A nano high-entropy ceramic with high hardness and amorphous-nanocrystalline dual-phase structure and a preparation method thereof

Abstract

The application belongs to the technical field of high-entropy ceramics and nanoceramics, and particularly relates to a nanometer high-entropy ceramic with high hardness and an amorphous-nanocrystalline dual-phase structure and a preparation method thereof. The high-entropy ceramic has an amorphous-nanocrystalline dual-phase structure. The nanometer high-entropy ceramic is composed of entropy-regulated nanocrystalline grains, an amorphous SiO2 matrix and zirconium oxide. The entropy-regulated nanocrystalline grains contain oxides of at least three kinds of elements selected from yttrium, cerium, hafnium, ytterbium and niobium. The entropy-regulated nanocrystalline grains are distributed in the amorphous SiO2 matrix, the amorphous SiO2 matrix is continuously distributed, and the nanocrystalline grains have a size of less than or equal to 100 nm. The preparation method comprises the following steps: preparing an amorphous high-energy-state ceramic powder by using a chemical precipitation method, and then preparing a bulk nanoceramic by using a rapid hot-pressing sintering method. The microstructure of the application is reasonable in design, the preparation process is simple and controllable, the obtained product has excellent performance, and the application is convenient for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of high-entropy ceramics and nanoceramics technology, specifically relating to a high-entropy nanoceramic with high hardness and an amorphous-nanocrystalline dual-phase structure and its preparation method. Background Technology

[0002] In 2015, the concept of high-entropy ceramics emerged from high-entropy alloys. Since then, the high-entropy ceramic family has rapidly expanded from its initial focus on oxides to include borides, carbides, sulfides, and silicides. Compared to traditional ceramics, high-entropy ceramics offer greater compositional flexibility and designability. The presence of internal lattice distortion promises to exhibit the four major high-entropy effects found in high-entropy alloys: thermodynamic high-entropy effect; crystallographic lattice distortion effect; kinetic hysteresis diffusion effect; and the cocktail effect in performance, potentially endowing materials with significantly superior properties compared to single-component materials. The superior properties of high-entropy ceramics make them promising for applications in ultra-high temperature thermal environmental protection, thermoelectricity, radiation-resistant materials for nuclear reactors, catalysis, electromagnetic wave absorption, and energy storage.

[0003] In recent years, researchers have discovered that two-phase or even multi-phase high-entropy ceramics possess superior and more comprehensive properties than single-phase high-entropy ceramics. For example, Qin et al. first reported a series of two-phase high-entropy ultra-high temperature ceramics composed of high-entropy borides and high-entropy carbides. The grain size and properties of the two phases can be controlled by changing the phase fraction. At the same time, the hardness and Young's modulus of the two-phase high-entropy ceramics are higher than the average value of a mixture of a single binary carbide and boride. [1] Kavak et al. prepared multiphase high-entropy diboride ceramics composed of a mixture of a high-entropy phase (Hf,TiWZr)B2 and non-high-entropy phases such as (Hf,Zr)O2 and (W,Ti)B. [2] This material exhibits good mechanical properties and wear resistance. Luo et al. prepared (Ti,Zr,Nb,Ta,Mo)C-Co high-entropy composite materials by liquid-phase sintering at relatively low temperatures. [3] Two-phase high-entropy composites possess high hardness and high toughness. Liu et al. prepared a high-entropy rare-earth niobate composite material composed of RENbO4 / RE3NbO7. [4] The study found that this two-phase high-entropy ceramic exhibits better overall performance than single-phase niobate. Therefore, the development of two-phase or multi-phase high-entropy ceramics is of great significance for further expanding the number of high-entropy ceramics and improving their performance.

[0004] To date, most reported high-entropy ceramics consist of micron-sized particles, meaning they cannot benefit from various nanoscale effects. It is well known that reducing the grain size of ceramic materials to the nanoscale can significantly improve various properties, especially mechanical properties. Therefore, developing nanoscale high-entropy ceramics is of great significance. Furthermore, most bulk high-entropy ceramics are currently produced through solid-state reactions and high-temperature sintering, typically exceeding 1600℃, and sometimes even above 2000℃, requiring holding at the highest temperature for several hours. This traditional method is not only time-consuming but also energy-intensive, greatly increasing the production cost of high-entropy ceramics and hindering their industrialization. Sintering bulk amorphous-nanocrystalline dual-phase nanoscale high-entropy ceramics under mild conditions is an important development direction for high-entropy materials.

