter of 10mm using a metal mold, and then placed in a cold isostatic pressing machine for 1min under a pressure of 230MPa;

[0044] 3) Finally, the disc after isostatic pressing is placed in an alumina crucible and placed in a silicon-molybdenum rod ultra-high temperature electric furnace, heated to 1300℃ at a rate of 5℃ / min and kept for 3h, and then naturally cooled to room temperature, to obtain a holmium and ytterbium co-doped calcium stannate color-changing material Ca 2.014 Ho 0.005 SnO4:0.001Yb 3+ .

[0045] Example 3

[0046] This example provides a holmium and ytterbium co-doped calcium stannate color-changing material, having the following general chemical formula Ca 2.015- x Ho 0.005 SnO4:xYb 3+ , wherein x is 0.01. The preparation method comprises the following steps:

[0047] 1) First, CaCO3(AR), SnO2(99.9%), Ho2O3(99.99%) and Yb2O3(99.99%) are poured into a nylon jar with agate balls in a molar ratio of 2.005:1:0.005:0.01, and a proper amount of alcohol is added for ball milling for 10h, and then dried and ground into powder;

[0048] 2) The powder is pressed into a disc with a diameter of 15mm using a metal mold, and then placed in a cold isostatic pressing machine for 3min under a pressure of 280MPa;

[0049] 3) Finally, the disc after isostatic pressing is placed in an alumina crucible and placed in a silicon-molybdenum rod ultra-high temperature electric furnace, heated to 1500℃ at a rate of 10℃ / min and kept for 5h, and then naturally cooled to room temperature, to obtain a holmium and ytterbium co-doped calcium stannate color-changing material Ca 2.005 Ho 0.005 SnO4:0.01Yb 3+ .

[0050] Example 4

[0051] This example provides a holmium and ytterbium co-doped calcium stannate color-changing material, having the following general chemical formula Ca 2.015-x Ho 0.005 SnO4:xYb 3+ , wherein x is 0.015. The preparation method comprises the following steps:

[0052] 1) First, CaCO3 (AR), SnO2 (99.9%), Ho2O3 (99.99%), and Yb2O3 (99.99%) were poured into a nylon jar containing agate balls at a molar ratio of 2:1:0.005:0.015, and then ball-milled for 6 h with appropriate amount of alcohol, and then dried and ground into powder;

[0053] 2) Use a metal mold to press the powder into a disc with a diameter of 12 mm, and then place it in a cold isostatic press at a pressure of 240 MPa for 2 minutes;

[0054] 3) Finally, the isostatically pressed wafer was placed in an alumina crucible and placed in a silicon-molybdenum rod ultrahigh temperature electric furnace, heated to 1450°C at 8°C / min and kept warm for 3.5 hours, and then naturally cooled to room temperature to obtain Ca2Ho co-doped with holmium and ytterbium. 0.005 SnO4:0.015Yb 3+ Calcium stannate color-changing material.

[0055] Example 5

[0056] This embodiment provides a holmium and ytterbium co-doped calcium stannate color-changing material having the following chemical formula: 2.015- x Ho 0.005 SnO4:xYb 3+ , wherein x is 0.02. The preparation method comprises the following steps:

[0057] 1) First, CaCO3 (AR), SnO2 (99.9%), Ho2O3 (99.99%), and Yb2O3 (99.99%) were poured into a nylon jar containing agate balls at a molar ratio of 1.995:1:0.005:0.02. An appropriate amount of alcohol was added and ball-milled for 9 hours. The mixture was then dried and ground into powder.

[0058] 2) Use a metal mold to press the powder into a disc with a diameter of 14 mm, and then place it in a cold isostatic press at a pressure of 260 MPa for 2 minutes;

[0059] 3) Finally, the isostatically pressed wafer was placed in an alumina crucible and placed in a silicon-molybdenum rod ultrahigh temperature electric furnace, heated to 1350°C at 6°C / min and kept at this temperature for 3.5h, and then naturally cooled to room temperature to obtain Ca2+ co-doped with holmium and ytterbium. 1.995 Ho 0.005 SnO4:0.02Yb 3+ Calcium stannate color-changing material.

[0060] Example 6

[0061] This embodiment provides a holmium-doped calcium stannate color-changing material having the following chemical formula: 2.015- x Ho 0.005 SnO4:xYb 3+ , wherein x is 0. The preparation method comprises the following steps:

[0062] 1) First, pour CaCO3 (AR), SnO2 (99.9%), and Ho2O3 (99.99%) into a nylon jar filled with agate balls at a molar ratio of 2.015:1:0.005, add appropriate amount of alcohol and ball mill for 8 hours, then dry and grind into powder;

[0063] 2) Use a metal mold to press the powder into a disc with a diameter of 13 mm, and then place it in a cold isostatic press at a pressure of 250 MPa for 2 minutes;

[0064] 3) Finally, the isostatically pressed wafer was placed in an alumina crucible and placed in a silicon-molybdenum rod ultrahigh temperature electric furnace, heated to 1400°C at 7°C / min and kept at this temperature for 4 hours, and then naturally cooled to room temperature to obtain Ca2O3 co-doped with holmium and ytterbium. 2.015 Ho 0.005 SnO4 calcium stannate color-changing material.

