Preparation method of hollow ceramic ball with porous shell structure

Abstract

The invention discloses a preparation method of a hollow ceramic ball with a porous shell structure, which comprises the following steps: firstly preparing ceramic slurry and a liquid core material, and then forming liquid drops of which the core layer is the liquid core material and the shell layer is the ceramic slurry through a coaxial extrusion process; dropwise adding the liquid drops into a heavy metal ion solution, and carrying out an ionic cross-linking reaction to obtain ceramic gel balls; then wiping the surfaces of the ceramic gel balls to be dry, and performing freezing treatment to obtain frozen ceramic gel balls; carrying out vacuum freeze drying on the frozen ceramic gel balls to sublimate moisture and form pores, so as to obtain freeze-dried ceramic gel balls; and finally, carrying out high-temperature sintering on the freeze-dried ceramic gel ball to obtain the hollow ceramic ball with the porous shell structure. According to the invention, a coaxial double-needle technology, a freeze-drying technology and a sintering technology are combined, and the hollow ceramic balls with high mechanical integrity, small thickness deviation and different pore characteristics are prepared by regulating and controlling the pore structure characteristics of the porous shell layer and the volume ratio of the core to the wall.

Description

Technical Field

[0001] The invention relates to the field of hollow ceramic ball preparation, in particular to a method for preparing hollow ceramic balls with a porous shell structure. Background Art

[0002] Due to their unique structural properties, hollow ceramic spheres have demonstrated significant application value in catalyst supports, thermal insulation materials, drug delivery systems, functional fillers, and phase change material encapsulation. In particular, the porous shell structure of hollow ceramic spheres, with its significantly increased specific surface area and optimized diffusion channel design, offers orders of magnitude advantages in gas-solid reaction efficiency and thermal barrier properties compared to traditional dense ceramics.

[0003] In the prior art, the template method is a typical process for preparing hollow ceramic balls. By coating the surface of the template with ceramic powder, the template is completely burned to form a hollow structure during the high-temperature roasting process, and the ceramic powder crystallizes to form a shell layer, thereby obtaining a hollow ceramic ball. However, this method has significant defects, including the fact that the template removal stage easily causes the collapse of the shell structure, resulting in a high loss rate of mechanical integrity; in addition, it may also cause thickness deviation and insufficient ability to control the pore structure. Although the sol-gel method can improve the uniformity of the shell layer, it is limited by the gel shrinkage effect, and the final product has a high pore size distribution dispersion coefficient, and the specific surface area usually has certain limitations. Although spray pyrolysis technology has the advantage of continuous production, the rapid thermal densification process will close the surface pores, requiring additional acid etching treatment, resulting in increased process complexity and increased wastewater treatment costs.

[0004] Therefore, developing a preparation method that can precisely control the porous shell structure and achieve both process economy and product consistency has become a key issue that urgently needs to be broken through in this technical field. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a method for preparing hollow ceramic balls with a porous shell structure.

[0006] The technical solution of the present invention to solve the above technical problem is to provide a method for preparing hollow ceramic balls with a porous shell structure, characterized in that the method comprises the following steps:

[0007] Step 1, preparing ceramic slurry: mixing ceramic powder, dispersant and water, and then adding gel raw materials until the gel raw materials are mixed evenly to obtain ceramic slurry;

[0008] Preparation of liquid core material: Mix thickener and water evenly to obtain liquid core material;

[0009] Step 2: Using a coaxial extrusion process, droplets are formed, each having a core layer of liquid core material and a shell layer of ceramic slurry; the droplets are then poured into a heavy metal ion solution for ion crosslinking reaction to obtain ceramic gel balls;

[0010] Step 3: After wiping the surface of the ceramic gel ball obtained in step 2 dry, freezing it to completely solidify it into a solid state, thereby obtaining a frozen ceramic gel ball;

[0011] Step 4: vacuum freeze-drying the frozen ceramic gel balls to sublime the water and form pores to obtain freeze-dried ceramic gel balls;

[0012] Step 5: sintering the freeze-dried ceramic gel balls at high temperature to obtain hollow ceramic balls with a porous shell structure.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] (1) The present invention combines coaxial double-needle technology, freeze-drying technology and sintering technology. By regulating the pore structure characteristics of the porous shell and the core-to-wall volume ratio, hollow ceramic balls with high mechanical integrity, small thickness deviation and different pore characteristics are prepared. The preparation process is simple and the structure is easy to regulate, which can achieve large-scale production.