[0005] Fu Le et al. have also conducted some research on dual-phase ceramics, such as in their paper "Transparent singlecrystalline ZrO2-SiO2 glass nanoceramic sintered by SPS". [5] and "Highlytranslucent and strong ZrO2-SiO2 nanocrystalline glass ceramic prepared bysol-gel method and spark plasma sintering with fine 3D microstructure fordental restoration" [6] This study involved the research of ZrO2-SiO2 dual-phase ceramics. Powder was prepared using the sol-gel method, and bulk ceramics were prepared using plasma-electro-spark sintering. The research found that the mechanical properties of this ceramic system were closely related to the ZrO2 content. The sample with a ZrO2 content of 65 mol% exhibited the highest average flexural strength (1014 MPa), a microhardness of 7.57 GPa, and Young's modulus and fracture toughness of 152 GPa and 6.5 MPa, respectively. 1 / 2 .

[0006] References:

[0007] [1]M.Qin,J.Gild,C.Hu,H.Wang,M.S.Bin Hoque,J.L.Braun,T.J.Harrington,P.E.Hopkins,K.S.Vecchio,J.Luo,Dual-phase high-entropy ultra-high temperatureceramics,J.Eur.Ceram.Soc.40(2020)5037-5050.

[0008] https: / / doi.org / 10.1016 / j.jeurceramsoc.2020.05.040.

[0009] [2]S.Kavak,K.Gürcan,M.Mansoor,M.Kaba,E.Ayas,A.Duygu,First principlescalculations and synthesis of multi-phase(HfTiWZr)B2 high entropy diborideceramics:Microstructural,mechanical and thermal characterization,J.Eur.Ceram.Soc.43(2023)768-782.

[0010] https: / / doi.org / 10.1016 / j.jeurceramsoc.2022.10.047.

[0011] [3]S.C.Luo,W.M.Guo,K.Plucknett,H.T.Lin,Low-temperature densificationof high-entropy(Ti,Zr,Nb,Ta,Mo)C—Co composites with high hardness and hightoughness,J.Adv.Ceram.11(2022)805-813.

[0012] https: / / doi.org / 10.1007 / s40145-022-0574-6.

[0013] [4]

[0014] https: / / doi.org / https: / / doi.org / 10.1016 / j.jeurceramsoc.2022.10.081.

[0015] [5]L.Fu,C.Wu,K.Grandfield,E.Unosson,J.Chang,H.Engqvist,W.Xia,Transparent single crystalline ZrO2-SiO2 glass nanoceramic sintered by SPS,J.Eur.Ceram.Soc.36(2016)3487-3494.

[0016] https: / / doi.org / 10.1016 / j.jeurceramsoc.2016.05.016.

[0017] [6]L.Fu,H.Engqvist,W.Xia,Highly translucent and strong ZrO2-SiO2nanocrystalline glass ceramic prepared by sol-gel method and spark plasmasintering with fine 3D microstructure for dental restoration,J.Eur.Ceram.Soc.37(2017)4067-4081.https: / / doi.org / 10.1016 / j.jeurceramsoc.2017.05.039.

[0018] Content of this invention

[0019] One of the objectives of this invention is to provide a nanoceramic with ultra-high hardness and good thermal stability, and with an amorphous-nanocrystalline dual-phase structure and different entropy states.

[0020] One of the objectives of this invention is to provide a method for preparing nanoceramics with an amorphous-nanocrystalline dual-phase structure and different entropy states under low-temperature sintering conditions. A schematic diagram of the microstructure of this nanoceramic system is shown below. Figure 1 As shown, entropy-regulated nanocrystals are distributed in an amorphous SiO2 matrix, the SiO2 matrix is ​​continuously distributed, and the nanocrystal size is less than or equal to 100 nm.

[0021] This invention discloses a high-entropy nanoceramic with high hardness and an amorphous-nanocrystalline dual-phase structure. The high-entropy nanoceramic has an amorphous-nanocrystalline dual-phase structure. The high-entropy nanoceramic is composed of entropy-regulated nanocrystals, an amorphous SiO2 matrix, and zirconium oxide. The entropy-regulated nanocrystals contain oxides of at least three elements selected from yttrium, cerium, hafnium, ytterbium, and niobium. The entropy-regulated nanocrystals are distributed in the amorphous SiO2 matrix, which is continuously distributed, and the nanocrystal size is less than or equal to 100 nm.

[0022] Preferably, the entropy-controlled nanocrystals contain oxides of at least three of the elements selected from yttrium, cerium, hafnium, ytterbium, and niobium.

[0023] The entropy-regulated nanocrystals contain 55-75% zirconium oxide in their molar percentage composition, preferably 65-70%.

[0024] This invention discloses a high-entropy nanoceramic with high hardness and an amorphous-nanocrystalline dual-phase structure, wherein the molar ratio of entropy-controlled nanocrystals to SiO2 is 5.5–7.5:4.5–2.5. Preferably, it is 6–7:4–3, more preferably 6.5–7:3–3.5, and even more preferably 6.5–6.8:3.5–3.2.

