A lattice-distorted monazite-type high-entropy phosphate ceramic material and a preparation method thereof

Abstract

The application discloses a kind of lattice distortion monazite type high-entropy phosphate ceramic materials and preparation method thereof, by reasonable cross-structure component design, precipitation reaction, high-temperature calcination and refinement granulation, solid solution reaction and ultra-high temperature flash sintering, monazite type high-entropy phosphate ceramic with lattice distortion effect is prepared.The preparation method of the application is simple and efficient, and the high-entropy phosphate ceramic material prepared has obvious lattice distortion effect.The lattice distortion is accompanied by a hysteresis diffusion effect, which reduces the diffusion speed of element particles, making the material have a slower corrosion reaction speed.The high-temperature CMAS corrosion resistance of the material is significantly better than that of conventional monazite type high-entropy phosphate ceramic, and it has application prospects in high-temperature and corrosion-resistant fields.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation, and specifically relates to a lattice-distorted monazite-type high-entropy phosphate ceramic material and its preparation method. Background Technology

[0002] Inspired by the development of high-entropy alloys, the concept of high entropy has recently expanded to include high-entropy ceramics, high-entropy glasses, and high-entropy composites. High-entropy materials exhibit relatively consistent structural effects: lattice distortion, high-entropy effects, retarded diffusion, and cocktail effects. All high-entropy materials are structurally ordered in the long range but highly disordered in their composition. Compared to alloy systems, the emergence of high-entropy ceramics offers more opportunities for inorganic solid solution materials with vast compositional spaces in terms of performance control and overcoming bottlenecks in material applications. The concept of high entropy significantly increases the design possibilities of phosphate systems. Systems with a configurational entropy greater than 1.61R (where R is the universal gas constant) are generally considered to have high entropy values, requiring at least five different elements to be in equal molar ratios. The design of high-entropy ceramics is often based on the complex composition of a single phase, requiring equal opportunities for ions to enter corresponding sites. Therefore, lattice distortion and entropy stabilization effects can affect performance, such as slowing down reaction rates.

[0003] Rare earth phosphates possess high melting points exceeding 2,000 degrees Celsius, low thermal conductivity, low Young's modulus, and excellent high-temperature phase stability. More importantly, research has found that rare earth phosphates do not react with Al2O3 at high temperatures, exhibiting chemical compatibility with such substances at high temperatures. These properties are significantly superior to yttrium-stabilized zirconia (YSZ), a material widely used in thermal insulation. In the field of high-temperature protection, thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs), as widely used thermal protection structures, can isolate alloy components from high-temperature airflows, significantly reducing the temperature of the internal matrix material and effectively extending the service life of structural components. Based on the performance requirements for next-generation high-temperature protection materials, rare earth phosphates are also considered candidate material systems for next-generation aero-engine thermal barrier / environmental barrier coatings. Furthermore, rare earth phosphates exhibit excellent resistance to environmental sedimentary deposition (CMAS) corrosion and molten salt corrosion in marine environments, making them stand out among numerous candidate materials.

[0004] However, current challenges include complex preparation processes for monazite-structured rare earth phosphates, difficulty in controlling byproduct impurities, challenges in controlling product powder morphology, and excessively long preparation cycles. These drawbacks significantly impact sintering and performance. The mainstream preparation method is co-precipitation, using rare earth nitrate solutions and ammonium phosphates as precipitants. Some methods also utilize rare earth oxides reacting with nitric acid to prepare solutions. These steps all involve controlling the degree of reaction, the completeness of precipitation, and the morphology of the precipitated powder. For example, in references [10.1016 / j.jeurceramsoc.2023.06.030] and [10.26599 / JAC.2023.9220736], improper drying methods led to powder agglomeration, and insufficient particle surface energy resulted in incomplete sintering due to insufficient sintering driving force. This invention proposes an efficient method for preparing corrosion-resistant monazite-type high-entropy phosphate ceramics with lattice distortion. Summary of the Invention

[0005] The purpose of this invention is to provide a lattice-distorted monazite-type high-entropy phosphate ceramic material and its preparation method, so as to solve the problems of high cost, poor uniformity and poor powder morphology in existing high-entropy phosphate ceramic preparation methods. Furthermore, the prepared high-entropy ceramic can withstand high temperatures of 1500℃ and has application potential in the field of high-temperature protection.

[0006] To achieve the above objectives, the present invention employs the following technical solution.

[0007] This invention first provides a high-entropy phosphate ceramic material, wherein the high-entropy phosphate ceramic material has a chemical composition of (Re1, Re2, ..., Re...). n )PO4, where Re1, Re2, ..., Re n Each element represents one of n different rare earth elements, where n equals 5 or 6. The high-entropy phosphate ceramic material is in the form of ceramic powder or ceramic bulk; the high-entropy phosphate ceramic material exhibits a lattice-distorted single-phase monazite structure; the lattice distortion refers to the change in the lattice constant and the accompanying shift in the lattice angle of the monazite structure of the high-entropy phosphate ceramic material relative to the XRD pattern of the standard PDF card of NdPO4.

[0008] Furthermore, the n different rare earth elements in the high-entropy phosphate ceramic material include main rare earth elements and doped rare earth elements; wherein the main rare earth elements account for 2 to 5 types, and include at least 2 types of La, Ce, Pr, and Nd, and at most 2 types of Sm, Eu, and Gd; wherein the doped rare earth elements account for 1 to 4 types, and include at least 1 type of Tb, Dy, and Ho, and at most 1 type of Er, Tm, Yb, Y, and Lu.

[0009] Furthermore, in the high-entropy phosphate ceramic material, n equals 5, and the five rare earth elements are in equimolar ratio.

