Hydro-thermal synthesis method of gallium oxide and application of gallium oxide in preparation of high-purity gallium oxide

Abstract

The invention discloses a hydrothermal synthesis method of gallium oxide and application in preparation of high-purity gallium oxide.According to the hydrothermal synthesis method, by introducing an oxidizing agent and an external electric field, the rate in the hydrothermal reaction process is increased, the hydrothermal reaction time can be greatly shortened under the mild condition, and the conversion rate of metal gallium is increased; and the reaction process is green and pollution-free, and can be used as an ideal choice for industrial production of high-purity gallium oxide.

Description

Technical Field

[0001] The invention relates to the technical field of high-purity metal oxide material synthesis, in particular to a hydrothermal synthesis method of gallium oxide and an application thereof in preparing high-purity gallium oxide. Background Art

[0002] Gallium oxide (Ga2O3) is a transparent ultra-wide bandgap oxide semiconductor material with a bandgap of about 4.8eV. It is the latest fourth-generation semiconductor material. Its breakdown electric field strength is as high as 8MV / cm, which is much higher than semiconductor materials such as silicon (1.1eV, 0.3MV / cm), gallium arsenide (1.4eV, 0.4MV / cm), silicon carbide (3.3eV, 2.5MV / cm), and gallium nitride (3.4eV, 3.3MV / cm). It also has unique ultraviolet transmittance characteristics (ultraviolet transmittance can reach more than 80%), as well as low energy loss, high thermal stability and chemical stability. It is the preferred semiconductor material for manufacturing high-temperature, high-frequency, high-power microelectronic devices, solar-blind ultraviolet photodetectors, and ultraviolet transparent conductive electrodes; at the same time, it can also be used as a substrate material for semiconductors such as GaN and ZnO.

[0003] There are many methods for preparing high-purity gallium oxide, but they all have certain disadvantages. For example:

[0004] 1. Chemical precipitation method: Use gallium metal as raw material, react with nitric acid, and use ammonia water as a precipitant to obtain a precursor, which is then washed, filtered, dried and calcined to obtain gallium oxide powder. This process has a long gallium dissolution cycle, reduced product uniformity, easy to introduce impurities, and produces nitrogen dioxide gas, causing environmental pollution.

[0005] 2. Electrolysis: The crude gallium is pretreated with acid washing for 2-3 times, and then washed with deionized water for 3-5 times, and then replaced with 6N high-purity gallium by electrolysis to obtain a purified solution containing gallium, which is then precipitated with ammonia water, and the precipitate is dried and roasted to obtain high-purity gallium oxide. The entire process is cumbersome and complicated, with a long cycle and high water consumption. A large amount of wastewater is discharged during the water washing process.

[0006] 3. Gallium ammonium sulfate method: 4N metal gallium is used as raw material, reacted with sulfuric acid to generate gallium sulfate solution, then gallium sulfate and ammonium sulfate are mixed in aqueous solution, cooled and crystallized at -10°C for 12-48h, and ammonium gallium sulfate double salt is precipitated by polymerization and crystallization. After the ammonium gallium sulfate is heated and dissolved in water, it is cooled and crystallized again for 2-6 times, and finally dried and roasted to obtain high-purity β-gallium oxide. This process does not require high purity of raw materials, but the whole process requires multiple crystallizations, and each crystallization cycle is too long, and the production efficiency is not high.

[0007] 4. Alkyl alcohol salt method: 4N metal gallium is used as raw material, reacted with alkyl alcohol for 0.5-24h, and then the alkyl alcohol gallium salt is obtained by vacuum distillation after the reaction is completed; the obtained alkyl alcohol gallium salt is then hydrolyzed in an aqueous solution containing alkyl alcohol under the catalysis of acetic acid or oxalic acid to obtain hydrated gallium oxide, and finally aged, filtered, dried and roasted to obtain high-purity gallium oxide. The entire process is green and environmentally friendly, but the process is complicated and cumbersome.

[0008] Therefore, it is necessary to design a hydrothermal synthesis method for gallium oxide. Summary of the invention

[0009] The present invention aims to provide a hydrothermal synthesis method of gallium oxide, which is used to solve the defects of low efficiency and strong pollution of gallium oxide synthesis in the prior art and promote the process of industrial preparation of high-purity gallium oxide.

