A pre-treatment gel microsphere and ceramic microsphere and a method for preparing the same

Abstract

The application provides a pretreated gel microsphere and a ceramic microsphere and a preparation method thereof, and belongs to the technical field of ceramic forming. The preparation method of the pretreated gel microsphere comprises the following steps: S1, placing the gel microsphere after washing treatment or first drying treatment into a first soaking liquid for soaking treatment, wherein the first soaking liquid comprises at least one of propylene glycol methyl ether, dioxane, pyridine and ethanol; S2, performing second drying treatment on the gel microsphere soaked in the first soaking liquid to obtain the pretreated gel microsphere. The preparation method of the pretreated gel microsphere is capable of obtaining the pretreated gel microsphere with volume expansion and large pore structure through the soaking treatment and the second drying treatment, so that the internal pressure of the microsphere can be reduced in the subsequent calcination process, and cracking of the microsphere can be avoided.

Description

Technical Field

[0001] This invention belongs to the field of ceramic forming technology, specifically relating to a pretreated gel microsphere and ceramic microsphere and their preparation method. Background Technology

[0002] Ceramic microspheres generally refer to inorganic non-metallic polycrystalline spheres or near-spheres with a particle size in the micrometer range. They come in solid, hollow, and porous forms and are widely used in industries such as military, pharmaceuticals, chemicals, environmental protection, and nuclear technology. The preparation method for ceramic microspheres typically involves first preparing gel microspheres using the sol-gel method, followed by washing, drying, and calcining the gel microspheres to obtain the ceramic microspheres.

[0003] For example, patent application CN111243770A discloses a method for preparing monodisperse uranium dioxide microspheres, including the following steps: (1)-(4) preparing gel microspheres using the sol-gel method; (5) continuously washing the gel microspheres from step (4) four times with trichloroethylene at a molar concentration of 0.5 mol / L, each washing time being 20 minutes, and then continuously washing them four times with ammonia and deionized water at a molar concentration of 0.5 mol / L, each washing time being 30 minutes; (6) dissolving the gel microspheres from step (5) in a sol-gel method. The microspheres are dried at 60-80°C for 12-24 hours to obtain dried microspheres; (7) the dried microspheres are calcined in air at 500-600°C for 5-7 hours to obtain UO3 microspheres, and then reduced in a reducing atmosphere at 700-800°C for 2-8 hours. The reducing atmosphere is a mixture of hydrogen and argon, and the ratio of hydrogen to argon is 1:(4-5) to obtain UO2 microspheres. Finally, they are sintered at 1600-1700°C in a pure hydrogen atmosphere for 5-8 hours to obtain dense uranium dioxide microspheres.

[0004] However, both the dried gel microspheres and the final ceramic microspheres are prone to cracking. Once cracked, the ceramic microspheres become weak ceramic powder, failing to meet application requirements and thus needing to be discarded. Researchers have investigated the cracking problem of gel microspheres and ceramic microspheres. (Ma Jianwei) [1] Propylene oxide was used during the gel drying process to make the gel pore size more uniform, resulting in Al2O3 aerogel dried at ambient pressure. (Liang Chen) [2] The wet gel was modified with tetraethyl silicate, a hydrophobic modifier, to consume excess hydroxyl groups on the surface of the wet gel, thereby reducing surface tension, supporting and enhancing the gel network structure, ensuring high porosity of the gel, and finally drying at atmospheric pressure to obtain aerogel powder. (Wu Zhigang) [3] ZrO2 aerogel with uniform particle size, large specific surface area, and large pore volume was synthesized using zirconium oxynitrate as raw material via an alcohol-water heating method combined with supercritical drying. The supercritical drying method, under high temperature and pressure, eliminated the influence of the liquid-gas interface on the gel pore size. [4]An equal volume of zirconium oxychloride solution and urea solution was mixed and heated in a water bath at 85°C for 6 hours. Heating resulted in a gel precipitate, which was separated by filtration. The gel was first washed with deionized water, then the solvent was replaced with anhydrous ethanol. The resulting aerogel was then dried using supercritical drying, yielding a final product with a specific surface area of ​​416.0 m². 2 / g, an aerogel with an average pore size of 10.2nm.

