Device and process for continuous preparation of α-phase silicon nitride by precursor method

Abstract

The invention discloses a device and a process for continuously preparing α-phase silicon nitride by a precursor method, and relates to the technical field of preparation of α-phase silicon nitride. In the process of the invention, raw silicon tetrachloride directly passes through an atomizer and reacts with liquid ammonia in a reactor in a mist form under the action of high-purity nitrogen. At the same time, the reaction temperature, reaction pressure and feed flow rate ratio of raw silicon tetrachloride and liquid ammonia are limited to ensure that the byproduct ammonium chloride solid generated by the reaction can be completely dissolved in the liquid ammonia, reduce the content of ammonium chloride impurities in the generated solid material precursor silanimide, improve the purity of the product and reduce the amount of impurity decomposition during subsequent calcination.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of α-phase silicon nitride, and in particular to a device and a process for continuously preparing α-phase silicon nitride by a precursor method. Background Art

[0002] Silicon nitride (Si3N4) has a variety of crystal structures, of which α phase and β phase are the two most common ones. α-phase silicon nitride (α-Si3N4) is an important ceramic material with higher crystallinity and more regular crystal structure than β-phase silicon nitride.

[0003] α-phase silicon nitride has a hexagonal crystal structure, which is more compact than β-phase silicon nitride. It has high strength, high hardness, good wear resistance, thermal shock resistance and chemical stability, as well as excellent high temperature stability and low thermal expansion coefficient. Due to its excellent mechanical and thermal properties, α-phase silicon nitride is widely used in high-performance ceramic materials, aerospace, automotive industry, electronic packaging and other fields.

[0004] At present, there are many preparation processes for α-phase silicon nitride. For example, Chinese invention patent CN105129750A discloses a method for preparing silicon nitride powder by atomization reaction method, which includes the following steps: atomizing silicon tetrachloride by pressure spraying, and the atomizing gas adopts an inert gas; the atomized silicon tetrachloride reacts with liquid ammonia at the interface, and the temperature in the tower body is controlled below -33.5°C during the reaction, and the supply of silicon tetrachloride is controlled during the reaction; the collected powder product is kept warm at 400-600°C to remove the ammonium chloride therein; the purified silyl imine is kept warm at 950-1100°C to decompose it to produce amorphous silicon nitride, and then kept warm at 1400-1600°C to crystallize the amorphous silicon nitride. Although this method can prepare high-quality silicon nitride, during the preparation process, the content of ammonium chloride impurities in the precursor is high, the subsequent impurity removal process is complicated, and the reaction needs to be controlled at low temperature, which consumes a lot of energy. Chinese invention patent CN110272283A discloses a method for producing silicon nitride powder, including: 1) using silicon tetrachloride and ammonia as raw materials to react and synthesize Si(NH)2 solid, a precursor of silicon nitride; 2) moving Si(NH)2 to a high-temperature furnace and calcining to obtain amorphous silicon nitride powder; 3) refining and briquetting the obtained silicon nitride powder and moving it to a high-temperature crystallization furnace and calcining to obtain crystalline silicon nitride powder. In the process of preparing silicon nitride powder, this patent requires the addition of liquid ammonia for cleaning when removing ammonium chloride impurities, which is complicated to operate and has low production efficiency. Chinese invention patent CN107954723B discloses a method for preparing α-phase silicon nitride powder, comprising the following steps: (1) silicon tetrachloride reacts with liquid ammonia at the interface of two liquid phases of an organic solvent and liquid ammonia to obtain a precursor silicon imine; the organic solvent is toluene or a mixture of toluene and xylene; (2) the silicon imine described in step (1) is thermally decomposed to obtain amorphous silicon nitride powder; (3) the amorphous silicon nitride powder described in step (2) is crystallized to obtain the α-phase silicon nitride powder. This patent requires the addition of an organic solvent during the preparation process, the product will contain carbon impurities, and the operation is complicated and cannot react continuously.

[0005] Therefore, in view of the above-mentioned problems existing in the existing α-phase silicon nitride preparation process, it is urgent to develop a new α-phase silicon nitride preparation process to solve the problems existing in the existing preparation process. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a device and a process for continuously preparing alpha-phase silicon nitride by a precursor method. The raw material silicon tetrachloride directly passes through an atomizer and reacts with liquid ammonia in a reactor in a mist form under the action of high-purity nitrogen. At the same time, the reaction temperature and reaction pressure are controlled and the feed flow rate ratio of the raw material silicon tetrachloride to the liquid ammonia is limited to ensure that the by-product ammonium chloride solid generated by the reaction can be completely dissolved in the liquid ammonia, reduce the content of ammonium chloride impurities in the generated solid material precursor silicon imine, improve the product purity and reduce the amount of impurity decomposition during subsequent calcination.

