A method for preparing zinc oxide-coated aluminum hydroxide powder

Abstract

A method for preparing zinc oxide-coated aluminum hydroxide powder comprises the following steps: using aluminum hydroxide of about 2-15 microns as a crystal nucleus, etching it with nitric acid, filtering and cleaning it for standby use; using sodium lauryl sulfate as a surface treatment agent, configuring it into an aqueous solution of a certain concentration, adding the etched aluminum hydroxide, and stirring; then adding an appropriate amount of zinc sulfate and urea, stirring and dissolving; then transferring the mixed solution to a reactor, placing it in a 100-120 degree oven to react for 2-4 hours, cooling, filtering, cleaning and drying, and obtaining zinc oxide-coated aluminum hydroxide powder. This method prepares zinc oxide-coated aluminum hydroxide powder, effectively improves the temperature resistance of aluminum hydroxide, and at the same time strengthens the compatibility of the powder as a filler with a substrate, significantly improves the filling property as a filler, and effectively improves the state of thermal conductive adhesive and gaskets using aluminum hydroxide as raw material.

Description

Technical Field

[0001] The present invention relates to the field of inorganic powder material preparation, and in particular to a method for preparing zinc oxide-coated aluminum hydroxide powder. Background Art

[0002] In recent years, with the rapid development of global industry, the role of powder materials has become increasingly prominent, especially aluminum hydroxide powder. As one of the key powder materials in industrial production, it is widely used in the field of thermal conductivity and flame retardancy. Aluminum hydroxide releases water of crystallization when heated, which has a flame retardant and cooling effect. Therefore, aluminum hydroxide is often used as a flame retardant to impart flame retardant properties to substrates. At the same time, aluminum hydroxide also has excellent thermal conductivity, low specific gravity, and good chemical stability, which makes it widely used in the field of thermal conductivity.

[0003] Traditionally, aluminum hydroxide powder is often decomposed into aluminum hydroxide slurry through sodium aluminate solution, and then the powder is obtained through filtering, washing and drying. However, aluminum hydroxide has poor heat resistance and a low decomposition temperature. It begins to dehydrate at around 230°C, which makes the temperature of some flame retardant substrates exceed the heat resistance range of aluminum hydroxide during processing, greatly limiting its application under high temperature conditions. In addition, aluminum hydroxide is mostly used as a filler in fields such as thermal conductivity and flame retardancy, but the filling capacity of conventional aluminum hydroxide on the market is limited and its compatibility with polymer base materials is poor, which seriously affects the mechanical properties and processing properties of the material, which also greatly limits the application of aluminum hydroxide.

[0004] Currently, the main methods for improving the heat resistance and filling properties of aluminum hydroxide include coupling agent modification, hydrothermal phase transition, and inorganic coating. Coupling agent modification involves modifying the aluminum hydroxide surface with silane or phthalate coupling agents. Larger amounts of coupling agents can improve thermal stability, but coupling agents are expensive, and the resulting increase in thermal stability and filling efficiency is minimal. Hydrothermal phase transition preheats the aluminum hydroxide to pre-dehydrate it on the low-temperature side, thereby increasing its heat resistance. However, this method partially converts the aluminum hydroxide to boehmite, whose decomposition endotherm is much lower than that of gibbsite. Furthermore, the oil absorption value typically increases after the phase transition, reducing filling properties. Inorganic coating is achieved by coating the surface of aluminum hydroxide with a layer of metal oxide, thereby improving the heat resistance and compatibility of the powder. For example, patent CN100580055C disperses aluminum hydroxide in water containing sodium hexametaphosphate to form a suspension, and adds zinc salt solution and alkali solution at the same time for coating. After filtering, washing, drying, and depolymerization, the surface is modified with a coupling agent. By coating the surface of aluminum hydroxide with a layer of zinc oxide, the synergistic flame retardant phenomenon of zinc oxide and aluminum hydroxide is utilized, and the coupling agent is used for modification at the same time, thereby improving the flame retardant efficiency and improving the mechanical properties of the material. However, this method can only modify aluminum hydroxide below 10 microns. At the same time, the zinc oxide-coated aluminum hydroxide composite inorganic flame retardant prepared by this method has a narrow range of application and is basically limited to use in the field of flame retardancy. In addition, the zinc oxide on the surface of the aluminum hydroxide is not tightly coated, resulting in high oil absorption and poor filling effect. Therefore, a coupling agent is used for modification later, but the cost of the coupling agent is high, and the filling effect is not significantly improved.