[0065] Example 7

[0066] This embodiment provides a holmium and ytterbium co-doped calcium stannate color-changing material having the following chemical formula: 2.015- x Ho 0.005 SnO4:xYb 3+ , wherein x is 0.07. The preparation method thereof comprises the following steps:

[0067] 1) First, CaCO3 (AR), SnO2 (99.9%), Ho2O3 (99.99%), and Yb2O3 (99.99%) were poured into a nylon jar containing agate balls at a molar ratio of 1.945:1:0.005:0.07. Then, appropriate amount of alcohol was added and ball-milled for 8 h, and then dried and ground into powder.

[0068] 2) Use a metal mold to press the powder into a disc with a diameter of 13 mm, and then place it in a cold isostatic press at a pressure of 250 MPa for 2 minutes;

[0069] 3) Finally, the isostatically pressed wafer was placed in an alumina crucible and placed in a silicon-molybdenum rod ultrahigh temperature electric furnace, heated to 1400°C at 7°C / min and kept at this temperature for 4 hours, and then naturally cooled to room temperature to obtain Ca2O3 co-doped with holmium and ytterbium. 1.945 Ho 0.005 SnO4:0.07Yb3+ Calcium stannate color-changing material.

[0070] Test Example 1

[0071] This test example examines the color change effect, color change rate, light intensity control rate, and up- and down-conversion luminous intensity regulation performance of the calcium stannate color-changing material of the present invention.

[0072] 1. Color change effect and color change rate

[0073] Test method: Use Shimadzu UV-visible spectrophotometer (UV-2600) to test the diffuse reflectance spectrum of the material, and use a BaSO4 white plate as a reference. First, test the reflectance spectrum of the calcium stannate color-changing material before color change. The test range is 200nm-1400nm, and the reflectance values ​​corresponding to different wavelengths are recorded as R0. After the test, irradiate the calcium stannate color-changing material with an ultraviolet LED lamp with a wavelength of 290nm for 5 minutes to fully change color. Then place the discolored calcium stannate color-changing material in a spectrophotometer to test the reflectance spectrum after color change. The test range is 200nm-1400nm, and the reflectance values ​​corresponding to different wavelengths are recorded as R1. Finally, calculate the color change rate of the calcium stannate color-changing material corresponding to different wavelengths. The calculation formula is ΔR1=(R0-R1)×100%.

[0074] The results showed that the general formula Ca 2.015-x Ho 0.005 SnO4:xYb 3+ The calcium stannate color-changing material shown changes from light yellow to black after being irradiated with 290nm ultraviolet light. The reflectivity spectrum of the calcium stannate color-changing material before and after color change was tested, and it was found that when the doping amount x was 0.005, the calcium stannate color-changing material had a maximum reflectivity change of 66.9% at 615nm. Figure 1 shown.

[0075] 2. Down-conversion luminous intensity control rate

[0076] Test method: Use a steady-state transient fluorescence spectrometer (Quanta Master8000) equipped with a xenon lamp to test the down-conversion luminescence (DC) emission spectrum of the calcium stannate color-changing material. The test range is 500nm-800nm. The spectrum test is carried out in a dark room. First, test the calcium stannate color-changing material before the color changes under the excitation light λ ex =461nm excitation down-conversion luminescence emission spectrum, the emission peak intensity at 551nm is obtained as I0. After the test, the calcium stannate color-changing material is irradiated with a UV LED lamp with a wavelength of 290nm for 5 minutes to fully change color. Then the color-changed calcium stannate color-changing material is measured under the excitation light λ ex= down-conversion luminescence emission spectrum under 461 nm excitation, the emission peak intensity at 551 nm is I1. Finally, the down-conversion luminescence intensity regulation rate of the calcium stannate color-changing material is calculated, and the calculation formula is ΔI DC = [(I0-I1) / I0] x 100%.

[0077] The results show that the calcium stannate color-changing material of the general formula Ca 2.015-x Ho 0.005 SnO4:xYb 3+ The calcium stannate color-changing material shown in the formula has down-conversion luminescence intensity regulation performance. By comparing the emission spectrum of the calcium stannate color-changing material after 461 nm excitation, the down-conversion luminescence intensity regulation rate ΔI DC When the doping amount x is 0.005, the maximum light intensity regulation rate value at 551 nm is 92.4%, as shown in the formula. Figure 2

[0078] 3. Up-conversion luminescence intensity regulation rate

[0079] Test method: use a steady-state transient fluorescence spectrometer (Quanta Master 8000) equipped with a xenon lamp to test the up-conversion luminescence (UC) emission spectrum of the calcium stannate color-changing material, the test range is 500 nm-800 nm, and the spectrum test is carried out in a dark room. First, test the calcium stannate color-changing material before color change under the excitation light λ ex = 980 nm excitation up-conversion luminescence emission spectrum, the emission peak intensity at 551 nm is I0. After the test, irradiate the calcium stannate color-changing material with a wavelength of 290 nm ultraviolet LED lamp for 5 min to make it fully color change. Then measure the calcium stannate color-changing material after color change under the excitation light λ ex = 980 nm excitation up-conversion luminescence emission spectrum, the emission peak intensity at 551 nm is I1. Finally, the up-conversion luminescence intensity regulation rate of the calcium stannate color-changing material is calculated, and the calculation formula is ΔI UC = [(I0-I1) / I0] x 100%.

