Cr2O3 coated high-entropy pyrochlore composite ceramic as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of high-entropy materials, and discloses a Cr2O3 coated high-entropy pyrochlore composite ceramic as well as a preparation method and application thereof, the composite ceramic is xCr2O3. (1-x) (La0. 2Nd0. 2Sm0. 2Gd0. 2Sc0. 2) 2Zr2O7, x is 5-20wt.%, Sb0. 2Sb0. 2Gd0. 2Sc0. 2) 2Zr2O7, Sb0. 2Sb0. 2Gd0. The preparation method comprises 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, adding the high-entropy pyrochlore powder into a CrCl3 solution after ball milling, stirring, drying to obtain CrCl3 coated high-entropy pyrochlore powder, pressing the CrCl3 coated high-entropy pyrochlore powder into blocks, carrying out cold sintering at 200-400 DEG C and 200-500 MPa, carrying out heat preservation at 800-900 DEG C, heating to 1500-1700 DEG C, and carrying out pressureless sintering. The composite ceramic is high in density, excellent in radiation resistance and leaching resistance and capable of being applied to the field of nuclear waste solidified bodies.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear waste solidification ceramics, and in particular, relates to a Cr2O3-coated high-entropy pyrochlore composite ceramic, a preparation method and an application thereof. Background Art

[0002] The safe disposal of high-level radioactive waste (HLW) is crucial to the sustainable development of the nuclear industry. Numerous studies have shown that pyrochlore-structured oxides (A2B2O7) are considered promising materials for HLW fixation due to their high chemical durability, high radiation resistance, and high thermodynamic stability. Recent reports have shown that compared with most ceramic materials including single-phase pyrochlore, (Eu 1- x G x )2(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ce 0.2 )2O7 and other high-entropy pyrochlore-structured oxide ceramics have anti-leaching properties and radiation resistance. Highly efficient anti-leaching properties can ensure the stability of waste during long-term storage, prevent harmful components such as radioactive substances from entering the environment or water bodies through leaching, and avoid potential threats to the ecological environment and human health. Although existing ceramic solids have shown good anti-leaching properties, there is still room for improvement in anti-leaching properties when facing more severe long-term environmental changes and more complex chemical solvent effects. Studies have shown that Cr2O3 has excellent anti-leaching and radiation resistance in weakly acidic, neutral, and alkaline environments. Therefore, further improving the anti-leaching properties of ceramic solids has become the key to current research. Summary of the invention

[0003] In order to solve the shortcomings and deficiencies in the prior art, the primary purpose of the present invention is to provide a Cr2O3-coated high-entropy pyrochlore composite ceramic. The composite ceramic has Cr2O3 coated on the surface of high-entropy pyrochlore particles and has excellent anti-leaching performance.

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

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

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A Cr2O3-coated high-entropy pyrochlore composite ceramic wherein the high-entropy pyrochlore has a chemical formula of xCr2O3·(1-x)(La0.2 Nd 0.2 Sm 0.2 G 0.2 Sc 0.2 )2Zr2O7, wherein x is 5-20wt.%.

[0008] Furthermore, the composite ceramic is prepared by sintering a mixed powder of lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide and zirconium oxide at 1400-1700°C to obtain high-entropy pyrochlore powder, adding the mixed powder to a CrCl3 solution and magnetically stirring the mixed powder after ball milling, and obtaining CrCl3-coated high-entropy pyrochlore powder after drying, and then cold-sintering the mixed powder at 200-400°C and 200-500MPa, then keeping the mixed powder at 800-900°C, and then heating the mixed powder to 1500-1700°C for pressureless sintering.

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

[0010] Preferably, the sintering time at 1400-1700° C. is 1-5 hours; the cold sintering time is 0.5-2 hours; the insulation time at 800-900° C. is 1-10 hours; and the pressureless sintering time at 1500-1700° C. is 5-48 hours.

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

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

[0013] The method for preparing the Cr2O3-coated high-entropy pyrochlore composite ceramic comprises the following steps:

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

[0015] S2. The mixed powder is sintered at 1400-1700° C. to obtain high entropy pyrochlore powder, which is crushed and then ball-milled with a solvent and zirconium oxide grinding balls, dried, and sieved to obtain high entropy pyrochlore powder;

[0016] S3. The high entropy pyrochlore powder was added to the CrCl3 solution and magnetically stirred at 50 to 80 ° C, and the CrCl3-coated high entropy pyrochlore powder was obtained after drying;

[0017] S4. After the CrCl3-coated high-entropy pyrochlore powder is pressed into a block, it is cold-sintered at 200-400°C and a pressure of 200-500MP, kept at 800-900°C for 1-10h, and then heated to 1500-1700°C and kept for 5-48h for pressureless sintering to obtain a composite ceramic of Cr2O3-coated high-entropy pyrochlore.

