A precursor, a preparation method thereof and a preparation method of nano-aluminum nitride powder

Abstract

The application relates to a precursor and a preparation method thereof and a preparation method of nano-aluminum nitride powder, and belongs to the technical field of ceramic materials. A preparation method of a precursor, the precursor being used for preparing aluminum-containing nano powder, comprises the following steps: (1) adding an aluminum salt, an organic carbon source, water and a precipitator into a closed device, and heating to not less than 150 DEG C to perform a hydrothermal reaction, so as to prepare a first precursor intermediate with a core-shell structure of carbon-coated aluminum hydroxide; (2) after the hydrothermal reaction is completed, the closed device is opened to make the mixture containing the first precursor intermediate in the closed device instantaneously erupt, so that a second precursor intermediate is obtained; the second precursor intermediate is collected, cleaned, dried, and the precursor is obtained. The precursor with the small grain size of the aluminum-containing compound, the good dispersibility, the reduced agglomeration and blockage and the high reaction activity can be obtained.

Description

Technical Field

[0001] This application relates to the field of ceramic materials technology, and in particular to a precursor and its preparation method and a method for preparing nano-aluminum nitride powder. Background Technology

[0002] AlN (AlN) is widely used in electronic packaging materials, optical materials, ceramic substrate materials, functional materials, and structural materials due to its excellent properties such as high room temperature thermal conductivity, low coefficient of thermal expansion, low dielectric loss, resistance to electromagnetic radiation, and good optical properties. The foundation of high-performance aluminum nitride ceramics is nano-aluminum nitride powder. The commonly used industrial method for preparing nano-aluminum nitride powder is the carbothermal reduction method. The key to preparing aluminum nitride powder using the carbothermal reduction method is the preparation of the precursor.

[0003] Currently, the precursor for preparing nano-aluminum nitride is generally a mixture of alumina and carbon, which will generate aluminum nitride under high temperature and nitrogen atmosphere. The basic requirements for the precursor in preparing nano-aluminum nitride are: alumina grain size should be nanoscale and as small as possible; carbon should be sufficient and uniformly distributed with the alumina; the precursor solid powder should be small and free from agglomeration or clumping; and it should facilitate carbothermic reduction. The quality of the precursor powder, powder contact conditions, and powder activity all have a significant impact on the reaction.

[0004] However, most existing precursors for preparing nano-aluminum nitride suffer from problems such as large alumina particle size, susceptibility to contamination by other elements, uneven mixing or agglomeration, requiring extensive crushing and ball milling, and low reactivity. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the objectives of this application include providing a precursor, a method for preparing the same, and a method for preparing nano-aluminum nitride powder. This method yields a precursor with small grain size, good dispersibility, reduced agglomeration and contact with additional elements, and high reactivity, all characteristic of aluminum-containing compounds.

[0006] In a first aspect, embodiments of this application provide a method for preparing a precursor, the precursor being used to prepare aluminum-containing nanopowders, comprising: (1) Aluminum salt, organic carbon source, water and precipitant are placed in a closed device and heated to not less than 150°C for hydrothermal reaction to obtain a first precursor intermediate with a core-shell structure of carbon-coated aluminum hydroxide. (2) After the hydrothermal reaction is completed, the sealed device is opened to make the mixture containing the first precursor intermediate inside the sealed device spray out instantaneously, and the second precursor intermediate is obtained. The second precursor intermediate is collected, washed and dried to obtain the precursor.

[0007] This application employs an aluminum salt, an organic carbon source, water, and a precipitant in a closed apparatus for a hydrothermal reaction. At a temperature not lower than 150°C, the precipitant slowly ionizes to release OH-.- , in order to be with Al 3+ The slow formation of aluminum hydroxide, coupled with the release of a large amount of CO2 gas from the precipitant, and the superposition of the saturated vapor pressure of water at high temperatures, keeps the reaction under extremely high pressure. This inhibits the growth of aluminum hydroxide crystals, causing them to continuously disperse and nucleate, ultimately yielding ultrafine nano-sized aluminum hydroxide. Simultaneously, at temperatures not lower than 150°C, water ionizes to release a large amount of H₂. + With OH - The process achieves an environment simultaneously characterized by strong acid and strong alkali. Under this environment, the organic carbon source can decompose and / or dehydrate to form carbon. The carbon adheres to the nuclei of the generated aluminum hydroxide crystals, ultimately coating the aluminum hydroxide to form a core-shell structure. Subsequent carbon generated by continuous dehydration will gradually aggregate and adhere to the outside of the core-shell structure, forming granular or blocky particles. The carbon coating of aluminum hydroxide further inhibits the growth and agglomeration of aluminum hydroxide crystals. This results in a first precursor intermediate with small crystal size, good dispersibility, and reduced agglomeration and contact with additional elements. During the instantaneous ejection, the extremely high pressure in the sealed device is released instantaneously, causing an air explosion effect. The mixture containing the first precursor intermediate in the sealed device undergoes violent collisions, ultimately forming fine powder. At the same time, the air explosion effect greatly increases the micropores of the carbon coating on the aluminum hydroxide, which can increase the activity of the carbon and increase the contact between aluminum hydroxide and nitrogen gas during the subsequent preparation of aluminum nitride, resulting in a highly reactive precursor.