[0025] This invention discloses a high-entropy nanoceramic with high hardness and an amorphous-nanocrystalline dual-phase structure, wherein the entropy-regulated nanocrystals are single-phase high-entropy nanoparticles.

[0026] In this invention, the composition of the high-entropy ceramic can be: 68 mol% (Y 0.05 Ce 0.07 Hf 0.07 Nb 0.07 Yb 0.07 Zr 0.35 )O x -32mol%SiO2.

[0027] In this invention, the composition of the high-entropy ceramic can be: 66 mol% (Y 0.05 Ce 0.07 Hf 0.07 Nb 0.07 Zr 0.40 )O x-34mol%SiO2.

[0028] In this invention, the composition of the high-entropy ceramic can be: 68 mol% (Y 0.05Ce 0.07Hf 0.07Nb 0.07Yb 0.07Zr 0.35) Ox - 32 mol% SiO2). This invention provides a method for preparing a high-entropy nano-ceramic with high hardness and an amorphous-nanocrystalline dual-phase structure, comprising preparing amorphous high-energy ceramic powder using a chemical precipitation method, and then preparing bulk nano-ceramic using a rapid hot-pressing sintering method. The specific steps are as follows:

[0029] 1) Mix ethanol, dilute hydrochloric acid solution and silicate ester solution, stir, and TEOS will hydrolyze to obtain solution 1;

[0030] 2) Dissolve the water-soluble zirconium salt in water, dilute with ethanol to obtain solution 2;

[0031] 3) Based on the different entropy states, at least three of the following are dissolved in ethanol to obtain solution 3;

[0032] 4) Mix solutions 1, 2, and 3, and stir until homogeneous to obtain solution 4;

[0033] 5) Add alkali dropwise to solution 4 obtained in step 4) and stir to induce a coprecipitation reaction to form a white precipitate. After coprecipitation is complete, collect the precipitate by vacuum filtration.

[0034] 6) Dry the precipitate obtained in step 5), then ball mill it, and calcine the resulting fine powder;

[0035] 7) The calcined powder from step 6) is hot-pressed and sintered to obtain dense nano-bulk high-entropy ceramic. During hot-pressing and sintering, the temperature is controlled at 1150-1300℃.

[0036] This invention discloses a method for preparing nano-high-entropy ceramics with high hardness and an amorphous-nanocrystalline dual-phase structure. In step 1), the silicate ester is preferably tetraethyl silicate (TEOS).

[0037] The stirring method in step 1) includes magnetic stirring. To ensure uniformity, the stirring time is 20-40 minutes.

[0038] Preferably, in step 1), the concentration of dilute hydrochloric acid is 0.3-0.5 mol / L; the volume ratio of TEOS, anhydrous ethanol and dilute hydrochloric acid is (10-15):(2-5):(0.5-1.5); and the hydrolysis reaction time is 0.25-1 h.

[0039] This invention discloses a method for preparing high-entropy nanoceramics with high hardness and an amorphous-nanocrystalline dual-phase structure. In step 2), the water-soluble zirconium salt is selected from at least one of zirconium oxychloride octahydrate (ZrOCl2·8H2O) and zirconium nitrate pentahydrate (Zr(NO3)4·5H2O). Preferably, in step 2), the concentration of zirconium oxychloride octahydrate dissolved in anhydrous ethanol is 0.1–0.3 mol / L.

[0040] This invention discloses a method for preparing a high-entropy nanoceramic with high hardness and an amorphous-nanocrystalline dual-phase structure. In step 3), the soluble yttrium salt is selected from at least one of yttrium nitrate and yttrium chloride. As a further preferred option, yttrium nitrate is yttrium nitrate hexahydrate (YN3O9·6H2O).

[0041] This invention discloses a method for preparing a high-entropy nanoceramic with high hardness and an amorphous-nanocrystalline dual-phase structure. In step 3), the soluble cerium salt is selected from at least one of cerium nitrate and cerium chloride. As a further preferred option, cerium nitrate is cerium nitrate hexahydrate (CeN3O9·6H2O).

[0042] The present invention discloses a method for preparing a high-entropy nano-ceramic with high hardness and an amorphous-nanocrystalline dual-phase structure. In step 3), the soluble hafnium salt is selected from at least one of hafnium tetrachloride (HfCl4) and hafnium hydroxide (H4HfO4).

[0043] This invention discloses a method for preparing a high-entropy nanoceramic with high hardness and an amorphous-nanocrystalline dual-phase structure. In step 3), the soluble ytterbium salt is selected from at least one of ytterbium chloride and ytterbium nitrate. Preferably, the ytterbium chloride is ytterbium chloride hexahydrate (YbCl3·6H2O).

[0044] This invention discloses a method for preparing a high-entropy nano-ceramic with high hardness and an amorphous-nanocrystalline dual-phase structure. In step 3), the soluble niobium salt is selected from at least one of niobium pentachloride (NbCl5) and niobium nitrate.

