Micron-sized gallium oxide powder, and preparation method and application thereof

Abstract

The application discloses micron-sized gallium oxide powder and a preparation method and application thereof, and the preparation method comprises the following steps: mixing gallium salt with water, stirring, and obtaining a gallium ion solution; adjusting the pH value of the solution to be less than or equal to 6 under stirring; performing a hydrothermal reaction to obtain a gallium oxide precursor; and calcining to obtain micron-sized gallium oxide powder. The micron-sized gallium oxide powder prepared by the application has excellent broadband reflection performance and stability, the solar reflectance reaches 93.4%, the average reflectivity in the mid-wave infrared band reaches 68.4%, the outdoor cooling performance can be significantly improved, the ultraviolet rays can be efficiently reflected, the cooling performance is further strengthened, and the micron-sized gallium oxide powder can maintain good physical and chemical properties under harsh environments such as high temperature, ultraviolet rays, acid and alkali, and can be widely used as a filler to prepare various heat insulation coatings, in particular, the micron-sized gallium oxide powder has a long service life in application and has more excellent applicability under harsh weather conditions.

Description

Technical Field

[0001] This invention belongs to the field of high-reflectivity filler preparation technology, and relates to a micron-sized gallium oxide powder, its preparation method and application. Background Technology

[0002] With the increasing global demand for energy conservation, emission reduction, and efficient thermal management technologies, passive daytime radiative cooling technology has attracted widespread attention both domestically and internationally due to its ability to achieve efficient cooling without energy consumption. The cooling performance of passive daytime radiative cooling materials is closely related to their spectral characteristics. The higher the reflectivity of the material in the solar radiation band (0.3-2.5μm) and mid-infrared (2.5-8μm), and the higher the emissivity within the atmospheric transparency window (8-13μm), the more significant the cooling effect, and it can even achieve an absolute cooling effect below the ambient temperature.

[0003] Radiation-cooling coatings based on disordered fillers possess advantages such as tunable spectral performance, low cost, and excellent weather resistance, making them the most promising candidates for large-scale production and application. These materials achieve strong reflection of sunlight through reflective fillers and obtain high emissivity by utilizing the intrinsic absorption of functional groups in the film-forming material at atmospheric windows. Therefore, the reflective filler not only needs a suitable band gap (>4.15 eV) to avoid absorption of sunlight but also requires a high refractive index (n) to increase the mismatch at the interface between the filler and the film-forming material (n~1.5) to improve scattering efficiency.

[0004] Various metal oxide materials, such as titanium dioxide (TiO2), zinc oxide (ZnO), and zirconium dioxide (ZrO2), are widely used as reflective fillers for reflecting sunlight due to their high refractive index. However, these metal oxides have narrow electronic band gaps (<3 eV), easily absorbing ultraviolet energy and limiting the improvement of cooling performance. To address these issues, researchers have proposed using high-bandgap fillers such as calcium carbonate (CaCO3), barium sulfate (BaSO4), alumina (Al2O3), and silicon dioxide (SiO2). However, these fillers have low refractive indices, often requiring high filler quantities to ensure strong solar reflection performance, which undoubtedly weakens the practicality of radiation cooling materials. Furthermore, according to Mie's law of scattering, to achieve high scattering efficiency, both types of fillers are often nanometer-sized, limiting their dominant reflection frequency band to the solar band, making it difficult to achieve efficient reflection in the mid-infrared band. Therefore, developing fillers with both high solar and mid-infrared reflectivity has significant application value.

[0005] Gallium oxide (Ga₂O₃) is a representative of fourth-generation ultra-wide bandgap semiconductors, with a theoretical bandgap of ~4.9 eV and a refractive index of ~1.9. It has wide applications in solar-blind ultraviolet detection, gas sensing, photocatalysis, and electroluminescence. Gallium oxide also possesses advantages such as stable physicochemical properties, safety and non-toxicity, good resin dispersibility, and ease of large-area fabrication. Furthermore, the absorption peak of gallium oxide is located within the atmospheric window, avoiding absorption in the mid-infrared band. Therefore, it holds promise as a broadband reflective filler.

[0006] Literature and patents have reported on the preparation of gallium oxide powder using hydrothermal methods. For example, researchers have proposed a method for preparing gallium hydroxyl oxide and gallium oxide powder using a hydrothermal method. This method uses gallium nitrate hydrate as a raw material, adjusts the pH of the precursor solution to 8 using ammonia water to obtain a hydrothermal reaction precursor, then performs a hydrothermal reaction on the separated precipitate to obtain gallium hydroxyl oxide, and finally anneals the gallium hydroxyl oxide to obtain β-Ga₂O₃ nanoparticles. The gallium oxide obtained by this method is in the form of spherical particles with a size distribution of 300-700 nm. Another example is a method for preparing monodisperse gallium oxide powder. This method uses metallic gallium with a purity of over 99.99% as a raw material, dissolves it in acid, adjusts the pH using sodium hydroxide to obtain a gallium hydroxyl oxide precursor, and finally calcines the precursor to obtain spherical gallium oxide with a D90 of 700-1000 nm. It is evident that the gallium oxide powders prepared by the aforementioned existing methods are all nanoscale in size. Furthermore, according to Kirchhoff's laws, the filler particle size should be comparable to the incident light wavelength to achieve effective reflection. As a result, existing nanoscale gallium oxide powders do not meet the requirements of radiation-cooled coatings for broadband reflective filler particle size. In addition, some researchers have proposed synthesizing micron-sized hollow gallium oxide microspheres using a combination of soft template and hydrothermal methods. These micron-sized hollow gallium oxide microspheres are assembled from gallium oxide nanorods, with a wall thickness of less than 200 nm and a size of less than 5 μm. While the aforementioned existing technologies mention the potential applications of gallium oxide nanoparticle assemblies (micron-sized hollow gallium oxide microspheres) in n-type field-effect transistors, high-temperature stable gas sensors, and solar-blind photodetectors, they do not actually explore the material's functionality, nor do they address the potential applications of micron-sized hollow gallium oxide microspheres in sunlight and infrared reflection, or in thermal insulation. In reality, the surface of micron-sized hollow gallium oxide microspheres is extremely rough. Therefore, using them as fillers in coatings not only fails to improve the coating's reflectivity but may even promote mid-infrared absorption, thus failing to meet the requirements for broadband reflective filler particle size in radiation-cooling coatings. In particular, the hollow structure of these micron-sized hollow gallium oxide microspheres, with its loose and thin shell, results in poor structural stability, making them prone to breakage and collapse in practical applications. This also prevents them from being used as fillers in coating preparation. Furthermore, to date, there are no publicly reported studies on the hydrothermal synthesis technology of micron-sized solid gallium oxide powder and its application in thermal insulation coatings. Therefore, obtaining a micron-sized gallium oxide powder, especially one with strong reflectivity in both the solar and mid-infrared bands, is crucial for developing radiation-cooling coatings with controllable performance, low cost, and excellent weather resistance. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a micron-sized gallium oxide powder with excellent broadband reflection performance and good stability, as well as its preparation method and application.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A method for preparing micron-sized gallium oxide powder includes the following steps:

[0010] S1. Mix gallium salt with water and stir to obtain a gallium ion solution;

[0011] S2. Adjust the pH of the gallium ion solution to ≤6 under stirring conditions to obtain the precursor solution;

[0012] S3. The precursor solution obtained in step S2 is subjected to a hydrothermal reaction to obtain gallium oxide precursor;

[0013] S4. Calcining the gallium oxide precursor obtained in step S3 to obtain micron-sized gallium oxide powder.

[0014] In a further improvement to the above preparation method, in step S2, a pH adjuster is added dropwise to the gallium ion solution obtained in step S1 to adjust the pH value of the gallium ion solution to 1-6; the dropwise addition rate of the pH adjuster is ≤5 mL / min; and the stirring speed is ≥200 rpm.

[0015] In a further improvement to the above preparation method, in step S2, the pH value of the gallium ion solution is adjusted to 2-4.5; the dropping rate of the pH adjuster is 1 mL / min-5 mL / min; and the stirring speed is 200 rpm-400 rpm.

[0016] In a further improvement to the above preparation method, the pH adjuster is one of an aqueous solution of hydrogen chloride, an aqueous solution of sodium hydroxide, or an ammonia solution.

[0017] In a further improvement to the above preparation method, in step S1, the gallium salt is at least one of gallium nitrate, gallium chloride, gallium sulfate, and gallium citrate; and the concentration of the gallium ion solution is 0.1 mol / L to 0.8 mol / L.

[0018] In a further improvement to the above preparation method, in step S1, the concentration of the gallium ion solution is 0.3 mol / L to 0.5 mol / L.

[0019] In a further improvement to the above preparation method, in step S3, the hydrothermal reaction is carried out in a reaction vessel; the temperature of the hydrothermal reaction is 100℃~250℃; and the time of the hydrothermal reaction is 1h~10h.

[0020] In a further improvement to the above preparation method, in step S3, the temperature of the hydrothermal reaction is 160℃~220℃; and the time of the hydrothermal reaction is 6h~8h.

[0021] In a further improvement to the above preparation method, in step S4, the calcination temperature is 500℃~1000℃; and the calcination time is 1h~6h.

[0022] In a further improvement to the above preparation method, in step S4, the calcination temperature is 800℃~950℃; and the calcination time is 1h~3h.

[0023] In a further improvement to the above preparation method, step S3, after the hydrothermal reaction is completed, includes the following treatment: centrifuging the product obtained after the hydrothermal reaction, washing and drying the solid material obtained after centrifugation to obtain gallium oxide precursor.

[0024] As a general technical concept, the present invention also provides a micron-sized gallium oxide powder, which is prepared by the above-described preparation method.

[0025] The above-mentioned micron-sized gallium oxide powder is further improved in that the micron-sized gallium oxide powder is β-Ga2O3; the shape of gallium oxide in the micron-sized gallium oxide powder is a solid rod; and the length of gallium oxide in the micron-sized gallium oxide powder is 1μm to 10μm.

[0026] As a general technical concept, the present invention also provides the application of the above-mentioned micron-sized gallium oxide powder as a filler in the preparation of heat-insulating coatings.

[0027] The present invention discloses a method for preparing micron-sized gallium oxide powder, which mainly involves a chemical reaction process to prepare a broadband reflective filler material with good electromagnetic wave reflection characteristics. The entire process includes raw material preparation, solution conditioning, hydrothermal reaction, and final drying and calcination. The specific working principle is as follows:

[0028] 1. Raw material preparation and solution conditioning

[0029] First, a certain amount of gallium salt is weighed and added to deionized water and stirred to ensure complete dissolution and the formation of a homogeneous gallium ion solution. To ensure that the pH value of the solution meets the requirements of the hydrothermal reaction, a pH adjuster (such as hydrogen chloride, sodium hydroxide solution, or ammonia) is slowly added and the amount is controlled during the pH adjustment process to bring the pH value of the solution to the preset value. At the same time, continuous stirring is used to control the reaction process, which can avoid local pH values ​​being too high or uneven precipitation formation leading to premature crystal nucleation. This provides a stable precursor solution for the subsequent hydrothermal reaction and also lays the foundation for the controllability of precursor formation and morphology.