[0008] In some embodiments of this application, the aluminum salt, organic carbon source, precipitant and water are in the molar ratio of Al, C, urea and water as 1:3~8:1~4:40~120.

[0009] This application uses aluminum salt, organic carbon source, precipitant and water in a suitable molar ratio of Al, C, urea and water to react and obtain a precursor with a suitable mass ratio of aluminum and carbon, which is beneficial for the complete reaction and conversion of aluminum into aluminum nitride in the subsequent preparation of aluminum nitride.

[0010] In some embodiments of this application, the pressure difference between the sealed device and the space of instantaneous eruption is 20 to 300 standard atmospheres.

[0011] This application employs a pressure difference of 20-300 standard atmospheres between the sealed device and the space of the instantaneous eruption. This creates a high pressure difference between the space of the instantaneous eruption and the pressure inside the sealed device. When the sealed device is opened for instantaneous eruption, the mixture in the instantaneous eruption undergoes an airburst effect under high pressure. This causes the mixture containing the first precursor intermediate to collide violently, resulting in a significant increase in the micropores of carbon coating the aluminum hydroxide, thereby obtaining a precursor with high reactivity.

[0012] In some embodiments of this application, aluminum salts include aluminum nitrate and its saturated hydrate, aluminum chloride and its saturated hydrate, aluminum sulfate and its saturated hydrate, or aluminum acetate and its saturated hydrate.

[0013] In some embodiments of this application, the aluminum salt is aluminum nitrate, aluminum nitrate nonahydrate, aluminum sulfate octadecahydrate, or aluminum chloride.

[0014] This application uses a suitable aluminum salt, which is conducive to dissolving in water to form Al. 3+ , to react with the OH released by the ionization of the precipitant - The reaction forms aluminum hydroxide.

[0015] In some embodiments of this application, the organic carbon source includes glucose, fructose, maltose, or sucrose.

[0016] In some embodiments of this application, the organic carbon source is glucose or maltose.

[0017] This application uses suitable organic carbon, which can be decomposed and / or dehydrated to form free carbon in a strong acid and strong alkali environment at a temperature not lower than 150°C, so that the generated free carbon attaches to the generated aluminum hydroxide crystal nucleus, and finally obtains a first precursor intermediate with a core-shell structure of aluminum hydroxide as the core and carbon as the shell.

[0018] In some embodiments of this application, the precipitant includes urea or ammonia.

[0019] In some embodiments of this application, the precipitant is urea.

[0020] This application uses a suitable precipitant that can slowly ionize and release OH-. - , in order to be with Al 3+ The slow production of aluminum hydroxide, along with the release of a large amount of CO2 gas, combined with the saturated vapor pressure of water at high temperatures, keeps the reaction under extremely high pressure, which can inhibit the growth of aluminum hydroxide crystals to some extent.

[0021] In some embodiments of this application, the hydrothermal reaction is carried out at 180~220°C and 20~300 standard atmospheres for 4~24 hours.

[0022] This application utilizes a hydrothermal reaction at suitable temperature and pressure, which facilitates the slow ionization of the precipitant to release OH-. - , with Al 3+ The slow production of aluminum hydroxide, coupled with the release of a large amount of CO2 gas, and the high saturated vapor pressure of water at high temperatures, keeps the reaction under extremely high pressure. This pressure inhibits the growth of aluminum hydroxide crystals to some extent, promoting continuous dispersion and nucleation. This results in small-sized, well-dispersed aluminum hydroxide crystals, reducing agglomeration and contact with additional elements, and producing a highly reactive precursor. Furthermore, it facilitates the ionization of water to produce a large amount of H+.+ With OH - By creating an environment that combines strong acid and strong alkali, the organic carbon source is converted into free carbon. The generated free carbon is adsorbed onto the aluminum hydroxide crystals, ultimately producing the first precursor intermediate with a core-shell structure of aluminum hydroxide as the core and carbon as the shell.

