Device and method for producing silicon nitride powder by liquid phase method

Abstract

The present invention provides a device and method for producing silicon nitride powder by a liquid phase method. The device comprises a first raw material supply unit, a second raw material supply unit, a tubular reactor, an aging reactor, a solid-liquid separation unit, a dynamic pyrolysis unit, a calcination unit, a nitrogen-containing inert gas supply unit, and a nitrogen-containing reducing gas supply unit. By using the device provided by the present invention, silicon nitride powder can be produced by a liquid phase method, the production process is easy to control, and silicon nitride powder with high purity, high α phase ratio, small particle size and uniformity can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of silicon nitride ceramic material preparation, and in particular to a device and method for producing silicon nitride powder by a liquid phase method. Background Art

[0002] Silicon nitride ceramics are a high-temperature structural ceramic material with excellent performance, featuring high mechanical strength, self-lubrication, good thermal stability, stable chemical properties, etc. It is widely used in metallurgy, chemical industry, machinery, electronics and other industries, and is an indispensable key material for new energy, high-end equipment, aerospace, military and other industries. At present, domestic silicon nitride powder is mainly used for low-end and medium-end applications, and the quality of powder in terms of α phase, particle size, oxygen content, metal impurities, etc. is still far behind that of foreign giants.

[0003] There are three commercial methods for preparing silicon nitride powder: direct nitridation of silicon powder, carbon thermal reduction, and ammonia solution. The direct nitridation of silicon powder is highly efficient and relatively low in cost, but it is difficult to synthesize silicon nitride powder with a high α-phase content and no free silicon. The common difficulty lies in strengthening solid-phase mass transfer and precisely controlling heat. The carbon thermal reduction method is low in cost, and the product has a high a-phase content and low metal impurity content, but the carbon and oxygen content easily exceed the standard. The ammonia solution can synthesize high-quality silicon nitride powder, but it is costly. The common difficulty lies in the precise regulation of the precursor synthesis reaction, the control of the hygroscopic protection cost in the preparation process, and continuous production.

[0004] Chinese patent CN13148966A discloses a method for preparing high-purity silicon nitride powder by ammonolysis, which includes adding solvent and silicon tetrachloride to a reaction container, controlling the temperature in the container to -25 to -35°C, dissolving liquid ammonia into the solvent, and reducing the pressure of the container to make the liquid ammonia vaporize and boil, disturbing the entire reaction system, and obtaining a silicon nitride precursor; collecting ammonia gas, pressurizing and liquefying it, and then passing it into the solvent again to realize ammonia gas circulation; burning the obtained silicon nitride precursor, collecting and purifying the gas generated by burning, crushing the burned silicon nitride precursor, and calcining the crushed silicon nitride precursor to obtain silicon nitride powder. However, the method has a low reaction temperature, harsh reaction conditions, and high requirements for equipment. Silicon tetrachloride is first added to the reaction container, and then liquid ammonia is added, and then the liquid ammonia is boiled and vaporized. The reaction process is violent and the process is uncontrollable. The precursor is not washed and burned directly, and organic matter and ammonium chloride are difficult to completely remove and difficult to recycle. The precursor after burning is crushed again. Impurities are easily introduced during the crushing process, the process continuity is poor, and the material is easily exposed to air, which will lead to an increase in the O content in the product.

[0005] Chinese patent CN110272283A discloses a method for producing silicon nitride powder, which uses silicon tetrachloride and ammonia as raw materials to react and synthesize Si(NH)2 solid, a precursor of silicon nitride, and obtains pure Si(NH)2 powder by washing and filtering; the Si(NH)2 is moved to a high-temperature furnace and calcined to obtain amorphous silicon nitride powder; the obtained silicon nitride powder is refined, pressed into blocks, and then moved to a high-temperature crystallization furnace and calcined to obtain crystalline silicon nitride powder. However, no organic solvent is added in this method, the reaction process is particularly violent, and the excess silicon tetrachloride and Cl in the powder are - Ions are high, increase the subsequent Cl removal - The difficulty affects the purity of the α phase in the final powder.

[0006] Chinese patent CN107954723A discloses a method for manufacturing α-phase silicon nitride powder, which is to react silicon tetrachloride with liquid ammonia at the interface of two liquid phases of an organic solvent and liquid ammonia to obtain a precursor aminosilicon or silicimide; the organic solvent is toluene or a mixture of toluene and xylene; the silicimide is thermally decomposed to obtain amorphous silicon nitride powder; the amorphous silicon nitride powder is crystallized to obtain α-phase silicon nitride powder. However, the process of this method is an intermittent operation, with poor production stability and continuity, complex operation control, and difficulty in industrial production. The thermal decomposition of the silicimide precursor is static calcination, and the powder is easy to agglomerate, resulting in carbon and chlorine residues in the silicon nitride powder, and it is difficult to control the particle size and shape of the silicon nitride powder.

[0007] Chinese patent CN105217583A discloses a method for preparing nano-high-purity silicon nitride, which uses silicon tetrachloride and ammonia as raw materials, and generates Si(NH)2 precursor by reacting ammonia dissolved in organic hydrocarbons with silicon tetrachloride, and then pyrolyzing the purified Si(NH)2 at 1000-1400°C to obtain silicon nitride powder with small particle size and high purity. However, this method requires first forming an organic hydrocarbon layer, and then spraying silicon tetrachloride to react with liquid ammonia dissolved in the organic hydrocarbon layer. The reaction yield is low and it is difficult to achieve industrial production. In addition, the high-temperature pyrolysis of the silicon imide precursor is carried out once, without staged calcination, and it is easy to agglomerate, resulting in carbon and chlorine residues in the silicon nitride powder, and it is difficult to control the particle size and shape of the silicon nitride powder.

[0008] In summary, the existing technology for preparing silicon nitride powder often has the problem of difficult control of the reaction process, making it difficult to obtain high-purity, high-α-phase-ratio, small-size and uniform silicon nitride powder. Summary of the invention

[0009] The main purpose of the present invention is to provide a device and method for producing silicon nitride powder by a liquid phase method, so as to solve the problem in the prior art that it is difficult to obtain silicon nitride powder with high purity, high α phase ratio, small particle size and uniformity.

[0010] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, there is provided a device for producing silicon nitride powder by a liquid phase method, which comprises: a first raw material supply unit for supplying a mixture of liquid ammonia and an organic solvent as a first raw material; a second raw material supply unit for supplying a mixture of silicon halide and an organic solvent as a second raw material; a tubular reactor, wherein a reaction microchannel is arranged in the tubular reactor, and the tubular reactor has a reaction raw material inlet and a pre-reaction slurry outlet, the reaction raw material inlet is connected to the first raw material supply unit and the second raw material supply unit respectively, and the tubular reactor is used to make the first raw material and the second raw material carry out a liquid phase pre-reaction in the reaction microchannel to form a pre-reaction slurry; an aging reactor, having a pre-reaction slurry inlet and an aging reaction slurry outlet, the pre-reaction slurry inlet is connected to the pre-reaction slurry outlet, and a stirring device is also arranged in the aging reactor, and the aging reactor is used to make the pre-reaction slurry in a stirring state. The invention relates to a method for preparing silicon nitride powder and a silicon nitride reactor, wherein the silicon nitride powder is subjected to an aging reaction under a state to form an aging reaction slurry; a solid-liquid separation unit having an aging reaction slurry inlet, a filtrate outlet and a solid phase outlet, the aging reaction slurry inlet being connected to the aging reaction slurry outlet; a dynamic pyrolysis unit having a solid phase inlet connected to the solid phase outlet, the dynamic pyrolysis unit being used to subject the solid phase discharged from the solid-liquid separation unit to low-temperature dynamic pyrolysis to form an amorphous silicon nitride powder; a calcination unit being connected to the outlet of the dynamic pyrolysis unit, being used to subject the amorphous silicon nitride powder to high-temperature calcination and crystallization to obtain a silicon nitride powder product; a nitrogen-containing inert gas supply unit being connected to the tubular reactor, the aging reaction kettle, the solid-liquid separation unit and the dynamic pyrolysis unit, being used to provide a nitrogen-containing inert gas; a nitrogen-containing reducing gas supply unit being used to provide a nitrogen-containing reducing gas, the calcination unit being switchably connected to the nitrogen-containing inert gas supply unit and / or the nitrogen-containing reducing gas supply unit.

