Device for preparing high-thermal-conductivity silicon nitride nano-powder from high-molecular-weight solid polycarbosilane

Abstract

The utility model discloses a device for preparing high-thermal-conductivity silicon nitride nano-powder by using high-molecular-weight solid polycarbosilane, and relates to a material synthesis device. Comprising a gas circulation atomization device and an ammonification pyrolysis device. The gas circulation atomization device comprises an atomization nozzle, a cyclone separator, a circulation fan, a solvent condensation device and corresponding connecting air pipes, and all the connecting parts are connected in a sealed mode. The ammoniation pyrolysis device is vertically installed and comprises three sections of heating areas. Atomizing the high-molecular-weight polycarbosilane organic solution into liquid drops in a gas circulation atomization device, drying and converting the liquid drops into PCS powder, and condensing and recycling the organic solvent at the same time; pCS powder is carried by carrier gas to enter an ammoniation pyrolysis device, and in the ammoniation pyrolysis device, the PCS powder is gradually heated and reacts in ammonia gas to generate silicon nitride powder. According to the device, a high-molecular-weight polycarbosilane solution can be atomized and dried into polycarbosilane powder, and then the polycarbosilane powder is heated, ammoniated and pyrolyzed into silicon nitride ceramic powder.

Description

Technical Field

[0001] The utility model relates to a material synthesis device, in particular to a device for preparing high-thermal-conductivity silicon nitride nano powder by utilizing high-molecular-weight solid polycarbosilane. Background Art

[0002] Silicon nitride ceramics also have excellent properties such as high strength (600-800MPa), good thermal conductivity, good thermal shock resistance, wear resistance, and corrosion resistance. It is a ceramic substrate material with excellent comprehensive performance. The preparation of high-performance silicon nitride ceramics requires silicon nitride ceramic powder with narrow particle size distribution, uniform particles, and low impurity content. At present, the methods for preparing silicon nitride powder mainly include direct nitridation of silicon powder, self-propagating high-temperature synthesis, carbon thermal reduction, and silicon imide thermal decomposition. Among them, the direct nitridation of silicon powder, self-propagating high-temperature synthesis, and carbon thermal reduction methods for preparing silicon nitride powder have simple raw material sources, short synthesis steps, and low costs. However, these methods use solid raw materials such as elemental silicon and silicon dioxide. The prepared silicon nitride powder is mixed with raw materials due to incomplete reaction of the solid raw materials, making it difficult to prepare high-purity silicon nitride powder. In addition, due to the influence of the raw materials, the prepared silicon nitride powder has a wide particle size distribution, which will affect the various properties of the final silicon nitride ceramics. The pyrolysis method of silicon imide is to directly react silicon tetrachloride with liquid ammonia to prepare silicon imide intermediates and then pyrolyze them to form silicon nitride powder. The silicon nitride powder prepared by this method has high particle size purity and a narrow particle size distribution range, but the raw material silicon tetrachloride is easily hydrolyzed and liquid ammonia is highly corrosive. The reaction needs to be carried out under high pressure conditions and has high requirements for equipment. Currently, only Ube of Japan has successfully implemented commercial production.

[0003] In addition to the above methods, the precursor conversion method can also be used to prepare silicon nitride ceramics. This method uses silicon-containing and oxygen-free organic substances such as polycarbosilane and polysilazane as precursors, processes and solidifies them, and then prepares ceramic materials through high-temperature inorganicization. This method has the advantages of high product purity and strong controllability of composition design. The core difficulty of using the precursor conversion method to prepare thermal conductive Si3N4 powder lies in the control of particle size, purity and crystallinity, which is closely related to the preparation device. When high molecular weight polycarbosilane is used as a precursor, the design and development of suitable equipment can give full play to the advantages of high molecular weight polycarbosilane (no cross-linking and curing after processing) and realize the batch preparation of high-purity and high thermal conductivity silicon nitride powder. There is currently no relevant information reported. Summary of the invention

[0004] The utility model aims to provide a device for preparing high thermal conductivity silicon nitride nano powder by using high molecular weight solid polycarbosilane.

