Device for preparing high-thermal-conductivity silicon nitride nano-powder by using meltable solid polycarbosilane

Abstract

The utility model discloses a device for preparing high-thermal-conductivity silicon nitride nano-powder by using meltable solid polycarbosilane, and relates to the field of material synthesis equipment. Comprising a PCS atomization-crosslinking tower, a fluidization-heat treatment furnace, a silicon nitride powder collector, a gas heat return pipe and a tail gas cooler, the PCS atomization-crosslinking tower is mounted above the fluidization-heat treatment furnace, and PCS crosslinking powder formed in the atomization-crosslinking tower directly falls into the fluidization-heat treatment furnace; a powder outlet of the fluidization-heat treatment furnace is connected with a silicon nitride powder collector, three fluidized bed heating sections are horizontally arranged in the fluidization-heat treatment furnace, the positions of the three fluidized bed heating sections are gradually lowered, and the heating temperature is gradually increased; the gas heat return pipe is installed in the furnace top cover, and tail gas is exhausted from the furnace top cover, cooled through the tail gas cooler and then emptied. The method can realize rapid and complete crosslinking of the powder, inhibits adhesion and agglomeration among powder particles in the reaction process, and realizes batch production of the high-purity and high-thermal-conductivity silicon nitride nano-powder.

Description

Technical Field

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

[0002] Silicon nitride ceramics have good thermal conductivity, high strength, and excellent thermal vibration resistance. They are excellent structural ceramics and are widely used in ceramic bearings, electronic packaging, thermal conductive substrates and other fields. The preparation of high-performance silicon nitride ceramics requires silicon nitride powder with appropriate particle size 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. However, due to the solid-phase reaction problem, the purity of the powder is difficult to improve in the direct nitridation of silicon powder, self-propagating high-temperature synthesis and carbon thermal reduction methods. Therefore, high-purity powder is mainly prepared by silicon imide thermal decomposition. Ube of Japan uses silicon imide thermal decomposition to achieve industrial production of high-quality silicon nitride powder, but due to the use of liquid ammonia and silicon tetrachloride raw materials, this preparation method requires high-pressure anti-corrosion equipment and has high requirements for equipment.

[0003] The precursor conversion method uses silicon-containing organic polysilicon carbosilane (PCS) as a precursor and pyrolyzes it in ammonia to prepare ceramics whose main component is silicon nitride. This method uses organic matter as the precursor (especially soluble and fusible organic matter) and can be formed through simple processing, with low requirements for molding equipment; in addition, the physical properties of the precursor can be adjusted by designing the elemental composition and molecular structure of the precursor to adapt to processing, and finally prepare the composition and morphology of the ceramic, and it is expected to prepare high-purity silicon nitride powder. However, there is currently no relevant equipment that can achieve the preparation of high-purity silicon nitride powder using fusible polycarbosilane as a precursor. Utility Model Content

[0004] The utility model aims to provide a device for preparing high thermal conductivity silicon nitride nano powder by using fusible solid polycarbosilane, which realizes the preparation of high-purity silicon nitride powder by using fusible solid polycarbosilane as a precursor.

[0005] The utility model is mainly composed of two parts. The first part is a PCS atomization-crosslinking tower for atomizing and crosslinking PCS, and the second part is a fluidization-heat treatment furnace for pyrolyzing PCS crosslinked powder into silicon nitride powder. The PCS atomization-crosslinking tower is installed above the fluidization-heat treatment furnace, and the PCS crosslinked powder formed in the atomization-crosslinking tower directly falls into the fluidization-heat treatment furnace; a silicon nitride powder collector, a gas heat recovery pipe and an exhaust gas cooler are also provided; the powder outflow outlet of the fluidization-heat treatment furnace is connected to the silicon nitride powder collector, and the position of the silicon nitride powder collector is lower than the powder outlet of the fluidization-heat treatment furnace. The silicon nitride powder collector is used to collect the formed silicon nitride powder; the fluidized-heat treatment furnace is provided with three fluidized bed heating sections, which are arranged horizontally, with the positions gradually decreasing and the heating temperature gradually increasing; the upper parts of the three fluidized bed heating sections share a furnace top cover space, the gas heat recovery pipe is installed inside the furnace top cover, the gas heat recovery pipe is used to utilize the waste heat of the tail gas of the fluidized-heat treatment furnace to preheat the raw material intake air, the tail gas cooler is arranged at the end of the fluidized-heat treatment furnace, i.e., above the third fluidized bed heating section, the tail gas is discharged from the furnace top cover, cooled by the tail gas cooler, and then discharged for treatment.

