Rare earth solid solutions, their preparation methods and uses

Abstract

This invention discloses a rare earth solid solution, its preparation method, and its uses. The rare earth solid solution has the following chemical composition: La a Ce b Sm c O x Wherein, a, b, c, and x are the molar proportions of La, Ce, Sm, and O, respectively; a:b:c = 0.8–1.5:1.5–2.5:0.1–1.4; x = (3a + 4b + 3c) / 2. The rare earth solid solution of this invention can be used in gypsum-based fire-retardant coatings for steel structures, effectively improving the solidification speed, bonding strength, and fire resistance limit of the fire-retardant coating.

Description

Technical Field

[0001] This invention relates to a rare earth solid solution, its preparation method and uses, and more particularly to a rare earth solid solution for improving the performance of gypsum-based fireproof coatings for steel structures, its preparation method and uses. Background Technology

[0002] Steel structures are one of the main structural forms used in buildings, but their fire resistance is poor, and they exhibit strength reduction and creep under high-temperature conditions. In the event of a fire, steel structures without fire protection measures are prone to large-scale collapse, causing significant personal injury and property damage. Therefore, scientific fire protection measures must be implemented for steel structures to minimize fire damage. Fire-retardant coatings for steel structures are widely used in steel structure buildings due to their advantages such as easy application, wide applicability, and low cost.

[0003] Non-intumescent fire-retardant coatings for steel structures commonly include cement-based and gypsum-based coatings. Cement-based coatings have high compressive strength but low adhesion to the protected structure, high dry density, and a significant increase in the weight of the steel structure. Furthermore, application of cement-based fire-retardant coatings requires temperatures above 0°C, making application impossible in northern winters. Gypsum-based fire-retardant coatings have a lower density than cement-based coatings, reducing structural load and offering better adhesion. However, gypsum-based coatings also suffer from slow setting, lower strength, and relatively lower fire resistance.

[0004] Literature reports fire-retardant coatings containing rare earth oxides as one component. For example, CN115403946A discloses a gypsum-based comprehensive modified steel structure fire-retardant coating and its preparation and application methods. This fire-retardant coating is composed of the following components by mass: 35-65 parts recycled α-high-strength gypsum, 5-15 parts sepiolite, 5-10 parts brucite fiber, 1-3 parts recycled waste polystyrene granules, 5-10 parts cenospheres, 10-20 parts perlite, 3-10 parts admixtures, 3-10 parts rare earth oxides, and 1-3 parts composite additives, and 80-120 parts tap water. However, the bonding strength of this gypsum-based fire-retardant coating remains relatively low. CN114790358A discloses a rare earth fireproof coating for building walls, comprising the following components in parts by weight: 8-12 parts of organosilicon modified alkyd resin, 4-6 parts of kaolin, 7-12 parts of propylene glycol, 8-12 parts of rare earth neodymium oxide, 12-17 parts of rare earth gadolinium oxide, 18-23 parts of silica aerogel suspension, 3-7 parts of stabilizer, 3-6 parts of moisture-proofing agent, 3-6 parts of preservative, 4-7 parts of nano titanium dioxide, 6-8 parts of nano magnesium aluminum silicate, and 30-40 parts of water.

[0005] Reports on rare earth solid solutions and their applications in fire-retardant coatings are still relatively few. CN115787138A discloses a low thermal conductivity insulating fiber felt and its preparation method. The fiber felt is woven from inorganic rare earth oxide nanofibers; the inorganic rare earth oxide nanofibers are inorganic rare earth oxide polynomial solid solutions, and the general chemical formula of the inorganic rare earth oxides is RE2O3. This patent document describes the application of rare earth oxide polynomial solid solutions to insulating fiber felts. Summary of the Invention

[0006] In view of this, one object of the present invention is to provide a rare earth solid solution that can be used to improve the performance of gypsum-based fire-retardant coatings for steel structures, including improving their bonding strength and fire resistance limit. Another object of the present invention is to provide a method for preparing the rare earth solid solution as described above. A further object of the present invention is to provide uses for the rare earth solid solution as described above. The present invention achieves the above objects using the following technical solutions.

[0007] On one hand, the present invention provides a rare earth solid solution for improving the performance of gypsum-based fire-retardant coatings for steel structures, wherein the rare earth solid solution has the following chemical composition: La a Ce b Sm c O x ,

[0008] Where a, b, c, and x are the molar parts of La, Ce, Sm, and O, respectively;

[0009] Where a:b:c = 0.8~1.5:1.5~2.5:0.1~1.4;

[0010] Where x = (3a + 4b + 3c) / 2.

