CN117986004B - A spinel-type high-entropy transparent ceramic and its preparation method and application - Google Patents

Abstract

The invention discloses a spinel-type high-entropy transparent ceramic and a preparation method and application thereof. The stoichiometric formula of the spinel-type high-entropy transparent ceramic is (Li _a Mg _b Zn _c Al _d Ga _e )O ₄ , wherein 0.3≤b+c≤0.9, 0.05≤a≤0.35, 2.05≤d+e≤2.35, b＞0, c＞0, d＞0, e＞0, and a+b+c+d+e＝3; five metal ions disorderly occupy the cation equivalent sites in the spinel structure. The spinel-type high-entropy transparent ceramic prepared by the invention has high light transmittance in a wide band of 230 to 7800 nm, especially in a band of 0.5 to 6 μm, and has an optical linear transmittance of more than 70%. At the same time, it has good mechanical properties and stability, and is suitable for the fields of medical instruments, light sources, lasers, infrared or protective windows; and the preparation method involved is relatively simple, easy to operate, and suitable for popularization and application.

Description

A spinel-type high-entropy transparent ceramic and its preparation method and application

Technical Field

The invention belongs to the field of transparent ceramic materials, and in particular relates to a spinel-type high-entropy transparent ceramic and a preparation method and application thereof.

Background Art

The concept of high entropy alloys provides a new route for material design. Some high entropy alloys have properties different from simple components, which have gradually expanded to include mechanical, electronic, ionic, magnetic, thermal and superconducting properties. The reports of specific properties found in high entropy alloys have stimulated researchers' interest in exploring complex compositions. In 2015, the concept of high entropy was introduced into the study of ceramic materials. In high entropy ceramics, similar to the design of high entropy alloys, four or more elements with a near molar ratio are randomly mixed to produce the maximum configuration entropy. However, compounds are not equivalent to alloys. Under the regulation of ordered anions, some properties of high entropy ceramics are difficult to directly predict and design. Therefore, the types of existing high entropy ceramics are relatively rare, and the main research directions are concentrated on thermal conductivity, thermoelectric properties, structure and other aspects.

Compared with the reports on optical high-entropy transparent ceramics, Chen et al. reported the preparation of fluoride high-entropy transparent ceramics (CeNdCaSrBaF ₁₂ ) by vacuum hot pressing, with a maximum transmittance of 60% at 1000nm (J.Am.Ceram.Soc., 2019, 103(2):750-6). Wang et al. provided a high-transmittance high-entropy transparent ceramic and a preparation method thereof, mainly preparing high-entropy transparent ceramics by co-doping with rare earth elements, with a transmittance of >80% at 1680nm (patent: CN111892400 A), but the system absorbs more light and the transmittance in the visible light range is limited. Therefore, high-entropy transparent ceramics still have poor optical quality, and other properties are rarely reported.

Summary of the invention

In view of the shortcomings of the prior art, the purpose of the present invention is to provide a spinel-type high-entropy transparent ceramic and its preparation method and application. Due to the "cocktail effect" of multiple elements that jointly regulate the performance, the spinel-type high-entropy transparent ceramic can simultaneously meet the high transmittance requirements of a wide band and show relatively excellent comprehensive performance. In addition, the preparation method of the present invention is relatively simple, has high stability, and is suitable for promotion and application.

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

A spinel high entropy transparent ceramic, the stoichiometric formula of which is (Li _a Mg _b Zn _c Al _d Ga _e )O ₄ , wherein 0.3≤b+c≤0.9, 0.05≤a≤0.35, 2.05≤d+e≤2.35, b＞0, c＞0, d＞0, e＞0, and a+b+c+d+e＝3; five metal ions disorderly occupy cation equivalent sites in the spinel structure.

The spinel high entropy transparent ceramic has a thickness of 1 mm, an optical transmittance range of 230 to 7800 nm, an optical linear transmittance of >70% in the range of 500 to 6000 nm, and an optical linear transmittance of >82% in the mid-infrared band of the atmospheric window of 3 to 5 μm.