[0005] In response to the above problems, the present invention improves the heat resistance of aluminum hydroxide by inorganically tightly coating the surface of aluminum hydroxide with a layer of zinc oxide, thereby improving the compatibility of aluminum hydroxide with the substrate. In addition, the zinc oxide-coated aluminum hydroxide powder prepared by the present invention has a high degree of sphericity and a smooth zinc oxide-coated surface, which greatly improves the filling property of aluminum hydroxide, is beneficial to the application of aluminum hydroxide in various fields, and also improves the state of colloids and gaskets prepared with aluminum hydroxide powder. Summary of the Invention

[0006] In order to overcome the problems of the current methods for improving the heat resistance of aluminum hydroxide powder, such as the lack of significant thermal stability improvement effect, poor filling property, high production cost and high oil absorption value, the present invention provides a method for preparing a zinc oxide-coated aluminum hydroxide composite powder material. The method uses aluminum hydroxide, nitric acid, zinc sulfate, sodium dodecyl sulfate and urea as raw materials, and coats a layer of zinc oxide on the surface of aluminum hydroxide by a hydrothermal method, thereby improving the heat resistance of aluminum hydroxide and significantly improving the thermal stability. After coating, the oil absorption value of aluminum hydroxide is low, and zinc, as a transition zone metal, has an empty orbital that can accept free electrons in the substrate, thereby greatly improving the compatibility of aluminum hydroxide with the substrate. For example, in the field of thermal conductivity, the present invention effectively improves the compatibility of aluminum hydroxide with silicone rubber substrates, and greatly improves the state of thermal conductive adhesives and thermal conductive gaskets prepared with aluminum hydroxide as raw material. In addition, the aluminum hydroxide powder after surface coating has a high degree of sphericity and a smooth surface, which increases and improves its filling property. The raw materials used in this method are easily available, the process is simple, the production equipment requirements are low, and it is easy to industrialize.

[0007] The method for preparing zinc oxide-coated aluminum hydroxide powder of the present invention comprises the following steps:

[0008] (1) Dilute nitric acid with a certain amount of deionized water to prepare a nitric acid solution of a certain concentration;

[0009] (2) Selecting an appropriate amount of aluminum hydroxide as a crystal nucleus, adding it to a nitric acid solution, stirring for a period of time, filtering, washing, and drying to obtain the etched aluminum hydroxide;

[0010] (3) dissolving a certain amount of sodium dodecyl sulfate in a certain amount of deionized water to prepare a sodium dodecyl sulfate solution of a certain concentration;

[0011] (4) Add the etched aluminum hydroxide to the sodium dodecyl sulfate solution and continue stirring for a period of time to obtain solution A;

[0012] (5) Continue to add a certain amount of zinc sulfate to solution A and stir at room temperature for a certain period of time to obtain solution B; (6) Then add a certain amount of urea to solution B and stir at room temperature for a certain period of time to obtain solution C; (7) Transfer solution C to a reactor and place it in an oven for a certain period of time. After the insulation time is over, place it in a room temperature environment, cool it down, take it out, filter it, wash it, and dry it to obtain zinc oxide-coated aluminum hydroxide composite powder.

[0013] The concentration of nitric acid solution A in step (1) is 0.1-0.2 mol / L;

[0014] In step (2), the aluminum hydroxide particle size D50 is 2-15 microns, and the addition amount is 400-800 g / L;

[0015] In step (2), the stirring speed is 200-300 r / min and the stirring time is 20-30 min;

[0016] In step (2), the drying temperature is 80-120° C. and the drying time is 6-8 h;

[0017] The concentration of the sodium dodecyl sulfate solution in step (3) is 0.01-0.02 mol / L;

[0018] In step (4), the stirring time is 30-40 min and the stirring speed is 300-400 r / min;