[0006] The atomization-cross-linking tower is provided with a PCS atomization nozzle, which is used to atomize the molten PCS into droplets. The atomization nozzle adopts a pressure type, air flow type, rotary atomizer, ultrasonic atomizer or electrostatic atomizer and other structures. The viscosity of the PCS melt is regulated according to different PCS melting temperatures and molecular weights, and then the size of the atomized PCS droplets is adjusted by using different types of atomization nozzles. The atomization nozzle has a separation hood in the atomization-cross-linking tower, and an inert gas is introduced into the separation hood. The PCS spray is carried out in the inert gas to ensure that the PCS melt is fully atomized before cross-linking. The cross-linking agent gas is introduced into the outside of the separation hood of the atomization-cross-linking tower. In the lower section of the atomization-cross-linking tower, the PCS droplets are mixed with the cross-linking agent gas to quickly complete the cross-linking curing process to form a PCS cross-linked powder.

[0007] The atomization-crosslinking tower has heating and temperature control functions, and the temperature control range is 200-400° C. The heating temperature can ensure that the PCS remains in a molten state during atomization and that the PCS droplets can be quickly crosslinked into PCS crosslinked powder.

[0008] The cross-linking agent gas is an unsaturated hydrocarbon such as gaseous cyclohexene, 1-hexene, 1-octene, or a halogenated hydrocarbon such as carbon tetrachloride and chlorobenzene; the amount of the cross-linking agent gas introduced is proportional to the amount of PCS introduced, and the mass ratio of the cross-linking agent gas to PCS is 1:20-1000. The cross-linking agent can ensure that the PCS droplets are completely cross-linked and cured and there is no excess cross-linking agent.

[0009] The atomization-crosslinking tower is vertically installed above the feed inlet of the fluidization-heat treatment furnace, and the PCS crosslinked powder formed in the atomization-crosslinking tower can directly fall into the first fluidized bed heating section of the fluidization-heat treatment furnace.

[0010] The fluidized-heat treatment furnace contains three fluidized bed heating sections. The first section is the decarbonization and ammoniation section, with a heating temperature of 400-700°C. The PCS cross-linked powder is decarbonized and ammonified into silazane powder; the second section is the high-temperature pyrolysis section, with a heating temperature of 700-1000°C. The silazane powder is pyrolyzed and inorganically formed into amorphous silicon nitride powder; the third section is the high-temperature crystallization section, with a heating temperature of 1500-1700°C. The amorphous silicon nitride powder is crystallized to form high-purity silicon nitride powder. Before the powder is heat treated, the fluidized bed is used for the powder fluidization process. The working gas of the first and second fluidized beds is a mixed gas of ammonia and inert gas, and the working gas of the third fluidized bed is inert gas.