[0018] Preferably, the rotation speed of the ball mill in steps S1 and S2 is 200-300 r / min, the time of the ball mill is 12-24 h, and the aperture of the sieve 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. The present invention uses CrCl3 solution as a precursor and introduces corrosion-resistant Cr2O3-coated high-entropy pyrochlore particles to prepare Cr2O3-coated high-entropy pyrochlore composite ceramics, which significantly improves the material's anti-leaching performance.

[0022] 2. The present invention significantly reduces the temperature holding time corresponding to the densification of the high-entropy pyrochlore composite ceramic through cold sintering-pressureless sintering, thereby reducing energy consumption. DETAILED DESCRIPTION

[0023] The content of the present invention is further described below in conjunction with specific examples, but it should not be construed as limiting the present invention. If not specifically indicated, the technical means used in the examples 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 the art.

[0024] Example 1

[0025] 1. According to the chemical formula (La 0.2 Nd 0.2 Sm 0.2 G 0.2 Sc 0.2 )2Zr2O7 Add lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, scandium oxide and zirconium oxide with a particle size of 1 μm into anhydrous ethanol and zirconium oxide balls, mill them in a planetary ball mill at a speed of 300 r / min for 24 h, dry and sieve to obtain a mixed powder;

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

[0027] 3. Add 8g of high entropy pyrochlore powder into 20wt% chromium chloride solution (2g of chromium chloride) and stir magnetically to obtain CrCl3-coated high entropy pyrochlore particle powder after drying;

[0028] 4. The CrCl3-coated high entropy pyrochlore particles were pressed into a block and then kept at 300°C and 300 MPa for 30 min, and then transferred to a muffle furnace for pressureless sintering at 1500°C for 10 h to obtain a Cr2O3-coated high entropy pyrochlore composite ceramic with a molecular formula of 0.2Cr2O3·0.8(La 0.2 Nd 0.2 Sm 0.2 G 0.2 Sc 0.2 )2Zr2O7.

[0029] The density of the prepared Cr2O3-coated high-entropy pyrochlore composite ceramic is 97.6%. The leaching rate of Cr element is 4.2×10 -6 g / (m 2 ·d), the leaching rates of La, Nd, Sm, Gd and Y were 3.8×10 - 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 leaching rate of Zr element is lower than the detection limit (less than 10 -9 g / (m 2 ·d)), showing excellent anti-leaching performance.

[0030] Example 2

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

[0032] The prepared Cr2O3-coated high entropy pyrochlore composite ceramic 0.15Cr2O3·0.85(La 0.2 Nd 0.2 Sm 0.2 G 0.2 Sc 0.2The density of 2Zr2O7 is 97.8%. The leaching rate of Cr element is 3.8×10 -6 g / (m 2 ·d), the leaching rates of La, Nd, Sm, Gd and Y were 3.6×10 -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 leaching rate of Zr element is lower than the detection limit (less than 10 -9 g / (m 2 ·d)), showing excellent anti-leaching performance.

[0033] Example 3

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

[0035] The density of the prepared Cr2O3-coated high-entropy pyrochlore composite ceramic is 98.5%. The leaching rate of Cr element is 1.3×10 -6 g / (m 2 ·d), the leaching rates of La, Nd, Sm, Gd and Y were 2.1×10 - 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 leaching rate of Zr element is lower than the detection limit (less than 10-9 g / (m 2 ·d)), showing excellent anti-leaching performance.

[0036] Example 4

[0037] The difference from Example 1 is that: in step 1, lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, scandium oxide and zirconium oxide, each with a particle size of 10 μm, are ball-milled in a planetary ball mill at a speed of 300 r / min for 24 hours, dried and sieved to obtain a mixed powder; in step 2, the mixed powder is pressed into a block and kept at 1600° C. for 5 hours to obtain a high-entropy pyrochlore powder; in step 4, the mixed powder is pressurelessly sintered in a muffle furnace at 1600° C. for 5 hours to obtain a Cr2O3-coated high-entropy pyrochlore composite ceramic, whose molecular formula is 0.2Cr2O3·0.8(La 0.2 Nd 0.2 Sm 0.2 G 0.2 Sc 0.2 )2Zr2O7.