[0019] In the step (4), the amount of aluminum hydroxide added after etching is 400-800 g / L;

[0020] In step (5), the amount of zinc sulfate added is 2-4 mol / L; the stirring time is 20-40 min, and the stirring speed is 200-400 r / min;

[0021] In step (6), the amount of urea added is 2-4 mol / L; the stirring speed is 200-400 r / min; and the stirring time is 20-40 min;

[0022] In the step (7), the oven is heated at a rate of 0.8 to 2.0°C / min, the reaction temperature is 100 to 120°C, and the holding time is 120 to 240 minutes;

[0023] The washing method in step (7) is to wash with deionized water for 3-5 times; then wash with ethanol for 3-5 times; the drying temperature is 85-110° C., and the drying time is 20-24 hours.

[0024] The formation mechanism and process of the preparation method of the single zinc oxide-coated aluminum hydroxide powder of the present invention are as follows:

[0025] First, aluminum hydroxide crystals are placed in a nitric acid solution and stirred. Nitric acid reacts with aluminum hydroxide to etch the surface of aluminum hydroxide, enhance the surface activity of aluminum hydroxide, and increase the attachment sites of other groups. Then sodium dodecyl sulfate is added. The sulfonic acid groups in sodium dodecyl sulfate will be adsorbed on the surface of the crystal nucleus through hydrogen bonding. Since the previous etching treatment has increased the reactive active sites, it helps the sulfonic acid groups to attach evenly and effectively to the surface of the aluminum hydroxide crystal nucleus. After zinc sulfate is added to provide a zinc source, the sulfonic acid groups in sodium dodecyl sulfate will attract Zn 2+ , making Zn 2+The sulfonic acid groups of dodecyl sulfonate adsorb onto the surface of aluminum hydroxide. Subsequently, as the temperature rises, urea begins to decompose, and the zinc ions on the aluminum hydroxide's surface react with it to form zinc hydroxide, which then coats the aluminum hydroxide surface with a layer of zinc hydroxide. As the reaction time increases, under the high-temperature, high-pressure reactor environment, the zinc hydroxide on the aluminum hydroxide surface dehydrates to form zinc oxide, ultimately producing zinc oxide-coated aluminum hydroxide powder.

[0026] Secondly, acid etching not only activates aluminum hydroxide, but also helps to modify the surface morphology of aluminum hydroxide. Its protrusions and corners have a relatively large specific surface area, so they will react with acid first during acid etching, thus becoming relatively rounded. After sodium dodecyl sulfate is adsorbed, Zn 2+ The sulfonic acid groups are adsorbed on the surface, urea is slowly decomposed after addition, and zinc hydroxide is slowly precipitated, so the coated surface is smooth. At the same time, in order to reduce the surface energy, it will approach a spherical shape during the slow precipitation process, and then slowly dehydrate into zinc oxide over time, so that the surface of the finally prepared coated product is smooth and the morphology is spherical.

[0027] The technical points and beneficial effects of the present invention are as follows:

[0028] 1. The zinc oxide-coated aluminum hydroxide powder prepared by the present invention has better temperature resistance than ordinary aluminum hydroxide. Ordinary aluminum hydroxide begins to dehydrate at 230°C, while the initial decomposition temperature of the composite powder of the present invention can be increased to 270-280°C, effectively expanding the application field of aluminum hydroxide.

[0029] 2. The zinc oxide-coated aluminum hydroxide powder prepared by the present invention has zinc oxide on its surface, which makes the composite powder have good compatibility with the substrate. Zinc in zinc oxide, as a transition zone metal element, has empty orbitals that can accommodate free electrons in the matrix. Therefore, zinc oxide has good compatibility with the substrate. The powder prepared by the present invention inherits the excellent compatibility of zinc oxide with the substrate.