[0007] The technical solution of the present invention is:

[0008] On the one hand, the present invention provides a device for continuously preparing α-phase silicon nitride by a precursor method, comprising a reactor, the reactor is connected to a liquid ammonia feed pipeline and a reactant discharge pipeline, an atomizer is arranged in the reactor, the atomizer is connected to a silicon tetrachloride feed pipeline and a nitrogen feed pipeline 1; the reactant discharge pipeline is connected to a feed port of a filter press, the filter press is connected to a liquid material collecting tank through a liquid material discharge pipeline, the filter press is connected to a silo 1 through a solid material discharge pipeline, the silo 1 is connected to a feed port of a decomposition furnace through a screw conveyor, the decomposition furnace is connected to a nitrogen feed pipeline 2; the discharge port of the decomposition furnace is connected to a feed port of a primary calcining furnace through a pipeline, the primary calcining furnace is connected to a nitrogen feed pipeline 3; the discharge port of the primary calcining furnace is connected to a feed port of a secondary calcining furnace through a pipeline, the secondary calcining furnace is connected to a nitrogen feed pipeline 4.

[0009] Preferably, a jacket is provided outside the reactor, the jacket is connected to a cooling water feed pipeline and a cooling water discharge pipeline, the reactor is provided with a temperature sensor, and a regulating valve is provided on the cooling water feed pipeline.

[0010] Preferably, the discharge port of the liquid material collecting tank is connected to the falling film evaporator through a pipeline, the liquid material discharge port of the falling film evaporator is connected to the feed port of the evaporating kettle through a pipeline, the gas material discharge ports of the falling film evaporator and the evaporating kettle are respectively connected to the feed port of the ammonia compressor through pipelines, the discharge port of the ammonia compressor is connected to the feed port of the condenser through a pipeline, the discharge port of the condenser is connected to the feed port of the liquid ammonia collecting tank through a pipeline, the discharge port of the liquid ammonia collecting tank is connected to the feed port of the liquid ammonia storage tank through a pipeline, and the liquid ammonia feed pipeline of the reactor is connected to the discharge port of the liquid ammonia storage tank.

[0011] Preferably, the silicon tetrachloride feed pipeline and the liquid ammonia feed pipeline are respectively provided with a pump, a regulating valve and a flow meter.

[0012] Preferably, the tail gas outlets of the decomposition furnace, the primary calcining furnace and the secondary calcining furnace are respectively connected to the tail gas treatment mechanism through pipelines, and bag dust collectors and induced draft fans are provided on the pipelines.

[0013] Preferably, the tail gas treatment mechanism comprises a primary quench spray tower, a secondary quench spray tower and a tertiary quench spray tower which are sequentially connected through pipelines.

[0014] On the other hand, the present invention provides a process for continuously preparing α-phase silicon nitride by a precursor method, which is carried out by the device for continuously preparing α-phase silicon nitride by the precursor method, comprising the following steps:

[0015] S1, under the action of nitrogen, silicon tetrachloride reacts with liquid ammonia entering the reactor in the form of mist through an atomizer, and the reaction temperature of the reactor is controlled to be 5-30°C, and the reaction pressure is 0.5-2MPa, wherein the feed flow ratio of silicon tetrachloride to liquid ammonia entering the reactor is 1:(30-50);

[0016] The reactants of the S2 reactor enter the filter press for solid-liquid separation, the liquid material enters the liquid material collection tank, and the solid material is pushed into the silo 1 through the agitator in the filter press;

[0017] The solid materials in S3 silo 1 are conveyed into the decomposition furnace through a screw conveyor for drying to remove ammonium chloride and liquid ammonia in the solid materials;

[0018] The dried solid material in S4 enters a primary calcining furnace and is calcined under nitrogen protection to obtain amorphous silicon nitride; the amorphous silicon nitride powder then enters a secondary calcining furnace and is calcined under nitrogen protection to obtain α-phase silicon nitride.

[0019] In the present invention, the reaction equation for preparing α-phase silicon nitride using silicon tetrachloride and liquid ammonia is as follows:

[0020] SiCl4+6NH3=Si(NH)2+4NH4Cl;

[0021] 3Si(NH)2=Si3N4+2NH3.

[0022] Preferably, in step S1, the feed flow ratio of silicon tetrachloride to nitrogen is 1:(5-10); in step S3, the drying temperature is 300-400°C.

[0023] Preferably, in step S4, the calcination temperature of the primary calcination furnace is 1000-1100°C.

[0024] Preferably, in step S4, the calcination temperature of the secondary calcination furnace is 1400-1600°C.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. Compared with the traditional preparation process, a large amount of organic solvent is used to dilute silicon tetrachloride, which leads to the problem of low reaction rate. The present invention does not use organic solvent to dilute silicon tetrachloride. The raw material silicon tetrachloride directly passes through an atomizer and reacts with liquid ammonia in the reactor in a mist form under the action of high-purity nitrogen, and the reaction rate is high; and the materials in the reactor are continuously in and out, and at the same time, the reaction temperature, reaction pressure and the feed flow ratio of the raw material silicon tetrachloride to liquid ammonia are limited to ensure that the byproduct ammonium chloride solid generated by the reaction can be completely dissolved in liquid ammonia, reduce the content of ammonium chloride impurities in the generated solid material precursor silanimide, improve the product purity and reduce the amount of impurity decomposition during subsequent calcination. The present invention is safe and controllable in reaction, can be continuously fed and unloaded, and does not need to use liquid ammonia to wash the precursor silanimide, while ensuring production efficiency, greatly reducing the content of ammonium chloride in the precursor silanimide.