The method for preparing the spinel high entropy transparent ceramic comprises the following steps:

(1) taking at least one of the oxides and salts corresponding to five metal ions of Li, Mg, Al, Zn and Ga as raw materials according to the stoichiometric ratio, mixing the raw materials, ball milling them, and then crushing and sieving them to obtain a powder;

(2) pressing the powder into a green blank, and then performing a cold isostatic pressing process to obtain a uniformly stacked green blank;

(3) The formed green body is pre-sintered at 1300-1600° C., then hot isostatically pressed at 1400-1700° C., and finally annealed to obtain the spinel high entropy transparent ceramic.

Preferably, in step (1), (Li _n1 Mg _n2 Zn _n3 Al _n4 Ga _n5 )O ₄ powder can also be used as raw material, wherein 0.3≤n2+n3≤0.9, 0.05≤n1≤0.35, 2.05≤n4+n5≤2.35, n2＞0, n3＞0, n4＞0, n5＞0, and n1+n2+n3+n4+n5＝3.

Preferably, (Li _n1 Mg _n2 Zn _n3 Al _n4 Ga _n5 )O ₄ powder is prepared according to the following method: Li ₂ O, MgO, Al ₂ O ₃ , ZnO and Ga ₂ O ₃ (or corresponding salt compounds) are configured in proportion and mixed evenly, and reacted at 1200-1300° C. for 2 hours. The average particle size of the powder is 60-700 nm and the purity is above 99%.

Preferably, in step (1), when _Li2O , MgO, _Al2O3 , ZnO _{and Ga2O3} are used as raw materials, the particle size of the raw materials is less than 400nm and the purity is above ₉₉ %. There is no requirement for the crystal shape, which can be any one of the corresponding raw materials.

Preferably, in step (1), the ball mill uses one of zirconium oxide balls, aluminum oxide balls and silicon nitride balls, and the ball-to-material ratio is 3 to 5:1; the ball milling solvent is anhydrous ethanol; the rotation speed is 120 to 320 r/min, and the ball milling time is 6 to 48 h.

Preferably, in step (1), the mesh size of the sieve is 200 meshes.

Preferably, in step (2), the pressure of the cold isostatic pressing treatment is 180 to 320 MPa, and the holding time is 5 to 15 minutes.

Preferably, in step (3), the pre-sintering parameter conditions are: pressureless sintering for 1 to 48 hours, the atmosphere is air or oxygen, and the air atmosphere is selected, and the comprehensive properties of the obtained ceramic are better.

Preferably, in step (3), when _Li2O , MgO, _Al2O3 , ZnO and _Ga2O3 are used as raw materials, the pre-sintering temperature is 1300-1600° _C ; when ₍ Li _n1 Mg _n2 Zn _n3 Al _n4 Ga _n5 )O ₄ powder is used as raw material, the pre-sintering temperature is 1400-1600°C.

Preferably, in step (3), the hot isostatic pressing sintering atmosphere is an argon atmosphere, the pressure is 180 MPa, and the sintering time is 1 to 12 hours.

Preferably, in step (3), the annealing atmosphere is air or an oxygen-rich atmosphere.

Preferably, in step (3), the annealing temperature is 800-1200° C. and the time is 0.5-48 hours. After annealing, the sample is successively subjected to grinding, mechanical polishing and chemical polishing to obtain the spinel high entropy transparent ceramic material.

The spinel high entropy transparent ceramic is used in medical instruments, light sources, lasers, infrared or protective windows.

Compared with the prior art, the beneficial effects of the present invention include:

The invention discloses a spinel-type high-entropy (Li _a Mg _b Zn _c Al _d Ga _e ) O ₄ ceramic material and a preparation method thereof. Under the action of high configurational entropy, multi-component oxides are easy to synthesize into a single phase, and there is no phenomenon of precipitation with temperature change, and no quenching treatment is required. Thus, the regulation of multiple elements that dominate different properties is used as one of the means for sintering and performance optimization of (Li _a Mg _b Zn _c Al _d Ga _e ) O ₄ spinel-type high-entropy transparent ceramics, and (Li _a Mg _b Zn _c Al _d Ga _e ) O ₄ spinel-type high-entropy transparent ceramics are prepared for the first time by combining the process of hot isostatic pressing sintering and annealing treatment. The combination of five metal elements effectively increases the configurational entropy value in the structure, reduces the Gibbs free energy in thermodynamics, thereby reducing the temperature during the sintering process, and effectively controls the rapid growth of grains at high temperatures and the appearance of intracrystalline pores. Different elements effectively regulate the comprehensive properties of the obtained (Li _a Mg _b Zn _c Al _d Ga _e )O ₄ transparent ceramics, so that the composition of the transparent ceramics can be designed as needed to regulate the performance according to usage and requirements.