[0023] In some embodiments of this application, the step (2) of collecting the second precursor intermediate for cleaning and drying includes: collecting the second precursor intermediate obtained by instantaneous spraying, filtering it, adding water to cover the second precursor intermediate, stirring and continuing to filter it, repeating 5-10 times; and then drying it at 40-100°C.

[0024] This application employs suitable conditions to clean the second precursor intermediate in order to obtain a relatively pure precursor.

[0025] Secondly, embodiments of this application provide a precursor prepared by the preparation method provided in the first aspect.

[0026] The precursor prepared by the preparation method provided in the first aspect of this application can inhibit the growth of aluminum hydroxide crystals, and the air explosion effect during the instantaneous eruption causes violent collisions between the mixture, resulting in a large increase in the micropores of carbon coating the aluminum hydroxide. As a result, the aluminum hydroxide in the precursor prepared by this method has a small crystal size, good dispersibility, less agglomeration and contact with additional elements, and high reactivity.

[0027] In some embodiments of this application, the carbon in the precursor has micropores.

[0028] The carbon precursor prepared by the preparation method provided in the first aspect of this application has a large number of micropores, which can increase the activity of carbon and increase the contact between aluminum hydroxide and nitrogen gas during the subsequent preparation of aluminum nitride, thereby exhibiting high reactivity.

[0029] In some embodiments of this application, the specific surface area of ​​the precursor is greater than 850 m². 2 / g; the specific surface area of ​​the micropores in the precursor is greater than 650m². 2 / g.

[0030] The precursor prepared by the preparation method provided in the first aspect of this application has a large specific surface area and microporous specific surface area. The carbon in it has high activity and can increase the contact between aluminum hydroxide and nitrogen gas during the subsequent preparation of aluminum nitride, thereby having high reactivity.

[0031] Thirdly, embodiments of this application provide a method for preparing nano-aluminum nitride powder, comprising: sintering the precursor provided in the second aspect at 1550~1800℃ for 4~6h under a nitrogen atmosphere by nitrogen reduction; and then decarbonizing at 550~750℃ for 4~6h under an air atmosphere to obtain nano-aluminum nitride powder.

[0032] This application uses the precursor provided in the second aspect to prepare aluminum nitride by carbothermal reduction. Because the aluminum hydroxide in the precursor provided in the second aspect has a small grain size, good dispersibility, fewer agglomerates and additional element contacts, and the carbon in the precursor has a large number of micropores, it can increase the activity of carbon and increase the contact between aluminum hydroxide and nitrogen gas during the subsequent preparation of aluminum nitride, resulting in high reactivity. When preparing aluminum nitride by carbothermal reduction, the contact between aluminum hydroxide and nitrogen gas is greatly increased, so the sintering temperature used is lower, the amount of nitrogen gas used is less, and the reaction time is less. At the same time, the aluminum nitride prepared by it has a concentrated particle size, good uniformity, no impurities, and high purity. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 A flowchart illustrating the method for preparing the precursor provided in this application embodiment.

[0035] Figure 2 The X-ray diffraction pattern of aluminum nitride prepared by the method for preparing nano-aluminum nitride powder provided in Example 1 of this application.

[0036] Figure 3 Scanning electron microscope (SEM) image of the precursor prepared by the method for preparing the precursor provided in Example 1 of this application.

[0037] Figure 4 Scanning electron microscope (SEM) image of the precursor prepared by the method for preparing the precursor provided in Comparative Example 1 of this application.

[0038] Figure 5 Scanning electron microscope (SEM) image of the precursor prepared by the method for preparing the precursor provided in Comparative Example 2 of this application. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0040] This application provides a method for preparing a precursor, which is used to prepare aluminum-containing nanopowders, such as... Figure 1 As shown, it includes: (1) Aluminum salt, organic carbon source, water and precipitant are placed in a closed device and heated to not less than 150°C for hydrothermal reaction to obtain a first precursor intermediate with a core-shell structure of carbon-coated aluminum hydroxide. (2) After the hydrothermal reaction is completed, the sealed device is opened to make the mixture containing the first precursor intermediate inside the sealed device spray out instantaneously, and the second precursor intermediate is obtained. The second precursor intermediate is collected, washed and dried to obtain the precursor.