[0027] 2. The device of the present invention continuously recovers liquid ammonia in the liquid material after pressure filtration through an evaporating kettle with a falling film evaporator, thereby realizing the recycling of liquid ammonia.

[0028] 3. The present invention uses a decomposition furnace and a two-stage calcining furnace to process the precursor silyl imine in stages, effectively separating impurities therein, thereby improving product quality and product yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic structural diagram of a device for continuously preparing α-phase silicon nitride by a precursor method of the present invention.

[0030] Figure 2 It is the XRD diagram of α-phase silicon nitride prepared in Example 1 of the present invention. The black line in the figure is the X-ray diffraction peak position of the α-phase silicon nitride prepared in Example 1, the red line is the X-ray diffraction peak position corresponding to the α-phase silicon nitride standard card, and the blue line is the X-ray diffraction peak position corresponding to the β-phase silicon nitride standard card.

[0031] Figure 3 It is the XRD diagram of α-phase silicon nitride prepared in Example 2 of the present invention. The black line in the figure is the X-ray diffraction peak position of the α-phase silicon nitride prepared in Example 2, the red line is the X-ray diffraction peak position corresponding to the α-phase silicon nitride standard card, and the blue line is the X-ray diffraction peak position corresponding to the β-phase silicon nitride standard card.

[0032] Figure 4 It is the XRD diagram of α-phase silicon nitride prepared in Example 3 of the present invention. The black line in the figure is the X-ray diffraction peak position of the α-phase silicon nitride prepared in Example 3, the red line is the X-ray diffraction peak position corresponding to the α-phase silicon nitride standard card, and the blue line is the X-ray diffraction peak position corresponding to the β-phase silicon nitride standard card.

[0033] In the figure, 1, reactor; 101, liquid ammonia feed pipeline; 102, reactant discharge pipeline; 103, silicon tetrachloride feed pipeline; 104, nitrogen feed pipeline 1; 105, jacket; 1051, cooling water feed pipeline; 1052, cooling water discharge pipeline; 106, temperature sensor; 2, filter press; 201, liquid material discharge pipeline; 202, solid material discharge pipeline; 3, liquid material collection tank; 4, silo 1; 5, screw conveyor; 6, decomposition furnace; 601, nitrogen feed pipeline 2; 7, silo 2; 8, primary calcination Calcination furnace; 801, nitrogen feed pipeline three; 9, silo three; 10, secondary calcining furnace; 1001, nitrogen feed pipeline four; 11, regulating valve; 1201, falling film evaporator; 1202, evaporating kettle; 1203, ammonia compressor; 1204, condenser; 1205, liquid ammonia collection tank; 13, liquid ammonia storage tank; 14, pump; 15, flow meter; 16, bag filter; 17, induced draft fan; 1801, primary quenching spray tower; 1802, secondary quenching spray tower; 1803, tertiary quenching spray tower; 19, silicon tetrachloride storage tank. DETAILED DESCRIPTION

[0034] In order to enable persons skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0035] The following examples of the continuous preparation of α-phase silicon nitride by the precursor method all adopt the following process: Figure 1 The device for continuously preparing α-phase silicon nitride by the precursor method shown in the figure comprises a reactor 1, a jacket 105 is arranged outside the reactor 1, the jacket 105 is connected to a cooling water feed pipeline 1501 and a cooling water discharge pipeline 1502, the reactor 1 is provided with a temperature sensor 106, and a regulating valve 11 is arranged on the cooling water feed pipeline 1501, and the reaction temperature of the reactor 1 is controlled by cooling water.

[0036] The top of the reactor 1 is connected with a liquid ammonia feed pipeline 101, and the bottom is connected with a reactant discharge pipeline 102. An atomizer is arranged in the reactor 1, and the atomizer is connected with a silicon tetrachloride feed pipeline 103 and a nitrogen feed pipeline 104, wherein the liquid ammonia feed pipeline 101 is connected with a liquid ammonia storage tank 13, and the silicon tetrachloride feed pipeline 103 is connected with a silicon tetrachloride storage tank 19; a pump 14, a regulating valve 11 and a flow meter 15 are arranged on the silicon tetrachloride feed pipeline 103 and the liquid ammonia feed pipeline 101, respectively, and the nitrogen feed pipeline 104 is connected with a high-purity nitrogen bottle. The raw silicon tetrachloride is not diluted with an organic solvent, and is directly fed to the reactor 1 by a flow meter 15 and a regulating valve 11 to control the feed speed pump 14, and reacts with the liquid ammonia entering the reactor 1 in a mist form through the atomizer under the action of high-purity nitrogen.