[0011] According to the rare earth solid solution of the present invention, preferably, c≤a <b。

[0012] According to the rare earth solid solution of the present invention, preferably, the particle size of the rare earth solid solution is ≤5μm.

[0013] On the other hand, the present invention also provides a method for preparing rare earth solid solutions as described above, preferably comprising the following steps:

[0014] 1) Provide a mixed rare earth salt solution containing the corresponding amounts of lanthanum salt, cerium salt and samarium salt according to the molar parts of La, Ce and Sm in the chemical composition of the rare earth solid solution;

[0015] 2) The mixed rare earth salt solution and ammonium bicarbonate solution are added dropwise to ammonium chloride solution in a co-current manner. After the reaction is completed, solid-liquid separation is performed to obtain rare earth solid solution precursor.

[0016] 3) The rare earth solid solution precursor is washed with water, then dried and calcined to obtain the rare earth solid solution.

[0017] According to the preparation method of the present invention, preferably:

[0018] In step 1), the lanthanum salt is lanthanum chloride, the cerium salt is cerium chloride, and the samarium salt is samarium chloride;

[0019] In step 1), the concentration of rare earth ions in the mixed rare earth salt solution is 0.5–1.5 mol / L;

[0020] In step 2), the concentration of ammonium bicarbonate solution is 2–5 mol / L; the concentration of ammonium chloride solution is 1–2.5 mol / L.

[0021] According to the preparation method of the present invention, preferably, in step 2), during the parallel drop addition, the molar ratio of rare earth ions in the mixed rare earth salt solution to ammonium ions in the ammonium bicarbonate solution is controlled to be 1:3.3 to 3.6.

[0022] According to the preparation method of the present invention, preferably, in step 2), the volume of the ammonium chloride solution is 5-20% of the volume of the reaction vessel.

[0023] According to the preparation method of the present invention, preferably, in step 2), when the reaction is added dropwise in parallel flow, the temperature of the reaction system is less than or equal to 35°C; and when the reaction is added dropwise in parallel flow, the pH value of the reaction system is controlled to be 7.5 to 8.5.

[0024] According to the preparation method of the present invention, preferably, in step 3), the calcination temperature is 700-1000℃ and the calcination time is 3-8h.

[0025] Furthermore, the present invention also provides the use of a rare earth solid solution in improving the performance of gypsum-based fire-retardant coatings for steel structures, wherein the rare earth solid solution has the following chemical composition: La a Ce b Sm c O x ,

[0026] Where a, b, c, and x are the molar parts of La, Ce, Sm, and O, respectively;

[0027] Where a:b:c = 0.8~1.5:1.5~2.5:0.1~1.4;

[0028] Where x = (3a + 4b + 3c) / 2.

[0029] The rare earth solid solution of the present invention can be used to improve the performance of gypsum-based steel structure fireproof coatings, effectively increasing the setting speed of the fireproof coatings, enhancing the bonding strength and improving the fire resistance limit performance at the same time. The rare earth solid solution prepared by the preparation method of the present invention has a small particle size and good dispersion performance in gypsum-based steel structure fireproof coatings, which is more conducive to improving the performance of the fireproof coatings. In addition, by using the rare earth solid solution of the present invention, no other surfactants or dispersants need to be added. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a SEM diagram of the rare earth solid solution obtained in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0032] A rare earth solid solution provided by the present invention can be used to improve the performance of gypsum-based steel structure fireproof coatings. The rare earth solid solution has the following chemical composition: La a Ce b Sm c O x .

[0033] La is the lanthanum element, Ce is the cerium element, Sm is the samarium element, and O is the oxygen element.

[0034] a, b, c, and x are the molar fractions of La, Ce, Sm, and O respectively.

[0035] a < b, c < b. In some specific embodiments, c ≤ a < b. Wherein, x = (3a + 4b + 3c) / 2.

[0036] In some embodiments, a:b:c = 0.8 - 1.5:1.5 - 2.5:0.1 - 1.4; preferably, a:b:c = 0.8 - 1.2:1.8 - 2.2:0.1 - 1; more preferably, a:b:c = 1 - 1.1:2.0 - 2.1:0.2 - 1.