[0041] This application employs an aluminum salt, an organic carbon source, water, and a precipitant in a closed apparatus for a hydrothermal reaction. At a temperature not lower than 150°C, the precipitant slowly ionizes to release OH-. - , in order to be with Al 3+ The slow formation of aluminum hydroxide, coupled with the release of a large amount of CO2 gas from the precipitant, and the superposition of the saturated vapor pressure of water at high temperatures, keeps the reaction under extremely high pressure. This inhibits the growth of aluminum hydroxide crystals, continuously dispersing and nucleating them, ultimately yielding ultrafine nanoscale aluminum hydroxide (with crystal sizes as small as 2 nm). Simultaneously, at temperatures not lower than 150°C, water ionizes to release a large amount of H₂. + With OH -The process achieves an environment simultaneously characterized by strong acid and strong alkali. Under this environment, the organic carbon source can decompose and / or dehydrate to form carbon. The carbon adheres to the surrounding nuclei of the generated aluminum hydroxide crystals, meaning the organic carbon source is converted into free carbon. The generated free carbon is adsorbed onto the outside of the aluminum hydroxide crystals, ultimately producing a first precursor intermediate with a core-shell structure of aluminum hydroxide as the core and carbon as the shell. The free carbon generated by subsequent dehydration will gradually aggregate and adhere to the outside of the core-shell structure to form granular or blocky particles. The carbon coating of aluminum hydroxide further inhibits the growth and agglomeration of aluminum hydroxide crystals. Thus, a first precursor intermediate with small aluminum hydroxide crystal size, good dispersibility, and reduced agglomeration and contact with additional elements can be obtained. Due to the high temperature of the water during the hydrothermal reaction, the water has a very high saturated vapor pressure, and the reaction releases a large amount of CO2 gas, resulting in an extremely high gas pressure inside the device after the hydrothermal reaction is completed. When the hydrothermal reaction is completed and a momentary eruption is performed, the extremely high pressure within the sealed device is released instantaneously, causing an airburst effect. The mixture containing the first precursor intermediate within the sealed device undergoes violent collisions, causing the solid particles to deform, tear, and disintegrate, ultimately forming a fine powder. Simultaneously, the airburst effect significantly increases the micropores of the carbon coating on the aluminum hydroxide, enhancing its activity and increasing the contact between aluminum hydroxide and nitrogen gas during subsequent aluminum nitride preparation, resulting in a highly reactive precursor. It is important to note that the momentary eruption must be performed after the hydrothermal reaction is complete and the temperature within the sealed device is still at the holding temperature. This ensures that the sealed device maintains high pressure during the momentary eruption, allowing for the instantaneous release of this pressure and the airburst effect, which in turn causes violent collisions within the mixture containing the first precursor intermediate.

[0042] In some embodiments of this application, the molar ratio of aluminum salt, organic carbon source, precipitant, and water is 1:3~8:1~4:40~120, where Al, C, urea, and water are respectively. Exemplarily, the molar ratio of aluminum salt and organic carbon source to Al and C can be, but is not limited to, 1:3, 1:4, 1:5, 1:6, 1:7, or 1:8. Using an appropriate molar ratio of Al, C, urea, and water in the reaction yields a precursor with a suitable mass ratio of aluminum and carbon, facilitating the complete reaction and conversion of aluminum to aluminum nitride during subsequent preparation.

[0043] In some embodiments of this application, the pressure difference between the sealed device and the space for instantaneous ejection is 20-300 standard atmospheres. Using a pressure difference of 20-300 standard atmospheres between the sealed device and the space for instantaneous ejection creates a high pressure difference between the space for instantaneous ejection and the sealed device. This allows the mixture ejected during instantaneous ejection to undergo an airburst effect under higher pressure when the sealed device is opened for instantaneous ejection. This results in violent collisions of the mixture containing the first precursor intermediate, significantly increasing the micropores of the carbon coating on the aluminum hydroxide, thereby obtaining a highly reactive precursor. As an example, the space for instantaneous ejection can be under standard atmospheric pressure or a vacuum. The space for instantaneous eruption is maintained at standard atmospheric pressure or in a vacuum state. Under the condition of maintaining a high pressure in the sealed device, the space for instantaneous eruption is maintained at a relatively low pressure. This is to facilitate maintaining a pressure difference of 20 to 300 standard atmospheres between the sealed device and the space for instantaneous eruption. Even if a high pressure difference is formed between the space for instantaneous eruption and the pressure in the sealed device, it is beneficial to cause violent collisions of the mixture containing the first precursor intermediate during instantaneous eruption.