[0011] Each of the three fluidized bed heating sections is heated and temperature controlled by a heating rod, and a porous gas distribution plate is installed at the bottom to evenly distribute and blow out the working gas. The blown working gas can blow up the powder and keep it in a fluidized boiling state. There is a partition in the middle of the fluidized bed heating section, which divides each section into two compartments connected at the bottom. The powder that falls from the atomization-crosslinking tower or is processed by the previous fluidized bed heating section first enters the first compartment, flows slowly downward, then enters the other compartment, slowly rises in the other compartment, and leaves the fluidized bed heating section from the top;

[0012] The three fluidized bed heating sections are arranged horizontally, and the positions of the first, second and third fluidized bed heating sections are gradually lowered to ensure that the powder can flow to the next fluidized bed heating section; finally, the crystalline silicon nitride powder treated by the third fluidized bed heating section is collected by a powder collector. The three fluidized bed heating sections share a furnace top cover, and the tail gas of the three fluidized bed heating sections is combined and discharged at the furnace top cover; a gas regenerator is set on the furnace top cover, and the gas regenerator uses high-temperature tail gas to preheat the incoming reaction gas; the tail gas is further cooled and then discharged.

[0013] The utility model has the following advantages:

[0014] (1) The device of the utility model utilizes an atomization crosslinking system to atomize fusible solid polycarbosilane to form nanoparticles, and simultaneously performs active gas crosslinking in the gas phase, which can give full play to the advantages of the high specific surface area of ​​the nanoparticles and realize rapid and complete crosslinking of the powder.

[0015] (2) Before the ammoniation pyrolysis reaction, a fluidized bed device is used to form a gas-solid fluid to achieve full contact between the cross-linked powder particles and the reaction atmosphere, thereby increasing the reaction speed and uniformity and inhibiting adhesion and agglomeration between the powder particles during the reaction.

[0016] (3) The device of the utility model can realize the mass production of high-purity and high-thermal-conductivity silicon nitride nanopowder. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the structure of a device for preparing high thermal conductivity silicon nitride nanopowder using fusible solid polycarbosilane.

[0018] Among them, PCS atomization-cross-linking tower 1, atomizing nozzle 101, separation cover 102, fluidizing-heat treatment furnace 2, first section 2A of fluidizing-heat treatment furnace, second section 2B of fluidizing-heat treatment furnace, third section 2C of fluidizing-heat treatment furnace, first section charging barrel rod 2A1, first section heating rod 2A2, first section middle isolation plate 2A3, first section gas distribution plate 2A4, first section air intake regulating valve 2A5, second section air intake regulating valve 2B5, second section gas preheater 2B6, third section air intake regulating valve 2C5, third section gas preheater 2C6, silicon nitride powder collector 3, gas heat recovery pipe 4, tail gas cooler 5, molten PCS A, nitrogen S, cross-linking agent cyclohexene T, ammonia-nitrogen mixed gas X, tail gas Y. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the utility model more clear, the following embodiments will further illustrate the utility model in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the utility model and are not used to limit the utility model. Existing conventional technical means may be used for those not clearly described in the utility model.

[0020] See also Figure 1 , the embodiment of the utility model comprises a PCS atomization-crosslinking tower 1, a fluidization-heat treatment furnace 2, a silicon nitride powder collector 3, a gas heat recovery pipe 4 and an exhaust gas cooler 5;

[0021] The PCS atomization-crosslinking tower 1 is installed above the fluidization-heat treatment furnace 2, and the PCS atomization-crosslinking tower 1 is used to atomize and crosslink the PCS; the PCS crosslinked powder formed in the PCS atomization-crosslinking tower 1 directly falls into the fluidization-heat treatment furnace 2, and the fluidization-heat treatment furnace 2 is used to convert the PCS crosslinked powder into silicon nitride powder.