[0010] In view of this, the scheme of the present invention is:

[0011] The hydrothermal synthesis method of gallium oxide comprises the following steps:

[0012] Mixing metal gallium and water, adding an oxidant under stirring at 100-240° C. and 0.5-22 MPa to carry out a hydrothermal synthesis reaction; the mass ratio of metal gallium to water is 1:(3-30);

[0013] After the reaction is completed, the solid-liquid mixture is filtered and washed to obtain a precipitate;

[0014] The precipitate is dried and cracked to obtain gallium oxide powder.

[0015] Furthermore, an electric field with an intensity of 5-20 kV / cm is added during the hydrothermal synthesis reaction process.

[0016] Preferably, under the condition of adding an electric field, the hydrothermal synthesis reaction temperature is 100-180° C. and the time is 1-2 h.

[0017] Preferably, the oxidant is oxygen or hydrogen peroxide; and / or, the molar ratio of the oxidant to metal gallium is (0.05-0.2):1.

[0018] Furthermore, during the hydrothermal synthesis process, the escaped gas is condensed, and the obtained condensed water is added to the hydrothermal synthesis process.

[0019] Furthermore, the cracking temperature is 600-800°C, and the cracking time is 2-6h.

[0020] Furthermore, the cracking process is carried out in an inert gas or a non-reducing gas.

[0021] Furthermore, deionized water is used in the washing process, and the washing liquid is recycled into the hydrothermal synthesis reaction for reuse.

[0022] Another object of the present invention is to propose the application of the hydrothermal synthesis method in the preparation of high-purity gallium oxide, wherein the purity of the metal gallium is above 5N. The high-purity gallium oxide refers to gallium oxide with a purity higher than 99.9995%.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The hydrothermal synthesis method of gallium oxide of the present invention promotes the rate of the hydrothermal reaction process by introducing an oxidant and an external electric field, and can significantly shorten the hydrothermal reaction time under relatively mild conditions and improve the conversion rate of metallic gallium; and the reaction process is green and pollution-free, and can be used as an ideal choice for industrial production of gallium oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the XRD diagram of gallium oxide powder obtained by the hydrothermal synthesis method of the present invention.

[0026] Figure 2 This is a SEM image of gallium oxide powder obtained by the hydrothermal synthesis method of the present invention.

[0027] Figure 3 Schematic diagram of the device used in the hydrothermal reaction stage of the hydrothermal synthesis method of the present invention.

[0028] Figure 3 In the figure: 1 is a reaction kettle; 2 is a stirrer; 3 is a thermocouple; 4 is an air duct; 5 is a water return pipe; 11 is a positive electrode plate, 12 is a negative electrode plate; 41 is a cooling ice water jacket; 42 is a condensing coil. DETAILED DESCRIPTION

[0029] The technical solution of the present invention will be clearly and completely described and verified in conjunction with the preferred embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] If the manufacturer of reagents or instruments is not specified in the examples, conventional products can be purchased from the market. If specific conditions are not specified, conventional conditions or conditions recommended by the manufacturer can be used.

[0031] In one embodiment, a method for hydrothermal synthesis of gallium oxide is provided, comprising the steps of:

[0032] 1) Mixing metal gallium and water, adding an oxidant under stirring at 100-240° C. and 0.5-22 MPa to carry out a hydrothermal synthesis reaction; the mass ratio of metal gallium to water is 1:(3-30);

[0033] 2) After the reaction is completed, the solid-liquid mixture is filtered and washed to obtain a precipitate;

[0034] 3) drying the precipitate and pyrolyzing it at 600-800° C. for 2-6 hours to obtain gallium oxide powder.

[0035] In the above embodiment, when the hydrothermal synthesis reaction time of step 1) is 4-6 hours, the yield of the obtained gallium oxide is above 98.5%. In addition, for high-purity metallic gallium, high-purity gallium oxide can be obtained through the above steps, which is green and pollution-free and suitable for the preparation of industrial high-purity gallium oxide.

[0036] In the above embodiment, the oxidant can be hydrogen peroxide or oxygen added to water, preferably hydrogen peroxide, with a molar ratio of (0.05-0.2):1 to metal gallium; preferably (0.1-0.2):1. The addition of hydrogen peroxide can generate a certain amount of active oxygen free radicals at high temperature, effectively promoting the valence state conversion of metal gallium and increasing the reaction rate.

[0037] In a preferred embodiment, the hydrothermal synthesis reaction in step 1) can also be set up with an external electric field, which promotes the generation of active oxygen free radicals on the one hand and the reduction activity of metal gallium on the other hand. The electric field strength is 5-20 kV / cm. Under this electric field strength, the conversion rate can be increased to more than 99.9% after only 1-2 hours of reaction.

