Preparation method of plate-like rare earth oxides

Abstract

This invention discloses a method for preparing plate-like rare earth oxides. A solution containing a carboxyl group is added to a mixture of a monocarboxylate containing a rare earth metal and water for reaction. Dynamic aging yields a plate-like precursor, which is then calcined to obtain the rare earth oxide. This method is industrially scalable, producing plate-like rare earth oxides with a thickness of less than 200 nm and a small particle size. These plate-like rare earth oxides are beneficial for improving the rigidity and adhesion of downstream products, showing promising application prospects in catalysts, coatings, functional ceramics, and functional fibers.

Description

Technical Field

[0001] This invention relates to a method for preparing flake-shaped rare earth oxides. Background Technology

[0002] Rare earth oxides are a class of widely used compounds. In the field of photocatalysis, cerium dioxide with different particle sizes and specific surface areas can be used as catalysts and are widely applied. Plate-like rare earth compounds possess a unique two-dimensional planar structure, exhibiting a variety of excellent properties, such as strong adhesion, excellent shielding performance, and light reflection capabilities.

[0003] CN102936030A discloses a method for producing monodisperse rare earth oxide ultrathin nanosheets. The method involves adding a mineralizing agent and rare earth acetate to anhydrous ethanol, stirring magnetically at room temperature until completely dissolved, obtaining a clear solution. Oleic acid, oleylamine, and 1-octadecene are then added to the clear solution and mixed with magnetic stirring. The anhydrous ethanol is removed, and the solution is heated in N2 to remove moisture, followed by heating to 310–360°C for further reaction. The reaction product is washed, centrifuged to obtain a filter cake, washed again, and then dispersed in n-hexane to obtain rare earth oxide nanomaterials. This method requires the use of large amounts of flammable and volatile organic solvents, resulting in high costs. Large-scale preparation can easily cause environmental pollution, and long-term exposure may affect the health of operators.

[0004] CN112919523A discloses a method for producing hexagonal plate-like rare earth cerium oxide. The method involves mixing an aqueous solution of sodium oleate and an aqueous solution of cerium nitrate or cerium chloride at room temperature to form a hydrophobic precipitate. Ammonia is then added dropwise to the mixed solution to dissolve the hydrophobic precipitate, forming a hydrophilic precipitate. A hydrothermal reaction is then carried out under sealed conditions. After the reaction is complete, the mixture is cooled, centrifuged, filtered, and the solid is washed with cyclohexane and dried to obtain a precursor. The precursor is then calcined to obtain hexagonal plate-like rare earth cerium oxide. This method requires a long reaction time under pressurized hydrothermal conditions. The precursor has a small particle size, necessitating centrifugal separation, making large-scale production difficult.

[0005] CN115594211A discloses a method for producing lanthanide metal oxide nanosheets. The method involves mixing lanthanide metals and sodium citrate at a molar ratio of 1–100:10, adding ultrapure water, and ultrasonically treating the mixture. The mixture is then centrifuged, washed with water, and freeze-dried to obtain a white powder. Finally, it is calcined at 500–1000°C under an inert gas atmosphere to obtain a black powder. This method requires centrifugation and freeze-drying, making it difficult to scale up production.

[0006] CN101780970A discloses a method for preparing large-particle rare earth oxides. A prepared rare earth salt solution is added to an oxalic acid solution with adjusted acidity, and precipitation is achieved by stirring to obtain rare earth oxalate precipitate. Stirring is stopped, and the precipitate is allowed to stand and age. The aged precipitate is then filtered, washed, and calcined to obtain a large-particle rare earth oxide product. CN1629074A discloses a method for preparing large-particle rare earth oxides. An ammonium-containing additive is added to a rare earth salt solution, followed by the addition of an oxalic acid solution for precipitation. The resulting precipitate is filtered, separated, dried, and calcined to obtain a particle size D. 50 Large rare earth oxide particles with a hexahedral shape greater than 15 μm. The above method cannot obtain plate-like rare earth oxides. Summary of the Invention

[0007] In view of this, one object of the present invention is to provide a method for preparing rare earth oxides, which can produce flake-like rare earth oxides. Furthermore, the rare earth oxides obtained by this method have a small particle size. Even further, this preparation method does not require the use of organic solvents, surfactants, or dispersants, and the production method can be industrialized.

