High-entropy pyrochlore ceramic and preparation method and application thereof

Abstract

The application belongs to the technical field of high-entropy materials, and discloses a high-entropy pyrochlore ceramic, a preparation method and application thereof. 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Er 0.2 )2M2O7, wherein M=Zr, Hf, Ti or Sn, is that lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, erbium oxide and zirconium oxide or hafnium oxide or titanium oxide or tin oxide are combined at 1400-1600 DEG C to form high-entropy pyrochlore powder, the high-entropy pyrochlore powder is mixed with zinc chloride, ball-milled and dried to obtain mixed powder, the mixed powder is mixed with a surfactant, the mixed powder is cold-sintered at 200-400 DEG C under a pressure of 200-500 MPa, and then vacuum sintered at 1300-1600 DEG C to obtain the high-entropy pyrochlore ceramic. The high-entropy pyrochlore ceramic has high purity, high density, excellent mechanical properties and leaching resistance, has a low sintering temperature and a short holding time, and has application prospects in the field of nuclear waste solidification.

Description

TECHNICAL FIELD

[0001] The present application 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

[0002] Safe disposal of high-level waste (HLW) is crucial for the sustainable development of the nuclear industry. A large number of studies have shown that pyrochlore-structured (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 immobilization materials. Recently, some reports have shown that high-entropy pyrochlore-structured oxide ceramics such as (Eu 1-x Gd x )2(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ce 0.2 )2O7 exhibit significantly improved water durability and radiation resistance compared to most ceramic materials, including single-phase pyrochlores. Therefore, high-entropy pyrochlores are considered to be a very promising HLW immobilization material. However, due to the poor thermal conductivity, high melting point and slow grain diffusion during sintering of high-entropy ceramics, the densification process often requires high temperatures (1400-1700℃) and long holding times (10-72h). For example, Li et al. reported the preparation of high-entropy pyrochlore La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 )2Zr2O7 with a density of only 71.4% by pressureless sintering at 1500℃ for 3h (F. Li, L. Zhou, J.-X. Liu, et al., High-entropy pyrochlores with low thermal conductivity for thermal barrier coating materials, J. Adv. Ceram. 8 (4) (2019) 576-582); Teng et al. prepared a nearly fully dense high-entropy pyrochlore (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2)2Zr2O7 (]Z. Teng, Y. Tan, S. Zeng, et al., Preparation and phase evolution of high-entropy oxides A2B2O7 with multiple elements at Aand B sites, J. Eur. Ceram. Soc. 41 (6) (2021) 3614–3620).

[0003] Since 2016, a new sintering technology—cold sintering—has emerged. This sintering process can obtain high-density ceramics under low-temperature and high-pressure conditions. For difficult-to-sinter materials, combining cold sintering with pressureless sintering can achieve dense ceramics at lower temperatures and shorter holding times compared to pressureless sintering, thus reducing sintering time and energy consumption. Currently, the raw materials used for cold sintering are mainly powders with a particle size of tens of nanometers, which increases sintering costs. Furthermore, during cold sintering, some liquid-phase sintering aids are added to improve sintering density, but these aids remain in the matrix to a certain extent, which can affect the matrix's properties. This invention introduces a new low-temperature sintering aid (zinc chloride, melting point: 283℃) to promote matrix densification during cold sintering. Subsequently, it volatilizes during pressureless sintering and does not react with the high-entropy pyrochlore in the matrix. After pressureless sintering, high-purity and dense high-density pyrochlore ceramics synthesized from micron-sized powders are obtained in a shorter holding time. Summary of the Invention

[0004] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a high-entropy calcined chlorite ceramic. This ceramic exhibits 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. This method uses ZnCl2 as a low-temperature sintering aid, and the addition of a surfactant reduces interparticle friction, promoting particle diffusion and densification under high pressure. High-entropy pyrochlore ceramics are prepared through cold sintering and vacuum pressureless sintering.

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

[0007] The chemical formula of a high-entropy calcined chlorite ceramic is (La 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Er 0.2 )2M2O7, where M = Zr, Hf, Ti or Sn.

[0008] Furthermore, the high-entropy calcined chlorite ceramic is prepared by mixing lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, erbium oxide, and zirconium oxide, hafnium oxide, titanium oxide, or tin oxide with a solvent and grinding balls, drying, and sieving to obtain mixed powder A; pressing the powder into blocks and sintering at 1400~1600℃ to form high-entropy calcined chlorite powder, adding zinc chloride, a solvent, and grinding balls, mixing, drying, and sieving to obtain mixed powder B; adding a surfactant, and cold sintering the mixed powder C at 200~400℃ and 200~500MPa, followed by vacuum sintering at 1300~1600℃.

