CN111908922A - Low-temperature synthesized rare earth hafnate high-entropy ceramic powder and preparation method thereof - Google Patents

Abstract

The invention relates to a low-temperature synthesis of rare earth hafnium salt high-entropy ceramic powder and a preparation method. The chemical formula of the rare earth hafnium salt high-entropy ceramic is (5RE _0.2 ) ₂ Hf ₂ O ₇ , wherein the rare earth element RE=La, Ce, Nd , Pr, Sm, Eu. The specific preparation process of the present invention is as follows: using hafnium tetrachloride (HfCl ₄ ) and hydrated rare earth nitrate (RE(NO ₃ ) ₃ xH ₂ O) as raw materials, selecting urea as a combustion agent, mixing through solutions, and mixing in an air atmosphere Under the condition of low temperature and low temperature, it burns to form fluffy powder. After high temperature decarbonization treatment, high purity (5RE _0.2 ) ₂ Hf ₂ O ₇ powder is obtained. The method has the advantages of high energy ball milling, spray pyrolysis and co-precipitation and other oxide high-entropy ceramic synthesis methods, and has the advantages of low synthesis temperature, simple operation and fast preparation speed.

Description

A kind of low temperature synthesis rare earth hafnium salt high entropy ceramic powder and preparation method

technical field

The invention belongs to the field of powder synthesis, and relates to a low-temperature synthesis of rare earth hafnium salt high-entropy ceramic powder and a preparation method.

Background technique

High-entropy ceramics (HECs), sometimes referred to as high-entropy compounds, are single-phase ceramics containing no less than four cations and anions. The concept of high-entropy ceramics comes from high-entropy alloys. High-entropy alloys exhibit excellent properties such as high strength and high hardness, making high-entropy ceramics a hot research topic in recent years. High-entropy ceramics have high hardness, low thermal and electrical conductivity, excellent dielectric properties, and excellent lithium-ion cycling stability, making them widely used as wear-resistant materials, thermal protection materials, dielectric materials, and lithium battery anode materials. Applications. At the same time, the pyrochlore-structured RE ₂ Hf ₂ O ₇ has the advantages of extremely low thermal conductivity, excellent phase stability and small change in thermal expansion coefficient under high temperature conditions. Prospective new thermal barrier coating materials.

At present, there are few studies on oxide high-entropy ceramics, and their preparation processes mainly include: high-energy ball milling, spray pyrolysis and co-precipitation, etc. These preparation methods have disadvantages such as high energy consumption, long production cycle, high equipment requirements and complex processes. Therefore, the combustion method has a very broad development prospect as a low-temperature synthetic ceramic technology with a simple process and a short preparation period.

Literature 1 "Z.Zhao,H.Xiang,F.Dai,et al.,(La _0.2 Ce _0.2 Nd _0.2 Sm _0.2 Eu _0.2 ) ₂ Zr ₂ O ₇ :A novel high-entropy ceramic with low thermal conductivity and sluggish grain growthrate [J]. Journal of Materials Science&Technology, 2019.35(11): 2647-2651. "Preparation of high-entropy ceramics (La _0.2 Ce _0.2 Nd _0.2 Sm _0.2 Eu _0.2 ) ₂ Zr ₂ O ₇ by co-precipitation method, during the preparation process The calcination and sintering temperatures are 1300°C and 1500°C, respectively. The preparation temperature of this method is relatively high. In addition, the addition of the precipitant may cause the local concentration to be too high, resulting in agglomeration or inhomogeneous composition.

Document 2 "K.Chen,X.Pei,L.Tang,et al.,A five-component entropy-stabilizedfluorite oxide[J].Journal of the European Ceramic Society,2018.38(11):4161-4164."Through high energy Five kinds of high-entropy ceramics with fluorite structure were prepared by ball milling-sintering-high-energy ball-milling-sintering method. This process has high calcination and sintering temperature, long holding time, and long time ball milling when mixing samples, which is time-consuming and energy-consuming.