[0022] The PCS atomization-cross-linking tower 1 is equipped with a PCS atomization nozzle 101. In the PCS atomization-cross-linking tower, the atomization nozzle 101 is heated to 380°C. The atomization nozzle 101 is used to keep the molten PCS in its liquid state and atomize it into droplets. A separation cover 102 is provided outside the atomization nozzle 101. The separation cover is a ring-shaped structure whose upper end is connected to the atomization nozzle and sealed, but whose lower end is open. Nitrogen S that assists in atomization is introduced into the inner space of the separation cover 102, and cross-linking agent cyclohexene T is introduced into the outer space of the separation cover 102. Under the action of the separation cover 102, after the molten PCS is sprayed out of the atomization nozzle 101, it will first be in the nitrogen atmosphere of the inner space of the isolation cover, and then driven by the airflow through the opening below the separation cover, and contact with the outer cross-linking agent cyclohexene to produce a cross-linking reaction. The separation cover 102 is used to separate the molten PCS A from the cross-linking agent cyclohexene T to ensure that the molten PCS A is fully atomized and does not contact the cross-linking agent cyclohexene T before being fully atomized, so as to avoid premature cross-linking reaction and affect the performance and quality of the product; in the lower section of the atomization-cross-linking tower 1, the PCS droplets are mixed with the cross-linking agent cyclohexene T and the cross-linking curing process is quickly completed to form PCS cross-linked powder.

[0023] The atomization-crosslinking tower 1 may have heating and temperature control functions, and the temperature control range is 200-400°C. The heating function is achieved by setting a heating element, and an electric heater may be used to provide the necessary heat. The heating element may be installed on the outside of the atomization-crosslinking tower 1 or embedded in the tower wall. A temperature sensor (such as a thermocouple, RTD, etc.) may be installed in the atomization-crosslinking tower 1 to monitor the temperature changes in the tower in real time. The temperature sensor transmits the temperature data to the control system to achieve the temperature control function; the control system may use a PLC.

[0024] The atomizing nozzle 101 may be a pneumatic nozzle assisted by nitrogen S;

[0025] The mass ratio of cross-linking agent cyclohexene T to PCS is 1:300. The atomized PCS droplets can completely absorb the cross-linking agent cyclohexene T and achieve complete cross-linking.

[0026] The PCS cross-linked powder formed in the PCS atomization-cross-linking tower 1 falls directly into the first heating section 2A of the fluidized-heat treatment furnace 1 .

[0027] The fluidized-heat treatment 2 includes three fluidized bed heating furnaces, which constitute three heating sections of the fluidized-heat treatment furnace, including the first section 2A of the fluidized-heat treatment furnace, the second section 2B of the fluidized-heat treatment furnace and the third section 2C of the fluidized-heat treatment furnace;

[0028] The heating temperature of the first section 2A of the fluidized-heat treatment furnace is 500°C, and the PCS cross-linked powder is decarbonized and aminated to form silazane powder in this section. The heating temperature of the second section 2B of the fluidized-heat treatment furnace is 1000°C, and the silazane powder in this section is pyrolyzed and inorganicized to form amorphous silicon nitride powder; the fluidized working gas of the first and second sections is ammonia-nitrogen mixed gas X. The heating temperature of the third section 2C of the fluidized-heat treatment furnace is 1600°C, and the amorphous silicon nitride powder in this section is crystallized to form high-purity crystalline silicon nitride powder; the fluidized working gas of the third section is nitrogen S.

[0029] The first section 2A of the fluidized-heat treatment furnace has a charging barrel 2A1 in the middle. The powder in the fluidized state flows in the charging barrel 2A1 and is heated and controlled by a heating rod 2A2. The heating rod 2A2 is arranged outside the charging barrel 2A and can heat 2A1 and the gas distribution plate 2A4 at the same time without contacting the material. The bottom of the charging barrel 2A1 is equipped with a first-stage gas distribution plate 2A4 that can evenly distribute and blow out the working gas. The blown ammonia-nitrogen mixed gas X blows up the PCS cross-linked powder in the charging barrel 2A1 and above the first-stage gas distribution plate 2A4 and maintains its fluidized state. The charging barrel 2A1 in the first section 2A of the fluidized-heat treatment furnace is equipped with an intermediate isolation plate 2A3, which is fixed in the middle position inside the charging barrel 2A1, but is at a distance from the gas distribution plate 2A4. The height of the upper part of the intermediate isolation plate 2A3 is higher than the powder inlet and outlet of the first section 2A, so that the intermediate isolation plate 2A3 divides the charging barrel 2A1 of the first section 2A into two left and right compartments that are connected at the bottom. The powder falling from the atomization-crosslinking tower 1 first enters the first compartment, then slowly flows downward and enters another compartment, and then the powder gradually rises in the other compartment, and finally leaves the first section 2A of the fluidized-heat treatment furnace from the top of the other compartment and enters the first compartment of the second section 2B of the fluidized-heat treatment furnace; the structures of the second section 2B of the fluidized-heat treatment furnace and the third section 2C of the fluidized-heat treatment furnace are the same as those of the first section.