[0011] Furthermore, in the tubular reactor, the diameter of the reaction microchannel is 2 to 4 cm and the length is 3 to 5 m.

[0012] Furthermore, the above device also includes: a static phase separation tank connected to the filtrate outlet, and the static phase separation tank is used to allow the filtrate to be statically separated to form an upper liquid ammonia layer and a lower solvent layer.

[0013] Furthermore, the static phase-separation tank has an upper liquid outlet and a lower liquid outlet, and the device also includes: an organic solvent supply unit, which is respectively connected to the first raw material supply unit and the second raw material supply unit, and is used to supply organic solvent; the lower liquid outlet is connected to the inlet of the organic solvent supply unit; a liquid ammonia supply unit, which is connected to the first raw material supply unit, and is used to supply liquid ammonia; and a silicon halide supply unit, which is connected to the second raw material supply unit, and is used to supply silicon halide.

[0014] Furthermore, the above-mentioned device also includes: an evaporation unit, having an upper liquid inlet and an ammonia outlet, the upper liquid inlet is connected to the upper liquid outlet; a condensation unit, having an ammonia inlet and a recovered liquid ammonia outlet, the ammonia inlet is connected to the ammonia outlet, and the recovered liquid ammonia outlet is connected to the liquid ammonia supply unit.

[0015] Furthermore, the solid-liquid separation unit is a filtering, drying and washing integrated machine, which has an aging reaction slurry inlet, a detergent inlet, a filtrate outlet and a solid phase outlet. The filtering, drying and washing integrated machine is used to filter, wash and dry the aging reaction slurry to obtain a filtrate and a solid phase; or, the solid-liquid separation unit includes a centrifuge and a stirring dryer connected in sequence, the centrifuge is provided with an aging reaction slurry inlet and a detergent inlet, the stirring dryer has a solid phase outlet, and the centrifuge is provided with a filtrate outlet.

[0016] Furthermore, the outlet for recovering liquid ammonia is also connected to the inlet for detergent.

[0017] Furthermore, the dynamic pyrolysis unit is a rotary kiln or a fluidized bed, and the calcination unit is a rotary kiln, an atmosphere kiln, a push plate kiln or a roller kiln.

[0018] According to another aspect of the present invention, a method for producing silicon nitride powder by a liquid phase method is also provided, which is carried out using the above-mentioned device for producing silicon nitride powder by a liquid phase method, and the above-mentioned method comprises the following steps: providing a mixed solution of liquid ammonia and an organic solvent as a first raw material, and providing a mixed solution of silicon halide and an organic solvent as a second raw material; introducing the first raw material and the second raw material into a tubular reactor to carry out a liquid phase pre-reaction in the reaction microchannel thereof to obtain a pre-reaction slurry; introducing the pre-reaction slurry into an aging reactor, and carrying out an aging reaction under stirring to form an aging reaction slurry; The aging reaction slurry is subjected to solid-liquid separation to obtain a filtrate and a solid phase; the solid phase is then fed into a dynamic pyrolysis unit to perform low-temperature dynamic pyrolysis to obtain an amorphous silicon nitride powder; the amorphous silicon nitride powder is subjected to high-temperature calcination and crystallization in a calcination unit to obtain a silicon nitride powder product; wherein the introduction process of the first raw material and the second raw material, the pre-reaction process, the aging reaction process, the solid-liquid separation process and the low-temperature dynamic pyrolysis are all carried out in a nitrogen-containing inert gas; and the high-temperature calcination and crystallization process is carried out in a nitrogen-containing inert gas and / or a nitrogen-containing reducing gas.

[0019] Furthermore, in the first raw material, the volume ratio of liquid ammonia to the organic solvent is 5-8:1, and in the second raw material, the volume ratio of silicon halide to the organic solvent is 1:2-9.

[0020] Furthermore, the organic solvent is selected from one or more of toluene, xylene, n-hexane, and hexane; the temperature of the liquid phase pre-reaction is -50 to 0°C, and the flow rates of the first raw material and the second raw material in the tubular reactor are 2 to 3 m / s, respectively.

[0021] Furthermore, the aging reaction temperature is -50 to 0°C, the time is 1 to 10 hours, and the stirring speed of the stirring device in the aging reaction kettle is 3 to 15 r / min.

[0022] Furthermore, the method further comprises: subjecting the filtrate to static phase separation in a static phase separation tank to obtain an upper liquid ammonia layer and a lower solvent layer.

[0023] Furthermore, the method further comprises: extracting the solvent in the lower solvent layer and returning it to the organic solvent supply unit.

[0024] Furthermore, the method further comprises: evaporating the material in the upper liquid ammonia layer to obtain ammonia gas; condensing the ammonia gas to form recovered liquid ammonia, and then returning the recovered liquid ammonia to the liquid ammonia supply unit.

[0025] Furthermore, the solid-liquid separation step includes: filtering, washing and drying the aging reaction slurry in a filtering, drying and washing integrated machine in sequence to obtain a filtrate and a solid phase; or, after centrifugal filtering the aging reaction slurry in a centrifuge, adding a detergent to the centrifuge for centrifugal washing, and finally drying the washed filter cake in a stirring dryer to obtain a solid phase; wherein the liquid phase separated in the centrifuge is the filtrate.

[0026] Furthermore, the method also includes: passing part of the recovered liquid ammonia into a drying and washing machine or a centrifuge for use as a detergent.

[0027] Furthermore, during the low-temperature dynamic pyrolysis process, the pyrolysis temperature is 500-1000°C, and the pyrolysis time is 0.5-2h; during the high-temperature calcination crystallization process, the calcination temperature is 1400-1700°C, and the calcination time is 1-3h.

[0028] Furthermore, the silicon halide is one or more of silicon tetrachloride, silicon tetrabromide and silicon tetraiodide.

[0029] Furthermore, the nitrogen-containing inert gas is nitrogen, or a mixture of nitrogen and argon; the nitrogen-containing reducing gas is a mixture of nitrogen and a reducing gas, and the reducing gas is hydrogen and / or ammonia.

[0030] By using the device provided by the present invention, silicon nitride powder can be produced by a liquid phase method, the production process is easy to control, and silicon nitride powder with high purity, high α phase ratio, small and uniform particle size can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0032] Figure 1A schematic structural diagram of an apparatus for producing silicon nitride powder using a liquid phase method according to an embodiment of the present invention is shown.

[0033] The above drawings include the following reference numerals:

[0034] 10. First raw material supply unit; 20. Second raw material supply unit; 30. Tubular reactor; 40. Aging reactor; 50. Solid-liquid separation unit; 60. Dynamic pyrolysis unit; 70. Calcination unit; 80. Static phase separation tank; 90. Organic solvent supply unit; 100. Liquid ammonia supply unit; 110. Silicon halide supply unit; 120. Evaporation unit; 130. Condensation unit. DETAILED DESCRIPTION

[0035] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0036] As described in the background technology section, the prior art for preparing silicon nitride powder often has the problem that the reaction process is difficult to control, and it is difficult to obtain high-purity, high-α-phase-ratio, small-particle-size and uniform silicon nitride powder. In order to solve this problem, the present invention provides a device for producing silicon nitride powder by a liquid phase method, such as Figure 1 As shown, the device includes a first raw material supply unit 10, a second raw material supply unit 20, a tubular reactor 30, an aging reactor 40, a solid-liquid separation unit 50, a dynamic pyrolysis unit 60, a calcination unit 70, a nitrogen-containing inert gas supply unit and a nitrogen-containing reducing gas supply unit; wherein,