In the process of preparing the spinel high entropy transparent ceramic material of the present invention, due to the mixing of multiple elements at equivalent sites, the structure has a high degree of disorder, the Gibbs free energy of the system is reduced, the sintering kinetic behavior of the ceramic is greatly changed, and the spinel high entropy transparent ceramic material with a grain size of less than 100 μm and uniform distribution is obtained, which can simultaneously meet the high transmittance of the visible light-infrared band, and the optical transmittance in the range of 3 to 5 μm in the mid-infrared band of the atmospheric window is >82%. At the same time, after the multi-components are mixed, the hardness of the transparent ceramic reaches 12.2±0.5GPa, the Young's modulus is about 265±12MPa, and the transparent ceramic reaches a theoretical sintering density of more than 99.7%. The comprehensive performance of the spinel high entropy transparent ceramic material is better than that of the existing high entropy transparent ceramic material system, and the preparation method involved is simple to operate, the raw materials are easy to obtain, the preparation conditions are stable and controllable, and it is suitable for industrial large-scale production.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron microscope photograph of raw material 2.

FIG2 is a comparison diagram of the XRD diffraction pattern of raw material 2 and a standard card of magnesium-aluminum spinel, wherein (LiMgZnAlGa) ₃ O ₄ corresponds to raw material 2.

FIG3 is a scanning electron microscope photograph of the mixed powder obtained by the raw material 6 after the corresponding pre-treatment steps.

FIG. 4 is a surface microstructure diagram of the spinel high-entropy transparent ceramic material obtained in Example 7.

FIG5 is a physical picture of the spinel high-entropy transparent ceramic material obtained in Example 7 after polishing on both sides.

FIG6 is a full spectrum transmittance curve of the 1 mm thick spinel high entropy transparent ceramic prepared in Example 6.

DETAILED DESCRIPTION

In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

Examples 1 to 10

A spinel high entropy transparent ceramic, the stoichiometric formula of which is shown in Table 1.

The preparation method of the spinel high entropy transparent ceramic comprises the following steps:

(1) Raw material pretreatment: using high-purity alumina balls as ball milling balls, weighing the materials in Table 1 and Table 2 as raw materials in a ball-to-material ratio of 3:1 to 5:1, mixing the materials, and ball milling them in a ball mill using anhydrous ethanol as a medium. The obtained slurry powder is dried, then crushed, and passed through a 200-mesh sieve to obtain a powder for standby use. The ball milling and drying conditions are shown in Table 1 and Table 2;

(2) green billet forming: the powder obtained in step (1) is subjected to pressing and forming to obtain a formed green billet; wherein the pressing and forming method includes but is not limited to the method of applying unidirectional axial pressure, and then the formed green billet is subjected to cold isostatic pressing to obtain a formed green billet; the specific steps include: firstly, a proper amount of the powder obtained in step (1) is loaded into a steel mold (such as a steel mold with a diameter of 20 mm, the material and diameter of the mold are customized according to actual needs), and then unidirectional pressing and forming is performed, and then cold isostatic pressing and forming is performed; wherein the conditions of unidirectional pressing and cold isostatic pressing are shown in Tables 1 and 2;

(3) Ceramic sintering: The formed green body obtained in step (2) is pre-sintered to obtain a ceramic sintered body with a density of >95%, and then hot isostatic pressing is performed. Finally, annealing is performed in an air atmosphere or an oxygen-rich atmosphere. After annealing, the sample is successively subjected to grinding, mechanical polishing, and chemical polishing to obtain the spinel high-entropy transparent ceramic with a thickness of 1 mm. The conditions of the pre-sintering, hot isostatic pressing, and annealing are shown in Table 3.

