Cr2o3-coated high-entropy pyrochlore composite ceramic, preparation method and application thereof

Abstract

The application belongs to the technical field of high-entropy materials, and discloses a composite ceramic of Cr2O3-coated high-entropy pyrochlore and a preparation method and application thereof. 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Sc 0.2 )2Zr2O7, wherein x is 5-20 wt.%; the composite ceramic is prepared by the following steps: sintering lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide and zirconium oxide at 1400-1700 DEG C to obtain high-entropy pyrochlore powder, stirring the high-entropy pyrochlore powder in a CrCl3 solution after ball milling, drying to obtain CrCl3-coated high-entropy pyrochlore powder, cold sintering the CrCl3-coated high-entropy pyrochlore powder at 200-400 DEG C and 200-500 MPa, then heat preservation at 800-900 DEG C, and then pressureless sintering at 1500-1700 DEG C. The composite ceramic has high density, excellent radiation resistance and leaching resistance, and can be applied in the field of nuclear waste solidification.

Description

Technical Field

[0001] This invention belongs to the field of nuclear waste solidification ceramic technology, specifically relating to a composite ceramic of Cr2O3 coated with high-entropy pyrochlore, its preparation method and application. Background Technology

[0002] The safe disposal of high-level radioactive waste (HLW) is crucial for the sustainable development of the nuclear industry. Numerous studies have shown that pyrochlore-structured oxides (A₂B₂O₇) possess high chemical durability, high radiation resistance, and high thermodynamic stability, making them promising HLW fixation materials. Recent reports indicate that (Eu) [a specific type of HLW] exhibits superior chemical durability, radiation resistance, and thermodynamic stability compared to most ceramic materials, including single-phase pyrochlore. 1- x Gd x )2(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ce 0.2 Oxide ceramics with high-entropy pyrochlore structures, such as Cr₂O₇, possess excellent leaching resistance and radiation resistance. Highly efficient leaching resistance ensures the stability of waste during long-term storage, preventing harmful components such as radioactive materials from entering the environment or water bodies through leaching, thus avoiding potential threats to the ecological environment and human health. Although existing ceramic solidification bodies have shown good leaching resistance, there is still room for improvement when facing more severe long-term environmental changes and more complex chemical solvents. Studies have shown that Cr₂O₃ exhibits excellent leaching resistance and radiation resistance in weakly acidic, neutral, and alkaline environments. Therefore, further improving the leaching resistance of ceramic solidification bodies has become a key research focus. Summary of the Invention

[0003] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a composite ceramic with Cr2O3-coated high-entropy pyrochlore. This composite ceramic, by coating Cr2O3 onto the surface of high-entropy pyrochlore particles, exhibits excellent resistance to leaching.

[0004] Another object of the present invention is to provide a method for preparing the above-mentioned Cr2O3-coated high-entropy pyrochlore composite ceramic. This method employs pressureless sintering to prepare a dense composite ceramic.

[0005] Another object of the present invention is to provide the application of the above-mentioned Cr2O3-coated high-entropy pyrochlore composite ceramic.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A composite ceramic in which Cr2O3-coated high-entropy pyrochlore has the chemical formula xCr2O3·(1-x)(La)0.2 Nd 0.2 Sm 0.2 Gd 0.2 Sc 0.2 )2Zr2O7, where x is 5-20 wt.%.

[0008] Furthermore, the composite ceramic is prepared by sintering a mixture of lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, and zirconium oxide powder at 1400–1700 °C to obtain high-entropy pyrochlore powder, which is then ball-milled and added to a CrCl3 solution under magnetic stirring. After drying, CrCl3-coated high-entropy pyrochlore powder is obtained, which is then pressed into blocks and cold-sintered at 200–400 °C and 200–500 MPa. Subsequently, it is held at 800–900 °C and then heated to 1500–1700 °C for pressureless sintering.

[0009] Preferably, the particle size of the lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, scandium oxide and zirconium oxide is 1 to 50 μm.

[0010] Preferably, the sintering time at 1400–1700℃ is 1–5 h; the cold sintering time is 0.5–2 h; the holding time at 800–900℃ is 1–10 h; and the pressureless sintering time at 1500–1700℃ is 5–48 h.