[0037] The first raw material supply unit 10 is used to supply a mixture of liquid ammonia and an organic solvent as the first raw material; the second raw material supply unit 20 is used to supply a mixture of silicon halide and an organic solvent as the second raw material; a reaction microchannel is provided in the tubular reactor 30, which has a reaction raw material inlet and a pre-reaction slurry outlet, and the reaction raw material inlet is connected to the first raw material supply unit 10 and the second raw material supply unit 20 respectively, and the tubular reactor 30 is used to make the first raw material and the second raw material perform a liquid phase pre-reaction in the reaction microchannel to form a pre-reaction slurry; the aging reactor 40 has a pre-reaction slurry inlet and an aging reaction slurry outlet, and the pre-reaction slurry inlet is connected to the pre-reaction slurry outlet, and the aging reactor 40 is also equipped with a stirring device, and the aging reactor 40 It is used to make the pre-reaction slurry undergo an aging reaction under stirring to form an aging reaction slurry; the solid-liquid separation unit 50 has an aging reaction slurry inlet, a filtrate outlet and a solid phase outlet, and the aging reaction slurry inlet is connected to the aging reaction slurry outlet; the dynamic pyrolysis unit 60 has a solid phase inlet, which is connected to the solid phase outlet, and the dynamic pyrolysis unit 60 is used to perform low-temperature dynamic pyrolysis of the solid phase discharged from the solid-liquid separation unit 50 to form an amorphous silicon nitride powder; the calcination unit 70 is connected to the outlet of the dynamic pyrolysis unit 60, and is used to perform high-temperature calcination and crystallization on the amorphous silicon nitride powder to obtain a silicon nitride powder product; the nitrogen-containing inert gas supply unit is connected to the tubular reactor 30, the aging reactor 40, the solid-liquid separation unit 50 and the dynamic pyrolysis unit 60, and is used to provide a nitrogen-containing inert gas; the nitrogen-containing reducing gas supply unit is used to provide a nitrogen-containing reducing gas, and the calcination unit 70 can be switchably connected to the nitrogen-containing inert gas supply unit and / or the nitrogen-containing reducing gas supply unit.

[0038] By using the above-mentioned device provided by the present invention, silicon nitride powder can be produced by liquid phase method. Specifically, since the reaction speed of liquid ammonia and liquid silicon halide is extremely fast and cannot be accurately controlled, the present invention uses an organic solvent as a diluent, and mixes with silicon halide and liquid ammonia to form a first raw material and a second raw material respectively, and then performs a liquid phase reaction, so that the reaction speed can be controlled. Moreover, the present invention uses a tubular reactor for pre-reaction, because the initial stage of the liquid phase reaction is extremely violent and the heat release is large. The tubular reactor belongs to a continuous flow reactor with a small tube diameter and extremely high heat transfer efficiency. Liquid phase synthesis is carried out in the confined space of the microchannel, and the mass transfer and heat transfer efficiency are enhanced by reducing the dispersion scale of the system. Therefore, the residence time and reaction temperature can be accurately controlled to avoid short flow and overtemperature phenomena of traditional stirred reactors. After the pre-reaction is completed, the present invention uses an aging reactor with a stirring device to ensure that the material coming out of the tubular reactor has enough residence time, and can be fully aged under stirring. The reaction can also effectively reduce the agglomeration of particles during growth.

[0039] The aging reaction slurry coming out of the aging reactor is a solid-liquid mixture, the main components of which are silicon nitride precursor, ammonium halide, liquid ammonia and organic solvent. Ammonium halide is dissolved in liquid ammonia, and the mixture after the reaction is filtered, and the solid phase is the silicon nitride precursor. Amorphous silicon nitride can be generated during the pyrolysis of the silicon nitride precursor, but due to the inevitable residual of a small amount of ammonium halide and organic solvent on the solid surface, inside the agglomerate and in the structural cavities, the conventional pyrolysis equipment adopts an atmosphere furnace, a tubular furnace, etc., which belongs to static calcination, and is easy to cause powder agglomeration, and the silicon nitride precursor is not completely decomposed, and the ammonium halide and organic solvent in the agglomerate cannot be completely volatilized in time and remain. Different from this, the present invention adopts low-temperature dynamic pyrolysis to the silicon nitride precursor, realizes the thorough pyrolysis of the silicon nitride precursor, and the pyrolysis process is in a dynamic state, there is mutual movement between the powder particles, the particles are not easy to agglomerate, and the ammonium halide and organic solvent are easily volatilized and removed, so the product purity can be significantly improved. Finally, the present invention further utilizes the calcination unit 70 to perform high-temperature calcination and crystallization on the amorphous silicon nitride powder, so that it is fully crystallized into a-phase silicon nitride powder.

[0040] The overall reaction mechanism is as follows:

[0041]

[0042] 3Si(NH)2(s)——→Si3N4(s)+2NH3(g)

[0043] Based on the above principles, the device of the present invention can use silicon halide and liquid ammonia as raw materials and organic solvent as diluent, and then send the mixture of liquid ammonia and organic solvent into a tubular reactor, quickly collide with the mixture of liquid ammonia and organic solvent, and mix instantly, and pre-react in the microchannel, and then send it for aging to fully react to obtain a silicon nitride precursor. Then, after low-temperature dynamic pyrolysis and high-temperature calcination crystallization, the final a-phase silicon nitride powder product can be obtained. The production process of the device of the present invention is easy to control, and can obtain high-purity, high-α-phase-ratio, small-particle-size and uniform silicon nitride powder.

[0044] In order to further improve the controllability of the reaction and the stability of the pre-reaction process, in a preferred embodiment, the diameter of the reaction microchannel in the tubular reactor 30 is 2 to 4 cm and the length is 3 to 5 m. Designing the size of the reaction microchannel of the tubular reactor to the above parameters is more conducive to the stable completion of the liquid phase pre-reaction, enhancing the mass transfer and heat transfer efficiency during the pre-reaction process, and is conducive to further improving the particle size uniformity of the final silicon nitride powder product.

[0045] As mentioned above, the aging reaction slurry is a solid-liquid mixture, the main components of which are silicon nitride precursor, ammonium halide, liquid ammonia and organic solvent. The silicon nitride precursor is aminosilicon Si(NH2)4, iminosilicon Si(NH)2, halogenaminosilicon Si(NH2) x X4-x and one or more of halogeniminosilicon SiNHX2. After being treated by the solid-liquid separation unit 50, the main components in the liquid phase are ammonium halide, liquid ammonia and organic solvent. In a preferred embodiment, the above-mentioned device also includes: a static phase separation tank 80, which is connected to the filtrate outlet, and the static phase separation tank 80 is used to allow the filtrate to be statically separated to form an upper liquid ammonia layer and a lower solvent layer. The static phase separation tank 80 can be used to statically separate the liquid phase into layers, the organic solvent is heavier and is located in the lower layer, and the upper layer is unreacted liquid ammonia in which the ammonium halide is dissolved, which is conducive to subsequent separation and recycling.

[0046] In a preferred embodiment, the static phase separation tank 80 has an upper liquid outlet and a lower liquid outlet, and the device further includes: an organic solvent supply unit 90, which is connected to the first raw material supply unit 10 and the second raw material supply unit 20, respectively, for supplying organic solvent; the lower liquid outlet is connected to the inlet of the organic solvent supply unit 90; a liquid ammonia supply unit 100, which is connected to the first raw material supply unit 10, for supplying liquid ammonia; and a silicon halide supply unit 110, which is connected to the second raw material supply unit 20, for supplying silicon halide. In this way, the lower organic solvent separated by static phase separation can be returned to the previous process for recycling.

[0047] In a preferred embodiment, the device further comprises: an evaporation unit 120 having an upper liquid inlet and an ammonia outlet, the upper liquid inlet being connected to the upper liquid outlet; a condensation unit 130 having an ammonia inlet and a liquid ammonia recovery outlet, the ammonia inlet being connected to the ammonia outlet, and the liquid ammonia recovery outlet being connected to the liquid ammonia supply unit 100. Through the evaporation unit 120 and the condensation unit 130, the liquid ammonia in the upper liquid ammonia phase obtained by liquid separation can be converted into ammonia gas and then condensed, so that the liquid ammonia and the ammonium halide dissolved therein can be separated and returned to the previous step for reuse.