[0005] The utility model comprises a gas circulation atomization device and an ammoniation pyrolysis device;

[0006] The gas circulation atomization device comprises an atomizing nozzle, a cyclone separator, a circulation fan, a solvent condensing device and corresponding connecting air ducts; all connecting parts are sealed connections; the cyclone separator, the circulation fan and the connecting air duct form a closed internal circulation loop, the cyclone separator is located below the atomizing nozzle, and is connected to the circulation fan through the air duct, the circulation fan extracts the carrier gas in the cyclone separator and blows it to the connecting air duct, and then returns to the cyclone separator; the atomizing nozzle is arranged in the connecting air duct, and a throttling orifice plate is arranged at the air outlet of the circulation fan; the inlet and outlet of the solvent condensing device are respectively located on both sides of the throttling orifice plate, and are connected to the connecting air duct;

[0007] The ammoniation pyrolysis device is installed vertically, and includes three heating zones, a gas preheater, a powder downpipe and a powder collection tank; the three heating zones are low temperature zone, medium temperature zone and high temperature zone from bottom to top; isolation plates with holes are provided between the three heating zones, and the isolation plates are used to ensure that the powder is in a gas-solid fluid state and reduce the up and down flipping of the powder between different heating zones in the ammoniation pyrolysis device; the powder downpipe and the powder collection tank are arranged below the ammoniation pyrolysis device;

[0008] After the nitrogen S and ammonia T are mixed, they are divided into three paths. The first path is to assist the atomization of the PCS solution through the atomizing nozzle; the second path of the mixed gas is preheated by the gas preheater and then sprayed out from the purge nozzle, and the PCS atomized powder after the solvent is separated passes through the conveying pipe in a gas-solid mixed state and enters the ammoniation pyrolysis device; the third path of gas is preheated by the gas preheater and then blows up the gas-solid fluid in the ammoniation pyrolysis device through the gas distribution plate, and slowly flows from the bottom to the top of the ammoniation pyrolysis device.

[0009] The gas circulation atomization device uses ammonia-nitrogen mixed gas as the working atmosphere, and the ammonia-nitrogen refluxes and circulates under the action of the circulation fan;

[0010] The cyclone separator, the circulating fan and the connecting air duct are provided with heating to heat the circulating ammonia-nitrogen mixed gas. The working temperature of the gas inside the gas circulating atomizing device is 100-300°C.

[0011] The atomizing nozzle can be a pressure type, air flow type, rotary atomizer, ultrasonic atomizer or electrostatic atomizer. The droplet size of the PCS solution after atomization is adjusted by the selection of the atomizing nozzle and the working conditions, and finally the particle size of the silicon nitride powder is controlled.

[0012] The gas circulation atomization device is a sealed cycle, and the gas supply speed is slightly greater than the gas discharge speed to reduce the organic solvent from entering the ammoniation pyrolysis device. The pressure of the gas circulation atomization device is greater than the pressure of the ammoniation pyrolysis device to ensure that the ammonia and nitrogen mixed gas in the ammoniation pyrolysis device does not flow back into the gas circulation atomization device.

[0013] The ratio of circulating gas to cooling reflux gas is 5:1 to 1:5; the organic solvent in the sprayed PCS solution can be condensed and recovered.

[0014] The ammoniation pyrolysis device is a heat treatment furnace installed vertically and heated in three stages, with the temperature gradually increasing from bottom to top. The heating temperature of the first stage is 400-700°C, the heating temperature of the second stage is 700-1000°C, and the heating temperature of the third stage is 1500-1700°C. PCS powder enters from the bottom of the ammoniation pyrolysis device under the purge of ammonia and nitrogen, and maintains its gas-solid mixed state (fluidized state). The gas-solid fluid continuously entering from the bottom flows to the top in the ammoniation pyrolysis device, and the PCS powder therein passes through the first, second, and third heating stages in turn. The powder temperature gradually increases, and ammoniation decarburization, high-temperature pyrolysis, and high-temperature crystallization reactions gradually occur to form silicon nitride powder, which is finally discharged from the top of the ammoniation pyrolysis device to the silicon nitride powder collection tank.

[0015] The working principle of the utility model is given below:

[0016] High molecular weight PCS is dissolved in an organic solvent to form a solution. The gas circulation atomization device is used to spray the solution into droplets. The organic solvent in the PCS solution evaporates and dries to form PCS powder in the hot circulating gas. The hot circulating gas containing organic solvent vapor and PCS powder passes through a cyclone separator to separate the PCS powder from the solvent. A part of the circulating high-temperature gas is directly circulated, and the other part is cooled. The organic solvent in the cooled gas is recovered by condensation, and the gas after the organic solvent is separated enters the circulation atomization device again. The PCS powder after the solvent is separated enters the ammoniation pyrolysis device through the purge of an ammonia / nitrogen mixture. In the ammoniation pyrolysis device, the PCS powder is gradually heated and reacted in ammonia to form silicon nitride powder, and the formed silicon nitride powder is collected into a powder collection tank through a powder downcomer.