[0030] The first section 2A, the second section 2B and the third section 2C of the fluidized-heat treatment furnace are arranged horizontally, and the position is gradually lowered. The powder outlet of the first section 2A is higher than the powder inlet of the second section 2B to ensure that the powder can flow to the next heating section. The final crystalline silicon nitride powder after multiple stages of fluidized heat treatment flows out from the outlet of the third section 2C of the fluidized-heat treatment furnace to the silicon nitride powder collector 3. The position of the silicon nitride powder collector 3 is lower than the powder outlet of the third section 2C, so that the silicon nitride powder finally formed is collected in the silicon nitride powder collector 3. The first section 2A, the second section 2B and the third section 2C of the fluidized-heat treatment furnace are combined into a furnace top cover space at the top, and the tail gas of the three sections is combined at the furnace top cover. A gas heat recovery pipe 4 for preheating the raw material intake gas is installed inside the furnace top cover. The gas heat recovery pipe 4 can use the waste heat of the tail gas combined in the heating section to preheat the ammonia-nitrogen mixed gas X and the nitrogen S. The tail gas Y discharged from the furnace top cover is cooled by the tail gas cooler 5 and then discharged for treatment.

[0031] The ammonia-nitrogen mixed gas X passes through the first-stage air intake regulating valve 2A5 and the second-stage air intake regulating valve 2B5, and enters the gas heat recovery pipe 4 after distribution; the nitrogen S enters the gas heat recovery pipe 4 through the third-stage air intake regulating valve 2C5. There are three groups of gas heat recovery pipes 4. The first group of heat recovery pipes corresponds to the first-stage air intake regulating valve 2A5 and the first heating section 2A; the second group of heat recovery pipes corresponds to the second-stage air intake regulating valve 2B5, the second-stage gas preheater 2B6 and the second heating section 2B. Since the temperature of the ammonia-nitrogen mixed gas X preheated by the gas heat recovery pipe 4 in the second heating section is not high enough, it needs to be heated again by the second-stage gas preheater 2B6 to make the temperature of the ammonia-nitrogen mixed gas X close to the working temperature of the second heating section 2B; similarly, the third group of heat recovery pipes corresponds to the three-stage air intake regulating valve 2A5 and the first heating section 2A; the second group of heat recovery pipes corresponds to the second-stage air intake regulating valve 2B5, the second-stage gas preheater 2B6 and the second heating section 2B. The temperature of the nitrogen S coming out of the reheat pipe is not high enough, so it is heated again by the third gas preheater 2B6 to make its temperature close to the working temperature of the third heating section 2C; the gas flow entering the first heating section 2A, the second heating section 2B and the third heating section 2C is adjusted by adjusting the first section air inlet regulating valve 2A5, the second section air inlet regulating valve 2B5 and the third section air inlet regulating valve 2C5 to adjust the powder in the three heating sections to maintain them in a fluidized state.