[0011] Preferably, the concentration of the CrCl3 solution is 20–70 wt%.

[0012] Preferably, the temperature of the magnetic stirring is 50-80℃, and the stirring speed is 50-200 r / min.

[0013] The preparation method of the Cr2O3-coated high-entropy pyrochlore composite ceramic includes the following steps:

[0014] S1. Lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, scandium oxide and zirconium oxide are mixed, and a solvent and zirconium oxide grinding balls are added for ball milling. After drying, the mixture is sieved to obtain a mixed powder.

[0015] S2. The mixed powder is sintered at 1400-1700℃ to obtain high-entropy pyrochlore powder. After crushing, solvent and zirconia grinding balls are added for ball milling. After drying, it is sieved to obtain high-entropy pyrochlore powder.

[0016] S3. Add the high-entropy pyrochlore powder to the CrCl3 solution and stir magnetically at 50-80℃. After drying, CrCl3-coated high-entropy pyrochlore powder is obtained.

[0017] S4. After pressing CrCl3-coated high-entropy pyrochlore powder into blocks, cold sintering is carried out at 200-400℃ and 200-500MPa, followed by holding at 800-900℃ for 1-10h, and then sintering without pressure at 1500-1700℃ for 5-48h to obtain Cr2O3-coated high-entropy pyrochlore composite ceramics.

[0018] Preferably, the ball milling speed in steps S1 and S2 is 200-300 r / min, the ball milling time is 12-24 h, and the sieve aperture is 100-200 mesh.

[0019] The Cr2O3-coated high-entropy pyrochlore composite ceramic is used in the field of nuclear waste solidification.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. This invention uses CrCl3 solution as a precursor and introduces corrosion-resistant Cr2O3 to coat high-entropy pyrochlore particles to prepare a composite ceramic of Cr2O3-coated high-entropy pyrochlore, which significantly improves the leaching resistance of the material.

[0022] 2. This invention significantly reduces the densification temperature holding time of high-entropy pyrochlore composite ceramics through cold sintering-pressureless sintering, thereby reducing energy consumption. Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments, but these should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0024] Example 1

[0025] 1. According to the chemical formula (La) 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Sc 0.2 Lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, scandium oxide, and zirconium oxide, all with a particle size of 1 μm, were added to anhydrous ethanol and zirconium oxide balls. The mixture was then ball-milled in a planetary ball mill at 300 r / min for 24 h. After drying, the mixture was sieved to obtain a mixed powder.

[0026] 2. After the mixed powder is pressed into briquettes, it is kept at 1600℃ for 2 hours and then ball-milled at 300 r / min for 24 hours to obtain high-entropy pyrochlore powder;

[0027] 3. Add 8g of high-entropy pyrochlore powder to a 20wt% chromium chloride solution (2g of chromium chloride) and stir magnetically. After drying, CrCl3-coated high-entropy pyrochlore particle powder is obtained.

[0028] 4. CrCl3-coated high-entropy pyrochlore granules were compressed into briquettes and held at 300℃ and 300MPa for 30 min. Subsequently, they were transferred to a muffle furnace and sintered at 1500℃ without pressure for 10 h to obtain a Cr2O3-coated high-entropy pyrochlore composite ceramic with the molecular formula 0.2Cr2O3·0.8(La 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Sc 0.2 )2Zr2O7.

[0029] The prepared Cr₂O₃-coated high-entropy pyrochlore composite ceramic had a density of 97.6%, and the Cr leaching rate was 4.2 × 10⁻⁶ using the 42-day MCC-1 leaching test method. -6 g / (m 2 The leaching rates of La, Nd, Sm, Gd, and Y were 3.8 × 10⁻⁶. - 6 g / (m 2 ·d), 1.3×10 -7 g / (m 2 ·d), 1.9×10 -6 g / (m 2 ·d), 2.5×10 -8 g / (m 2 ·d), 4.2×10 -7 g / (m 2 ·d), the Zr leaching rate is below the detection limit (less than 10). -9 g / (m 2 ·d)) exhibits excellent resistance to leaching.

[0030] Example 2

[0031] The difference from Example 1 is that in step 3, 8.5g of high-entropy pyrochlore powder is added to a 15wt% chromium chloride solution (1.5g of chromium chloride) and stirred magnetically. After drying, CrCl3-coated high-entropy pyrochlore particle powder is obtained.