[0037] According to a specific embodiment of the present invention, a:b:c = 1:2:0.2 - 1.

[0038] The particle size of the rare earth solid solution ≤ 5 μm. Such a rare earth solid solution contains three rare earth elements of lanthanum, cerium, and samarium, has a small particle size, good dispersion performance in gypsum-based steel structure fireproof coatings, can effectively increase the setting speed of the fireproof coatings, and improve the bonding strength while improving the fire resistance performance.

[0039] The present invention also provides a method for preparing the rare earth solid solution as described above, the method comprising the following steps: (1) a mixing step; (2) a reaction and separation step; and (3) a drying and calcination step. These are described in detail below.

[0040] <Mixing Steps>

[0041] Provide a mixed rare earth salt solution containing the corresponding amounts of lanthanum salt, cerium salt, and samarium salt, according to the molar proportions of La, Ce, and Sm in the chemical composition of the rare earth solid solution.

[0042] In some implementations, according to the molar proportions of La, Ce, and Sm in the chemical composition of the rare earth solid solution, corresponding amounts of lanthanum salt solution, cerium salt solution, and samarium salt solution can be mixed to obtain a mixed rare earth salt solution.

[0043] In other embodiments, according to the molar proportions of La, Ce, and Sm in the chemical composition of the rare earth solid solution, the corresponding amounts of lanthanum salt, cerium salt, and samarium salt can be dissolved in a certain amount of water to obtain a mixed rare earth salt solution.

[0044] In this invention, the lanthanum salt can be selected from lanthanum chloride, lanthanum nitrate, or lanthanum sulfate, preferably lanthanum chloride. The cerium salt can be selected from cerium chloride, cerium nitrate, or cerium sulfate, preferably cerium chloride. The samarium salt can be selected from samarium chloride, samarium nitrate, or samarium sulfate, preferably samarium chloride.

[0045] The concentration of rare earth ions in the mixed rare earth salt solution can be 0.5 to 1.5 mol / L, for example, 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.3 mol / L, and 1.5 mol / L.

[0046] <Reaction and Separation Steps>

[0047] The mixed rare earth salt solution and ammonium bicarbonate solution were added dropwise to an ammonium chloride solution in a parallel flow to react. After the reaction was completed, solid-liquid separation was performed to obtain a rare earth solid solution precursor. This invention surprisingly reveals that the rare earth solid solution prepared in this way has advantages in improving the performance of gypsum-based fire-retardant coatings for steel structures.

[0048] The concentration of ammonium bicarbonate solution can be 2 to 5 mol / L, for example, 2 mol / L, 2.5 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, 4.5 mol / L, and 5 mol / L.

[0049] During the co-current dropwise addition, the molar ratio of rare earth ions in the mixed rare earth salt solution to ammonium ions in the ammonium bicarbonate solution is controlled to be 1:3.3 to 3.6, for example, 1:3.3, 1:3.4, 1:3.5, or 1:3.6. Preferably, it is 1:3.3 to 3.4.

[0050] When the reaction is added dropwise in parallel flow, the temperature of the reaction system is less than or equal to 35°C, preferably less than or equal to 30°C, and more preferably less than or equal to 25°C.

[0051] When adding the reaction solution dropwise in parallel, the pH of the reaction system is controlled to be between 7.5 and 8.5.

[0052] The concentration of the ammonium chloride solution can be 1–2.5 mol / L, for example, 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2.0 mol / L, 2.3 mol / L, or 2.5 mol / L. The volume of the ammonium chloride solution can be 5–20% of the volume of the reaction vessel, preferably 10–20%, and more preferably 10–15%.

[0053] In this invention, after the addition is complete, the reaction needs to be stirred for 20 to 50 minutes, preferably 30 to 40 minutes.

[0054] After the reaction is complete, the reaction solution is separated into solid and liquid phases to obtain a solid, which is a rare earth solid solution precursor. Solid-liquid separation can be achieved by filtration or centrifugation, with filtration being preferred.

