A method for preparing silicon nitride ultra-pure powder by a silicon amine group exchange method

Abstract

The application relates to a method for preparing super-pure silicon nitride powder by a silicon amine group exchange method, belonging to the field of materials. In the method, hexamethyldisilazane (HMDZ) and SiCl4 are reacted in an organic solvent, the Cl atoms in the SiCl4 are removed from the reaction system in the form of a by-product (CH3)3SiCl, HMDZ and SiCl4 form [Si(NH)2] in the organic solvent, and the [Si(NH)2] is converted into [Si(CH3)3] under the action of NH3 and heating m [Si(CH3)3] n polymer; the latter forms a Si(NH)2(s) silicon amine precursor precipitate under the action of NH3 and heating, and finally, the silicon amine precursor precipitate is heated and decomposed to form super-pure Si3N4 powder. The synthesis process condition is mild, and high-pressure synthesis conditions are avoided. By adjusting the concentration of HMDZ in the organic solvent and the gas feeding rate of SiCl4, the particle size of the final silicon nitride powder can be directly controlled, and the adjustment is convenient. The cost is low, and the product purity is high.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of material preparation, and in particular to a method for preparing silicon nitride ultra-pure powder by a silicon amine group exchange method. BACKGROUND

[0002] Si3N4ceramics have been widely used in bearing manufacturing, high-temperature heating sheets, electronic packaging and other fields due to its good mechanical strength, good insulation performance, good thermal conductivity and superior thermal shock resistance. Si3N4powder is the basic raw material for sintering Si3N4ceramics. To prepare high-performance Si3N4structural ceramics, the Si3N4powder needs to have moderate particle size, uniform particle size distribution, good morphology distribution and low oxygen and impurities. Currently, there are four main methods for preparing Si3N4powder [Xiang M, et al. Research progress of silicon nitride powder preparation technology and powder quality [J]. Chemical Industry and Engineering Progress, 2022, 73(1): 73-84]. The earliest method is SiO2carbonthermal nitridation:

[0003] 3SiO2+6C+2N2→Si3N4(s)+6CO(g) (1)

[0004] This synthesis method has a wide range of raw material sources and a simple process, and has been widely used in commercial applications. However, due to the solid-phase reaction, Si3N4powder prepared inevitably contains SiC impurities, as well as unreacted SiO2and C powder, which requires complex purification methods to remove impurities.

[0005] To further improve the purity of Si3N4powder, people use nitrogen, ammonia or mixed gas to directly react with silicon to prepare Si3N4powder. In this method, Si powder is preheated to a certain temperature in nitrogen, and Si3N4powder is prepared by self-propagating combustion reaction. On this basis, by adding auxiliary diluent, increasing the nitrogen partial pressure and using fluidized bed process, the reaction rate of the raw material silicon can be improved to improve the purity of the synthesized Si3N4powder.

[0006] 3Si(s, l, g) + 2N2→ Si3N4(s) (2)

[0007] The above two preparation methods use solid raw materials (silicon dioxide or silicon) to prepare Si3N4powder. The high temperature in the synthesis reaction often leads to sintering of Si3N4powder, resulting in large Si3N4powder particles and wide particle size distribution. Further crushing and classification are needed to obtain Si3N4powder with uniform particle size. The high hardness of Si3N4powder requires high requirements for the crushing equipment, and new impurities cannot be avoided in the crushing process, which is not conducive to the preparation of high-purity Si3N4powder.

[0008] The gas phase synthesis method is a method of directly synthesizing Si3N4 using a gaseous Si source and NH3, N2 and H2 at high temperature. In this method, the silicon-containing compound is gasified and then pyrolyzed and precipitated with NH3, N2 and H2 or a mixture thereof at high temperature to form Si3N4 powder. The main reaction process is as follows (taking SiCl4 as an example):

[0009] 3SiCl4+2N2+6 H2→Si3N4(s)+12HCl (3)

[0010] The Si3N4 powder prepared by gas-phase synthesis of Si3N4 has uniform particle size distribution, good crystallization, and purity superior to the two aforementioned synthesis methods using solid raw materials; however, this method requires extreme heating methods such as high-temperature resistance furnaces, plasma or lasers, and is currently only in the laboratory research stage.

[0011] The preparation of Si3N4 powder by thermal decomposition of silanamine precursor is to dissolve SiCl4 in an organic solvent and react with NH3 to form a silanamine precursor, and then heat the silanamine precursor at 1100-1600℃ to decompose it into Si3N4 powder:

[0012] SiCl4(g)+6NH3(l)→Si(NH)2(s)+NH4Cl·xNH3(l) (4)

[0013] Si(NH)2→Si3N4 (5)

[0014] Currently, Ube Corporation in Japan uses this method to produce high-purity Si3N4 powder using liquid ammonia and SiCl4 as raw materials, and has achieved commercial application. However, this method still has some drawbacks. First, the byproduct NH4Cl formed during the synthesis of the silanamine precursor must be dissolved in liquid ammonia to be removed, and liquid ammonia must be used to clean the silanamine precursor. Second, the synthesis process requires high pressure to maintain the liquid ammonia in a liquid state, necessitating the use of high-pressure and corrosion-resistant synthesis equipment, which places high demands on the equipment.