[0045] In step 5), the preferred alkali is ammonia.

[0046] To avoid severe clumping and sediment deposition, in step 5), the solution is magnetically stirred during the addition of ammonia solution. After co-precipitation is complete, the precipitate is collected by vacuum filtration.

[0047] In step 6), the drying temperature is set to 50-80℃. The drying time is 10-30 hours, preferably 20-28 hours.

[0048] In step 6), the calcination temperature is 500-700℃ and the calcination time is 0.5-1.5h.

[0049] The ball milling described in step 6) uses a planetary ball mill with a milling speed of 500-700 rpm and a milling time of 2-6 hours.

[0050] In step 6), the equipment used for calcination includes a muffle furnace.

[0051] In step 7), the temperature of rapid hot pressing sintering is 1150-1300℃, the holding time at the highest temperature is 3-5 minutes, and the sintering pressure is 30-60MPa.

[0052] Dense biphase nanoceramics with different entropy states were prepared according to the above preparation method.

[0053] The beneficial effects of this invention: Nanoceramics with different entropy states prepared by the method of this invention have an amorphous-nanocrystalline dual-phase structure. Figure 1 Furthermore, this invention allows for flexible control of the type and concentration of doped ions to obtain ceramic materials in different entropy states, including low-entropy, medium-entropy, and high-entropy states. Additionally, the powder synthesized in this invention is an amorphous high-energy powder, enabling the sintering of ceramic materials in different entropy states at lower temperatures, reducing preparation costs. This material has excellent industrialization prospects. Moreover, the microhardness of the product obtained by this invention is significantly higher than that of existing products. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the microstructure of the nanoceramic of the present invention.

[0055] Figure 2 These are the XRD patterns of the nano-ceramic powders prepared in Examples 1, 2 and 3 of this invention after calcination.

[0056] Figure 3 This is a scanning electron microscope image of the high-entropy nano-ceramic powder prepared in Example 3 of the present invention.

[0057] Figure 4 This is a transmission electron microscope (TEM) image of the medium-entropy nano-ceramic powder prepared in Example 2 of this invention.

[0058] Figure 5 This is a transmission electron microscope (TEM) image of the high-entropy nano-ceramic powder prepared in Example 3 of this invention.

[0059] Figure 6 These are scanning electron microscope images of the fracture surfaces of the high-entropy nano-ceramic bulk material prepared in Example 3 of the present invention. (a) is a high-entropy nano-ceramic material with a sintering temperature of 1170℃; (b) and (c) are high-entropy nano-ceramic materials with a sintering temperature of 1230℃.

[0060] Figure 7 These are XRD patterns of the nano-ceramic bulk materials prepared at a sintering temperature of 1170℃ in Examples 1, 2 and 3 of this invention.

[0061] Figure 8 These are XRD patterns of the nano-ceramic bulk materials prepared at a sintering temperature of 1230℃ in Examples 1, 2 and 3 of this invention.

[0062] Figure 9 This is the XRD pattern of the high-entropy ceramic block prepared in Comparative Example 1 of this invention.

[0063] Figure 10 This is a transmission electron microscope (TEM) image of the high-entropy nanoceramic prepared at a sintering temperature of 1170℃ in Example 3 of the present invention.

[0064] Figure 11 The image shows the transmission electron microscopy (TEM) energy dispersive spectroscopy (EDS) results of the high-entropy ceramic bulk material prepared in Example 3 at a sintering temperature of 1170℃.

[0065] Figure 12 This is a graph showing the grain size change trend of the nanoceramics prepared in Examples 1, 2 and 3 of this invention after annealing heat treatment.

[0066] Figure 13 This is a graph showing the change trend of Vickers hardness of the nano-ceramics prepared in Examples 1, 2 and 3 of this invention after annealing heat treatment. Detailed Implementation

[0067] Example 1 (Preparation of Low-Entropy Ceramics):

[0068] 1) Mix 23.5 mL TEOS, 5 mL anhydrous ethanol and 1.75 mL dilute hydrochloric acid (concentration of 0.4 mol / L), and carry out hydrolysis reaction for 0.5 h to obtain solution 1;

[0069] 2) Dissolve 24.6g of ZrOCl2·8H2O powder in 10mL of deionized water, and dilute with ethanol to 0.2mol / L to obtain solution 2;

[0070] 3) Mix 5.7g YN3O9·6H2O, 9.1g CeN3O9·6H2O, and 6.7g HfCl4, and dissolve them in 10mL of ethanol to obtain solution 3;

[0071] 4) Mix solutions 1, 2, and 3 and stir until homogeneous to obtain solution 4.