[0055] This invention proposes a method to simultaneously co-precipitate lanthanum, cerium, and samarium in a rare earth solid solution by mixing lanthanum, cerium, and samarium salts in specific proportions and adding them dropwise in a parallel flow. The ratio of rare earth ions to ammonium ions in the ammonium bicarbonate solution is controlled, with an excess of 10-20% ammonium ions. This maintains the pH of the reaction system at 7.5-8.5, while simultaneously controlling the reaction temperature to reduce the reactivity of the materials. In this low-temperature, weakly alkaline environment, lanthanum, cerium, and samarium can be co-precipitated, providing a precursor with small particle size, uniform morphology, and uniform elemental composition within the monomer particles for subsequent solid solution preparation. This solves the problem of the inability to simultaneously precipitate lanthanum, cerium, and samarium. Using ammonium chloride as a substrate also provides a stable environment for the reaction. The resulting rare earth solid solution contains cerium, which increases the setting speed of fire-retardant coatings; lanthanum, which improves the fire resistance limit of fire-retardant coatings; and samarium, which enhances the adhesion strength of fire-retardant coatings.

[0056] <Drying and Scorching Steps>

[0057] The rare earth solid solution precursor obtained above was washed with water, then dried and calcined to obtain the rare earth solid solution.

[0058] In this invention, the rare earth solid solution precursor obtained above can be washed with deionized water, distilled water or purified water.

[0059] The drying temperature can be 50-80℃, and the drying time can be 2-10 hours.

[0060] The calcination temperature is 700–1000℃, for example, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, or 1000℃. 800–1000℃ is preferred. The calcination time can be 2–8 hours.

[0061] According to a specific embodiment of the present invention, the method for preparing rare earth solid solutions includes the following steps:

[0062] 1) According to the mole fractions of La, Ce, and Sm in the chemical composition of rare earth solid solutions, the corresponding amounts of lanthanum salt solution, cerium salt solution, and samarium salt solution are mixed to obtain a mixed rare earth salt solution;

[0063] 2) At a temperature of 25°C or less, the mixed rare earth salt solution and ammonium bicarbonate solution are added dropwise to an ammonium chloride solution in a parallel flow to react. After the reaction is completed, the solid and liquid are separated to obtain a rare earth solid solution precursor. During the parallel flow dropwise addition, the molar ratio of rare earth ions in the mixed rare earth salt solution to ammonium ions in the ammonium bicarbonate solution is controlled to be 1:3.3 to 3.6.

[0064] 3) The rare earth solid solution precursor is washed with water, then dried and calcined to obtain the rare earth solid solution.

[0065] <Application>

[0066] This invention also provides the use of a rare earth solid solution in improving the performance of gypsum-based fire-retardant coatings for steel structures, the rare earth solid solution having the following chemical composition: La a Ce b Sm c O x ,

[0067] Where a, b, c, and x are the mole fractions of La, Ce, Sm, and O, respectively;

[0068] Where a:b:c = 0.8~1.5:1.5~2.5:0.1~1.4;

[0069] Where x = (3a + 4b + 3c) / 2. This is beneficial for improving the bonding strength and fire resistance limit of fire-retardant coatings, as well as for increasing the solidification speed of fire-retardant coatings. A detailed introduction to rare earth solid solutions has been provided above and will not be repeated here.

[0070] In use, the rare earth solid solution of the present invention can be added to the gypsum-based fire-retardant coating for steel structures and mixed evenly to obtain the improved gypsum-based fire-retardant coating for steel structures. Then, the improved gypsum-based fire-retardant coating for steel structures is sprayed onto a sample. The amount of rare earth solid solution added is: the mass ratio of rare earth solid solution to gypsum-based fire-retardant coating for steel structures is 5-10:100, for example, 6:100.

[0071] There are no particular restrictions on the source of gypsum-based fire-retardant coatings for steel structures; commercially available coatings can be used, or you can formulate your own according to the recipe.

[0072] The test methods for the following embodiments and comparative examples are described below:

[0073] SEM: Tests were performed using a Zeiss Sigma 500 electron microscope.

[0074] Particle size d 50 The test was conducted using a laser particle size analyzer (model: Bettersize2600) from Dandong Bettersize, with water as the dispersion medium.

[0075] Fire retardant coating performance test: Tested according to GB14907-2018.

[0076] Example 1

[0077] Preparation of rare earth solid solutions La1Ce2Sm 0.2 O 5.8 The steps are as follows:

[0078] Lanthanum chloride solution, cerium chloride solution, and samarium chloride solution were mixed in a molar ratio of La, Ce, and Sm of 1:2:0.2 to obtain a mixed rare earth salt solution; wherein the total concentration of rare earth ions in the mixed rare earth salt solution was 0.5 mol / L.

