A kind of flaky transparent yttrium oxide powder and its preparation method and application

Abstract

The present invention relates to the technical field of transparent yttrium oxide ceramics, and in particular to a flaky transparent yttrium oxide powder, a preparation method and application thereof. The present invention provides a preparation method of a flaky transparent yttrium oxide powder, comprising the following steps: after adding an oxalic acid solution to a soluble yttrium salt solution having a hydrogen ion concentration of 1 to 3 mol / L for precipitation reaction, cyclically agglomerating and aging the obtained precipitate to obtain a precipitate; calcining the precipitate to obtain the flaky transparent yttrium oxide powder; the calcination temperature is 950 to 1500°C; the molar ratio of oxalic acid in the oxalic acid solution to the soluble yttrium salt in the soluble yttrium salt solution is (2.5 to 5): 1. The preparation method can prepare the flaky transparent yttrium oxide powder without introducing additives.

Description

Technical Field

[0001] The invention relates to the technical field of transparent yttrium oxide ceramics, and in particular to a flaky transparent yttrium oxide powder and a preparation method and application thereof. Background Art

[0002] Yttrium oxide is an important rare earth oxide. It has the unique electronic layer structure of rare earth elements, high electric charge, strong polarization, diversity of electronic energy levels and spectral lines, active chemical properties and other excellent characteristics, which makes yttrium oxide have broad application prospects. Yttrium oxide powder is an important ceramic raw material, belonging to the cubic crystal system, with excellent heat resistance, corrosion resistance and high temperature stability, melting point greater than 2400℃, dielectric constant of 12-20 and other high-quality characteristics. At the same time, in the application field of high-tech ceramics, the microscopic morphology and properties of the powder determine its physical and chemical properties and application fields.

[0003] At present, the microscopic morphology of commercial yttrium oxide powder on the market and the yttrium oxide prepared by the related technology is mostly amorphous and nearly spherical, and there is no preparation of yttrium oxide powder with flake shape and good light transmittance. Summary of the invention

[0004] The purpose of the present invention is to provide a flaky transparent yttrium oxide powder and a preparation method and application thereof. The flaky transparent yttrium oxide powder prepared by the preparation method is flaky and has good light transmittance and high density.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a flaky transparent yttrium oxide powder, comprising the following steps:

[0007] After adding an oxalic acid solution to a soluble yttrium salt solution having a hydrogen ion concentration of 1 to 3 mol / L for precipitation reaction, the obtained precipitate is cyclically agglomerated and aged to obtain a precipitate;

[0008] calcining the precipitate to obtain the flaky transparent yttrium oxide powder;

[0009] The calcination temperature is 950-1500°C;

[0010] The molar ratio of oxalic acid in the oxalic acid solution to the soluble yttrium salt in the soluble yttrium salt solution is (2.5-5):1.

[0011] Preferably, the preparation of the soluble yttrium salt solution having a hydrogen ion concentration of 1 to 3 mol / L comprises: adjusting the hydrogen ion concentration in the soluble yttrium salt solution to 1 to 3 mol / L using a strong acid solution to obtain the soluble yttrium salt solution having a hydrogen ion concentration of 1 to 3 mol / L.

[0012] Preferably, the concentration of the soluble yttrium salt solution is 0.1-1 mol / L;

[0013] The soluble yttrium salt in the soluble yttrium salt solution includes yttrium nitrate and / or yttrium chloride.

[0014] Preferably, the adding of the oxalic acid solution is dripping the oxalic acid solution, and the dripping rate is 0.2-1.6 L / h;

[0015] The process of adding the oxalic acid solution is carried out under stirring, and the stirring speed is 100-200 rpm.

[0016] Preferably, the precipitation reaction is carried out under stirring;

[0017] The stirring temperature is 70-90° C., the rotation speed is 100-200 rpm, and the time is 1-6 hours.

[0018] Preferably, the agglomeration is carried out under heating conditions;

[0019] The heating temperature is 70-90°C.

[0020] Preferably, the number of cycles is 2 times;

[0021] The first reunion lasts for 2 to 5 hours, and the second reunion lasts for 6 to 24 hours.

[0022] Preferably, the calcination time is 2 to 8 hours.

[0023] The present invention also provides a flaky transparent yttrium oxide powder, wherein the flaky transparent yttrium oxide powder is YH(C2O4)2·3H2O, and the D50 of the flaky transparent yttrium oxide powder is 90-125 μm.