[0008] This invention provides a method for preparing rare earth oxides, comprising the following steps:

[0009] A solution of a carboxyl-containing substance is added to a mixture of a monocarboxylic acid salt containing rare earth metals and water for reaction. Dynamic aging yields a sheet-like precursor, which is then calcined to obtain rare earth oxides.

[0010] The carboxyl-containing substance is selected from one or more dicarboxylic acids or dicarboxylic acid salts, and the rare earth oxide has a plate-like structure.

[0011] According to the preparation method of the present invention, preferably, the preparation method does not require the use of organic solvents, surfactants and dispersants.

[0012] According to the preparation method of the present invention, preferably, the dicarboxylic acid is oxalic acid; the dicarboxylic acid salt is an alkali metal oxalate or ammonium oxalate.

[0013] According to the preparation method of the present invention, preferably, the molar ratio of rare earth ions to oxalate ions in the reaction system is 1:1.55 to 1.62.

[0014] According to the preparation method of the present invention, preferably, the monocarboxylate of the rare earth metal is selected from one or more of rare earth formate, rare earth acetate, and rare earth propionate.

[0015] According to the preparation method of the present invention, preferably, the mass ratio of the monocarboxylate of rare earth metal (calculated as rare earth oxide) to the volume ratio of water in the mixture is (40-140) g: 1 L.

[0016] According to the preparation method of the present invention, preferably, the reaction temperature is 40-80°C; the time for adding the solution of the carboxyl-containing substance to the mixture of the monocarboxylic acid salt containing rare earth metal and water is 15-50 min.

[0017] According to the preparation method of the present invention, preferably, the dynamic aging is carried out under stirring conditions, with a stirring speed of 100-300 rpm and a stirring time of 30-120 min.

[0018] According to the preparation method of the present invention, preferably, the average particle size D of the sheet-like precursor is... 50 The particle size is 2–10 μm, and the sheet thickness is less than 200 nm. According to the preparation method of the present invention, preferably, the particle size D of the rare earth oxide is... 50 The thickness is 2–10 μm, and the sheet thickness is less than 200 nm.

[0019] The preparation method of this invention can obtain flake-shaped rare earth oxides. These rare earth oxides have a small particle size. This preparation method eliminates the need for organic solvents, surfactants, or dispersants, thus improving safety during production. This preparation method is industrially feasible. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the preparation method of the present invention.

[0021] Figure 2 This is a SEM image of the plate-like rare earth oxides obtained in Example 1. Detailed Implementation

[0022] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0023] D 50 This indicates the particle size at which the cumulative particle size distribution of the sample reaches 50%.

[0024] The "dynamic aging" mentioned in this invention refers to the precipitation of crystals in the mixture under stirring conditions.

[0025] <Production Methods of Rare Earth Oxides>

[0026] This invention discovers that adding a solution of a carboxyl-containing substance to a mixture of a monocarboxylate containing a rare earth metal and water can yield flake-like rare earth oxides. The method for producing the rare earth oxides of this invention includes the following steps: (1) a step of forming a precipitate; (2) a step of obtaining a precursor; and (3) a calcination step. These are described in detail below.

[0027] Steps to form a precipitate

[0028] A solution of a carboxyl-containing substance is added to a mixture of a rare earth metal monocarboxylate and water. The carboxyl-containing substance and the rare earth metal monocarboxylate react, and the reaction product is dynamically aged to obtain a precipitate.

[0029] Solutions of carboxyl-containing substances are typically aqueous solutions. Carboxyl-containing substances can be selected from one or more dicarboxylic acids or dicarboxylic acid salts. Dicarboxylic acids are organic acids containing two carboxyl groups. The dicarboxylic acid of the present invention can be an aliphatic dicarboxylic acid or an aromatic dicarboxylic acid, preferably an aliphatic dicarboxylic acid. The number of carbon atoms in an aliphatic dicarboxylic acid can be 4 to 10, preferably 4 to 9, more preferably 4 to 7. The number of carbon atoms in an aromatic dicarboxylic acid can be 8 to 16, preferably 8 to 15, more preferably 8 to 13. Examples of dicarboxylic acids include, but are not limited to, oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, isophthalic acid, and terephthalic acid. According to one embodiment of the present invention, the dicarboxylic acid is oxalic acid. The dicarboxylic acid salt is an alkali metal salt or ammonium salt of the above-mentioned dicarboxylic acid. According to one embodiment of the present invention, the dicarboxylic acid salt is an alkali metal oxalate or ammonium oxalate.