[0010] Furthermore, in the high-entropy phosphate ceramic material, n equals 6, and the molar ratio of the 6 rare earth elements satisfies: (0.9-1.1): (0.9-1.1): (0.9-1.1): (0.9-1.1): (0.9-1.1): (0.9-1.1): (0.9-1.1).

[0011] This invention also provides a method for preparing the above-mentioned lattice-distorted monazite-type high-entropy phosphate ceramic powder material, the preparation steps of which include:

[0012] S1. Composition design: On the basis of ensuring the monazite-type structure, select the main rare earth elements, and then select rare earth elements with relatively small ionic radii as dopants across the structure. The total number of rare earth elements is five or six to maintain a high configuration entropy value.

[0013] S2. Weigh the raw materials: Weigh the required rare earth nitrate and ammonium phosphate raw material powders according to the ratio, and add deionized water to prepare solutions.

[0014] S3, Reaction Precipitation: Mix the various rare earth nitrate solutions and stir thoroughly to form a rare earth nitrate mixed solution; then use ammonium phosphate as a precipitant, add the ammonium phosphate solution prepared in S2 dropwise to the rare earth nitrate mixed solution while stirring to promote the reaction. The reaction produces a large amount of precipitate, forming a precipitate suspension.

[0015] S4. Washing and drying: After ultrasonic dispersion, the precipitated suspension is washed by centrifugation with deionized water and ethanol. Finally, it is placed in a freeze dryer with deionized water as the medium and dried under vacuum to obtain powder. The powder obtained at this time is a phosphate precursor carrying water of crystallization.

[0016] S5. Heat treatment: The phosphate precursor is calcined at high temperature to remove impurities and moisture, and coarse phosphate powder is obtained.

[0017] S6. Refining the powder: Using a high-energy ball mill, the coarse phosphate powder is further ground with ethanol as a medium to the submicron or nanoscale. The ground powder slurry is then completely dried to obtain fine phosphate powder.

[0018] S7. Solid solution reaction and sintering: The fine phosphate powder is subjected to ultra-high temperature flash sintering. During the sintering process, a solid solution reaction occurs to obtain the monazite-type high-entropy phosphate ceramic powder material with lattice distortion.

[0019] This invention also provides a method for preparing the above-mentioned lattice-distorted monazite-type high-entropy phosphate ceramic bulk material, the preparation steps of which are as follows:

[0020] i) Execute S1-S6 in sequence.

[0021] ii) The phosphate fine powder is granulated and pressed into tablets to obtain phosphate ceramic green bodies. Specifically, a 5% (w / w) polyvinyl alcohol (PVA) aqueous solution is used as a binder, with an addition amount of 5% to 10% of the material mass. After being uniformly mixed with the phosphate fine powder, the mixture is passed through a 250-micron sieve. The powder gradually becomes spherical with uniform particle size and is then loaded into a mold and pressed into ceramic green bodies under a uniaxial pressure of at least 250 MPa.

[0022] iii) The phosphate ceramic green body is sintered according to the ultra-high temperature flash sintering process in step S7 to obtain the high-entropy phosphate ceramic block.

[0023] Preferably, the rare earth element composition design in step S1 includes 2 to 5 main rare earth elements, of which at least 2 are selected from La, Ce, Pr, and Nd; and at most 2 are selected from Sm, Eu, and Gd. Rare earth elements with larger ionic radii are chosen as the main elements to serve as a stable framework for the monazite structure, ensuring that smaller ionic radius elements cannot maintain their single-phase state after entering the crystal lattice. Furthermore, a significant difference in ionic size theoretically further increases lattice distortion.

[0024] Preferably, in the rare earth element composition design of step S1, 1 to 4 types of rare earth elements are incorporated, including at least one of Tb, Dy, and Ho; and at most one of Er, Tm, Yb, Y, and Lu.

[0025] Preferably, in step S2, the weighing ratio of the precipitant ammonium phosphate salt to the rare earth nitrate salt satisfies the molar ratio of phosphorus and all rare earth elements as: P:RE = (1.1~2.0):1.

[0026] Preferably, in step S2, the raw material rare earth nitrate powder contains nitrates of 5 different rare earth metal ions, and the 5 nitrates are mixed in an equimolar ratio of the metal ions. Alternatively, in step S2, the raw material rare earth nitrate powder contains nitrates of 6 different rare earth metal ions, and the ratio is as follows: (0.9-1.1):(0.9-1.1):(0.9-1.1):(0.9-1.1):(0.9-1.1):(0.9-1.1).

[0027] Preferably, the rare earth nitrate powder used in step S2 is a raw material powder containing water of crystallization, specifically: lanthanum nitrate hexahydrate, cerium nitrate hexahydrate, praseodymium nitrate hexahydrate, neodymium nitrate hexahydrate, samarium nitrate hexahydrate, europium nitrate hexahydrate, gadolinium nitrate hexahydrate, terbium nitrate hexahydrate, dysprosium nitrate pentahydrate, holmium nitrate pentahydrate, erbium nitrate pentahydrate, thulium nitrate pentahydrate, ytterbium nitrate pentahydrate, yttrium nitrate tetrahydrate, and lutetium nitrate hexahydrate. The precipitant ammonium phosphate salt is any one of diammonium hydrogen phosphate and ammonium dihydrogen phosphate.

[0028] Preferably, in step S3, the ammonium phosphate solution is added dropwise to the rare earth nitrate mixed solution at a rate of 0.05 g / s to 0.30 g / s, the temperature of the constant temperature magnetic stirring is 50℃ to 80℃, the speed of the magnetic stirring is 500 to 800 r / min, and the stirring time is 6 h to 24 h.

