A method for preparing high-performance silicon nitride powder by carbothermal reduction nitridation

Abstract

The invention relates to the technical field of silicon nitride powders, and provides a method for preparing high-performance silicon nitride powders by a carbothermal reduction nitridation method, which solves the problem that silicon carbide and silicon oxynitride impurities are easily generated during large-scale preparation of silicon nitride powders by the existing carbothermal reduction nitridation method, and the purity of the silicon nitride powders is not high. The method comprises the following steps: 1) preparing raw materials: silicon oxide powder, a catalyst, deionized water, and carbon black; 2) wet high-energy ball milling; 3) drying; 4) carbothermal reduction nitridation sintering; and 5) high-temperature decarbonization to obtain high-performance silicon nitride powders.

Description

Technical Field

[0001] The invention relates to the technical field of silicon nitride powder, and in particular to a method for preparing high-performance silicon nitride powder by a carbothermal reduction nitridation method. Background Art

[0002] Silicon nitride has the characteristics of high strength and hardness, high thermal conductivity, high electrical insulation, high chemical stability and high temperature resistance. It is a ceramic material with excellent comprehensive performance. Silicon nitride ceramics have a wide range of applications. At present, they are mainly used in transmission bearing balls for new energy vehicles, grinding and wear-resistant media in the machinery industry, bones in the medical industry, silicon single crystal release agents in the photovoltaic industry, and high thermal conductivity and high strength ceramic substrates in the electronics industry. Among them, silicon nitride powder is the basis of the performance of silicon nitride ceramics. Silicon nitride powder with high purity, fine particle size and narrow particle size distribution plays a decisive role in the preparation of high-performance silicon nitride ceramics. At present, the preparation methods of silicon nitride powder mainly include direct nitridation of silicon powder, carbon thermal reduction method, self-propagating method, thermal decomposition of silicon ammonia salt, etc.

[0003] The direct nitridation of silicon powder is considered to be a cheap and simple method for industrial production of silicon nitride powder. Chinese patent application No. 202410226081.0 discloses a method for preparing α-phase silicon nitride powder, comprising the following steps: (1) Screening: Silicate powder with a particle size of D50 = 2-5 μm is screened to obtain six groups of silicon powder; three groups of silicon powder with particle sizes of <500 nm, 1.5-5 μm and 10-40 μm are mixed as mixed powder I; silicon powder with particle sizes of 500 nm-1.5 μm, 5-10 μm and >40 μm are mixed as mixed powder II; (2) Batching: Mixing mixed powder I or mixed powder II with silicon nitride powder to obtain a mixture; (3) Charging: Loading the mixture into the furnace, evacuating and introducing protective gas; (4) Firing: Firing under an atmosphere of heated nitrogen or nitrogen-hydrogen mixed gas to obtain the mixture. The invention has low energy consumption, more complete reaction, easy control of the reaction process, good powder quality and high α-phase silicon nitride content. Although hydrogen can be added as a reducing gas in the silicon powder nitriding process to participate in the reaction, help control the reaction temperature and reaction rate, and accelerate the nitriding reaction, thereby increasing the α-phase content in the nitriding product, hydrogen has a series of safety issues in industrial production, including but not limited to hydrogen leakage and diffusion, hydrogen explosion, hydrogen control system reliability, pipeline design and installation, etc., which greatly increase the resistance to factory safety production.

