High-entropy pyrochlore ceramic as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of high-entropy materials, and discloses high-entropy pyrochlore ceramic as well as a preparation method and application thereof. The chemical formula of the high-entropy pyrochlore ceramic is (La0. 2Nd0. 2Sm0. 2Gd0. 2Er0. 2) 2M2O7, M is Zr, Hf, Ti or Sn, lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, erbium oxide and zirconium oxide or hafnium oxide or titanium oxide or tin oxide are sintered at the temperature of 1400-1600 DEG C to synthesize high-entropy pyrochlore powder, the high-entropy pyrochlore powder is mixed with tin chloride, ball-milled and dried to obtain mixed powder, the mixed powder is mixed with a surfactant, the mixed powder is mixed at the temperature of 200-400 DEG C, ball-milled and dried, and the high-entropy pyrochlore ceramic is obtained. And carrying out cold sintering under the pressure of 200-500MPa, and then carrying out vacuum sintering at the temperature of 1300-1600 DEG C, thereby obtaining the The high-entropy pyrochlore ceramic disclosed by the invention is high in purity, high in density, excellent in mechanical property and leaching resistance, low in sintering temperature and short in heat preservation time, and has an application prospect in the field of nuclear waste curing.

Description

Technical Field

[0001] The present invention belongs to the technical field of high entropy ceramics, and in particular, relates to a high entropy pyrochlore ceramic and a preparation method and 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 structure (A2B2O7) oxides have high chemical durability, high radiation resistance, and high thermodynamic stability, and are therefore considered to be one of the most promising HLW fixation materials. Recently, some 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 show significantly improved water durability and radiation resistance. Therefore, high-entropy pyrochlore is considered to be a promising HLW immobilization material. However, due to the poor thermal conductivity, high melting point and slow grain diffusion of high-entropy ceramics during sintering, the densification process often requires higher temperatures (1400-1700°C) and longer holding times (10-72h). For example, Li et al. reported that a high-entropy pyrochlore La with a density of only 71.4% was prepared by pressureless sintering at 1500°C for 3h. 0.2 Nd 0.2 Sm 0.2 Eu 0.2 G 0.2 )2Zr2O7(]F.Li,L.Zhou,J.-X.Liu,et al.,High-entropy pyrochlores with low thermal conductivity forthermal barrier coating materials,J.Adv.Ceram.8(4)(2019)576-582); Teng et al. prepared almost completely dense high-entropy pyrochlore (La) at 1500℃ for 40h. 0.2 Nd 0.2 Sm 0.2 Eu 0.2 G 0.2)2Zr2O7(]Z.Teng, Y.Tan, S.Zeng, et al., Preparation and phase evolution of high-entropyoxides A2B2O7 with multiple elements at Aand B sites, J.Eur.Ceram.Soc.41(6)(2021)3614-3620).

[0003] In 2016, a new sintering technology, cold sintering, began to emerge. This sintering process can obtain ceramics with higher density under low temperature and high pressure conditions. For difficult-to-sinter materials, cold sintering combined with pressureless sintering can obtain dense ceramics at lower temperatures and shorter insulation times compared to pressureless sintering, thereby reducing sintering time and energy consumption. At present, the raw materials for cold sintering mainly use powders of tens of nm, which will increase the sintering cost. At the same time, in order to improve the sintering density during the cold pressing sintering process, some liquid phase sintering aids will be added, and these aids will remain in the matrix to a certain extent, which will have a certain impact on the performance of the matrix. This patent introduces a new low-temperature sintering aid (zinc chloride, melting point: 283°C) to promote the densification of the matrix during the cold sintering process, which then volatilizes during the pressureless sintering process and does not react with the matrix high entropy pyrochlore. After pressureless sintering, a high-purity and dense micron powder synthesized noble pyrochlore ceramic is obtained in a shorter insulation time. Summary of the invention

[0004] In order to solve the shortcomings and deficiencies in the prior art, the primary purpose of the present invention is to provide a high-entropy pyrochlore ceramic having high density (above 98%), stable chemical properties and low nuclide leaching rate.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned high-entropy pyrochlore ceramics. The method uses ZnCl3 as a low-temperature sintering aid, adds a surfactant to reduce the friction between particles and promote particle diffusion and densification under high pressure, and prepares high-entropy pyrochlore ceramics through cold sintering and vacuum pressureless sintering.

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

[0007] A high entropy pyrochlore ceramic has the chemical formula (La 0.2 Nd 0.2 Sm 0.2 G 0.2 Er 0.2 )2M2O7, where M=Zr, Hf, Ti or Sn.

[0008] Furthermore, the high entropy pyrochlore ceramic is prepared by adding a solvent and grinding balls to lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, erbium oxide, zirconium oxide, hafnium oxide, titanium oxide, or tin oxide, mixing the mixture, drying, and sieving to obtain a mixed powder A; sintering the mixture at 1400-1600° C. to form a high entropy pyrochlore powder, adding zinc chloride, a solvent, and grinding balls to mix the mixture, drying, and sieving to obtain a mixed powder B; and then adding a surfactant, cold sintering the mixed powder C at 200-400° C. and a pressure of 200-500 MPa, and then vacuum sintering at 1300-1600° C. to obtain the obtained product.