[0080] The results show that the calcium stannate color-changing material of the general formula Ca 2.015-x Ho 0.005 SnO4:xYb 3+ The calcium stannate color-changing material shown in the formula has up-conversion luminescence intensity regulation performance. By comparing the emission spectrum of the calcium stannate color-changing material after 980 nm excitation, the up-conversion luminescence intensity regulation rate ΔI UC When the doping amount x is 0.005, the maximum light intensity regulation rate value at 551 nm is 95.03%, as shown in the formula. Figure 3

[0081] Test example 2

[0082] ​​This test example investigates the color change effect, color change rate, light intensity control rate, and up- and down-conversion luminous intensity regulation performance of the calcium stannate color-changing material of the present invention.

[0083] Test method: Same as Test Example 1.

[0084] Test material 1: calcium stannate material prepared in Example 1 of the present invention;

[0085] Test material 2: calcium stannate material prepared in Example 2 of the present invention;

[0086] Test material 3: calcium stannate material prepared in Example 3 of the present invention;

[0087] Test material 4: calcium stannate material prepared in Example 4 of the present invention;

[0088] Test material 5: calcium stannate material prepared in Example 5 of the present invention;

[0089] Test material 6: calcium stannate material prepared in Example 6 of the present invention;

[0090] Test material 7: calcium stannate material prepared in Example 7 of the present invention.

[0091] The test results are shown in Table 1 below:

[0092] Table 1

[0093]

[0094] It can be seen from the above test results that the calcium stannate color-changing material prepared by the present invention has a more obvious color-changing effect, a higher color-changing rate and a higher light intensity control rate, and has both up-conversion luminescence intensity regulation and down-conversion luminescence intensity regulation performance.

Claims

1. A calcium stannate color-changing material, characterized in that: The calcium stannate color-changing material has the following chemical formula: Ca 2.015-x Ho 0.005 SnO4:xYb 3+ , where 0<x≤0.

07.

2. The calcium stannate color-changing material according to claim 1, characterized in that: x is 0.

005.

3. A method for preparing the calcium stannate color-changing material according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: 1) First, pour CaCO3, SnO2, Ho2O3 and Yb2O3 into a nylon jar filled with agate balls, add appropriate amount of alcohol, ball mill, and dry and grind into powder; 2) Use a metal mold to press the powder into a disc, and then place it in a cold isostatic press for a period of time; 3) Finally, the isostatically pressed disc is placed in an alumina crucible, placed in a silicon-molybdenum rod ultrahigh temperature electric furnace, heated and kept warm, and then naturally cooled to room temperature to obtain the calcium stannate color-changing material.

4. The preparation method according to claim 3, characterized in that In step 1), the molar ratio of CaCO3, SnO2, Ho2O3, and Yb2O3 is (1.945-2.015):1:0.005:(0-0.07).

5. The preparation method according to claim 4, characterized in that In step 1), the molar ratio of CaCO3, SnO2, Ho2O3, and Yb2O3 is 2.01:1:0.005:0.

005.

6. The preparation method according to claim 5, characterized in that In step 3), the temperature is raised to 1300-1500° C. and kept at this temperature for 3-5 hours.

7. The preparation method according to claim 6, characterized in that In step 3), the temperature is raised to 1400° C. and kept at this temperature for 4 h.

8. The preparation method according to claim 7, characterized in that The heating rate is 5-10℃ / min.

9. The preparation method according to claim 8, characterized in that The heating rate is 7°C / min.

10. The preparation method according to claim 3, characterized in that In step 1), the ball milling time is 5 to 10 hours.

11. The preparation method according to claim 10, characterized in that: In step 1), the ball milling time is 8 h.

12. The preparation method according to claim 3, characterized in that In step 2), the product is placed in a cold isostatic press and maintained at a pressure of 230 to 280 MPa for 1 to 3 minutes.

13. The preparation method according to claim 12, characterized in that In step 2), the sample was placed in a cold isostatic press and maintained at a pressure of 250 MPa for 2 minutes.

14. The preparation method according to claim 3, characterized in that In step 2), the powder is pressed into discs with a diameter of 10 to 15 mm.

15. The preparation method according to claim 14, characterized in that In step 2), the powder was pressed into discs with a diameter of 13 mm.

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