Reference 3 "Chellali, M.R., et al., On the homogeneity of high entropy oxides: An investigation at the atomic scale[J]. Scripta Materialia, 2019.166:58-63." Using spray pyrolysis to prepare a variety of calcium For the single-phase oxide high-entropy ceramics with titanium ore structure, the process is carried out at a temperature of 1150°C to 1250°C and a pressure of 900 mbar, so the process requires higher equipment and increases the production cost.

Reference 4 "A.Mao, H.Xiang, Z.Zhang, et al., Solution combustion synthesis and magnetic property of rock-salt(Co _0.2 Cu _0.2 Mg _0.2 Ni _0.2 Zn _0.2 )O high-entropy oxidenanocrystalline powder[J]. Journal of Magnetism and Magnetic Materials, 2019.484:245-252. "(Co _0.2 Cu _0.2 Mg _0.2 Ni _0.2 Zn _0.2 )O high entropy oxide was prepared by combustion method at a temperature of 823-1173K and a holding time of 30min For ceramics, the preparation temperature required by this process is low, the preparation period is short, and the operation is simple; in addition, the powder produced is fluffy, the particles are small, and the agglomeration is not easy to occur.

SUMMARY OF THE INVENTION

technical problem to be solved

In order to avoid the shortcomings of the prior art, the present invention proposes a low-temperature synthesis of rare earth hafnium salt high-entropy ceramic powder and a preparation method, which solves many problems in the preparation process. The molten salt method has the advantages of low preparation temperature, short holding time, simple operation, good controllability of powder composition, morphology and high powder activity, and has become a ceramic powder synthesis technology with broad development prospects.

Technical solutions

A low-temperature synthesis of rare earth hafnium salt high-entropy ceramic powder is characterized in that: the chemical formula of the rare earth hafnium salt high-entropy ceramic is (5RE _0.2 ) ₂ Hf ₂ O ₇ , wherein the rare earth element RE=La, Ce, Nd, Pr, Sm, Eu; powder particles as small as 100nm, with pyrochlore structure characteristics.

A preparation method for the low-temperature synthesis of rare earth hafnium salt high-entropy ceramic powder is characterized in that the steps are as follows:

Step 1. Preparation of hafnium nitrate solution: Dissolve hafnium tetrachloride powder in deionized water and stir well; drop excess ammonia water into the solution, and react for half an hour to obtain a white flocculent precipitate; The precipitation is repeatedly left to stand and clean for 4 to 5 times, then the beaker containing the white precipitate is placed in a water bath constant temperature magnetic stirrer with a temperature of 50 to 80 °C, excess concentrated nitric acid is added, and heated while stirring, until a clear solution is obtained;

Step 2: Weigh the hydrated rare earth nitrate according to the molar ratio of hafnium element and rare earth element as 1:1, and add rare earth element RE (NO ₃ containing five elements in the same molar ratio to the hafnium nitrate solution obtained in step 1) ) ₃ ; According to the principle of valence balance of redox reaction, add a burning agent to the mixed solution; put the beaker containing the mixed solution in a water bath constant temperature magnetic stirrer with a temperature of 70 to 90 ° C, and stir while heating until the solution is clear, At the same time, adjust the pH value of the solution to 1-5; the hydrated rare earth nitrate RE(NO ₃ ) ₃ ·xH ₂ O _, RE=La, Ce, Nd, Pr, Sm, Eu;

Step 3: Heat the preheated solution prepared in Step 2 at a combustion reaction temperature of 400 to 600 ° C for 0.5 to 1 h. After the solvent is completely evaporated to dryness, the remaining colloidal substance undergoes a violent combustion reaction to form a fluffy Powder; the obtained powder is subjected to high temperature heat treatment at 800-1200°C for 1-3 hours, and after removing excess carbon residue, high-purity rare earth hafnium salt high-entropy ceramic powder with good crystallinity is obtained.