[0030] 2. The principle of hydrothermal reaction

[0031] Hydrothermal reaction is a method of carrying out a chemical reaction in a solution under high temperature and high pressure. For gallium nitrate, at high temperature, its hydrolysis product—gallium hydroxide—further reacts to yield gallium hydroxyl oxide (GaOOH). When the solution pH is ≤ 6, an appropriate amount of OH... - After being adsorbed by GaOOH, it promotes the preferential growth of GaOOH along the c-axis (001), resulting in a rod-like structure and a large aspect ratio. However, further increasing the pH of the reaction leads to excess OH... - These particles quickly adsorb onto the initial crystal faces of GaOOH primary particles, hindering their growth and resulting in smaller, stacked spindle-shaped particle structures. In summary, the pH-adjusted gallium ion solution, sealed in a hydrothermal reactor and reacted under set temperature and pressure, promotes crystal growth and directional alignment, thus forming a broadband reflective filler with the desired morphology. Specifically, by controlling the reaction pH, time, and temperature under specific conditions, the filler material can achieve microstructures with lengths reaching several micrometers, a wide size distribution, and a higher proportion of large powder particles.

[0032] 3. Separation and washing of products

[0033] After the reaction is complete, the hydrothermal reactor will naturally cool to room temperature, at which point the product is removed. Solid-liquid separation is then performed by centrifugation to obtain the solid product. This step aims to remove liquid byproducts from the reaction through physical separation. After separation, the solid product is washed multiple times with deionized water and ethanol to remove residual impurities and unreacted substances, ensuring the purity of the final material.

[0034] 4. Drying and calcination of precursors

[0035] The washed solid product is dried at a set temperature to further remove moisture, followed by calcination. High-temperature heat treatment can transform the simple orthorhombic GaOOH into hexagonal α-Ga₂O₃. In particular, calcination above 500℃ can further transform α-Ga₂O₃ into monoclinic β-Ga₂O₃. Monoclinic β-Ga₂O₃ exhibits superior broadband reflectivity compared to α-Ga₂O₃. This step aims to effectively improve the optical properties of the broadband reflective filler through calcination at a specific temperature, enhancing its reflectivity in the 0.3-8μm range and strengthening the material's structural stability, ultimately obtaining a filler with broadband reflective characteristics.

[0036] Compared with the prior art, the advantages of the present invention are as follows:

[0037] (1) In view of the shortcomings of existing gallium oxide powder preparation methods, such as the difficulty in controllable synthesis and the difficulty in preparing micron-sized large-scale powders, and the resulting defects such as the inability of gallium oxide powder to have strong reflectivity in both the solar and mid-infrared bands and poor stability, this invention creatively proposes a method for preparing micron-sized gallium oxide powder. Gallium salt is used as raw material to first prepare gallium ion solution, and the pH value of the gallium ion solution is adjusted to ≤6 under stirring conditions to obtain a precursor solution. Then, the precursor solution is subjected to hydrothermal reaction. During the hydrothermal reaction, gallium ions gradually form stable gallium hydroxyl oxide (GaOOH) crystals under the condition of pH ≤6. At the same time, through uniform nucleation and crystal growth process, a micron-sized gallium oxide precursor with good structure is formed. On this basis, the micron-sized gallium oxide precursor is calcined. During the calcination process, the micron-sized gallium hydroxyl oxide (GaOOH) crystal undergoes a phase transition to transform into monoclinic β-Ga2O3, thereby obtaining micron-sized gallium oxide powder with excellent broadband reflectivity, good chemical stability and good thermal stability. Compared with conventional gallium oxide powder, the gallium oxide powder prepared by this invention has a micron-sized structure and the following advantages: (a) It has excellent reflectivity, with a solar reflectance of 93.4% in the 0.3-2.5μm band and an average reflectivity of 68.4% in the 2.5-8μm band, which can significantly improve outdoor cooling performance. It can also efficiently reflect ultraviolet rays, which can enhance cooling performance; (b) It has high chemical and thermal stability, and can maintain good physical and chemical properties in harsh environments such as high temperature, ultraviolet rays, and acids and alkalis, which makes it exhibit a longer service life in applications, especially showing better applicability under harsh climatic conditions.

[0038] (2) In this invention, the pH value of the precursor solution was further optimized to be 1–6, particularly 2–4.5. Under these conditions, the hydrothermal reaction can be carried out to ensure a suitable reaction environment, resulting in gallium oxide with good crystal structure and morphology, ultimately improving the reflectivity of the material. Furthermore, improper pH control can lead to defects such as uneven particle size and unstable material properties. In particular, excessively high pH can inhibit crystal growth along dominant crystal planes, resulting in small powder particle size and difficulty in obtaining micron-sized large particles. In addition, using hydrogen chloride and sodium hydroxide to adjust the solution pH value can avoid side reactions caused by complex acidic and alkaline solutions, thereby ensuring the formation of high-purity gallium oxide.

[0039] (3) In this invention, the concentration of the gallium ion solution was further optimized to be 0.1 mol / L to 0.8 mol / L, and in particular, the concentration of the gallium ion solution was 0.3 mol / L to 0.5 mol / L. Under these conditions, it is possible to ensure that an appropriate crystal nucleation rate and growth rate are obtained, thereby ensuring the morphology and crystal integrity of the gallium oxide precursor material. In particular, when the concentration of the gallium ion solution is too low, the nucleation rate is much lower than the growth rate, and the overall powder particle size is too large. Although it can effectively reflect mid-wave infrared light, it cannot take into account the strong reflection characteristics of the solar light band. On the other hand, when the concentration of the gallium ion solution is too high, the nucleation rate is greater than the growth rate, resulting in a smaller powder particle size. Although it can effectively reflect sunlight, it cannot take into account the strong reflection characteristics of the mid-wave infrared band. It can be seen that both excessively high and excessively low concentrations of gallium salts will affect the formation of the gallium oxide precursor, thereby affecting the powder morphology and crystal structure, and ultimately making it difficult to obtain micron-sized gallium oxide powder.