[0072] 5) Slowly add NH4OH solution (dropping rate of about 5 mL / min) to solution 4 obtained in step 4) to induce co-precipitation reaction and form a white precipitate. Stir the solution magnetically during the addition of ammonia solution until the pH of the solution reaches about 7, and the co-precipitation is completed. Collect the precipitate by vacuum filtration.

[0073] 6) Place the precipitate obtained in step 5) in a forced-air drying oven for drying at 80°C for 1 day.

[0074] 7) The precipitate obtained in step 6) is placed in a muffle furnace for calcination at a temperature of 700°C for 1 hour. The calcined powder is then subjected to planetary ball milling to obtain low-entropy ceramic powder. The specific composition and abbreviation are shown in Table 1. Table 1 shows the composition, entropy state, sintering parameters and sample abbreviations of the nanoceramics prepared in Examples 1, 2 and 3 of this invention.

[0075] 8) The low-entropy ceramic powder obtained in step 7) was subjected to rapid hot pressing sintering. Two sintering temperatures were tried: 1170℃ and 1230℃. When the sintering temperature was 1170℃, the holding time at the highest temperature was 5 min; when the sintering temperature was 1230℃, the holding time at the highest temperature was 4 min. The sintering pressure was 50 MPa in both cases to obtain dense nano-low-entropy ceramic blocks. The sintering parameters and sample names are shown in Table 1.

[0076] Example 2 (Preparation of medium-entropy ceramics):

[0077] 1) Mix 22.8 mL TEOS, 4.8 mL ethanol and 1.68 mL dilute hydrochloric acid (concentration of 0.4 mol / L), and carry out hydrolysis reaction for 0.5 h to obtain solution 1;

[0078] 2) Dissolve 21.4g of ZrOCl2·8H2O powder in 10mL of deionized water, and dilute with ethanol to 0.2mol / L to obtain solution 2;

[0079] 3) Mix 5.7g YN3O9·6H2O, 9.1g CeN3O9·6H2O, 6.7g HfCl4, and 5.7g NbCl5, and dissolve them in 10mL of ethanol to obtain solution 3;

[0080] 4) Mix solutions 1, 2, and 3, and stir until homogeneous to obtain solution 4;

[0081] 5) Slowly add NH4OH solution (dropping rate of about 5 mL / min) to solution 4 obtained in step 4) to induce a co-precipitation reaction, the process being the same as step 5) in Example 1;

[0082] 6) The precipitate obtained in step 5) is dried, calcined, and ball-milled, following the same process as the corresponding steps in Example 1. The specific composition and abbreviation of the obtained medium-entropy ceramic powder are shown in Table 1.

[0083] 7) The medium-entropy ceramic powder obtained in step 6) is subjected to rapid hot pressing sintering. The sintering process and parameters are the same as in Example 1 to obtain dense nano-medium-entropy ceramic blocks. The sintering parameters and sample names are shown in Table 1.

[0084] Example 3 (Preparation of high-entropy ceramics, composition 68 mol% (Y)) 0.05 Ce 0.07 Hf 0.07 Nb 0.07 Yb 0.07 Zr 0.35 )O x -32 mol% SiO2):

[0085] 1) Mix 21.5 mL TEOS, 4.7 mL ethanol and 1.62 mL dilute hydrochloric acid (concentration of 0.4 mol / L), and carry out hydrolysis reaction for 0.5 h to obtain solution 1;

[0086] 2) Dissolve 18.7g of ZrOCl2·8H2O powder in 10mL of deionized water, and dilute with ethanol to 0.2mol / L to obtain solution 2;

[0087] 3) Mix 5.7g YN3O9·6H2O, 9.1g CeN3O9·6H2O, 6.7g HfCl4, 5.7g NbCl5, and 8.1g YbCl3·6H2O, and dissolve them in 10mL of ethanol to obtain solution 3;

[0088] 4) Mix solutions 1, 2, and 3, and stir until homogeneous to obtain solution 4;

[0089] 5) Slowly add NH4OH solution (dropping rate of about 5 mL / min) to solution 4 obtained in step 4) to induce a co-precipitation reaction, the process being the same as step 5) in Example 1;

[0090] 6) The precipitate obtained in step 5) is dried, calcined, and ball-milled, following the same process as the corresponding steps in Example 1. The specific composition and abbreviation of the obtained high-entropy ceramic powder are shown in Table 1.

[0091] 7) The medium-entropy ceramic powder obtained in step 6) is subjected to rapid hot pressing sintering. The sintering process and parameters are the same as in Example 1 to obtain dense nano high-entropy ceramic blocks. The sintering parameters and sample names are shown in Table 1.