[0030] 3. The zinc oxide-coated aluminum hydroxide powder prepared by the present invention has a smooth surface and a spherical morphology, and has good filling properties, which is conducive to the application of aluminum hydroxide as a filler in various fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Scanning electron microscope (SEM) photos of Example 1 of the present invention

[0032] Figure 2 Scanning electron microscope (SEM) photos of Example 2 of the present invention

[0033] Figure 3 Scanning electron microscope (SEM) photos of Example 3 of the present invention

[0034] Figure 4 Scanning electron microscope (SEM) photos of the comparative example 1 of the present invention

[0035] Figure 5 Scanning electron microscope (SEM) photos of the comparative example 2 of the present invention

[0036] Figure 6 Scanning electron microscope (SEM) photos of the blank examples of the present invention DETAILED DESCRIPTION

[0037] The present invention is further described below with reference to the examples. It should be noted that the following are only preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications and replacements based on the technical solutions and inventive concepts provided by the present invention should be covered within the scope of protection of the present invention.

[0038] The specific implementation steps of the present invention are as follows:

[0039] Dilute nitric acid with a certain amount of deionized water to prepare a 0.1-0.2 mol / L nitric acid solution; select 2-15 micron aluminum hydroxide as a crystal nucleus, add it to the nitric acid solution at an addition amount of 400-800 g / L, stir it at a speed of 200-300 r / min for 20-30 minutes, then filter, wash, and dry at 80-120°C for 6-8 hours to obtain the etched aluminum hydroxide; dissolve a certain amount of sodium dodecyl sulfate in a certain amount of deionized water to prepare a 0.01-0.02 mol / L sodium dodecyl sulfate solution; and add the etched aluminum hydroxide to the sodium dodecyl sulfate solution at an addition amount of 400-800 g / L, stir at 300-400 r / min for 30-40 minutes, which is solution A; continue to 2-4 mol / L zinc sulfate is added to solution A, and the mixture is stirred at 200-400 r / min for 20-40 minutes to obtain solution B; 2-4 mol / L urea is then added to solution B, and the mixture is stirred at 200-400 r / min for 20-40 minutes to obtain solution C; solution C is transferred to a reactor, placed in an oven, and heated at a heating rate of 0.8-2.0°C / min to a reaction temperature of 100-120°C; the reaction temperature is kept at this temperature for 120-240 minutes. After the heating time is over, the reaction temperature is kept at room temperature, and the mixture is taken out after cooling, washed with deionized water for 3-5 times, and then washed with ethanol for 3-5 times. The mixture is then placed in an oven and dried at 85-110°C for 20-24 hours to obtain zinc oxide-coated aluminum hydroxide powder.

[0040] Example 1

[0041] Use quantitative deionized water to dilute nitric acid to prepare a 0.1 mol / L nitric acid solution; select 2 micron aluminum hydroxide as the crystal nucleus, add it to the nitric acid solution at an addition amount of 400 g / L, stir at a speed of 200 r / min for 20 minutes, then filter, wash, and dry at 80 ° C for 8 hours to obtain the etched aluminum hydroxide; use quantitative deionized water to dissolve a certain amount of sodium dodecyl sulfate to prepare a 0.02 mol / L sodium dodecyl sulfate solution; and add the etched aluminum hydroxide to the sodium dodecyl sulfate solution at an addition amount of 400 g / L, stir at 300 r / min for 30 minutes, which is solution A; continue to 4 mol / L zinc sulfate was added to solution A, and the mixture was stirred at 400 r / min for 40 min to obtain solution B; 4 mol / L urea was then added to solution B, and the mixture was stirred at 400 r / min for 40 min to obtain solution C; solution C was transferred to a reactor, placed in an oven, and heated at a rate of 2.0°C / min to a reaction temperature of 120°C; the mixture was kept warm for 240 min. After the holding time was over, the mixture was placed at room temperature, cooled, taken out, washed with deionized water 5 times, and then washed with ethanol 5 times. The mixture was then placed in an oven and dried at 85°C for 24 h to obtain zinc oxide-coated aluminum hydroxide composite powder.