[0030] The mixture of rare earth metal monocarboxylate and water may contain rare earth metal monocarboxylate and water, or other components, but shall not contain organic solvents, surfactants, or dispersants. Preferably, the mixture of rare earth metal monocarboxylate and water is a mixture composed of rare earth metal monocarboxylate and water.

[0031] In a mixture of a rare earth metal monocarboxylate and water, the rare earth metal monocarboxylate is the solute, and water is the dispersion medium or solvent. The monocarboxylic acid used to prepare the rare earth metal monocarboxylate is an organic acid containing one carboxyl group. The monocarboxylic acid of this invention can be an aliphatic monocarboxylic acid or an aromatic monocarboxylic acid, preferably an aliphatic monocarboxylic acid. The aliphatic monocarboxylic acid can have 1 to 8 carbon atoms, preferably 1 to 6, more preferably 1 to 3. The aromatic dicarboxylic acid can have 7 to 15 carbon atoms, preferably 7 to 13, more preferably 7 to 9. Examples of monocarboxylic acids include, but are not limited to, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, benzoic acid, and phenylacetic acid.

[0032] According to one embodiment of the present invention, the monocarboxylate of a rare earth metal can be selected from one or more of rare earth formate, rare earth acetate, and rare earth propionate. In some embodiments, the monocarboxylate of the rare earth metal is rare earth formate. In other embodiments, the monocarboxylate of the rare earth metal is rare earth acetate.

[0033] The rare earth element in the monocarboxylate of a rare earth metal can be scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), or lutetium (Lu). Preferably, the rare earth element is selected from one or more of lanthanum, cerium, and yttrium. In some embodiments, the rare earth element in the monocarboxylate of a rare earth metal is lanthanum. In other embodiments, the rare earth element in the monocarboxylate of a rare earth metal is cerium. In some embodiments, the rare earth element in the monocarboxylate of a rare earth metal is yttrium.

[0034] According to one embodiment of the present invention, the molar ratio of rare earth ions to oxalate in the monocarboxylate of rare earth metals is 1:(1.55-1.62). In some embodiments, the molar ratio of rare earth ions to oxalate is 1:(1.56-1.60). In other embodiments, the molar ratio of rare earth ions to oxalate is 1:(1.58-1.59). This facilitates the complete reaction of the raw materials to obtain the precipitated product.

[0035] According to one embodiment of the present invention, a solution containing a carboxyl group is added dropwise to a mixture of a rare earth metal monocarboxylate and water. This improves the yield of flake-shaped rare earth oxides and increases particle size uniformity. The dropwise addition time of the carboxyl group-containing solution is 15–50 min; preferably 20–40 min. In some embodiments, the dropwise addition time is 25–35 min. In other embodiments, the dropwise addition time is 28–30 min. In this invention, the dropwise addition time of the carboxyl group-containing solution refers to the time elapsed from the start of dropwise addition of the carboxyl group-containing solution to the mixture of the rare earth metal monocarboxylate and water until the dropwise addition of the carboxyl group-containing solution is completed.

[0036] The concentration of the carboxyl-containing substance solution of the present invention can be 180-280 g / L; preferably 200-270 g / L; more preferably 220-250 g / L.

[0037] In a mixture of rare earth metal monocarboxylate and water, the mass ratio of the rare earth metal monocarboxylate to the volume of water is (40–140) g:1 L; preferably (50–120) g:1 L; more preferably (80–110) g:1. The mass of the rare earth metal monocarboxylate is based on rare earth oxides. This improves the yield of flake-like rare earth oxides and increases particle size uniformity.

[0038] The process of adding a solution of a carboxyl-containing substance to a mixture of a rare earth metal monocarboxylate and water requires controlling the temperature of the reaction system. The temperature can be 40–85°C; preferably 50–80°C. In some embodiments, the temperature is 60–70°C. This improves particle size uniformity.

[0039] Controlling the above parameters within the scope of this invention helps to slow down the nucleation rate of crystals, increase the size of crystal particles, form a two-dimensional planar structure, and control the thickness and particle size of the generated precipitate.

[0040] Dynamic aging refers to aging under agitated conditions. The agitation time can be 30–120 minutes; preferably 40–90 minutes. In some embodiments, the agitation time is 60–70 minutes. This helps to form flake-like rare earth oxides.

[0041] The stirring speed can be 100–300 rpm. In some embodiments, the stirring speed is 150–250 rpm. In other embodiments, the stirring speed is 200–230 rpm.

