Preparation method and device of nano gallium nitride powder material

Abstract

The invention provides a preparation method and device of a nano gallium nitride powder material, and belongs to the field of nano metal nitride materials. The method comprises the following steps: carrying out hydrothermal reaction on metal gallium, a surfactant and water to obtain a reaction product; carrying out solid-liquid separation and drying on the reaction product to obtain a nano hydroxyl gallium oxide precursor; carrying out low-temperature pre-sintering treatment on the nano hydroxyl gallium oxide precursor in a tubular furnace in a nitrogen atmosphere to obtain a pre-sintered intermediate; switching a nitrogen atmosphere into an ammonia atmosphere, and carrying out high-temperature nitriding treatment on the pre-sintered intermediate to obtain gallium nitride powder; and carrying out annealing treatment on the gallium nitride powder to remove residual impurities, reduce defect density and improve powder dispersity. According to the preparation method, the gallium nitride powder with the nano structure is prepared by taking metal gallium as a raw material and adopting a two-step short-flow process, and the core advantage is a synergistic effect of two technologies of nano hydroxyl gallium oxide precursor morphology control through a surfactant-assisted hydrothermal method and hierarchical multi-section calcination annealing treatment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanometer metal nitride materials, and particularly relates to a preparation method and device of nanometer gallium nitride powder material. BACKGROUND

[0002] In the modern semiconductor and optoelectronic field, the rapid development of 5G communication, new energy vehicles, high-efficiency lighting and other industries has given rise to an urgent demand for high-performance semiconductor materials. As the core representative of the third-generation wide-bandgap semiconductor material, gallium nitride has become an indispensable basic material in the fields of blue LED, ultraviolet detector, high-temperature high-power device, etc. due to its 3.4eV band gap, excellent breakdown field strength of about 3.3MV / cm, and excellent thermal stability and chemical stability. And the nanometer gallium nitride powder exhibits unique optical, electrical and high surface activity due to quantum size effect, surface effect and small size effect, and has great application potential in catalysis, adsorption and composite ceramic preparation, which has attracted widespread attention from scientific research and industry.

[0003] The current preparation technology of nanometer gallium nitride powder still faces many challenges. In the preparation method using metal gallium as raw material, the existing technology either causes insufficient reaction due to large surface tension of metal gallium, low conversion efficiency of nanometer gallium hydroxide precursor, or needs complex grinding and mixing process, which not only increases energy consumption and production cost, but also easily introduces impurities to affect the product quality purity; other preparation routes based on gallium salt or gallium oxide generally have the problems of complicated process flow, long reaction time and high equipment requirement, and some methods need multiple high-temperature calcination or subsequent crushing treatment, which not only increases the operation complexity, but also increases the risk of product morphology unevenness and impurity introduction. Therefore, it is of great significance to develop a technology for preparing nanometer gallium nitride powder by efficient two-step method using metal gallium as raw material, which can solve the problems of low efficiency, high cost and difficult control of product quality of existing methods. SUMMARY

[0004] The present application provides a preparation method and device of nanometer gallium nitride powder material to provide an efficient two-step method for preparing nanometer gallium nitride powder material using metal gallium.

[0005] In a first aspect, the embodiments of the present application provide a preparation method of nanometer gallium nitride powder material, which comprises: Under the conditions of stirring and heating, the metal gallium, the surfactant and the water are subjected to hydrothermal reaction to obtain a reaction product; The reaction product is subjected to solid-liquid separation to obtain a solid separation product, and the solid separation product is dried to obtain a nanometer gallium hydroxide precursor; warming the nanometer gallium hydroxyl oxide precursor to a first set temperature at a first set warming rate under a nitrogen atmosphere, and keeping the nanometer gallium hydroxyl oxide precursor at the first set temperature for a first set holding time to perform a low-temperature pre-burning treatment, to obtain a pre-burning intermediate; switching the nitrogen atmosphere to an ammonia atmosphere, and warming the pre-burning intermediate to a second set temperature at a second set warming rate, and keeping the pre-burning intermediate at the second set temperature for a second set holding time to perform a high-temperature nitriding treatment, to obtain a gallium nitride powder; cooling the gallium nitride powder to a third set temperature, and keeping the gallium nitride powder at the third set temperature for a third set holding time to perform an annealing treatment, to remove residual impurities, reduce defect density, and improve powder dispersibility; The ammonia flow rate of the ammonia atmosphere is 20 mL / min to 80 mL / min, the second set temperature is 800°C to 1100°C, the second set warming rate is 5°C / min to 20°C / min, and the second set holding time is 2h to 6h.

[0006] Optionally, the liquid-solid ratio of the water to the metallic gallium is (10-30):1.

[0007] Optionally, the molar mass of the surfactant is 1% to 10% of the molar mass of the metallic gallium.

[0008] Optionally, the surfactant includes one or more of sodium dodecyl sulfate, cetyltrimethylammonium bromide, and polyethylene glycol.

[0009] Optionally, the hydrothermal reaction includes the following parameters: a stirring speed of 800 r / min to 1200 r / min, a reaction temperature of 160°C to 220°C, and a reaction time of 2h to 10h.

[0010] Optionally, the nitrogen flow rate of the nitrogen atmosphere is 100 mL / min to 200 mL / min, the first set temperature is 400°C to 600°C, the first set warming rate is 2°C / min to 10°C / min, and the first set holding time is 0.5h to 2h.

[0011] Optionally, the third set temperature is 700°C to 800°C, and the third set holding time is 0.5h to 1.5h.

[0012] Optionally, the mass purity of the metallic gallium is 6N. The mass purity of the nitrogen and ammonia is 5N. The mass purity of the surfactant is analytical purity.

[0013] In a second aspect, the embodiments of the present application provide a device for preparing nano-gallium nitride powder material, which is suitable for the method of any one of the embodiments of the first aspect. The device comprises a tube furnace, which is used for sequentially performing low-temperature pre-burning treatment, high-temperature nitriding treatment and annealing treatment on nano-gallium oxyhydroxide precursor. The tube furnace comprises: a tube furnace body, which is internally provided with an internal reaction chamber; a gas inlet pipeline and a tail gas pipeline, which are arranged on the tube furnace body; a gas diffusion platform, which is arranged inside the internal reaction chamber and is used for uniformly distributing reaction gas introduced from the gas inlet pipeline to a reaction area.

[0014] Optionally, the gas diffusion platform is internally provided with a multi-tube gas outlet device, and the surface is provided with uniformly distributed gas outlets. The upper part of the gas diffusion platform is used for placing a boron nitride crucible for carrying the nano-gallium oxyhydroxide precursor.

[0015] Compared with the prior art, the above technical solution provided by the embodiments of the present application has the following advantages: The embodiments of the present application provide a method for preparing nano-gallium nitride powder material. The method uses metallic gallium as a basic raw material, and prepares nano-structured gallium nitride powder through a two-step short-process technology. The core advantage lies in the synergistic innovation of "surfactant-assisted hydrothermal method for nano-gallium oxyhydroxide precursor morphology control" and "staged multi-section calcination and annealing treatment".

[0016] Firstly, a surfactant-assisted hydrothermal method is proposed. The morphology of nano-gallium oxyhydroxide precursor is controlled to inhibit powder agglomeration, so that nano-powder with uniform morphology is obtained, which is convenient for subsequent high-temperature nitriding to obtain nano-gallium nitride powder. In the hydrothermal process, the amphiphilic structure (hydrophilic group + hydrophobic group) of the surfactant is used to control the "nucleation-growth-dispersion" whole process of nano-material formation at the molecular level, promote uniform nucleation of gallium oxyhydroxide, reduce particle size, and at the same time, through the dual action of "steric hindrance + electrostatic repulsion" of the surfactant, the dispersion stability of the nano-material is improved, the particle agglomeration is inhibited, and the uniformity of the powder morphology is ensured. The present application can further optimize the type and amount of dispersant to control the morphology, growth direction and size of nano-structure, so as to realize the control of particle size distribution, morphology and dispersibility of nano-material.

[0017] Secondly, through the hierarchical multi-stage calcination process of "low-temperature pre-burning + high-temperature nitriding + annealing to eliminate defects", the deficiencies of the traditional high-temperature nitriding process in defect control are solved. Due to the non-uniform reaction characteristics between gas and solid, it is easy to cause high defect density of product lattice points, prominent linear defects and surface defects, and high defects of macroscopic agglomeration and porosity. The application guides the slow diffusion of the reaction gas through the low-temperature pre-burning stage, avoids the imbalance of the atmosphere concentration, and at the same time forms loose and uniform nano-gallium hydroxide precursor; through precise control of the heating rate and the nitrogen source flow in the high-temperature nitriding stage, the directional and ordered growth of gallium nitride grains along the low surface energy crystal surface is realized, and the particle agglomeration and surface hardening are avoided to affect the diffusion reaction of ammonia gas to the inside; the annealing treatment fills the residual vacancies through atomic thermal migration, and uses active nitrogen species to eliminate surface oxidation defects.