[0004] The carbon thermal reduction nitridation method has the characteristics of simple method, low cost, high purity, small particle size and good uniformity of particle size distribution of the prepared powder, which is very suitable for the large-scale production of high-performance silicon nitride powder. However, when using the carbon thermal reduction nitridation method to prepare silicon nitride powder, because the raw materials contain carbonaceous materials such as carbon black, the reduction nitridation temperature range of silicon nitride overlaps to a large extent with the temperature range of silicon carbide generation, resulting in the prepared silicon nitride powder usually having more silicon carbide and silicon oxynitride impurities, which affects the purity and application of silicon nitride powder, greatly limiting the large-scale application of the carbon thermal reduction nitridation method to prepare silicon nitride powder. Summary of the invention

[0005] Therefore, in order to solve the above problems, the present invention provides a method for preparing high-performance silicon nitride powder by carbothermal reduction nitridation, which solves the problem that silicon carbide and silicon oxynitride impurities are easily generated during large-scale preparation of silicon nitride powder by the existing carbothermal reduction nitridation method, and the purity of silicon nitride powder is not high.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing high-performance silicon nitride powder by carbothermal reduction nitridation comprises the following steps:

[0008] S1. Preparation of raw materials: silicon oxide powder, catalyst, deionized water, carbon black;

[0009] S2, wet high-energy ball milling: taking the silicon oxide powder, the catalyst and deionized water, ball milling, then adding the carbon black, stirring and mixing evenly to obtain a suspension slurry;

[0010] S3, drying: drying the suspension slurry obtained in step S2 to obtain a precursor powder with a moisture content of less than 1%;

[0011] S4, carbon thermal reduction nitriding sintering: introducing N2 as a reaction gas into the sintering furnace for sintering, adjusting the pressure to 0.2-6.0 MPa, raising the temperature to 1300-1700°C, and keeping the temperature for 3-20 hours to obtain a reaction powder;

[0012] S5, high temperature decarbonization: the reaction powder obtained in step S4 is subjected to high temperature decarbonization, the decarbonization temperature is 600-800° C., to obtain high performance silicon nitride powder.

[0013] Wherein, the catalyst is: one or a mixture of any proportion of Si powder, Si3N4 powder, Fe powder, Ca powder, FeO powder, MgO powder, and CaO powder;

[0014] Furthermore, the particle size of the silicon oxide powder after being processed in step S2 is 0.5-1.0 micrometers.

[0015] Furthermore, the added amount of the catalyst is 0.1 to 5w% of the total amount of silicon oxide powder.

[0016] Furthermore, the molar ratio of the carbon black to the silicon oxide powder is 0.8-3.

[0017] Furthermore, the solid content of the suspended slurry is 5-50%.

[0018] Furthermore, the flow rate of N2 is 5-40 L / min.

[0019] Furthermore, the drying is any one of spray drying, filter pressing and drying.

[0020] By adopting the above technical solution, the beneficial effects of the present invention are:

[0021] By significantly improving the conventional carbothermal reduction nitridation method, the formation of silicon carbide and silicon oxynitride impurities can be suppressed, the purity of silicon nitride powder can be greatly improved, and the technical problem of large-scale preparation of high-performance silicon nitride powder by carbothermal reduction nitridation can be effectively solved.

[0022] 1. The present invention uses silicon oxide (SiO) as the silicon source, which is composed of a silicon atom and an oxygen atom. Silicon oxide has higher activity than silicon dioxide, and can reduce the reduction temperature, nitridation temperature and nitridation time of the carbon thermal reduction nitridation reaction process, and effectively inhibit the formation of impurities such as silicon carbide and silicon oxynitride during the nitridation reaction process. Specifically: (1) In the carbon thermal reduction nitridation reaction, the high activity of silicon oxide enables it to react with the reducing agent (carbon black) at a relatively low temperature to release silicon atoms, providing more active silicon atoms for the subsequent nitridation reaction, thereby lowering the reduction temperature of the entire reaction; (2) Since the silicon atoms released by silicon oxide have high activity, they can more easily react with nitrogen to form silicon nitride. In this process, the high activity of silicon oxide also helps to lower the nitridation temperature, allowing the reaction to proceed at a lower temperature; (3) Under the same reaction conditions, the reaction system using silicon oxide as the silicon source can reach reaction equilibrium faster, thereby shortening the nitridation time; (4) When using silicon oxide as the silicon source, its high activity enables the reaction to proceed more rapidly and completely, thereby effectively inhibiting the formation of these impurities.