[0015] Hexamethyldisilazane [(CH3)3SiNHSi(CH3)3, HMDZ] can undergo a group exchange reaction with the silicon-chlorine in chlorosilanes, forming a new silicon-nitrogen bond structure. Using HMDZ and chlorosilanes to synthesize polysilazanes through silanamine exchange can replace direct ammonolysis, avoiding the difficult separation of the byproduct NH4Cl from the silanamine precursor. This method has the potential to produce ultrapure Si3N4 powder at low cost. Currently, no research has reported on this technology. Summary of the Invention

[0016] The present invention aims to address the existing problem of difficult separation of the byproduct NH₄Cl from the silanamine precursor by providing a low-cost method for preparing ultrapure silicon nitride powder using a silanamine group exchange method. This method, which uses HMDZ and chlorosilane for silanamine exchange to synthesize polysilazane, can replace the direct ammonolysis method, avoiding direct contact between the byproduct NH₄Cl and the silanamine precursor, simplifying the separation process and subsequent processing steps.

[0017] The present invention uses hexamethyldisilazane [(CH3)3SiNHSi(CH3)3, HMDZ] to react with SiCl4 in an organic solvent, removes the Cl atom in SiCl4 from the reaction system in the form of a by-product (CH3)3SiCl, and forms [Si(NH)2] m [Si(CH3)3] n polymer; the latter forms Si(NH)2 silanamine precursor precipitate under the action of NH3 and heating, and finally the silanamine precursor precipitate is filtered and heated to decompose to form ultrapure Si3N4 powder.

[0018] The specific steps of the present invention are as follows:

[0019] 1) The mixture of HMDZ (hexamethylenediamine) and an organic solvent is first cooled, and a measured amount of SiCl4 gas is introduced while continuing to cool. The SiCl4 gas reacts with HMDZ to form an intermediate. The mixture is stirred at a low temperature for a period of time, and the reaction solution is slowly heated to distill off the by-product (CH3)3SiCl. As the by-product (CH3)3SiCl is evaporated and removed, the intermediate in the reaction solution continues to undergo a condensation reaction with HMDZ to form [Si(NH)2] m [Si(CH3)3] n polymer solution;

[0020] 2) The polymer solution formed in step 1) is further heated to distill off the excess HMDZ, and ammonia is introduced into the solution to [Si(NH)2] m [Si(CH3)3] n The polymer solution reacts with ammonia to form a silanamine pre-suspension;

[0021] 3) filtering the preliminary suspension of silicamine obtained in step 2) and collecting the silicamine precursor precipitate, and washing the precipitate with the organic solvent in step 1) to remove impurities;

[0022] 4) pyrolyzing the silanamine precursor precipitate under a nitrogen atmosphere to form Si3N4 powder;

[0023] 5) Purify and recover the organic solvent and HMDZ.

[0024] In step 1), during the reaction, the initial concentration of HMDZ and the rate of SiCl4 introduction were adjusted to control the production of [Si(NH)2] m [Si(CH3)3] n The molecular weight of the polymer, thereby controlling the final silicon nitride particle size;

[0025] The molar ratio of HMDZ to SiCl4 can be 2.1 to 3:1, and the excess HMDZ raw material ensures that the chlorine element in SiCl4 can be completely removed as (CH3)3SiCl.

[0026] The HMDZ and organic solvent mixture needs to be cooled before the SiCl4 gas is introduced, and the cooling temperature is -20 to 10°C.

[0027] The stirring time is 1 to 6 hours.

[0028] The organic solvent has a boiling point higher than that of (CH3)3SiCl, does not contain oxygen or nitrogen, and is an inert organic solvent that does not react with HMDZ, (CH3)3SiCl, or SiCl4. Examples of the organic solvent include xylene, toluene, cyclohexane, and petroleum ether with a boiling point range of 60-90 degrees Celsius.

[0029] In step 3), the precipitate can be washed 1 to 5 times; the organic solvent used for washing is the organic solvent used in step 1).

[0030] In step 4), the pyrolysis temperature may be 1000-1600°C.

[0031] In step 5), the specific steps of purifying and recovering the organic solvent and HMDZ may be:

[0032] (1) HMDZ recovery: (CH3)3SiCl collected in step 1) reacts with ammonia to re-form HMDZ, and NH4Cl is filtered out and then purified by distillation;

[0033] (2) Recovery of organic solvent: The solvent filtered in step 3) is purified by distillation; the recovered and purified organic solvent and HMDZ can continue to participate in the reaction in step 1) to reduce costs.

[0034] The beneficial effects of the present invention are:

[0035] 1. Use HMDZ and SiCl4 to synthesize silanamine precursors. The synthesis process conditions are mild and avoid high-pressure synthesis conditions.

[0036] 2. By adjusting the concentration of HMDZ in the organic solvent and the ventilation rate of SiCl4, the particle size of the final silicon nitride powder can be directly controlled, which is easy to adjust.

[0037] 3. The Cl atoms in SiCl4 are removed in the form of (CH3)3SiCl, and (CH3)3SiCl can be synthesized into hexamethyldisilazane HMDZ and the organic solvent can be recycled and reused at low cost.

[0038] 4. Ultimately, only one by-product, NH4Cl, is produced, and the silanamine precursor does not come into contact with the by-product NH4Cl, making it easy to clean and improving product purity. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 [Si(NH)2] m [Si(CH3)3] n Polymer reaction route.