[0018] Thus a method for preparing nano-gallium nitride powder material by two-step method of metal gallium is provided. BRIEF DESCRIPTION OF DRAWINGS

[0019] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0021] Figure 1 A flowchart of a preparation method of nano-gallium nitride powder material provided by the embodiments of the present application is shown in the figure. Figure 2 A schematic diagram of the overall structure of a tube furnace provided by the embodiments of the present application is shown in the figure. Figure 3 A sectional view of a tube furnace provided by the embodiments of the present application is shown in the figure. Reference signs: 1-gas inlet pipeline; 2-tail gas pipeline; 3-flange sealing ring; 4-tube furnace body; 5-internal reaction chamber; 6-gas outlet; 7-nano-gallium hydroxide precursor; 8-boron nitride crucible; 9-gas diffusion platform; 10-multi-tube gas outlet device. DETAILED DESCRIPTION

[0022] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0023] The range descriptions described herein, such as numerical range, ratio range, etc., include all possible subranges and single values within the range, for example, the range description of "1 to 6" or "1-6" covers all subranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "include", "contain" and the like used herein mean "including but not limited to"; the relationship terms "first", "second" and the like are only used to distinguish different entities or operations, and do not imply actual sequence or relationship; "and / or" means that multiple cases can exist independently or simultaneously; "at least one", "multiple", "at least one" and the like refer to any combination of the corresponding objects, including single or multiple combinations of the objects. The proportional relationship involved herein, such as mass ratio, molar ratio, etc., should be understood as the corresponding relationship between the front and the rear in the proportional form according to the description order. The raw materials, reagents, instruments and equipment used herein can be purchased or prepared by existing methods.

[0024] Figure 1 A flowchart of a preparation method of a nano-gallium nitride powder material provided by the embodiments of the present application.

[0025] As shown in Figure 1 The embodiments of the present application provide a preparation method of a nano-gallium nitride powder material, which comprises the following steps: S1, under stirring and heating conditions, hydrothermal reaction is performed on metal gallium, a surfactant and water to obtain a reaction product; S2, solid-liquid separation is performed on the reaction product to obtain a solid separation product, and the solid separation product is dried to obtain a nano-hydroxyl gallium oxide precursor; S3, under a nitrogen atmosphere, the nano-hydroxyl gallium oxide precursor is heated to a first set temperature at a first set heating rate, and is kept at the first set temperature for a first set holding time to perform low-temperature pre-burning treatment, to obtain a pre-burning intermediate; S4, the nitrogen atmosphere is switched to an ammonia atmosphere, and the pre-burning intermediate is heated to a second set temperature at a second set heating rate, and is kept at the second set temperature for a second set holding time to perform high-temperature nitriding treatment, to obtain a gallium nitride powder; S5, cooling the gallium nitride powder to a third set temperature, and keeping the third set temperature for a third set holding time to perform annealing treatment, so as to remove residual impurities, reduce defect density and improve powder dispersibility.

[0026] S1 is a hydrothermal reaction to prepare reactants. This step is a key step for forming a nano-gallium hydroxide precursor. The role is to make metal gallium react with water to generate gallium hydroxide under the conditions of high pressure, heating and stirring in a hydrothermal reactor, and to intervene in the reaction process by a surfactant. Metal gallium is used as a gallium source, which gradually dissolves in the hydrothermal environment and reacts with water molecules to generate a gallium hydroxide precursor. Stirring can uniformly disperse liquid metal gallium in water, break the local concentration difference of the reaction system, and avoid agglomeration of metal gallium leading to uneven reaction. Heating provides kinetic energy for the reaction of metal gallium and water, and promotes the reaction to generate gallium hydroxide. The addition of a surfactant is crucial. The hydrophilic group and the hydrophobic group in the amphiphilic structure of the surfactant can guide the "uniform nucleation-ordered growth" of gallium hydroxide at the molecular level, and at the same time inhibit particle agglomeration, laying a foundation for the subsequent formation of a nano-gallium hydroxide precursor with uniform morphology and nano size. Finally, through this step, solid metal gallium is converted into a nano-gallium hydroxide powder product, which is convenient for subsequent high-temperature nitriding to obtain a nano-gallium nitride powder.

[0027] S2 is a solid-liquid separation and drying to obtain a nano-gallium hydroxide precursor. The core role of this step is "purification + structure fixation". On the one hand, solid-liquid separation (such as centrifugation) can separate the solid gallium hydroxide powder in the reaction product from the solvent of the residual surfactant; subsequent high-purity water washing can further remove the soluble impurities (such as excess surfactant) adsorbed on the surface of the solid particles, avoiding the influence of residual impurities on the quality purity of the subsequent nitriding reaction; on the other hand, the drying process can remove the adsorbed water and crystal water in the solid particles, so that the structure of gallium hydroxide is stabilized. If water remains, the water will rapidly evaporate during subsequent high-temperature treatment, which will cause the particles to crack or agglomerate, destroying the nano structure. At the same time, the residual water molecules will affect the conversion to gallium nitride powder, affecting the purity and conversion rate of the gallium nitride powder. Through this step, a pure, dry, and well-dispersed nano-gallium hydroxide precursor is finally obtained, providing "high activity and low impurity" raw materials for the subsequent nitriding reaction.

[0028] S3 step is a low-temperature pre-sintering treatment in a nitrogen atmosphere. This step is a "pre-treatment buffer" before the nano-hydroxyl gallium precursor is nitrided, and its role is to eliminate interference and stabilize the nano-hydroxyl gallium precursor structure. First, nitrogen, as an inert protective gas, can completely replace the air (especially oxygen and moisture) in the tube furnace. The reaction for preparing gallium nitride powder at high temperature is easily affected by oxygen and moisture, leading to incomplete reaction, or reverse reaction and oxidation reaction. If residual oxygen is present, it will cause the surface of the gallium nitride powder to oxidize to form gallium oxide, affecting the purity of the product. If residual moisture is present, it will cause a secondary reaction with the nano-hydroxyl gallium precursor, resulting in abnormal powder morphology, and will also affect the conversion reaction of gallium nitride, affecting the purity and conversion rate of the product. Second, low-temperature pre-sintering at 400-600°C can cause the hydroxyl gallate to slowly release residual hydroxyl groups (to form a more stable gallate-based pre-sintering intermediate), rather than direct nitriding. In addition, the small particles of the precursor have a large specific surface area and high surface energy, and are in an unstable state. If they are suddenly raised to a very high reaction temperature, the diffusion of atoms on the surface of the particles will be accelerated, causing them to tend to adhere to the surface of large particles, pushing the grain boundaries of small particles to move in a direction with lower energy, resulting in the fusion of adjacent small particles or the occurrence of hardening and agglomeration. Slow heating and holding can prevent the nano-hydroxyl gallium precursor from breaking due to thermal stress, ensuring that the pre-sintering intermediate is loose and uniform, and providing a channel for the subsequent penetration of ammonia.

[0029] S4 step is a high-temperature nitriding treatment in an ammonia atmosphere. This step is the "core conversion link" of the preparation process, and its role is to convert the pre-sintering intermediate (gallium oxide-based pre-sintering intermediate) into gallium nitride. Ammonia, as a nitrogen source, decomposes into active nitrogen species (such as NH2 and NH) at a high temperature of 800-1100°C. These active species can chemically react with gallium elements in the pre-sintering intermediate, gradually replacing oxygen elements to form gallium nitride. High temperature not only promotes the decomposition of ammonia, but also provides sufficient energy for the nitriding reaction, promoting the complete reaction and the ordered growth of gallium nitride grains, and improving the crystallinity. Precise control of the heating rate and holding time can prevent excessive growth of gallium nitride grains or incomplete local nitriding. Through this step, the chemical conversion of the nano-hydroxyl gallium precursor to gallium nitride is achieved, and a gallium nitride powder product is obtained.

[0030] S5 is an annealing process to improve the quality of the nanometer gallium nitride powder. The annealing process can repair defects and stabilize the structure. During the nitriding process, the gallium nitride powder is prone to form defects such as crystal lattice vacancies and dislocations due to rapid atomic migration at high temperatures, and a trace of oxide layer may be left on the surface (reacted with trace oxygen in the furnace). The annealing temperature of 700-800 ℃ can provide moderate thermal motion energy for atoms, so that the atoms at the vacancies can rearrange to fill the defects, and active nitrogen species can further eliminate the surface oxide layer. The holding process ensures that the defects are repaired completely, and avoids the decline of the electrical and optical properties of the product due to incomplete treatment. Finally, through the annealing process, the nanometer gallium nitride powder with high crystallinity, few defects and stable morphology is obtained.

[0031] Therefore, the application utilizes the double active groups of the surfactant to regulate the hydrothermal reaction process of metallic gallium and water, realizes the precise control of the morphology and size of the nanometer gallium oxyhydroxide precursor through the specific adsorption of the hydrophilic group to the gallium source and the intermediate product in the reaction and the steric hindrance effect of the hydrophobic group, and then converts the nanometer gallium oxyhydroxide precursor into the nanometer gallium nitride powder with high crystallinity and uniform size through the multi-stage high-temperature nitriding process of “low-temperature pre-burning + high-temperature nitriding + annealing to eliminate defects”.