The hydrated rare earth nitrate (RE(NO ₃ ) ₃ .xH ₂ O) includes: hydrated lanthanum nitrate La(NO ₃ ) ₃ .xH ₂ O, Liuhe cerium nitrate Ce(NO ₃ ) ₃ .6H ₂ O, Liuhe Water rubidium nitrate Nd(NO ₃ ) ₃ ·6H ₂ O, Liuhe water praseodymium nitrate Pr(NO ₃ ) ₃ ·6H ₂ O, Liuhe water samarium nitrate Sm(NO ₃ ) ₃ ·6H ₂ O and Liuhe water europium nitrate Eu( NO ₃ ) ₃ ·6H ₂ O, the above-mentioned hydrated rare earth nitrates are all in molar ratio, and the ratio of five optional rare earth nitrates is 1:1:1:1:1.

The combustion agent is urea CO(NH ₂ ) ₂ , the purity is analytically pure, and the ratio of hafnium tetrachloride to urea is 1:1.5-3 in terms of mass ratio.

beneficial effect

The invention proposes a low-temperature synthesis of rare earth hafnium salt high-entropy ceramic powder and a preparation method. The chemical formula of the rare earth hafnium salt high-entropy ceramic is (5RE _0.2 ) ₂ Hf ₂ O ₇ , wherein the rare earth element RE=La, Ce, Nd, Pr, Sm, Eu. The specific preparation process of the present invention is as follows: using hafnium tetrachloride (HfCl ₄ ) and hydrated rare earth nitrate (RE(NO ₃ ) ₃ xH ₂ O) as raw materials, selecting urea as a combustion agent, mixing through solutions, and mixing in an air atmosphere Under the condition of low temperature and low temperature, it burns to form fluffy powder. After high temperature decarbonization treatment, high purity (5RE _0.2 ) ₂ Hf ₂ O ₇ powder is obtained. The method has the advantages of high energy ball milling, spray pyrolysis and co-precipitation and other oxide high-entropy ceramic synthesis methods, and has the advantages of low synthesis temperature, simple operation and fast preparation speed.

The main features of the preparation of (5RE _0.2 ) ₂ Hf ₂ O ₇ powder by the present invention are: because the precursor exists in the form of a solution, the process of high-energy ball-milling and mixing is omitted, and the problem of time-consuming energy consumption is overcome. By introducing the burning agent urea, the invention can trigger a violent redox reaction in the solution under low temperature conditions, can simply and quickly synthesize the required ceramic powder, and solves the problems of high energy consumption and long production cycle existing in the current preparation process. , high equipment requirements and complex processes and other shortcomings. In addition, the powder produced by the invention is fluffy and difficult to agglomerate, the particles are small, the size powder is uniform, and the powder activity is high. Fig. 1 is a high-magnification topography of the synthesized (5RE _0.2 ) ₂ Hf ₂ O ₇ powder. It can be seen from Fig. 1 that the ceramic powder prepared by the present invention has small particles (about 100 nm) and uniform distribution; Figs. 2 and 3 For the XRD pattern and high-resolution TEM image of the synthesized (5RE _0.2 ) ₂ Hf ₂ O ₇ powder, it can be seen from FIGS. 2 and 3 that the ceramic powder prepared by the present invention has obvious pyrochlore structure characteristics.

Description of drawings

Figure 1 shows the high magnification topography of the synthesized (5RE _0.2 ) ₂ Hf ₂ O ₇ powder

Figure 2 is the XRD pattern of the synthesized (5RE _0.2 ) ₂ Hf ₂ O ₇ powder

Figure 3 is a high-resolution TEM image of the synthesized (5RE0.2)2Hf2O7 powder

Detailed ways

The present invention will now be further described in conjunction with the embodiments and accompanying drawings:

The concrete process of the present invention is:

Step 1: Preparation of hafnium nitrate solution: Weigh a certain mass of hafnium tetrachloride powder and dissolve it in deionized water, after fully stirring; drop excess ammonia water into the solution, and react for half an hour to obtain a white flocculent precipitate; The obtained white precipitate was repeatedly left to stand for cleaning 4 to 5 times, and then the beaker containing the white precipitate was placed in a water bath constant temperature magnetic stirrer with a temperature of 50 to 80 ° C, and excess concentrated nitric acid was added, and heated while stirring, until obtained. clear solution.