[0038] In the above embodiment, the hydrothermal synthesis reaction is carried out by adding an electric field, and the XRD pattern of the gallium oxide powder finally obtained is as follows: Figure 1 As shown, SEM electron microscope images are as follows Figure 2 As shown, it can be confirmed that the product obtained by the above hydrothermal synthesis method is gallium oxide, and is in the shape of rice grains with a length of 1-1.5μm.

[0039] Personnel skilled in the art may optionally perform the cracking in a cracking boat, wherein the cracking boat is made of one of quartz glass, boron nitride, platinum and graphite.

[0040] In another embodiment, the apparatus for the hydrothermal synthesis step of the above embodiment is provided, such as Figure 3As shown, it includes a reactor 1, and an electric field positive plate 11 and a negative plate 12 are respectively arranged on the left and right sides of the reactor 1. An electric heating wire (not shown) is also arranged near the inner wall of the reactor 1; a common stirrer 2 and a thermocouple 3 are also arranged, which are used for mixing and stirring and temperature monitoring respectively. The upper part of the reactor 1 is connected with an air guide pipe 4 for discharging the gas generated by the reaction. The air guide pipe 4 is connected with a cooling ice water jacket 41 near the reactor 1, and the air inlet end is located at the lower part of the cooling ice water jacket 41, and the air outlet end is located at the top of the cooling ice water jacket 41; the bottom of the cooling ice water jacket 41 is connected with a return water pipe 5. A condensation coil 42 is arranged in the cooling ice water jacket 41, which is used to condense the gas entering the cooling ice water jacket 41. After the gas is condensed, it adheres to the outer surface of the coil 42, and then gathers to the bottom of the cooling ice water jacket 41 and enters the reactor 1 along the return water pipe 5.

[0041] In the above-mentioned gallium oxide hydrothermal synthesis process, firstly, a measured amount of metal gallium, water and hydrogen peroxide are added into the reactor 1, and the agitator 2 is started. The electric field strength formed by the positive plate 11 and the negative plate 12 is controlled to be 5-20 kV / cm, and the conditions of 100-240° C. and 0.5-22 MPa are controlled. The above-mentioned condensation reflux separation gas method is used for the generated gas components to improve the reaction conversion rate of metal gallium.

[0042] As an option for those skilled in the art, the hydrothermal synthesis device includes necessary valves and other instruments and meters for monitoring, which are not described in detail here.

[0043] Example 1

[0044] A hydrothermal synthesis method for high-purity gallium oxide comprises the following steps:

[0045] 1) Hydrothermal synthesis reaction of metal gallium and water: 5N metal gallium and water were mixed at a mass ratio of 1:10, and hydrogen peroxide with a molar amount of 10% of the metal gallium was added, and the mixture was put into a hydrothermal synthesis reactor for reaction at a reaction temperature of 100° C., a reaction pressure of 1.5 MPa, and a reaction time of 6 h;

[0046] 2) Filtration and washing of the solid-liquid mixture: After the reaction is completed, the solid-liquid mixture is filtered and washed twice with 25° C. deionized water to obtain a white precipitate;

[0047] 3) Drying and cracking of the precipitate: The filtered precipitate was placed in a quartz boat for drying, nitrogen was continuously introduced, and the mixture was kept at 800° C. for 3 h for cracking, and finally 5N high-purity gallium oxide powder was obtained.

[0048] Example 2

[0049] A hydrothermal synthesis method for high-purity gallium oxide comprises the following steps:

[0050] 1) Hydrothermal synthesis reaction of metal gallium and water: 6N metal gallium and water were mixed at a mass ratio of 1:20, and hydrogen peroxide with a molar amount of 10% of the metal gallium was added, and the mixture was put into a hydrothermal synthesis reactor for reaction at a reaction temperature of 120° C., a reaction pressure of 2.5 MPa, and a reaction time of 4 h;

[0051] 2) Filtration and washing of the solid-liquid mixture: After the reaction is completed, the solid-liquid mixture is filtered and washed twice with 30° C. deionized water and three times with anhydrous ethanol to obtain a white precipitate;

[0052] 3) Drying and cracking of the precipitate: The filtered precipitate was placed in a quartz boat for drying, nitrogen was continuously introduced, and the mixture was kept at 750° C. for 4 h for cracking, and finally 6N high-purity gallium oxide powder was obtained.