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

[0010] Preferably, the sintering time at 1400-1600° C. is 1-5 hours; the cold sintering time is 0.5-2 hours; and the vacuum sintering time is 1-10 hours.

[0011] Preferably, the particle size of the zinc chloride is 1 to 10 μm, and the zinc chloride is 1 to 10 wt % of the high-entropy pyrochlore powder.

[0012] Preferably, the solvent is anhydrous ethanol, the surfactant is polyvinyl alcohol, polypropylene alcohol or deionized water, and the surfactant is 1 to 5 wt.% of the high-entropy pyrochlore powder.

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

[0014] S1. Lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, scandium oxide, zirconium oxide, hafnium oxide, titanium oxide, or tin oxide are mixed with a solvent and a grinding ball, dried, sieved, and the mixed powder is kept at 1400 to 1600° C. for 1 to 5 hours to obtain a high entropy pyrochlore;

[0015] S2. The high entropy pyrochlore and the zinc chloride solvent were ball-milled and mixed, and the mixture was dried and sieved to obtain a high entropy pyrochlore powder;

[0016] S3. Grind the high-entropy pyrochlore powder and surfactant for 10 to 30 minutes, cold-sinter the ground powder at 200 to 400° C. and 200 to 500 MPa for 0.5 to 2 hours, and then sinter at 1300 to 1600° C. in vacuum for 1 to 10 hours to obtain high-entropy pyrochlore ceramics.

[0017] Preferably, the rotation speed of the ball mill in steps S1 and S2 is 200-300 r / min, and the time of the ball mill is 12-24 h.

[0018] The application of the high entropy pyrochlore ceramic in the field of nuclear waste solidification.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention uses micron powder raw materials through cold sintering-vacuum pressureless sintering to prepare (La 0.2 Nd 0.2 Sm 0.2 G 0.2 Er) 2Zr2O7 high entropy pyrochlore has a short sintering and heat preservation time, which can reduce production costs.

[0021] 2. The present invention introduces a low-temperature sintering aid ZnCl3 to improve the density of the sample during the cold-pressing sintering process, and then the sintering aid volatilizes after the pressureless vacuum sintering, and will not remain in the matrix, thereby ensuring the purity of the sample. In addition, the addition of a surfactant can reduce the friction between particles and promote particle diffusion and densification under high pressure.

[0022] 3. Compared with ceramics prepared by pressureless sintering, the high-entropy pyrochlore ceramics prepared by the present invention have higher density (more than 98%), more stable chemical properties, and lower nuclide leaching rate, and have application prospects in the field of nuclear waste solidification. 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 Er 0.2 )2Zr2O7, adding lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, erbium oxide and zirconium oxide in equal molar ratios and with a particle size of 1 μm to anhydrous ethanol and zirconium oxide balls, milling them in a planetary ball mill at a speed of 300 r / min for 24 h, drying and sieving to obtain a mixed powder;

[0026] 2. The mixed powder was pressed into blocks and kept at 1500°C for 2 hours to obtain single-phase high-entropy pyrochlore, which was then crushed and added to 5wt.% ZnCl3 (1μm), anhydrous ethanol and zirconium oxide balls, and ball-milled in a planetary ball mill at a speed of 300r / min for 24 hours. After drying and sieving, high-entropy pyrochlore powder was obtained;

[0027] 3. The high entropy pyrochlore powder was mixed with 5wt.% polyvinyl alcohol and ground for 30min, placed in a WC mold and cold sintered at 300℃ and 300MPa for 60min, then placed in a pressureless furnace and sintered at 1500℃ for 5h, and then cooled to room temperature to obtain (La 0.2 Nd 0.2 Sm 0.2 G 0.2 Er)2Zr2O7 high entropy pyrochlore ceramics.

[0028] The density of the high entropy pyrochlore ceramic is 98.2%. In the MCC-1 leaching test in deionized water at 90°C, the leaching rates of La, Nd, Sm, Gd, Er and Zr are 3.2x10 -6 , 5.8x10 -7 ,8.8x10 -6 , 4.3x10 -7 、6.8x10 -6 and 6.3x10 -7 .

[0029] Example 2

[0030] The difference from Example 1 is that: ZnCl3 is not added in step 2, the mixed powder is placed in a WC mold and cold sintered at 400°C and 300MPa for 60min, and then placed in a pressureless furnace and sintered at 1600°C for 5h, and then cooled to room temperature to obtain (La 0.2 Nd 0.2 Sm 0.2 G 0.2 Er)2Zr2O7 high entropy pyrochlore ceramics.

[0031] The density of the high entropy pyrochlore ceramic is 99.2%. In the MCC-1 leaching test in deionized water at 90°C, the leaching rates of La, Nd, Sm, Gd, Er and Zr are 1.8x10 -6 , 3.2x10 -7 , 5.6x10 -6 , 2.4x10 -7 , 1.3x10 -7 and 3.9x10 -7 .