Step 2: To the hafnium nitrate solution obtained in Step 1, add hydrated rare earth element nitrate (RE(NO ₃ ) ₃ ·xH ₂ O, RE=La, Ce, Nd, Pr, Sm) with the same molar ratio of five elements , Eu), the molar ratio of the total amount of rare earth elements required to the hafnium element is 1:1; according to the principle of valence balance of the redox reaction, 1 to 1.5 times the calculated amount of urea is added to the mixed solution as a combustion agent. Put the beaker containing the mixed solution in a water bath constant temperature magnetic stirrer with a temperature of 70-90°C, stir while heating, until the solution is clear, and adjust the pH value of the solution to 1-5 at the same time.

Step 3: Place the preheated beaker containing the solution prepared in Step 2 on a flat-panel heater with a temperature of 400-600°C for 0.5-1h. During the heating process, the solution undergoes a violent chemical reaction and generates a large amount of water vapor. After the solvent is completely evaporated to dryness, the remaining colloidal material undergoes a violent combustion reaction to form a fluffy powder; the obtained powder is heat treated at a high temperature of 800-1200 °C for 1-3 hours, and after removing excess carbon residue, a good crystallinity can be obtained. High-purity rare earth hafnate high-entropy ceramic ((5RE _0.2 ) ₂ Hf ₂ O ₇ ) powder.

Example 1:

In this example, a combustion method is used to prepare rare earth hafnium salt high-entropy ceramic ((La _0.2 Ce _0.2 Pr _0.2 Sm _0.2 Eu _0.2 ) ₂ Hf ₂ O ₇ ) powder.

Step 1: Weigh a certain mass of hafnium tetrachloride powder, dissolve it in deionized water, and stir it thoroughly; drop excess ammonia water into the solution, and react for half an hour to obtain a white flocculent precipitate; repeat the obtained white precipitate Let stand for cleaning for 4 to 5 times, then place the beaker containing the white precipitate in a water bath constant temperature magnetic stirrer with a temperature of 50 to 80 °C, add excess concentrated nitric acid, and stir while heating until a clear solution is obtained.

Step 2: To the obtained solution, add hydrated lanthanum nitrate (La(NO ₃ ) ₃ ·xH ₂ O), hexahydrate cerium nitrate (Ce(NO ₃ ) ₃ ·6H ₂ O) with the same molar ratio of rare earth elements, Praseodymium nitrate in Liuheshui (Pr(NO ₃ ) ₃ ·6H ₂ O), Samarium nitrate in Liuheshui (Sm(NO ₃ ) ₃ ·6H ₂ O) and Europium nitrate in Liuheshui (Eu(NO ₃ ) ₃ ·6H ₂ O) , the total amount of rare earth elements required and the molar ratio of hafnium element are 1:1; according to the principle of valence balance of redox reaction, 1-1.5 times the calculated amount of urea is added to the mixed solution as a combustion agent, and the mixed solution is filled with mixed solution. The beaker of the solution is placed in a water bath constant temperature magnetic stirrer with a temperature of 70-90°C, and stirring is performed while heating until the solution is clear, and the pH value of the solution is adjusted to 1-5 at the same time.

Step 3: Heat the beaker containing the prepared mixed solution on a flat-plate heater with a temperature of 400-600°C. After the combustion reaction, a yellow-brown fluffy powder is obtained, and the obtained powder is heated at a high temperature of 800-1200°C After heat treatment to remove excess carbon residue, high-purity (La _0.2 Ce _0.2 Pr _0.2 Sm _0.2 Eu _0.2 ) ₂ Hf ₂ O ₇ powder with good crystallinity can be obtained.

Example 2:

In this example, the combustion method is used to prepare rare earth hafnium salt high-entropy ceramic ((La _0.2 Nd _0.2 Pr _0.2 Sm _0.2 Eu _0.2 ) ₂ Hf ₂ O ₇ ) powder.