[0015] (2) The present invention adopts coaxial double-needle technology to realize synchronous extrusion of ceramic slurry and water, and realizes complete encapsulation of water by slurry by regulating parameters such as rheological properties and propulsion speed of slurry; then, the ionic cross-linking reaction of slurry is used to realize shaping; then, the porous structure and hollow structure of the shell are constructed by freezing and freeze-drying; finally, hollow ceramic balls with porous shell structure are obtained by sintering. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is an overall diagram of the hollow ceramic ball prepared in Example 1 of the present invention;

[0017] Figure 2 This is a cross-sectional view of the hollow ceramic ball prepared in Example 1 of the present invention;

[0018] Figure 3 This is an electron microscope image of the outer surface of the hollow ceramic sphere prepared in Example 1 of the present invention;

[0019] Figure 4 This is a cross-sectional view of a hollow ceramic ball prepared in Example 2 of the present invention;

[0020] Figure 5 This is an electron microscope image of the inner surface of the hollow ceramic ball prepared in Example 2 of the present invention;

[0021] Figure 6 This is an electron microscope image of the outer surface of the hollow ceramic sphere prepared in Example 2 of the present invention;

[0022] Figure 7 This is an electron microscope image of the cross section of the hollow ceramic sphere prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0023] The specific embodiments of the present invention are given below. The specific embodiments are only used to further illustrate the present invention and do not limit the scope of protection of the present invention.

[0024] The present invention provides a method for preparing a hollow ceramic ball having a porous shell structure (hereinafter referred to as the method), characterized in that the method comprises the following steps:

[0025] Step 1: Prepare ceramic slurry and liquid core material:

[0026] Prepare ceramic slurry: Mix ceramic powder, dispersant and water evenly, then add gel raw materials until the gel raw materials are evenly mixed without agglomeration to obtain a uniform ceramic slurry;

[0027] Preparation of liquid core material: Mix thickener and water evenly to obtain liquid core material;

[0028] Preferably, in step 1, the mixing process of the ceramic powder, dispersant and water is: stirring speed is 600-800 r / min, stirring time is 30-60 min, and stirring temperature is room temperature (i.e. normal temperature).

[0029] Preferably, in step 1, the mixing process of the gel raw materials is: stirring for 2 to 3 hours in an environment of 60 to 90° C. and a stirring speed of 700 to 1000 r / min.

[0030] Preferably, in step 1, the ceramic powder is at least one of alumina powder, silica powder, titanium dioxide powder, silicon carbide powder, silicon nitride powder, mullite powder or phosphogypsum powder; the dispersant is diammonium hydrogen citrate; and the gel raw material is sodium alginate.

[0031] Preferably, in step 1, the particle size of the ceramic powder is less than 200 μm.

[0032] Preferably, in step 1, the mass of the ceramic powder accounts for 20-40% of the total mass of the ceramic slurry, the mass of the dispersant accounts for 0.2-0.5% of the mass of the ceramic powder, the mass of water accounts for 60-80% of the total mass of the ceramic slurry; and the mass of the gel raw material accounts for 1-2% of the total mass of the ceramic slurry.

[0033] Preferably, in step 1, the thickener is at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose, polyvinyl alcohol, pectin, hydroxyethyl cellulose, sodium hydroxyethyl cellulose or xanthan gum.

[0034] Preferably, in step 1, the mass of the thickener accounts for 0.5-1.5% of the mass of the liquid core material.

[0035] Preferably, in step 1, the mixing process of the thickener and water is: stirring for 2 to 3 hours in an environment of 40 to 80° C., and a stirring speed of 600 to 800 r / min.