[0005] Based on the above existing technologies, in order to prevent the shrinkage and cracking of gel microspheres and thus maintain the structure of ceramic microspheres, the following aspects are the main approaches: (1) enhancing the mechanical strength of the gel; (2) increasing the pore size of the gel; (3) reducing the surface tension of the liquid phase during water washing; (4) using supercritical drying technology that eliminates the gas-liquid interface; (5) using freeze-drying to evaporate the solvent; and (6) making the gel surface hydrophobic during water washing.

[0006] However, among the existing technologies mentioned above, while freeze-drying can avoid the gas-liquid interface, it creates a discontinuous density transition region at the freezing point of the solvent, which disrupts the gel structure. Furthermore, at low temperatures, the sublimation of the solvent from the gel is a slow mass transfer process, and solvent crystallization further damages the gel structure, ultimately resulting in a gel powder with a destroyed gel structure. While supercritical drying can produce crack-free gel microspheres, this method is cumbersome and costly. Although other methods can also reduce cracking of gel microspheres, the effects are not significant enough, and further optimization is still possible.

[0007] [1] Ma Jianwei. Preparation of Al2O3 aerogel by atmospheric pressure drying sol-gel method [D]. Tianjin University, 2009.

[0008] [2] Wu Zhigang. Preparation, characterization and application of ZrO2 and ZrO2-SiO2 composite oxide aerogels [D]. Shanxi University, 2004.

[0009] [3] Liang Chen. Preparation and performance study of zirconia aerogel porous materials [D]. Harbin Institute of Technology, 2015.

[0010] [4]Zhang L, Xu J, Sun L, et al. Zirconium oxide aerogel for effective enrichment of phosphopeptides with high binding capacity [J]. Analytical and bioanalytical chemistry, 2011, 399: 3399-3405. Summary of the Invention

[0011] This invention is based on the inventors' discovery and understanding of the following facts and problems: Gel microspheres prepared by the sol-gel method have a high organic content and require washing. However, the washing process increases the capillary force on the gel microspheres, leading to a decrease in the average pore size and pore volume. This prevents the gases produced by the oxidation and decomposition of organic matter during subsequent calcination from escaping from the microspheres, resulting in excessive internal pressure and cracking. Therefore, it is necessary to optimize the drying process of the gel microspheres.

[0012] This invention aims to at least partially address one of the technical problems in related technologies. To this end, embodiments of this invention provide a pretreated gel microsphere and ceramic microsphere, and a method for preparing the same.

[0013] The method for preparing pretreated gel microspheres according to an embodiment of the present invention includes the following steps:

[0014] S1. The gel microspheres after washing or first drying are immersed in a first immersion solution, wherein the first immersion solution includes at least one of propylene glycol methyl ether, dioxane, pyridine and ethanol.

[0015] S2. The gel microspheres soaked in the first soaking solution are subjected to a second drying treatment to obtain pretreated gel microspheres.

[0016] The advantages and technical effects of the pretreated gel microsphere preparation method of this invention are as follows:

[0017] (1) The object of treatment is the gel microspheres after washing or the gel microspheres after the first drying treatment. These gel microspheres are at risk of cracking during the subsequent calcination process. The preparation method of the pretreated gel microspheres in this embodiment of the invention is to pretreat the object of treatment to prevent cracking during the subsequent calcination process.

[0018] (2) In step S1, the first soaking solution is used as the soaking solution to soak the gel microspheres after washing or first drying treatment. The first soaking solution includes at least one of propylene glycol methyl ether, dioxane, pyridine and ethanol. Since the first soaking solution has low surface tension, low saturated evaporation pressure and is miscible with water, the swelling property of the gel microspheres can be used to increase its pore structure. That is, the molecules of the first soaking solution will enter the gaps between the polymer chains of the gel microspheres, increase the volume between the chain segments, thereby expanding the volume of the gel microspheres and increasing the pore structure.

[0019] (3) Step S2 involves a second drying process on the gel microspheres soaked in the first soaking solution in order to reduce the surface tension of the gel microspheres during the drying process, thereby maximizing the maintenance of the pore structure of the gel microspheres after swelling.

[0020] (4) Compared with the gel microspheres after washing or the first drying treatment, the pretreated gel microspheres prepared by the method of this embodiment have a larger pore structure and specific surface area. The gas from the oxidation and decomposition of organic matter during the subsequent calcination process can easily escape from the pretreated gel microspheres. The pretreated gel microspheres will not break due to excessive internal pressure, thus obtaining dense ceramic microspheres with smooth surface and no cracks.