Step 1: Weigh a certain mass of hafnium tetrachloride powder, dissolve it in deionized water, and stir it thoroughly; drop excess ammonia water into the solution, and react for half an hour to obtain a white flocculent precipitate; repeat the obtained white precipitate Let stand for cleaning for 4 to 5 times, then place the beaker containing the white precipitate in a water bath constant temperature magnetic stirrer with a temperature of 50 to 80 °C, add excess concentrated nitric acid, and stir while heating until a clear solution is obtained.

Step 2: To the obtained solution, add lanthanum nitrate (La(NO ₃ ) ₃ ·6H ₂ O) and rubidium nitrate (Nd(NO ₃ ) ₃ ·6H ₂ O) with the same molar ratio of rare earth elements , Liuheshui praseodymium nitrate (Pr(NO ₃ ) ₃ ·6H ₂ O), Liuheshui samarium nitrate (Sm(NO ₃ ) ₃ ·6H ₂ O) and Liuheshui europium nitrate (Eu(NO ₃ ) ₃ ·6H ₂ O) ), the molar ratio of the total amount of rare earth elements required to the hafnium element is 1:1; according to the principle of valence balance in the redox reaction, 1.2 to 1.8 times the calculated amount of urea is added to the mixed solution as a combustion agent. The beaker of the mixed solution is placed in a water bath constant temperature magnetic stirrer with a temperature of 70-90°C, and the solution is stirred while heating until the solution is clear, and the pH value of the solution is adjusted to 1-5 at the same time.

Step 3: Place the beaker containing the prepared mixed solution on a flat-panel heater with a temperature of 400-600°C for 0.5-1h, and after the combustion reaction, obtain a yellow-brown fluffy powder, and obtain a powder with a temperature of 800-600°C. High-temperature heat treatment at 1200℃ for 1-3h, after removing excess carbon residue, high-purity (La _0.2 Nd _0.2 Pr _0.2 Sm _0.2 Eu _0.2 ) ₂ Hf ₂ O ₇ powder with good crystallinity can be obtained.

Example 3:

In this example, the combustion method is used to prepare rare earth hafnium salt high-entropy ceramic ((La _0.2 Ce _0.2 Nd _0.2 Sm _0.2 Eu _0.2 ) ₂ Hf ₂ O ₇ ) powder.

Step 1: Weigh a certain mass of hafnium tetrachloride powder, dissolve it in deionized water, and stir it thoroughly; drop excess ammonia water into the solution, and react for half an hour to obtain a white flocculent precipitate; repeat the obtained white precipitate Let stand for cleaning for 4 to 5 times, then place the beaker containing the white precipitate in a water bath constant temperature magnetic stirrer with a temperature of 50 to 80 °C, add excess concentrated nitric acid, and stir while heating until a clear solution is obtained.

Step 2: To the obtained solution, add hydrated lanthanum nitrate (La(NO ₃ ) ₃ ·xH ₂ O), hexahydrate cerium nitrate (Ce(NO ₃ ) ₃ ·6H ₂ O) with the same molar ratio of rare earth elements, Liuheshui rubidium nitrate (Nd(NO ₃ ) ₃ ·6H ₂ O), Liuheshui samarium nitrate (Sm(NO ₃ ) ₃ ·6H ₂ O) and Liuheshui europium nitrate (Eu(NO ₃ ) ₃ ·6H ₂ O) , the total amount of rare earth elements required and the molar ratio of hafnium element are 1:1; according to the principle of valence balance of redox reaction, 1-1.5 times the calculated amount of urea is added to the mixed solution as a combustion agent, and the mixed solution is filled with mixed The beaker of the solution is placed in a constant temperature magnetic stirrer in a water bath with a temperature of 70-90°C, and stirring is performed while heating until the solution is clear, and the pH value of the solution is adjusted to 1-5 at the same time.

Step 3: The beaker containing the prepared mixed solution is placed on a flat-plate heater with a temperature of 400-600°C for 0.5-1h, and after combustion reaction, fluffy powder is obtained, and the obtained powder is heated at a high temperature of 800-1200°C After heat treatment for 1-3 hours, after removing excess carbon residue, high-purity (La _0.2 Ce _0.2 Nd _0.2 Sm _0.2 Eu _0.2 ) ₂ Hf ₂ O ₇ powder with good crystallinity can be obtained.