[0023] 2. Use wet ball milling to grind silicon dioxide at high energy to improve its reactivity, and add an appropriate amount of carbon black to mix it so that the carbon black can be fully coated on the surface of silicon dioxide, increasing the contact area between the two, effectively increasing the degree of carbon thermal reduction nitridation reaction, and improving the purity of silicon nitride powder after the reaction.

[0024] 3. By adding a certain amount of reaction catalyst, the catalyst can form a certain liquid phase with silicon oxide at a lower temperature, reduce the system temperature, effectively promote the carbon thermal reduction nitridation reaction, and avoid the formation of silicon carbide impurities at high temperature.

[0025] 4. During the carbon thermal reduction nitriding sintering process, flowing nitrogen at a certain pressure is continuously introduced. Increasing the gas pressure can increase the effective contact area between nitrogen and silicon oxide. The continuous flowing nitrogen can take away the CO, CO2 and other gases produced in the reaction process, promote the reaction, avoid the formation of silicon carbide and silicon oxynitride impurities, and effectively improve the purity of silicon nitride powder after the reaction.

[0026] 5. The carbon thermal reduction nitridation method adopted in the present invention is used to prepare silicon nitride powder. The obtained silicon nitride powder is a high-purity and high-activity powder with an average particle size of 0.5 to 3 microns, an O content of less than 1.5%, a C content of less than 500 ppm, an impurity content of less than 0.5%, an α phase content of 50 to 96%, and a β phase content of 0 to 50%, wherein the α phase and β phase contents can be adjusted and controlled by the reaction temperature. DETAILED DESCRIPTION

[0027] Example 1

[0028] A method for preparing high-performance silicon nitride powder by carbothermal reduction nitridation comprises the following steps:

[0029] S1. Preparation of raw materials: silicon oxide powder, CaO powder, deionized water, carbon black;

[0030] S2, wet high-energy ball milling: take the silicon oxide powder, CaO powder and deionized water, ball mill to obtain a suspension slurry, the weight ratio of the CaO powder to the silicon oxide powder is 0.5:100, the weight ratio of the deionized water to the silicon oxide powder is 3:1, the ball milling time is 2 hours, the average particle size of the mixture after ball milling is 0.8 microns, and then add the carbon black, stir and mix evenly to obtain a suspension slurry, the molar ratio of the carbon black to the silicon oxide powder is 1.5:1;

[0031] S3, drying: drying the suspension slurry obtained in step S2, wherein the drying process is firstly performed by filter pressing for preliminary drying, and then performed by a high-temperature oven for secondary drying, wherein the temperature of the high-temperature oven is 120° C., and the drying time is 6 hours, and after drying, a precursor powder having a moisture content of 0.5% is obtained;

[0032] S4, carbon thermal reduction nitriding sintering: N2 is introduced into the sintering furnace as a reaction gas for sintering, the pressure is adjusted to 2MPa, the nitrogen flow rate is 10L / min, the temperature is increased to 1350°C, and the heat preservation time is 10h to obtain a reaction powder;

[0033] S5, high temperature decarbonization: the reaction powder obtained in step S4 is subjected to high temperature decarbonization, the temperature is increased to 750° C., the time is 5 hours, and high performance silicon nitride powder is obtained.

[0034] The high-performance silicon nitride powder prepared in this example was tested, and its average particle size was 0.9 micrometers, the O content was 0.9%, the C content was 450 ppm, and the α-phase content was 94%.