[0036] Step 2: Using a coaxial extrusion process, droplets are formed, each having a core layer of liquid core material and a shell layer of ceramic slurry; the droplets are then poured into a heavy metal ion solution for ion crosslinking reaction to obtain ceramic gel balls;

[0037] Preferably, in step 2, the coaxial extrusion process is specifically: using a coaxial double-needle device, the ceramic slurry obtained in step 1 is input and extruded through the outer layer flow channel, and the liquid core material obtained in step 1 is input and extruded through the inner layer flow channel to form droplets in which the core layer is liquid core material and the shell layer is ceramic slurry, and the shell layer completely wraps the core layer.

[0038] Preferably, in step 2, the coaxial double-needle device has a double-layer flow channel, namely an outer layer flow channel and an inner layer flow channel; the outer tube is arranged on the outside of the inner tube, and the two are coaxially nested and arranged in concentric circles; the inside of the inner tube is the inner layer flow channel, and the annular area formed between the outer tube and the inner tube is the outer layer flow channel; the outer diameter of the outer tube is 3.75-4 mm, and the wall thickness of the outer tube is 0.25-0.5 mm; the outer diameter of the inner tube is 0.65-1.85 mm, and the wall thickness of the inner tube is 0.15-0.25 mm; the upper end of the inner tube is higher than the upper end of the outer tube (preferably: the upper end of the inner tube is 10-15 mm higher than the upper end of the outer tube).

[0039] Preferably, in step 2, the parameters of the coaxial extrusion process are: the advancing speed of the liquid core material is 0.02-0.1 ml / min, the advancing speed of the ceramic slurry is 0.1-0.5 ml / min, continuous extrusion or intermittent extrusion is adopted, and the ambient temperature is room temperature.

[0040] Preferably, in step 2, the metal ions in the heavy metal ion solution are calcium ions, zinc ions, iron ions, aluminum ions or barium ions.

[0041] Preferably, in step 2, the mass fraction of metal ions in the heavy metal ion solution is 20 to 40 wt%.

[0042] Preferably, in step 2, the temperature of the ionic crosslinking reaction is room temperature, and the time is 4 to 6 hours.

[0043] Step 3: After wiping the surface of the ceramic gel ball obtained in step 2 dry, freezing it to completely solidify it into a solid state, thereby obtaining a frozen ceramic gel ball;

[0044] Preferably, in step 3, the ceramic gel balls obtained in step 2 are first washed with water to remove the heavy metal ion solution on the surface of the ceramic gel balls, and then the surface is wiped dry until there is no obvious moisture.

[0045] Preferably, in step 3, the freezing treatment temperature is -15 to -80°C for 10 to 24 hours, until the ceramic gel balls are completely solidified and the water therein is frozen and crystallized. The freezing treatment environment is a refrigerator, a low-temperature constant temperature device, or a liquid nitrogen cooling device.

[0046] Step 4: vacuum freeze-drying the frozen ceramic gel balls to sublime the water and form pores to obtain freeze-dried ceramic gel balls;

[0047] Preferably, in step 4, the vacuum freeze drying time is 48 to 72 hours, the temperature is -30 to -60°C (preferably -60°C), and the vacuum degree is 10 to 100 Pa (preferably 20 Pa), until the water in the ceramic gel balls is completely sublimated. The freeze drying environment is a freeze dryer.

[0048] Step 5: sintering the freeze-dried ceramic gel balls at high temperature to obtain hollow ceramic balls with a porous shell structure (referred to as hollow ceramic balls).

[0049] Preferably, in step 5, the high-temperature sintering process includes sequentially performing heating, holding the maximum temperature constant, and cooling; during the heating process, the heating rate is 3-5°C / min, the maximum temperature is 1000-1500°C, the maximum temperature is held constant for 1-2 hours, and during the cooling process, the cooling rate does not exceed 10°C / min until the temperature reaches 100°C. Sintering is performed in a muffle furnace.

[0050] Preferably, in step 5, the particle size of the hollow ceramic balls having a porous shell structure is in the millimeter order (particle size distribution is 3 to 8 mm), and the pores on the shell are in the micron order.