Example 4:

In this example, the combustion method is used to prepare rare earth hafnium salt high-entropy ceramic ((La _0.2 Ce _0.2 Nd _0.2 Pr _0.2 Eu _0.2 ) ₂ Hf ₂ O ₇ ) powder.

Step 1: Weigh a certain mass of hafnium tetrachloride powder, dissolve it in deionized water, and stir it thoroughly; drop excess ammonia water into the solution, and react for half an hour to obtain a white flocculent precipitate; repeat the obtained white precipitate Let stand for cleaning for 4 to 5 times, then place the beaker containing the white precipitate in a water bath constant temperature magnetic stirrer with a temperature of 50 to 80 °C, add excess concentrated nitric acid, and stir while heating until a clear solution is obtained.

Step 2: To the obtained solution, add hydrated lanthanum nitrate (La(NO ₃ ) ₃ ·xH ₂ O), hexahydrate cerium nitrate (Ce(NO ₃ ) ₃ ·6H ₂ O) with the same molar ratio of rare earth elements, Liuheshui rubidium nitrate (Nd(NO ₃ ) ₃ ·6H ₂ O), Liuheshui praseodymium nitrate (Pr(NO ₃ ) ₃ ·6H ₂ O) and Liuheshui europium nitrate (Eu(NO ₃ ) ₃ ·6H ₂ O) , the total amount of rare earth elements required and the molar ratio of hafnium element are 1:1; according to the principle of valence balance of redox reaction, 1-1.5 times the calculated amount of urea is added to the mixed solution as a combustion agent, and the mixed solution is filled with mixed The beaker of the solution is placed in a constant temperature magnetic stirrer in a water bath with a temperature of 70-90°C, and stirring is performed while heating until the solution is clear, and the pH value of the solution is adjusted to 1-5 at the same time.

Step 3: The beaker containing the prepared mixed solution is placed on a flat-plate heater with a temperature of 400-600°C for 0.5-1h, and after combustion reaction, fluffy powder is obtained, and the obtained powder is heated at a high temperature of 800-1200°C After heat treatment for 1-3 hours, after removing excess carbon residue, high-purity (La _0.2 Ce _0.2 Nd _0.2 Pr _0.2 Eu _0.2 ) ₂ Hf ₂ O ₇ powder with good crystallinity can be obtained.

Example 5:

In this example, the combustion method is used to prepare rare earth hafnium salt high-entropy ceramic ((La _0.2 Ce _0.2 Nd _0.2 Pr _0.2 Sm _0.2 ) ₂ Hf ₂ O ₇ ) powder.

Step 1: Weigh a certain mass of hafnium tetrachloride powder, dissolve it in deionized water, and stir it thoroughly; drop excess ammonia water into the solution, and react for half an hour to obtain a white flocculent precipitate; repeat the obtained white precipitate Let stand for cleaning for 4 to 5 times, then place the beaker containing the white precipitate in a water bath constant temperature magnetic stirrer with a temperature of 50 to 80 °C, add excess concentrated nitric acid, and stir while heating until a clear solution is obtained.

Step 2: To the obtained solution, add hydrated lanthanum nitrate (La(NO ₃ ) ₃ ·xH ₂ O), hexahydrate cerium nitrate (Ce(NO ₃ ) ₃ ·6H ₂ O) with the same molar ratio of rare earth elements, Liuheshui rubidium nitrate (Nd(NO ₃ ) ₃ ·6H ₂ O), Liuheshui praseodymium nitrate (Pr(NO ₃ ) ₃ ·6H ₂ O) and Liuheshui samarium nitrate (Sm(NO ₃ ) ₃ ·6H ₂ O) , the total amount of rare earth elements required and the molar ratio of hafnium element are 1:1; according to the principle of valence balance of redox reaction, 1-1.5 times the calculated amount of urea is added to the mixed solution as a combustion agent, and the mixed solution is filled with mixed solution. The beaker of the solution is placed in a constant temperature magnetic stirrer in a water bath with a temperature of 70-90°C, and stirring is performed while heating until the solution is clear, and the pH value of the solution is adjusted to 1-5 at the same time.