[0048] Amorphous silicon nitride can be generated during the pyrolysis of silicon nitride precursor, but due to the inevitable residual of a small amount of ammonium halide and organic solvent on the solid surface, inside the agglomerate and in the structural cavities, in order to further remove these impurities and improve product purity, in a preferred embodiment, the solid-liquid separation unit 50 is a filtering, drying and washing integrated machine, which has an aging reaction slurry inlet, a detergent inlet, a filtrate outlet and a solid phase outlet, and the filtering, drying and washing integrated machine is used to filter, wash and dry the aging reaction slurry to obtain a filtrate and a solid phase; or, the solid-liquid separation unit 50 includes a centrifuge and a stirring dryer connected in sequence, the centrifuge is provided with an aging reaction slurry inlet and a detergent inlet, the stirring dryer has a solid phase outlet, and the centrifuge is provided with a filtrate outlet. The solid phase can be washed in advance using the above-mentioned device before pyrolysis, which has a better promoting effect on further improving purity.

[0049] Compared with the centrifuge and stirring dryer connected in series, it is more preferable to use a filtering, drying and washing integrated machine as the solid-liquid separation unit 50. This is because the integrated process effectively reduces the chance of contact with the outside air during the process, further suppressing the increase of impurity oxygen content in the product.

[0050] Preferably, the outlet for recovering liquid ammonia is also connected to the inlet for washing agent. In this way, the recovered liquid ammonia obtained by the condensing unit can be used as washing agent to wash the filter cake.

[0051] In order to make the low-temperature dynamic pyrolysis process and the high-temperature calcination crystallization process more complete, promote the silicon nitride product to have a higher purity and a phase ratio, and further reduce the particle size to improve the particle size uniformity, in a preferred embodiment, the dynamic pyrolysis unit 60 is a rotary furnace or a fluidized bed, and the calcination unit 70 is a rotary furnace, an atmosphere furnace, a push plate kiln or a roller kiln. In addition, the above-mentioned dynamic pyrolysis unit 60 and calcination unit 70 can also be the same rotary furnace, as long as the temperature and atmosphere are switched at different stages, which should be understood by those skilled in the art and will not be repeated here.

[0052] According to another aspect of the present invention, a method for producing silicon nitride powder by a liquid phase method is also provided, which is carried out using the above-mentioned device for producing silicon nitride powder by a liquid phase method, and the method comprises the following steps: providing a mixture of liquid ammonia and an organic solvent as a first raw material, and providing a mixture of silicon halide and an organic solvent as a second raw material; introducing the first raw material and the second raw material into a tubular reactor 30 to perform a liquid phase pre-reaction in the reaction microchannel thereof to obtain a pre-reaction slurry; introducing the pre-reaction slurry into an aging reactor 40, performing an aging reaction under stirring to form an aging reaction slurry; slurry; performing solid-liquid separation on the aging reaction slurry to obtain a filtrate and a solid phase; then sending the solid phase into a dynamic pyrolysis unit 60 to perform low-temperature dynamic pyrolysis to obtain an amorphous silicon nitride powder; performing high-temperature calcination and crystallization on the amorphous silicon nitride powder in a calcination unit 70 to obtain a silicon nitride powder product; wherein the introduction process of the first raw material and the second raw material, the pre-reaction process, the aging reaction process, the solid-liquid separation process and the low-temperature dynamic pyrolysis are all carried out in a nitrogen-containing inert gas; and the high-temperature calcination and crystallization process is carried out in a nitrogen-containing inert gas and / or a nitrogen-containing reducing gas.

[0053] By using the above method provided by the present invention, silicon nitride powder can be produced by liquid phase method. Specifically, since the reaction speed of liquid ammonia and liquid silicon halide is extremely fast and cannot be accurately controlled, the present invention uses an organic solvent as a diluent, and is mixed with silicon halide and liquid ammonia to form a first raw material and a second raw material, and then a liquid phase reaction is carried out, so that the reaction speed can be controlled. Moreover, the present invention uses a tubular reactor for pre-reaction, because the initial stage of the liquid phase reaction is extremely violent and the heat release is large. The tubular reactor belongs to a continuous flow reactor with a small tube diameter and extremely high heat transfer efficiency. Liquid phase synthesis is carried out in the confined space of the microchannel, and the mass transfer and heat transfer efficiency are enhanced by reducing the dispersion scale of the system. Therefore, the residence time and reaction temperature can be accurately controlled to avoid short flow and overtemperature phenomena of traditional stirred reactors. After the pre-reaction is completed, the present invention uses an aging reactor with a stirring device to ensure that the material coming out of the tubular reactor has enough residence time, and can be fully aged under stirring. The reaction can also effectively reduce the agglomeration of particles during growth.

[0054] The aging reaction slurry coming out of the aging reactor is a solid-liquid mixture, the main components of which are silicon nitride precursor, ammonium halide, liquid ammonia and organic solvent. Ammonium halide is dissolved in liquid ammonia, and the mixture after the reaction is filtered, and the solid phase is the silicon nitride precursor. Amorphous silicon nitride can be generated during the pyrolysis of the silicon nitride precursor, but due to the inevitable residual of a small amount of ammonium halide and organic solvent on the solid surface, inside the agglomerate and in the structural cavities, the conventional pyrolysis equipment adopts an atmosphere furnace, a tubular furnace, etc., which belongs to static calcination, and is easy to cause powder agglomeration, and the silicon nitride precursor is not completely decomposed, and the ammonium halide and organic solvent in the agglomerate cannot be completely volatilized in time and remain. Different from this, the present invention adopts low-temperature dynamic pyrolysis to the silicon nitride precursor, realizes the thorough pyrolysis of the silicon nitride precursor, and the pyrolysis process is in a dynamic state, there is mutual movement between the powder particles, the particles are not easy to agglomerate, and the ammonium halide and organic solvent are easily volatilized and removed, so the product purity can be significantly improved. Finally, the present invention further utilizes the calcination unit 70 to perform high-temperature calcination and crystallization on the amorphous silicon nitride powder, so that it is fully crystallized into a-phase silicon nitride powder.

[0055] Based on the above principles, the method of the present invention can use silicon halide and liquid ammonia as raw materials and organic solvent as diluent, and then send the mixture of liquid ammonia and organic solvent into a tubular reactor, quickly collide with the mixture of liquid ammonia and organic solvent, and mix instantly, and pre-react in the microchannel, and then send it for aging to fully react to obtain a silicon nitride precursor. Then, after low-temperature dynamic pyrolysis and high-temperature calcination crystallization, the final a-phase silicon nitride powder product can be obtained. The production process of the device of the present invention is easy to control, and can obtain high-purity, high α-phase ratio, small and uniform silicon nitride powder.

[0056] In order to make the liquid phase reaction more stable and control the reaction rate within a more suitable range, in a more preferred embodiment, the volume ratio of liquid ammonia to organic solvent in the first raw material is 5 to 8:1, and the volume ratio of silicon halide to organic solvent in the second raw material is 1:2 to 9.

[0057] The participation of the organic solvent of the present invention plays a key role in the stability of the reaction. It can effectively reduce the impurity content in silicon nitride by maintaining the reaction speed within an appropriate range, and increase the proportion of α phase therein (if the reaction is too violent, the formed powder will carry impurity elements due to agglomeration or excessive particle size, and affect the proportion of α phase). In order to better play the above role, the organic solvent is selected from one or more of toluene, xylene, n-hexane, and hexane. In addition, in order to make the pre-reaction more stable, in a preferred embodiment, the temperature of the above-mentioned liquid phase pre-reaction is -50 to 0°C, and the flow rates of the first raw material and the second raw material in the tubular reactor 30 are 2 to 3 m / s, respectively. Controlling the reaction temperature and the flow rate in the tubular reactor within the above range can not only stabilize the pre-reaction, but also enable the pre-reaction slurry to enter the aging reaction stage in time, promote the silicon nitride precursor to grow more fully and uniformly, and provide conditions for improving the particle size uniformity of the final product. More preferably, the aging reaction temperature is -50 to 0°C, the time is 1 to 10 hours, and the stirring speed of the stirring device in the aging reaction kettle 40 is 3 to 15 r / min.