[0042] Steps to obtain the precursor

[0043] The precipitate was filtered, washed and dried sequentially to obtain a sheet-like precursor.

[0044] In some embodiments, the filtration method is vacuum filtration. In other embodiments, the filtration method is centrifugal filtration.

[0045] In some embodiments, the filtered solid product is rinsed with 2 to 5 times its mass of water. In other embodiments, the filtered solid product is dispersed in 2 to 5 times its mass of water, stirred and washed, and then filtered again.

[0046] The drying time can be 6 to 18 hours, preferably 10 to 18 hours. In some embodiments, the drying time is 10 to 12 hours.

[0047] The drying temperature can be 50–80°C, preferably 50–70°C; more preferably 60–70°C. In some embodiments, the drying temperature is 60–65°C.

[0048] Plate-like precursor particle size D 50 The particle size is 2–10 μm. In some embodiments, the particle size D of the plate-like precursor is... 50 It is 3–6 μm.

[0049] The sheet-like precursor particles have a sheet thickness of less than 200 nm. In some embodiments, the sheet thickness is less than 150 nm. In other embodiments, the sheet thickness is less than 120 nm.

[0050] roasting steps

[0051] The present invention involves calcining the precursor to obtain flake-shaped rare earth oxides.

[0052] The calcination temperature can be 600–1400°C; preferably 700–1200°C; more preferably 800–1000°C. In some embodiments, the calcination temperature is 900–950°C. The calcination time can be 60–250 min; preferably 80–200 min; more preferably 90–150 min. In some embodiments, the calcination time is 120–130 min. The above calcination conditions are beneficial for maintaining the morphology of the precursor, resulting in plate-like rare earth oxides. Such calcination conditions can prevent the plate-like structure of the rare earth oxides from being destroyed and can also reduce adhesion.

[0053] The particle size D of the plate-like rare earth oxides obtained by the method of the present invention 50 The particle size can be 2–10 μm; preferably 3–8 μm. In some embodiments, the particle size of the plate-like rare earth oxide is 4–6 μm.

[0054] The thickness of the flake-shaped rare earth oxide of the present invention is less than 200 nm; preferably, less than 180 nm; more preferably, less than 150 nm; and most preferably, less than 120 nm.

[0055] The rare earth oxides of this invention are beneficial for improving the rigidity and adhesion of downstream products, showing promising application prospects in catalysts, coatings, functional ceramics, functional fibers, and other fields. The testing methods are described below:

[0056] Scanning electron microscope (SEM) images: Tests were performed using a ZEISS Sigma 500 scanning electron microscope. The thickness of the plate-like rare earth oxides was determined from the SEM images.

[0057] Particle size D 50 The Mastersizer 3000 laser particle size analyzer was used for testing.

[0058] Example 1

[0059] At 80°C, a 250 g / L oxalic acid solution was added dropwise to a mixture of lanthanum acetate and water. The mass-to-volume ratio of lanthanum acetate to water in the mixture was 80 g / L, and the mass of lanthanum acetate was calculated as lanthanum oxide. After the oxalic acid solution was completely added, the mixture was stirred at 150 rpm for 40 min to age, yielding a precipitate. The molar ratio of lanthanum ions to oxalate ions was 1:1.58. The oxalic acid solution was added over a period of 23 min.

[0060] The precipitate was vacuum filtered to obtain a solid product. The solid product was washed with three times its mass of water and then dried at 60°C for 8 hours to obtain a sheet-like precursor. Sheet-like precursor D 50 It has a diameter of 4.46 μm and a thickness of less than 150 nm.

[0061] The sheet-like precursor was calcined at 800℃ for 90 min to obtain sheet-like rare earth oxides. Figure 2 This is a SEM image of the plate-like rare earth oxides obtained in Example 1. Figure 2 It can be seen that the rare earth oxides obtained in Example 1 are in flake form. The average particle size D of the flake-shaped rare earth oxides is... 50 It has a diameter of 4.52 μm and a thickness of less than 150 nm.

[0062] Example 2

[0063] At 60°C, a 220 g / L ammonium oxalate solution was added dropwise to a mixture of cerium formate and water. The mass-to-volume ratio of cerium formate to water in the mixture was 110 g / L, and the mass of cerium formate was expressed as cerium trioxide. After the ammonium oxalate solution was completely added, the mixture was stirred at 200 rpm for 60 min to age, yielding a precipitate. The molar ratio of cerium ions to oxalate ions was 1:1.55. The addition time of the ammonium oxalate solution was 30 min.