[0079] 1000 mL of a mixed rare earth salt solution and 900 mL of a 2 mol / L ammonium bicarbonate solution, prepared according to the above steps, were added dropwise in parallel to 150 mL of a 1 mol / L ammonium chloride solution as the base liquid. The volume of the reaction vessel was 3 L. After the reaction, solid-liquid separation was performed to obtain the rare earth solid solution precursor. During the parallel dropwise addition, the molar ratio of rare earth ions in the mixed rare earth solution to ammonium ions in the ammonium bicarbonate solution was controlled at 1:3.6. The temperature of the reaction system was 25 °C, and the pH value of the reaction system was 8.5.

[0080] The rare earth solid solution precursor was washed with deionized water and then dried at 80°C for 2 hours. The dried precursor was then calcined at 700°C for 2 hours to obtain the rare earth solid solution. The particle size d of the obtained rare earth solid solution is... 50 The size is 3.4 μm, and its SEM image is shown below. Figure 1 .

[0081] Example 2

[0082] Preparation of rare earth solid solutions La1Ce2Sm 0.5 O 6.25 The steps are as follows:

[0083] Lanthanum chloride solution, cerium chloride solution, and samarium chloride solution were mixed in a molar ratio of La, Ce, and Sm of 1:2:0.5 to obtain a mixed rare earth salt solution; wherein the total concentration of rare earth ions in the mixed rare earth salt solution was 1 mol / L.

[0084] 1000 mL of a mixed rare earth salt solution and 1133 mL of a 3 mol / L ammonium bicarbonate solution, prepared according to the above steps, were added dropwise in parallel to 300 mL of a 1.5 mol / L ammonium chloride solution as the base liquid. The volume of the reaction vessel was 3 L. After the reaction, solid-liquid separation was performed to obtain the rare earth solid solution precursor. During the parallel dropwise addition, the molar ratio of rare earth ions in the mixed rare earth solution to ammonium ions in the ammonium bicarbonate solution was controlled at 1:3.4. The temperature of the reaction system was 20 °C, and the pH value of the reaction system was 8.0.

[0085] The rare earth solid solution precursor was washed with deionized water and then dried at 70°C for 5 hours. The dried precursor was then calcined at 800°C for 6 hours to obtain the rare earth solid solution. The particle size d of the obtained rare earth solid solution is... 50 It is 4.2 μm.

[0086] Example 3

[0087] Preparation of rare earth solid solution La1Ce2Sm1O7. The steps are as follows:

[0088] Lanthanum chloride solution, cerium chloride solution, and samarium chloride solution were mixed in a molar ratio of La, Ce, and Sm of 1:2:1 to obtain a mixed rare earth salt solution; wherein the total concentration of rare earth ions in the mixed rare earth salt solution was 1.5 mol / L.

[0089] 1000 mL of a mixed rare earth salt solution and 990 mL of a 5 mol / L ammonium bicarbonate solution, prepared according to the above steps, were added dropwise in parallel to 600 mL of a 2.5 mol / L ammonium chloride solution as the base liquid. The volume of the reaction vessel was 3 L. After the reaction, solid-liquid separation was performed to obtain the rare earth solid solution precursor. During the parallel dropwise addition, the molar ratio of rare earth ions in the mixed rare earth solution to ammonium ions in the ammonium bicarbonate solution was controlled at 1:3.3. The temperature of the reaction system was 18 °C, and the pH value of the reaction system was 7.5.

[0090] The rare earth solid solution precursor was washed with deionized water and then dried at 50°C for 6 hours. The dried precursor was then calcined at 1000°C for 2 hours to obtain the rare earth solid solution. The particle size d of the obtained rare earth solid solution is... 50 It is 5.0 μm.

[0091] Comparative Example 1

[0092] The only difference from Example 1 is that the ammonium chloride solution used as the substrate is replaced with water. The particle size d of the resulting rare earth solid solution is... 50 It is 12μm.

[0093] Application Example 1

[0094] The rare earth solid solution obtained in Example 1 was mixed with a gypsum-based fire-retardant coating for steel structures to obtain an improved gypsum-based fire-retardant coating for steel structures. The mass ratio of the rare earth solid solution to the gypsum-based fire-retardant coating for steel structures was 6:100. The improved gypsum-based fire-retardant coating for steel structures was sprayed onto samples for fire resistance testing. The gypsum-based fire-retardant coating for steel structures was formed by mixing 60 parts gypsum, 10 parts sepiolite, 5 parts magnesium hydroxide, 5 parts polystyrene particles, 10 parts cenospheres, and 10 parts perlite, then adding 100 parts water and stirring until homogeneous.