[0058] In a preferred embodiment, the method further includes: allowing the filtrate to stand and separate phases in a standing phase separation tank 80 to obtain an upper liquid ammonia layer and a lower solvent layer. The standing phase separation tank 80 can be used to stand and separate the liquid phase into layers, wherein the organic solvent is heavier and is located in the lower layer, while the upper layer is unreacted liquid ammonia in which ammonium halide is dissolved, which is beneficial for subsequent separation and recycling. More preferably, the method further includes: extracting the solvent in the lower solvent layer and returning it to the organic solvent supply unit 90. Evaporating the material in the upper liquid ammonia layer to obtain ammonia gas; condensing the ammonia gas to form recovered liquid ammonia, and then returning the recovered liquid ammonia to the liquid ammonia supply unit 100.

[0059] Amorphous silicon nitride can be generated during the pyrolysis of silicon nitride precursors. However, due to the inevitable residual presence of a small amount of ammonium halide and organic solvent on the solid surface, inside the agglomerate, and in the structural cavities, in order to further remove these impurities and improve product purity, in a preferred embodiment, the solid-liquid separation step includes: filtering, washing, and drying the aging reaction slurry in a filtering, drying, and washing integrated machine in sequence to obtain a filtrate and a solid phase; or, after the aging reaction slurry is centrifuged in a centrifuge, detergent is added to the centrifuge for centrifugal washing, and finally the washed filter cake is dried in a stirring dryer to obtain a solid phase; wherein the liquid phase separated in the centrifuge is the filtrate. The solid phase can be washed in advance using the above steps before pyrolysis, which has a better promoting effect on further improving purity. In addition, the above process is also conducive to reducing the treatment of residues such as organic solvents and ammonium halides during subsequent pyrolysis and calcination, and reducing energy consumption.

[0060] Compared with the centrifuge and stirring dryer connected in series, it is more preferable to use a filtering, drying and washing integrated machine as the solid-liquid separation unit 50. This is because the integrated process effectively reduces the chance of contact with the outside air during the process, further suppressing the increase of impurity oxygen content in the product.

[0061] Preferably, the above method further comprises: passing part of the recovered liquid ammonia into a drying and washing machine or a centrifuge for use as a detergent.

[0062] In a preferred embodiment, during the low-temperature dynamic pyrolysis process, the pyrolysis temperature is 500-1000°C and the pyrolysis time is 0.5-2h; during the high-temperature calcination crystallization process, the calcination temperature is 1400-1700°C and the calcination time is 1-3h. The above conditions are more conducive to the pyrolysis and crystallization, thereby obtaining a silicon nitride powder product with higher purity and a higher proportion of a phase.

[0063] Preferably, the silicon halide is one or more of silicon tetrachloride, silicon tetrabromide and silicon tetraiodide. The nitrogen-containing inert gas is nitrogen or a mixture of nitrogen and argon; the nitrogen-containing reducing gas is a mixture of nitrogen and a reducing gas, and the reducing gas is hydrogen and / or ammonia.

[0064] In summary, the above device and method provided by the present invention have the following beneficial effects:

[0065] 1. Use tubular reactors for pre-reaction of liquid phase reactions and conduct liquid phase synthesis in millimeter-level confined spaces. By reducing the dispersion scale of the system, the mass transfer and heat transfer efficiency are enhanced, the residence time and reaction temperature are precisely controlled, and short-flow and over-temperature phenomena of traditional stirred reactors are avoided.

[0066] 2. Silicon halide reacts violently with liquid ammonia. Silicon tetrachloride and liquid ammonia are diluted with organic solvents respectively. The synthesis reaction rate can be accurately controlled by adjusting the temperature, the ratio of silicon halide to organic solvent, the ratio of organic solvent to liquid ammonia, and the feeding rate of the two materials, which is beneficial to control the particle size and particle size distribution of the precursor and avoid precursor agglomeration.

[0067] 3. Ammonium halide is dissolved in liquid ammonia. Recycled liquid ammonia is used as a detergent to reduce the introduction of impurities. The residual ammonium chloride and organic solvent in the silicon nitride precursor can be fully removed through multiple washings. The liquid ammonia washing liquid can be combined with the filtered filtrate for treatment as the filtrate without adding additional equipment, avoiding the treatment of organic solvents and ammonium halides and other residues in the subsequent drying, pyrolysis and calcination processes. Compared with the traditional heating volatilization method for removing organic solvents and ammonium halides at this stage, it not only has high energy consumption, but also is difficult to recover.

[0068] 4. Low-temperature dynamic calcination can achieve complete pyrolysis of the silicon nitride precursor, effectively remove a small amount of adsorbed ammonium halide and organic solvent, and avoid powder agglomeration during the calcination process, which leads to the presence of a small amount of ammonium chloride and organic solvent on the surface of the silicon nitride precursor, inside the agglomerates and in the structural cavities, which cannot be fully removed.

[0069] Based on the above reasons, the silicon nitride powder product of the present invention has high purity, high a phase, low oxygen content, good monodispersity and small particle size; the present invention can realize the comprehensive recycling of materials in the whole process, the recycling process is simple, the recycling rate of organic solvents and liquid ammonia is high, the recycling cost is low, and it is green and environmentally friendly; moreover, the present invention is easy to realize the continuity and automation of the process, is suitable for large-scale production, closed-loop circulation of materials, low production cost, and good economic and environmental benefits.

[0070] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0071] Raw materials: silicon tetrachloride, purity>99.99%; liquid ammonia, purity>99.99%; toluene, purity>99.9%.

[0072] Implementation 1:

[0073] This embodiment adopts Figure 1 The device shown in the figure produces silicon nitride powder by liquid phase method, as follows:

[0074] Use high-purity nitrogen to replace the air in the powder preparation system to an inert environment to ensure that O2<1ppm and H2O<1ppm in the atmosphere. Mix 40 volumes of liquid ammonia at -40°C and 5 volumes of toluene to form the first raw material, which is fed into the tubular reactor at a flow rate of 2m / s using a shielded pump; at the same time, mix 2 volumes of silicon tetrachloride at -40°C and 6 volumes of toluene to form the second raw material, which is added to the tubular reactor at a flow rate of 2m / s. The tubular reactor has a diameter of 2cm and a pipeline length of 3m. The two streams of materials react rapidly after instantaneous mixing to form a pre-reaction slurry.

[0075] The pre-reaction slurry is passed into an aging reactor with a stirring unit and stays for 1 hour to form an aging reaction slurry at -40°C to ensure full reaction. The aging reaction slurry is sent to a three-in-one filtering, washing and drying device, and filtered first to obtain a filtrate and a filter cake. The filtrate is toluene, liquid ammonia and ammonium chloride dissolved in liquid ammonia. After the filtrate is sent to a phase separation tank and allowed to stand for 30 minutes, the lower liquid is a toluene phase, which is returned as a raw material, and the upper liquid is a liquid ammonia phase dissolved in ammonium chloride. It is sent to an evaporator and heated to 10°C to evaporate the liquid ammonia into gas, and then condensed to -40°C by a condenser. The liquid is returned as a raw material, and the solid at the bottom of the evaporator is ammonium chloride. The filter cake is a silicon nitride precursor solid and a small amount of liquid ammonia, toluene and ammonium chloride remaining in the silicon nitride precursor. The filter cake is then washed with liquid ammonia, filtered after washing, and washed and filtered 5 times in total, and then dried with hot nitrogen to obtain a silicon nitride precursor.

[0076] The silicon nitride precursor is then added to a rotary furnace via a conveyor. The rotation number of the rotary furnace is set to 1 rpm. The silicon nitride precursor is calcined at 800°C for 2 hours in a nitrogen atmosphere to thermally decompose the silicon nitride precursor into amorphous silicon nitride powder. The silicon nitride precursor is then sent to a push plate furnace for high-temperature calcination. It is calcined at 1500°C for 2 hours in a nitrogen atmosphere to obtain the product silicon nitride powder.