[0092] Control group (preparation of high-entropy ceramics, composition 68 mol% (Y)) 0.05 Ce 0.07 La 0.07 Ta 0.07 Ba 0.07 Zr 0.35 )O x -32mol%SiO2)

[0093] 1) Mix 14.3 mL TEOS, 3.8 mL ethanol and 1.8 mL dilute hydrochloric acid (concentration of 0.4 mol / L), and carry out hydrolysis reaction for 0.5 h to obtain solution 1;

[0094] 2) Dissolve 22.5g of ZrOCl2·8H2O powder in 10mL of deionized water, and dilute with ethanol to 0.2mol / L to obtain solution 2;

[0095] 3) Mix 3.8g YN3O9·6H2O, 6.1g CeN3O9·6H2O, 4.9g LaCl3·6H2O, 5.0g TaCl5, and 3.4g BaCl2·2H2O, and dissolve them in 10mL of ethanol to obtain solution 3;

[0096] 4) Mix solutions 1, 2, and 3, and stir until homogeneous to obtain solution 4;

[0097] 5) Slowly add NH4OH solution (dropping rate of about 5 mL / min) to solution 4 obtained in step 4) to induce a co-precipitation reaction, the process being the same as step 5) in Example 1;

[0098] 6) The precipitate obtained in step 5) is dried, calcined, and ball-milled, following the same process as the corresponding steps in Example 1. The specific composition and abbreviation of the obtained high-entropy ceramic powder are shown in Table 1.

[0099] 7) The medium-entropy ceramic powder obtained in step 6) was subjected to rapid hot pressing sintering. The sintering process and parameters were the same as in Example 1 (1230℃-4min) to obtain dense nano high-entropy ceramic blocks. The sintering parameters and sample names are shown in Table 1.

[0100] Results and Analysis

[0101] Figure 1 This is a schematic diagram of the microstructure of the high-entropy nanoceramic prepared in this invention. The entropy-controlled nanocrystals are uniformly distributed in the amorphous SiO2 matrix, and the ceramic has a nanocrystalline and amorphous dual-phase structure.

[0102] The XRD patterns of the low-entropy, medium-entropy, and high-entropy ceramic powders prepared in Examples 1, 2, and 3 are as follows: Figure 2 As shown in the figure, the powders obtained in Examples 1 to 3 have a low degree of crystallinity and are basically amorphous powders.

[0103] Scanning electron microscope (SEM) images of the high-entropy ceramic powder prepared in Example 3, as shown below. Figure 3 As shown in the figure, the powder particles are irregularly shaped and about 20 micrometers in size, and there are also a small amount of nanoparticles.

[0104] Transmission electron microscopy (TEM) images of the medium-entropy ceramic powder prepared in Example 2 are shown below. Figure 4 As shown, from Figure 4 In image a, the powder particles can be seen to have agglomerated together, as seen in the high-resolution image ( Figure 4 (b) It can be seen that the powder is basically amorphous, but contains a small amount of nanocrystals. Energy dispersive spectroscopy (EDS) analysis shows that the constituent elements (Zr, Si, O, Y, Ce, Hf) in this medium-entropy powder are uniformly distributed within the particles.

[0105] Transmission electron microscopy images of the high-entropy ceramic powder prepared in Example 3, as shown below. Figure 5 As shown, from Figure 4 As can be seen in image a, the powder particles are submicron particles, as observed in the high-resolution image ( Figure 5 b) It can be seen that the powder is basically amorphous, but contains a small amount of nanocrystals. The energy dispersive spectroscopy (EDS) analysis results show that the constituent elements (Zr, Si, O, Y, Ce, Hf, Yb, Nb) in this high-entropy powder are uniformly distributed within the particles.

[0106] Scanning electron microscope (SEM) images of the fracture surfaces of the high-entropy ceramic bulk material prepared in Example 3 are shown below. Figure 6 As shown, from Figure 6 As can be seen in image a, after sintering at 1170℃, virtually no pores are visible on the fracture surface, indicating that the high-entropy ceramic has reached a high degree of densification. From... Figure 6 As shown in image b, after sintering at 1230℃, the fracture surface shows virtually no pores, and the fracture is relatively smooth, indicating brittle fracture. High-magnification images reveal spherical high-entropy nanoparticles. Figure 6 c).

[0107] The XRD patterns of the low-entropy, medium-entropy, and high-entropy ceramic bulk materials prepared in Examples 1, 2, and 3 are as follows: Figure 7 As shown, low-entropy and medium-entropy ceramics, after sintering at 1170℃, are mainly composed of a tetragonal phase structure, accompanied by a small amount of monoclinic phase and crystalline CeO2. High-entropy ceramics, on the other hand, are composed of a single-phase solid solution with a single tetragonal phase structure.