[0021] (5) The preparation method of the pretreated gel microspheres in the embodiments of the present invention is simple, feasible, highly applicable, and easy to promote and apply in industrial production.

[0022] In some embodiments, in step S1, the soaking temperature is 20-25°C and the time is 12-24 hours.

[0023] In some embodiments, in step S2, the second drying process is far-infrared drying and / or vacuum drying.

[0024] In some embodiments, in step S2, the vacuum degree of the vacuum drying is maintained at -0.08 to -0.1 MPa.

[0025] In some embodiments, in step S2, the temperature of the second drying process is 60–80°C, and the time is 12–48 h.

[0026] In some embodiments, in step S2, after the soaking treatment, the gel microspheres are separated from the first soaking solution, and then the gel microspheres are soaked in a second soaking solution, the second soaking solution including at least one of propylene glycol methyl ether, dioxane, pyridine and ethanol; then the gel microspheres soaked in the second soaking solution are subjected to the second drying treatment to obtain the pretreated gel microspheres.

[0027] In addition, this embodiment of the invention also provides a pretreated gel microsphere, which is obtained by the preparation method of the pretreated gel microsphere.

[0028] The advantages and technical effects of the pretreated gel microspheres in this invention are as follows:

[0029] Compared to gel microspheres after washing or the first drying process, the pretreated gel microspheres prepared by the method of this embodiment have a larger pore structure and specific surface area. During the subsequent calcination process, the gases from the oxidation and decomposition of organic matter can easily escape from the pretreated gel microspheres. The pretreated gel microspheres will not rupture due to excessive internal pressure. The prepared ceramic microspheres have a smooth, crack-free surface and good internal density.

[0030] In addition, this invention also provides a method for preparing ceramic microspheres, comprising the following steps: calcining the pretreated gel microspheres in an oxidizing atmosphere to obtain ceramic microspheres.

[0031] The advantages and technical effects of the method for preparing ceramic microspheres according to embodiments of the present invention are as follows:

[0032] The ceramic microspheres prepared in this embodiment of the invention use the pretreated gel microspheres as raw materials, resulting in ceramic microspheres with smooth, crack-free surfaces and good density.

[0033] In some embodiments, the heating rate of the calcination treatment does not exceed 1°C / min, and / or the calcination treatment is carried out in stages: first, it is kept at 190–210°C for 4–6 hours, then at 270–290°C for 2–4 hours, then at 350–370°C for 4–6 hours, and finally at 390–410°C for 2–4 hours.

[0034] Furthermore, this embodiment of the invention also provides a ceramic microsphere, obtained by the method for preparing the ceramic microsphere.

[0035] The advantages and technical effects of the ceramic microspheres in this invention are as follows:

[0036] The ceramic microspheres of this invention have a smooth, crack-free surface and good density, which can meet the requirements of industries such as military, pharmaceutical, chemical, environmental protection, and nuclear technology. Attached Figure Description

[0037] Figure 1 This is a schematic flowchart illustrating the preparation method of pretreated gel microspheres and the preparation method of ceramic microspheres according to embodiments of the present invention.

[0038] Figure 2 A stereomicroscopic photograph of the gel microspheres after the first drying treatment in Example 1;

[0039] Figure 3 This is a stereomicroscopic photograph of the pretreated gel microspheres from Example 1;

[0040] Figure 4 A stereomicroscope photograph of the ceramic microspheres of Example 1;

[0041] Figure 5 A stereomicroscope photograph of the ceramic microspheres in Comparative Example 1;

[0042] Figure 6 This is a stereomicroscopic image of the pretreated gel microspheres in Comparative Example 2.

[0043] Figure 7 This is a stereomicroscope image of the ceramic microspheres in Comparative Example 2. Detailed Implementation

[0044] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0045] This invention provides a method for preparing pretreated gel microspheres, such as... Figure 1 As shown, it includes the following steps:

[0046] S1. The gel microspheres after washing or first drying are immersed in a first immersion solution, wherein the first immersion solution includes at least one of propylene glycol methyl ether, dioxane, pyridine and ethanol.