[0040] Figure 2 This is a schematic diagram of the silanamine precursor synthesis process. It includes a stirred reactor 1, an HMDZ inlet 1a, a xylene inlet 1b, a vent pipe 2, a SiCl4 inlet 2a, an NH3 inlet 2b, a N2 inlet 2c, a distillation column 3, a condenser 4, a (CH3)3SiCl2 receiving tank 5, and a silanamine precursor filter 6. DETAILED DESCRIPTION

[0041] The present invention will be further described with reference to the following embodiments with reference to the accompanying drawings.

[0042] The present invention adopts the reaction of HMDZ and SiCl4 in an organic solvent, removes the Cl atom in SiCl4 from the reaction system in the form of by-product (CH3)3SiCl, and forms [Si(NH)2] m [Si(CH3)3] n polymer; the latter forms Si(NH)2(s) silanamine precursor precipitate under the action of NH3 and heating, and finally the silanamine precursor precipitate is heated and decomposed to form ultrapure Si3N4 powder.

[0043] The specific steps are as follows:

[0044] 1) The mixture of HMDZ and organic solvent is first cooled, and a measured amount of SiCl4 gas is introduced during the cooling process. The SiCl4 gas reacts with HMDZ to form an intermediate. The mixture is stirred for a certain period of time while maintaining a low temperature. The reaction solution is then slowly heated to distill out the by-product (CH3)3SiCl. As (CH3)3SiCl is removed, the intermediate in the reaction solution continues to undergo a polycondensation reaction with HMDZ to form [Si(NH)2] m [Si(CH3)3] n Polymers, reaction processes such as Figure 1 shown.

[0045] During the reaction, the generated [Si(NH)2] can be controlled by adjusting the initial HMDZ concentration and the SiCl4 introduction rate. m [Si(CH3)3] n The molecular weight of the polymer controls the final silicon nitride particle size.

[0046] The molar ratio of HMDZ to SiCl4 is 2.1 to 3:1. Excess HMDZ ensures that the chlorine element in SiCl4 can be completely removed as (CH3)3SiCl. (HMDZ is in excess)

[0047] The HMDZ and organic solvent mixture is cooled to -20 to 10° C. before the SiCl 4 gas is introduced.

[0048] The stirring time is 1 to 6 hours;

[0049] The organic solvent is an inert organic solvent having a boiling point higher than that of (CH3)3SiCl, does not contain oxygen or nitrogen, and does not react with HMDZ, (CH3)3SiCl, or SiCl4.

[0050] 2) The polymer solution formed in step 1) is further heated to distill off the excess HMDZ, and ammonia is introduced into the solution to [Si(NH)2] m [Si(CH3)3] n The polymer reacts with ammonia and precipitates as a silanol precursor.

[0051] 3) Filtering the solution in step 2) and collecting the silanamine precursor precipitate, and washing the precipitate 1 to 5 times with the organic solvent in step 1).

[0052] 4) The silanamine precursor is precipitated and pyrolyzed at 1000-1600° C. in a nitrogen atmosphere to form Si 3 N 4 powder.

[0053] 5) Purify and recover the organic solvent and HMDZ.

[0054] HMDZ recovery involves reacting the (CH3)3SiCl2 collected in step 1) with ammonia to reform HMDZ. After filtering out the NH4Cl, the HMDZ distilled in step 2) is mixed and purified by distillation. Organic solvent recovery involves distilling and purifying the solvent filtered in step 3). The recovered and purified organic solvent and HMDZ can continue to participate in the reaction in step 1), reducing costs.

[0055] Specific examples are given below.

[0056] Example 1

[0057] 1) If Figure 2In a 150L stirred reactor 1, 26kg of HMDZ was added through the HMDZ inlet 1a, followed by 70L of xylene through the xylene inlet 1b. After mixing, the mixture was cooled to -5°C with continuous stirring. While the mixture was still cooled, 17kg of SiCl₄ gas (HMDZ:SiCl₄ molecular ratio of 2.2:1.0) was slowly introduced through the SiCl₄ inlet 2a. After the SiCl₄ introduction was complete, the mixture was stirred at -5°C for 3 hours. N₂ was introduced through the N₂ inlet 2c with continuous stirring. The temperature was slowly raised. As the mixture heated and remained boiling, the byproduct (CH₃)₃SiCl in the solution evaporated. The (CH₃)₃SiCl vapor passed through a distillation column 3 and was condensed in a condenser 4 and collected in a (CH₃)₃SiCl receiving tank 5.

[0058] 2) Remove the (CH3)3SiCl produced by the stirred synthesis reactor 1 through continuous distillation, then close the valve of the (CH3)3SiCl receiving tank 5. Continue heating the stirred synthesis reactor 1 to boiling reflux, and introduce NH3, [Si(NH)2] m [Si(CH3)3] n The polymer reacts with NH3 to form a silanamine pre-suspension.

[0059] 3) The silanamine precursor suspension in the stirred synthesis reactor 1 is drained into the silanamine precursor filter 7 to filter and collect the silanamine precursor, and the silanamine precursor is washed three times with xylene.