[0077] Implementation 2:

[0078] This embodiment adopts Figure 1 The device shown in the figure produces silicon nitride powder by liquid phase method, as follows:

[0079] Use high-purity nitrogen to replace the air in the powder preparation system to an inert environment to ensure that O2<1ppm and H2O<1ppm in the atmosphere. Mix 30 volumes of liquid ammonia at -40°C and 5 volumes of toluene to form the first raw material, which is fed into the tubular reactor at a flow rate of 2m / s using a shielded pump; at the same time, mix 2 volumes of silicon tetrachloride at -40°C and 4 volumes of toluene to form the second raw material, which is added to the tubular reactor at a flow rate of 2m / s. The tubular reactor has a diameter of 2cm and a pipeline length of 3m. The two streams of materials react rapidly after instantaneous mixing to form a pre-reaction slurry.

[0080] The pre-reaction slurry is passed into an aging reactor with a stirring unit and stays for 1 hour to form an aging reaction slurry at -40°C to ensure full reaction. The aging reaction slurry is sent to a three-in-one filtering, washing and drying device, and filtered first to obtain a filtrate and a filter cake. The filtrate is toluene, liquid ammonia and ammonium chloride dissolved in liquid ammonia. After the filtrate is sent to a phase separation tank and allowed to stand for 30 minutes, the lower liquid is a toluene phase, which is returned as a raw material, and the upper liquid is a liquid ammonia phase dissolved in ammonium chloride. It is sent to an evaporator and heated to 10°C to evaporate the liquid ammonia into gas, and then condensed to -40°C by a condenser. The liquid is returned as a raw material, and the solid at the bottom of the evaporator is ammonium chloride. The filter cake is a silicon nitride precursor solid and a small amount of liquid ammonia, toluene and ammonium chloride remaining in the silicon nitride precursor. The filter cake is then washed with liquid ammonia, filtered after washing, and washed and filtered 5 times in total, and then dried with hot nitrogen to obtain a silicon nitride precursor.

[0081] The silicon nitride precursor is then added to a rotary furnace via a conveyor. The rotation number of the rotary furnace is set to 1 rpm. The silicon nitride precursor is calcined at 800°C for 2 hours in a nitrogen atmosphere to thermally decompose the silicon nitride precursor into amorphous silicon nitride powder. The silicon nitride precursor is then sent to a push plate furnace for high-temperature calcination. It is calcined at 1500°C for 2 hours in a nitrogen atmosphere to obtain the product silicon nitride powder.

[0082] Example 3

[0083] This embodiment adopts Figure 1 The device shown in the figure produces silicon nitride powder by liquid phase method, as follows:

[0084] Use high-purity nitrogen to replace the air in the powder preparation system to an inert environment to ensure that O2<1ppm and H2O<1ppm in the atmosphere. Mix 25 volumes of liquid ammonia at -50°C and 5 volumes of toluene to form the first raw material, which is fed into the tubular reactor at a flow rate of 3m / s using a shielded pump; at the same time, mix 2 volumes of silicon tetrachloride at -50°C and 18 volumes of toluene to form the second raw material, which is added to the tubular reactor at a flow rate of 3m / s. The tubular reactor has a diameter of 2cm and a pipeline length of 3m. The two streams of materials react rapidly after instantaneous mixing to form a pre-reaction slurry.

[0085] The pre-reaction slurry is passed into an aging reactor with a stirring unit and stays for 1 hour to form an aging reaction slurry at -50°C to ensure full reaction. The aging reaction slurry is sent to a three-in-one filtering, washing and drying device, and filtered first to obtain a filtrate and a filter cake. The filtrate is toluene, liquid ammonia and ammonium chloride dissolved in liquid ammonia. After the filtrate is sent to a phase separation tank and allowed to stand for 30 minutes, the lower liquid is a toluene phase, which is returned as a raw material, and the upper liquid is a liquid ammonia phase dissolved in ammonium chloride. It is sent to an evaporator and heated to 10°C to evaporate the liquid ammonia into gas, and then condensed to -50°C by a condenser. The liquid is returned as a raw material, and the solid at the bottom of the evaporator is ammonium chloride. The filter cake is a silicon nitride precursor solid and a small amount of liquid ammonia, toluene and ammonium chloride remaining in the silicon nitride precursor. The filter cake is then washed with liquid ammonia, filtered after washing, and washed and filtered 5 times in total, and then the filter cake is dried with hot nitrogen to obtain a silicon nitride precursor.

[0086] The silicon nitride precursor is then added to a rotary furnace via a conveyor. The rotation number of the rotary furnace is set to 1 rpm. The silicon nitride precursor is calcined at 800°C for 2 hours in a nitrogen atmosphere to thermally decompose the silicon nitride precursor into amorphous silicon nitride powder. The silicon nitride precursor is then sent to a push plate furnace for high-temperature calcination. It is calcined at 1500°C for 2 hours in a nitrogen atmosphere to obtain the product silicon nitride powder.

[0087] Example 4

[0088] This embodiment adopts Figure 1 The device shown in the figure produces silicon nitride powder by liquid phase method, as follows:

[0089] Use high-purity nitrogen to replace the air in the powder preparation system with an inert environment to ensure that O2 < 1ppm and H2O < 1ppm in the atmosphere. Mix 45 volumes of liquid ammonia at -10°C and 5 volumes of toluene to form the first raw material, which is fed into the tubular reactor at a flow rate of 1.6m / s using a shielded pump; at the same time, mix 2 volumes of silicon tetrachloride at -10°C and 2 volumes of toluene to form the second raw material, which is added to the tubular reactor at a flow rate of 1.6m / s. The tubular reactor has a diameter of 2cm and a pipeline length of 3m. The two streams of materials react rapidly after instantaneous mixing to form a pre-reaction slurry.

[0090] The pre-reaction slurry is passed into an aging reactor with a stirring unit and stays for 1 hour to form an aging reaction slurry at -10°C to ensure full reaction. The aging reaction slurry is sent to a three-in-one filtering, washing and drying device, and filtered first to obtain a filtrate and a filter cake. The filtrate is toluene, liquid ammonia and ammonium chloride dissolved in liquid ammonia. After the filtrate is sent to a phase separation tank and allowed to stand for 30 minutes, the lower liquid is a toluene phase, which is returned as a raw material, and the upper liquid is a liquid ammonia phase dissolved in ammonium chloride. It is sent to an evaporator and heated to 10°C to evaporate the liquid ammonia into gas, and then condensed to -40°C by a condenser. The liquid is returned as a raw material, and the solid at the bottom of the evaporator is ammonium chloride. The filter cake is a silicon nitride precursor solid and a small amount of liquid ammonia, toluene and ammonium chloride remaining in the silicon nitride precursor. The filter cake is then washed with liquid ammonia, filtered after washing, and washed and filtered 5 times in total, and then dried with hot nitrogen to obtain a silicon nitride precursor.

[0091] The silicon nitride precursor is then added to a rotary furnace via a conveyor. The rotation number of the rotary furnace is set to 1 rpm. The silicon nitride precursor is calcined at 800°C for 2 hours in a nitrogen atmosphere to thermally decompose the silicon nitride precursor into amorphous silicon nitride powder. The silicon nitride precursor is then sent to a push plate furnace for high-temperature calcination. It is calcined at 1500°C for 2 hours in a nitrogen atmosphere to obtain the product silicon nitride powder.

[0092] Implementation 5:

[0093] This embodiment adopts Figure 1 The device shown in the figure produces silicon nitride powder by liquid phase method, as follows:

[0094] Use high-purity nitrogen to replace the air in the powder preparation system to an inert environment to ensure that O2<1ppm and H2O<1ppm in the atmosphere. Mix 40 volumes of liquid ammonia at -40°C and 5 volumes of toluene to form the first raw material, which is fed into the tubular reactor at a flow rate of 2m / s using a shielded pump; at the same time, mix 2 volumes of silicon tetrachloride at -40°C and 6 volumes of toluene to form the second raw material, which is added to the tubular reactor at a flow rate of 2m / s. The tubular reactor has a diameter of 2cm and a pipeline length of 3m. The two streams of materials react rapidly after instantaneous mixing to form a pre-reaction slurry.