[0051] Example 1:

[0052] (1) 20 g of alumina powder, 0.6 g of diammonium hydrogen citrate, and 80 g of water were magnetically stirred at room temperature and 800 rpm for 30 min until uniformly mixed; then 1.5 g of sodium alginate was added and stirred at 60° C. and 1000 rpm for 150 min until uniformly mixed to form a ceramic slurry;

[0053] 1g of sodium carboxymethyl cellulose and 99g of water were magnetically stirred at 60°C and 800 rpm for 150 min until uniformly mixed to form a liquid core material;

[0054] (2) At room temperature, a coaxial extrusion process was used with a ceramic slurry advancing speed of 2 mm / min and a liquid core material advancing speed of 1.5 mm / min to form droplets with a core layer of liquid core material and a shell layer of ceramic slurry. The droplets were then poured into a 500 ml calcium chloride solution with a mass fraction of 20 wt% for 5 h to undergo an ionic crosslinking reaction to obtain ceramic gel spheres.

[0055] (3) The ceramic gel balls were taken out, the surface was cleaned with deionized water, and then the surface moisture was wiped off with a non-woven fabric. The balls were then placed in a low-temperature environment of -20°C for 12 hours to completely solidify them into a solid state, thereby obtaining frozen ceramic gel balls.

[0056] (4) placing the frozen ceramic gel balls in a freeze dryer and freeze-drying them at a temperature of -58°C and a vacuum degree of 10 Pa for 48 hours to allow the water to sublime and form pores, thereby obtaining freeze-dried ceramic gel balls;

[0057] (5) The freeze-dried ceramic gel balls were placed in a muffle furnace for high-temperature sintering with a heating rate of 3°C / min, a maximum temperature of 1400°C, a constant temperature time of the maximum temperature of 2 h, and a cooling rate of 5°C / min until the temperature dropped to 100°C, thereby obtaining hollow ceramic balls with a porous shell structure.

[0058] Depend on Figure 1 It can be seen that the diameter of the hollow ceramic ball is 5mm, the particles are full, the surface has no collapse, and the whole body is white.

[0059] Depend on Figure 2 It can be seen that the shell thickness of the hollow ceramic ball is uniform and the internal hollow volume is large.

[0060] Depend on Figure 3 It can be seen that the outer surface of the shell of the hollow ceramic sphere has a large number of micropores, and the pore size distribution range is 1 to 20 μm.

[0061] Example 2:

[0062] (1) 16 g of α-Al2O3 powder, 4 g of TiO2 powder, 0.6 g of diammonium hydrogen citrate, and 80 g of deionized water were magnetically stirred at room temperature and 800 r / min for 30 min until uniform; then 1.5 g of sodium alginate was added and stirred at 60°C and 1000 r / min for 2 h until uniform, to form a ceramic slurry;

[0063] 1.5 g of sodium carboxymethyl cellulose and 98.5 g of water were magnetically stirred at 60°C and 800 rpm for 150 min until uniformly stirred to form a liquid core material;

[0064] (2) At room temperature, a coaxial extrusion process was used with the ceramic slurry advancing at a speed of 2.3 mm / min and the liquid core material advancing at a speed of 1.5 mm / min to form droplets with a core layer of liquid core material and a shell layer of ceramic slurry. The droplets were then poured into a 500 ml calcium chloride solution with a mass fraction of 20 wt% for 5 h to undergo an ionic crosslinking reaction to obtain ceramic gel spheres.

[0065] (3) The ceramic gel balls were taken out, the surface was cleaned with deionized water, and then the surface moisture was wiped off with a non-woven fabric. The balls were then placed in a low-temperature environment of -20°C for 12 hours to completely solidify them into a solid state, thereby obtaining frozen ceramic gel balls.

[0066] (4) placing the frozen ceramic gel balls in a freeze dryer and freeze-drying them at a temperature of -58°C and a vacuum degree of 10 Pa for 48 hours to allow the water to sublime and form pores, thereby obtaining freeze-dried ceramic gel balls;

[0067] (5) The freeze-dried ceramic gel balls were placed in a muffle furnace for high-temperature sintering with a heating rate of 3°C / min, a maximum temperature of 1400°C, a constant temperature time of the maximum temperature of 2 h, and a cooling rate of 5°C / min until the temperature dropped to 100°C, thereby obtaining hollow ceramic balls with a porous shell structure.