[0060] 4) The collected silanamine precursor was transferred to a rotary furnace under anhydrous and oxygen-free conditions, and slowly heated to 1400° C. for pyrolysis, ultimately obtaining 4.3 kg of silicon nitride powder.

[0061] 5) The (CH3)3SiCl collected in step 1) is mixed with the HMDZ and xylene filtered in step 3), and NH3 is introduced into the mixture. The mixture is filtered to remove the NH4Cl, and the HMDZ and xylene solvent are recovered and purified by distillation. The recovered and purified HMDZ and xylene solvent can be added to step 1) to participate in the reaction.

[0062] Analysis of the silicon nitride powder revealed a particle size range of 500 to 1000 nm using a scanning electron microscope (SEM). An elemental analyzer revealed an oxygen content of less than 0.1%, a carbon content of less than 0.15%, and no chlorine. The Si:N ratio was 3:4, indicating complete conversion to Si₃N₄. XRD analysis revealed a α-Si₃N₄ phase concentration of >95%.

[0063] Example 2

[0064] 1) In 150L stirred synthesis kettle 1, 14kg HMDZ was fed into the HMDZ feed inlet la, and 90 liters of xylene was fed into the solvent inlet lb. After mixing, the mixed solution was cooled to 5°C while continuously stirring. The mixed solution was kept at a cool state, and 8.5kg SiCl4 gas was slowly fed into the SiCl4 feed inlet 2a (HMDZ:SiCl4 molar ratio = 2.4:1.0). When the SiCl4 feeding was completed, the mixed solution was kept at 5°C for 3.5h while continuously stirring. N2 was fed into the N2 feed inlet 2c, and the mixed solution was slowly warmed up while continuously stirring. As the mixed solution was warmed up and kept at a boiling state, the by-product (CH3)3SiCl in the solution was evaporated. The (CH3)3SiCl vapor passed through the distillation column 3, and was collected in the (CH3)3SiCl receiving tank 5 through the condensation effect of the condenser 4;

[0065] 2) Same as step 2) of Example 1;

[0066] 3) Same as step 3) of Example 1;

[0067] 4) Same as step 4) of Example 1. Finally, 2.1kg of silicon nitride powder was obtained.

[0068] 5) Same as step 5) of Example 1.

[0069] The silicon nitride powder was analyzed. The powder particle size range was 300-500nm by SEM test. The oxygen content of the silicon nitride powder was <0.1%, the carbon content was <0.15%, no chlorine was detected, Si:N was 3:4, and the complete conversion to Si3N4 was achieved. The α-Si3N4 phase was >95% by XRD test.

[0070] Example 3

[0071] 1) In 200L stirred synthesis kettle 1, 30kg HMDZ was fed into the HMDZ feed inlet la, and 100 liters of toluene was fed into the solvent inlet lb. After mixing, the mixed solution was cooled to 5°C while continuously stirring. The mixed solution was kept at a cool state, and 17kg SiCl4 gas was slowly fed into the SiCl4 feed inlet 2a (HMDZ:SiCl4 molar ratio = 2.6:1.0). When the SiCl4 feeding was completed, the mixed solution was kept at 5°C for 2.5h while continuously stirring. N2 was fed into the N2 feed inlet 2c, and the mixed solution was slowly warmed up while continuously stirring. As the mixed solution was warmed up and kept at a boiling state, the by-product (CH3)3SiCl in the solution was evaporated. The (CH3)3SiCl vapor passed through the distillation column 3, and was collected in the (CH3)3SiCl receiving tank 5 through the condensation effect of the condenser 4;

[0072] 2) Same as step 2) of Example 1;

[0073] 3) Same as step 3) of Example 1;

[0074] 4) Same as step 4) of example 1, finally get 4.1 kg of silicon nitride powder;

[0075] 5) Same as step 5) of example 1, recover HMDZ and toluene.

[0076] The silicon nitride powder is analyzed, and the particle size range of the powder is 500-700 nm by scanning electron microscopy (SEM). The oxygen content of the silicon nitride powder is <0.1%, the carbon content is <0.15%, no chlorine is detected, Si:N is 3:4, and it is completely converted into Si3N4 by elemental analysis. The α-Si3N4 phase is >95% by XRD.

[0077] Example 4

[0078] 1) In 200L synthesis kettle 1 with stirring, 34.5kg HMDZ was put into the HMDZ adding port 1a, and 150 liters of cyclohexane was put into the solvent port 1b. After mixing, the mixed solution was cooled to 5°C. The mixed solution was kept in a cooling state, and 17kg SiCl4 gas was slowly introduced into the SiCl4 inlet port 2a (HMDZ:SiCl4 molecular ratio was 3.0:1.0). When the SiCl4 was introduced, the mixed solution was kept at 5°C for 2.5h, N2 was introduced from the N2 inlet port 2c and continuously stirred, and then slowly warmed up. As the mixed solution was warmed up and maintained in a boiling state, the by-product (CH3)3SiCl in the solution was evaporated, and the (CH3)3SiCl vapor passed through the distillation column 3 and was collected in the (CH3)3SiCl receiving tank 5 under the condensation action of the condenser 4;

[0079] 2) Same as step 2) of example 1;

[0080] 3) Same as step 3) of example 1;

[0081] 4) Same as step 4) of example 1, finally get 4.2 kg of silicon nitride powder;

[0082] 5) Same as step 5) of example 1, recover HMDZ and toluene.