[0038] The density of the prepared Cr2O3-coated high-entropy pyrochlore composite ceramic is 99.3%. The leaching rate of Cr element is 5.8×10 -7 g / (m 2 ·d), the leaching rates of La, Nd, Sm and Y were 6.3×10 -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 were lower than the detection limit (less than 10 -9 g / (m 2 ·d)), showing excellent anti-leaching performance.

[0039] Example 5

[0040] The difference from Example 1 is that: in step 1, lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, scandium oxide and zirconium oxide with a particle size of 10 μm are added; in step 3, 8.5 g of high-entropy pyrochlore powder is added to a 15 wt% chromium chloride solution (1.5 g of chromium chloride) under vacuum and magnetically stirred, and CrCl3-coated high-entropy pyrochlore particle powder is obtained after drying. In step 4, the CrCl3-coated high-entropy pyrochlore particle powder is pressed into a block and then cold-sintered and kept warm at 400°C and 300 MPa for 30 minutes, and then transferred to a muffle furnace for pressureless sintering and keeping warm at 1600°C for 5 hours to obtain a Cr2O3-coated high-entropy pyrochlore composite ceramic, whose molecular formula is 0.15Cr2O3·0.85(La 0.2 Nd 0.2 Sm 0.2 G 0.2 Sc 0.2 )2Zr2O7.

[0041] The density of the prepared Cr2O3-coated high-entropy pyrochlore composite ceramic is 98.4%. The leaching rate of Cr element is 4.8×10 -6 g / (m 2 ·d), the leaching rates of La, Nd, Sm, Gd and Y were 7.2×10 - 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 leaching rate of Zr element is lower than the detection limit (less than 10 -9 g / (m 2 ·d)), showing excellent anti-leaching performance.

[0042] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A Cr2O3-coated high-entropy pyrochlore composite ceramic, characterized in that: The chemical formula of high entropy pyrochlore in the composite ceramic is xCr2O3·(1-x)(La 0.2 Nd 0.2 Sm 0.2 G 0.2 Sc 0.2 )2Zr2O7, wherein x is 5 to 20 wt.%.

2. The Cr2O3-coated high-entropy pyrochlore composite ceramic according to claim 1, characterized in that: The composite ceramic is a mixture of lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide and zirconium oxide according to the chemical formula (La 0.2 Nd 0.2 Sm 0.2 G 0.2 Sc 0.2 )2Zr2O7 molar ratio of mixed powder is sintered at 1400-1700°C to obtain high entropy pyrochlore powder, which is added into CrCl3 solution and magnetically stirred after ball milling. After drying, CrCl3 coated high entropy pyrochlore powder is obtained, and then the briquette is cold sintered at 200-400°C and 200-500MPa, then kept at 800-900°C, and then heated to 1500-1700°C for pressureless sintering.

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

4. The Cr2O3-coated high-entropy pyrochlore composite ceramic according to claim 2, characterized in that: The sintering time at 1400-1700° C. is 1-5 hours; the cold sintering time is 0.5-2 hours; the heat preservation time at 800-900° C. is 1-10 hours; and the pressureless sintering time at 1500-1700° C. is 5-48 hours.

5. The Cr2O3-coated high-entropy pyrochlore composite ceramic according to claim 2, characterized in that: The concentration of the CrCl3 solution is 20-70wt%.

6. The Cr2O3-coated high-entropy pyrochlore composite ceramic according to claim 2, characterized in that: The temperature of the magnetic stirring is 50-80° C., and the stirring speed is 50-200 r / min.

7. The method for preparing the Cr2O3-coated high-entropy pyrochlore composite ceramic according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, scandium oxide and zirconium oxide are mixed in a molar ratio according to the chemical formula LaNdSmGdSc)2Zr2O7, a solvent and zirconium oxide balls are added for ball milling, and then dried and sieved to obtain a mixed powder; S2. The mixed powder is sintered at 1400-1700° C. to obtain high entropy pyrochlore powder, which is crushed and then ball-milled with a solvent and zirconium oxide grinding balls, dried, and sieved to obtain high entropy pyrochlore powder; S3. The high entropy pyrochlore powder was added to the CrCl3 solution and magnetically stirred at 50 to 80 ° C, and the CrCl3-coated high entropy pyrochlore powder was obtained after drying; S4. After the CrCl3-coated high-entropy pyrochlore powder is pressed into a block, it is cold-sintered at 200-400°C and a pressure of 200-500MP, kept at 800-900°C for 1-10h, and then heated to 1500-1700°C and kept for 5-48h for pressureless sintering to obtain a composite ceramic of Cr2O3-coated high-entropy pyrochlore.

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

9. Application of the Cr2O3 coated high entropy pyrochlore composite ceramic according to claim 1 or 2 in the field of nuclear waste solidification.