[0095] The results of the fire resistance test are shown in Table 1.

[0096] Application Example 2

[0097] The only difference from Application Example 1 is that the rare earth solid solution used was prepared in Example 2. The results of the fire resistance test are shown in Table 1.

[0098] Application Example 3

[0099] The only difference from Application Example 1 is that the rare earth solid solution used was prepared in Example 3. The results of the fire resistance test are shown in Table 1.

[0100] Application Comparison Example 1

[0101] The only difference from Application Example 1 is that the rare earth solid solution used was replaced with a mixture of lanthanum oxide, cerium oxide, and samarium oxide (in which the molar ratio of lanthanum oxide, cerium oxide, and samarium oxide was 1:2:0.2; lanthanum oxide, cerium oxide, and samarium oxide were commercially available). The results of the refractory performance test are shown in Table 1.

[0102] Application Comparison Example 2

[0103] The only difference from Application Example 1 is that the rare earth solid solution used was prepared in Comparative Example 1. The results of the fire resistance test are shown in Table 1.

[0104] Table 1

[0105]

[0106] As shown in the table, the gypsum-based fire-retardant coating with the addition of the lanthanum-cerium-samarium rare earth solid solution of the present invention exhibits significantly improved bonding strength and fire resistance limit, and significantly shortened drying time (i.e., increased solidification speed) compared to the coating with the addition of a mixture of lanthanum-cerium-samarium oxides. This indicates that the rare earth solid solution of the present invention can effectively improve the performance of the gypsum-based fire-retardant coating.

[0107] The rare earth solid solution prepared by the method of the present invention has advantages in improving the performance of gypsum-based fireproof coatings for steel structures.

[0108] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. The use of a rare earth solid solution in improving the adhesion strength of gypsum-based fire-retardant coatings for steel structures, characterized in that, The rare earth solid solution has the following chemical composition: La a Ce b Sm c O x , Where a, b, c, and x are the molar parts of La, Ce, Sm, and O, respectively; Where a:b:c = 0.8~1.5:1.5~2.5:0.1~1.4; Where x = (3a + 4b + 3c) / 2.

2. The use according to claim 1, characterized in that, c≤a <b。 3. The use according to claim 1, characterized in that, The particle size of the rare earth solid solution is ≤5μm.

4. The use according to claim 1, characterized in that, Rare earth solid solutions are prepared by the following steps: 1) Provide a mixed rare earth salt solution containing the corresponding amounts of lanthanum salt, cerium salt and samarium salt according to the molar parts of La, Ce and Sm in the chemical composition of the rare earth solid solution; 2) The mixed rare earth salt solution and ammonium bicarbonate solution are added dropwise to ammonium chloride solution in a co-current manner. After the reaction is completed, solid-liquid separation is performed to obtain rare earth solid solution precursor. 3) The rare earth solid solution precursor is washed with water, then dried and calcined to obtain the rare earth solid solution.

5. The use according to claim 4, characterized in that: In step 1), the lanthanum salt is lanthanum chloride, the cerium salt is cerium chloride, and the samarium salt is samarium chloride; In step 1), the concentration of rare earth ions in the mixed rare earth salt solution is 0.5–1.5 mol / L; In step 2), the concentration of ammonium bicarbonate solution is 2–5 mol / L; the concentration of ammonium chloride solution is 1–2.5 mol / L.

6. The use according to claim 4, characterized in that, In step 2), during the parallel droplet addition, the molar ratio of rare earth ions in the mixed rare earth salt solution to ammonium ions in the ammonium bicarbonate solution is controlled to be 1:3.3 to 3.

6.

7. The use according to claim 4, characterized in that, In step 2), the volume of the ammonium chloride solution is 5-20% of the volume of the reaction vessel.

8. The use according to claim 4, characterized in that, In step 2), when adding the reaction mixture in parallel flow, the temperature of the reaction system is less than or equal to 35°C; when adding the reaction mixture in parallel flow, the pH value of the reaction system is controlled to be 7.5 to 8.

5.

9. The use according to claim 4, characterized in that, In step 3), the calcination temperature is 700–1000℃ and the calcination time is 3–8 hours.

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