[0064] The precipitate was centrifuged and filtered to obtain a solid product. The solid product was dispersed and washed with water at twice its mass, then filtered. The resulting solid was dried at 65°C for 12 hours to obtain a sheet-like precursor. Sheet-like precursor D 50 It has a diameter of 5.96 μm and a thickness of less than 150 nm.

[0065] The plate-like precursor was calcined at 900℃ for 120 min to obtain plate-like rare earth oxides. The particle size D of the plate-like rare earth oxides was determined. 50 It has a diameter of 5.84 μm and a thickness of less than 150 nm.

[0066] Example 3

[0067] At 50°C, a 220 g / L oxalic acid solution was added dropwise to a mixture of yttrium acetate and water. The mass-to-volume ratio of yttrium acetate to water in the mixture was 80 g / L, and the mass of yttrium acetate was expressed as yttrium oxide. After the oxalic acid solution was completely added, the mixture was stirred at 200 rpm for 70 min to age, yielding a precipitate. The molar ratio of yttrium ions to oxalate ions was 1:1.56. The oxalic acid solution was added over a period of 30 min.

[0068] The precipitate was vacuum filtered to obtain a solid product. The solid product was washed with 5 times its mass of water and then dried at 60°C for 10 hours to obtain a sheet-like precursor. Sheet-like precursor D 50 It has a diameter of 3.32 μm and a thickness of less than 120 nm.

[0069] The plate-like precursor was calcined at 900℃ for 150 min to obtain plate-like rare earth oxides. The particle size D of the plate-like rare earth oxides was determined. 50 It has a diameter of 3.54 μm and a thickness of less than 120 nm.

[0070] 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. A method for preparing plate-like rare earth oxides, characterized in that, Includes the following steps: A solution of a carboxyl-containing substance is added dropwise to a mixture of a monocarboxylic acid salt containing rare earth metals and water. The reaction temperature is 40–80 °C. Dynamic aging yields a plate-like precursor, which is then calcined to obtain plate-like rare earth oxides. Wherein, the carboxyl-containing substance is selected from alkali metal oxalates or ammonium oxalate; the concentration of the solution of the carboxyl-containing substance is 220-250 g / L; In the mixture of rare earth metal monocarboxylate salt and water, the monocarboxylic acid used to prepare the rare earth metal monocarboxylate salt is an aliphatic monocarboxylic acid with 1 to 3 carbon atoms; in the mixture, the mass ratio of the rare earth metal monocarboxylate salt to the volume of water, calculated as rare earth oxides, is (40 to 140) g: 1 L. The molar ratio of rare earth ions to oxalate ions in the monocarboxylate of rare earth metals is 1:(1.55–1.62); the dynamic aging is carried out under stirring conditions at a stirring speed of 100–300 rpm; the average particle size D of the plate-like precursor is... 50 The thickness is 2–10 μm, and the sheet thickness is less than 200 nm; The particle size D of the plate-like rare earth oxide 50 The thickness is 2–10 μm, and the sheet thickness is less than 200 nm.

2. The preparation method according to claim 1, characterized in that, In the reaction system, the molar ratio of rare earth ions to oxalate ions is 1:1.55 to 1.

60.

3. The preparation method according to claim 1, characterized in that, The rare earth metal monocarboxylate is selected from one or more of rare earth formate, rare earth acetate, and rare earth propionate.

4. The preparation method according to claim 1, characterized in that, In the mixture, the mass ratio of the monocarboxylate of rare earth metals (calculated as rare earth oxides) to the volume ratio of water is (50–120) g: 1 L.

5. The preparation method according to claim 1, characterized in that, The time for adding a solution of a carboxyl-containing substance to a mixture of a monocarboxylic acid salt containing rare earth metals and water is 15–50 min.

6. The preparation method according to claim 1, characterized in that, The stirring speed is 150–250 rpm, and the stirring time is 30–120 min.

7. The preparation method according to claim 1, characterized in that, The average particle size D of the plate-like precursor 50 The thickness is 3–6 μm, and the sheet thickness is less than 150 nm.

8. The preparation method according to claim 1, characterized in that, The particle size D of the plate-like rare earth oxide 50 The thickness is 3–8 μm, and the sheet thickness is less than 180 nm.

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