[0068] Depend on Figure 4 It can be seen that the porous ceramic sphere shell obtained after sintering has uniform thickness and large internal hollow volume.

[0069] Depend on Figure 5 It can be seen that the inner surface of the shell has a large number of microporous structures with a pore size distribution range of 0.2 to 1 μm.

[0070] Depend on Figure 6 It can be seen that the outer surface of the shell has a large number of microporous structures with a pore size distribution range of 0.5 to 5 μm.

[0071] Depend on Figure 7 It can be seen that the shell cross section has a large number of microporous structures with a pore size distribution range of 0.5 to 5 μm.

[0072] Example 3:

[0073] (1) 16 g of α-Al2O3 powder, 4 g of mullite powder, 0.6 g of diammonium hydrogen citrate, and 80 g of deionized water were magnetically stirred at room temperature and 800 r / min for 30 min until uniform; then 1.5 g of sodium alginate was added and stirred at 60°C and 1000 r / min for 2 h until uniform, to form a ceramic slurry;

[0074] 1.5 g of pectin and 98.5 g of water were magnetically stirred at 60°C and 800 rpm for 150 min until uniformly mixed to form a liquid core material;

[0075] (2) At room temperature, a coaxial extrusion process was used with the ceramic slurry advancing at a speed of 2.1 mm / min and the liquid core material advancing at a speed of 1.2 mm / min to form droplets with a core layer of liquid core material and a shell layer of ceramic slurry. The droplets were then poured into a 500 ml calcium chloride solution with a mass fraction of 20 wt% for 5 h to undergo an ionic crosslinking reaction to obtain ceramic gel spheres.

[0076] (3) The ceramic gel balls were taken out, the surface was cleaned with deionized water, and then the surface moisture was wiped off with a non-woven fabric. The balls were then placed in a low-temperature environment of -20°C for 12 hours to completely solidify them into a solid state, thereby obtaining frozen ceramic gel balls.

[0077] (4) placing the frozen ceramic gel balls in a freeze dryer and freeze-drying them at a temperature of -45°C and a vacuum degree of 10 Pa for 60 hours to allow the water to sublime and form pores, thereby obtaining freeze-dried ceramic gel balls;

[0078] (5) The freeze-dried ceramic gel balls were placed in a muffle furnace for high-temperature sintering with a heating rate of 4°C / min, a maximum temperature of 1500°C, a constant temperature time of the maximum temperature of 2 h, and a cooling rate of 5°C / min until the temperature dropped to 100°C, thereby obtaining hollow ceramic balls with a porous shell structure.

[0079] Example 4:

[0080] (1) 12 g of α-Al2O3 powder, 8 g of silicon carbide powder, 0.6 g of diammonium hydrogen citrate, and 80 g of deionized water were magnetically stirred at room temperature and 800 rpm for 30 min until uniformly mixed; then 1.5 g of sodium alginate was added and stirred at 60°C and 1000 rpm for 2 h until uniformly mixed to form a ceramic slurry;

[0081] 1.5 g of sodium hydroxyethyl cellulose and 98.5 g of water were magnetically stirred at 60°C and 800 rpm for 150 min until uniformly stirred to form a liquid core material;

[0082] (2) At room temperature, a coaxial extrusion process was used with the ceramic slurry advancing at a speed of 2.5 mm / min and the liquid core material advancing at a speed of 1.6 mm / min to form droplets with a core layer of liquid core material and a shell layer of ceramic slurry. The droplets were then poured into a 500 ml calcium chloride solution with a mass fraction of 20 wt% for 6 hours to undergo an ionic crosslinking reaction to obtain ceramic gel spheres.

[0083] (3) The ceramic gel balls were taken out, their surfaces were cleaned with deionized water, and then the surface moisture was wiped off with a non-woven fabric. The balls were then placed in a low-temperature environment of -20°C for 20 hours to completely solidify them into a solid state, thereby obtaining frozen ceramic gel balls.