[0035] Example 2

[0036] A method for preparing high-performance silicon nitride powder by carbothermal reduction nitridation comprises the following steps:

[0037] S1. Preparation of raw materials: silicon oxide powder, FeO powder, deionized water, carbon black;

[0038] S2, wet high-energy ball milling: take the silicon oxide powder, FeO powder and deionized water, ball mill to obtain a suspension slurry, the weight ratio of the FeO powder to the silicon oxide powder is 1:100, the weight ratio of the deionized water to the silicon oxide powder is 2:1, the ball milling time is 1 hour, the average particle size of the mixture after ball milling is 1 micron, then add the carbon black, stir and mix evenly to obtain a suspension slurry, the molar ratio of the carbon black to the silicon oxide powder is 2:1;

[0039] S3, drying: drying the suspension slurry obtained in step S2, wherein the drying process is spray drying, and the air inlet temperature is 260° C. After drying, a precursor powder having a moisture content of 0.6% is obtained;

[0040] S4, carbon thermal reduction nitriding sintering: N2 is introduced into the sintering furnace as a reaction gas for sintering, the pressure is adjusted to 3MPa, the nitrogen flow rate is 8L / min, the temperature is increased to 1450°C, and the heat preservation time is 10h to obtain a reaction powder;

[0041] S5, high temperature decarbonization: the reaction powder obtained in step S4 is subjected to high temperature decarbonization, the temperature is increased to 650° C., the time is 5 hours, and high performance silicon nitride powder is obtained.

[0042] The high-performance silicon nitride powder prepared in this example was tested and found to have an average particle size of 1.5 microns, an O content of 1%, a C content of 500 ppm, and an α-phase content of 90%.

[0043] Example 3

[0044] A method for preparing high-performance silicon nitride powder by carbothermal reduction nitridation comprises the following steps:

[0045] S1. Preparation of raw materials: silicon oxide powder, MgO powder, deionized water, carbon black;

[0046] S2, wet high-energy ball milling: take the silicon oxide powder, MgO powder and deionized water, ball mill to obtain a suspension slurry, the weight ratio of the MgO powder to the silicon oxide powder is 1.5:100, the weight ratio of the deionized water to the silicon oxide powder is 4:1, the ball milling time is 1 hour, the average particle size of the mixture after ball milling is 0.8 microns, and then add the carbon black, stir and mix evenly to obtain a suspension slurry, the molar ratio of the carbon black to the silicon oxide powder is 2:1;

[0047] S3, drying: drying the suspension slurry obtained in step S2, wherein the drying process is firstly performed by filter pressing for preliminary drying, and then performed by secondary drying in a high-temperature oven, wherein the specific drying temperature is 120° C. and the drying time is 6 hours, and after drying, a precursor powder having a moisture content of 0.55% is obtained;

[0048] S4, carbon thermal reduction nitriding sintering: N2 is introduced into the sintering furnace as a reaction gas for sintering, the pressure is adjusted to 2MPa, the nitrogen flow rate is 15L / min, the temperature is increased to 1550°C, and the heat preservation time is 8h to obtain a reaction powder;

[0049] S5, high temperature decarbonization: the reaction powder obtained in step S4 is subjected to high temperature decarbonization, the temperature is increased to 650° C., the time is 5 hours, and high performance silicon nitride powder is obtained.

[0050] The high-performance silicon nitride powder prepared in this example was tested, and its average particle size was 1.5 microns, the O content was 0.8%, the C content was 400 ppm, and the α-phase content was 90%.

[0051] Comparative Example 1

[0052] The difference from Example 1 is that this comparative example uses silicon dioxide instead of silicon oxide in Example 1 to perform carbothermal reduction nitridation to prepare silicon nitride powder. The specific implementation steps are as follows:

[0053] (1) mixing silica powder, CaO powder and deionized water and then performing wet high-energy ball milling, wherein the weight ratio of CaO to silica is 1.5:100, the weight ratio of deionized water to silica is 4:1, the ball milling time is 1 hour, and the average particle size after ball milling is 0.8 microns; adding carbon black to the slurry after ball milling and stirring to obtain a uniformly mixed suspension slurry, wherein the mass molar ratio of carbon black to silica is 2:1;