[0029] Preferably, in step S4, centrifugation is used to wash and separate the precipitate from the suspension. The centrifugation washing step is as follows:

[0030] S41. After the first centrifugation, pour out all the liquid and add ethanol. Stir the precipitate and use ultrasound to evenly disperse it in the ethanol. Test the pH value of the mixture.

[0031] S42. After the second centrifugation, test the pH value of the supernatant and pour out all the acidic liquid. Add deionized water and stir the precipitate evenly to disperse it in the deionized water. Repeat this step until the pH is neutral. At this point, pour out all the liquid, add deionized water to the remaining precipitate, stir, and use ultrasound to evenly disperse the precipitate in the deionized water.

[0032] Preferably, the freeze-drying in step S4 uses liquid nitrogen as a coolant. The precipitate dispersed in deionized water in S42 is frozen and placed in a cold trap. It is then dried under vacuum at -40 degrees Celsius for at least 12 to 36 hours to form a dried powder, which is a phosphate precursor carrying water of crystallization.

[0033] Preferably, the heat treatment time in step S5 is 1~6 h, and the heat treatment temperature is 1050 ℃~1200 ℃ to remove free water, crystal water and impurities.

[0034] Preferably, in step S6, the high-energy ball milling uses zirconia balls as the grinding medium and ethanol as the dispersant. The ball-to-material ratio is 10:1, the rotation speed is 800~1200 r / min, and the effective ball milling time is 1~2 hours. Vibration milling is performed in reverse every 0.1 hours.

[0035] Preferably, in step S7, high-temperature flash sintering involves using carbon felt as a conductive medium and rapidly heating the sinter to a sintering temperature of 1400℃~1600℃ within seconds using an instantaneous ultra-high voltage at a heating rate of approximately 400℃ / s, and holding at that temperature for 0.5~3 min.

[0036] Compared with existing technologies, its advantages are as follows:

[0037] The present invention describes a simple, efficient, low-cost, safe, and high-purity method for preparing monazite-type high-entropy phosphate ceramics with lattice distortion. Compared to the relatively regular unit cells of traditional monazite-type high-entropy phosphate materials, this method utilizes the compositional space and transstructural ion substitution of the high-entropy system. Specifically, it randomly distributes five or six different rare earth elements at the same ion site, causing a change in the local ion bonding environment. To adapt to this energy difference, lattice distortion and high-entropy effects are generated, allowing the solid solution to maintain a single-phase structure at high temperatures. Furthermore, the lattice distortion is accompanied by a retarded diffusion effect, which reduces the diffusion rate of elemental particles, resulting in a slower corrosion reaction rate. High-energy ball milling ensures thorough and uniform mixing of the raw materials and further reduces the particle size, resulting in a powder product with uniform elemental mixing and small particle size. This increases the overall surface energy, promotes sintering densification, reduces preparation costs, and significantly shortens the material preparation cycle. The densification process employs a high-temperature flash sintering method, reducing sintering time to minutes or even seconds, significantly shortening the sintering cycle. The resulting lattice-distorted monazite-type single-phase high-entropy phosphate ceramic material exhibits high phase purity and uniform element distribution. It maintains phase stability under CMAS corrosion at high temperatures (1300 ℃), making it a promising candidate system for high-temperature protective materials in more demanding service environments.

[0038] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0039] Figure 1 This is a comparison of the X-ray diffraction patterns of the monazite-structured high-entropy phosphate ceramic materials prepared in Examples 1 and 3 of this invention with standard PDF cards, as well as the refinement results.

[0040] Figure 2 These are scanning electron microscope images of the high-entropy phosphate ceramic block with a monazite structure of Embodiment 3 of the present invention, after being corroded by CMAS at 1300 °C. Detailed Implementation

[0041] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Example 1

[0044] The preparation method of (LaCeNdSmEuDy)PO4 monazite-type high-entropy phosphate ceramic powder and ceramic bulk includes the following steps:

[0045] (1) Composition design: The main elements in the rare earth element composition design are five types, including: La, Ce, Nd, Sm and Eu; and one type of doped element, including: Dy.

[0046] (2) Weighing raw materials: Weigh 4.6765g of La(NO3)3·6H2O, 5.2106g of Ce(NO3)3·6H2O, 5.2602g of Nd(NO3)3·6H2O, 5.3336g of Sm(NO3)3·6H2O, 5.3527g of Eu(NO3)3·6H2O, and 5.2630g of Dy(NO3)3·5H2O powder according to the molar ratio of P:RE=1.5:1. Weigh 14.2625g of (NH4)2HPO4 and place them in beakers respectively. Dilute them with 250mL of deionized water to obtain ammonium phosphate solution and rare earth nitrate solution. Then mix the rare earth nitrate solutions to obtain rare earth nitrate mixed solution.

[0047] (3) Mixed precipitation: Ammonium phosphate solution was added dropwise to rare earth nitrate mixed solution at a rate of 0.1 g / s and stirred to promote precipitation reaction. The temperature of the constant temperature magnetic stirring was 80℃; the speed of magnetic stirring was 800 r / min; and the stirring time was 12 h.

[0048] (4) Washing and drying: The precipitate after the precipitation reaction was separated from the acid solution by centrifugation. In this embodiment, the washing steps are as follows: After the first centrifugation, all liquid was poured out and ethanol was added. The precipitate was stirred and dispersed evenly in the ethanol, and the pH of the mixture was tested to be approximately 1. After the second centrifugation, the pH of the supernatant was tested to be approximately 2. All acidic liquid was poured out and deionized water was added. The precipitate was stirred and dispersed evenly in the deionized water. The separation and dilution steps with deionized water were repeated twice. The pH of the supernatant was tested to be neutral. At this time, all liquid was poured out and deionized water was added to the same volume. The precipitate was stirred and dispersed evenly in the deionized water. The mixture was placed in a beaker and freeze-dried. Liquid nitrogen was used as a coolant. The frozen raw material was placed in a cold trap and dried at -40 degrees Celsius under vacuum for at least 16 hours to obtain the freeze-dried powder, which is the phosphate precursor carrying water of crystallization.