[0044] In some embodiments of this application, the aluminum salt includes aluminum nitrate and its saturated hydrate, aluminum chloride and its saturated hydrate, aluminum sulfate and its saturated hydrate, or aluminum acetate and its saturated hydrate. Exemplarily, the aluminum salt is aluminum nitrate, aluminum nitrate nonahydrate, aluminum sulfate octadecahydrate, or aluminum chloride. Using a suitable aluminum salt facilitates dissolution in water to form Al. 3+ , to react with the OH released by the ionization of the precipitant - The reaction forms aluminum hydroxide.

[0045] In some embodiments of this application, the organic carbon source includes glucose, fructose, maltose, or sucrose. For example, glucose or maltose is used as the organic carbon source. Using suitable organic carbon, in a strong acid and strong alkali environment at a temperature not lower than 150°C, carbon can be decomposed and / or dehydrated to form carbon, allowing the carbon to adhere around the generated aluminum hydroxide crystal nucleus. That is, the organic carbon source is converted into free carbon, which is then adsorbed onto the outside of the aluminum hydroxide crystal, ultimately yielding a first precursor intermediate with a core-shell structure of aluminum hydroxide as the core and carbon as the shell. It should be noted that when the organic carbon source is a polysaccharide, the polysaccharide is first decomposed into monosaccharides, which are then dehydrated to form carbon; when the organic carbon source is a monosaccharide, carbon is directly formed through dehydration.

[0046] In some embodiments of this application, the precipitant includes urea or ammonia. As an example, urea is used as the precipitant. Using a suitable precipitant allows for the slow ionization and release of OH-. - , in order to be with Al 3+The slow production of aluminum hydroxide, coupled with the release of a large amount of CO2 gas, and the high saturated vapor pressure of water at high temperatures, keeps the reaction under extremely high pressure, which can inhibit the growth of aluminum hydroxide crystals to some extent. It should be noted that urea is first hydrolyzed to ammonia, and the ammonia then ionizes to release OH-. - The following reaction occurs: CO(NH2)2 + 3H2O → 2NH3·H2O + CO2, NH3·H2O NH4 + + OH - Al 3+ + 3OH - →Al(OH)3↓; Therefore, using urea as a precipitant can further and slowly release OH. - , in order to be with Al 3+ The reaction proceeds slowly, producing aluminum hydroxide while releasing a large amount of CO2 gas. Combined with the saturated vapor pressure of water at high temperatures, the reaction can continue under extremely high pressure, which further helps to inhibit the growth of aluminum hydroxide crystals.

[0047] In some embodiments of this application, the hydrothermal reaction is carried out at 180-220 °C and 20-300 standard atmospheres for 4-24 hours. Exemplarily, the hydrothermal reaction temperature can be, but is not limited to, 180 °C, 185 °C, 190 °C, 195 °C, 200 °C, 205 °C, 210 °C, 215 °C, and 220 °C. Conducting the hydrothermal reaction at suitable temperature and pressure facilitates the slow ionization of the precipitant, releasing OH-. - , with Al 3+ The slow production of aluminum hydroxide, coupled with the release of a large amount of CO2 gas, and the high saturated vapor pressure of water at high temperatures, keeps the reaction under extremely high pressure. This pressure inhibits the growth of aluminum hydroxide crystals to some extent, promoting continuous dispersion and nucleation. This results in small-sized, well-dispersed aluminum hydroxide crystals, reducing agglomeration and contact with additional elements, and producing a highly reactive precursor. Furthermore, it facilitates the ionization of water to produce a large amount of H+. + With OH -The reaction creates an environment of both strong acid and strong alkali, causing the organic carbon source to convert into free carbon. This free carbon is then adsorbed onto the aluminum hydroxide crystals, ultimately producing a first precursor intermediate with a core-shell structure of aluminum hydroxide as the core and carbon as the shell. It should be noted that in a closed apparatus at 180–220 °C, where the precipitant simultaneously releases a large amount of CO2 gas, a pressure of 20–300 atmospheres can be achieved without the need for additional pressure settings. At this pressure, the growth of aluminum hydroxide crystals can be inhibited to some extent, thus promoting the formation of small-sized and well-dispersed aluminum hydroxide crystals. It should also be noted that the temperature is generally increased from room temperature to 180–220 °C at a rate of 1–10 °C / min, following the apparatus operating instructions.