[0009] Preferably, the particle size of the lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, erbium oxide, zirconium oxide, hafnium oxide, titanium oxide, and tin oxide is 1~50 μm.

[0010] Preferably, the sintering time at 1400~1600℃ is 1~5h; the cold sintering time is 0.5~2h; and the vacuum sintering time is 1~10h.

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

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

[0013] The preparation method of the high-entropy calcined chlorite ceramic includes the following steps:

[0014] S1. Lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, erbium oxide, zirconium oxide, hafnium oxide, titanium oxide, or tin oxide are mixed with solvent and grinding balls, dried, and sieved to obtain a mixed powder. The powder is then kept at 1400~1600℃ for 1~5h to obtain high-entropy pyrochlore.

[0015] S2. High-entropy pyrochlore is ball-milled and mixed with zinc chloride solvent, dried and sieved to obtain high-entropy pyrochlore powder;

[0016] S3. Mix and grind the high-entropy calcined chlorite powder and surfactant for 10-30 min. Then, cold sinter the ground powder at 200-400℃ and 200-500MPa for 0.5-2 h, and then vacuum sinter at 1300-1600℃ for 1-10 h to obtain high-entropy calcined chlorite ceramic.

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

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

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

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

[0021] This invention introduces the low-temperature sintering aid ZnCl2 to improve sample density during cold pressing sintering. Afterward, the sintering aid volatilizes during pressureless vacuum sintering, leaving no residue in the matrix and ensuring sample purity. Furthermore, the addition of a surfactant reduces interparticle friction, promoting particle diffusion and densification under high pressure.

[0022] The high-entropy calcined chlorite ceramics prepared by this invention have higher density (over 98%), more stable chemical properties, and lower nuclide leaching rate compared to ceramics prepared by pressureless sintering, and have promising applications in the field of nuclear waste solidification. 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. Example 1

[0024] According to the chemical formula (La) 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Er 0.2 Lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, erbium oxide and zirconium oxide in equimolar ratio with a particle size of 1µm were added to anhydrous ethanol and zirconium oxide balls. The mixture was ball-milled in a planetary ball mill at 300r / min for 24h, dried and sieved to obtain a mixed powder.

[0025] The mixed powder was briquetted and kept at 1500℃ for 2 hours to obtain single-phase high-entropy pyrochlore. Then it was crushed and added to 5wt.% ZnCl2 (1µm), anhydrous ethanol and zirconium oxide balls. The mixture was ball-milled in a planetary ball mill at 300r / min for 24 hours. After drying and sieving, high-entropy pyrochlore powder was obtained.

[0026] High-entropy pyrochlore powder was mixed and ground with 5 wt.% polyvinyl alcohol for 30 min, then placed in a WC mold and cold-sintered at 300℃ and 300 MPa for 60 min. It was then placed in a pressureless furnace and sintered under vacuum at 1500℃ for 5 h, followed by cooling to room temperature to obtain (La... 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Er)2Zr2O7 high-entropy calcined greenstone ceramics.

[0027] The high-entropy calcined greenstone ceramic has a density of 98.2%. MCC-1 leaching tests were conducted in deionized water at 90℃, and the leaching rates of La, Nd, Sm, Gd, Er, and Zr were 3.2 x 10⁻⁶. -6 5.8x10 -7 8.8x10 -6 4.3x10 -7 6.8x10 -6 and 6.3x10 -7 . Example 2

[0028] The difference from Example 1 is that ZnCl2 is not added in step 2. The mixed powder is placed in a WC mold and cold-sintered at 400°C and 300MPa for 60 min. Then it is placed in a pressureless furnace and sintered under vacuum at 1600°C for 5 h, and then cooled to room temperature to obtain (La). 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Er)2Zr2O7 high-entropy calcined greenstone ceramics.

[0029] The high-entropy calcined greenstone ceramic has a density of 99.2%. MCC-1 leaching tests were conducted in deionized water at 90℃, and the leaching rates of La, Nd, Sm, Gd, Er, and Zr were 1.8 x 10⁻⁶. -6 3.2x10 -7 5.6x10 -6 2.4x10 -7 1.3x10 -7 and 3.9x10 -7 . Example 3

[0030] The difference from Example 1 is that: 10 wt.% ZnCl2 was added in step 2; and in step 3, the mixed powder was placed in a WC mold and cold-sintered at 300°C and 300 MPa for 60 min, then placed in a pressureless furnace for vacuum sintering at 1600°C for 2 h, and then cooled to room temperature to obtain (La) 0.2 Nd 0.2 Sm 0.2 Gd 0.2Er)2Zr2O7 high-entropy calcined greenstone ceramics.