[0037] The reactant discharge pipeline 102 is connected to the feed port of the filter press 2, and a valve is provided on the pipeline. The filter press 2 is connected to the liquid material collection tank 3 through the liquid material discharge pipeline 201, and the filter press 2 is connected to the silo-4 through the solid material discharge pipeline 202. Valves are provided on the liquid material discharge pipeline 201 and the solid material discharge pipeline 202. The reactants of the reactor 1 enter the filter press 2 for solid-liquid separation, the liquid material containing ammonium chloride and liquid ammonia enters the liquid material collection tank 3, and the precursor silimide solid material is pushed into the silo-4 through the agitator in the filter press 2. Two filter presses 2 can be set in parallel, one for backup and the other for use, to achieve continuous production.

[0038] The discharge port of the liquid material collecting tank 3 is connected to the falling film evaporator 1201 through a pipeline, and a pump 14 is arranged on the pipeline; the liquid material discharge port of the falling film evaporator 1201 is connected to the feed port of the evaporating kettle 1202 through a pipeline, the gas material discharge ports of the falling film evaporator 1201 and the evaporating kettle 1202 are respectively connected to the feed port of the ammonia compressor 1203 through pipelines, the discharge port of the ammonia compressor 1203 is connected to the feed port of the condenser 1204 through a pipeline, and the discharge port of the condenser 1204 is connected to the feed port of the liquid ammonia collecting tank 1205 through a pipeline; the discharge port of the liquid ammonia collecting tank 1205 is connected to the feed port of the liquid ammonia storage tank 13 through a pipeline, a pump 14 is arranged on the pipeline, and a pressure balance pipe is connected between the liquid ammonia collecting tank 1205 and the liquid ammonia storage tank 13. Among them, two sets of falling film evaporator 1201 and evaporating kettle 1202 are arranged in parallel, one for backup and the other for use, so as to realize continuous production.

[0039] The liquid material obtained by filter pressing is pumped 14 to an evaporator 1202 with a falling film evaporator 1201. The liquid ammonia in the liquid material is heated and evaporated to obtain ammonia gas. This part of the ammonia gas enters the ammonia compressor 1203 and the condenser 1204 in turn, and liquid ammonia is obtained after compression and condensation. The liquid ammonia is temporarily stored in a liquid ammonia collection tank 1205 and then pumped 14 to a liquid ammonia storage tank 13 as a raw material for preparing α-phase silicon nitride; the ammonium chloride remaining after the liquid material evaporates remains in the evaporator 1202 and is packaged after being sent out.

[0040] The silo 1 4 is connected to the feed port of the decomposition furnace 6 through a screw conveyor 5, and the decomposition furnace 6 is connected to a nitrogen feed pipeline 2 601; the discharge port of the decomposition furnace 6 is connected to the silo 2 7 through a pipeline, and the silo 2 7 is connected to the feed port of the primary calcining furnace 8 through the screw conveyor 5, and the primary calcining furnace 8 is connected to a nitrogen feed pipeline 3 801; the discharge port of the primary calcining furnace 8 is connected to the silo 3 9 through a pipeline, and the silo 3 9 is connected to the feed port of the secondary calcining furnace 10 through the screw conveyor 5, and the secondary calcining furnace 10 is connected to a nitrogen feed pipeline 4 1001; wherein, the nitrogen feed pipeline 2 601, the nitrogen feed pipeline 3 801 and the nitrogen feed pipeline 4 1001 are respectively connected to high-purity nitrogen bottles; the tail gas outlets of the decomposition furnace 6, the primary calcining furnace 8 and the secondary calcining furnace 10 are respectively connected to the tail gas treatment mechanism through pipelines, and bag dust collectors 16 and induced draft fans 17 are arranged on the pipelines. Specifically, the tail gas treatment mechanism includes a primary quench spray tower 1801, a secondary quench spray tower 1802 and a tertiary quench spray tower 1803 which are sequentially connected through pipelines, and absorbs ammonia and hydrogen chloride in the tail gas by spraying water.

[0041] The solid material of precursor silicon imide in silo 1 4 enters the decomposition furnace 6 through the screw conveyor 5 for drying, and the ammonium chloride and liquid ammonia therein are removed. The mixed gas impurities generated during the drying process enter the tail gas treatment mechanism for tail gas treatment under the action of the high-purity nitrogen flow. The dried precursor silicon imide enters the silo 2 7 and then enters the primary calcining furnace 8 under the action of the screw conveyor 5. It is calcined under the protection of nitrogen to obtain amorphous silicon nitride powder. The ammonia released during the calcination process enters the tail gas treatment mechanism for tail gas treatment. The amorphous silicon nitride powder enters the silo 3 9 and then enters the secondary calcining furnace 10 under the action of the screw conveyor 5. It is calcined under the protection of nitrogen to obtain α-phase silicon nitride powder.