[0032] 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 fusible solid polycarbosilane, characterized in that It includes a PCS atomization-crosslinking tower for atomizing and crosslinking PCS, a fluidization-heat treatment furnace for pyrolyzing PCS crosslinked powder into silicon nitride powder, a silicon nitride powder collector, a gas heat recovery pipe and an exhaust gas cooler; The PCS atomization-crosslinking tower is installed above the fluidization-heat treatment furnace, and the PCS cross-linked powder formed in the atomization-cross-linking tower directly falls into the fluidization-heat treatment furnace; the powder outflow port of the fluidization-heat treatment furnace is connected to the silicon nitride powder collector, the position of the silicon nitride powder collector is lower than the powder outflow port of the fluidization-heat treatment furnace, and the silicon nitride powder collector is used to collect the formed silicon nitride powder; three fluidized bed heating sections are provided in the fluidization-heat treatment furnace, and the three fluidized bed heating sections are horizontally arranged, the positions are gradually lowered, and the heating temperature is gradually increased; the upper parts of the three fluidized bed heating sections share a furnace roof space, and the gas heat recovery pipe is installed inside the furnace roof, and the gas heat recovery pipe is used to use the waste heat of the tail gas of the fluidization-heat treatment furnace to preheat the raw material intake air, and the tail gas cooler is arranged above the end of the fluidization-heat treatment furnace, and the tail gas is discharged from the furnace roof and cooled by the tail gas cooler before being emptied for treatment.

2. A device for preparing high thermal conductivity silicon nitride nanopowder using fusible solid polycarbosilane as claimed in claim 1, characterized in that The atomization-crosslinking tower is provided with a PCS atomization nozzle, which is used to atomize the molten PCS into droplets. The PCS atomization nozzle adopts a pressure type, air flow type, rotary atomizer, ultrasonic atomizer or electrostatic atomizer.

3. A device for preparing high thermal conductivity silicon nitride nanopowder using fusible solid polycarbosilane as claimed in claim 2, characterized in that The PCS atomizing nozzle has a separation hood in the atomizing-cross-linking tower. Inert gas is introduced into the separation hood, and PCS spraying is carried out in the inert gas to ensure that the PCS melt is fully atomized before cross-linking; cross-linking agent gas is introduced into the outside of the separation hood. In the lower section of the atomizing-cross-linking tower, PCS droplets are mixed with the cross-linking agent gas to complete cross-linking and curing to form PCS cross-linked powder.

4. A device for preparing high thermal conductivity silicon nitride nanopowder using fusible solid polycarbosilane as claimed in claim 1, characterized in that The atomization-crosslinking tower is vertically installed above the feed inlet of the fluidization-heat treatment furnace, and the PCS crosslinked powder formed in the atomization-crosslinking tower directly falls into the first fluidized bed heating section of the fluidization-heat treatment furnace.

5. A device for preparing high thermal conductivity silicon nitride nanopowder using fusible solid polycarbosilane as claimed in claim 1, characterized in that The fluidized-heat treatment furnace includes three fluidized bed heating sections, the first section is a decarbonization and ammoniation section, the heating temperature is 400-700°C, the PCS cross-linked powder is decarbonized and ammonified into silazane powder; the second section is a high-temperature pyrolysis section, the heating temperature is 700-1000°C, the silazane powder is pyrolyzed and inorganically formed into amorphous silicon nitride powder; the third section is a high-temperature crystallization section, the heating temperature is 1500-1700°C, the amorphous silicon nitride powder is crystallized to form high-purity silicon nitride powder.

6. A device for preparing high thermal conductivity silicon nitride nanopowder using fusible solid polycarbosilane as claimed in claim 5, characterized in that The three fluidized bed heating sections, each of which is heated and temperature controlled by a heating rod, is provided at the bottom with a porous gas distribution plate for evenly distributing and blowing out the working gas, and a partition is provided in the middle of the fluidized bed heating section, which divides each section into two compartments connected at the bottom, and the powder falling from the atomization-cross-linking tower or processed by the previous fluidized bed heating section first enters the first compartment, flows downward, and then enters the other compartment, in which the powder rises and leaves the fluidized bed heating section from the top.

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