[0040] (4) In this invention, the hydrothermal reaction temperature was further optimized to 100℃~250℃ and the time to 1h~10h. In particular, the hydrothermal reaction temperature was optimized to 180℃~220℃ and the time to 6h~8h. Under these conditions, the precursor powder prepared has ideal particle size and morphology, laying a good foundation for the broadband reflectance performance of the subsequent calcined product. Specifically, if the hydrothermal reaction temperature is too low or the time is too short, the product particles will be too small. If the hydrothermal reaction temperature is too high or the time is too long, the cost will increase, and it may even lead to the nucleation rate being greater than the growth rate, ultimately resulting in particles that are too small. It can be seen that the temperature and time of the hydrothermal reaction are one of the key factors affecting the final performance of the material.

[0041] (5) In this invention, the calcination temperature is further optimized to 500℃~1000℃ and the time to 1h~6h, particularly to 800℃~900℃ and 1h~3h. Under these conditions, calcination ensures phase transformation to obtain a specific crystal form (β-Ga2O3) and maintains the integrity of the gallium oxide crystal phase, preventing particle agglomeration. This results in the calcined product exhibiting excellent broadband reflectivity and thermal stability. Specifically, excessively low calcination temperatures can lead to incomplete crystallization or the formation of an undesirable crystal form, while excessively high temperatures can cause particle agglomeration. Therefore, calcination temperature and time are key factors affecting the crystal phase structure and properties of the material.

[0042] (6) This invention also provides an application of micron-sized gallium oxide powder as a filler in the preparation of heat-insulating coatings. Micron-sized gallium oxide powder has excellent broadband reflectivity and can efficiently reflect solar radiation heat across the entire wavelength range and most of the mid-wave infrared heat radiated from the environment. Its working wavelength is wider than that of reflective fillers added to traditional heat-insulating coatings. Therefore, it can be used alone as a filler or in combination with traditional reflective fillers to effectively block heat from entering the coating and significantly improve the cooling performance of the heat-insulating coating. It is particularly noteworthy that the micron-sized gallium oxide powder of this invention has a very high reflectivity to ultraviolet light, while traditional reflective fillers, such as titanium dioxide, all have ultraviolet absorption. Therefore, replacing traditional fillers with micron-sized gallium oxide powder can effectively improve the ultraviolet aging life of the coating. The above advantages make the heat-insulating coating prepared with micron-sized gallium oxide powder as a filler suitable for multiple fields such as construction, industrial equipment, automobiles, and ships. Attached Figure Description

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0044] Figure 1 This is a flowchart illustrating the preparation process of micron-sized gallium oxide powder in Example 1 of the present invention.

[0045] Figure 2 The image shows the XRD pattern of the micron-sized gallium oxide powder obtained in Example 1 of this invention.

[0046] Figure 3 This is a SEM image of the micron-sized gallium oxide powder obtained in Example 1 of the present invention.

[0047] Figure 4 This is a particle size distribution diagram of the micron-sized gallium oxide powder obtained in Example 1 of the present invention.

[0048] Figure 5 The image shows the reflectance spectrum of the micron-sized gallium oxide powder prepared in Example 1 of this invention in the solar radiation band.

[0049] Figure 6 The image shows the infrared reflectance spectrum of the micron-sized gallium oxide powder prepared in Example 1 of this invention.

[0050] Figure 7 This is a SEM image of the micron-sized gallium oxide powder obtained in Example 2 of the present invention.

[0051] Figure 8 This is a SEM image of the micron-sized gallium oxide powder obtained in Example 3 of the present invention.

[0052] Figure 9This is a SEM image of the nanoscale gallium oxide powder prepared in Comparative Example 1.

[0053] Figure 10 This is a SEM image of the submicron-sized gallium oxide powder prepared in Comparative Example 2. Detailed Implementation

[0054] To address the shortcomings of existing hydrothermal methods in preparing gallium oxide powder, which cannot meet the particle size requirements of radiation-cooled coatings for broadband reflective fillers, this invention provides a method for preparing micron-sized gallium oxide powder with strong reflectivity in both the solar and mid-infrared bands, comprising the following steps:

[0055] S1. Mix gallium salt with water and stir to obtain a gallium ion solution.

[0056] S2. Adjust the pH of the gallium ion solution to ≤6 under stirring conditions to obtain the precursor solution.

[0057] S3. The precursor solution obtained in step S2 is subjected to a hydrothermal reaction to obtain gallium oxide precursor.

[0058] S4. Calcining the gallium oxide precursor obtained in step S3 to obtain micron-sized gallium oxide powder.

[0059] In the preparation method of the present invention, in step S2, a pH adjuster is added dropwise to the gallium ion solution obtained in step S1 to adjust the pH value of the gallium ion solution to 1 to 6, for example, pH values ​​of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, and more preferably, the pH value of the gallium ion solution is adjusted to 2 to 4.5.

[0060] In the preparation method of the present invention, in step S2, the dropping rate of the pH adjuster is ≤5 mL / min, for example, the dropping rate is 0.5 mL / min, 1 mL / min, 1.5 mL / min, 2 mL / min, 2.5 mL / min, 3 mL / min, 3.5 mL / min, 4 mL / min, 4.5 mL / min, or 5 mL / min. More preferably, the dropping rate of the pH adjuster is 1 mL / min to 5 mL / min.

[0061] In the preparation method of the present invention, in step S2, the stirring speed is ≥200 rpm, for example, the stirring speed is 200 rpm, 220 rpm, 240 rpm, 260 rpm, 300 rpm, 330 rpm, 360 rpm, 400 rpm, or 500 rpm, and more preferably, the stirring speed is 200 rpm to 400 rpm.

[0062] In the preparation method of the present invention, the pH adjuster is one of hydrogen chloride aqueous solution, sodium hydroxide aqueous solution, or ammonia solution.

[0063] In the preparation method of the present invention, in step S1, the gallium salt is at least one of gallium nitrate, gallium chloride, gallium sulfate, and gallium citrate.