[0017] The utility model has the following advantages:

[0018] 1. The utility model device utilizes a gas circulation atomization system to atomize high molecular weight polycarbosilane to form nanoparticles, which can effectively control the grain size and shape. In addition, the ammonia pyrolysis device is used to carry out ammonia decarburization, high temperature pyrolysis and other reactions on the atomized nano PCS powder in the form of gas-solid fluid, thereby avoiding the phenomenon of powder agglomeration during the reaction process and realizing the preparation of high-purity and fine-grained silicon nitride powder.

[0019] 2. The utility model integrates the circulating atomization device with the subsequent ammoniation pyrolysis device to reduce the problems of nano powder accumulation and adhesion during the preparation process and the pollution caused by the contact of intermediate products with air, further improve the powder purity, reduce the O content, and improve the thermal conductivity of the powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the device structure for preparing high thermal conductivity silicon nitride nanopowder using high molecular weight solid polycarbosilane.

[0021] The symbols in the figure are: atomizing circulation device 1, atomizing nozzle 101, cyclone separator 201, circulating fan 202, connecting air duct 203, solvent condenser 204, throttling orifice plate 205, purge nozzle 206, conveying pipe 207, ammoniation pyrolysis device 3, ammoniation pyrolysis device first stage heating 3a, second stage heating 3b, third stage heating 3c, gas preheater 301, gas distribution plate 302, separation baffle 303, high temperature cyclone separator 304, tail gas cooling filter 305, powder down pipe 401, powder collection tank 402, PCS solution R, ammonia S, nitrogen T, xylene X, tail gas Y. DETAILED DESCRIPTION

[0022] The present invention is further described below with specific embodiments:

[0023] like Figure 1 The device embodiment of the utility model for preparing high thermal conductivity silicon nitride nanopowder by using high molecular weight solid polycarbosilane comprises a gas circulation atomization device 1 and an ammoniation pyrolysis device 3;

[0024] The gas circulation atomization device 1 is composed of a cyclone separator 201, a circulation fan 202, a connecting air duct 203, a solvent condenser 204, a throttling orifice plate 205, a purge nozzle 206, a delivery pipe 207 and other components; the cyclone separator 201, the circulation fan 202, and the connecting air duct 203 form a closed internal circulation loop, and the circulation fan 202 extracts the carrier gas in the cyclone separator 201 and blows it to the connecting air duct 203, and then returns it to the cyclone separator 201; the cyclone separator 201 is located below the atomizing nozzle 101 , connected to the circulating fan 202 through an air duct, used to separate the PCS powder from the carrier gas; the PCS powder settles to the bottom of the cyclone separator 201 after gas-solid separation in the cyclone separator 201, and the ammonia-nitrogen mixed gas with xylene vapor passes through the cyclone separator 201 and enters the connecting air duct 203 through the circulating fan 202, and is separated into two branches under the flow regulation of the throttle orifice plate 205; one branch directly flows back to the position where the atomizing nozzle 101 is located, and the other branch enters the solvent condenser 204;

[0025] The atomizing nozzle 101 is disposed in the connecting air duct 203 , and the throttling orifice plate 205 is disposed at the air outlet of the circulating fan 202 (and is also located in the connecting air duct 203 ). The inlet and outlet of the solvent condenser 204 are respectively located on both sides of the throttling orifice plate 205 and are connected to the connecting air duct 203 .

[0026] The purge nozzle 206 is provided at one end of the delivery pipe 207, and the other end of the delivery pipe 207 is connected to the ammoniation pyrolysis device 3. The PCS powder particles in the cyclone separator 201 are formed into a gas-solid mixed fluid state under the action of the mixed gas of nitrogen B and ammonia C sprayed from the purge nozzle 206, and enter the ammoniation pyrolysis device 3 through the delivery pipe 207.

[0027] The ammoniation pyrolysis device 3 is composed of a continuous three-stage heating device, a gas preheater 301, a gas distribution plate 302, a separation baffle 303, a high-temperature cyclone separator 304, an exhaust gas cooling filter 305, a powder downpipe 401 and a powder collection tank 402. The gas circulation atomization device 1 uses an ammonia-nitrogen mixed gas as the working atmosphere, and the ammonia-nitrogen refluxes under the action of the circulation fan 202. The cyclone separator 201, the circulation fan 202 and the connecting air duct 203 are provided with heating, which is used to heat the circulating ammonia-nitrogen mixed gas to 100-300°C.