[0032] The prepared Cr2O3-coated high-entropy pyrochlore composite ceramic 0.15Cr2O3·0.85(La) 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Sc 0.2The density of 2Zr2O7 was 97.8%. Using the 42-day MCC-1 leaching test method, the Cr element leaching rate was 3.8 × 10⁻⁶. -6 g / (m 2 The leaching rates of La, Nd, Sm, Gd, and Y were 3.6 × 10⁻⁶. -6 g / (m 2 ·d), 1.5×10 -7 g / (m 2 ·d), 1.3×10 -6 g / (m 2 ·d), 3.2×10 -8 g / (m 2 ·d), 1.8×10 -7 g / (m 2 ·d), the Zr leaching rate is below the detection limit (less than 10). -9 g / (m 2 ·d)) exhibits excellent resistance to leaching.

[0033] Example 3

[0034] The difference from Example 1 is that in step 4, the CrCl3-coated high-entropy pyrochlore particles are compressed into briquettes and then cold-sintered at 400℃ and 300MPa for 30 min. Subsequently, they are transferred to a muffle furnace for pressureless sintering at 1500℃ for 5 h to obtain a Cr2O3-coated high-entropy pyrochlore composite ceramic with the molecular formula 0.2Cr2O3·0.8(La 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Sc 0.2 )2Zr2O7.

[0035] The prepared Cr₂O₃-coated high-entropy pyrochlore composite ceramic had a density of 98.5%, and the Cr leaching rate was 1.3 × 10⁻⁶ using the 42-day MCC-1 leaching test method. -6 g / (m 2 The leaching rates of La, Nd, Sm, Gd, and Y were 2.1 × 10⁻⁶. - 6 g / (m 2 ·d), 5.8×10 -8 g / (m 2 ·d), 1.9×10 -6 g / (m 2 ·d), 3.6×10 -8 g / (m 2 ·d), 4.8×10 -8 g / (m 2 ·d), the Zr leaching rate is below the detection limit (less than 10).-9 g / (m 2 ·d)) exhibits excellent resistance to leaching.

[0036] Example 4

[0037] The difference from Example 1 is as follows: In step 1, lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, scandium oxide, and zirconium oxide, all with a particle size of 10 μm, are ball-milled in a planetary ball mill at 300 r / min for 24 h, dried, and sieved to obtain a mixed powder; in step 2, the mixed powder is briquetted and held at 1600℃ for 5 h to obtain high-entropy pyrochlore powder; in step 4, it is sintered without pressure in a muffle furnace at 1600℃ for 5 h to obtain a Cr2O3-coated high-entropy pyrochlore composite ceramic with the molecular formula 0.2Cr2O3·0.8(La 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Sc 0.2 )2Zr2O7.

[0038] The prepared Cr₂O₃-coated high-entropy pyrochlore composite ceramic had a density of 99.3%, and the Cr leaching rate was 5.8 × 10⁻⁶ using the 42-day MCC-1 leaching test method. -7 g / (m 2 The leaching rates of La, Nd, Sm, and Y were 6.3 × 10⁻⁶. -7 g / (m 2 ·d), 2.8×10 -7 g / (m 2 ·d), 3.6×10 -7 g / (m 2 ·d), 4.2×10 -7 g / (m 2 •d), the leaching rates of Zr and Gd elements are below the detection limit (less than 10). -9 g / (m 2 ·d)) exhibits excellent resistance to leaching.

[0039] Example 5

[0040] The difference from Example 1 is as follows: In step 1, lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, scandium oxide, and zirconium oxide, all with a particle size of 10 μm, are used. In step 3, 8.5 g of high-entropy pyrochlore powder is added to a 15 wt% chromium chloride solution (1.5 g chromium chloride) under vacuum and magnetically stirred. After drying, CrCl3-coated high-entropy pyrochlore particles are obtained. In step 4, the CrCl3-coated high-entropy pyrochlore particles are compressed into briquettes and cold-sintered at 400℃ and 300 MPa for 30 min. Then, they are transferred to a muffle furnace and sintered at 1600℃ without pressure for 5 h to obtain a Cr2O3-coated high-entropy pyrochlore composite ceramic with the molecular formula 0.15Cr2O3·0.85(La 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Sc 0.2 )2Zr2O7.