[0064] In the preparation method of the present invention, in step S1, the concentration of the gallium ion solution is 0.1 mol / L to 0.8 mol / L, for example, the concentration of the gallium ion solution is 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, or 0.8 mol / L. More preferably, the concentration of the gallium ion solution is 0.3 mol / L to 0.5 mol / L.

[0065] In the preparation method of the present invention, in step S3, the hydrothermal reaction is carried out in a reaction vessel.

[0066] In the preparation method of the present invention, in step S3, the temperature of the hydrothermal reaction is 100℃~250℃, for example, the temperature of the hydrothermal reaction is 100℃, 120℃, 140℃, 150℃, 160℃, 180℃, 190℃, 200℃, 220℃, 230℃, or 250℃, and more preferably, the temperature of the hydrothermal reaction is 160℃~220℃.

[0067] In the preparation method of the present invention, in step S3, the hydrothermal reaction time is 1h to 10h, for example, the hydrothermal reaction time is 1h, 2h, 3h, 4h, 5h, 6h, 6.5h, 7h, 7.3h, 7.8h, 8h, 8.5h, 8.6h, 8.8h, 9h, 9.5h, or 10h, and more preferably, the hydrothermal reaction time is 6h to 8h.

[0068] In the preparation method of the present invention, in step S4, the calcination temperature is 500℃~1000℃, for example, the calcination temperature is 500℃, 600℃, 700℃, 750℃, 800℃, 850℃, 880℃, 900℃, 920℃, 950℃, 980℃, or 1000℃, and more preferably, the calcination temperature is 800℃~950℃.

[0069] In the preparation method of the present invention, in step S4, the calcination time is 1h to 6h, for example, the calcination time is 1h, 1.5h, 2h, 2.6h, 2.8h, 3h, 3.5h, 4h, 5h, 6h, and more preferably, the calcination time is 1h to 3h.

[0070] In the preparation method of the present invention, step S3, after the hydrothermal reaction is completed, further includes the following treatment: centrifuging the product obtained after the hydrothermal reaction, washing and drying the solid material obtained after centrifugation to obtain gallium oxide precursor.

[0071] As another objective of this invention, this invention also provides a micron-sized gallium oxide powder, which is prepared by the above-described preparation method.

[0072] In this invention, the micron-sized gallium oxide powder is β-Ga2O3.

[0073] In this invention, the potassium oxide in the micron-sized gallium oxide powder is in the shape of a solid rod.

[0074] In this invention, the length (particle size) of gallium oxide in the micron-sized gallium oxide powder is 1 μm to 10 μm.

[0075] As a third objective of the present invention, the present invention also provides the application of the above-mentioned micron-sized gallium oxide powder as a filler in the preparation of heat-insulating coatings.

[0076] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0077] In the following embodiments of the present invention, unless otherwise specified, the materials and instruments used are commercially available, the equipment used is conventional equipment, and the data obtained are the average values ​​of more than three repeated experiments.

[0078] Example 1

[0079] A method for preparing micron-sized gallium oxide powder, the process flow diagram of which is shown below. Figure 1 As shown, it includes the following steps:

[0080] S1. Mix gallium salt with water and stir to obtain a gallium ion solution, specifically:

[0081] Weigh a certain amount of gallium nitrate, add it to 50 mL of deionized water, and stir until completely dissolved to obtain a gallium ion solution with a concentration of 0.3 mol / L (0.16 g / mL).

[0082] S2. Adjust the pH of the gallium ion solution to ≤6 under stirring conditions to obtain the precursor solution, specifically as follows:

[0083] Under stirring conditions, a 1 mol / L hydrogen chloride solution was slowly added dropwise to the gallium ion solution described above, while stirring and monitoring the pH value of the solution until the pH value reached 2.5, thus obtaining the precursor solution. In this step, the hydrogen chloride solution was added at a rate of 3 mL / min, and the stirring speed was 300 rpm.

[0084] S3. The precursor solution obtained in step S2 is subjected to a hydrothermal reaction to obtain the gallium oxide precursor, specifically as follows:

[0085] The pH-adjusted precursor solution was transferred to a 100 mL hydrothermal reactor, sealed, and placed at 190 °C for hydrothermal reaction for 6 hours. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The product was then removed, and the solid was separated by centrifugation. The obtained solid was washed three times each with deionized water and ethanol, and then dried in an 80 °C drying oven for 12 hours to obtain the gallium oxide precursor.

[0086] S4. The gallium oxide precursor obtained in step S3 is calcined to obtain micron-sized gallium oxide powder, specifically:

[0087] The dried gallium oxide precursor was placed in a muffle furnace and heated to 800°C at a heating rate of 2°C / min. The temperature was maintained for 2 hours and then naturally cooled to room temperature to obtain micron-sized gallium oxide powder.

[0088] The morphology, structure and phase composition of the product were analyzed using SEM, XRD and other characterization methods. The reflectance of the product in the 0.3-2.5μm and 2.5-8μm bands was measured by UV-Vis-NIR diffuse reflectance spectrometry and Fourier transform infrared spectrometry with integrating sphere.

[0089] The gallium oxide prepared by this invention has excellent broadband reflectivity, reflecting 93.4% of solar irradiance and 68.4% of mid-wave infrared energy. It can be used in heat insulation and cooling coatings to improve cooling performance and meet the cooling needs of buildings, industrial equipment, automobiles and ships.

[0090] Figure 2 This is the XRD pattern of the micron-sized gallium oxide powder obtained in Example 1 of this invention. Figure 2 It can be seen that the characteristic diffraction peaks of the micron-sized gallium oxide powder correspond to the standard card (JCPDS No. 431012) of β-Ga2O3, and the diffraction peaks are sharp, indicating that the micron-sized gallium oxide powder prepared in Example 1 is β-Ga2O3 with complete crystal structure and high crystallinity.