[0042] Example 1

[0043] The process of continuously preparing α-phase silicon nitride by the precursor method of this embodiment comprises the following steps:

[0044] Under the action of nitrogen, silicon tetrachloride S1 reacts with liquid ammonia entering reactor 1 in atomized form through an atomizer, and the reaction temperature of reactor 1 is controlled to be 5°C and the reaction pressure is 0.5MPa, wherein the feed flow ratio of silicon tetrachloride, liquid ammonia and nitrogen entering reactor 1 is 1:30:5;

[0045] The reactants of S2 reactor 1 enter filter press 2 for solid-liquid separation, the liquid material enters liquid material collection tank 3, and the solid material enters through the agitator in filter press 2 and is pushed into silo 1 4;

[0046] The liquid material in the S3 liquid material collection tank 3 is pumped 14 to an evaporator 1202 with a falling film evaporator 1201, and the ammonia gas generated after heating and evaporation is compressed and condensed to obtain liquid ammonia, which is then pumped 14 to a liquid ammonia storage tank 13 as a raw material for preparing α-phase silicon nitride; the solid material in the silo 1 4 is dried in the decomposition furnace 6 through a screw conveyor 5, and the drying temperature is 300°C to remove ammonium chloride and liquid ammonia in the solid material;

[0047] The solid material after S4 drying enters the primary calcining furnace 8 and is calcined at 1000°C under nitrogen protection to obtain amorphous silicon nitride; the amorphous silicon nitride powder then enters the secondary calcining furnace 10 and is calcined at 1400°C under nitrogen protection to obtain α-phase silicon nitride; the exhaust gas generated by the decomposition furnace 6, the primary calcining furnace 8 and the secondary calcining furnace 10 is sent to the exhaust gas treatment mechanism for treatment.

[0048] The XRD pattern of the α-phase silicon nitride prepared in this embodiment is as follows: Figure 2 As shown by Figure 2 It can be seen that the X-ray diffraction peak position of the silicon nitride prepared in this embodiment overlaps with the X-ray diffraction peak position corresponding to the α-phase silicon nitride standard card, indicating that the silicon nitride prepared in this embodiment is indeed α-phase silicon nitride.

[0049] The chloride ion content in the α-phase silicon nitride prepared in this example was determined to be 50 ppm by ion chromatography.

[0050] Example 2

[0051] The process of continuously preparing α-phase silicon nitride by the precursor method of this embodiment comprises the following steps:

[0052] Under the action of nitrogen, silicon tetrachloride S1 reacts with liquid ammonia entering reactor 1 in atomized form through an atomizer, and the reaction temperature of reactor 1 is controlled to be 17.5°C and the reaction pressure is 1.25MPa, wherein the feed flow ratio of silicon tetrachloride, liquid ammonia and nitrogen entering reactor 1 is 1:40:7.5;

[0053] The reactants of S2 reactor 1 enter filter press 2 for solid-liquid separation, the liquid material enters liquid material collection tank 3, and the solid material enters through the agitator in filter press 2 and is pushed into silo 1 4;

[0054] The liquid material in the S3 liquid material collection tank 3 is pumped 14 to an evaporator 1202 with a falling film evaporator 1201, and the ammonia gas generated after heating and evaporation is compressed and condensed to obtain liquid ammonia, which is then pumped 14 to a liquid ammonia storage tank 13 as a raw material for preparing α-phase silicon nitride; the solid material in the silo 1 4 is dried in the decomposition furnace 6 through a screw conveyor 5, and the drying temperature is 350°C to remove ammonium chloride and liquid ammonia in the solid material;

[0055] The dried solid material in S4 enters the primary calcining furnace 8 and is calcined at 1050°C under nitrogen protection to obtain amorphous silicon nitride; the amorphous silicon nitride powder then enters the secondary calcining furnace 10 and is calcined at 1500°C under nitrogen protection to obtain α-phase silicon nitride; the exhaust gas generated by the decomposition furnace 6, the primary calcining furnace 8 and the secondary calcining furnace 10 is sent to the exhaust gas treatment mechanism for treatment.

[0056] The XRD pattern of the α-phase silicon nitride prepared in this embodiment is as follows: Figure 3 As shown by Figure 3 It can be seen that the X-ray diffraction peak position of the silicon nitride prepared in this embodiment overlaps with the X-ray diffraction peak position corresponding to the α-phase silicon nitride standard card, indicating that the silicon nitride prepared in this embodiment is indeed α-phase silicon nitride.

[0057] The chloride ion content in the α-phase silicon nitride prepared in this example was determined to be 55 ppm by ion chromatography.