[0031] The high-entropy calcined greenstone ceramic has a density of 99.5%. In an MCC-1 leaching test conducted in deionized water at 90℃, the leaching rates of La, Nd, Sm, Gd, Er, and Zr were 7.3 x 10⁻⁶. -7 1.5x10 -7 8.5x10 -7 3.6x10 -7 2.8x10 -7 and 1.3x10 -8 . Example 4

[0032] The difference from Example 1 is that: in step 1, the particle size of lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, erbium oxide, and zirconium oxide is all 10µm; in step 3, the mixed powder is loaded into a WC mold and cold-sintered at 400℃ and 400MPa for 60 min, then placed in a pressureless furnace for vacuum sintering at 1600℃ for 5 h, and then cooled to room temperature to obtain (La 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Er)2Zr2O7 high-entropy calcined greenstone ceramics.

[0033] The high-entropy calcined greenstone ceramic has a density of 98.5%. MCC-1 leaching tests were conducted in deionized water at 90℃, and the leaching rates of La, Nd, Sm, Gd, Er, and Zr were 2.3 x 10⁻⁶. -6 6.3x10 -6 3.3x10 -6 7.3x10 -7 6.6x10 -7 and 1.3x10 -7 . Example 5

[0034] The difference from Example 1 is as follows: in step 1, the particle size of lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, erbium oxide, and zirconium oxide is 10µm; in step 2, 10wt.% ZnCl2 (1µm) is added; and in step 3, the mixed powder is placed in a WC mold and cold-sintered at 400℃ and 400MPa for 60min, then placed in a pressureless furnace for vacuum sintering at 1600℃ for 2h, and then cooled to room temperature to obtain (La 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Er)2Zr2O7 high-entropy calcined greenstone ceramics.

[0035] The high-entropy calcined chlorite ceramic has a density of 99%. MCC-1 leaching tests were conducted in deionized water at 90℃, and the leaching rates of La, Nd, Sm, Gd, Er, and Zr were 3.0 x 10⁻⁶. -6 5.0x10 -7 8x10 -6 4.0x10 -7 6x10 -6 and 5x10 -7 .

[0036] 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 high-entropy calcined chlorite ceramic, characterized in that, The chemical formula of the high-entropy pyrochlore ceramic is (La 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Er 0.2 )2M2O7, where M = Zr, Hf, Ti or Sn; the high-entropy pyrochlore ceramic is prepared by mixing lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, erbium oxide with zirconium oxide or hafnium oxide or titanium oxide or tin oxide, adding solvent and grinding balls, drying and sieving to obtain mixed powder A; pressing it into briquettes and sintering at 1400~1600℃ for 1~5h to synthesize high-entropy pyrochlore, then crushing it to obtain high-entropy pyrochlore powder, adding zinc chloride, solvent and grinding balls, mixing, drying and sieving to obtain mixed powder B, and then adding surfactant to prepare mixed powder. C is prepared by cold sintering the mixed powder C at 200~400℃ and 200~500MPa for 0.5~2h, followed by vacuum pressureless sintering at 1300~1600℃ for 1~10h; the particle size of the lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, erbium oxide, zirconium oxide, hafnium oxide, titanium oxide, and tin oxide is 1~50μm; the amount of zinc chloride used is 1~10wt% of the high-entropy pyrochlore powder; the surfactant is polyvinyl alcohol, polyacryl alcohol, or deionized water, and the amount of the surfactant used is 1~5wt.% of the high-entropy pyrochlore powder.

2. The high-entropy calcined chlorite ceramic according to claim 1, characterized in that, The zinc chloride has a particle size of 1~10 μm.

3. The high-entropy calcined chlorite ceramic according to claim 1, characterized in that, All solvents used are anhydrous ethanol.

4. The method for preparing high-entropy pyrochlore ceramics according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Lanthanum oxide, neodymium oxide, samarium oxide, gadolinium oxide, erbium oxide, zirconium oxide, hafnium oxide, titanium oxide, or tin oxide are mixed with a solvent and grinding balls by ball milling. After drying, the mixture is sieved to obtain mixed powder A. The powder A is then pressed into briquettes and kept at 1400~1600℃ for 1~5h to obtain high-entropy pyrochlore. The powder A is then crushed to obtain high-entropy pyrochlore powder. S2. High-entropy pyrochlore powder is ball-milled and mixed with zinc chloride and solvent, then dried and sieved to obtain mixed powder B; S3. Mix and grind the obtained mixed powder B with the surfactant for 10~30 min. Then, cold sinter the ground powder at 200~400℃ and 200~500MPa for 0.5~2 h, and then vacuum pressureless sinter at 1300~1600℃ for 1~10 h to obtain high-entropy calcined chlorite ceramic.

5. The method for preparing high-entropy calcined chlorite ceramics according to claim 4, characterized in that, The ball milling speed in steps S1 and S2 is 200~300 r / min, and the ball milling time is 12~24 h.