[0091] Figure 3 This is a SEM image of the micron-sized gallium oxide powder obtained in Example 1 of the present invention.

[0092] Figure 4 This is a particle size distribution diagram of the micron-sized gallium oxide powder obtained in Example 1 of the present invention.

[0093] Depend on Figure 3 and Figure 4 It is known that the gallium oxide powder obtained by the present invention has a size in the micrometer range and the shape of gallium oxide is a solid rod. The particle size (length) of the rod-shaped gallium oxide is distributed in the range of 1 to 10 μm, and the average length reaches ~5 μm. The size is significantly larger than that of gallium oxide obtained by the existing hydrothermal method.

[0094] Figure 5The image shows the reflectance spectrum of the micron-sized gallium oxide powder prepared in Example 1 of this invention in the solar radiation band.

[0095] Figure 6 The image shows the infrared reflectance spectrum of the micron-sized gallium oxide powder prepared in Example 1 of this invention.

[0096] Depend on Figure 5 and Figure 6 It can be seen that the micron-sized rod-shaped gallium oxide prepared by this invention exhibits excellent broadband reflectivity, with a solar reflectance R... 0.3-2.5μm The average reflectance R in the mid-infrared band reached 93.4%. 2.5-8μm The purity reached 68.4%, which is superior to commercially available titanium dioxide and hollow glass microspheres. Therefore, the micron-sized gallium oxide powder of this invention can be used in thermal insulation and cooling coatings to improve cooling performance and meet the cooling needs of buildings, industrial equipment, automobiles, and ships.

[0097] The results above show that the micron-sized gallium oxide powder prepared by this invention is a micron-sized product with a complete crystal structure and R 0.3-2.5μm =93.4%, R 2.5-8μm =68.4%, exhibiting excellent broadband reflectivity. Simultaneously, the micron-sized gallium oxide powder prepared by this invention also possesses high chemical and thermal stability, maintaining good physical and chemical properties under harsh environments such as high temperature, ultraviolet radiation, and acid / alkali conditions, resulting in a long service life in applications.

[0098] Example 2

[0099] A method for preparing micron-sized gallium oxide powder includes the following steps:

[0100] S1. Mix gallium salt with water and stir to obtain a gallium ion solution, specifically:

[0101] Weigh a certain amount of gallium nitrate, add it to 100 mL of deionized water, and stir until completely dissolved to obtain a gallium ion solution with a concentration of 0.4 mol / L.

[0102] S2. Adjust the pH of the gallium ion solution to ≤6 under stirring conditions to obtain the precursor solution, specifically as follows:

[0103] Under stirring conditions, a 1.5 mol / L sodium hydroxide solution was slowly added dropwise to the gallium ion solution described above, while stirring and monitoring the pH value of the solution until the pH value of the solution reached 5, thus obtaining the precursor solution. In this step, the sodium hydroxide solution was added at a rate of 2 mL / min, and the stirring speed was 400 rpm.

[0104] S3. The precursor solution obtained in step S2 is subjected to a hydrothermal reaction to obtain the gallium oxide precursor, specifically as follows:

[0105] The pH-adjusted precursor solution was transferred to a 150 mL hydrothermal reactor, sealed, and placed at 150 °C for hydrothermal reaction for 6 hours. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The product was then removed, and the solid was separated by centrifugation. The obtained solid was washed three times each with deionized water and ethanol, and then dried in a 70 °C drying oven for 10 hours to obtain the gallium oxide precursor.

[0106] S4. The gallium oxide precursor obtained in step S3 is calcined to obtain micron-sized gallium oxide powder, specifically:

[0107] The dried gallium oxide precursor was placed in a muffle furnace and heated to 700°C at a heating rate of 2°C / min. The temperature was maintained for 3 hours and then naturally cooled to room temperature to obtain micron-sized gallium oxide powder.

[0108] Figure 7 This is a SEM image of the micron-sized gallium oxide powder obtained in Example 2 of the present invention. Figure 7 It can be seen that the micron-sized gallium oxide powder prepared in Example 2 of the present invention is a micron-sized product, and the shape of gallium oxide is a solid rod, but its average length is smaller than that of the micron-sized gallium oxide powder prepared in Example 1.

[0109] In addition, tests showed that the gallium oxide micron powder had a uniform particle size distribution and R... 0.3-2.5μm =90.1%, R 2.5-8μm =57.3%, and the reflection performance is stable over a wide frequency range.

[0110] Example 3

[0111] A method for preparing micron-sized gallium oxide powder includes the following steps:

[0112] S1. Mix gallium salt with water and stir to obtain a gallium ion solution, specifically:

[0113] Weigh a certain amount of gallium nitrate, add it to 80 mL of deionized water, and stir until completely dissolved to obtain a gallium ion solution with a concentration of 0.5 mol / L.

[0114] S2. Adjust the pH of the gallium ion solution to ≤6 under stirring conditions to obtain the precursor solution, specifically as follows:

[0115] Under stirring conditions, a 1 mol / L sodium hydroxide solution was slowly added dropwise to the gallium ion solution described above, while stirring and monitoring the pH value of the solution until the pH value reached 3.5, thus obtaining the precursor solution. In this step, the sodium hydroxide solution was added at a rate of 5 mL / min, and the stirring speed was 200 rpm.

[0116] S3. The precursor solution obtained in step S2 is subjected to a hydrothermal reaction to obtain the gallium oxide precursor, specifically as follows:

[0117] The pH-adjusted precursor solution was transferred to a 200 mL hydrothermal reactor, sealed, and placed at 180 °C for hydrothermal reaction for 7 hours. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The product was then removed, and the solid was separated by centrifugation. The obtained solid was washed three times each with deionized water and ethanol, and then dried in a 50 °C drying oven for 6 hours to obtain the gallium oxide precursor.