[0032] Example 3

[0033] The difference from Example 1 is that 10 wt.% ZnCl3 is added in step 2, the mixed powder is placed in a WC mold in step 3 and cold sintered at 300°C and 300 MPa for 60 min, then placed in a pressureless furnace and sintered at 1600°C for 2 h, and then cooled to room temperature to obtain (La 0.2 Nd 0.2 Sm 0.2G 0.2 Er)2Zr2O7 high entropy pyrochlore ceramics.

[0034] The density of the high entropy pyrochlore ceramic is 99.5%. In the MCC-1 leaching test in deionized water at 90°C, the leaching rates of La, Nd, Sm, Gd, Er and Zr are 7.3x10 -7 , 1.5x10 -7 , 8.5x10 -7 , 3.6x10 -7 , 2.8x10 -7 and 1.3x10 -8 .

[0035] Example 4

[0036] The difference from Example 1 is that in step 1, the particle sizes of lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, scandium oxide and zirconium oxide are all 10 μm, and in step 3, the mixed powder is placed in a WC mold and cold sintered at 400°C and 400 MPa for 60 min, then placed in a pressureless furnace and sintered at 1600°C for 5 h, and then cooled to room temperature to obtain (La 0.2 Nd 0.2 Sm 0.2 G 0.2 Er)2Zr2O7 high entropy pyrochlore ceramics.

[0037] The density of the high entropy pyrochlore ceramic is 98.5%. In the MCC-1 leaching test in deionized water at 90°C, the leaching rates of La, Nd, Sm, Gd, Er and Zr are 2.3x10 -6 , 6.3x10 -6 , 3.3x10 -6 ,7.3x10 -7 , 6.6x10 -7 and 1.3x10 -7 .

[0038] Example 5

[0039] The difference from Example 1 is that in step 1, the particle sizes of lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, scandium oxide and zirconium oxide are all 10 μm, 10 wt.% ZnCl3 (1 μm) is added in step 2, and in step 3, the mixed powder is placed in a WC mold and cold sintered at 400°C and 400 MPa for 60 min, then placed in a pressureless furnace and sintered at 1600°C for 2 h in vacuum, and then cooled to room temperature to obtain (La 0.2 Nd 0.2 Sm 0.2 G 0.2 Er)2Zr2O7 high entropy pyrochlore ceramics.

[0040] The density of the high entropy pyrochlore ceramic is 99%. In the MCC-1 leaching test in deionized water at 90°C, the leaching rates of La, Nd, Sm, Gd, Er and Zr are 3.0x10 -6 , 5.0x10 -7 , 8x10 -6 , 4.0x10 -7 , 6x10 -6 and 5x10 -7 .

[0041] 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 high entropy pyrochlore ceramic, characterized in that: The chemical formula of the high entropy pyrochlore ceramic is (La 0.2 Nd 0.2 Sm 0.2 G 0.2 Er 0.2 )2M2O7, where M=Zr, Hf, Ti or Sn.

2. The high entropy pyrochlore ceramic according to claim 1, characterized in that: The high entropy pyrochlore ceramic is prepared by adding solvent and grinding balls to lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, erbium oxide and zirconium oxide or hafnium oxide or titanium oxide or tin oxide, mixing them, drying and sieving to obtain mixed powder A; sintering the pressed powders at 1400-1600° C. to form high entropy pyrochlore powder, adding zinc chloride, solvent and grinding balls to mix them, drying and sieving to obtain mixed powder B, adding surfactant, cold sintering the mixed powder C at 200-400° C. and pressure of 200-500 MPa, and then vacuum sintering at 1300-1600° C.

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

4. The high entropy pyrochlore ceramic according to claim 2, characterized in that: The sintering time at 1400-1600° C. is 1-5 hours; the cold sintering time is 0.5-2 hours; and the vacuum sintering time is 1-10 hours.

5. The high entropy pyrochlore ceramic according to claim 2, characterized in that: The particle size of the zinc chloride is 1 to 10 μm. The zinc chloride is 1 to 10 wt % of the high entropy pyrochlore powder.

6. The high entropy pyrochlore ceramic according to claim 2, characterized in that: The solvents are all anhydrous ethanol, the surfactant is polyvinyl alcohol, polypropylene alcohol or deionized water, and the surfactant is 1 to 5 wt.% of the high entropy pyrochlore powder.

7. The method for preparing high entropy pyrochlore ceramics 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, zirconium oxide, hafnium oxide, titanium oxide, or tin oxide are mixed with a solvent and a grinding ball, dried, sieved, and the mixed powder is kept at 1400 to 1600° C. for 1 to 5 hours to obtain a high entropy pyrochlore; S2. The high entropy pyrochlore and the zinc chloride solvent are ball-milled, dried, and sieved to obtain a high entropy pyrochlore powder; S3. Grind the high-entropy pyrochlore powder and surfactant for 10 to 30 minutes, cold-sinter the ground powder at 200 to 400° C. and 200 to 500 MPa for 0.5 to 2 hours, and then sinter at 1300 to 1600° C. in vacuum for 1 to 10 hours to obtain high-entropy pyrochlore ceramics.

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

9. Use of the high entropy pyrochlore ceramic according to any one of claims 1 to 6 in the field of nuclear waste solidification.