[0024] The present invention also provides the use of the flaky transparent yttrium oxide powder described in the above technical solution in the field of preparing transparent ceramics or high temperature resistant demoulding.

[0025] The present invention provides a method for preparing a flaky transparent yttrium oxide powder, comprising the following steps: after adding an oxalic acid solution to a soluble yttrium salt solution having a hydrogen ion concentration of 1 to 3 mol / L for precipitation reaction, cyclically agglomerating and aging the obtained precipitate to obtain a precipitate; calcining the precipitate to obtain the flaky transparent yttrium oxide powder; the calcination temperature is 950 to 1500° C.; the molar ratio of oxalic acid in the oxalic acid solution to the soluble yttrium salt in the soluble yttrium salt solution is (2.5 to 5): 1. The present invention is more conducive to the formation of crystalline precipitation by controlling the acidity (hydrogen ion concentration) of the soluble yttrium salt solution, and the amorphous amorphous precipitation particles are very small, have no obvious lattice, are arranged in a disordered manner, and have a loose structure. At the same time, high acidity can dissolve amorphous non-crystalline precipitates faster and inhibit the formation of amorphous precipitates. As the reaction proceeds, yttrium ions will eventually deposit into crystalline precipitates (dense crystalline yttrium hydrogen oxalate trihydrate) with relatively regular internal arrangement, compact structure, and larger particles. Further, after the agglomeration process, the small particles of Y2(C2O4)3·10H2O agglomerate to transform into denser YH(C2O4)2·3H2O crystals with larger particles. The aging process undergoes Ostwald ripening and cooling crystallization, which will dissolve the smaller crystalline particles and deposit them again on the larger crystalline particles, thereby further increasing the crystal particle size, making the large particle crystals more dense, and further improving their optical transmittance level. At the same time, the flaky transparent yttrium oxide powder prepared by the preparation method has good fluidity, smooth particle surface, and high bulk density, and is expected to be used as a high temperature resistant release agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a 1000-fold optical microscope image of the flaky transparent yttrium oxide powder described in Example 1;

[0027] Figure 2 This is a SEM image of the flaky transparent yttrium oxide powder described in Example 1;

[0028] Figure 3 This is a 1000x optical microscope image of the precursor obtained after the precipitation reaction described in Example 1 is completed;

[0029] Figure 4 This is a 1000-fold optical microscope image of the precipitate described in Example 1;

[0030] Figure 5 The XRD diagrams of the precursor obtained after the precipitation reaction described in Example 1, and the precipitate after aging for 6 hours, aging for 12 hours, and aging for 24 hours;

[0031] Figure 6 This is a 1000-fold optical microscope image of the flaky transparent yttrium oxide powder described in Example 2;

[0032] Figure 7This is a SEM image of the flaky transparent yttrium oxide powder described in Example 2;

[0033] Figure 8 This is a 1000-fold optical microscope image of the flaky transparent yttrium oxide powder described in Example 3;

[0034] Fig. 9 This is a SEM image of the flaky transparent yttrium oxide powder described in Example 3;

[0035] Fig.10 This is a 500-fold optical microscope image of the yttrium oxide described in Comparative Example 1;

[0036] Fig.11 This is a 500-fold optical microscope image of the yttrium oxide described in Comparative Example 2;

[0037] Fig.12 This is a comparison photo of the flaky transparent yttrium oxide powder described in Example 2 and the yttrium oxide powder described in Comparative Example 2. DETAILED DESCRIPTION

[0038] The present invention provides a method for preparing a flaky transparent yttrium oxide powder, comprising the following steps:

[0039] After adding an oxalic acid solution to a soluble yttrium salt solution having a hydrogen ion concentration of 1 to 3 mol / L for precipitation reaction, the obtained precipitate is cyclically agglomerated and aged to obtain a precipitate;

[0040] calcining the precipitate to obtain the flaky transparent yttrium oxide powder;

[0041] The calcination temperature is 950-1500°C;

[0042] The molar ratio of oxalic acid in the oxalic acid solution to the soluble yttrium salt in the soluble yttrium salt solution is (2.5-5):1;

[0043] The preparation method does not add additives.

[0044] In the present invention, unless otherwise specified, all preparation raw materials are commercially available products well known to those skilled in the art.