[0028] Infusible but soluble PCS with a number average molecular weight of 5000 to 13000 is prepared into a solution A with a concentration of 20% to 50% with xylene X, and the PCS solution R is sprayed into the gas circulation atomization device 1 through the atomizing nozzle 101. The atomizing nozzle 101 is selected to be a gas pressure atomizing nozzle, which uses an ammonia-nitrogen mixed gas to assist in spraying and atomizing the PCS solution R. The sprayed PCS solution R droplets are converted into PCS powder in the high-temperature circulating ammonia-nitrogen mixed gas as the solvent xylene evaporates, and xylene vapor is also mixed into the ammonia-nitrogen mixed gas. After the PCS powder undergoes gas-solid separation in the cyclone separator 201, it settles to the bottom of the cyclone separator 201. The ammonia-nitrogen mixed gas with xylene vapor passes through the cyclone separator 201 and enters the connecting air duct 203 through the circulating fan 202, and is separated into two branches under the action of the throttling orifice plate 205; one branch directly returns to the location of the atomizing nozzle 101, and the other branch enters the solvent condenser 204; the flow ratio of the directly refluxed gas to the gas entering the solvent condenser is 2:1. The mixed gas entering the solvent condenser 204 undergoes condensation of xylene vapor, and xylene X is recovered through the pipeline. A part of the remaining ammonia-nitrogen mixed gas is discharged as tail gas Y, and a part enters the connecting air duct 203 through the outlet channel of the solvent condenser 204, and continues to be circulated as a carrier gas. The flow rate of the exhaust gas Y is slightly smaller than the flow rate of the ammonia-nitrogen mixed gas entering the atomizing nozzle 101, so that the pressure of the gas circulation atomizing device 1 can be maintained greater than the pressure of the ammoniation pyrolysis device 3, and the xylene vapor entering the ammoniation pyrolysis device can be reduced.

[0029] After the nitrogen S and ammonia T are mixed, they are divided into three paths. The first path is passed through the aforementioned atomizing nozzle 101 to assist the atomization of the PCS solution. The second path of the mixed gas is preheated by the gas preheater 301 and then sprayed out from the purge nozzle 206, and the PCS atomized powder after the solvent is separated passes through the conveying pipe 207 in a gas-solid mixed state and enters the ammoniation pyrolysis device 3. The third path of gas is preheated by the gas preheater 301 and then blows up the gas-solid fluid in the ammoniation pyrolysis device 3 through the gas distribution plate 302, and slowly flows from the bottom to the top of the ammoniation pyrolysis device 3.

[0030] The reaction area in the ammoniation pyrolysis device 3 adopts three continuous heating sections from bottom to top, including: the first heating zone 3a at the bottom, which is a low-temperature zone with a heating temperature of 400-700°C, and is the ammoniation heating section for PCS powder. In this heating section, PCS powder is ammoniation-decarburized to form silazane powder; the middle section is the second heating zone 3b, which is a medium-temperature zone with a heating temperature of 700-1000°C. In this heating section, silazane powder undergoes inorganic transformation and is gradually deaminated and decarburized to form amorphous silicon nitride powder; the top is the third heating zone 3c, which is a high-temperature zone with a heating temperature of 1500-1700°C and is used for high-temperature crystallization treatment. Amorphous silicon nitride powder is converted into crystalline silicon nitride in this heating section.

[0031] A porous separation baffle 303 is provided between the first heating section 3a and the second heating section 3b of the ammoniation pyrolysis device 3, and between the second heating section 3b and the third heating section 3c. The separation baffle 303 reduces the up and down movement of the powder in the ammoniation pyrolysis device 3 while ensuring that the powder flows upward in a gas-solid fluid state. The separation baffle 303 has holes, and the separation baffle 303 is used to reduce the up and down movement of the powder between different heating sections in the ammoniation pyrolysis device while ensuring that the powder is in a gas-solid fluid state.

[0032] The high-temperature cyclone separator 304 is used to separate the silicon nitride powder from the tail gas after the reaction. The high-temperature cyclone separator 304 is arranged on the top of the ammoniation pyrolysis device 3 and is connected to the tail gas cooling filter 305 .