[0047] S2. The gel microspheres soaked in the first soaking solution are subjected to a second drying treatment to obtain pretreated gel microspheres.

[0048] The gel microspheres are first soaked in a soaking solution, utilizing their swelling property to increase their pore structure. The first soaking solution penetrates the gaps between the polymer chains of the gel microspheres, increasing the volume between chain segments and thus causing the gel microspheres to expand and enlarge their pore structure. Then, the gel microspheres soaked in the first soaking solution undergo a second drying treatment, where the gel microspheres and the first soaking solution are dried together. During this second drying process, because the surface tension of the first soaking solution is lower than that of water, the gel microspheres are subjected to less surface tension, thus maximizing the preservation of the swollen pore structure and preventing shrinkage and cracking. This results in pretreated gel microspheres with a larger pore structure and specific surface area. In the subsequent calcination process, gases from the oxidation and decomposition of organic matter easily escape from the pretreated gel microspheres, preventing them from rupturing due to excessive internal pressure, resulting in dense ceramic microspheres with a smooth, crack-free surface.

[0049] It should be noted that the gel microspheres in step S1 can be gel microspheres prepared by the sol-gel method and after washing. At this time, the gel microspheres contain a lot of water. The pre-treated gel microsphere preparation method of this embodiment replaces the traditional drying method in the prior art to obtain pre-treated gel microspheres. The pre-treated gel microspheres are then calcined to obtain ceramic microspheres. Alternatively, the gel microspheres in step S1 can also be gel microspheres prepared by the sol-gel method and after washing and a first drying treatment. Although most of the water has been removed after the first drying treatment, some free water and crystal water will inevitably remain. Moreover, the gel microspheres may shrink to a certain extent after the first drying treatment. Therefore, if the subsequent calcination treatment is carried out directly, there is still a significant risk of cracking. Therefore, the pre-treated gel microsphere preparation method of this embodiment is added between the first drying treatment and the calcination treatment to expand the pore structure of the gel microspheres after the first drying treatment, which can effectively avoid the problem of cracking of the gel microspheres during the calcination process. The sol-gel method mentioned here can be an external gel method or an internal gel method. The present invention does not impose any particular restrictions on the washing and first drying processes in step S1. They can be any method in the prior art, as long as it can ensure that the obtained gel microspheres are not cracked. If the gel powder is already in use, the preparation method of the pretreated gel microspheres in the present invention will not be applicable.

[0050] The soaking described in steps S2 and S3 means immersing the gel microspheres in the first soaking solution, meaning the amount of the first soaking solution added must completely submerge the gel microspheres. If the gel microspheres are not completely submerged, the exposed parts of the gel microspheres will shrink and crack.

[0051] In some embodiments, in step S1, the soaking temperature is 20–25°C, such as 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, etc., and the time is 12–24 hours, such as 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, etc. Within the above temperature range, the first soaking solution will not evaporate too quickly, allowing the gel spheres to fully swell. If the soaking temperature is too low, the required time will be too long, which is not conducive to improving work efficiency. If the soaking temperature is too high, the first soaking solution will evaporate too quickly, which is not conducive to the full swelling of the gel microspheres.

[0052] In some embodiments, in step S2, the second drying process is far-infrared drying and / or vacuum drying. Both of these drying methods are simple to operate and low in cost.

[0053] In some embodiments, in step S2, the vacuum degree of the vacuum drying is maintained between -0.08 and -0.1 MPa, for example, -0.08 MPa, -0.085 MPa, -0.09 MPa, -0.095 MPa, -0.1 MPa, etc. Vacuum drying within this vacuum range helps maintain the pore structure of the gel microspheres after swelling and prevents shrinkage and cracking. When the vacuum is too low, the boiling point of the first soaking solution will decrease, which may cause the first soaking solution to boil, which is not conducive to the second drying process. When the vacuum is too high, it may damage the pore structure of the gel microspheres after volume expansion.