Density testing method: Archimedean drainage method, _ρmeasured =( _wa ×( _ρf - _ρa ))/(0.99983×(wa-wf))+ _ρa , where _wa is the weight of the sample after drying (g), _ρf is the density of deionized water (g/ ^cm3 ), _ρa is the density of air (g/ ^cm3 ), and _wf is the buoyant weight of the sample in deionized water (g).

Table 1 shows the ball milling and drying conditions corresponding to different (Li _n1 Mg _n2 Zn _n3 Al _n4 Ga _n5 )O ₄ powders as raw materials.

The different (Li _n1 Mg _n2 Zn _n3 Al _n4 Ga _n5 )O ₄ powders in Table 1 were prepared according to the following steps: Li ₂ O, MgO, Al ₂ O ₃ , ZnO and Ga ₂ O ₃ were configured and mixed uniformly according to corresponding proportions, and the powders were reacted at 1200-1300°C for 2 h.

Table 1 List of ball milling and drying conditions for different (Li _a Mg _b Zn _c Al _d Ga _e )O ₄ powders as raw materials

Table 2 shows the ball milling, drying and calcination conditions when the oxides and salts corresponding to the five metal ions Li, Mg, Al, Zn and Ga are used as raw materials. The raw materials in Table 2 are weighed according to the following stoichiometric formula: (Li _1/6 Mg _1/3 Zn _1/3 Al _13/12 Ga _13/12 )O _4. Note that the purpose of "calcination" described in Table 2 is to remove the crystal water in the raw materials and decompose the metal salts, and the "heating rate" corresponds to the temperature rise in the "calcination" stage.

Table 2 List of ball milling and drying conditions for the oxides and salts corresponding to the five metal ions Li, Mg, Al, Zn and Ga as raw materials

Table 3 shows the raw materials corresponding to the spinel high entropy transparent ceramics described in Examples 1 to 10 and the process parameters of each step.

Table 3 Raw materials corresponding to the spinel high entropy transparent ceramics described in Examples 1 to 10 and process parameters of each step

Note: P1 in Table 3 indicates pressureless sintering, and the _O2 in the annealing atmosphere is an oxygen-rich atmosphere with a concentration of 30%.

The scanning electron microscope photograph and phase composition of raw material 2 are shown in Figures 1 and 2 respectively. It can be seen from Figures 1 and 2 that the synthesized particles are uniform and fine, with a particle size in the range of 60 to 700 nm; compared with the standard card, the phase of the used (Li _n1 Mg _n2 Zn _n3 Al _n4 Ga _n5 )O ₄ powder is spinel phase.

The scanning electron microscope photograph of the mixed powder obtained by the corresponding pretreatment steps of raw material 6 is shown in Figure 3. It can be seen that the obtained mixed particles are fine, with a particle size in the range of 50 to 400 nm; the mixed powder is a mixed phase of five compounds: lithium oxide, magnesium oxide, zinc oxide, aluminum oxide, and gallium oxide.

Figures 4 and 5 are respectively the surface microstructure of the spinel high entropy transparent ceramic material obtained in Example 7 and the actual picture after polishing on both sides; it can be seen that: the grains after high-temperature sintering are uniform and there is no abnormal growth phenomenon, indicating that the spinel high entropy transparent ceramic has good light transmission performance.

The full spectrum transmittance curve of the 1 mm thick transparent ceramic prepared by raw material 9 in Example 6 of the present invention is shown in Figure 6. It can be seen from the figure that the optical transmittance range of the obtained spinel high-entropy transparent ceramic material is in the range of 230 to 7800 nm, covering the visible light to the infrared band in the atmospheric window, among which the transmittance at 500 to 6000 nm is >70%, meeting the needs of multiple bands, especially in the infrared band of 3 to 5 μm in the atmospheric window, the optical transmittance exceeds 82%.

The transparent ceramics prepared in Example 5 were tested for Vickers hardness with a hardness tester (430SVD model) under a load of 0.5 kg for 15 seconds. The elastic modulus was measured by pulse excitation technology (IET) on GrindoSonic MK7. Five samples were tested for hardness and Young's modulus. The hardness of the ceramics obtained by the test reached 12.2±0.5GPa (mean±standard deviation), and the Young's modulus was 265±12MPa (mean±standard deviation).