[0048] In some embodiments of this application, step (2) of collecting the second precursor intermediate for cleaning and drying includes: collecting the second precursor intermediate obtained by instantaneous spraying, filtering it, adding water to cover the second precursor intermediate, stirring, and continuing to filter, repeating this process 5-10 times; and then drying it at 40-100 ℃. The second precursor intermediate is cleaned under suitable conditions to obtain a relatively pure precursor.

[0049] This application provides a precursor prepared by the above-described preparation method.

[0050] The precursor prepared by the above method can inhibit the growth of aluminum hydroxide crystals, and the air explosion effect during the instantaneous eruption causes violent collisions between the mixture, which greatly increases the micropores of carbon covering the aluminum hydroxide. As a result, the aluminum hydroxide in the precursor prepared by this method has small crystal size, good dispersibility, less agglomeration and contact with additional elements, and high reactivity.

[0051] In some embodiments of this application, the carbon precursor has micropores. The carbon precursor prepared by the above preparation method has a large number of micropores, which can increase the activity of carbon and increase the contact between aluminum hydroxide and nitrogen gas during the subsequent preparation of aluminum nitride, thereby exhibiting higher reactivity.

[0052] In some embodiments of this application, the specific surface area of ​​the precursor is greater than 850 m². 2 / g; the specific surface area of ​​the micropores in the precursor is greater than 650m². 2 / g. The precursor prepared by the above method has a large specific surface area and microporous specific surface area. The carbon in it has high activity and can increase the contact between aluminum hydroxide and nitrogen gas during the subsequent preparation of aluminum nitride, thus exhibiting high reactivity.

[0053] This application provides a method for preparing nano-aluminum nitride powder, comprising: sintering the above-mentioned precursor at 1550~1800 ℃ for 4~6 h in a nitrogen atmosphere by nitrogen reduction; and then decarbonizing at 550~750 ℃ ​​for 4~6 h in an air atmosphere to obtain nano-aluminum nitride powder.

[0054] Aluminum nitride is prepared by carbothermal reduction using the above-mentioned precursor. Due to the small grain size and good dispersibility of the aluminum hydroxide in the precursor, there are fewer agglomerates and additional element contacts. In addition, the carbon in the precursor has a large number of micropores, which can increase the activity of carbon and increase the contact between aluminum hydroxide and nitrogen gas during the subsequent preparation of aluminum nitride. The reaction activity is high. When preparing aluminum nitride by carbothermal reduction, the contact between aluminum hydroxide and nitrogen gas is greatly increased. Therefore, the sintering temperature is lower, the amount of nitrogen gas used is less, and the reaction time is less. At the same time, the aluminum nitride prepared by carbothermal reduction has a concentrated particle size, good uniformity, no impurities, and high purity.

[0055] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0056] Example 1 This embodiment provides a method for preparing a precursor, which is used to prepare aluminum-containing nanopowders, including: (1) Weigh AlCl3, glucose, urea and water according to the molar ratio of Al, C, urea and water of 1:4:2:100. Mix and stir them and pour them into a closed device for hydrothermal reaction. Heat the device from room temperature to 220 ℃ at a heating rate of 5 ℃ / min and keep it at the temperature for 10 h for hydrothermal reaction. The closed device can reach about 48 standard atmospheres, so that aluminum salt is converted into aluminum hydroxide and the first precursor intermediate with a core-shell structure of carbon-coated aluminum hydroxide is obtained. (2) When the heat preservation is completed and the temperature in the sealed device is still at the heat preservation temperature, the sealed device is quickly opened to make the mixture containing the first precursor intermediate in the sealed device spray out instantaneously, and the second precursor intermediate is obtained. The second precursor intermediate is collected and filtered, and then water is added to cover the second precursor intermediate. After stirring, the filtration is continued, and this process is repeated 5 times. Then, it is dried in an 80℃ constant temperature oven for 12 h to obtain the precursor.