[0041] The prepared Cr₂O₃-coated high-entropy pyrochlore composite ceramic had a density of 98.4%, and the Cr leaching rate was 4.8 × 10⁻⁶ using the 42-day MCC-1 leaching test method. -6 g / (m 2 The leaching rates of La, Nd, Sm, Gd, and Y were 7.2 × 10⁻⁶. - 6 g / (m 2 ·d), 6.5×10 -7 g / (m 2 ·d), 7.7×10 -6 g / (m 2 ·d), 5.6×10 -8 g / (m 2 ·d), 3.8×10 -6 g / (m 2 ·d), the Zr leaching rate is below the detection limit (less than 10). -9 g / (m 2 ·d)) exhibits excellent resistance to leaching.

[0042] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A composite ceramic of Cr2O3-coated high-entropy pyrochlore, characterized in that, The high-entropy pyrochlore in the composite ceramic has the chemical formula xCr2O3·(1-x) (La 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Sc 0.2 )2Zr2O7, wherein x is 5~20 wt.%; the composite ceramic is made by combining lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, scandium oxide and zirconium oxide according to the chemical formula (La) 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Sc 0.2 The high-entropy pyrochlore powder was obtained by sintering a mixture of Zr2O7 in a molar ratio at 1400~1700℃. After ball milling, it was added to a CrCl3 solution and magnetically stirred. After drying, CrCl3-coated high-entropy pyrochlore powder was obtained. The powder was then pressed into blocks and cold sintered at 200~400℃ and 200~500MPa. Subsequently, it was held at 800~900℃ and then heated to 1500~1700℃ for pressureless sintering.

2. The composite ceramic of Cr2O3-coated high-entropy pyrochlore according to claim 1, characterized in that, The particle sizes of the lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, scandium oxide, and zirconium oxide are all 1~50 μm.

3. The composite ceramic of Cr2O3-coated high-entropy pyrochlore according to claim 1, characterized in that, The sintering time at 1400~1700℃ is 1~5h; the cold sintering time is 0.5~2h; the holding time at 800~900℃ is 1~10h; and the pressureless sintering time at 1500~1700℃ is 5~48h.

4. The composite ceramic of Cr2O3-coated high-entropy pyrochlore according to claim 1, characterized in that, The concentration of the CrCl3 solution is 20~70wt%.

5. The composite ceramic of Cr2O3-coated high-entropy pyrochlore according to claim 1, characterized in that, The temperature of the magnetic stirring is 50~80℃, and the stirring speed is 50~200r / min.

6. The method for preparing Cr2O3-coated high-entropy pyrochlore composite ceramics according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, scandium oxide, and zirconium oxide are arranged according to the chemical formula (La... 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Sc 0.2 The 2Zr2O7 molecules were mixed in a stoichiometric ratio, and then ball-milled with solvent and zirconium oxide grinding balls. After drying, the mixture was sieved to obtain a mixed powder. S2. The mixed powder is sintered at 1400~1700℃ to obtain high-entropy pyrochlore powder. After crushing, solvent and zirconia grinding balls are added for ball milling. After drying, it is sieved to obtain high-entropy pyrochlore powder. S3. Add the high-entropy pyrochlore powder to the CrCl3 solution and stir magnetically at 50~80℃. After drying, CrCl3-coated high-entropy pyrochlore powder is obtained. S4. After pressing CrCl3-coated high-entropy pyrochlore powder into blocks, cold sintering is carried out at 200~400℃ and 200~500MPa, followed by holding at 800~900℃ for 1~10h, and then sintering without pressure at 1500~1700℃ for 5~48h to obtain Cr2O3-coated high-entropy pyrochlore composite ceramics.

7. The method for preparing the composite ceramic of Cr2O3-coated high-entropy pyrochlore according to claim 6, characterized in that, In steps S1 and S2, the ball milling speed is 200~300 r / min, the ball milling time is 12~24 h, and the sieve aperture is 100~200 mesh.

8. The application of the Cr2O3-coated high-entropy pyrochlore composite ceramic as described in claim 1 in the field of nuclear waste solidification.