[0045] The invention adds an oxalic acid solution to a soluble yttrium salt solution with a hydrogen ion concentration of 1-3 mol / L for precipitation reaction, and then cyclically aggregates and ages the obtained precipitate to obtain the precipitate.

[0046] In the present invention, the preparation of the soluble yttrium salt solution with a hydrogen ion concentration of 1 to 3 mol / L preferably includes: using a strong acid solution to adjust the hydrogen ion concentration in the soluble yttrium salt solution to 1 to 3 mol / L to obtain the soluble yttrium salt solution with a hydrogen ion concentration of 1 to 3 mol / L.

[0047] In the present invention, the concentration of the soluble yttrium salt solution is preferably 0.1-1 mol / L, more preferably 0.3-0.8 mol / L, and most preferably 0.4-0.6 mol / L. In the present invention, the soluble yttrium salt in the soluble yttrium salt solution preferably includes yttrium nitrate and / or yttrium chloride, more preferably yttrium nitrate; when the soluble yttrium salt is yttrium nitrate and yttrium chloride, the present invention does not have any special restrictions on the ratio of yttrium nitrate and yttrium chloride, and can be mixed in any ratio.

[0048] In the present invention, the strong acid solution preferably includes a nitric acid solution or a hydrochloric acid solution, and more preferably includes a nitric acid solution. The present invention does not have any special restrictions on the concentration and dosage of the strong acid solution, and the concentration and dosage well known to those skilled in the art are used to ensure that the concentration of hydrogen ions in the prepared soluble yttrium salt solution with a hydrogen ion concentration of 1 to 3 mol / L is within the range of 1 to 3 mol / L. The present invention does not have any special restrictions on the mixing process, and the process well known to those skilled in the art can be used.

[0049] In the present invention, the concentration of hydrogen ions in the soluble yttrium salt solution with a hydrogen ion concentration of 1 to 3 mol / L is 1 to 3 mol / L. In an embodiment of the present invention, the concentration of hydrogen ions in the soluble yttrium salt solution with a hydrogen ion concentration of 1 to 3 mol / L may be 1 mol / L, 2 mol / L or 3 mol / L.

[0050] In the present invention, the concentration of the oxalic acid solution is preferably 1-1.5 mol / L, more preferably 1.1-1.4 mol / L, and most preferably 1.2-1.3 mol / L. In an embodiment of the present invention, the concentration of the oxalic acid solution may be 1 mol / L or 1.5 mol / L.

[0051] In the present invention, the molar ratio of oxalic acid in the oxalic acid solution to the soluble yttrium salt in the soluble yttrium salt solution is (2.5-5):1, preferably (3-4.5):1, and more preferably (3.5-4):1. In an embodiment of the present invention, the molar ratio of oxalic acid in the oxalic acid solution to the soluble yttrium salt in the soluble yttrium salt solution may be 2.5:1 or 5:1.

[0052] In the present invention, the addition of oxalic acid solution is preferably the dripping of oxalic acid solution; the dripping rate is preferably 0.2~1.6L / h, more preferably 0.3~0.6L / h, and most preferably 0.4~0.5L / h. In an embodiment of the present invention, the dripping rate may be 0.5L / h, 0.6L / h or 1.6L / h. In the present invention, the process of adding the oxalic acid solution is preferably carried out under stirring, and the stirring speed is preferably 100~200rpm, more preferably 120~180rpm, and most preferably 140~160rpm. In an embodiment of the present invention, the stirring speed may be 190rpm, 100rpm or 200rpm.

[0053] In the present invention, the temperature of the precipitation reaction is preferably 70-90°C, more preferably 72-78°C, and most preferably 74-76°C; the precipitation reaction is preferably carried out under stirring, and the stirring speed is preferably 100-200rpm, more preferably 120-180rpm, and most preferably 140-160rpm; the time is preferably 1-6h, more preferably 1.5-2.5h, and most preferably 1.8-2.2h. In an embodiment of the present invention, the temperature of the precipitation reaction can be 80°C, 90°C or 70°C; the stirring speed can be 190rpm, 100rpm or 200rpm; and the time can be 2h, 2.5h or 6h.