[0083] The silicon nitride powder is analyzed, and the particle size range of the powder is 500-700 nm by scanning electron microscopy (SEM). The oxygen content of the silicon nitride powder is <0.1%, the carbon content is <0.15%, no chlorine is detected, Si:N is 3:4, and it is completely converted into Si3N4 by elemental analysis. The α-Si3N4 phase is >95% by XRD.

[0084] Example 5

[0085] 1) The mixture of HMDZ and organic solvent is cooled first, and then the metered SiCl4 gas is introduced while continuously cooling, the SiCl4 gas reacts with HMDZ to form an intermediate, the reaction solution is slowly heated, and the by-product (CH3)3SiCl is distilled out. With the removal of (CH3)3SiCl, the intermediate in the reaction solution continues to undergo polycondensation reaction with HMDZ to form [Si(NH)2] m [Si(CH3)3] n Polymer solution; during the reaction, the initial concentration of HMDZ is adjusted to 20wt%, and the SiCl4 introduction rate is controlled to 70mL / min to control the production of [Si(NH)2] m [Si(CH3)3] n The molecular weight of the polymer is controlled, thereby controlling the final silicon nitride particle size; the reaction time is 3h; the molar ratio of HMDZ to SiCl4 is 3:1, and the mixture of HMDZ and organic solvent needs to be cooled before the introduction of SiCl4 gas, and the cooling temperature is -10°C. The organic solvent is xylene.

[0086] 2) The polymer solution formed in step 1) is continuously heated, and the excess HMDZ is distilled out, and ammonia gas is introduced into the solution, and [Si(NH)2] m [Si(CH3)3] n The polymer reacts with ammonia to form a silicon amine precursor suspension; the heating temperature is 100°C, the ammonia introduction rate is 30mL / min, and the reaction time is 2h.

[0087] 3) The silicon amine precursor suspension obtained in step 2) is filtered and the silicon amine precursor precipitate is collected, and the precipitate is washed with the organic solvent in step 1); the number of times of washing the precipitate can be 3 times; the organic solvent is xylene.

[0088] 4) The silicon amine precursor precipitate is pyrolyzed under a nitrogen atmosphere to form Si3N4 powder; the pyrolysis temperature is 1400°C, and the nitrogen flow rate is 70mL / min.

[0089] 5) Same as step 5) of Example 1.

[0090] The silicon nitride powder is analyzed, and the powder particle size range is 300-600nm by scanning electron microscopy (SEM). The oxygen content of the silicon nitride powder is <0.1%, the carbon content is <0.15%, no chlorine is detected, Si:N is 3:4, and it is completely converted to Si3N4. The α-Si3N4 phase is >95% by XRD.

[0091] Example 6

[0092] 1) The mixture of HMDZ and organic solvent is first cooled, and a measured amount of SiCl4 gas is introduced during the cooling process. The SiCl4 gas reacts with HMDZ to form an intermediate. The reaction solution is slowly heated to raise the temperature, and the by-product (CH3)3SiCl is distilled out. As (CH3)3SiCl is removed, the intermediate in the reaction solution continues to undergo condensation reaction with HMDZ to form [Si(NH)2] m [Si(CH3)3] n During the reaction, the initial HMDZ concentration was adjusted to 25 wt% and the SiCl4 introduction rate was 80 mL / min to control the production of [Si(NH)2] m [Si(CH3)3] n The molecular weight of the polymer is controlled to control the final silicon nitride particle size; the reaction time is 3.5 hours; the molar ratio of HMDZ to SiCl4 is 2.8:1, and the HMDZ and organic solvent mixture needs to be cooled to 0°C before the SiCl4 gas is introduced. The organic solvent is xylene.

[0093] 2) The polymer solution formed in step 1) is further heated to distill off the excess HMDZ, and ammonia is introduced into the solution to [Si(NH)2] m [Si(CH3)3] n The polymer reacts with ammonia to form a silanamine pre-suspension; the heating temperature is 110° C., the ammonia introduction rate is 25 mL / min, and the reaction time is 3.5 h.

[0094] 3) Filtering the preliminary suspension of silanamine obtained in step 2) and collecting the silanamine precursor precipitate, and washing the precipitate with the organic solvent in step 1); the washing precipitate may be performed four times; the organic solvent is xylene.

[0095] 4) Pyrolyzing the silanamine precursor precipitate in a nitrogen atmosphere to form Si3N4 powder; the pyrolysis temperature is 1500°C, and the nitrogen flow rate is 80 mL / min.

[0096] 5) Same as step 5) in Example 1.

[0097] Analysis of the silicon nitride powder revealed a particle size range of 500-800 nm using a scanning electron microscope (SEM). An elemental analyzer revealed an oxygen content of less than 0.1%, a carbon content of less than 0.15%, and no chlorine. The Si:N ratio was 3:4, indicating complete conversion to Si₃N₄. XRD analysis revealed a α-Si₃N₄ phase concentration of >90%.