[0095] The pre-reaction slurry is passed into an aging reactor with a stirring unit and stays for 1 hour to form an aging reaction slurry at -40°C to ensure full reaction. The aging reaction slurry is sent to a three-in-one filtering, washing and drying device, and filtered first to obtain a filtrate and a filter cake. The filtrate is toluene, liquid ammonia and ammonium chloride dissolved in liquid ammonia. After the filtrate is sent to a phase separation tank and allowed to stand for 30 minutes, the lower liquid is a toluene phase, which is returned as a raw material, and the upper liquid is a liquid ammonia phase dissolved in ammonium chloride. It is sent to an evaporator and heated to 10°C to evaporate the liquid ammonia into gas, and then condensed to -40°C by a condenser. The liquid is returned as a raw material, and the solid at the bottom of the evaporator is ammonium chloride. The filter cake is a silicon nitride precursor solid and a small amount of liquid ammonia, toluene and ammonium chloride remaining in the silicon nitride precursor. The filter cake is then washed with liquid ammonia, filtered after washing, and washed and filtered 5 times in total, and then dried with hot nitrogen to obtain a silicon nitride precursor.

[0096] The silicon nitride precursor is then added to a rotary furnace via a conveyor. The rotation speed of the rotary furnace is set to 3 rpm. The silicon nitride precursor is calcined at 500°C for 2 hours in a nitrogen atmosphere to thermally decompose the silicon nitride precursor into amorphous silicon nitride powder. The silicon nitride precursor is then sent to a push plate furnace for high-temperature calcination. It is calcined at 1400°C for 3 hours in a nitrogen atmosphere to obtain the product silicon nitride powder.

[0097] Implementation 6:

[0098] This embodiment adopts Figure 1 The device shown in the figure produces silicon nitride powder by liquid phase method, as follows:

[0099] Use high-purity nitrogen to replace the air in the powder preparation system to an inert environment to ensure that O2<1ppm and H2O<1ppm in the atmosphere. Mix 40 volumes of liquid ammonia at -40°C and 5 volumes of toluene to form the first raw material, which is fed into the tubular reactor at a flow rate of 2m / s using a shielded pump; at the same time, mix 2 volumes of silicon tetrachloride at -40°C and 6 volumes of toluene to form the second raw material, which is added to the tubular reactor at a flow rate of 2m / s. The tubular reactor has a diameter of 2cm and a pipeline length of 3m. The two streams of materials react rapidly after instantaneous mixing to form a pre-reaction slurry.

[0100] The pre-reaction slurry is passed into an aging reactor with a stirring unit and stays for 1 hour to form an aging reaction slurry at -40°C to ensure full reaction. The aging reaction slurry is sent to a three-in-one filtering, washing and drying device, and filtered first to obtain a filtrate and a filter cake. The filtrate is toluene, liquid ammonia and ammonium chloride dissolved in liquid ammonia. After the filtrate is sent to a phase separation tank and allowed to stand for 30 minutes, the lower liquid is a toluene phase, which is returned as a raw material, and the upper liquid is a liquid ammonia phase dissolved in ammonium chloride. It is sent to an evaporator and heated to 10°C to evaporate the liquid ammonia into gas, and then condensed to -40°C by a condenser. The liquid is returned as a raw material, and the solid at the bottom of the evaporator is ammonium chloride. The filter cake is a silicon nitride precursor solid and a small amount of liquid ammonia, toluene and ammonium chloride remaining in the silicon nitride precursor. The filter cake is then washed with liquid ammonia, filtered after washing, and washed and filtered 5 times in total, and then dried with hot nitrogen to obtain a silicon nitride precursor.

[0101] The silicon nitride precursor is then added to a rotary furnace via a conveyor. The rotation speed of the rotary furnace is set to 3 rpm. The silicon nitride precursor is calcined at 1000°C for 0.5 h in a nitrogen atmosphere to thermally decompose the silicon nitride precursor into amorphous silicon nitride powder. The silicon nitride precursor is then sent to a push plate furnace for high-temperature calcination. It is calcined at 1700°C for 1 h in a nitrogen atmosphere to obtain the product silicon nitride powder.

[0102] Implementation column 7:

[0103] This embodiment adopts Figure 1 The device shown in the figure produces silicon nitride powder by liquid phase method, as follows:

[0104] Use high-purity nitrogen to replace the air in the powder preparation system to an inert environment to ensure that O2 is less than 1ppm and H2O is less than 1ppm in the atmosphere. Mix 40 volumes of liquid ammonia at -40°C and 5 volumes of normal hexane to form the first raw material, which is fed into the tubular reactor at a flow rate of 2m / s using a shielded pump; at the same time, mix 2 volumes of silicon tetrachloride at -40°C and 6 volumes of normal hexane to form the second raw material, which is added to the tubular reactor at a flow rate of 2m / s. The tubular reactor has a diameter of 2cm and a pipeline length of 3m. The two streams of materials react rapidly after instantaneous mixing to form a pre-reaction slurry.

[0105] The pre-reaction slurry is passed into an aging reactor with a stirring unit and stays for 1 hour to form an aging reaction slurry at -40°C to ensure full reaction. The aging reaction slurry is sent to a three-in-one filtering, washing and drying device, and filtered first to obtain a filtrate and a filter cake. The filtrate is n-hexane, liquid ammonia and ammonium chloride dissolved in liquid ammonia. After the filtrate is sent to a phase separation tank and allowed to stand for 30 minutes, the lower liquid is a n-hexane phase, which is returned as a raw material, and the upper liquid is a liquid ammonia phase dissolved in ammonium chloride. It is sent to an evaporator and heated to 10°C to evaporate the liquid ammonia into gas, and then condensed to -40°C by a condenser. The liquid is returned as a raw material, and the solid at the bottom of the evaporator is ammonium chloride. The filter cake is a silicon nitride precursor solid and a small amount of liquid ammonia, n-hexane and ammonium chloride remaining in the silicon nitride precursor. The filter cake is then washed with liquid ammonia, filtered after washing, and washed and filtered 5 times in total, and then dried with hot nitrogen to obtain a silicon nitride precursor.

[0106] The silicon nitride precursor is then added to a rotary furnace via a conveyor. The rotation number of the rotary furnace is set to 1 rpm. The silicon nitride precursor is calcined at 800°C for 2 hours in a nitrogen atmosphere to thermally decompose the silicon nitride precursor into amorphous silicon nitride powder. The silicon nitride precursor is then sent to a push plate furnace for high-temperature calcination. It is calcined at 1500°C for 2 hours in a nitrogen atmosphere to obtain the product silicon nitride powder.

[0107] Comparative Example 1

[0108] The difference from Example 1 is that the tubular reactor is eliminated and the materials are directly reacted in the aging reactor.

[0109] Comparative Example 2

[0110] The difference from Example 1 is that the rotary furnace is replaced by a static pyrolysis furnace, and the silicon nitride precursor is subjected to low-temperature pyrolysis in the static pyrolysis furnace.