[0118] S4. The gallium oxide precursor obtained in step S3 is calcined to obtain micron-sized gallium oxide powder, specifically:

[0119] The dried gallium oxide precursor was placed in a muffle furnace and heated to 900°C at a heating rate of 3°C / min. The temperature was maintained for 1 hour and then naturally cooled to room temperature to obtain micron-sized gallium oxide powder.

[0120] Figure 8 This is a SEM image of the micron-sized gallium oxide powder obtained in Example 3 of the present invention. Figure 8 It can be seen that the micron-sized gallium oxide powder prepared in Example 2 of the present invention is a micron-sized product, and the gallium oxide is in the shape of a solid rod.

[0121] Testing revealed that the product exhibits high crystallinity, significantly enhanced broadband reflectivity, and R... 0.3-2.5μm =92.6%, R 2.5-8μm =67.0%, suitable for heat insulation and reflective materials.

[0122] Example 4

[0123] A method for preparing micron-sized gallium oxide powder includes the following steps:

[0124] S1. Mix gallium salt with water and stir to obtain a gallium ion solution, specifically:

[0125] Weigh out a certain amount of gallium nitrate, add it to 120 mL of deionized water, and stir until completely dissolved to obtain a gallium ion solution with a concentration of 0.3 mol / L.

[0126] S2. Adjust the pH of the gallium ion solution to ≤6 under stirring conditions to obtain the precursor solution, specifically as follows:

[0127] Under stirring conditions, a 1 mol / L hydrogen chloride solution was slowly added dropwise to the gallium ion solution described above, while simultaneously monitoring the pH value of the solution until the pH value reached 3, thus obtaining the precursor solution. In this step, the hydrogen chloride solution was added at a rate of 1 mL / min, and the stirring speed was 300 rpm.

[0128] S3. The precursor solution obtained in step S2 is subjected to a hydrothermal reaction to obtain the gallium oxide precursor, specifically as follows:

[0129] The pH-adjusted precursor solution was transferred to a 250 mL hydrothermal reactor, sealed, and placed at 200 °C for hydrothermal reaction for 8 hours. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The product was then removed, and the solid was separated by centrifugation. The obtained solid was washed four times each with deionized water and ethanol, and then dried in a 70 °C drying oven for 8 hours to obtain the gallium oxide precursor.

[0130] S4. The gallium oxide precursor obtained in step S3 is calcined to obtain micron-sized gallium oxide powder, specifically:

[0131] The dried gallium oxide precursor was placed in a muffle furnace and heated to 700°C at a heating rate of 3°C / min. The temperature was maintained for 1.5 hours and then naturally cooled to room temperature to obtain micron-sized gallium oxide powder.

[0132] Testing revealed that the product is micron-sized with uniform particle size, and the gallium oxide is in a solid rod shape. It also exhibits excellent reflectivity within the 0.3–8 μm range. Specifically, R… 0.3-2.5μm =91.5%, R 2.5-8μm =66.8%, suitable for heat insulation and reflective materials.

[0133] Comparative Example 1

[0134] A method for preparing gallium oxide powder includes the following steps:

[0135] S1. Weigh a certain mass of gallium nitrate, add it to 50 mL of deionized water, and stir until completely dissolved to obtain a gallium ion solution with a concentration of 0.3 mol / L.

[0136] S2. Under stirring conditions, a 1.5 mol / L sodium hydroxide solution is slowly added dropwise to the gallium ion solution above, while stirring and monitoring the pH value of the solution until the pH value of the solution is 10, thus obtaining the precursor solution. In this step, the sodium hydroxide solution is added at a rate of 1 mL / min, and the stirring speed is 300 rpm.

[0137] S3. The pH-adjusted precursor solution was transferred to a 100 mL hydrothermal reactor, sealed, and placed at 220 °C for hydrothermal reaction for 3 hours. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The product was then removed, and the solid was separated by centrifugation. The obtained solid was washed three times each with deionized water and ethanol, and then dried in a 90 °C drying oven for 6 hours to obtain the gallium oxide precursor.

[0138] S4. Place the dried gallium oxide precursor in a muffle furnace and heat it to 900°C at a heating rate of 5°C / min. Hold the temperature for 5 hours and allow it to cool naturally to room temperature to obtain gallium oxide powder.

[0139] Figure 9 This is a SEM image of the nanoscale gallium oxide powder prepared in Comparative Example 1. Figure 9 It can be seen that the gallium oxide powder prepared in Comparative Example 1 is nanoscale.

[0140] Tests showed that the gallium oxide powder prepared in Comparative Example 1 had a significantly reduced particle size, and the R of this product was... 0.3-2.5μm =78.0%, R 2.5-8μm =30.2%, the reflection advantage of broadband, especially mid-wave infrared band, has disappeared.

[0141] Comparative Example 2

[0142] A method for preparing gallium oxide powder includes the following steps:

[0143] S1. Weigh a certain mass of gallium nitrate, add it to 80 mL of deionized water, and stir until completely dissolved to obtain a gallium ion solution with a concentration of 1.0 mol / L.

[0144] S2. Under stirring conditions, a 1.0 mol / L sodium hydroxide solution is slowly added dropwise to the gallium ion solution above, while stirring and monitoring the pH value of the solution until the pH value of the solution is 7, thus obtaining the precursor solution. In this step, the sodium hydroxide solution is added at a rate of 1 mL / min, and the stirring speed is 300 rpm.

[0145] S3. The pH-adjusted precursor solution was transferred to a 150 mL hydrothermal reactor, sealed, and placed at 90 °C for hydrothermal reaction for 1 hour. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The product was then removed, and the solid was separated by centrifugation. The obtained solid was washed once with deionized water and once with ethanol, and then dried in a 60 °C drying oven for 6 hours to obtain the gallium oxide precursor.

[0146] S4. Place the dried gallium oxide precursor in a muffle furnace and heat it to 900°C at a heating rate of 2°C / min. Hold the temperature for 2 hours and allow it to cool naturally to room temperature to obtain gallium oxide powder.