[0057] This embodiment also provides a method for preparing nano-aluminum nitride powder, comprising: sintering the above-mentioned precursor at 1650 °C for 4 h under a nitrogen atmosphere by nitrogen reduction; and then decarburizing at 650 °C for 4 h under an air atmosphere to obtain nano-aluminum nitride powder. The nano-aluminum nitride powder was analyzed by X-ray diffraction (XRD) using a Bruker / D8advance spectrometer, and the results are as follows. Figure 2 As shown. Figure 2As the results show, the aluminum nitride prepared in this embodiment is free of impurities and amorphous phases, exhibiting high purity. This demonstrates that the aluminum nitride prepared from the precursor using the method of this application, when prepared by carbothermal reduction, has few impurities and high purity.

[0058] Example 2 This embodiment provides a method for preparing a precursor, which is used to prepare aluminum-containing nanopowders, including: (1) Weigh Al(NO3)3, maltose powder, urea and water according to the molar ratio of Al, C, urea and water of 1:5:2.5:80. Mix and stir them and pour them into a closed device for hydrothermal reaction. Heat the device from room temperature to 190 ℃ at a heating rate of 2 ℃ / min and keep it at the temperature for 12 h for hydrothermal reaction. The closed device can reach about 21.7 standard atmospheres, so that aluminum salt is converted into aluminum hydroxide and the first precursor intermediate with a core-shell structure of carbon-coated aluminum hydroxide is obtained. (2) When the heat preservation is completed and the temperature in the sealed device is still at the heat preservation temperature, the sealed device is quickly opened to make the mixture containing the first precursor intermediate in the sealed device spray out instantaneously, and the second precursor intermediate is obtained. The second precursor intermediate is collected and filtered, and then water is added to cover the second precursor intermediate. After stirring, the filtration is continued, and this process is repeated 5 times. Then, it is dried in an 80 ℃ constant temperature oven for 12 h to obtain the precursor.

[0059] This embodiment also provides a method for preparing nano-aluminum nitride powder, comprising: sintering the above-mentioned precursor at 1650 °C for 4 h under a nitrogen atmosphere by nitrogen reduction; and then decarbonizing at 650 °C for 4 h under an air atmosphere to obtain nano-aluminum nitride powder.

[0060] Comparative Example 1 This comparative example provides a method for preparing a precursor, which differs from Example 1 in that: after the heat preservation is completed, the mixture containing the first precursor intermediate is cooled to room temperature, and the mixture in the sealed device is taken out and ball-milled at 200 rpm for 120 min; then filtered, water is added, and after stirring, filtration is repeated 5 times; then dried in an 80 ℃ constant temperature oven for 12 h to obtain the precursor.

[0061] In this comparative example, the above-mentioned precursor was prepared into nano-aluminum nitride using the same method as in Example 1.

[0062] Comparative Example 2 This comparative example provides a method for preparing a precursor, which differs from Example 1 in that: after the heat preservation is completed, the mixture containing the first precursor intermediate in the sealed device is cooled to room temperature, filtered, water is added, stirred and filtered again, and this process is repeated 5 times; then it is dried in an 80 ℃ constant temperature oven for 12 h to obtain the precursor.

[0063] In this comparative example, the above-mentioned precursor was prepared into nano-aluminum nitride using the same method as in Example 1.

[0064] The preparation methods of Examples 1-2 and Comparative Examples 1-2 are shown in Table 1.

[0065] Table 1. Preparation methods of Examples 1-2 and Comparative Examples 1-2

[0066] Note: In Table 1, " / " indicates that this step is not included.

[0067] Experimental Example 1 In this experiment, the specific surface area and micropore specific surface area of ​​the precursors prepared in Examples 1-2 and Comparative Examples 1-2 were detected using a BET specific surface area analyzer, and the results are shown in Table 2.

[0068] Table 2. Specific surface area and microporous specific surface area of ​​the precursor

[0069] As shown in Table 1, the specific surface area of ​​the precursors prepared in Examples 1 and 2 is greater than 850 m². 2 / g; the specific surface area of ​​the micropores in the precursor is greater than 650 m². 2 / g; that is, the precursors prepared in Examples 1-2 have a large number of micropores, which can increase the activity of carbon and increase the contact between aluminum hydroxide and nitrogen gas during the subsequent preparation of aluminum nitride, thus having high reactivity.

[0070] This application describes the use of aluminum salt, organic carbon source, water, and precipitant in a closed device for hydrothermal reaction at a temperature not lower than 150°C. After the hydrothermal reaction is completed, the mixture in the closed device with a high saturated vapor pressure is instantaneously ejected, causing the mixture to collide violently with each other, eventually forming fine powder. This significantly increases the number of micropores of carbon coating the aluminum hydroxide, thereby increasing the activity of carbon and increasing the contact between aluminum hydroxide and nitrogen gas during the subsequent preparation of aluminum nitride, thus obtaining a precursor with high reactivity.