[0033] A powder downcomer 401 and a powder collecting tank 402 are provided below the ammoniation pyrolysis device 3. The powder downcomer 401 is connected to the powder collecting tank 402. The powder downcomer 401 is located at the upper part of the third heating zone 3c. The crystallized silicon nitride powder formed by the third heating zone 3c falls from the top of the powder downcomer 401 and is collected in the powder collecting tank 402. The tail gas Y is discharged after the suspended silicon nitride powder is separated by the high-temperature cyclone separator 304. The separated tail gas Y is cooled by the tail gas cooling filter 305 and the residual silicon nitride powder is filtered before being discharged.

[0034] The above embodiments are only preferred embodiments of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of application of the present invention shall still fall within the scope of the patent coverage of the present invention.

Claims

1. A device for preparing high thermal conductivity silicon nitride nanopowder using high molecular weight solid polycarbosilane, characterized in that It includes a gas circulation atomization device and an ammoniation pyrolysis device; The gas circulation atomization device comprises an atomizing nozzle, a cyclone separator, a circulation fan, a solvent condensing device and corresponding connecting air ducts; all connecting parts are sealed connections; the cyclone separator, the circulation fan and the connecting air duct form a closed internal circulation loop, the cyclone separator is located below the atomizing nozzle, and is connected to the circulation fan through the air duct, the circulation fan extracts the carrier gas in the cyclone separator and blows it to the connecting air duct, and then returns to the cyclone separator; the atomizing nozzle is arranged in the connecting air duct, and a throttling orifice plate is arranged at the air outlet of the circulation fan; the inlet and outlet of the solvent condensing device are respectively located on both sides of the throttling orifice plate, and are connected to the connecting air duct; The ammoniation pyrolysis device is vertically installed and includes three heating zones and a gas preheater. The three heating zones are, from bottom to top, a low temperature zone, a medium temperature zone, and a high temperature zone. An isolation plate with holes is provided between each zone of the three heating zones. The isolation plate is used to ensure that the powder is in a gas-solid fluid state to reduce the up and down movement of the powder between different heating zones in the ammoniation pyrolysis device. A powder downcomer and a powder collecting tank are provided below the ammoniation pyrolysis device; After the nitrogen S and ammonia T are mixed, they are divided into three paths. The first path is to assist the atomization of the PCS solution through the atomizing nozzle; the second path of the mixed gas is preheated by the gas preheater and then sprayed out from the purge nozzle, and the PCS atomized powder after the solvent is separated passes through the conveying pipe in a gas-solid mixed state and enters the ammoniation pyrolysis device; the third path of gas is preheated by the gas preheater and then blows up the gas-solid fluid in the ammoniation pyrolysis device through the gas distribution plate, and slowly flows from the bottom to the top of the ammoniation pyrolysis device.

2. A device for preparing high thermal conductivity silicon nitride nanopowder using high molecular weight solid polycarbosilane as claimed in claim 1, characterized in that The cyclone separator, the circulating fan and the connecting air duct are provided with heating to heat the circulating ammonia-nitrogen mixed gas. The working temperature of the gas inside the gas circulating atomizing device is 100-300°C.

3. A device for preparing high thermal conductivity silicon nitride nanopowder using high molecular weight solid polycarbosilane as claimed in claim 1, characterized in that The atomizing nozzle adopts a pressure type, air flow type, rotary atomizer, ultrasonic atomizer or electrostatic atomizer. The droplet size of the PCS solution after atomization is adjusted by the selection of the atomizing nozzle and the working conditions to control the particle size of the silicon nitride powder.

4. A device for preparing high thermal conductivity silicon nitride nanopowder using high molecular weight solid polycarbosilane as claimed in claim 1, characterized in that The gas circulation atomization device is a sealed circulation, and the gas supply speed is greater than the gas discharge speed to reduce the organic solvent entering the ammoniation pyrolysis device; the pressure of the gas circulation atomization device is greater than the pressure of the ammoniation pyrolysis device to ensure that the ammonia and nitrogen mixed gas in the ammoniation pyrolysis device does not flow back into the gas circulation atomization device.

5. A device for preparing high thermal conductivity silicon nitride nanopowder using high molecular weight solid polycarbosilane as claimed in claim 1, characterized in that The ammoniation pyrolysis device is a heat treatment furnace with gradually increasing temperature from bottom to top. The heating temperature of the first section of the three-section heating zone is 400-700°C, the heating temperature of the second section is 700-1000°C, and the heating temperature of the third section is 1500-1700°C.

6. A device for preparing high thermal conductivity silicon nitride nanopowder using high molecular weight solid polycarbosilane as claimed in claim 1, characterized in that The silicon nitride powder prepared by the device is discharged from the top of the ammoniation pyrolysis device and reaches the powder collection tank through the powder downcomer.

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