[0053] Example 3

[0054] A hydrothermal synthesis method for high-purity gallium oxide comprises the following steps:

[0055] S1. Hydrothermal synthesis reaction of metal gallium and water: 5N metal gallium and water are mixed at a mass ratio of 1:10, and 20% molar amount of metal gallium is added, and the mixture is put into a hydrothermal synthesis reactor for reaction at a reaction temperature of 150° C., a reaction pressure of 2.0 MPa, and a reaction time of 4 h;

[0056] S2. Filtration and washing of the solid-liquid mixture: After the reaction is completed, the solid-liquid mixture is filtered and washed twice with 45° C. deionized water to obtain a white precipitate;

[0057] S3. Drying and cracking of the precipitate: The filtered precipitate is placed in a boron nitride boat for drying, oxygen is continuously introduced, and the precipitate is kept at 800° C. for 4 hours for cracking, and finally 5N high-purity gallium oxide powder is obtained.

[0058] Example 4

[0059] For step 1) of Example 1, an electric field of 5 kV / cm was added, and the reaction time was adjusted to 2 h while the other steps remained unchanged.

[0060] Example 5

[0061] For step 1) of Example 2, an electric field of 20 kV / cm was added, and the reaction time was adjusted to 1 h while the other steps remained unchanged.

[0062] Example 6

[0063] For step 1) of Example 3, an electric field of 10 kV / cm was added, and the reaction time was adjusted to 1.5 h while the other steps remained unchanged.

[0064] Comparative Example 1

[0065] The hydrothermal synthesis method of gallium oxide is different from that of Example 1 in that no hydrogen peroxide is added.

[0066] Comparative Example 2

[0067] The hydrothermal synthesis method of gallium oxide is different from that of Example 4 in that no hydrogen peroxide is added.

[0068] Comparative Example 3

[0069] The hydrothermal synthesis method of gallium oxide is different from that of Example 4 in that the electric field strength is 1 kV / cm.

[0070] The reaction conditions, reaction time and yield of the gallium oxide powder obtained in the examples and comparative examples are shown in Table 1.

[0071] Table 1:

[0072] Group Reaction time Electric field strength kV / cm Gallium oxide yield % Example 1 6 0 99.1 Example 2 4 0 98.6 Example 3 4 0 98.9 Example 4 2 5 99.9 Example 5 1 20 99.9 Example 6 1.5 10 99.9 Comparative Example 1 6 0 93.1 Comparative Example 2 2 5 95.3 Comparative Example 3 2 1 99.2

[0073] It is not difficult to see from Table 1 that, under the premise of adding electric fields of different strengths, Examples 4-6 all improve the yield of gallium oxide in a shorter time compared to Examples 1-3. In Comparative Examples 1 and 4, no hydrogen peroxide was added, and the yield of gallium oxide decreased to varying degrees. In Comparative Example 3, the yield decreased relatively when the electric field strength was reduced, indicating that under the condition that other conditions remain unchanged, the appropriate electric field strength and oxidizing environment can synergistically improve the conversion efficiency of the metal gallium reaction.

[0074] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A hydrothermal synthesis method of gallium oxide, characterized in that the steps include: Mixing metal gallium and water, adding an oxidant under stirring at 100-240° C. and 0.5-22 MPa to carry out a hydrothermal synthesis reaction; the mass ratio of metal gallium to water is 1:(3-30); After the reaction is completed, the solid-liquid mixture is filtered and washed to obtain a precipitate; The precipitate is dried and cracked to obtain gallium oxide powder.

2. The hydrothermal synthesis method according to claim 1, characterized in that: During the hydrothermal synthesis reaction, an electric field with a strength of 5-20 kV / cm is added.

3. The hydrothermal synthesis method according to claim 2, characterized in that: The hydrothermal synthesis reaction time is 1-2h.

4. The hydrothermal synthesis method according to claim 2, characterized in that: The oxidant is oxygen or hydrogen peroxide; and / or the molar ratio of the oxidant to metal gallium is (0.05-0.2):

1.

5. The hydrothermal synthesis method according to claim 1, characterized in that: During the hydrothermal synthesis process, the escaped gas is condensed, and the obtained condensed water is added to the hydrothermal synthesis process.

6. The hydrothermal synthesis method according to claim 1, characterized in that: The cracking temperature is 600-800° C., and the cracking time is 2-6 hours.

7. The hydrothermal synthesis method according to claim 1, characterized in that: The cracking process is completed in an inert gas or a non-reducing gas.

8. The hydrothermal synthesis method according to claim 1, characterized in that: Deionized water is used in the washing process, and the washing liquid is recycled and reused in the hydrothermal synthesis reaction.

9. Application of the hydrothermal synthesis method according to any one of claims 1 to 8 in the preparation of high-purity gallium oxide, characterized in that: The purity of the metal gallium is 5N or higher.

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