[0032] In some embodiments, the ammonia flow rate of the ammonia atmosphere is 20-80 mL / min, the second set temperature is 800-1100 ℃, the second set heating rate is 5-20 ℃ / min, and the second set holding time is 2-6 h.

[0033] The ammonia flow rate of the high-temperature nitriding process is limited to 20-80 mL / min, which can provide sufficient nitrogen source, ensure that the ammonia is decomposed into sufficient active nitrogen species at high temperature, provide sufficient raw materials for the reaction between the pre-burning intermediate and nitrogen, ensure that the nitriding reaction proceeds efficiently, and completely eliminate the water and oxygen species generated in the reaction to avoid side reactions. The second set temperature of the high-temperature nitriding process is limited to 800-1100 ℃, which can promote the decomposition of ammonia, provide sufficient energy for the nitriding reaction, promote the conversion of the pre-burning intermediate to gallium nitride, and promote the ordered growth of gallium nitride grains to improve the crystallinity of the product. The second set heating rate of the high-temperature nitriding process is limited to 5-20 ℃ / min, which can accelerate the heating efficiency on the premise of ensuring the stability of the structure of the pre-burning intermediate, shorten the production cycle, maintain the uniformity of the temperature in the core reaction area, and ensure the consistency of the nitriding reaction. The second set holding time of the high-temperature nitriding process is limited to 2-6 h, which can ensure that the pre-burning intermediate is completely converted into gallium nitride, avoid the residue of unreacted gallium nitride powder, and ensure the composition, quality purity and structural integrity of the gallium nitride product.

[0034] In some embodiments, the liquid-solid ratio of water to metallic gallium is (10-30):1.

[0035] The liquid-solid ratio of water to gallium is limited to (10-30):1, which can balance the nanometer size of the product and the production efficiency. The size of the product can be prevented from increasing due to excessive reactant (gallium) in the reaction kettle, ensuring the smooth formation of the nanoscale size of the product. The concentration of the reactant is maintained, ensuring the yield of the nanohydroxyl gallate precursor in a unit volume, which meets the needs of industrial production.

[0036] In some embodiments, the molar amount of the surfactant is 1%-10% of the molar amount of gallium.

[0037] The molar amount of the surfactant is limited to 1%-10% of the molar amount of gallium, which can accurately control the morphology of the nanohydroxyl gallate precursor, and at the same time, play an anti-agglomeration role, promote the uniform nucleation and ordered growth of the nanohydroxyl gallate precursor, and obtain nanoscale nanohydroxyl gallate precursor with good dispersion and uniform size.

[0038] In some embodiments, the surfactant includes one or more of sodium dodecyl sulfate, hexadecyl trimethyl ammonium bromide, and polyethylene glycol.

[0039] In some embodiments, the hydrothermal reaction includes the following parameters: the stirring speed is 800 r / min-1200 r / min, the reaction temperature is 160°C-220°C, and the reaction time is 2h-10h.

[0040] The stirring speed of the hydrothermal reaction is limited to 800 r / min-1200 r / min, which can ensure that the gallium, the surfactant, and the water are fully mixed, eliminate the local concentration difference of the reaction system, let the reaction proceed in a uniform environment, and ensure the consistency of the particle size and morphology of the nanohydroxyl gallate precursor. The reaction temperature of the hydrothermal reaction is limited to 160°C-220°C, which can provide suitable kinetic energy for the reaction of gallium and water, which can not only promote the reaction to generate hydroxyl gallate efficiently, but also control the growth rate of the nanohydroxyl gallate precursor particles to form a structure that meets the nanometer size requirements. The reaction time of the hydrothermal reaction is limited to 2h-10h, which can ensure that the gallium fully participates in the reaction, avoid the residual of unreacted metal, ensure the conversion rate of the nanohydroxyl gallate precursor, and provide sufficient and high-activity raw materials for the subsequent nitriding process.

[0041] In some embodiments, the nitrogen flow rate of the nitrogen atmosphere is 100 mL / min-200 mL / min, the first set temperature is 400°C-600°C, the first set heating rate is 2°C / min-10°C / min, and the first set holding time is 0.5h-2h.

[0042] The nitrogen flow rate of the low-temperature pre-burning treatment is limited to 100-200 mL / min, which can efficiently replace the air and moisture in the tube furnace to build an inert protective atmosphere and avoid the reaction between the nano-hydroxyl gallium precursor and the air components, while maintaining the stability of the atmosphere in the furnace; the first set temperature of the low-temperature pre-burning treatment is limited to 400-600°C, which can gently remove the residual hydroxyl, adsorbed water and crystal water in the hydroxyl gallium, and convert them into a gallium oxide-based pre-burning intermediate with a more stable structure, while the low temperature helps to maintain the loose structure of the gallium nitride powder to provide a channel for subsequent ammonia penetration; the first set heating rate of the low-temperature pre-burning treatment is limited to 2-10°C / min, which can slowly increase the furnace temperature to avoid thermal stress of the nano-hydroxyl gallium precursor particles due to sudden temperature rise, damage the structural integrity of the pre-burning intermediate, and avoid the hardening phenomenon of surface agglomeration, which affects the subsequent ammonia entering the interior and ensures the particle dispersion of the pre-burning intermediate; the first set holding time of the low-temperature pre-burning treatment is limited to 0.5-2h, which can ensure the complete removal of hydroxyl in the nano-hydroxyl gallium precursor, and make the composition and structure of the pre-burning intermediate uniform and consistent to lay a foundation for the uniform reaction of subsequent high-temperature nitriding.

[0043] In some embodiments, the third set temperature is 700-800°C, and the third set holding time is 0.5-1.5h.

[0044] The third set temperature of the annealing treatment is limited to 700-800°C, which can provide moderate energy to make the atoms in the gallium nitride particles produce thermal motion, promote lattice vacancy filling and dislocation repair, and eliminate the surface trace of the oxide layer to improve the structural integrity of the product; the third set holding time of the annealing treatment is limited to 0.5-1.5h, which can ensure sufficient defect repair to make the crystal structure of the gallium nitride more regular, while avoiding structural changes caused by excessive treatment, and ultimately improving the electrical, optical performance and structural stability of the gallium nitride powder.

[0045] In some embodiments, the mass purity of metallic gallium is 6N; The mass purity of nitrogen and ammonia is 5N; The mass purity of the surfactant is analytical pure.

[0046] The mass purity of metallic gallium is limited to 6N (99.9999%), which can exclude metal impurities such as iron and aluminum to ensure that no impurity defect centers are formed during the subsequent nitriding process, and to ensure the electrical performance (such as carrier mobility) and optical performance (such as luminous intensity) of the gallium nitride, meeting the basic requirements of product application performance.

[0047] By limiting the purity of nitrogen and ammonia to 5N (99.999%), impurities such as oxygen, moisture, and hydrocarbons in the gases can be removed, maintaining the purity of the reaction environment and providing a clean atmosphere for the stable conversion of nano-gallium hydroxyl oxide precursors, thus ensuring the quality purity and crystallinity of gallium nitride.

[0048] Limiting the purity of the surfactant to analytical grade avoids the introduction of additional organic impurities, ensures no carbon residue is generated during drying and high-temperature processing, and further guarantees the purity of gallium nitride powder.

[0049] In some embodiments, in step S2, the obtained powder product is washed with high-purity water more than 20 times, the drying temperature is 80℃~140℃, and the drying time is 2h~12h.

[0050] Washing with high-purity water more than 20 times can thoroughly remove residual surfactants and other impurities adsorbed on the surface of gallium hydroxyl oxide powder, ensuring the purity of the nano-gallium hydroxyl oxide precursor and avoiding interference from impurities in the subsequent nitriding reaction. A drying temperature of 80–140℃ can gently remove adsorbed water and crystal water from the nano-gallium hydroxyl oxide precursor, preventing agglomeration of gallium hydroxyl oxide while dehydrating it, and maintaining the chemical composition and nanostructure stability of the nano-gallium hydroxyl oxide precursor. A drying time of 2–12 hours ensures complete removal of moisture from the nano-gallium hydroxyl oxide precursor, keeping it dry and providing a structurally stable, moisture-free raw material for the subsequent low-temperature pre-calcination process.

[0051] Figure 2 This is a schematic diagram of the overall structure of the tubular furnace provided in the embodiments of this application; Figure 3 This is a cross-sectional view of a tubular furnace provided in an embodiment of this application.

[0052] like Figure 2 and Figure 3 As shown, this application provides an apparatus for preparing nano-gallium nitride powder materials. The apparatus is adapted to the method of any embodiment of the first aspect. The apparatus includes a tube furnace, which is used to sequentially perform low-temperature pre-calcination, high-temperature nitridation, and annealing treatments on nano-gallium hydroxyl oxide precursors. The tube furnace includes: The furnace body is tubular, with an internal reaction chamber inside. The air inlet pipe and the exhaust pipe are located on the tubular furnace body; A gas diffusion platform, located inside the internal reaction chamber, is used to evenly distribute the reaction gas introduced from the inlet pipe to the reaction area.