[0054] In some embodiments, in step S2, the temperature of the second drying treatment is 60–80°C, such as 60°C, 65°C, 70°C, 75°C, 80°C, etc., and the time is 12–48 hours, such as 12 hours, 15 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, 45 hours, 48 ​​hours, etc. During the second drying treatment, the gel microspheres tend to shrink, but because they are immersed in the first soaking solution, a swelling effect also occurs. Performing the second drying treatment within this range helps the two effects to cancel each other out, maximizing the maintenance of the pore structure of the gel microspheres after swelling and preventing shrinkage and cracking. When the temperature of the second drying treatment is too low, the removal rate of the first soaking solution and residual washing solvent in the gel microspheres is too slow, which is not conducive to improving production efficiency. When the temperature of the second drying treatment is too high, the evaporation rate of the residual washing solvent in the gel microspheres and the first soaking solution is too fast, which does not help maintain the pore structure of the gel microspheres after swelling.

[0055] In some embodiments, in step S2, after the soaking treatment, the gel microspheres are separated from the first soaking solution, and then the gel microspheres are soaked in a second soaking solution, the second soaking solution comprising at least one of propylene glycol methyl ether, dioxane, pyridine, and ethanol; then the gel microspheres soaked in the second soaking solution are subjected to the second drying treatment to obtain the pretreated gel microspheres. Because the first soaking solution may contain residual water from the soaking of the gel microspheres, and water has a high surface tension, it will cause the pores of the gel microspheres to shrink during the subsequent second drying treatment, which is not conducive to maintaining a large pore structure. Therefore, it is preferable to replace the soaking solution with the second soaking solution to ensure that there is no water in the second soaking solution during the second drying treatment, which is beneficial for the gel microspheres to maintain a large pore structure. It should be noted that the type of the second soaking solution can be the same as or different from the type of the first soaking solution.

[0056] In addition, this embodiment of the invention also provides a pretreated gel microsphere, which is obtained by the preparation method of the pretreated gel microsphere.

[0057] Compared to untreated gel microspheres, the pretreated gel microspheres in this embodiment of the invention have a larger specific surface area and pores, and a smooth, crack-free surface. During the subsequent calcination process, the gases from the oxidation and decomposition of organic matter can easily escape from the pretreated gel microspheres, and the pretreated gel microspheres will not rupture due to excessive internal pressure. The resulting ceramic microspheres have a smooth, crack-free surface and good internal density.

[0058] In addition, this invention also provides a method for preparing ceramic microspheres, comprising the following steps: calcining the pretreated gel microspheres in an oxidizing atmosphere to obtain ceramic microspheres.

[0059] Because the pretreated gel microspheres have a larger pore structure, the gases from the decomposition of organic matter during calcination can completely escape from the pores, reducing the risk of cracking due to excessive internal pressure in the gel microspheres, and ultimately obtaining crack-free ceramic microspheres.

[0060] In some embodiments, the calcination treatment is carried out in stages: first, it is held at 190–210°C, for example, 190°C, 195°C, 200°C, 205°C, 210°C, etc., for 4–6 hours, for example, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, etc.; then, it is held at 270–290°C, for example, 270°C, 275°C, 280°C, 285°C, 290°C, etc., for 2–4 hours, for example, 2 hours, 2.5 hours, 3 hours. The calcination process involves several stages, including calcination at 350–370℃ (e.g., 350℃, 355℃, 360℃, 365℃, 370℃) for 4–6 hours (e.g., 4h, 4.5h, 5h, 5.5h, 6h), and finally at 390–410℃ (e.g., 390℃, 395℃, 400℃, 405℃, 410℃) for 2–4 hours (e.g., 2h, 2.5h, 3h, 3.5h, 4h). This phased calcination process ensures that the organic matter in the pretreated gel microspheres is fully removed.

[0061] In some embodiments, the heating rate of the calcination treatment does not exceed 1°C / min, for example, 0.2°C / min, 0.4°C / min, 0.6°C / min, 0.8°C / min, 1°C / min, etc. A smaller heating rate allows for the slow release of gases generated by the decomposition of organic matter, helping to prevent the ceramic microspheres from cracking.

[0062] Furthermore, this embodiment of the invention also provides a ceramic microsphere, obtained by the method for preparing the ceramic microsphere.

[0063] The pretreated gel microspheres have a large pore structure. After calcination, the pores shrink, resulting in ceramic microspheres with a smooth surface, no cracks, and a dense interior.

[0064] The ceramic microspheres in this invention embodiment are not limited in type. They can be any type of ceramic microsphere used in the military, pharmaceutical, chemical, environmental protection, nuclear technology and other industries, including but not limited to ceramic microspheres made of cerium oxide, zirconium oxide, alumina, silicon oxide or uranium oxide.