[0058] Example 3

[0059] The process of continuously preparing α-phase silicon nitride by the precursor method of this embodiment comprises the following steps:

[0060] Under the action of nitrogen, silicon tetrachloride S1 reacts with liquid ammonia entering reactor 1 in atomized form through an atomizer, and the reaction temperature of reactor 1 is controlled to be 30°C and the reaction pressure is 2MPa, wherein the feed flow ratio of silicon tetrachloride, liquid ammonia and nitrogen entering reactor 1 is 1:50:10;

[0061] The reactants of S2 reactor 1 enter filter press 2 for solid-liquid separation, the liquid material enters liquid material collection tank 3, and the solid material enters through the agitator in filter press 2 and is pushed into silo 1 4;

[0062] The liquid material in the S3 liquid material collection tank 3 is pumped 14 to an evaporator 1202 with a falling film evaporator 1201, and the ammonia gas generated after heating and evaporation is compressed and condensed to obtain liquid ammonia, which is then pumped 14 to a liquid ammonia storage tank 13 as a raw material for preparing α-phase silicon nitride; the solid material in the silo 1 4 is dried by a screw conveyor 5 into a decomposition furnace 6 at a drying temperature of 400°C to remove ammonium chloride and liquid ammonia in the solid material;

[0063] The solid material after S4 drying enters the primary calcining furnace 8 and is calcined at 1100°C under nitrogen protection to obtain amorphous silicon nitride; the amorphous silicon nitride powder then enters the secondary calcining furnace 10 and is calcined at 1600°C under nitrogen protection to obtain α-phase silicon nitride; the exhaust gas generated by the decomposition furnace 6, the primary calcining furnace 8 and the secondary calcining furnace 10 is sent to the exhaust gas treatment mechanism for treatment.

[0064] The XRD pattern of the α-phase silicon nitride prepared in this embodiment is as follows: Figure 4 As shown by Figure 4 It can be seen that the X-ray diffraction peak position of the silicon nitride prepared in this embodiment overlaps with the X-ray diffraction peak position corresponding to the α-phase silicon nitride standard card, indicating that the silicon nitride prepared in this embodiment is indeed α-phase silicon nitride.

[0065] The chloride ion content in the α-phase silicon nitride prepared in this example was determined to be 45 ppm by ion chromatography.

[0066] Comparative Example 1

[0067] The preparation process of α-phase silicon nitride in Comparative Example 1 adopts the method for preparing silicon nitride powder by the atomization reaction method disclosed in Chinese invention patent CN105129750A, which specifically includes the following steps:

[0068] S1 controls the temperature in the reaction tower to -40°C, adds 125L of liquid ammonia, and sprays silicon tetrachloride into the tower body through a pressure atomizer. The supply rate is 0.3L / min, and the total supply is 3L. The gas used for spraying is high-purity nitrogen, and the gas pressure is 3.5MPa;

[0069] After S2 reacts, the silicimide solid and liquid ammonia containing ammonium chloride are discharged, and silicimide solid powder is obtained after filtration; the collected powder product is placed in a low-temperature calcining furnace, and the temperature is raised from room temperature to 500°C in 1 hour, and kept warm for 8 hours. During this period, ammonia gas is continuously introduced at a ventilation rate of 10L / min, thereby removing the ammonium chloride in the powder product, and finally obtaining 1.45kg of the product;

[0070] S3 puts the purified precursor silyl imine into a tubular furnace, raises the temperature from room temperature to 1000°C for 3 hours, and keeps it at 1000°C for 3 hours to decompose the precursor to produce amorphous silicon nitride. During this period, ammonia is continuously introduced at a ventilation rate of 3L / min; the ammonia is replaced with nitrogen at a ventilation rate of 3L / min, and the temperature is raised from 1000°C to 1550°C for 2.5 hours. It is kept at 1550°C for 5 hours, and finally 1.1kg of crystalline silicon nitride is obtained.

[0071] Although Comparative Example 1 can prepare silicon nitride, during the preparation process, the content of ammonium chloride impurities in the precursor silanimide is high, and the reaction needs to be carried out at a low temperature, which consumes a lot of energy.

[0072] Comparative Example 2

[0073] The preparation process of α-phase silicon nitride in Comparative Example 2 adopts the production method of silicon nitride powder disclosed in Chinese invention patent CN110272283A, which specifically includes the following steps:

[0074] S1 repeatedly replaces the gas in the tubular reactor 1 with nitrogen to anhydrous and oxygen-free conditions. After the silicon tetrachloride is sent to the tubular reactor 1, a mixture of nitrogen and ammonia is introduced into the tubular reactor 1 together (the molar ratio of nitrogen and ammonia is 1:1). The direction of gas introduction is consistent with the flow direction of silicon tetrachloride. The temperature of the tubular reactor 1 is controlled at -50°C. The mixed product after the reaction is filtered through a filter to obtain solid products of silyl imine and ammonium chloride. The silicon tetrachloride is returned to the silicon tetrachloride storage tank 19 and recycled in the reaction system. The solid products of silyl imine and ammonium chloride obtained by filtration are sent to a washing and filtering kettle, and then liquid ammonia is introduced for cleaning to remove the by-product of ammonium chloride. The liquid ammonia after cleaning is recycled for recycling;

[0075] S2: The cleaned and dried silicon imide is moved into a high-temperature furnace, and heated to 800°C and calcined for 4 hours under the protection of a flowing ammonia atmosphere to obtain amorphous silicon nitride powder;

[0076] S3: The obtained amorphous silicon nitride powder is finely ground by air flow grinding and crystalline silicon nitride powder is added as a grinding aid. After being pressed into blocks, it is moved into a high-temperature crystallization furnace, heated to 1500° C. in a nitrogen atmosphere, and calcined for 1 hour to obtain submicron equiaxed α-phase silicon nitride powder.