[0108] The XRD patterns of the low-entropy, medium-entropy, and high-entropy ceramic bulk materials prepared in Examples 1, 2, and 3 are as follows: Figure 8 As shown, low-entropy ceramics, after sintering at 1230℃, are mainly composed of tetragonal and ZrSiO4 phases, accompanied by a small amount of crystalline CeO2 phase. Medium-entropy ceramics, after sintering at 1230℃, are mainly composed of tetragonal and monoclinic phases, accompanied by a small amount of ZrSiO4 and crystalline CeO2 phase. High-entropy ceramics, on the other hand, are single-phase solid solutions with a single tetragonal phase structure.

[0109] The XRD pattern of the high-entropy ceramic bulk material prepared for the control group is shown below. Figure 9As shown, the ceramic is mainly composed of a tetragonal phase, but it also forms Y2SiO7 and CeSiO7 phases. This ceramic is not a single-phase high-entropy ceramic, indicating that only ceramic powders with specific chemical compositions can form single-phase high-entropy ceramics.

[0110] Transmission electron microscopy images of the high-entropy ceramic bulk material prepared in Example 3, as shown below. Figure 10 As shown, from Figure 10 As can be seen in image a, the high-entropy nanoparticles exhibit a dark contrast, with a size of approximately 100 nanometers, while the amorphous SiO2 matrix exhibits a bright contrast. This high-entropy ceramic is polycrystalline and possesses a tetragonal phase structure. Figure 10 b). As can be seen in the scanned transmission image ( Figure 10 (b) The high-entropy nanoparticles exhibit bright contrast, with interconnected particles forming a complex three-dimensional structure; the amorphous SiO2 matrix exhibits dark contrast and acts as the matrix. (From high-resolution scanning transmission images...) Figure 10 (b) It can be seen that the high-entropy nanoparticles have a complete lattice with no obvious lattice defects; through measurement, it can be known that ( Figure 10 b) The lattice spacings are 3.09 and 3.09, respectively. These correspond to the (101) and (002) crystal planes of the tetragonal phase structure, respectively. Geometric phase analysis results indicate the presence of lattice stress caused by lattice distortion within the high-entropy nanoparticles. Figure 10 b).

[0111] The transmission electron microscopy (TEM) energy dispersive spectroscopy (EDS) analysis results of the high-entropy ceramic bulk prepared in Example 3 are as follows: Figure 11 As shown, Zr, O, Y, Ce, Hf, Yb, and Nb are uniformly distributed within the nanoparticles, forming high-entropy nano-oxide particles, while Si is mainly distributed in the matrix, forming the SiO2 amorphous matrix together with O.

[0112] The grain size variation trends of the low-entropy, medium-entropy, and high-entropy ceramic bulks prepared in Examples 1, 2, and 3 after different annealing treatments are shown in the following figures: Figure 12 As shown, the grain sizes of the low-entropy, medium-entropy, and high-entropy ceramic bulks after sintering at 1170℃ were 34.2 nm, 40.8 nm, and 47.6 nm, respectively. Grain coarsening was significant during annealing. After heat treatment at 800℃ for 3 h and 1000℃ for 3 h, the grain sizes of the low-entropy ceramic increased to 37.8 nm and 58.1 nm, respectively; the grain sizes of the medium-entropy ceramic increased to 48.5 nm and 57.5 nm, respectively; and the grain sizes of the high-entropy ceramic increased to 52.0 nm and 70.0 nm, respectively.

[0113]

[0114] Table 1

[0115] The Vickers hardness variation trends of the low-entropy, medium-entropy, and high-entropy ceramic blocks prepared in Examples 1, 2, and 3 after different annealing treatments are shown in the following figures: Figure 13 As shown, the Vickers hardness (microhardness) of the low-entropy, medium-entropy, and high-entropy ceramic blocks after sintering at 1170℃ were 9.3 GPa, 9.6 GPa, and 10.4 GPa, respectively. After sintering at 1230℃, the Vickers hardness (microhardness) of the low-entropy, medium-entropy, and high-entropy ceramic blocks were 9.7 GPa, 9.9 GPa, and 11.0 GPa, respectively. This indicates that the hardness of the material increases with increasing entropy. Furthermore, compared to the hardness after sintering, the hardness of the material did not change significantly after annealing. Testing showed that the Vickers hardness (microhardness) of the control group sample prepared in the control group was 4.9 GPa, significantly lower than that of the low-entropy, medium-entropy, and high-entropy ceramics prepared in Examples 1, 2, and 3. This indicates that only a specific combination of elements can form single-phase high-entropy nanoparticles and achieve high hardness.

Claims

1. A nanoceramic having a high hardness and a non-crystalline-nanocrystalline dual phase structure, characterized by: The ceramic has an amorphous-nanocrystalline dual-phase structure; the nanoceramic is composed of entropy-regulated nanocrystals and an amorphous SiO2 matrix, wherein the entropy-regulated nanocrystals contain oxides of at least three elements selected from yttrium, cerium, hafnium, ytterbium, and niobium; the entropy-regulated nanocrystals are distributed in the amorphous SiO2 matrix, the amorphous SiO2 matrix is ​​continuously distributed, and the nanocrystal size is less than or equal to 100 nm; The entropy-regulated nanocrystals contain 55-75% zirconium oxide in molar percentage; the molar ratio of the entropy-regulated nanocrystals to SiO2 is 5.5-7.5:4.5-2.