[0049] (5) Heat treatment: The freeze-dried powder is heat-treated for 2 hours at a temperature of 1200 °C to remove free water, crystal water and impurities, and to obtain coarse phosphate ceramic powder.

[0050] (6) Refining the powder: The high-energy ball milling method used zirconia balls as the grinding medium and ethanol as the dispersant was ball milling with a ball-to-material ratio of 10:1, a rotation speed of 1000 r / min, and an effective ball milling time of 1 h. Vibration milling was carried out in reverse every 0.1 h to grind the coarse phosphate ceramic powder to the submicron or nanoscale. The ground powder slurry was then completely dried to obtain fine phosphate powder. For the preparation of high-entropy phosphate ceramic powder, step (7) was directly performed to sinter the fine phosphate powder at high temperature by flash evaporation.

[0051] Granulation and pressing: For the preparation of high-entropy phosphate ceramic blocks, the phosphate fine powder obtained above is granulated and pressed into tablets to obtain phosphate ceramic green bodies. Specifically, a 5% polyvinyl alcohol (PVA) aqueous solution is used as a binder and added to the phosphate fine powder. After uniform mixing, the powder is passed through a 250-micron sieve. The powder gradually becomes a spherical shape with uniform particle size and is then loaded into a mold. The block ceramic green body is compacted with a uniaxial pressure of 300 MPa and then taken out. The ceramic green body is then subjected to high-temperature flash sintering in step (7).

[0052] (7) Sintering: The sintering method adopts high-temperature flash sintering, using carbon felt as a conductive medium, so that the phosphate fine powder or ceramic green body is heated to the sintering temperature at a rate of 400℃ / s, with a maximum temperature of 1500℃, and held for 3 min. The high-entropy phosphate ceramic powder and high-entropy phosphate ceramic bulk body are obtained.

[0053] Example 2

[0054] The preparation method of (CePrNdSmTbY)PO4 monazite-type high-entropy phosphate ceramic powder and ceramic bulk includes the following steps:

[0055] (1) Composition design: The main elements in the rare earth element composition design are four types, including Ce, Pr, Nd and Sm; and the doped phase elements are two types, including Tb and Y.

[0056] (2) Weighing raw materials: Weigh 5.2106g of Ce(NO3)3·6H2O, 5.2201g of Pr(NO3)3·6H2O, 5.2602g of Nd(NO3)3·6H2O, 5.3336g of Sm(NO3)3·6H2O, 5.4363g of Tb(NO3)3·6H2O, and 4.5961g of Y(NO3)3·4H2O powder according to the molar ratio of P:RE=1.1:1. Weigh 10.4591g of (NH4)2HPO4 and place them in beakers respectively. Dilute them with 250mL of deionized water to obtain ammonium phosphate solution and rare earth nitrate solution. Then mix the rare earth nitrate solutions to obtain rare earth nitrate mixed solution.

[0057] (3) Mixed precipitation: Ammonium phosphate solution was added dropwise to rare earth nitrate mixed solution at a rate of 0.2 g / s and stirred to promote precipitation reaction. The temperature of the constant temperature magnetic stirring was 70℃; the speed of magnetic stirring was 700 r / min; and the stirring time was 6 h.

[0058] (4) Washing and drying: The precipitate after the precipitation reaction was separated from the acid solution by centrifugation. In this embodiment, the washing steps are as follows: After the first centrifugation, all liquid was poured out and ethanol was added. The precipitate was stirred and dispersed evenly in the ethanol, and the pH of the mixture was tested to be approximately 1. After the second centrifugation, the pH of the supernatant was tested to be approximately 2. All acidic liquid was poured out and deionized water was added. The precipitate was stirred and dispersed evenly in the deionized water. The separation and dilution steps with deionized water were repeated twice. The pH of the supernatant was tested to be neutral. At this time, all liquid was poured out and deionized water was added to the same volume. The precipitate was stirred and dispersed evenly in the deionized water. The mixture was placed in a beaker and freeze-dried. Liquid nitrogen was used as a coolant. The frozen raw material was placed in a cold trap and dried at -40 degrees Celsius under vacuum for at least 24 hours to obtain the freeze-dried powder, which is the phosphate precursor carrying water of crystallization.

[0059] (5) Heat treatment: The freeze-dried powder is heat-treated for 4 hours at a temperature of 1100 °C to remove free water, water of crystallization and impurities to obtain coarse phosphate powder.

[0060] (6) Powder Refinement: The high-energy ball milling method used zirconia balls as the grinding medium and ethanol as the dispersant was ball milling with a ball-to-material ratio of 10:1, a rotation speed of 950 r / min, and an effective ball milling time of 1 h. Vibration milling was carried out in reverse every 0.1 h to grind the coarse phosphate ceramic powder to the submicron or nanoscale. The ground powder slurry was then completely dried to obtain fine phosphate powder. For the preparation of high-entropy phosphate ceramic powder, step (7) was directly performed, and the fine phosphate powder was subjected to high-temperature flash sintering.

[0061] Granulation and pressing: For the preparation of high-entropy phosphate ceramic blocks, the phosphate fine powder obtained above is granulated and pressed into tablets to obtain phosphate ceramic green bodies. Specifically, a 5% polyvinyl alcohol (PVA) aqueous solution is used as a binder, and 5%-10% of the material is added to the phosphate fine powder and mixed evenly. After passing through a 250-micron sieve, the powder gradually becomes a spherical shape with uniform particle size and is then loaded into a mold. The green body is compacted with a uniaxial pressure of 270 MPa and the block ceramic green body is taken out. Then, the ceramic green body is subjected to high-temperature flash sintering in step (7).