[0054] In the present invention, the agglomeration is preferably carried out under heating conditions; the heating temperature is preferably 70-90°C, more preferably 75-85°C, and most preferably 78-82°C. The heating is preferably carried out under stirring conditions, and the stirring speed is preferably 100-200rpm, more preferably 120-180rpm, and most preferably 140-160rpm. In an embodiment of the present invention, the heating temperature may be 80°C, 70°C or 90°C; the stirring speed may be 190rpm, 100rpm or 200rpm; in the present invention, the number of cycles is preferably 2 times, and the time for the first agglomeration is preferably 2-5h, more preferably 2.5-4.5h, and most preferably 3-4h. The time for the second agglomeration is preferably 4-24h, more preferably 10-20h, and most preferably 13-16h. In an embodiment of the present invention, the time for the first agglomeration may be 2h, 3h or 5h; the time for the second agglomeration may be 4h, 6h or 24h.

[0055] In the present invention, the aging condition is preferably standing still, and the standing still is divided into a first standing still and a second standing still; the present invention has no special limitation on the process of the first standing still and the second standing still, and a process familiar to those skilled in the art can be used to ensure cooling to room temperature.

[0056] After the second standing is completed, the present invention preferably further comprises filtration. The present invention does not have any special limitation on the filtration process, and the filtration process may be performed using a process well known to those skilled in the art.

[0057] In the present invention, the preparation of the mixed solution and the precipitate is preferably carried out in a closed reactor.

[0058] After obtaining the precipitate, the present invention calcines the precipitate to obtain the flaky transparent yttrium oxide powder.

[0059] In the present invention, the calcination temperature is 950-1500°C, more preferably 1000-1400°C, and most preferably 1200-1300°C; the calcination time is preferably 2-8h, more preferably 3-7h, and most preferably 4-5h. In the present invention, the calcination is preferably carried out in air or oxygen atmosphere. In an embodiment of the present invention, the calcination temperature may be 1500°C, 1200°C or 950°C; the calcination time may be 2h, 6h or 8h.

[0060] In the present invention, since oxalic acid is a dibasic weak acid, it is ionized in two steps, and there is a large amount of nitric acid in the mixed solution including the soluble yttrium salt and nitric acid. The dissociation constant of nitric acid is higher than that of oxalic acid. At the same temperature, the acid with a large dissociation constant has a strong ability to donate protons. Due to the common ion effect, less oxalate is produced, which affects the precipitation of yttrium oxalate, resulting in the need for excessive oxalic acid (several times the theoretical amount). The specific reaction is as follows: H2C2O4⇌H + +HC2O4 − HC2O4−⇌H + +C2O4 2− ; HNO3→H + +NO3 − ;C2O4 2− +Y 3+ →Y2(C2O4)3; After the first heating of the newly precipitated precursor, regular large block particles are generated from amorphous agglomerates of a large number of small particles. After static aging, the phase changes from Y2(C2O4)3·10H2O to YH(C2O4)2·3H2O. The generation of YH(C2O4)2·3H2O increases the calcination stability of the precursor, so that the calcined yttrium oxide can also maintain a similar morphology and good density.

[0061] The present invention also provides a flaky transparent yttrium oxide powder, wherein the flaky transparent yttrium oxide powder is YH(C2O4)2·3H2O, and the D50 of the flaky transparent yttrium oxide powder is 90-125 μm.

[0062] In the present invention, the flaky transparent yttrium oxide powder is preferably a flaky transparent yttrium oxide powder prepared by the preparation method described in the above technical solution.

[0063] The present invention also provides the use of the flaky transparent yttrium oxide powder described in the above technical solution in the field of preparing transparent ceramics or high temperature resistant demoulding. The present invention has no special limitation on the method of the application, and the method well known to those skilled in the art can be used.

[0064] The following is a detailed description of the flaky transparent yttrium oxide powder provided by the present invention, its preparation method and application in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0065] Example 1

[0066] 3 L of 0.2 mol / L yttrium nitrate solution was added to a closed reactor, and 0.55 L of 5 mol / L nitric acid solution was added to obtain a mixed solution with a hydrogen ion concentration of 1 mol / L;

[0067] Under stirring (rotation speed of 190 rpm), 1 L of 1.5 mol / L oxalic acid solution was slowly added dropwise to the mixed solution at a rate of 0.5 L / h, and a precipitation reaction was carried out at 80° C. for 2 h, and then the mixture was heated at 80° C. for 2 h, stirring and heating were stopped, and the mixture was allowed to stand and age until it naturally cooled to room temperature, and then stirring (rotation speed of 190 rpm) and heating to 80° C. and heat preservation were continued for 4 h, and the mixture was allowed to stand and age and naturally cooled to room temperature, and filtered to obtain a precipitate;