[0053] In some embodiments, the gas diffusion platform is equipped with a multi-pipe gas outlet device inside and has uniformly distributed gas outlets on its surface. Above the gas diffusion platform is placed a boron nitride crucible that carries the nano-gallium oxyhydroxide precursor.

[0054] In some embodiments, the end of the tubular furnace body is sealed by a flange sealing ring with holes, and the gas inlet pipeline and the tail gas pipeline pass through the flange sealing ring.

[0055] It should be noted that the functions of the various components of the tubular furnace are as follows: The tubular furnace body and the internal reaction chamber: The tubular furnace body has precise temperature control function (can realize temperature adjustment and stable heat preservation of 400-1100℃), providing the required temperature conditions for the three stages of low-temperature pre-burning treatment, high-temperature nitriding treatment and annealing treatment; the internal reaction chamber is a closed space that can maintain the stability of the inert / reaction atmosphere (nitrogen, ammonia), avoid the intrusion of external air, and ensure that the nano-gallium oxyhydroxide precursor, pre-burning intermediate and nitriding product can react in a controllable environment.

[0056] Gas inlet pipeline and tail gas pipeline: The gas inlet pipeline is used to accurately deliver nitrogen or ammonia gas to the internal reaction chamber, and can pass in nitrogen gas during the low-temperature pre-burning treatment stage and switch to ammonia gas during the high-temperature nitriding treatment stage, meeting the atmosphere requirements of different process stages; the tail gas pipeline is used to discharge the waste gas (such as unreacted ammonia and water vapor) after reaction to the tail gas treatment device, avoiding the direct discharge of waste gas which may cause safety risks (ammonia is irritating) and environmental pollution, while maintaining the stability of the internal reaction chamber pressure.

[0057] Gas diffusion platform (including multi-tube gas outlet device and uniform gas outlet): This is a key component to ensure uniform reaction, the multi-tube gas outlet device can preliminarily disperse the gas (nitrogen / ammonia) introduced by the gas inlet pipeline, and then uniformly deliver the gas to the surrounding of the nano-gallium oxyhydroxide precursor through the small gas outlets uniformly distributed on the surface, avoiding the problem of "partial powder nitriding sufficient, partial nitriding insufficient" caused by local gas concentration difference. For example, without this platform, ammonia gas is easy to accumulate locally in the internal reaction chamber, leading to excessive nitriding of some gallium nitride powder and insufficient nitriding of some gallium nitride powder, resulting in uneven morphology and composition of the final nano-gallium nitride powder.

[0058] Boron nitride crucible: used to carry the nano-gallium oxyhydroxide precursor, its role is "high temperature resistance + reaction pollution prevention", boron nitride material can withstand high temperature above 1200℃, matching the temperature requirement of high-temperature nitriding stage; at the same time, it has strong chemical inertness and will not react with nano-gallium oxyhydroxide precursor, ammonia or gallium nitride, avoiding the pollution of container material to the product, ensuring the quality purity of gallium nitride powder. If ordinary ceramic crucible is used, it may react with ammonia at high temperature to generate impurities, affecting the quality of the product.

[0059] Flange sealing ring: located at both ends of the tubular furnace body, the role is to seal the internal reaction chamber, prevent nitrogen, ammonia leakage during the reaction (ammonia leakage has irritability, nitrogen leakage will destroy the inert atmosphere), while avoiding the entry of external air into the internal reaction chamber, to ensure the stability of the atmosphere, to provide a pure environment for low temperature pre-burning treatment, high temperature nitriding treatment and annealing treatment. If the sealing is not good, it will lead to the loss of control of the atmosphere, and the nitriding reaction will fail or the product impurities will exceed the standard.

[0060] In summary, the preparation method and device of the nano-gallium nitride powder material provided by the application have the following advantages: (1) The preparation method of the nano-gallium nitride powder material provided by the application uses metal gallium as the basic raw material, and prepares nano-structured gallium nitride powder through a two-step short process. The core advantage lies in the synergistic innovation of "surfactant-assisted hydrothermal method nano-hydroxyl gallate precursor morphology control" and "multi-stage calcination annealing treatment". The raw material has strong adaptability, and is compatible with a variety of gallium-containing raw materials in addition to metal gallium. At the same time, the two-step process greatly simplifies the preparation process, and has excellent process compatibility and potential for large-scale production, and can realize continuous operation.

[0061] (2) The preparation method of the nano-gallium nitride powder material provided by the application proposes a surfactant-assisted hydrothermal method, which controls the morphology of nano-hydroxyl gallate precursor, inhibits powder agglomeration, and obtains nano-powder with uniform morphology, which is convenient for subsequent high-temperature nitriding treatment to obtain nano-gallium nitride powder. In the hydrothermal process, the amphiphilic structure (hydrophilic group + hydrophobic group) of the surfactant is used to control the "nucleation-growth-dispersion" whole process of nano-material formation at the molecular level, promote the uniform nucleation of hydroxyl gallate, reduce the particle size, and at the same time, through the dual action of "steric hindrance + electrostatic repulsion" of the surfactant, improve the dispersion stability of the nano-material, inhibit the particle agglomeration, and ensure the uniformity of the powder morphology. The application can further optimize the type and amount of dispersant to control the morphology, growth direction and size of nano-structure, and realize the control of particle size distribution, morphology and dispersion of nano-material.

[0062] (3) The application provides a preparation method of a nano-gallium nitride powder material. The method is characterized by a hierarchical multi-stage calcination process of "low-temperature pre-burning + high-temperature nitriding + annealing to eliminate defects", which solves the defects in the traditional high-temperature nitriding process in the aspect of defect control. Due to the non-uniform reaction characteristics between gas and solid, the product is prone to have high lattice point defect density, prominent linear defects and surface defects, and high macro-agglomeration and porosity. The application guides the slow diffusion of the reaction gas in the low-temperature pre-burning stage, avoids the imbalance of the gas concentration, and forms loose and uniform nano-gallium hydroxide oxide precursor. In the high-temperature nitriding stage, the heating rate and the nitrogen source flow are accurately controlled to realize the directional and ordered growth of gallium nitride grains along the low surface energy crystal surface, avoid particle agglomeration and surface hardening, and thus affect the diffusion reaction of ammonia gas to the inside. The annealing treatment fills the residual vacancies through atomic thermal migration, and eliminates the surface oxidation defects by using active nitrogen species.

[0063] The application will be further described below in combination with specific examples. The experimental methods not specified in the following examples are generally determined according to national standards / industry standards / the content disclosed herein. If there is no corresponding national standard / industry standard / the content disclosed herein, the general international standard, the conventional condition or the condition suggested by the manufacturer is used.

[0064] Example 1 The application provides a preparation device of a nano-gallium nitride powder material, which is composed of a hydrothermal reaction kettle and a tubular furnace.

[0065] As shown in Figure 2 and Figure 3 , the tubular furnace comprises a tubular furnace body 4 and an internal reaction chamber 5. The internal reaction chamber 5 is located in the internal reaction chamber 5 of the tubular furnace body 4. The tubular furnace body 4 has a heating and insulation function, which is used for adjusting the temperature in the internal reaction chamber 5.

[0066] The tubular furnace body 4 is provided with a flange sealing ring 3 with holes. The flange 3 is located at the left and right ends of the tubular furnace body, which is used for sealing and preventing gas leakage in the tubular furnace. The flange sealing ring 3 comprises an air inlet pipeline 1 and two tail gas pipelines 2. The air inlet pipeline 1 directly penetrates into the inside of the gas diffusion platform 9 and is connected with the multi-tube gas outlet device 10.

[0067] The internal reaction chamber 5 includes a gas diffusion platform 9, a boron nitride crucible 8 and a nano-hydroxyl gallate precursor 7, which is placed in the boron nitride crucible 8 and is placed on the gas diffusion platform 9. The gas diffusion platform 9 has a multi-tube gas outlet device 10 inside, which uniformly disperses the nitrogen or ammonia gas introduced through the gas inlet 1. The surface of the gas diffusion platform 9 has uniform and fine gas outlets 6 for uniformly dispersing the nitrogen or ammonia gas introduced through the multi-tube gas outlet device 10 around the boron nitride crucible 8 and the nano-hydroxyl gallate precursor 7, ensuring that the gas concentration around the nano-hydroxyl gallate precursor remains consistent during the reaction. The gas in the internal reaction chamber 5 is discharged through the tail gas outlet 2 on the sealing flange 3 to the tail gas treatment device.