[0062] (7) Sintering: The sintering method adopts high-temperature flash sintering, using carbon felt as a conductive medium, so that the phosphate fine powder or ceramic green body is heated to the sintering temperature at a rate of 400℃ / s, with a maximum temperature of 1450℃, and held for 2 min. The high-entropy phosphate ceramic powder or high-entropy phosphate ceramic block is obtained.

[0063] Example 3

[0064] The preparation method of (LaNdSmTbDyEr)PO4 monazite-type high-entropy phosphate ceramic bulk includes the following steps:

[0065] (1) Composition design: The main elements in the rare earth element composition design are three types, including: La, Nd and Sm; the dopants are three types, including: Tb, Dy and Er.

[0066] (2) Weighing raw materials: Weigh 4.6765g of La(NO3)3·6H2O, 5.2602g of Nd(NO3)3·6H2O, 5.3336g of Sm(NO3)3·6H2O, 5.4364g of Tb(NO3)3·6H2O, 5.2630g of Dy(NO3)3·5H2O, and 5.3202g of Er(NO3)3·5H2O powder according to the molar ratio of P:RE=1.5:1. Weigh 14.2625g of (NH4)2HPO4 and place them in beakers respectively. Dilute them with 250mL of deionized water to obtain ammonium phosphate solution and rare earth nitrate solution. Then mix the rare earth nitrate solutions to obtain rare earth nitrate mixed solution.

[0067] (3) Mixed precipitation: Ammonium phosphate solution was added dropwise to rare earth nitrate mixed solution at a rate of 0.15 g / s and stirred to promote precipitation reaction. The temperature of the constant temperature magnetic stirring was 60℃; the speed of magnetic stirring was 700 r / min; and the stirring time was 12 h.

[0068] (4) Washing and drying: The precipitate after the precipitation reaction was separated from the acid solution by centrifugation. In this embodiment, the washing steps are as follows: After the first centrifugation, all liquid was poured out and ethanol was added. The precipitate was stirred and dispersed evenly in the ethanol, and the pH of the mixture was tested to be approximately 1. After the second centrifugation, the pH of the supernatant was tested to be approximately 2. All acidic liquid was poured out and deionized water was added. The precipitate was stirred and dispersed evenly in the deionized water. The separation and dilution steps with deionized water were repeated twice. The pH of the supernatant was tested to be neutral. At this time, all liquid was poured out and deionized water was added to the same volume. The precipitate was stirred and dispersed evenly in the deionized water. The mixture was placed in a beaker and freeze-dried. Liquid nitrogen was used as a coolant. The frozen raw material was placed in a cold trap and dried at -40 degrees Celsius under vacuum for at least 30 hours to obtain the freeze-dried powder, which is the phosphate precursor carrying water of crystallization.

[0069] (5) Heat treatment: The freeze-dried powder is heat-treated for 3 hours at a temperature of 1200 °C to remove free water, water of crystallization and impurities to obtain coarse phosphate powder.

[0070] (6) Powder Refinement: The high-energy ball milling method used zirconia balls as the grinding medium and ethanol as the dispersant was ball milling with a ball-to-material ratio of 10:1, a rotation speed of 900 r / min, and an effective ball milling time of 1.5 h. Vibration milling was carried out in reverse every 0.1 h to grind the coarse phosphate ceramic powder to the submicron or nanoscale. The ground powder slurry was then completely dried to obtain fine phosphate powder. For the preparation of high-entropy phosphate ceramic powder, step (7) was directly performed, and the fine phosphate powder was subjected to high-temperature flash sintering.

[0071] Granulation and pressing: The phosphate fine powder obtained above is granulated and pressed into tablets to obtain phosphate ceramic green bodies. Specifically, a 5% polyvinyl alcohol (PVA) aqueous solution is used as a binder. The amount of the binder is 5%-10% of the material. The mixture is added to the phosphate fine powder and then passed through a 250-micron sieve. The powder gradually becomes a spherical shape with uniform particle size and is then placed into a mold. The mold is compacted with a uniaxial pressure of 250 MPa and the block ceramic green body is taken out. Then, the ceramic green body is subjected to high-temperature flash sintering in step (7).

[0072] (7) Sintering: The sintering method adopts high-temperature flash sintering, using carbon felt as a conductive medium, so that the phosphate fine powder or ceramic green body is heated to the sintering temperature at a rate of 400℃ / s, with a maximum temperature of 1400℃, and held for 2 min. The high-entropy phosphate ceramic powder and high-entropy phosphate ceramic bulk body are obtained.

[0073] Example 4

[0074] The preparation method of (CeNdSmEuDy)PO4 monazite-type high-entropy phosphate powder includes the following steps:

[0075] (1) Composition design: The main elements in the rare earth element composition design are four types, including Ce, Nd, Sm and Eu; and one doped element is Dy.

[0076] (2) Weighing raw materials: Weigh 5.2106g of Ce(NO3)3·6H2O, 5.2602g of Nd(NO3)3·6H2O, 5.3336g of Sm(NO3)3·6H2O, 5.3527g of Eu(NO3)3·6H2O, and 5.2630g of Dy(NO3)3·5H2O powder according to the molar ratio of P:RE=2.0:1. Weigh 15.8472g of (NH4)2HPO4 and dilute each with deionized water in a beaker to form nitrate solution and ammonium phosphate solution. Mix the nitrates and add 250mL of deionized water to form a rare earth nitrate mixed solution.