[0077] In the process of preparing α-phase silicon nitride powder in Comparative Example 2, liquid ammonia needs to be added again for cleaning when removing the ammonium chloride impurities, which results in complicated operation and low production efficiency.

[0078] Comparative Example 3

[0079] The preparation process of α-phase silicon nitride in Comparative Example 3 adopts the preparation method of α-phase silicon nitride powder disclosed in Chinese invention patent CN107954723B, which specifically includes the following steps:

[0080] S1 controls the temperature in the reactor to -45°C, places a mixed solution of 200 volumes of toluene and 200 volumes of xylene and 100 volumes of liquid ammonia in the reactor, and allows them to stand for stratification; mixes 5 volumes of silicon tetrachloride with 95 volumes of toluene, places the nozzle of the silicon tetrachloride feeding pipe into the toluene layer in the reactor, and injects the mixed solution of silicon tetrachloride and toluene into the toluene layer by pressurizing nitrogen in the feeding tank, controls the feeding rate to 3 mL / min, diffuses silicon tetrachloride to the liquid interface of toluene and liquid ammonia, stirs continuously with a stirring paddle, and rotates at a speed of 1000 rpm. The speed was 70 rpm, and silicon tetrachloride reacted with liquid ammonia at the interface of toluene and liquid ammonia. The reaction temperature was -45 °C and the reaction time was 1 h to generate white flocculent powder. The white powder was filtered, and the toluene and liquid ammonia were recovered by distillation filtration through the filter element at the bottom of the reactor. The white solid was returned to the reactor for recycling. The white solid was left in the reactor, and the white solid was washed with liquid ammonia and stirred evenly to wash away toluene and the reaction by-product ammonium chloride. The washed white solid was transferred to a vacuum drying oven, and the drying temperature was 120 °C, the time was 4 h, and the vacuum degree was 7 × 10-2 Pa; the dried white solid was placed in an alumina crucible, and the residual ammonium chloride and organic solvent were removed in an atmosphere furnace. The specific conditions were as follows: temperature was 600°C, time was 2h, nitrogen atmosphere was circulated (nitrogen flow rate was 40mL / min), and silyl imine solid was obtained;

[0081] S2: in an atmosphere furnace, thermally decomposing the silanimide solid obtained in step S1 at a nitrogen flow rate of 40 mL / min and 1000° C. for 2 h to obtain amorphous silicon nitride powder;

[0082] S3: In an atmosphere furnace, the amorphous silicon nitride powder obtained in step S2 is crystallized in a circulating nitrogen atmosphere (nitrogen flow rate 40 mL / min) at 1400° C. for 2 h, and finally a high α-phase submicron silicon nitride powder with uniform morphology is obtained.

[0083] In Comparative Example 3, when preparing α-phase silicon nitride powder, an organic solvent needs to be added, resulting in the presence of carbon impurities in the prepared α-phase silicon nitride powder. In addition, the operation is complicated and continuous reaction cannot be performed.

[0084] Comparative Example 4

[0085] The difference from Example 1 is that in step S1, the feed flow ratio of silicon tetrachloride to liquid ammonia entering the reactor is 1:10.

[0086] The chloride ion content in the α-phase silicon nitride prepared in Comparative Example 4 was determined to be 160 ppm by ion chromatography.

[0087] In summary, in the process of the present invention, the raw material silicon tetrachloride directly passes through an atomizer and reacts with the liquid ammonia in the reactor in a mist form under the action of high-purity nitrogen. At the same time, the reaction temperature and reaction pressure are controlled and the feed flow rate ratio of the raw material silicon tetrachloride to the liquid ammonia is limited to ensure that the by-product ammonium chloride solid generated by the reaction can be completely dissolved in the liquid ammonia, thereby reducing the content of ammonium chloride impurities in the generated solid material precursor silanimide, improving the product purity and reducing the amount of impurity decomposition during subsequent calcination.