[0065] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0066] Example 1

[0067] A method for preparing pretreated gel microspheres and ceramic microspheres, such as... Figure 1 As shown, it includes the following steps:

[0068] (1) Gel microspheres were prepared by sol-gel method: A mixed solution of ZrO(NO3)2 and Y(NO3)3 was prepared as a precursor solution with a molar concentration of 1.6 mol / L for ZrO(NO3)2 and 0.36 mol / L for Y(NO3)3. Then, 2.3 mL of concentrated nitric acid was added to 28.74 mL of the precursor solution to form a Zr / Y solution. A mixed solution of HMTA and urea was prepared with a molar concentration of 3 mol / L for both HMTA and urea. 20 mL of the mixed solution of HMTA and urea was mixed with the Zr / Y solution at 5 °C to form a clear and transparent gel solution. The gel solution was dispersed in hot silicone oil at 90 °C to form gel microspheres.

[0069] (2) The gel microspheres obtained in step (1) were subjected to a combined washing process of trichloroethylene washing, 0.5 mol / L ammonia washing, and propylene glycol methyl ether washing. Specifically, the microspheres were washed four times in trichloroethylene for 30 min each time to remove residual silicone oil from the surface of the gel microspheres. Then, they were washed four times in 0.5 mol / L ammonia for 30 min each time to remove residual organic matter such as ammonium nitrate, urea, and HMTA from the gel microspheres. Finally, they were washed four times in propylene glycol methyl ether for 30 min each time to remove moisture from the gel microspheres.

[0070] (3) The gel microspheres obtained in step (2) were subjected to far-infrared drying at 60℃ for 12 hours (first drying treatment). The stereomicroscopic image of the obtained gel microspheres is shown below. Figure 2 As shown;

[0071] (4) Soak the gel microspheres obtained in step (3) in propylene glycol methyl ether (first soaking solution) for 24 hours at a soaking temperature of 20°C. The amount of propylene glycol methyl ether added should completely cover the gel microspheres to make them swell and thus expand the pore size of the gel microspheres.

[0072] (5) Discard the old propylene glycol methyl ether (first soaking solution) and add new propylene glycol methyl ether (second soaking solution). The amount of new propylene glycol methyl ether (second soaking solution) added should completely cover the gel microspheres.

[0073] (6) The gel microspheres soaked in fresh propylene glycol methyl ether (second soaking solution) were placed in a vacuum drying oven at 60°C and dried for 24 hours (second drying treatment). The vacuum degree was maintained at -0.08MPa to obtain pretreated gel microspheres.

[0074] (7) The pretreated gel microspheres obtained in step (6) were placed in a muffle furnace for calcination at a heating rate of 0.5℃ / min. The temperature was maintained at 200℃ for 6 hours, 280℃ for 2 hours, 360℃ for 4 hours and 400℃ for 2 hours in an air atmosphere, and finally ZrO2 ceramic microspheres were obtained.

[0075] Stereoscopic images of the pretreated gel microspheres obtained in this embodiment are shown below. Figure 3 As shown in the figure, the surface of the pretreated gel microspheres is smooth and crack-free, with a measured cracking rate of 0%. Stereoscopic images of the prepared ceramic microspheres are shown below. Figure 4 As shown, from Figure 4 It can be seen that the ceramic microspheres also have a smooth surface without cracks, and the measured crack rate is 0%.

[0076] Example 2

[0077] A method for preparing pretreated gel microspheres and ceramic microspheres, such as... Figure 1 As shown, it includes the following steps:

[0078] Steps (1)-(3) are the same as in Example 1.

[0079] (4) Soak the gel microspheres obtained in step (3) in propylene glycol methyl ether (first soaking solution) for 12 hours at a soaking temperature of 25°C. The amount of propylene glycol methyl ether (first soaking solution) added should completely cover the gel microspheres to make them swell and thus expand the pore size of the gel microspheres.

[0080] (5) Discard the old propylene glycol methyl ether (first soaking solution) and add new propylene glycol methyl ether (second soaking solution). The amount of new propylene glycol methyl ether (second soaking solution) added should completely cover the gel microspheres.

[0081] (6) The gel microspheres soaked in new propylene glycol methyl ether (second soaking solution) were placed in a far-infrared drying oven at 80°C and dried for 24 hours to obtain pretreated gel microspheres.