[0077] (3) Mixed precipitation: Ammonium phosphate solution was added dropwise to rare earth nitrate mixed solution at a rate of 0.30 g / s and stirred to carry out precipitation reaction. The temperature of the constant temperature magnetic stirring was 50℃; the speed of magnetic stirring was 500 r / min; and the stirring time was 24h.

[0078] (4) Washing and drying: The precipitate was separated from the acid by centrifugation. The washing steps were as follows: After the first centrifugation, all liquid was poured out and ethanol was added. The precipitate was stirred and dispersed evenly in the ethanol. The pH of the mixture was tested to be approximately 1. After the second centrifugation, the pH of the supernatant was tested to be approximately 2. All acidic liquid was poured out and deionized water was added. The precipitate was stirred and dispersed evenly in the deionized water. This step was repeated twice until the pH was neutral. All liquid was poured out and deionized water was added to the same volume. The precipitate was stirred and dispersed evenly in the deionized water. The mixture was placed in a beaker and freeze-dried. Liquid nitrogen was used as a coolant. The frozen raw material was placed in a cold trap and dried at -40 degrees Celsius under vacuum for at least 12 hours. The freeze-dried powder obtained was the phosphate precursor carrying water of crystallization.

[0079] (5) Heat treatment: The freeze-dried powder is heat-treated for 6 hours at a temperature of 1050 °C to remove free water, water of crystallization and impurities from the coarse phosphate powder.

[0080] (6) Refining the powder: The high-energy ball milling method used zirconia balls as the grinding medium and ethanol as the dispersant was ball milling with a ball-to-material ratio of 10:1, a rotation speed of 1200 r / min, and an effective ball milling time of 1 h. Vibration milling was carried out in reverse every 0.1 h to grind the coarse phosphate ceramic powder to the submicron or nanoscale. The ground powder slurry was completely dried to obtain fine phosphate powder.

[0081] (7) Sintering: High-temperature flash sintering is adopted, and carbon felt is used as a conductive medium to raise the temperature of the fine phosphate powder to the sintering temperature at a rate of 400℃ / s, with a maximum temperature of 1600℃, and hold for 0.5 min to obtain the high-entropy phosphate ceramic powder.

[0082] Example 5

[0083] The preparation method of (CeNdSmTbY)PO4 monazite-type high-entropy phosphate ceramic bulk includes the following steps:

[0084] (1) Composition design: The main elements in the rare earth element composition design are three types, including Ce, Nd and Sm; the dopant elements are two types, including Tb and Y.

[0085] (2) Weighing raw materials: Weigh 5.2106g of Ce(NO3)3·6H2O, 5.2602g of Nd(NO3)3·6H2O, 5.3336g of Sm(NO3)3·6H2O, 5.4363g of Tb(NO3)3·6H2O and 4.5961g of Y(NO3)3·4H2O powder according to the molar ratio of P:RE=1.1:1. Weigh 8.7159g of (NH4)2HPO4 according to the molar ratio of P:RE=1.1:1. Dilute each of them with deionized water and place them in beakers to form nitrate solution and ammonium phosphate solution. Mix the nitrates and add 250mL of deionized water to form rare earth nitrate mixed solution.

[0086] (3) Mixed precipitation: Ammonium phosphate solution was added dropwise to rare earth nitrate mixed solution at a rate of 0.2 g / s and stirred to carry out precipitation reaction. The temperature of the constant temperature magnetic stirring was 70℃; the speed of magnetic stirring was 700 r / min; and the stirring time was 6 h.

[0087] (4) Washing and drying: The precipitate was separated from the acid by centrifugation. The washing steps were as follows: After the first centrifugation, all liquid was poured out and ethanol was added. The precipitate was stirred and dispersed evenly in the ethanol. The pH of the mixture was tested to be approximately 1. After the second centrifugation, the pH of the supernatant was tested to be approximately 2. All acidic liquid was poured out and deionized water was added. The precipitate was stirred and dispersed evenly in the deionized water. This step was repeated twice until the pH was neutral. All liquid was poured out and deionized water was added to the same volume. The precipitate was stirred and dispersed evenly in the deionized water. The mixture was placed in a beaker and freeze-dried. Liquid nitrogen was used as a coolant. The frozen raw material was placed in a cold trap and dried at -40 degrees Celsius under vacuum for at least 36 hours. The freeze-dried powder obtained was the phosphate precursor carrying water of crystallization.

[0088] (5) Heat treatment: The freeze-dried powder is heat-treated for 1 hour at a temperature of 1200 °C to remove free water, water of crystallization and impurities to obtain coarse phosphate powder.

[0089] (6) Refining the powder: The high-energy ball milling method used zirconia balls as the grinding medium and ethanol as the dispersant was ball milling with a ball-to-material ratio of 10:1, a rotation speed of 800 r / min, and an effective ball milling time of 2h. Vibration milling was carried out in reverse every 0.1h to grind the coarse phosphate ceramic powder to the submicron or nanoscale. The ground powder slurry was completely dried to obtain fine phosphate powder.

[0090] Granulation and tableting: The phosphate fine powder obtained above is granulated and tableted to obtain phosphate ceramic green body. Specifically, a 5% (w / w) polyvinyl alcohol (PVA) aqueous solution is used as a binder, and 5%-10% (w / w) of the material is added to the phosphate fine powder and mixed evenly. After being passed through a 250-micron sieve, the powder gradually becomes spherical with uniform particle size and is then loaded into a mold. It is then compacted with a uniaxial pressure of 290 MPa and the block ceramic green body is removed.

[0091] (7) Sintering: The sintering method adopts high-temperature flash sintering, using carbon felt as a conductive medium, so that the ceramic green body is heated to the sintering temperature at a rate of 400℃ / s, the maximum temperature is 1450℃, and the temperature is held for 2 min to obtain the high-entropy phosphate ceramic block.