[0098] Example 7

[0099] 1) The mixture of HMDZ and organic solvent is first cooled, and a measured amount of SiCl4 gas is introduced during the cooling process. The SiCl4 gas reacts with HMDZ to form an intermediate. The reaction solution is slowly heated to raise the temperature, and the by-product (CH3)3SiCl is distilled out. As (CH3)3SiCl is removed, the intermediate in the reaction solution continues to undergo condensation reaction with HMDZ to form [Si(NH)2] m [Si(CH3)3] n During the reaction, the initial HMDZ concentration was adjusted to 30 wt% and the SiCl4 introduction rate was 90 mL / min to control the production of [Si(NH)2] m [Si(CH3)3] n The molecular weight of the polymer is controlled to control the final silicon nitride particle size; the reaction time is 4 hours; the molar ratio of HMDZ to SiCl4 is 2.2:1, and the HMDZ and organic solvent mixture needs to be cooled to 5°C before the SiCl4 gas is introduced. The organic solvent is xylene.

[0100] 2) The polymer solution formed in step 1) is further heated to distill off the excess HMDZ, and ammonia is introduced into the solution to [Si(NH)2] m [Si(CH3)3] n The polymer reacts with ammonia to form a silanamine pre-suspension; the heating temperature is 120° C., the ammonia introduction rate is 40 mL / min, and the reaction time is 3 h.

[0101] 3) Filtering the preliminary suspension of silanamine obtained in step 2) and collecting the silanamine precursor precipitate, and washing the precipitate with the organic solvent in step 1); the washing precipitate can be performed 5 times; the organic solvent is xylene.

[0102] 4) Pyrolyzing the silanamine precursor precipitate in a nitrogen atmosphere to form Si3N4 powder; the pyrolysis temperature is 1300°C, and the nitrogen flow rate is 80 mL / min.

[0103] 5) Same as step 5) in Example 1.

[0104] Analysis of the silicon nitride powder revealed a particle size range of 600-1000 nm using a scanning electron microscope (SEM). An elemental analyzer revealed an oxygen content of less than 0.1%, a carbon content of less than 0.15%, no chlorine, and a Si:N ratio of 3:4, indicating complete conversion to Si₃N₄. XRD analysis revealed a α-Si₃N₄ phase concentration of >96%.

[0105] Example 8

[0106] 1) The mixture of HMDZ and organic solvent is first cooled, and a measured amount of SiCl4 gas is introduced during the cooling process. The SiCl4 gas reacts with HMDZ to form an intermediate. The reaction solution is slowly heated to raise the temperature, and the by-product (CH3)3SiCl is distilled out. As (CH3)3SiCl is removed, the intermediate in the reaction solution continues to undergo condensation reaction with HMDZ to form [Si(NH)2] m [Si(CH3)3] n During the reaction, the initial HMDZ concentration was adjusted to 12 wt% and the SiCl4 introduction rate was 55 mL / min to control the production of [Si(NH)2] m [Si(CH3)3] n The molecular weight of the polymer is controlled to control the final silicon nitride particle size; the reaction time is 2.2 hours; the molar ratio of HMDZ to SiCl4 is 2.4:1, and the HMDZ and organic solvent mixture needs to be cooled to -18°C before the SiCl4 gas is introduced. The organic solvent is toluene.

[0107] 2) The polymer solution formed in step 1) is further heated to distill off the excess HMDZ, and ammonia is introduced into the solution to [Si(NH)2] m [Si(CH3)3] n The polymer reacts with ammonia to form a silanamine pre-suspension; the heating temperature is 85° C., the ammonia introduction rate is 22 mL / min, and the reaction time is 1.2 h.

[0108] 3) Filtering the preliminary suspension of silanamine obtained in step 2) and collecting the silanamine precursor precipitate, and washing the precipitate with the organic solvent in step 1); the washing precipitate may be performed once; the organic solvent is toluene.

[0109] 4) Pyrolyzing the silanamine precursor precipitate in a nitrogen atmosphere to form Si3N4 powder; the pyrolysis temperature is 1100°C, and the nitrogen flow rate is 55 mL / min.

[0110] 5) Same as step 5) in Example 1.

[0111] Example 9

[0112] 1) The mixture of HMDZ and organic solvent is first cooled, and a measured amount of SiCl4 gas is introduced during the cooling process. The SiCl4 gas reacts with HMDZ to form an intermediate. The reaction solution is slowly heated to raise the temperature, and the by-product (CH3)3SiCl is distilled out. As (CH3)3SiCl is removed, the intermediate in the reaction solution continues to undergo condensation reaction with HMDZ to form [Si(NH)2] m [Si(CH3)3] nDuring the reaction, the initial HMDZ concentration was adjusted to 18 wt% and the SiCl4 introduction rate was adjusted to 65 mL / min to control the production of [Si(NH)2] m [Si(CH3)3] n The molecular weight of the polymer is controlled to control the final silicon nitride particle size; the reaction time is 2.8 hours; the molar ratio of HMDZ to SiCl4 is 2.6:1, and the HMDZ and organic solvent mixture needs to be cooled to -12°C before the SiCl4 gas is introduced. The organic solvent is xylene.

[0113] 2) The polymer solution formed in step 1) is further heated to distill off the excess HMDZ, and ammonia is introduced into the solution to [Si(NH)2] m [Si(CH3)3] n The polymer reacts with ammonia to form a silanamine pre-suspension; the heating temperature is 95° C., the ammonia introduction rate is 28 mL / min, and the reaction time is 1.8 h.