[0082] (7) The pretreated gel microspheres obtained in step (6) were placed in a muffle furnace for calcination at a heating rate of 0.5℃ / min. The temperature was maintained at 200℃ for 6 hours, 280℃ for 4 hours, 360℃ for 6 hours and 400℃ for 2 hours in an air atmosphere, and finally ZrO2 ceramic microspheres were obtained.

[0083] In this embodiment, the pretreated gel microspheres had smooth, crack-free surfaces, with a measured cracking rate of 0%. The obtained ceramic microspheres also had smooth, crack-free surfaces, with a measured cracking rate of 0%.

[0084] Example 3

[0085] A method for preparing pretreated gel microspheres and ceramic microspheres is the same as in Example 1, except that the first soaking solution and the second soaking solution used are both dioxane.

[0086] In this embodiment, the pretreated gel microspheres had a smooth, crack-free surface, with a measured cracking rate of 1%. The obtained ceramic microspheres also had a smooth, crack-free surface, with a measured cracking rate of 2%.

[0087] Example 4

[0088] A method for preparing pretreated gel microspheres and ceramic microspheres is the same as in Example 1, except that the first soaking solution and the second soaking solution used are both pyridine.

[0089] In this embodiment, the pretreated gel microspheres had a smooth, crack-free surface, with a measured cracking rate of 1%. The obtained ceramic microspheres also had a smooth, crack-free surface, with a measured cracking rate of 2%.

[0090] Example 5

[0091] A method for preparing pretreated gel microspheres and ceramic microspheres is the same as in Example 1, except that the first soaking solution and the second soaking solution used are both ethanol.

[0092] In this embodiment, the pretreated gel microspheres had a smooth, crack-free surface, with a measured cracking rate of 2%. The obtained ceramic microspheres also had a smooth, crack-free surface, with a measured cracking rate of 2%.

[0093] Example 6

[0094] A method for preparing pretreated gel microspheres and ceramic microspheres is the same as in Example 1, except that the first soaking solution and the second soaking solution used are both mixtures of propylene glycol methyl ether and ethanol, with a mass ratio of 1:1.

[0095] In this embodiment, the pretreated gel microspheres had smooth, crack-free surfaces, with a measured cracking rate of 0%. The obtained ceramic microspheres also had smooth, crack-free surfaces, with a measured cracking rate of 0%.

[0096] Example 7

[0097] A method for preparing pretreated gel microspheres and ceramic microspheres is the same as in Example 1, except that the first soaking solution and the second soaking solution used are both mixtures of dioxane and pyridine, with a mass ratio of 1:2.

[0098] In this embodiment, the pretreated gel microspheres had a smooth, crack-free surface, with a measured cracking rate of 1%. The obtained ceramic microspheres also had a smooth, crack-free surface, with a measured cracking rate of 2%.

[0099] Example 8

[0100] A method for preparing pretreated gel microspheres and ceramic microspheres is the same as in Example 1, except that step (5) is omitted and step (6) is performed directly: the gel microspheres soaked in propylene glycol methyl ether (first soaking solution) are placed in a far-infrared drying oven at 80°C and dried for 24 hours to obtain pretreated gel microspheres.

[0101] In this embodiment, the pretreated gel microspheres had a smooth, crack-free surface, with a measured cracking rate of 1%. The obtained ceramic microspheres also had a smooth, crack-free surface, with a measured cracking rate of 2%.

[0102] Example 9

[0103] A method for preparing pretreated gel microspheres and ceramic microspheres is the same as in Example 1, except that step (3) is omitted.

[0104] In this embodiment, the pretreated gel microspheres had smooth, crack-free surfaces, with a measured cracking rate of 0%. The obtained ceramic microspheres also had smooth, crack-free surfaces, with a measured cracking rate of 0%.

[0105] Comparative Example 1

[0106] A method for preparing gel microspheres and ceramic microspheres includes the following steps:

[0107] Steps (1)-(3) are the same as in Example 1.

[0108] Step (4) involves placing the gel microspheres obtained in step (3) into a muffle furnace for calcination at a heating rate of 0.5℃ / min. The microspheres are then kept at 200℃ for 6 hours, 280℃ for 2 hours, 360℃ for 4 hours, and 400℃ for 2 hours in an air atmosphere, ultimately yielding ZrO2 ceramic microspheres.