[0068] Example 2 The embodiment provides a preparation method of nano-gallium nitride powder material, which specifically comprises the following steps: S21, metal gallium, surfactant sodium dodecyl sulfate (SDS) and water are added to a high-pressure reaction kettle, wherein the liquid-solid ratio of water to metal gallium is 20:1, and the molar amount of SDS is 2% of the molar amount of metal gallium. The reaction kettle is tightly sealed and heated to a reaction temperature of 200℃ under the condition that the stirring speed is 1000 r / min, and a hydroxyl gallate precursor-containing reaction product is obtained after 5h of heat preservation; S22, after the reaction is completed, the product after the reaction is subjected to solid-liquid separation, and the solid separation product is collected. The solid separation product is washed with high-purity water for more than 20 times, and then dried at a temperature of 90℃ for 12h to obtain a pure and dry nano-hydroxyl gallate precursor; S23, the nano-hydroxyl gallate precursor is placed in the tube furnace of example 1. First, high-purity nitrogen gas (mass purity 5N) is introduced for 30 minutes to remove air and moisture in the furnace, and the nitrogen flow rate is 200mL / min. Then, the nano-hydroxyl gallate precursor is heated to a set temperature of 600℃ at a set heating rate of 5℃ / min under a nitrogen atmosphere, and a low-temperature pre-burning treatment is performed for a set holding time of 2h to obtain a pre-burning intermediate; S24, the atmosphere in the tube furnace is switched from nitrogen to ammonia gas (mass purity 5N), and the ammonia flow rate is 50mL / min. Then, the pre-burning intermediate is heated to a set temperature of 850℃ at a set heating rate of 10℃ / min, and a high-temperature nitriding treatment is performed for a second set holding time of 4h to obtain a gallium nitride powder; S25, after the high-temperature nitriding is completed, the gallium nitride powder is slowly cooled to a set temperature of 800℃, and an annealing treatment is performed for a set holding time of 1h. After the annealing is completed, the natural cooling is obtained, and a nano-gallium nitride powder is obtained.

[0069] Product characterization: using the method of this example, the conversion rate of nano-hydroxyl gallium precursor is 99.71%. Through scanning electron microscope (SEM) test analysis, the obtained nano-gallium nitride powder is uniform spherical particles in appearance, and the particle size is about 80nm-100nm.

[0070] Example 3 This example provides a method for preparing a nano-gallium nitride powder material, which specifically comprises the following steps: S31, metal gallium, surfactant sodium dodecyl sulfate (SDS) and water are added to a high-pressure reaction kettle, wherein the liquid-solid ratio of water to metal gallium is 30:1, and the molar amount of SDS is 8% of the molar amount of metal gallium. Tighten and seal the reaction kettle, heat to a reaction temperature of 180℃ under the condition of stirring speed of 1200r / min, and keep the reaction for 6h to obtain a reaction product containing hydroxyl gallium precursor; S32, after the reaction is completed, the product after the reaction is subjected to solid-liquid separation, and the solid separation is collected. The solid separation is washed with high-purity water for more than 20 times, and then dried at a temperature of 80℃ for 12h to obtain pure and dry nano-hydroxyl gallium precursor; S33, the nano-hydroxyl gallium precursor is placed in the tube furnace of example 1. First, high-purity nitrogen gas (mass purity 5N) is introduced for 30 minutes to remove air and moisture in the furnace, and the nitrogen flow rate is 200mL / min. Subsequently, the nano-hydroxyl gallium precursor is heated to a set temperature of 600℃ at a set heating rate of 5℃ / min under a nitrogen atmosphere, and a low-temperature pre-burning treatment is carried out for a set holding time of 1h to obtain a pre-burning intermediate; S34, the atmosphere in the tube furnace is switched from nitrogen to ammonia (mass purity 5N), and the ammonia flow rate is 30mL / min. Then, the pre-burning intermediate is heated to a set temperature of 900℃ at a set heating rate of 8℃ / min, and a high-temperature nitriding treatment is carried out for a set holding time of 4h to obtain a gallium nitride powder; S35, after the high-temperature nitriding is completed, the gallium nitride powder is slowly cooled to a set temperature of 800℃, and an annealing treatment is carried out for a set holding time of 1.5h. After annealing is completed, natural cooling is carried out to obtain a nano-gallium nitride powder.

[0071] Product characterization: using the method of this example, the conversion rate of nano-hydroxyl gallium precursor is 99.89%. Through scanning electron microscope (SEM) test analysis, the obtained nano-gallium nitride powder is uniform short rod-shaped particles in appearance, and the particle size is about 50nm-90nm in diameter and 150nm-400nm in length.

[0072] Example 4 This example provides a method for preparing a nano-gallium nitride powder material, which specifically comprises the following steps: S41, metal gallium, surfactant cetyltrimethylammonium bromide (CTAB) and water are added into a high-pressure reaction kettle, wherein the liquid-solid ratio of water to metal gallium is 30:1, and the molar amount of CTAB is 1% of the molar amount of metal gallium. The reaction kettle is tightly sealed and heated to a reaction temperature of 210°C under the condition that the stirring speed is 1200 r / min, and then the reaction is kept for 5 h, and a reaction product containing a hydroxyl gallium oxide precursor is obtained; S42, after the reaction is completed, the reaction product is subjected to solid-liquid separation, and the solid separation product is collected. The solid separation product is washed with high-purity water for more than 20 times, and then dried at a temperature of 100°C for 12 h to obtain a pure and dry nano-hydroxyl gallium oxide precursor; S43, the nano-hydroxyl gallium oxide precursor is placed in the tube furnace of Example 1. First, high-purity nitrogen gas (mass purity 5N) is introduced for 30 minutes to remove air and moisture in the furnace, and the nitrogen flow rate is 200 mL / min. Subsequently, the nano-hydroxyl gallium oxide precursor is heated to a set temperature of 600°C at a set heating rate of 5°C / min under a nitrogen atmosphere, and low-temperature calcination treatment is performed for a set holding time of 1.5 h to obtain a calcination intermediate; S44, the atmosphere in the tube furnace is switched from nitrogen to ammonia gas (mass purity 5N), and the ammonia flow rate is 50 mL / min. Then, the calcination intermediate is heated to a set temperature of 1100°C at a set heating rate of 10°C / min, and high-temperature nitriding treatment is performed for a set holding time of 3 h to obtain a gallium nitride powder; S45, after the high-temperature nitriding is completed, the gallium nitride powder is slowly cooled to a set temperature of 750°C, and annealing treatment is performed for a set holding time of 1.5 h. After the annealing is completed, natural cooling is performed to obtain a nano-gallium nitride powder.

[0073] Product characterization: by using the method of the present embodiment, the conversion rate of the nano-hydroxyl gallium oxide precursor is 99.45%. Through scanning electron microscope (SEM) test analysis, the obtained nano-gallium nitride powder is a short rod-shaped particle with uniform morphology, and the particle size is about 60 nm to 100 nm in diameter and 200 nm to 400 nm in length.

[0074] Example 5 The present embodiment provides a method for preparing a nano-gallium nitride powder material, which specifically comprises the following steps: S51, metal gallium, surfactant cetyltrimethylammonium bromide (CTAB) and water are added into a high-pressure reaction kettle, wherein the liquid-solid ratio of water to metal gallium is 30:1, and the molar amount of CTAB is 1% of the molar amount of metal gallium. The reaction kettle is tightly sealed and heated to a reaction temperature of 210°C under the condition that the stirring speed is 1200 r / min, and then the reaction is kept for 5 h, and a reaction product containing a hydroxyl gallium oxide precursor is obtained; S52, after the reaction, the product after the reaction is subjected to solid-liquid separation, and the solid separation product is collected. The solid separation product is washed with high-purity water for more than 20 times, and then dried at a temperature of 110°C for 12h to obtain a pure and dry nano-gallium oxyhydroxide precursor; S53, the nano-gallium oxyhydroxide precursor is placed in the tube furnace of Example 1. First, high-purity nitrogen (mass purity 5N) is introduced for 30 minutes to remove air and moisture in the furnace, and the nitrogen flow rate is 100mL / min. Subsequently, the nano-gallium oxyhydroxide precursor is heated to a set temperature of 600°C at a set heating rate of 5°C / min under a nitrogen atmosphere, and a low-temperature calcination treatment is performed for a set holding time of 1.5h to obtain a calcination intermediate; S54, the atmosphere in the tube furnace is switched from nitrogen to ammonia (mass purity 5N), and the ammonia flow rate is 40mL / min. Then, the calcination intermediate is heated to a set temperature of 1000°C at a set heating rate of 10°C / min, and a high-temperature nitriding treatment is performed for a set holding time of 4h to obtain a gallium nitride powder; S55, after the high-temperature nitriding is completed, the gallium nitride powder is slowly cooled to a set temperature of 700°C, and an annealing treatment is performed for a set holding time of 1.5h. After the annealing is completed, it is naturally cooled to obtain a nano-gallium nitride powder.

[0075] Product characterization: using the method of this embodiment, the conversion rate of the nano-gallium oxyhydroxide precursor is 99.45%. Through scanning electron microscope (SEM) test analysis, the obtained nano-gallium nitride powder is a short rod-shaped particle with uniform morphology, with a particle size of about 40nm-80nm in diameter and 400nm-600nm in length.