[0092] XRD analysis of the crystal structure and morphology of the high-entropy phosphate ceramic powders or bulk materials prepared in each embodiment revealed that the high-entropy phosphate ceramic powders or bulk materials prepared in each embodiment of the present invention are all high-entropy phosphate ceramic materials with a single-phase monazite structure, and their crystal structure morphology all exhibit lattice distortion and changes in lattice constant. For example, Figure 1 The (LaCeNdSmEuDy)PO4 high-entropy phosphate ceramic powder prepared in Example 1 ( Figure 1 The left image in the figure shows the (LaNdSmTbDyEr)PO4 high-entropy phosphate ceramic bulk obtained in Example 3. Figure 1 The XRD patterns and refinement results are shown in the right figure in both XRD patterns. The lower part of both XRD patterns is a standard PDF card comparison pattern of NdPO4. Both figures show that its crystal structure is consistent with that of NdPO4 with monazite structure. No second phase diffraction peaks or diffraction peaks of impurities or oxide raw materials were found, which reflects that the phase purity of the high-entropy phosphate ceramic powder or bulk prepared in the two examples is good. Secondly, as shown in Table 1 below, the lattice constant values ​​of the (LaCeNdSmEuDy)PO4 high-entropy phosphate ceramic powder prepared in Example 1 and the (LaNdSmTbDyEr)PO4 high-entropy phosphate ceramic bulk prepared in Example 3, obtained from the refined XRD patterns, show that the lattice constants of both have changed significantly, accompanied by a shift in the lattice angle, indicating the generation of lattice distortion. In addition, because the doped phase rare earth element in Example 1 is small, with only one element Dy, while Example 3 has three doped phase rare earth elements: TbDyEr, the degree of lattice distortion in Example 3 is higher, which is manifested as lattice constant shrinkage and increased lattice angle shift.

[0093] Table 1

[0094]

[0095] Using the hexa- and pentagonal high-entropy phosphate ceramic blocks prepared in Examples 3 and 5 respectively as the objects of CMAS corrosion testing and analysis, the results show that, regardless of whether they are hexa- or pentagonal high-entropy phosphate ceramic blocks prepared in this invention, after long-term high-temperature CMAS corrosion, a uniform, densely packed barrier layer can form on their surface to prevent CMAS from penetrating into the high-entropy phosphate ceramic blocks of this invention. For example, Figure 2 The image shows the cross-sectional microstructure of the (LaNdSmTbDyEr)PO4 high-entropy phosphate ceramic bulk prepared in Example 3 after isothermal etching at 1300℃ for 10 hours using CMAS (a mixture of CaO, MgO, Al2O3, and SiO2 glass powder in a molar ratio of 33:9:13:45). As can be seen from the image, CMAS failed to penetrate the interior of the high-entropy phosphate, and a dense product layer formed on the surface of the high-entropy phosphate ceramic bulk. This layer is produced by the reaction between the phosphate and molten CMAS during the etching process, and is likely an apatite mineral composed of calcium, rare earth elements, and phosphorus. Its dense accumulation at the interface prevents further etching by the molten CMAS. Furthermore, the thickness of the etching reaction products (as shown in the attached image) can be observed. Figure 2 (Dark contrast portion) The corrosion rate was calculated to be an average of 1.2 μm / h after a 10-hour corrosion reaction time, which is much lower than the corrosion rate of 1.9-2.2 μm / h for low-entropy monocomponent rare earth phosphates such as lanthanum phosphate. The corrosion rate data for low-entropy monocomponent rare earth phosphates here are from [10.26599 / JAC.2025.9221041] and [10.1111 / jace.19165].

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A lattice-distorted monazite-type high-entropy phosphate ceramic material, characterized in that: the high-entropy phosphate ceramic material is in the form of a ceramic powder or a ceramic bulk; the high-entropy phosphate ceramic material has a crystal structure of a lattice-distorted single-phase monazite structure; the lattice distortion refers to that, in the monazite structure of the high-entropy phosphate ceramic material, the lattice constant is changed and the lattice angle is offset relative to the XRD pattern of the standard PDF card of NdPO 4; the n different rare earth elements include main rare earth elements and doped rare earth elements; the main rare earth elements are 2 to 5 in number and at least include 2 of La, Ce, Pr and Nd and at most include 2 of Sm, Eu and Gd; the doped rare earth elements are 1 to 4 in number and at least include 1 of Tb, Dy and Ho and at most include 1 of Er, Tm, Yb, Y and Lu; in the high-entropy phosphate ceramic material, n is equal to 5 and the 5 rare earth elements are in an equimolar ratio; in the high-entropy phosphate ceramic material, n is equal to 6 and the molar ratio of the 6 rare earth elements satisfies (0.9-1.1) :(0.9-1.1) :(0.9-1.1) :(0.9-1.1) :(0.9-1.1) :(0.9-1.1); and the high-entropy phosphate ceramic material is in the form of a ceramic powder, and the preparation steps include: S1, selecting main rare earth elements and doped rare earth elements, the total number of rare earth elements being 5 or 6; the main rare earth elements are 2 to 5 in number and at least include 2 of La, Ce, Pr and Nd and at most include 2 of Sm, Eu and Gd; the doped rare earth elements are 1 to 4 in number and at least include 1 of Tb, Dy and Ho and at most include 1 of Er, Tm, Yb, Y and Lu; S2, weighing ammonium phosphate salt and each rare earth nitrate raw material powder, and respectively adding deionized water to prepare solutions; the ratio of the two satisfies that the molar ratio of phosphorus element and all rare earth elements is P: RE = (1.1-2.0) : 1; S3, mixing each rare earth nitrate solution to form a mixed rare earth nitrate solution, and adding the ammonium phosphate salt solution prepared in S2 drop by drop to form a precipitate suspension; S4, after ultrasonic dispersion, the precipitate suspension is centrifuged and washed, and then freeze-dried to obtain a phosphate precursor; S5, the phosphate precursor is heat-treated to obtain a phosphate coarse powder; S6, the phosphate coarse powder is refined and dried to obtain a phosphate fine powder; and S7, the phosphate fine powder is subjected to ultra-high temperature flash sintering, and a solid solution reaction occurs in the sintering process to obtain the high-entropy phosphate ceramic powder material; and the high-entropy phosphate ceramic material is in the form of a ceramic bulk, and the preparation steps include: I) sequentially performing the steps S1 to S6; II) granulating and tabletting the phosphate fine powder to obtain a phosphate ceramic green body; polyvinyl alcohol aqueous solution is used as a binder and the addition amount is 5% to 10% of the mass of the material; and the tabletting is performed by pressing the ceramic green body under a uniaxial pressure of at least 250 MPa. The high-entropy phosphate ceramic material has a chemical composition of (Re1, Re2, …, Re n )PO4, wherein Re1, Re2, …, Re n represent n different rare earth elements, respectively, wherein n is equal to 5 or 6. ​ ​ ​ ​ ​ ​ 2. The crystal lattice distorted monazite-type high-entropy phosphate ceramic material of claim 1, wherein: ​ 3. The crystal lattice distorted monazite-type high-entropy phosphate ceramic material of claim 1, wherein: ​ 4. The method for preparing the lattice-distorted monazite-type high-entropy phosphate ceramic material according to claim 1, characterized in that, ​ ​ ​ ​ ​ ​ ​ ​ ​ 5. The method of claim 4, wherein the lattice-distorted monazite-type high-entropy phosphate ceramic material is prepared by the following steps of: preparing a precursor powder by mixing a plurality of metal oxides, metal hydroxides, or metal salts; and sintering the precursor powder at a temperature of 800-1200 °C in an atmosphere of nitrogen, argon, or vacuum. ​ ​ ​ III) sintering the phosphate ceramic green body according to the ultra-high temperature flash sintering process in step S7 to obtain the high-entropy phosphate ceramic bulk.