[0111] Table 1 Silicon nitride powder product indicators

[0112]

[0113] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for producing silicon nitride powder by a liquid phase method, characterized in that: The method adopts a device for producing silicon nitride powder by a liquid phase method, and the device comprises: A first raw material supply unit (10) is used to supply a mixed liquid of liquid ammonia and an organic solvent as a first raw material; A second raw material supply unit (20) is used to supply a mixed liquid of silicon halide and an organic solvent as a second raw material; A tubular reactor (30), wherein a reaction microchannel is provided in the tubular reactor (30), wherein the reaction microchannel has a reaction raw material inlet and a pre-reaction slurry outlet, wherein the reaction raw material inlet is connected to the first raw material supply unit (10) and the second raw material supply unit (20), respectively, and the tubular reactor (30) is used to cause the first raw material and the second raw material to undergo a liquid phase pre-reaction in the reaction microchannel to form a pre-reaction slurry; in the tubular reactor (30), the reaction microchannel has a diameter of 2 to 4 cm and a length of 3 to 5 m; An aging reaction kettle (40) has a pre-reaction slurry inlet and an aging reaction slurry outlet, the pre-reaction slurry inlet is connected to the pre-reaction slurry outlet, and the aging reaction kettle (40) is also provided with a stirring device, and the aging reaction kettle (40) is used to make the pre-reaction slurry undergo an aging reaction under stirring to form an aging reaction slurry; A solid-liquid separation unit (50) having an aging reaction slurry inlet, a filtrate outlet, and a solid phase outlet, wherein the aging reaction slurry inlet is connected to the aging reaction slurry outlet; A dynamic pyrolysis unit (60) having a solid phase inlet, the solid phase inlet being connected to the solid phase outlet, the dynamic pyrolysis unit (60) being used to perform low-temperature dynamic pyrolysis on the solid phase discharged from the solid-liquid separation unit (50) to form amorphous silicon nitride powder; A calcination unit (70), connected to the outlet of the dynamic pyrolysis unit (60), for performing high-temperature calcination and crystallization on the amorphous silicon nitride powder to obtain the silicon nitride powder product; a nitrogen-containing inert gas supply unit connected to the tubular reactor (30), the aging reactor (40), the solid-liquid separation unit (50) and the dynamic pyrolysis unit (60), and used for providing nitrogen-containing inert gas; A nitrogen-containing reducing gas supply unit, used for providing nitrogen-containing reducing gas, wherein the calcining unit (70) is switchably connected to the nitrogen-containing inert gas supply unit and / or the nitrogen-containing reducing gas supply unit; Wherein, the method comprises the following steps: Providing a mixed liquid of liquid ammonia and an organic solvent as a first raw material, and providing a mixed liquid of silicon halide and an organic solvent as a second raw material; The first raw material and the second raw material are introduced into the tubular reactor (30) to perform a liquid phase pre-reaction in the reaction microchannel thereof to obtain a pre-reaction slurry; the temperature of the liquid phase pre-reaction is -50 to 0°C, and the flow rates of the first raw material and the second raw material in the tubular reactor (30) are respectively 2 to 3 m / s; The pre-reaction slurry is introduced into an aging reaction kettle (40) and an aging reaction is performed under stirring to form an aging reaction slurry; the aging reaction temperature is -50 to 0°C, the time is 1 to 10 hours, and the stirring speed of the stirring device in the aging reaction kettle (40) is 3 to 15 r / min; The aged reaction slurry is subjected to solid-liquid separation to obtain a filtrate and a solid phase; the solid phase is then sent to a dynamic pyrolysis unit (60) to perform low-temperature dynamic pyrolysis to obtain an amorphous silicon nitride powder; The amorphous silicon nitride powder is subjected to high-temperature calcination and crystallization in a calcination unit (70) to obtain the silicon nitride powder product; Among them, the process of introducing the first raw material and the second raw material, the pre-reaction process, the aging reaction process, the solid-liquid separation process and the low-temperature dynamic pyrolysis are all carried out in a nitrogen-containing inert gas; the high-temperature calcination crystallization process is carried out in a nitrogen-containing inert gas and / or a nitrogen-containing reducing gas.

2. The method for producing silicon nitride powder by liquid phase method according to claim 1, characterized in that: In the first raw material, the volume ratio of the liquid ammonia to the organic solvent is 5-8:1, and in the second raw material, the volume ratio of the silicon halide to the organic solvent is 1:2-9.

3. The method for producing silicon nitride powder by liquid phase method according to claim 2, characterized in that: The organic solvent is selected from one or more of toluene, xylene and hexane.

4. The method for producing silicon nitride powder by a liquid phase method according to any one of claims 1 to 3, characterized in that: The device further comprises: a static phase separation tank (80) connected to the filtrate outlet; the method further comprises: performing static phase separation on the filtrate in the static phase separation tank (80) to obtain an upper liquid ammonia layer and a lower solvent layer.

5. The method for producing silicon nitride powder by liquid phase method according to claim 4, characterized in that: The static phase separation tank (80) has an upper liquid outlet and a lower liquid outlet, and the device further comprises: an organic solvent supply unit (90) connected to the first raw material supply unit (10) and the second raw material supply unit (20) respectively, for supplying the organic solvent; the lower liquid outlet is connected to the inlet of the organic solvent supply unit (90); a liquid ammonia supply unit (100) connected to the first raw material supply unit (10) for supplying the liquid ammonia; and a silicon halide supply unit (110) connected to the second raw material supply unit (20) for supplying the silicon halide; the method further comprises: extracting the solvent in the lower solvent layer and returning it to the organic solvent supply unit (90).

6. The method for producing silicon nitride powder by liquid phase method according to claim 5, characterized in that: The device further comprises: an evaporation unit (120) having an upper liquid inlet and an ammonia outlet, the upper liquid inlet being connected to the upper liquid outlet; a condensation unit (130) having an ammonia inlet and a recovered liquid ammonia outlet, the ammonia inlet being connected to the ammonia outlet, and the recovered liquid ammonia outlet being connected to the liquid ammonia supply unit (100); the method further comprises: evaporating the material in the upper liquid ammonia layer to obtain ammonia; condensing the ammonia to form recovered liquid ammonia, and then returning the recovered liquid ammonia to the liquid ammonia supply unit (100).

7. The method for producing silicon nitride powder by liquid phase method according to claim 6, characterized in that: The solid-liquid separation step comprises: The solid-liquid separation unit (50) is a filtering, drying and washing integrated machine, the filtering, drying and washing integrated machine having the aging reaction slurry inlet, the detergent inlet, the filtrate outlet and the solid phase outlet; the aging reaction slurry is filtered, washed and dried in the filtering, drying and washing integrated machine in sequence to obtain the filtrate and the solid phase; or, The solid-liquid separation unit (50) comprises a centrifuge and a stirring dryer which are connected in sequence, the centrifuge being provided with the aging reaction slurry inlet and the detergent inlet, the stirring dryer having the solid phase outlet, and the centrifuge being provided with the filtrate outlet; after the aging reaction slurry is centrifugally filtered in the centrifuge, a detergent is added to the centrifuge for centrifugal washing, and finally the washed filter cake is dried in the stirring dryer to obtain the solid phase; wherein the liquid phase separated in the centrifuge is the filtrate.

8. The method for producing silicon nitride powder by liquid phase method according to claim 7, characterized in that: The recovered liquid ammonia outlet is also connected to the detergent inlet; the method further comprises: passing part of the recovered liquid ammonia into the drying and washing machine or the centrifuge for use as a detergent.

9. The method for producing silicon nitride powder by a liquid phase method according to any one of claims 1 to 3, characterized in that: During the low-temperature dynamic pyrolysis process, the pyrolysis temperature is 500-1000° C. and the pyrolysis time is 0.5-2 hours; during the high-temperature calcination crystallization process, the calcination temperature is 1400-1700° C. and the calcination time is 1-3 hours.

10. The method for producing silicon nitride powder by a liquid phase method according to any one of claims 1 to 3, characterized in that: The silicon halide is one or more of silicon tetrachloride, silicon tetrabromide and silicon tetraiodide.

11. The method for producing silicon nitride powder by a liquid phase method according to any one of claims 1 to 3, characterized in that: The nitrogen-containing inert gas is nitrogen, or a mixture of nitrogen and argon; the nitrogen-containing reducing gas is a mixture of nitrogen and a reducing gas, and the reducing gas is hydrogen and / or ammonia.

12. The method for producing silicon nitride powder by liquid phase method according to claim 1, characterized in that: The dynamic pyrolysis unit (60) is a rotary kiln or a fluidized bed, and the calcination unit (70) is a rotary kiln, a push plate kiln or a roller kiln.

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