[0084] (4) placing the frozen ceramic gel balls in a freeze dryer and freeze-drying them at a temperature of -55°C and a vacuum degree of 20 Pa for 48 hours to allow the water to sublime and form pores, thereby obtaining freeze-dried ceramic gel balls;

[0085] (5) The freeze-dried ceramic gel balls were placed in a muffle furnace for high-temperature sintering with a heating rate of 5°C / min, a maximum temperature of 1450°C, a constant temperature time of 2 h at the maximum temperature, and a cooling rate of 5°C / min until the temperature dropped to 100°C, thereby obtaining hollow ceramic balls with a porous shell structure.

[0086] Example 5:

[0087] (1) 10 g of α-Al2O3 powder, 10 g of silica powder, 0.6 g of diammonium hydrogen citrate, and 80 g of deionized water were magnetically stirred at room temperature and 800 r / min for 30 min until uniformly mixed; then 1.5 g of sodium alginate was added and stirred at 60°C and 1000 r / min for 2 h until uniformly mixed to form a ceramic slurry;

[0088] 1.5 g of sodium carboxymethyl cellulose and 98.5 g of water were magnetically stirred at 60°C and 800 rpm for 150 min until uniformly stirred to form a liquid core material;

[0089] (2) At room temperature, a coaxial extrusion process was used with the ceramic slurry advancing at a speed of 2.3 mm / min and the liquid core material advancing at a speed of 1.5 mm / min to form droplets with a core layer of liquid core material and a shell layer of ceramic slurry. The droplets were then poured into a 500 ml barium chloride solution with a mass fraction of 20 wt% for 5 h to undergo an ionic crosslinking reaction to obtain ceramic gel spheres.

[0090] (3) The ceramic gel balls were taken out, the surface was cleaned with deionized water, and then the surface moisture was wiped off with a non-woven fabric. The balls were then placed in a low-temperature environment of -20°C for 12 hours to completely solidify them into a solid state, thereby obtaining frozen ceramic gel balls.

[0091] (4) placing the frozen ceramic gel balls in a freeze dryer and freeze-drying them at a temperature of -58°C and a vacuum degree of 10 Pa for 48 hours to allow the water to sublime and form pores, thereby obtaining freeze-dried ceramic gel balls;

[0092] (5) The freeze-dried ceramic gel balls were placed in a muffle furnace for high-temperature sintering with a heating rate of 3°C / min, a maximum temperature of 1250°C, a constant temperature time of 2 h at the maximum temperature, and a cooling rate of 5°C / min until the temperature dropped to 100°C, thereby obtaining hollow ceramic balls with a porous shell structure.

[0093] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A method for preparing hollow ceramic balls with a porous shell structure, characterized in that: The method comprises the following steps: Step 1, preparing ceramic slurry: mixing ceramic powder, dispersant and water, and then adding gel raw materials until the gel raw materials are mixed evenly to obtain ceramic slurry; Preparation of liquid core material: Mix thickener and water evenly to obtain liquid core material; Step 2: Using a coaxial extrusion process, droplets are formed, each having a core layer of liquid core material and a shell layer of ceramic slurry; the droplets are then poured into a heavy metal ion solution for ion crosslinking reaction to obtain ceramic gel balls; Step 3: After wiping the surface of the ceramic gel ball obtained in step 2 dry, freezing it to completely solidify it into a solid state, thereby obtaining a frozen ceramic gel ball; Step 4: vacuum freeze-drying the frozen ceramic gel balls to sublime the water and form pores to obtain freeze-dried ceramic gel balls; Step 5: sintering the freeze-dried ceramic gel balls at high temperature to obtain hollow ceramic balls with a porous shell structure.

2. The method for preparing hollow ceramic balls with a porous shell structure according to claim 1, wherein: In step 1, the mixing process of the ceramic powder, dispersant and water is: stirring speed is 600-800 r / min, stirring time is 30-60 min, and stirring temperature is room temperature; In step 1, the mixing process of the gel raw materials is: stirring for 2 to 3 hours in an environment of 60 to 90° C. and a stirring speed of 700 to 1000 r / min.

3. The method for preparing hollow ceramic balls with a porous shell structure according to claim 1, wherein: In step 1, the ceramic powder is at least one of alumina powder, silica powder, titanium dioxide powder, silicon carbide powder, silicon nitride powder, mullite powder or phosphogypsum powder; the dispersant is diammonium hydrogen citrate; and the gel raw material is sodium alginate.