6. The method for preparing the lattice-distorted monazite-type high-entropy phosphate ceramic material according to claim 4 or 5, characterized in that: The raw material rare earth nitrate powder in step S2 comprises nitrate of five different rare earth metal ions, and the five nitrate salts are proportioned according to the equimolar ratio of metal ions.

7. The method of claim 4 or 5, wherein the method comprises: The raw material rare earth nitrate powder in step S2 comprises nitrate of six different rare earth metal ions, and the proportioning ratio satisfies the molar ratio of metal ions: (0.9-1.1): (0.9-1.1): (0.9-1.1): (0.9-1.1): (0.9-1.1): (0.9-1.1). ​ 8. The method of claim 4 or 5, wherein the method is characterized by: In step S3, the ammonium phosphate solution is added dropwise into the rare earth nitrate mixed solution at a speed of 0.05 g / s to 0.30 g / s, and stirring is performed at the same time to promote the reaction to generate a large amount of precipitate; the temperature of the constant-temperature magnetic stirring is 50°C to 80°C; the rotating speed of the magnetic stirring is 500 r / min to 800 r / min; and the stirring time is 6 h to 24 h.

9. The method of claim 4 or 5, wherein the method is characterized by, In step S4, the precipitate in the precipitate suspension is separated out by using a centrifugal method, and the centrifugal washing steps are as follows: S41, after the first centrifugal separation, all the liquid is poured out, ethanol is added, the precipitate is stirred and uniformly dispersed in the ethanol by using ultrasonic waves, and the pH value of the mixed solution is tested; S42, after the second centrifugal separation, the pH value of the supernatant is tested, all the acidic liquid is poured out, deionized water is added, the precipitate is stirred and uniformly dispersed in the deionized water, and this step is repeated until the pH value is neutral; at this time, all the liquid is poured out, deionized water is added to the remaining precipitate, the precipitate is stirred and uniformly dispersed in the deionized water by using ultrasonic waves; In step S4, the freeze-drying uses liquid nitrogen as a cooling agent to freeze the precipitate dispersed in the deionized water in S42 and place it in a cold trap, and the precipitate is dried at -40°C under vacuum for at least 12 h to 36 h to form a dry powder, which is the phosphate precursor carrying crystal water.

10. The method of claim 4 or 5, wherein the method of preparing the lattice-distorted monazite-type high-entropy phosphate ceramic material is characterized by: In step S5, the heat treatment time is 1 h to 6 h, and the heat treatment temperature is 1050°C to 1200°C to remove free water, crystal water and impurities.

11. The method of claim 4 or 5, wherein the method is characterized by: In step S6, the refined phosphate coarse powder refers to further grinding the phosphate coarse powder to a submicron or nanometer level using high-energy ball milling with ethanol as a medium, wherein zirconia balls are used as grinding media and ethanol is used as a dispersant for ball milling, the ball-to-material ratio is 10:1, the rotating speed is 800 r / min to 1200 r / min, and the effective ball milling time is 1 h to 2 h.

12. The method of claim 4 or 5, wherein the lattice-distorted monazite-type high-entropy phosphate ceramic material is prepared by the following steps of: preparing a precursor powder by mixing a plurality of metal phosphates; and sintering the precursor powder at a temperature of 800-1,000°C for 1-10 hours in a reducing atmosphere. In step S7, high-temperature flash sintering: carbon felt is used as a conductive medium, and the sintering object is rapidly heated to a sintering temperature of 1400°C to 1600°C within a few seconds at a heating rate of 400°C / s through a transient ultra-high voltage, and the temperature is kept for 0.5 min to 3 min.

Images