[0109] Stereoscopic images of the ceramic microspheres prepared in this comparative example are shown below. Figure 5 As shown. From Figure 5 As can be seen, the obtained ceramic microspheres are severely cracked, with a measured cracking rate of 95%. The ceramic microspheres are also severely pulverized and have virtually no strength.

[0110] Comparative Example 2

[0111] A method for preparing pretreated gel microspheres and ceramic microspheres is the same as in Example 1, except that step (5) involves discarding the old propylene glycol methyl ether (first soaking solution) and separating the gel microspheres; step (6) involves sending the gel microspheres obtained in step (5) into a vacuum drying oven at 60°C for 24 hours, maintaining the vacuum degree at -0.08 MPa, to obtain pretreated gel microspheres.

[0112] Stereoscopic images of the pretreated gel microspheres prepared in this comparative example are shown below. Figure 6 As shown, some of the pretreated gel microspheres cracked, with a cracking rate of 1%. Stereomicroscopic images of the obtained ceramic microspheres are shown below. Figure 7 As shown, some ceramic microspheres have cracked, and the measured cracking rate of ceramic microspheres is 10%.

[0113] Comparing Example 1 and Comparative Example 1, both used gel microspheres after the first drying treatment, and the calcination process for the gel microspheres was the same. The only difference was that the pre-treated gel microsphere preparation method was not used. Based on the gel microspheres and ceramic microspheres prepared in Example 1 and Comparative Example 1, the pre-treated gel microsphere preparation method provided by this invention effectively reduces the risk of cracking during calcination, avoids waste of gel microspheres, and achieves the goal of "turning waste into treasure."

[0114] By comparing Example 1 and Comparative Example 2, it can be seen that if the gel microspheres are dried a second time on their own instead of being dried while soaked, it is not conducive to maintaining the pore structure of the sol microspheres after swelling. Consequently, the ceramic microspheres obtained after subsequent calcination will also crack.

[0115] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0116] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing pretreated gel microspheres for ceramic microspheres, characterized in that, Includes the following steps: S1. The gel microspheres, after washing or after washing and first drying, are immersed in a first soaking solution for immersion treatment; wherein the washing treatment is a combined washing treatment of trichloroethylene, ammonia, and propylene glycol methyl ether, and the first soaking solution includes at least one of propylene glycol methyl ether, dioxane, pyridine, and ethanol; the soaking temperature is 20-25°C and the time is 12-24 hours. S2. The gel microspheres soaked in the first soaking solution are subjected to a second drying treatment to obtain pretreated gel microspheres.

2. The method for preparing pretreated gel microspheres according to claim 1, characterized in that, In step S2, the second drying process is far-infrared drying and / or vacuum drying.

3. The method for preparing pretreated gel microspheres according to claim 2, characterized in that, In step S2, the vacuum degree of the vacuum drying is maintained at -0.08 to -0.1 MPa.

4. The method for preparing pretreated gel microspheres according to claim 2, characterized in that, In step S2, the temperature of the second drying process is 60-80°C, and the time is 12-48 hours.

5. The method for preparing pretreated gel microspheres according to claim 1, characterized in that, In step S2, after the soaking treatment, the gel microspheres are separated from the first soaking solution, and then the gel microspheres are soaked in a second soaking solution, the second soaking solution including at least one of propylene glycol methyl ether, dioxane, pyridine and ethanol; then the gel microspheres soaked in the second soaking solution are subjected to the second drying treatment to obtain the pretreated gel microspheres.

6. A pretreated gel microsphere, characterized in that, Obtained by the preparation method according to any one of claims 1-5.

7. A method for preparing ceramic microspheres, characterized in that, The process includes the following steps: calcining the pretreated gel microspheres according to claim 6 in an oxidizing atmosphere to obtain ceramic microspheres; wherein the heating rate of the calcination process does not exceed 1℃ / min; and / or, the calcination process is carried out in stages: first, holding at 190~210℃ for 4~6h, then holding at 270~290℃ for 2~4h, then holding at 350~370℃ for 4~6h, and finally holding at 390~410℃ for 2~4h.

8. A ceramic microsphere, characterized in that, Obtained by the preparation method described in claim 7.

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