[0054] (2) drying the suspension slurry obtained in step (1), specifically, performing preliminary drying by filter pressing, and then performing secondary drying in a high-temperature oven, specifically, the drying temperature is 120° C., the drying time is 6 h, and the moisture content of the powder after drying is 0.55%, thereby obtaining a precursor mixed powder;

[0055] (3) subjecting the precursor powder obtained in step (2) to a carbon thermal reduction nitridation sintering reaction to obtain a reaction powder; the nitrogen pressure of the carbon thermal reduction nitridation reaction is 2 MPa, the nitrogen flow rate is 15 L / min, the reaction sintering temperature is 1500° C., and the sintering time is 8 h;

[0056] (4) The reaction powder obtained in step (3) is subjected to high-temperature decarbonization treatment to obtain silicon nitride powder; the decarbonization temperature is 650° C. and the time is 5 hours.

[0057] The silicon nitride powder prepared in this comparative example was tested and found to have an average particle size of 1.5 microns, an O content of 6%, a C content of 3%, and an α-phase content of 70%.

[0058] It can be seen from the results of Example 1 and Comparative Example 1 that the silicon nitride powder prepared by carbon thermal reduction nitridation using silicon dioxide as the raw material has a low powder purity and it is difficult to avoid the formation of silicon carbide impurity phase; while the silicon nitride powder prepared by using silicon oxide as the raw material has a very high purity, can effectively inhibit the formation of silicon carbide and silicon oxynitride impurity phases, and has a fine powder particle size and a high α phase content, and is suitable for preparing high-performance silicon nitride powder.

[0059] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, it should be understood by those skilled in the art that various changes may be made to the present invention in form and details without departing from the spirit and scope of the present invention as defined by the appended claims, all of which are within the scope of protection of the present invention.

Claims

1. A method for preparing high-performance silicon nitride powder by carbothermal reduction nitridation, characterized in that: The following steps are involved: S1. Preparation of raw materials: silicon oxide powder, catalyst, deionized water, carbon black; S2, wet high-energy ball milling: taking the silicon oxide powder, the catalyst and deionized water, ball milling, then adding the carbon black, stirring and mixing evenly to obtain a suspension slurry; S3, drying: drying the suspension slurry obtained in step S2 to obtain a precursor powder with a moisture content of less than 1%; S4, carbon thermal reduction nitriding sintering: introducing N2 as a reaction gas into the sintering furnace for sintering, adjusting the pressure to 0.2-6.0 MPa, raising the temperature to 1300-1700°C, and keeping the temperature for 3-20 hours to obtain a reaction powder; S5, high temperature decarbonization: the reaction powder obtained in step S4 is subjected to high temperature decarbonization, the decarbonization temperature is 600-800° C., to obtain high performance silicon nitride powder. Wherein, the catalyst is: one or a mixture of any proportion of Si powder, Si3N4 powder, Fe powder, Ca powder, FeO powder, MgO powder and CaO powder.

2. The method for preparing high-performance silicon nitride powder by carbothermal reduction nitridation according to claim 1, characterized in that: The particle size of the silicon oxide powder after being processed in step S2 is 0.5-1.0 micrometers.

3. The method for preparing high-performance silicon nitride powder by carbothermal reduction nitridation according to claim 1, characterized in that: The added amount of the catalyst is 0.1-5w% of the total amount of silicon oxide powder.

4. The method for preparing high-performance silicon nitride powder by carbothermal reduction nitridation according to claim 1, characterized in that: The molar ratio of the carbon black to the silicon oxide powder is 0.8-3.

5. The method for preparing high-performance silicon nitride powder by carbothermal reduction nitridation according to claim 1, characterized in that: The solid content of the suspension slurry is 5-50%.

6. The method for preparing high-performance silicon nitride powder by carbothermal reduction nitridation according to claim 1, characterized in that: The flow rate of N2 is 5-40 L / min.

7. The method for preparing high-performance silicon nitride powder by carbothermal reduction nitridation according to claim 1, characterized in that: The drying is any one of spray drying, filter pressing and drying.