4. The method for preparing hollow ceramic balls with a porous shell structure according to claim 1, wherein: In step 1, the particle size of the ceramic powder is less than 200 μm; In step 1, the mass of the ceramic powder accounts for 20-40% of the total mass of the ceramic slurry, the mass of the dispersant accounts for 0.2-0.5% of the mass of the ceramic powder, the mass of water accounts for 60-80% of the total mass of the ceramic slurry; and the mass of the gel raw material accounts for 1-2% of the total mass of the ceramic slurry.

5. The method for preparing hollow ceramic balls with a porous shell structure according to claim 1, wherein: In step 1, the thickener is at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose, polyvinyl alcohol, pectin, hydroxyethyl cellulose, sodium hydroxyethyl cellulose or xanthan gum; In step 1, the mass of the thickener accounts for 0.5 to 1.5% of the mass of the liquid core material; In step 1, the mixing process of the thickener and water is: stirring for 2 to 3 hours in an environment of 40 to 80° C. and a stirring speed of 600 to 800 r / min.

6. The method for preparing hollow ceramic balls with a porous shell structure according to claim 1, wherein: In step 2, the coaxial extrusion process is specifically as follows: using a coaxial double-needle device, the ceramic slurry obtained in step 1 is input and extruded through the outer layer flow channel, and the liquid core material obtained in step 1 is input and extruded through the inner layer flow channel to form a droplet in which the core layer is the liquid core material and the shell layer is the ceramic slurry, and the shell layer completely surrounds the core layer; In step 2, the outer and inner flow channels of the coaxial double needle device are arranged; the outer tube is arranged on the outside of the inner tube, and the two are coaxially nested and arranged in concentric circles; the interior of the inner tube is the inner flow channel, and the annular area formed between the outer tube and the inner tube is the outer flow channel; the outer diameter of the outer tube is 3.75-4 mm, and the wall thickness of the outer tube is 0.25-0.5 mm; the outer diameter of the inner tube is 0.65-1.85 mm, and the wall thickness of the inner tube is 0.15-0.25 mm; the upper end of the inner tube is higher than the upper end of the outer tube; In step 2, the parameters of the coaxial extrusion process are: the advancing speed of the liquid core material is 0.02-0.1 ml / min, the advancing speed of the ceramic slurry is 0.1-0.5 ml / min, continuous extrusion or intermittent extrusion is adopted, and the ambient temperature is room temperature.

7. The method for preparing hollow ceramic balls with a porous shell structure according to claim 1, wherein: In step 2, the metal ions in the heavy metal ion solution are calcium ions, zinc ions, iron ions, aluminum ions or barium ions; In step 2, the mass fraction of metal ions in the heavy metal ion solution is 20 to 40 wt%; In step 2, the temperature of the ionic crosslinking reaction is room temperature, and the time is 4 to 6 hours.

8. The method for preparing hollow ceramic balls with a porous shell structure according to claim 1, wherein: In step 3, the ceramic gel balls obtained in step 2 are first washed with water to remove the heavy metal ion solution on the surface of the ceramic gel balls, and then the surface is wiped dry until there is no obvious moisture; In step 3, the freezing treatment temperature is -15 to -80°C and the time is 10 to 24 hours.

9. The method for preparing hollow ceramic balls with a porous shell structure according to claim 1, wherein: In step 4, the vacuum freeze-drying time is 48 to 72 hours, the temperature is -30 to -60°C, and the vacuum degree is 10 to 100 Pa.

10. The method for preparing hollow ceramic balls with a porous shell structure according to claim 1, wherein: In step 5, the high-temperature sintering process includes heating, constant temperature at the highest temperature, and cooling in sequence; the heating rate during the heating process is 3 to 5°C / min, the highest temperature is 1000 to 1500°C, the constant temperature time at the highest temperature is 1 to 2 hours, and the cooling rate during the cooling process does not exceed 10°C / min until the temperature drops to 100°C; In step 5, the particle size of the hollow ceramic spheres with a porous shell structure is in the millimeter order, and the pores on the shell are in the micrometer order.

Images