[0042] Example 2

[0043] Use quantitative deionized water to dilute nitric acid to prepare a 0.15 mol / L nitric acid solution; select 8 micron aluminum hydroxide as the crystal nucleus, add it to the nitric acid solution at an addition amount of 600 g / L, stir at a speed of 300 r / min for 30 minutes, then filter, wash, and dry at 100 ° C for 7 hours to obtain the etched aluminum hydroxide; use quantitative deionized water to dissolve a certain amount of sodium dodecyl sulfate to prepare a 0.02 mol / L sodium dodecyl sulfate solution; and add the etched aluminum hydroxide to the sodium dodecyl sulfate solution at an addition amount of 600 g / L, stir at 300 r / min for 30 minutes, which is solution A; continue to 3 mol / L zinc sulfate was added to solution A, and the mixture was stirred at 300 r / min for 30 min to obtain solution B; 3 mol / L urea was then added to solution B, and the mixture was stirred at 300 r / min for 30 min to obtain solution C; solution C was transferred to a reactor, placed in an oven, and heated at a rate of 1.6°C / min to a reaction temperature of 110°C; the mixture was kept warm for 180 min. After the holding time was over, the mixture was placed at room temperature, cooled, taken out, washed with deionized water 5 times, and then washed with ethanol 5 times, and then placed in an oven at 100°C for 24 h to obtain zinc oxide-coated aluminum hydroxide composite powder.

[0044] Example 3

[0045] A 0.2 mol / L nitric acid solution was prepared by diluting nitric acid with a certain amount of deionized water; 15 micron aluminum hydroxide was selected as a crystal nucleus, and 800 g / L of aluminum hydroxide was placed in the nitric acid solution, stirred at 300 r / min for 30 minutes, then filtered, washed, and dried at 120°C for 6 hours to obtain the etched aluminum hydroxide; a certain amount of sodium dodecyl sulfate was dissolved in a certain amount of deionized water to prepare a 0.01 mol / L sodium dodecyl sulfate solution; and the etched aluminum hydroxide was added to the sodium dodecyl sulfate solution in an amount of 800 g / L, stirred at 400 r / min for 40 minutes to obtain Solution A; 2 mol / L zinc sulfate was added to solution A, and the mixture was stirred at 200 r / min for 20 min to obtain solution B; 2 mol / L urea was then added to solution B, and the mixture was stirred at 200 r / min for 20 min to obtain solution C; solution C was transferred to a reactor, placed in an oven, and heated at a rate of 0.8 °C / min to a reaction temperature of 100 °C; the mixture was kept warm for 240 min. After the holding time was over, the mixture was placed at room temperature, cooled, taken out, washed with deionized water 3 times, and then washed with ethanol 3 times, and then placed in an oven at 85 °C for 24 h to obtain zinc oxide-coated aluminum hydroxide powder.

[0046] Comparative Example 1 (without sodium lauryl sulfate)

[0047] The difference between Comparative Example 1 and Example 3 is that sodium lauryl sulfate is not added. The specific preparation method is as follows: nitric acid is diluted with a certain amount of deionized water to prepare a 0.2 mol / L nitric acid solution; 15 micron aluminum hydroxide is selected as a crystal nucleus, and 800 g / L is added to the nitric acid solution, and the crystal nucleus is stirred at 300 r / min for 30 min, and then filtered, washed, and dried at 120 ° C for 6 h to obtain the etched aluminum hydroxide; the etched aluminum hydroxide is added to deionized water in an amount of 800 g / L, and stirred at 400 r / min for 40 min to obtain solution A; and the etched aluminum hydroxide is added to the deionized water in an amount of 800 g / L, and stirred at 400 r / min for 40 min to obtain solution A. 2 mol / L zinc sulfate was stirred at 200 r / min for 20 min to obtain solution B; 2 mol / L urea was then added to solution B and stirred at 200 r / min for 20 min to obtain solution C; solution C was transferred to a reactor and placed in an oven and heated at a rate of 0.8 °C / min to a reaction temperature of 100 °C; the temperature was kept at room temperature for 240 min. After the temperature was maintained at room temperature, the solution was taken out after cooling, washed with deionized water for 3 times, then washed with ethanol for 3 times, and then placed in an oven at 85 °C for 24 h to obtain zinc oxide-coated aluminum hydroxide powder.