The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims (10)

1. A spinel high entropy transparent ceramic, characterized in that its stoichiometric formula is (Li _a Mg _b Zn _c Al _d Ga _e )O ₄ , wherein 0.3≤b+c≤0.9, 0.05≤a≤0.35, 2.05≤d+e≤2.35, b＞0, c＞0, d＞0, e＞0, and a+b+c+d+e=3; five metal ions disorderly occupy the cation equivalent sites in the spinel structure. 2. The method for preparing the spinel high entropy transparent ceramic according to claim 1, characterized in that it comprises the following steps: (1) taking at least one of the oxides and salts corresponding to five ions of Li, Mg, Al, Zn and Ga as raw materials according to the stoichiometric ratio, mixing the raw materials, ball milling them, and then crushing and sieving them to obtain a powder; (2) pressing the powder into a green blank, and then performing a cold isostatic pressing process to obtain a formed green blank; (3) Pre-sintering the formed green body at 1300-1600° C., then hot isostatic pressing sintering at 1400-1700° C., and finally annealing to obtain the spinel high entropy transparent ceramic. 3. The method for preparing spinel high-entropy transparent ceramics according to claim 2, characterized in that in step (1), (Li _n1 Mg _n2 Zn _n3 Al _n4 Ga _n5 )O ₄ powder can also be used as a raw material, wherein 0.3≤n2+n3≤0.9, 0.05≤n1≤0.35, 2.05≤n4+n5≤2.35, n2＞0, n3＞0, n4＞0, n5＞0, and n1+n2+n3+n4+n5=3. 4. The method for preparing spinel high-entropy transparent ceramics according to claim 3 is characterized in that the (Li _n1 Mg _n2 Zn _n3 Al _n4 Ga _n5 )O ₄ powder is prepared according to the following method: Li ₂ O, MgO, Al ₂ O ₃ , ZnO and Ga ₂ O ₃ or corresponding salt compounds are used as raw materials, configured in proportion and mixed evenly, and reacted at 1200-1300°C for 2 hours. 5. The method for preparing the spinel high entropy transparent ceramic according to any one of claims 2 to 4, characterized in that, in step (1), the ball milling uses one of zirconium oxide balls, aluminum oxide balls and silicon nitride balls, and the ball-to-material ratio is 3 to 5:1; the ball milling solvent is anhydrous ethanol; the rotation speed is 120 to 320 r/min, and the ball milling time is 6 to 48 h; The mesh size of the sieving in step (1) is 200 meshes. 6. The method for preparing spinel high-entropy transparent ceramics according to claim 5, characterized in that the pressure of the cold isostatic pressing treatment in step (2) is 180-320 MPa, and the holding time is 5-15 min. 7. The method for preparing the spinel high-entropy transparent ceramic according to any one of claims 2 to 4, characterized in that the pre-sintering parameter conditions in step (3) are: pressureless sintering for 1 to 48 hours in an atmosphere of air or oxygen. 8. The method for preparing spinel high-entropy transparent ceramics _according to claim 3 or 4, characterized in that, in step (3), when _Li2O , MgO, _Al2O3 , ZnO and _Ga2O3 are taken as raw materials, the pre-sintering temperature is 1300~1600℃; when (Li _n1 Mg _n2 Zn _{n3 Al n4} Ga _n5 )O ₄ powder is taken as raw material, the pre-sintering temperature is 1400~1600℃. 9. The method for preparing the spinel high-entropy transparent ceramic according to any one of claims 2 to 4, characterized in that the hot isostatic pressing sintering in step (3) is performed in an argon atmosphere at a pressure of 180 MPa and for a sintering time of 1 to 12 h; The annealing atmosphere in step (3) is air or oxygen-rich atmosphere; The annealing temperature in step (3) is 800-1200° C. and the annealing time is 0.5-48 h. 10. Use of the spinel high entropy transparent ceramic according to claim 1 in the preparation of medical instruments, light sources, lasers, infrared or protective windows.