[0114] 3) Filtering the preliminary suspension of silanamine obtained in step 2) and collecting the silanamine precursor precipitate, and washing the precipitate with the organic solvent in step 1); the washing precipitate may be performed twice; the organic solvent is xylene.

[0115] 4) Pyrolyzing the silanamine precursor precipitate in a nitrogen atmosphere to form Si3N4 powder; the pyrolysis temperature is 1300°C, and the nitrogen flow rate is 65 mL / min.

[0116] 5) Same as step 5) in Example 1.

[0117] Example 10

[0118] 1) The mixture of HMDZ and organic solvent is first cooled, and a measured amount of SiCl4 gas is introduced during the cooling process. The SiCl4 gas reacts with HMDZ to form an intermediate. The reaction solution is slowly heated to raise the temperature, and the by-product (CH3)3SiCl is distilled out. As (CH3)3SiCl is removed, the intermediate in the reaction solution continues to undergo condensation reaction with HMDZ to form [Si(NH)2] m [Si(CH3)3] n During the reaction, the initial HMDZ concentration was adjusted to 22 wt% and the SiCl4 introduction rate was 75 mL / min to control the production of [Si(NH)2] m [Si(CH3)3] nThe molecular weight of the polymer is controlled to control the final silicon nitride particle size; the reaction time is 3.2 hours; the molar ratio of HMDZ to SiCl4 is 2.9:1, and the HMDZ and organic solvent mixture needs to be cooled to -8°C before the SiCl4 gas is introduced. The organic solvent is xylene.

[0119] 2) The polymer solution formed in step 1) is further heated to distill off the excess HMDZ, and ammonia is introduced into the solution to [Si(NH)2] m [Si(CH3)3] n The polymer reacts with ammonia to form a silanamine pre-suspension; the heating temperature is 105° C., the ammonia introduction rate is 32 mL / min, and the reaction time is 2.2 h.

[0120] 3) Filtering the preliminary suspension of silanamine obtained in step 2) and collecting the silanamine precursor precipitate, and washing the precipitate with the organic solvent in step 1); the washing precipitate may be performed three times; the organic solvent is xylene.

[0121] 4) Pyrolyzing the silanamine precursor precipitate in a nitrogen atmosphere to form Si3N4 powder; the pyrolysis temperature is 1450°C, and the nitrogen flow rate is 75 mL / min.

[0122] 5) Same as step 5) in Example 1.

[0123] Example 11

[0124] 1) The mixture of HMDZ and organic solvent is first cooled, and a measured amount of SiCl4 gas is introduced during the cooling process. The SiCl4 gas reacts with HMDZ to form an intermediate. The reaction solution is slowly heated to raise the temperature, and the by-product (CH3)3SiCl is distilled out. As (CH3)3SiCl is removed, the intermediate in the reaction solution continues to undergo condensation reaction with HMDZ to form [Si(NH)2] m [Si(CH3)3] n During the reaction, the initial HMDZ concentration was adjusted to 20 wt% and the SiCl4 introduction rate was 70 mL / min to control the production of [Si(NH)2] m [Si(CH3)3] n The molecular weight of the polymer is controlled to control the final silicon nitride particle size; the reaction time is 2 hours; the molar ratio of HMDZ to SiCl4 is 2.3:1, and the HMDZ and organic solvent mixture needs to be cooled to 2°C before the SiCl4 gas is introduced. The organic solvent is cyclohexane.

[0125] 2) The polymer solution formed in step 1) is further heated to distill off the excess HMDZ, and ammonia is introduced into the solution to [Si(NH)2]m [Si(CH3)3] n The polymer solution was heated, and excess HMDZ was distilled off. Ammonia was introduced into the solution, and the [Si(NH)2]

[0126] 3) The silicon amine precursor precipitate obtained in step 2) was filtered and collected, and the precipitate was washed with the organic solvent in step 1); the number of times of washing the precipitate can be 4; and the organic solvent was cyclohexane.

[0127] 4) The silicon amine precursor precipitate was pyrolyzed under a nitrogen atmosphere to form Si3N4 powder; the pyrolysis temperature was 1550°C, and the nitrogen flow rate was 85 mL / min.

[0128] 5) The same as step 5) in Example 1.

[0129] Example 12

[0130] 1) The mixture of HMDZ and an organic solvent was first cooled, and metered SiCl4 gas was introduced while continuously cooling, and the SiCl4 gas reacted with the HMDZ to form an intermediate. The reaction solution was slowly heated, and byproduct (CH3)3SiCl was distilled off. With the removal of (CH3)3SiCl, the intermediate in the reaction solution continued to undergo polycondensation with HMDZ to form [Si(NH)2] m [Si(CH3)3] n The polymer solution; during the reaction, the initial concentration of HMDZ was adjusted to 32 wt%, and the SiCl4 introduction rate was 95 mL / min to control the generation of [Si(NH)2] m [Si(CH3)3] n The molecular weight of the polymer, so as to control the size of the final silicon nitride particles; the reaction time was 4 h; the molar ratio of HMDZ to SiCl4 was 2.7:1; the mixture of HMDZ and an organic solvent needed to be cooled before the introduction of SiCl4 gas, and the cooling temperature was 10°C. The organic solvent was xylene.