Step 3: Place the beaker containing the prepared mixed solution on a flat-panel heater with a temperature of 400-600°C for 0.5-1h, and after the combustion reaction, obtain a yellow-brown fluffy powder, and obtain a powder with a temperature of 800-600°C. High-temperature heat treatment at 1200°C for 1-3 hours, after removing excess carbon residue, high-purity (La _0.2 Ce _0.2 Nd _0.2 Pr _0.2 Sm _0.2 ) ₂ Hf ₂ O ₇ powder with good crystallinity can be obtained.

Claims (4)

1. a low-temperature synthesis of rare earth hafnium salt high-entropy ceramic powder, is characterized in that: rare earth hafnium salt high-entropy ceramic chemical formula is (5RE _0.2 ) ₂ Hf ₂ O ₇ , wherein rare earth element RE=La, Ce, Nd, Pr, Sm, Eu; powder particles as small as 100nm, with pyrochlore structure characteristics. 2. a preparation method of the described low temperature synthesis rare earth hafnium salt high entropy ceramic powder of claim 1, is characterized in that step is as follows: Step 1. Preparation of hafnium nitrate solution: Dissolve hafnium tetrachloride powder in deionized water and stir well; drop excess ammonia water into the solution, and react for half an hour to obtain a white flocculent precipitate; The precipitation is repeatedly left to stand and clean for 4 to 5 times, then the beaker containing the white precipitate is placed in a water bath constant temperature magnetic stirrer with a temperature of 50 to 80 °C, excess concentrated nitric acid is added, and heated while stirring, until a clear solution is obtained; Step 2: Weigh the hydrated rare earth nitrate according to the molar ratio of hafnium element and rare earth element as 1:1, and add rare earth element RE (NO ₃ containing five elements in the same molar ratio to the hafnium nitrate solution obtained in step 1) ) ₃ ; According to the principle of valence balance of redox reaction, add a burning agent to the mixed solution; put the beaker containing the mixed solution in a water bath constant temperature magnetic stirrer with a temperature of 70 to 90 ° C, and stir while heating until the solution is clear, At the same time, the pH value of the solution is adjusted to 1-5; the hydrated rare earth nitrate RE(NO ₃ ) ₃ ·xH ₂ O, RE=La, Ce, Nd, Pr, Sm, Eu; Step 3: Heat the preheated solution prepared in Step 2 at a combustion reaction temperature of 400 to 600 ° C for 0.5 to 1 h. After the solvent is completely evaporated to dryness, the remaining colloidal substance undergoes a violent combustion reaction to form a fluffy Powder; the obtained powder is subjected to high temperature heat treatment at 800-1200°C for 1-3 hours, and after removing excess carbon residue, high-purity rare earth hafnium salt high-entropy ceramic powder with good crystallinity is obtained. 3 . The method according to claim 2 , wherein the hydrated rare earth nitrate (RE(NO ₃ ) ₃ .xH ₂ O) comprises: hydrated lanthanum nitrate La(NO ₃ ) ₃ .xH ₂ O, hexahydrate Cerium nitrate Ce(NO ₃ ) ₃ · 6H ₂ O, rubidium nitrate Nd(NO ₃ ) ₃ · 6H ₂ O, Pr(NO ₃ ) ₃ · 6H ₂ O, samarium nitrate Sm( NO ₃ ) ₃ ·6H ₂ O and Hexahydrate Europium nitrate Eu(NO ₃ ) ₃ ·6H ₂ O, the above-mentioned hydrated rare earth nitrates are all in molar ratio, and the ratio of five optional rare earth nitrates is 1:1 :1:1:1. 4. The method according to claim 2, characterized in that: the combustion agent is urea CO(NH ₂ ) ₂ , the purity is analytically pure, and hafnium tetrachloride and urea are in mass ratio, and the ratio is 1:1.5～ 3.

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