[0076] Example 6 The embodiment provides a preparation method of a nano-gallium nitride powder material, which specifically comprises the following steps: S61, metal gallium, a surfactant polyethylene glycol (PEG) and water are added to a high-pressure reaction kettle, wherein the liquid-solid ratio of water to metal gallium is 30:1, and the molar amount of PEG is 10% of the molar amount of metal gallium. The reaction kettle is tightly sealed and sealed, heated to a reaction temperature of 190°C under the condition that the stirring speed is 1200r / min, and kept for 6h to obtain a reaction product containing a gallium oxyhydroxide precursor; S62, after the reaction, the product after the reaction is subjected to solid-liquid separation, and the solid separation product is collected. The solid separation product is washed with high-purity water for more than 20 times, and then dried at a temperature of 90°C for 12h to obtain a pure and dry nano-gallium oxyhydroxide precursor; S63, the nanometer gallium hydroxyl oxide precursor is put into the tube furnace of example 1. First, high-purity nitrogen (mass purity 5N) is passed for 30 minutes to remove air and moisture in the furnace, and the nitrogen flow rate is 100 mL / min. Subsequently, the nanometer gallium hydroxyl oxide precursor is heated to a set temperature of 600℃ at a set heating rate of 5℃ / min under a nitrogen atmosphere, and low-temperature pre-sintering treatment is carried out for a set holding time of 2h, to obtain a pre-sintering intermediate; S64, the atmosphere in the tube furnace is switched from nitrogen to ammonia (mass purity 5N), and the ammonia flow rate is 40 mL / min. Then, the pre-sintering intermediate is heated to a set temperature of 950℃ at a set heating rate of 10℃ / min, and high-temperature nitriding treatment is carried out for a set holding time of 3h, to obtain a gallium nitride powder; S65, after the high-temperature nitriding is completed, the gallium nitride powder is slowly cooled to a set temperature of 700℃, and annealing treatment is carried out for a set holding time of 1.5h. After the annealing is completed, natural cooling is carried out, to obtain a nanometer gallium nitride powder.

[0077] Product characterization: by using the method of this example, the conversion rate of the nanometer gallium hydroxyl oxide precursor is 99.62%. Through scanning electron microscope (SEM) test analysis, the obtained nanometer gallium nitride powder is a particle with uniform morphology, and the particle size is about 80nm-120nm.

[0078] Example 7 The example provides a preparation method of a nanometer gallium nitride powder material, which specifically comprises the following steps: S71, metal gallium, a surfactant polyethylene glycol (PEG), and water are added into a high-pressure reaction kettle, wherein the liquid-solid ratio of water to metal gallium is 30:1, and the molar amount of PEG is 5% of the molar amount of metal gallium. The reaction kettle is tightly sealed and heated to a reaction temperature of 200℃ under the condition that the stirring speed is 1000r / min, and a gallium hydroxyl oxide precursor-containing reaction product is obtained after holding for 4h; S72, after the reaction is completed, the product after the reaction is subjected to solid-liquid separation, and the solid separation product is collected. The solid separation product is washed with high-purity water for more than 20 times, and then dried at a temperature of 100℃ for 12h, to obtain a pure and dry nanometer gallium hydroxyl oxide precursor; S73, the nanometer gallium hydroxyl oxide precursor is put into the tube furnace of example 1. First, high-purity nitrogen (mass purity 5N) is passed for 30 minutes to remove air and moisture in the furnace, and the nitrogen flow rate is 100 mL / min. Subsequently, the nanometer gallium hydroxyl oxide precursor is heated to a set temperature of 600℃ at a set heating rate of 5℃ / min under a nitrogen atmosphere, and low-temperature pre-sintering treatment is carried out for a set holding time of 1h, to obtain a pre-sintering intermediate; S74, switch the atmosphere in the tube furnace from nitrogen to ammonia (mass purity 5N) with a flow rate of 40 mL / min. Then, heat the pre-sintered intermediate to a set temperature of 1100°C at a set heating rate of 10°C / min, and perform high-temperature nitriding treatment for a set holding time of 3 h to obtain gallium nitride powder; S75, after the high-temperature nitriding is completed, slowly cool the gallium nitride powder to a set temperature of 750°C, and perform annealing treatment for a set holding time of 1.5 h. After the annealing is completed, naturally cool to obtain nano-gallium nitride powder.

[0079] Product characterization: using the method of this embodiment, the conversion rate of nano-gallium hydroxide precursor is 99.59%. Through scanning electron microscope (SEM) test analysis, the obtained nano-gallium nitride powder is a uniform granular morphology with a particle size of about 100 nm to 150 nm.

[0080] Comparative Example 1 The implementation method for preparing gallium nitride powder in this comparative example is the same as that in Example 2, except that no surfactant is added in the hydrothermal process, and the high-temperature nitriding process still uses staged calcination and annealing treatment.

[0081] Using the treatment method of this comparative example, the obtained gallium nitride powder is weighed and subjected to scanning electron microscope test analysis, and the results are that the conversion rate of gallium hydroxide precursor is 99.73%, the morphology of gallium nitride powder is a rod-shaped product with a diameter of 300 nm to 500 nm and a length of 2 μm to 3 μm, and the dispersibility is good.

[0082] Comparative Example 2 The implementation method for preparing gallium nitride powder in this comparative example is the same as that in Example 2, except that a surfactant is added in the hydrothermal process, but no staged calcination and annealing treatment is performed.

[0083] Using the treatment method of this comparative example, the obtained gallium nitride powder is weighed and subjected to scanning electron microscope test analysis, and the results are that the conversion rate of gallium hydroxide precursor is 99.56%, the morphology of gallium nitride powder is an irregular shape with a diameter of 500 nm to 2 μm, and the agglomeration phenomenon easily occurs.

[0084] Comparative Example 3 The implementation method for preparing gallium nitride powder in this comparative example is the same as that in Example 2, except that no surfactant is added in the hydrothermal process, and no staged calcination and annealing treatment is performed.

[0085] Using the treatment method of this comparative example, the obtained gallium nitride powder is weighed and subjected to scanning electron microscope test analysis, and the results are that the conversion rate of gallium hydroxide precursor is 99.69%, the morphology of gallium nitride powder is an irregular rod-shaped product with a diameter of 300 nm to 600 nm and a length of 2 μm to 4 μm, and the agglomeration phenomenon easily occurs.

[0086] The conversion rate of the nano-gallium hydroxyl oxide precursor and the morphology parameters of the nano-gallium nitride powder of Examples 2-7 and Comparative Examples 1-3 are summarized in Table 1.

[0087] Table 1 Conversion rate of nano-gallium hydroxyl oxide precursor and morphology parameters of nano-gallium nitride powder

[0088] The differences between different examples and comparative examples can be directly compared through the above experimental data effect table. The specific analysis is as follows: Example 2: The hydroxyl oxidant precursor is prepared by using a lower concentration (2%) of anionic surfactant SDS assisted hydrothermal method, and then treated by "low temperature pre-burning + high temperature nitriding + annealing to eliminate defects", which can realize the conversion of the precursor to gallium nitride powder at a lower nitriding reaction temperature (850°C). The conversion rate of the hydroxyl oxidant precursor reached 99.71%, and the obtained gallium nitride powder was uniform spherical particles with a particle size of about 80-100 nm.

[0089] Example 3: The hydroxyl oxidant precursor is prepared by using a higher concentration (8%) of anionic surfactant SDS assisted hydrothermal method, and then treated by "low temperature pre-burning + high temperature nitriding + annealing to eliminate defects", which can realize the conversion of the precursor to gallium nitride powder at a nitriding reaction temperature (900°C), and slightly improve the conversion rate and size. The conversion rate of the hydroxyl oxidant precursor reached 99.89%, and the obtained gallium nitride powder was uniform short rod-shaped particles with a particle size of about 50-90 nm in diameter and 150-400 nm in length.

[0090] Example 4: The hydroxyl oxidant precursor is prepared by using a lower concentration (1%) of cationic surfactant CTAB assisted hydrothermal method, and then treated by "low temperature pre-burning + high temperature nitriding + annealing to eliminate defects", which can realize the conversion of the precursor to gallium nitride powder at a nitriding reaction temperature (1100°C). The conversion rate of the hydroxyl oxidant precursor reached 99.45%, and the obtained nano-gallium nitride powder was uniform short rod-shaped particles with a particle size of about 60-100 nm in diameter and 200-400 nm in length.

[0091] Example 5: Hydroxyl oxidant precursor was prepared by using higher concentration (3%) of cationic surfactant CTAB assisted hydrothermal method, and then was treated by "low temperature pre-burning + high temperature nitridation + annealing to eliminate defects", which can realize the conversion of precursor to gallium nitride powder at the nitridation reaction temperature (1000℃), and slight change of temperature will not affect the conversion rate of hydroxyl oxidant precursor. The conversion rate of hydroxyl oxidant precursor reached 99.45%, and the obtained nano gallium nitride powder was short rod-shaped particles with uniform morphology, and the particle size was about 40nm-80nm in diameter and 400nm-600nm in length.