5. The high-hardness nanoceramic with an amorphous-nanocrystalline dual-phase structure is prepared by the following steps: 1) Mix ethanol, dilute hydrochloric acid solution and silicate ester solution, stir, and TEOS will hydrolyze to obtain solution 1; 2) Dissolve the water-soluble zirconium salt in water, dilute with ethanol to obtain solution 2; 3) Based on different entropy states, at least three of the following are dissolved in ethanol to obtain solution 3; 4) Mix solutions 1, 2, and 3, and stir until homogeneous to obtain solution 4; 5) Add alkali dropwise to solution 4 obtained in step 4) and stir to induce a coprecipitation reaction to form a white precipitate. After coprecipitation is complete, collect the precipitate by vacuum filtration. 6) Dry the precipitate obtained in step 5), then ball mill it, and calcine the resulting fine powder; 7) The calcined powder from step 6) is hot-pressed and sintered to obtain dense nano-bulk ceramic. During hot-pressing and sintering, the temperature is controlled at 1150-1300℃.

2. The nanoceramic with high hardness and an amorphous-nanocrystalline dual-phase structure according to claim 1, characterized in that: The molar ratio of entropy-regulated nanocrystals to SiO2 is 6.5~7:3.5~3.

3. The nanoceramics with high hardness and amorphous-nanocrystalline dual-phase structure according to claim 1, characterized in that: The molar ratio of entropy-regulated nanocrystals to SiO2 is 6.5~6.8:3.2~3.

5.

4. The nanoceramics with high hardness and amorphous-nanocrystalline dual-phase structure according to claim 1, characterized in that: The entropy-regulated nanocrystals are single-phase high-entropy nanoparticles.

5. A nanoceramic with high hardness and an amorphous-nanocrystalline dual-phase structure according to claim 1, characterized in that: The ceramic composition is: 65 mol% (Y) 0.05 Ce 0.07 Hf 0.07 Zr 0.46 )O x -35mol%SiO2; or The composition of the ceramic is: 66 mol% (Y 0.05 Ce 0.07 Hf 0.07 Nb 0.07 Zr 0.40 )O x - 34 mol% SiO2; or The ceramic composition is: 68 mol% (Y) 0.05 Ce 0.07 Hf 0.07 Nb 0.07 Yb 0.07 Zr 0.35 )O x -32mol%SiO2.

6. The nanoceramic with high hardness and an amorphous-nanocrystalline dual-phase structure according to claim 1, characterized in that: In step 1), the silicate ester is tetraethyl silicate; In step 1), the concentration of dilute hydrochloric acid is 0.3-0.5 mol / L; the volume ratio of TEOS, anhydrous ethanol and dilute hydrochloric acid is (10-15):(2-5):(0.5-1.5); and the hydrolysis reaction time is 0.25-1h. In step 2), the water-soluble zirconium salt is selected from at least one of zirconium oxychloride octahydrate and zirconium nitrate pentahydrate; In step 2), the concentration of zirconium oxychloride octahydrate dissolved in anhydrous ethanol is 0.1~0.3 mol / L; The soluble yttrium salt is selected from at least one of yttrium nitrate and yttrium chloride; Soluble cerium salts are selected from at least one of cerium nitrate and cerium chloride; The soluble hafnium salt is selected from at least one of hafnium tetrachloride and hafnium hydroxide; The soluble ytterbium salt is selected from at least one of ytterbium chloride and ytterbium nitrate; The soluble niobium salt is selected from at least one of niobium pentachloride and niobium nitrate.

7. The nanoceramics with high hardness and amorphous-nanocrystalline dual-phase structure according to claim 1, characterized in that: In step 5), the alkali is ammonia.

8. A nanoceramic with high hardness and an amorphous-nanocrystalline dual-phase structure according to claim 1, characterized in that: In step 6), the drying temperature is set to 50-80℃; In step 6), the calcination temperature is 500-700℃, and the calcination time is 0.5-1.5h; The ball milling described in step 6) uses a planetary ball mill with a milling speed of 500-700 rpm and a milling time of 2-6 hours. In step 6), the equipment used for calcination includes a muffle furnace.

9. The nanoceramics with high hardness and amorphous-nanocrystalline dual-phase structure according to claim 1, characterized in that: In step 7), the temperature of rapid hot pressing sintering is 1150-1300℃, the holding time at the highest temperature is 3-5 minutes, and the sintering pressure is 30-60 MPa.

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