[0071] Experimental Example 2 In this experiment, the nano-aluminum nitride powders prepared in Example 1 and Comparative Examples 1-2 were examined using scanning electron microscopy (SEM, ZEISS / Gemini 300). The results are as follows: Figures 3-5 As shown.

[0072] Depend on Figure 3 It can be seen that the aluminum nitride prepared using the precursor obtained in Example 1 via carbothermal reduction exhibits a concentrated particle size distribution of 200–400 nm and good uniformity. Figure 4The results show that the aluminum nitride prepared using the precursor obtained in Comparative Example 1 via carbothermal reduction exhibits uneven material distribution. Figure 5 The results show that the aluminum nitride prepared by the precursor obtained by Comparative Example 2 has an uneven material distribution when it is prepared by carbothermal reduction.

[0073] This application describes the use of aluminum salt, organic carbon source, water, and precipitant in a closed device for hydrothermal reaction at a temperature not lower than 150°C. After the hydrothermal reaction is completed, the mixture in the closed device with a high saturated vapor pressure is instantaneously ejected, causing the mixture to collide violently with each other, ultimately forming a precursor. Because the aluminum hydroxide in this precursor has a small crystal size, good dispersibility, fewer agglomerates and contact with additional elements, and high reactivity, the aluminum nitride prepared by the carbothermal reduction method has a concentrated particle size, good uniformity, no impurities, and high purity.

[0074] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A method for preparing a precursor, wherein the precursor is used to prepare aluminum-containing nanopowders, characterized in that, include: (1) Aluminum salt, organic carbon source, water and precipitant are placed in a closed device and heated to not less than 150°C for hydrothermal reaction to obtain a first precursor intermediate with a core-shell structure of carbon-coated aluminum hydroxide. (2) After the hydrothermal reaction is completed, the sealed device is opened to make the mixture containing the first precursor intermediate in the sealed device spray out instantaneously, and the second precursor intermediate is obtained. The second precursor intermediate is collected, cleaned and dried to obtain the precursor.

2. The preparation method according to claim 1, characterized in that, The aluminum salt, organic carbon source, precipitant, and water are in a molar ratio of Al, C, urea, and water of 1:3~8:1~4:40~120.

3. The preparation method according to claim 2, characterized in that, The pressure difference between the sealed device and the space where the instantaneous eruption occurs is 20 to 300 standard atmospheres.

4. The preparation method according to claim 2, characterized in that, The aluminum salts include aluminum nitrate and its saturated hydrate, aluminum chloride and its saturated hydrate, aluminum sulfate and its saturated hydrate, or aluminum acetate and its saturated hydrate. Preferably, the aluminum salt is aluminum nitrate, aluminum nitrate nonahydrate, aluminum sulfate octadecahydrate, or aluminum chloride.

5. The preparation method according to claim 2, characterized in that, The organic carbon source includes glucose, fructose, maltose, or sucrose; Preferably, the organic carbon source is glucose or maltose.

6. The preparation method according to claim 2, characterized in that, The precipitant includes urea or ammonia; preferably urea.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The hydrothermal reaction is carried out at 180~220℃ and 20~300 standard atmospheres for 4~24 hours.

8. The preparation method according to any one of claims 1 to 6, characterized in that, The step (2) of collecting the second precursor intermediate for cleaning and drying includes: collecting the second precursor intermediate obtained by instantaneous spraying, filtering it, adding water to cover the second precursor intermediate, stirring and continuing to filter it, repeating 5-10 times; and then drying it at 40-100℃.

9. A precursor prepared by the preparation method according to any one of claims 1 to 8; Preferably, the carbon in the precursor has micropores; Preferably, the specific surface area of ​​the precursor is greater than 850 m². 2 / g; the specific surface area of ​​the micropores in the precursor is greater than 650m². 2 / g.

10. A method for preparing nano-aluminum nitride powder, characterized in that, include: The precursor described in claim 9 was subjected to nitrogen reduction sintering at 1550~1800℃ for 4~6h under a nitrogen atmosphere; Then, carbon removal is carried out by holding the material at 550~750℃ for 4~6 hours in an air atmosphere to obtain nano-aluminum nitride powder.

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