[0068] The precipitate was calcined at 1500° C. for 2 h to obtain flaky transparent yttrium oxide powder (D50=124.7 μm);

[0069] Figure 1 is a 1000-fold optical microscope image of the flaky transparent yttrium oxide powder. Figure 1 It can be seen that the yttrium oxide powder is a translucent square flake particle with a smooth and translucent surface and compact and dense particles.

[0070] Figure 2 is a SEM image of the flaky transparent yttrium oxide powder. Figure 2 It can be seen that the crystals on the surface of the powder particles are closely arranged;

[0071] Figure 3 This is a 1000-fold optical microscope image of the precursor obtained after the precipitation reaction is completed. Figure 4 is a 1000-fold optical microscope image of the precipitate, Figure 3 and Figure 4 It can be seen that after the precursor obtained after the precipitation reaction is completed is heated and stirred for 24 hours, amorphous agglomerates of a large number of small particles are generated into regular block-shaped large particles;

[0072] The precursor obtained after the precipitation reaction is aged, and the XRD curves after different aging times are tested. Figure 5 is the XRD diagram of the precipitate obtained after the precursor is aged for 0 h, 6 h, 12 h and 24 h after the precipitation reaction is completed; Figure 5 It can be seen that the aging time is Y2(C2O4)3·10H2O at 0h, and a small amount of YH(C2O4)2·3H2O diffraction peaks begin to appear at 6h. After 12h, the proportion of YH(C2O4)2·3H2O diffraction peaks further increases, and after 24h, all of them become YH(C2O4)2·3H2O. The Y2(C2O4)3·10H2O precursor obtained by precipitation becomes YH(C2O4)2·3H2O after heating and stirring for 24h. The phase changes during the aging process of the precipitate, from Y2(C2O4)3·10H2O to YH(C2O4)2·3H2O. The generation of YH(C2O4)2·3H2O increases the calcination stability of the precursor, so that the calcined yttrium oxide can also maintain a similar morphology and good density.

[0073] Example 2

[0074] 3 L of 0.1 mol / L yttrium nitrate solution was added to a closed reactor, and 1.7 L of 5 mol / L nitric acid solution was added to obtain a mixed solution with a hydrogen ion concentration of 2 mol / L;

[0075] Under stirring (rotation speed of 100 rpm), 1.5 L of 1 mol / L oxalic acid solution was slowly added dropwise to the mixed solution at a rate of 0.6 L / h, and a precipitation reaction was carried out at 90° C. for 2.5 h, and then heated at 90° C. for 3 h, stirring and heating were stopped, and the mixture was allowed to stand and age until it naturally cooled to room temperature, and then stirring (rotation speed of 100 rpm) and heating to 90° C. and heat preservation were continued for 6 h, and the mixture was allowed to stand and age and naturally cooled to room temperature, and filtered to obtain a precipitate;

[0076] The precipitate was calcined at 1200° C. for 6 h to obtain flaky transparent yttrium oxide powder (D50=109.32 μm);

[0077] Figure 6 is a 1000-fold optical microscope image of the flaky transparent yttrium oxide powder. Figure 6 It can be seen that the powder particles are dense square flakes with a smooth and transparent surface;

[0078] Figure 7 is a SEM image of the flaky transparent yttrium oxide powder. Figure 7 It can be seen that the fine grains of powder particles are closely arranged on the same plane.

[0079] Example 3

[0080] 3 L of 1 mol / L yttrium nitrate solution was added into a closed reactor, and 0.2 L of 5 mol / L nitric acid solution was added to obtain a mixed solution with a hydrogen ion concentration of 3 mol / L;

[0081] Under stirring (rotation speed of 200 rpm), 10 L of 1.5 mol / L oxalic acid solution was slowly added to the mixed solution at a rate of 1.6 L / h, and the precipitation reaction was carried out at 70°C for 6 h (the TEM image of the obtained precursor is shown in FIG. Figure 1 After that, the mixture was heated at 70°C for 5 h, stirring and heating were stopped, and the mixture was allowed to stand for aging until it naturally cooled to room temperature. Stirring (speed was 200 rpm) and heating to 70°C were continued for 24 h, and the mixture was allowed to stand for aging and naturally cooled to room temperature. The mixture was filtered to obtain a precipitate (TEM image as shown in FIG. Figure 2 shown);