[0131] 2) The polymer solution formed in step 1) was continuously heated, and excess HMDZ was distilled off. Ammonia was introduced into the solution, and the [Si(NH)2] m [Si(CH3)3] n The polymer solution was heated, and excess HMDZ was distilled off. Ammonia was introduced into the solution, and the [Si(NH)2]

[0132] 3) The silicon amine precursor precipitate obtained in step 2) was filtered and collected, and the precipitate was washed with the organic solvent in step 1); the number of times of washing the precipitate can be 5; and the organic solvent was xylene.

[0133] 4) The silicon amine precursor is pyrolyzed under nitrogen atmosphere to form Si3N4 powder; the temperature of the pyrolysis is 1600℃, and the nitrogen flow rate is 95 mL / min.

[0134] 5) Same as step 5) of Example 1.

[0135] The present application adopts methyldisilazane to react with SiCl4 in an organic solvent to form an intermediate polymer, then the intermediate polymer is heated to ammonolysis to form a silicon amine precursor, and finally the silicon amine precursor is heated to pyrolysis to form silicon nitride powder. The reaction process avoids high pressure and has mild conditions; the by-product formed by the reaction of methyldisilazane and SiCl4 is recycled to methyldisilazane by ammonolysis, and methyldisilazane and the organic solvent can be recycled by distillation, and finally only ammonium chloride by-product is produced. The silicon amine precursor does not contact with the by-product, so it is easy to clean and has no impurity residues, thereby improving the purity of the powder.

[0136] The above examples are only the preferred embodiments of the present application and should not be considered as limiting the scope of the present application. Any equivalent changes and improvements made according to the scope of the present application should still belong to the scope of the present application.

Claims

1. A method for preparing ultrapure silicon nitride powder by a silanol-amine group exchange method, characterized in that The following steps are involved: 1) The mixture of hexamethyldisilazane and organic solvent is first cooled, and a measured amount of SiCl4 gas is introduced during the cooling process. The SiCl4 gas reacts with hexamethyldisilazane to form an intermediate. The reaction solution is slowly heated to raise the temperature, and the by-product (CH3)3SiCl is distilled out. As (CH3)3SiCl is removed, the intermediate in the reaction solution continues to undergo polycondensation with hexamethyldisilazane to form [Si(NH)2] m [Si(CH3)3] n polymer solution; 2) Continue heating the polymer solution formed in step 1) to distill off the excess hexamethyldisilazane, and pass ammonia into the solution to [Si(NH)2] m [Si(CH3)3] n The polymer solution reacts with ammonia to form a silanamine pre-suspension; 3) filtering the preliminary suspension of silanamine obtained in step 2) and collecting the silanamine precursor precipitate, and washing the precipitate with the organic solvent in step 1); 4) precipitating the silanamine precursor and pyrolyzing it in a nitrogen atmosphere to form Si3N4 powder; 5) Recover and purify the organic solvent and hexamethyldisilazane.

2. The method for preparing ultrapure silicon nitride powder by a silanol-amine group exchange method as claimed in claim 1, characterized in that In step 1), during the reaction, the initial concentration of hexamethyldisilazane and the SiCl4 introduction rate are adjusted to control the generated [Si(NH)2] m [Si(CH3)3] n The molecular weight of the polymer is used to control the final silicon nitride particle size.

3. The method for preparing ultrapure silicon nitride powder by a silanol-amine group exchange method as claimed in claim 1, characterized in that In step 1), the molar ratio of hexamethyldisilazane to SiCl4 is 2.1 to 3:1, and the excess hexamethyldisilazane ensures that the chlorine element in SiCl4 can be completely removed as (CH3)3SiCl.

4. The method for preparing ultrapure silicon nitride powder by a silanol group exchange method as claimed in claim 1, characterized in that In step 1), the hexamethyldisilazane and organic solvent mixture is cooled to -20 to 10° C. before the SiCl 4 gas is introduced.

5. The method for preparing ultrapure silicon nitride powder by a silicon amine group exchange method as claimed in claim 1, characterized in that In step 1), the organic solvent is an inert organic solvent having a boiling point higher than that of hexamethyldisilazane, does not react with hexamethyldisilazane and SiCl 4 , and does not contain oxygen or nitrogen.

6. The method for preparing ultrapure silicon nitride powder by a silanol-amine group exchange method as claimed in claim 1, characterized in that In step 3), the precipitate is washed 1 to 5 times.

7. The method for preparing ultrapure silicon nitride powder by a silicon-amine group exchange method as claimed in claim 1, characterized in that In step 4), the pyrolysis temperature is 1000-1600°C.

8. The method for preparing ultrapure silicon nitride powder by a silicon-amine group exchange method as claimed in claim 1, characterized in that In step 5), the specific steps of recovering and purifying the organic solvent and hexamethyldisilazane are: (1) Recovery of hexamethyldisilazane: (CH3)3SiCl collected in step 1) reacts with ammonia to re-form hexamethyldisilazane, after which NH4Cl is filtered out and mixed with the hexamethyldisilazane distilled in step 2) and purified by distillation; (2) Recovery of organic solvent: The solvent filtered in step 3) is purified by distillation; the recovered purified organic solvent and hexamethyldisilazane continue to participate in the reaction in step 1) to reduce costs.

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