[0048] Comparative Example 2 (no etching)

[0049] The difference between Comparative Example 2 and Example 3 is that the aluminum hydroxide is not etched. The specific preparation method is as follows: a certain amount of sodium dodecyl sulfate is dissolved in a certain amount of deionized water to prepare a 0.01 mol / L sodium dodecyl sulfate solution; and 15 microns of unetched aluminum hydroxide is added to the sodium dodecyl sulfate solution in an amount of 800 g / L, and stirred at 400 r / min for 40 minutes to obtain Solution A; 2 mol / L zinc sulfate is further added to Solution A, and stirring is continued at 200 r / min for 20 minutes. That is solution B; then add 2 mol / L urea to solution B, continue stirring at 200 r / min for 20 minutes, which is solution C; transfer solution C to a reactor, place it in an oven and heat it to a reaction temperature of 100°C at a rate of 0.8°C / min; keep it warm for 240 minutes. After the insulation time is over, place it in a room temperature environment, cool it down, take it out, wash it with deionized water 3 times, then wash it with ethanol 3 times, and then place it in an oven at 85°C for 24 hours to obtain zinc oxide-coated aluminum hydroxide powder.

[0050] Blank example

[0051] The blank example is the 15 micron ordinary aluminum hydroxide that was not coated in Example 3.

[0052] The products obtained from Examples 1-3, Comparative Examples 1-2 and the blank example were subjected to performance testing and characterization (Table 1 and accompanying drawings).

[0053] The performance test and characterization methods are as follows:

[0054] Morphology testing method: The micromorphology of the samples was observed using a COXEM desktop scanning electron microscope.

[0055] Particle size test method: LS-609 laser particle size analyzer was used to test the particle size of the sample, focusing on the change of D50.

[0056] Viscosity test method: Fill the same amount of aluminum hydroxide powder into the same silicone oil, disperse it using the same process, and use NDJ-8S rotational viscometer to test the viscosity.

[0057] Initial decomposition temperature test method: 5 mg of the powder sample prepared in the examples and comparative examples was heated from 50°C to 1000°C at a heating rate of 10°C / min using a METTLER TOLEDO thermogravimetric analyzer (TGA). The thermogravimetric curve was then measured and the data was processed.

[0058] Oil absorption test method: The test is performed based on patent ZL 202111578448.8, a method for detecting the oil absorption value of micron-sized inorganic powders.

[0059] Table 1

[0060]

[0061] According to the performance characterization and electron microscope scanning results:

[0062] (1) In terms of particle size: Compared with Example 3, Comparative Examples 1, 2, and the blank, Example 3 has a slightly larger particle size than Comparative Examples 1, 2, and the blank because it is successfully coated with a layer of zinc oxide. However, Comparative Examples 1 and 2 contain fine-particle zinc oxide that is not coated on the surface of aluminum hydroxide, so the particle size test results are significantly lower than those of the blank.

[0063] (2) In terms of oil absorption: Since the surface of Example 3 is coated with a layer of zinc oxide, the surface is smoother and the morphology is spherical. Therefore, compared with Comparative Examples 1, 2 and the blank, Example 3 has the lowest oil absorption. Since the surfaces of Comparative Examples 1 and 2 are not completely coated with a layer of zinc oxide, the surfaces become rougher, and there is fine-grained zinc oxide precipitated in the powder that is not coated on the surface of aluminum hydroxide. Therefore, the oil absorption is higher than that of the blank.

[0064] (3) Maximum filling amount: Examples 1, 2, and 3 have relatively high maximum filling amounts due to their smooth surface coating and spherical morphology. The maximum filling amount of Example 3 is increased by 400-600 parts relative to Comparative Examples 1 and 2 and the blank. Comparative Examples 1 and 2 have precipitated fine-particle zinc oxide, which plays a lubricating and filling role during the filling process. Therefore, the maximum filling amount is increased relative to the blank.

[0065] (4) Initial decomposition temperature: Examples 1, 2, and 3 are coated with a dense layer of zinc oxide, which greatly improves heat resistance and increases the initial decomposition temperature from 230°C to about 280°C. Comparative Examples 1 and 2 do not show a significant increase in initial decomposition temperature compared to the blank due to incomplete coating.