[0092] Example 6: Hydroxyl oxidant precursor was prepared by using higher concentration (10%) of nonionic surfactant PEG assisted hydrothermal method, and then was treated by "low temperature pre-burning + high temperature nitridation + annealing to eliminate defects", which can realize the conversion of precursor to gallium nitride powder at the nitridation reaction temperature (950℃). The conversion rate of hydroxyl oxidant precursor reached 99.62%, and the obtained nano gallium nitride powder was particles with uniform morphology, and the particle size was about 80nm-120nm.

[0093] Example 7: Hydroxyl oxidant precursor was prepared by using lower concentration (5%) of nonionic surfactant PEG assisted hydrothermal method, and then was treated by "low temperature pre-burning + high temperature nitridation + annealing to eliminate defects", which can realize the conversion of precursor to gallium nitride powder at the nitridation reaction temperature (1100℃). The conversion rate of hydroxyl oxidant precursor reached 99.59%, and the obtained nano gallium nitride powder was particles with uniform morphology, and the particle size was about 100nm-150nm.

[0094] Comparative Example 1: Metal gallium hydrothermal reaction was used to prepare hydroxyl oxidant precursor without adding anionic surfactant SDS, but the high temperature nitridation process used staged calcination and annealing treatment, which was heated to the nitridation reaction temperature (850℃) in turn and then was annealed, which can be converted to gallium nitride powder. The product size was significantly larger than that of Example 2, but the product dispersion was relatively good, and the powder was not easy to agglomerate. The conversion rate of hydroxyl oxidant precursor reached 99.73%, and the obtained gallium nitride powder had a rod-shaped product with a diameter of 300nm-500nm and a length of 2μm-3μm.

[0095] Comparative Example 2: Metal gallium hydrothermal reaction was used to prepare hydroxyl oxidant precursor with the addition of anionic surfactant SDS, but the high temperature nitridation process did not use staged calcination and annealing treatment, but directly and quickly heated to the nitridation reaction temperature (850℃), which can be converted to gallium nitride powder. But the product size was significantly larger than that of Example 2, and the product morphology was irregular, and the powder was easy to agglomerate. The conversion rate of hydroxyl oxidant precursor reached 99.56%, and the obtained gallium nitride powder had an irregular shape with a diameter of 500nm-2μm.

[0096] Comparative Example 3: Without adding anionic surfactant SDS in the process of preparing hydroxyl oxidant precursor by hydrothermal reaction of metal gallium, and without using staged calcination and annealing treatment in the process of high-temperature nitridation, but directly and rapidly heating to the nitridation reaction temperature (850°C), gallium nitride powder can be converted. However, the product size is larger than that of Example 2, Comparative Example 1 and Comparative Example 2, the product is irregular, the edge damage phenomenon is more, and the agglomeration of the powder is more serious. The conversion rate of the hydroxyl oxidant precursor reaches 99.69%, and the morphology of the obtained gallium nitride powder is irregular rod-shaped product with a diameter of 300nm-600nm and a length of 2μm-4μm.

[0097] In the process of preparing gallium hydroxide precursor by hydrothermal reaction of metal gallium, the surfactant plays a synergistic role of "electrostatic adsorption stabilization, steric hindrance regulation and micellar confinement", which hinders the agglomeration of gallium hydroxide nanoparticles, the steric hindrance layer inhibits the excessive growth of crystal grains, and the micellar confinement promotes uniform nucleation, accurately regulates the micro-morphology of the gallium hydroxide precursor, and finally makes the product stable and maintained at the nanoscale. In the subsequent "low-temperature pre-burning + high-temperature nitridation + annealing defect elimination" nitridation reaction process, the oxygen atoms in the precursor are replaced by nitrogen atoms, and finally the high-dispersity nanoscale gallium nitride powder is prepared.

[0098] Due to the different charge properties (with or without charge, positive or negative charge) and molecular structures (hydrophobic chain length, hydrophilic end type) of different surfactants, the adsorption mechanism (electrostatic adsorption / hydrogen bond adsorption) of anionic surfactant sodium dodecyl sulfate (SDS), cationic surfactant cetyltrimethylammonium bromide (CTAB) and non-ionic surfactant polyethylene glycol (PEG) to gallium hydroxide crystal nucleus, the selective inhibition ability of crystal face and the regulation of solution microenvironment (micellar morphology, dispersion stability) exist essential differences. The core reason of the difference of product morphology is that the ionic surfactant (SDS, CTAB) guides directional growth through "charge-driven selective crystal face inhibition", and the non-ionic PEG promotes isotropic particles due to "non-selective steric hindrance". SDS will preferentially adsorb on the weakly positively charged gallium hydroxide crystal nucleus high surface energy crystal face (such as {001}) through electrostatic interaction, strongly inhibit the growth of the crystal face, make the crystal extend along the low surface energy crystal face (such as {100}), and finally form nanometer short rod; the hydrophilic end of CTAB is positively charged (-N(CH3)3 - ), which will preferentially adsorb on the weakly negatively charged gallium hydroxide crystal nucleus high surface energy crystal face (such as {100}), strongly inhibit the growth of the crystal face, make the crystal extend along the low surface energy crystal face (such as {001}), and finally form nanometer long rod; the hydrophilic end of PEG is neutral (-CH2CH2O-), which will not selectively adsorb on the crystal face, and the product will be isotropic particles. +), it will be adsorbed on the low surface energy crystal face (such as {100}) of the weakly negative crystal nucleus, inhibiting its growth, and then the crystal will expand along the high surface energy crystal face (such as {001}), showing nanosheet shape; while the non-ionic surfactant PEG is chargeless, only forming weak hydrogen bonds with the hydroxyl groups of the crystal nucleus through ether oxygen bonds, and being randomly adsorbed on all crystal faces without selective inhibition, the crystal grows isotropically, and finally forms spherical or irregular small particles.

[0099] The addition amount of the surfactant will also directly affect the morphology of the gallium hydroxide oxide precursor, and then determine the size and morphology of the final gallium nitride powder: The anionic surfactant sodium dodecyl sulfate (SDS) regulates the morphology of the gallium hydroxide oxide product through effects such as electrostatic adsorption and steric hindrance. When the addition amount is low, SDS cannot completely cover the surface of the particles, and can only partially inhibit the growth of high surface energy crystal faces, resulting in a morphology mainly composed of small particles; when the addition amount is high, the micelles can completely cover the surface of all gallium hydroxide oxide particles, making the particles have uniform electric properties, which on the one hand realizes efficient dispersion through "like charges repel", and on the other hand provides a "directional template" for crystal growth, making the crystal slowly extend along the axis of the micelles, showing a short rod shape, resulting in differences in the morphology of the product formed.

[0100] The synergistic effect of selective electrostatic adsorption and limited steric hindrance of the cationic surfactant cetyltrimethylammonium bromide (CTAB) causes the following phenomena: when the addition amount is low, CTAB is dispersed in the form of monomers, can only partially cover the surface of the particles, has weak inhibitory effect on the radial crystal faces, and has insufficient constraint on the axial growth, resulting in a short rod shape; when the addition amount is high, the micelles formed by CTAB have hydrophobic chains that are easily entangled with each other, which in turn causes the short rods to aggregate and form "rod-shaped aggregates", making the size larger.

[0101] The "steric hindrance layer" effect of the non-ionic surfactant polyethylene glycol (PEG) inhibits the Ostwald ripening process of "small crystal nucleus dissolution and large crystal nucleus growth", blocks particle aggregation, and limits excessive crystal growth, but different PEG addition amounts have the following effect on the size of the gallium hydroxide oxide particles: low concentration: the number of PEG molecules cannot cover the surface of all crystal nuclei, and the unadsorbed crystal nuclei will still aggregate and grow through ripening, resulting in large particle size; high concentration: PEG achieves adsorption and coverage of the crystal nucleus surface, and the three effects of steric hindrance preventing aggregation, active site occupation inhibiting growth, and uniform nucleation promoting dispersion are balanced, inhibiting excessive growth of the crystal nucleus, resulting in small particle size.

[0102] From the results of Comparative Example 1, when the metal gallium does not participate in the reaction with the surfactant in the process of preparing the hydroxyl oxidant precursor by the hydrothermal reaction, even if the high-temperature nitriding process uses the staged calcination and annealing treatment, the size of the gallium nitride powder ultimately formed is still large. The reason is that the process of preparing the gallium hydroxide precursor by the hydrothermal method of the metal gallium lacks the key regulation of “particle dispersion” and “crystal growth”, is easy to be mutually adsorbed and aggregated by the Van der Waals force and hydrogen bond, small particles continuously adhere to form large aggregates, and each crystal face of the crystal loses the selective adsorption constraint. Due to the difference in surface energy of each surface, the atomic activity of the high-surface-energy crystal face is high, so that the powder particle grows preferentially along the dominant growth direction. At the same time, the metal gallium has poor dispersibility in water, and is easy to appear in the local area with excessively high concentration, so that the product is rapidly accumulated here, further aggravating the problem of particle size increase.