[0147] Figure 10 This is a SEM image of the submicron-sized gallium oxide powder prepared in Comparative Example 2. Figure 10 It can be seen that the gallium oxide powder prepared in Comparative Example 2 is submicron in size (approximately several hundred nanometers, less than 1 micrometer), and its length is significantly smaller than that of the micron-sized gallium oxide powder prepared in Example 1. Furthermore, testing showed that the powder particle size of the product was reduced, indicating it was not a micron-sized product. Therefore, the R0 of this product was... 0.3-2.5μm =82.0%, R2.5-8μm =39.3%, the reflectivity advantage in both the solar band and the mid-infrared band has disappeared.

[0148] Comparative Example 3

[0149] A method for preparing a gallium oxide precursor includes the following steps:

[0150] S1. Weigh a certain mass of gallium nitrate, add it to 50 mL of deionized water, and stir until completely dissolved to obtain a gallium ion solution with a concentration of 0.3 mol / L.

[0151] S2. Under stirring conditions, a 1.0 mol / L hydrogen chloride solution is slowly added dropwise to the gallium ion solution above, while stirring and monitoring the pH value of the solution until the pH value of the solution is 3, thus obtaining the precursor solution. In this step, the hydrogen chloride solution is added at a rate of 1 mL / min, and the stirring speed is 300 rpm.

[0152] S3. The precursor solution obtained in step S2 is subjected to a hydrothermal reaction to obtain the gallium oxide precursor, specifically as follows:

[0153] The pH-adjusted precursor solution was transferred to a 100 mL hydrothermal reactor, sealed, and placed at 200 °C for hydrothermal reaction for 3 hours. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The product was then removed, and the solid was separated by centrifugation. The obtained solid was washed three times each with deionized water and ethanol, and then dried in an 80 °C drying oven for 12 hours to obtain the gallium oxide precursor.

[0154] Testing revealed that the product's crystal structure is GaOOH with a simple orthorhombic crystal system. 0.3-2.5μm =80.0%, R 2.5-8μm =20.7%, indicating poor reflectivity.

[0155] Compared with conventional gallium oxide powder, the gallium oxide powder prepared by this invention has a micron-sized particle size and a solid rod shape, which has the following advantages: (a) It has excellent reflectivity, with a solar reflectance of 93.4% in the 0.3-2.5μm band and an average reflectivity of 68.4% in the 2.5-8μm band, which can significantly improve outdoor cooling performance. It can also efficiently reflect ultraviolet rays, which can also enhance cooling performance; (b) It has high chemical and thermal stability, and can maintain good physical and chemical properties in harsh environments such as high temperature, ultraviolet rays, and acids and alkalis, which makes it exhibit a longer service life in applications. In particular, it shows better applicability under harsh climatic conditions, which is a significant technological advancement.

[0156] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing micron-sized gallium oxide powder, characterized in that, Includes the following steps: S1. Mix gallium salt with water and stir to obtain a gallium ion solution; S2. Adjust the pH of the gallium ion solution to ≤6 under stirring conditions to obtain the precursor solution; S3. The precursor solution obtained in step S2 is subjected to a hydrothermal reaction to obtain gallium oxide precursor; S4. Calcining the gallium oxide precursor obtained in step S3 to obtain micron-sized gallium oxide powder.

2. The preparation method according to claim 1, characterized in that, In step S2, a pH adjuster is added dropwise to the gallium ion solution obtained in step S1 to adjust the pH value of the gallium ion solution to 1-6; the dropwise addition rate of the pH adjuster is ≤5 mL / min; and the stirring speed is ≥200 rpm.

3. The preparation method according to claim 2, characterized in that, In step S2, the pH value of the gallium ion solution is adjusted to 2-4.5; the dropping rate of the pH adjuster is 1 mL / min-5 mL / min; and the stirring speed is 200 rpm-400 rpm.

4. The preparation method according to claim 2, characterized in that, The pH adjuster is one of the following: aqueous solution of hydrogen chloride, aqueous solution of sodium hydroxide, or ammonia.

5. The preparation method according to any one of claims 1 to 4, characterized in that, In step S1, the gallium salt is at least one selected from gallium nitrate, gallium chloride, gallium sulfate, and gallium citrate; the concentration of the gallium ion solution is 0.1 mol / L to 0.8 mol / L. In step S3, the hydrothermal reaction is carried out in a reactor; the temperature of the hydrothermal reaction is 100℃~250℃; and the time of the hydrothermal reaction is 1h~10h. In step S4, the calcination temperature is 500℃~1000℃; the calcination time is 1h~6h.

6. The preparation method according to claim 5, characterized in that, In step S1, the concentration of the gallium ion solution is 0.3 mol / L to 0.5 mol / L; In step S3, the temperature of the hydrothermal reaction is 160℃~220℃; the time of the hydrothermal reaction is 6h~8h. In step S4, the calcination temperature is 800℃~950℃; the calcination time is 1h~3h.

7. The preparation method according to claim 6, characterized in that, In step S3, after the hydrothermal reaction is completed, the following treatment is also included: centrifuging the product obtained after the hydrothermal reaction, washing and drying the solid material obtained after centrifugation to obtain gallium oxide precursor.

8. A micron-sized gallium oxide powder, characterized in that, The micron-sized gallium oxide powder is prepared by the preparation method according to any one of claims 1 to 7.

9. The micron-sized gallium oxide powder according to claim 8, characterized in that, The micron-sized gallium oxide powder is β-Ga2O3; the gallium oxide in the micron-sized gallium oxide powder is in the shape of a solid rod; the length of the gallium oxide in the micron-sized gallium oxide powder is 1μm to 10μm.

10. The application of the micron-sized gallium oxide powder as described in claim 8 or 9 as a filler in the preparation of thermal insulation coatings.

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