[0082] The precipitate was calcined at 950° C. for 8 h to obtain flaky transparent yttrium oxide powder (D50=98.21 μm);

[0083] Figure 8 is a 1000-fold optical microscope image of the flaky transparent yttrium oxide powder. Figure 8 It can be seen that the surface of the powder particles is flat and dense, and the particles are square flakes;

[0084] Fig. 9 is a SEM image of the flaky transparent yttrium oxide powder. Fig. 9 It can be seen that the nano-grains on the surface of the powder particles are densely arranged.

[0085] Comparative Example 1

[0086] Referring to Example 1, the difference is that the concentration of the yttrium nitrate solution is 0.2 mol / L, the pH of the obtained mixed solution is 2, the temperature of the precipitation reaction is room temperature (26°C), and yttrium oxide (regular agglomerates of small particles, D50=18.13 μm) is obtained;

[0087] Fig.10 is a 500-fold optical microscope image of the yttrium oxide, Fig.10 It can be seen that the yttrium oxide powder is amorphous agglomerates of small particles.

[0088] Comparative Example 2

[0089] Referring to Example 2, the difference is that after the precipitation reaction is completed, the heating, standing, heating and standing processes are not performed, and the precipitation reaction is directly cooled naturally and filtered, and then calcined at 1200° C. for 6 h to obtain yttrium oxide (amorphous agglomerates, D50=7.68 μm);

[0090] Fig.11is a 500-fold optical microscope image of the yttrium oxide, Fig.11 It can be seen that the powder particles are neatly and closely arranged;

[0091] Fig.12 The flaky transparent yttrium oxide powder described in Example 2 (left) and the yttrium oxide described in Comparative Example 2 (right) are compared in real pictures. Fig.12 It can be seen that the conventional yttrium oxide described in Comparative Example 2 is a white powder, and the yttrium oxide powder described in Example 2 is transparent.

[0092] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a flaky transparent yttrium oxide powder, characterized in that: The following steps are involved: After adding an oxalic acid solution to a soluble yttrium salt solution having a hydrogen ion concentration of 1 to 3 mol / L for precipitation reaction, the obtained precipitate is cyclically agglomerated and aged to obtain a precipitate; calcining the precipitate to obtain the flaky transparent yttrium oxide powder; The calcination temperature is 950-1500°C; The molar ratio of oxalic acid in the oxalic acid solution to the soluble yttrium salt in the soluble yttrium salt solution is (2.5-5):1; The precipitation reaction is carried out under stirring; The stirring temperature is 70-90°C, the speed is 100-200 rpm, and the time is 1-6 hours; The agglomeration is carried out under heating conditions, the heating temperature is 70-90° C.; the heating is carried out under stirring conditions, the stirring speed is 100-200 rpm; The number of cycles is 2 times; The first reunion lasts 2 to 5 hours, and the second reunion lasts 6 to 24 hours; The first aging and the second aging process are both to stand and age until naturally cooled to room temperature; The D50 of the flaky transparent yttrium oxide powder is 90-125 μm.

2. The preparation method according to claim 1, characterized in that The preparation of the soluble yttrium salt solution with a hydrogen ion concentration of 1-3 mol / L comprises: using a strong acid solution to adjust the hydrogen ion concentration in the soluble yttrium salt solution to 1-3 mol / L, thereby obtaining the soluble yttrium salt solution with a hydrogen ion concentration of 1-3 mol / L.

3. The preparation method according to claim 2, characterized in that: The concentration of the soluble yttrium salt solution is 0.1-1 mol / L; The soluble yttrium salt in the soluble yttrium salt solution includes yttrium nitrate and / or yttrium chloride.

4. The preparation method according to claim 1, characterized in that: The adding of the oxalic acid solution is performed by dripping the oxalic acid solution, and the dripping rate is 0.2-1.6 L / h; The process of adding the oxalic acid solution is carried out under stirring, and the stirring speed is 100-200 rpm.

5. The preparation method according to claim 1, characterized in that: The calcination time is 2 to 8 hours.

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