[0066] (5) Morphology: The products prepared in Examples 1, 2, and 3 have smooth surfaces and spherical morphologies. In Comparative Example 1, sodium dodecyl sulfate was not added as an intermediate bridge, and the hydrothermally generated zinc oxide was not coated on the aluminum hydroxide, but self-nucleated to form separate zinc oxide particles, so there were many fine-grained zinc oxide particles. In Comparative Example 2, the coated aluminum hydroxide was not etched, resulting in insufficient active sites of the aluminum hydroxide during the coating process. Therefore, the aluminum hydroxide surface was not successfully coated with zinc oxide, and only part of the surface had fine zinc oxide particles attached. Most of the generated zinc oxide self-nucleated to form more fine zinc oxide particles, which is similar to Comparative Example 1.

Claims

1. A method for preparing zinc oxide-coated aluminum hydroxide powder, characterized in that: The following steps are involved: (1) Dilute nitric acid with a certain amount of deionized water to prepare a nitric acid solution of a certain concentration; (2) Selecting an appropriate amount of aluminum hydroxide as a crystal nucleus, adding it to a nitric acid solution, stirring for a period of time, filtering, washing, and drying to obtain the etched aluminum hydroxide; (3) dissolving a certain amount of sodium dodecyl sulfate in a certain amount of deionized water to prepare a sodium dodecyl sulfate solution of a certain concentration; (4) Adding the etched aluminum hydroxide to the sodium dodecyl sulfate solution and continuing to stir for a period of time to obtain solution A; (5) Continue to add a certain amount of zinc sulfate to solution A and stir at room temperature for a certain period of time to obtain solution B; (6) Then add a certain amount of urea to solution B and stir at room temperature for a certain period of time to obtain solution C; (7) Solution C is transferred to a reactor and placed in an oven for a certain period of time. After the holding time is over, it is placed in a room temperature environment. After cooling, it is taken out for filtration, washing, and drying to obtain zinc oxide-coated aluminum hydroxide composite powder.

2. The method for preparing a zinc oxide coated aluminum hydroxide powder according to claim 1, wherein The concentration of the nitric acid solution in step (1) is 0.1-0.2 mol / L.

3. The method for preparing a zinc oxide coated aluminum hydroxide powder according to claim 1, wherein The particle size D50 of the aluminum hydroxide in step (2) is 2-15 microns, and the addition amount is 400-800 g / L.

4. The method for preparing a zinc oxide-coated aluminum hydroxide powder according to claim 1, wherein The stirring speed in step (2) is 200-300 r / min, and the stirring time is 20-30 min.

5. The method for preparing a zinc oxide coated aluminum hydroxide powder according to claim 1, wherein The drying temperature in step (2) is 80-120° C., and the drying time is 6-8 hours.

6. The method for preparing a zinc oxide-coated aluminum hydroxide powder according to claim 1, wherein: The concentration of the sodium lauryl sulfonate solution described in step (3) is 0.01-0.02 mol / L.

7. The method for preparing zinc oxide-coated aluminum hydroxide powder according to claim 1, wherein: The stirring time in step (4) is 30-40 min, and the stirring speed is 300-400 r / min.

8. The method for preparing zinc oxide-coated aluminum hydroxide powder according to claim 1, wherein: The amount of aluminum hydroxide added after etching in step (4) is 400-800 g / L.

9. The method for preparing a zinc oxide-coated aluminum hydroxide powder according to claim 1, wherein: The amount of zinc sulfate added in step (5) is 2-4 mol / L; the stirring time is 20-40 min, and the stirring speed is 200-400 r / min.

10. The method for preparing zinc oxide-coated aluminum hydroxide powder according to claim 1, wherein: The amount of urea added in step (6) is 2-4 mol / L; the stirring speed is 200-400 r / min, and the stirring time is 20-40 min.

11. The method for preparing zinc oxide-coated aluminum hydroxide powder according to claim 1, wherein: The oven heating rate described in step (7) is 0.8-2.0°C / min, the reaction temperature is 100-120°C, and the holding time is 120-240min.

12. The method for preparing zinc oxide-coated aluminum hydroxide powder according to claim 1, wherein: The washing method described in step (7) is to wash with deionized water 3-5 times, and then wash with ethanol 3-5 times; The drying temperature is 85-110° C., and the drying time is 20-24 hours.

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