Claims

1. A process for continuously preparing α-phase silicon nitride by a precursor method, characterized in that: The device for continuously preparing α-phase silicon nitride by a precursor method is as follows: comprising a reactor (1), the reactor (1) being connected to a liquid ammonia feed pipeline (101) and a reactant discharge pipeline (102), an atomizer being arranged in the reactor (1), the atomizer being connected to a silicon tetrachloride feed pipeline (103) and a nitrogen feed pipeline (104); the reactant discharge pipeline (102) being connected to a feed port of a filter press (2), the filter press (2) being connected to a liquid material collection tank (3) via a liquid material discharge pipeline (201), the filter press (2) being connected to a solid material collection tank (3) via a liquid material discharge pipeline (201), The material discharge pipeline (202) is connected to the first silo (4), and the first silo (4) is connected to the feed port of the decomposition furnace (6) through a screw conveyor (5), and the decomposition furnace (6) is connected to the second nitrogen feed pipeline (601); the discharge port of the decomposition furnace (6) is connected to the feed port of the first calcining furnace (8) through a pipeline, and the first calcining furnace (8) is connected to the third nitrogen feed pipeline (801); the discharge port of the first calcining furnace (8) is connected to the feed port of the second calcining furnace (10) through a pipeline, and the second calcining furnace (10) is connected to the fourth nitrogen feed pipeline (1001); The process for continuously preparing α-phase silicon nitride by a precursor method comprises the following steps: S1, under the action of nitrogen, silicon tetrachloride in atomized form reacts with liquid ammonia entering a reactor (1) through an atomizer, the reaction temperature of the reactor (1) is controlled to be 5-30°C, and the reaction pressure is controlled to be 0.5-2MPa, wherein the feed flow ratio of silicon tetrachloride to liquid ammonia entering the reactor (1) is 1:(30-50); The reactants of the S2 reactor (1) enter the filter press (2) for solid-liquid separation, the liquid material enters the liquid material collection tank (3), and the solid material is pushed into the silo (4) through the agitator in the filter press (2); The solid material in the S3 silo (4) is conveyed to the decomposition furnace (6) through the screw conveyor (5) for drying to remove ammonium chloride and liquid ammonia in the solid material; The dried solid material in S4 enters a primary calcining furnace (8) and is calcined under nitrogen protection to obtain amorphous silicon nitride powder; the amorphous silicon nitride powder then enters a secondary calcining furnace (10) and is calcined under nitrogen protection to obtain α-phase silicon nitride.

2. The process for continuously preparing α-phase silicon nitride by a precursor method according to claim 1, characterized in that: The reactor (1) is provided with a jacket (105) outside, the jacket (105) is connected to a cooling water feed pipeline (1051) and a cooling water discharge pipeline (1052), the reactor (1) is provided with a temperature sensor (106), and the cooling water feed pipeline (1051) is provided with a regulating valve (11).

3. The process for continuously preparing α-phase silicon nitride by a precursor method according to claim 1, characterized in that: The discharge port of the liquid material collecting tank (3) is connected to the falling film evaporator (1201) through a pipeline, the liquid material discharge port of the falling film evaporator (1201) is connected to the feed port of the evaporating kettle (1202) through a pipeline, the gas material discharge ports of the falling film evaporator (1201) and the evaporating kettle (1202) are respectively connected to the feed port of the ammonia compressor (1203) through pipelines, the discharge port of the ammonia compressor (1203) is connected to the feed port of the condenser (1204) through a pipeline, the discharge port of the condenser (1204) is connected to the feed port of the liquid ammonia collecting tank (1205) through a pipeline, the discharge port of the liquid ammonia collecting tank (1205) is connected to the feed port of the liquid ammonia storage tank (13) through a pipeline, and the liquid ammonia feed pipeline (101) of the reactor (1) is connected to the discharge port of the liquid ammonia storage tank (13).

4. The process for continuously preparing α-phase silicon nitride by a precursor method according to claim 1, characterized in that: The silicon tetrachloride feed pipeline (103) and the liquid ammonia feed pipeline (101) are respectively provided with a pump (14), a regulating valve (11) and a flow meter (15).

5. The process for continuously preparing α-phase silicon nitride by a precursor method according to claim 1, characterized in that: The tail gas outlets of the decomposition furnace (6), the primary calcining furnace (8) and the secondary calcining furnace (10) are respectively connected to the tail gas treatment mechanism through pipelines, and a bag filter (16) and an induced draft fan (17) are arranged on the pipelines.

6. The process for continuously preparing α-phase silicon nitride by a precursor method as claimed in claim 5, characterized in that: The tail gas treatment mechanism comprises a primary quenching spray tower (1801), a secondary quenching spray tower (1802) and a tertiary quenching spray tower (1803) which are sequentially connected via pipelines.

7. The process for continuously preparing α-phase silicon nitride by a precursor method according to claim 1, characterized in that: In step S1, the feed flow ratio of silicon tetrachloride to nitrogen is 1:(5-10); in step S3, the drying temperature is 300-400°C.

8. The process for continuously preparing α-phase silicon nitride by a precursor method according to claim 1, characterized in that: In step S4, the calcination temperature of the primary calcination furnace (8) is 1000-1100°C.

9. The process for continuously preparing α-phase silicon nitride by a precursor method according to claim 1, characterized in that: In step S4, the calcination temperature of the secondary calcination furnace (10) is 1400-1600°C.

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