[0103] From the results of Comparative Example 2, when the metal gallium participates in the reaction with the surfactant in the process of preparing the hydroxyl oxidant precursor by the hydrothermal reaction, the morphology of the gallium hydroxide precursor is controlled to be nanoscale size, but the high-temperature nitriding process does not use the staged calcination and annealing treatment, but directly and rapidly heats to the reaction temperature, the size of the gallium nitride powder ultimately formed is still large, and the aggregation phenomenon is more obvious. The reason is that the process is not subjected to the treatment of “low-temperature pre-burning + high-temperature nitriding + annealing defect elimination”, but is directly heated to the reaction temperature, so that the sudden increase in high temperature easily increases the particle surface atomic energy and accelerates atomic diffusion, so that adjacent small particles are easy to adhere and fuse, causing sintering aggregation; at the same time, Ostwald ripening is strengthened, small particles are dissolved due to high surface energy, and their atoms are deposited on large particles, so that the large particles continue to grow, thereby reducing the surface energy; in addition, the precursor not subjected to the pretreatment is easy to rapidly decompose at high temperature, the high-concentration Ga-based active species generated is easy to aggregate, and the local overheating caused by the reaction heat further promotes the formation of large particles.

[0104] From the results of Comparative Example 3, when the metal gallium neither participates in the reaction with the surfactant in the process of preparing the hydroxyl oxidant precursor by the hydrothermal reaction, nor uses the staged calcination and annealing treatment in the high-temperature nitriding process, but directly and rapidly heats to the reaction temperature, the size of the gallium nitride powder ultimately formed is larger than that of Comparative Examples 1 and 2, and the morphology is more irregular, further aggravating the aggregation phenomenon. The reason is that the large-particle gallium hydroxide precursor generated by the hydrothermal reaction of the metal gallium irregularly grows by Ostwald ripening when directly subjected to the high-temperature nitriding process, and the atomic diffusion between the particles further aggravates the powder aggregation phenomenon. Promote the further increase in the size of the product, and the aggregation phenomenon is more obvious.

[0105] In addition, one or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages: In the embodiments of the present application, a two-step short process of "surfactant-assisted hydrothermal method for preparing nano-gallium hydroxide precursor + hierarchical multi-stage calcination annealing" is adopted, which greatly simplifies the traditional preparation process. The raw material has strong adaptability, and is compatible with various gallium-containing raw materials except gallium metal, without complex pretreatment. Meanwhile, the process has excellent compatibility and can realize continuous operation, avoiding the problems of traditional process steps being complicated and production cycle being long, and can meet the needs of industrial large-scale production of nano-gallium nitride powder.

[0106] In the embodiments of the present application, the surfactant-assisted hydrothermal method is innovatively proposed, which uses the amphiphilic structure (hydrophilic group + hydrophobic group) of surfactant to intervene in the formation process of nano-gallium hydroxide precursor from the molecular level: the specific adsorption of hydrophilic group with gallium source and reaction intermediate product promotes uniform nucleation; the hydrophobic group inhibits particle agglomeration through the dual action of steric hindrance and electrostatic repulsion. By optimizing the type and amount of surfactant, the morphology, growth direction and size of nano-gallium hydroxide precursor can be further controlled, and finally the nano-gallium hydroxide precursor with good dispersion and uniform size is obtained, which lays a foundation for subsequent high-temperature nitridation to prepare high-quality nano-gallium nitride.

[0107] In the embodiments of the present application, in view of the problems of traditional high-temperature nitridation method, such as many lattice defects and particle agglomeration caused by gas-solid heterogeneous reaction, a hierarchical multi-stage calcination process of "low-temperature pre-burning + high-temperature nitridation + annealing to eliminate defects" is designed: low-temperature pre-burning can replace the impurity atmosphere in the furnace and form loose gallium nitride powder, which ensures the subsequent penetration of ammonia gas; high-temperature nitridation promotes the ordered growth of gallium nitride grains along the low surface energy crystal surface through precise temperature control and nitrogen source flow, avoiding surface hardening and agglomeration; annealing treatment fills the lattice vacancies by atomic thermal migration and eliminates the surface oxide layer, finally obtaining nano-gallium nitride powder with high crystallinity, low defects and stable morphology, which significantly improves the electrical and optical properties of the product.

[0108] In the embodiments of the present application, the supporting tubular furnace device provides stable support for the preparation process: the tubular furnace body has precise temperature control function, which can meet the temperature requirements of multiple stages; the gas diffusion platform (including multi-tube gas outlet device and uniform gas outlet) ensures the uniform distribution of nitrogen and ammonia, avoiding local reaction unevenness; boron nitride crucible is high-temperature resistant and has strong chemical inertness, which prevents the contamination of the product by the container material; the flange sealing ring ensures the sealing of the internal reaction chamber and maintains a pure atmosphere. The whole device and process are highly compatible, which further ensures the product quality and uniformity, and avoids reaction failure or product defects caused by device problems.

[0109] In the embodiments of the present application, the provided method has the advantages of short process flow, simple operation, uniform morphology, high reaction efficiency, etc., and can inhibit the formation of defects such as particle agglomeration, vacancies and stacking caused by high-temperature solid-phase reaction, thereby improving the crystallinity and quality of the product. It is an ideal method for producing nano-gallium nitride powder.

[0110] The foregoing detailed description of the application has been presented for purposes of illustration and description. Various modifications and changes can be made to these embodiments without departing from the spirit and scope of the application. It is intended that the scope of the application should not be limited by the particular representative embodiments described in this application. The description was only made in order to fully achieve and convey the scope of the application.

Claims

1. A method for preparing nano-gallium nitride powder material, characterized in that, The method comprises: under stirring and heating conditions, subjecting metallic gallium, a surfactant and water to a hydrothermal reaction to obtain a reaction product; subjecting the reaction product to solid-liquid separation to obtain a solid separation product, and drying the solid separation product to obtain a nano-hydroxyl gallium precursor; under a nitrogen atmosphere, heating the nano-hydroxyl gallium precursor to a first set temperature at a first set heating rate, and maintaining the first set temperature for a first set holding time to perform a low-temperature pre-burning treatment to obtain a pre-burning intermediate; switching the nitrogen atmosphere to an ammonia atmosphere, heating the pre-burning intermediate to a second set temperature at a second set heating rate, and maintaining the second set temperature for a second set holding time to perform a high-temperature nitriding treatment to obtain a gallium nitride powder; cooling the gallium nitride powder to a third set temperature, and maintaining the third set temperature for a third set holding time to perform an annealing treatment to remove residual impurities, reduce defect density and improve powder dispersibility; wherein the ammonia flow rate of the ammonia atmosphere is 20 mL / min to 80 mL / min, the second set temperature is 800°C to 1100°C, the second set heating rate is 5°C / min to 20°C / min, and the second set holding time is 2h to 6h.

2. The method of claim 1, wherein, The liquid-solid ratio of the water to the metallic gallium is (10-30):

1.

3. The method of claim 1, wherein, The molar mass of the surfactant is 1% to 10% of the molar mass of the metallic gallium.

4. The method of claim 3, wherein, The surfactant comprises one or more of sodium dodecyl sulfate, cetyltrimethylammonium bromide and polyethylene glycol.

5. The method of claim 1, wherein, The hydrothermal reaction comprises the following parameters: stirring speed of 800 r / min to 1200 r / min, reaction temperature of 160°C to 220°C, and reaction time of 2h to 10h.

6. The method of claim 1, wherein, The nitrogen flow rate of the nitrogen atmosphere is 100 mL / min to 200 mL / min, the first set temperature is 400°C to 600°C, the first set heating rate is 2°C / min to 10°C / min, and the first set holding time is 0.5h to 2h.

7. The method of claim 1, wherein, The third set temperature is 700°C to 800°C, and the third set holding time is 0.5h to 1.5h.

8. The method of claim 1, wherein, The mass purity of the metallic gallium is 6N; The mass purity of the nitrogen and ammonia is 5N; The mass purity of the surfactant is analytical purity.

9. A device for preparing nano-gallium nitride powder material, characterized in that, The device is adapted to the method of any one of claims 1 to 8, and comprises a tube furnace for sequentially performing low-temperature pre-burning treatment, high-temperature nitriding treatment and annealing treatment on the nano-hydroxyl gallium precursor, and the tube furnace comprises: a tube furnace body provided with an internal reaction chamber inside; an air inlet pipeline and an exhaust pipeline, both of which are arranged on the tube furnace body; a gas diffusion platform arranged inside the internal reaction chamber and used for uniformly distributing reaction gas introduced from the air inlet pipeline to a reaction area.

10. The apparatus of claim 9, wherein, The internal reaction chamber is provided with a multi-tube gas outlet device, and the surface is provided with uniformly distributed gas outlets. The upper part of the gas diffusion platform is used for placing a boron nitride crucible for carrying the nano-hydroxyl gallium precursor.

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