Silicon magnesium nitride powder, step-by-step gas pressure self-propagating preparation method and application thereof

Abstract

This application relates to a silicon nitride magnesium powder, its stepwise gas-pressure self-propagating preparation method, and its application, belonging to the technical field of high-performance ceramic powder materials. The method involves uniformly mixing magnesium powder, silicon nitride powder, and inorganic salt powder, placing them in a self-propagating reaction system, first performing multi-point ignition under a low-pressure argon atmosphere, and then switching to high-pressure nitrogen conditions to complete the reaction, obtaining silicon nitride magnesium composite powder; subsequently, through multi-step cleaning and low-temperature annealing treatment, the silicon nitride magnesium powder is obtained; the particle size is 1.2μm~2.5μm; the molar content of magnesium is 25%~45%, the molar content of silicon nitride is 55%~75%, the oxygen content is <0.2wt.%, and the specific surface area is 2.0m². 2 / g~8.0m 2 / g; applicable to sintering aids, refractory materials, composite material reinforcing phases and electronic packaging substrates, etc.

Description

Technical Field

[0001] This application relates to the field of high-performance ceramic materials technology, and in particular to magnesium silicon nitride powder, its stepwise gas pressure self-propagating preparation method and application. Background Technology

[0002] The self-propagating high-temperature synthesis method for magnesium silicon nitride powder has advantages such as low energy consumption, fast reaction speed, and simple process. The basic principle of this technology is to use magnesium powder and silicon nitride powder as raw materials, and to initiate an exothermic reaction through local ignition in a high-pressure nitrogen atmosphere. The heat generated by the reaction itself is used to maintain the spontaneous propagation of the reaction wave, and finally synthesize the target product.

[0003] However, due to the unidirectional or asymmetric propagation of the reaction wave, the internal temperature field and reaction process of the reaction system are uneven, causing local overheating and resulting in a large amount of magnesium powder volatilization. At the same time, due to insufficient heat in other areas, unreacted raw material nuclei remain, leading to uneven composition of the final product, difficulty in further improving the conversion rate, and the potential introduction of impurity phases. Secondly, magnesium powder has a low melting and boiling point, making it highly volatile under the high temperatures generated by the self-propagating reaction, especially at the moment of reaction initiation, where intense exothermic release at a single point exacerbates local magnesium evaporation. The volatilized magnesium vapor condenses in the cooler parts of the reaction vessel and is easily oxidized by residual oxygen, forming impurities such as magnesium oxide, which adhere to the target product, leading to increased oxygen content and decreased purity in the powder, severely affecting the sintering performance and thermal conductivity of subsequent ceramic materials.

[0004] Most existing technologies complete the ignition and reaction process under a constant high-pressure nitrogen atmosphere. This single pressure environment makes it difficult to differentiate and control different stages of the reaction. While a high-pressure environment is beneficial for the nitriding reaction, it may also exacerbate the reaction intensity at the moment of ignition, which is not conducive to suppressing the initial volatilization of magnesium. In addition, residual air in the reaction vessel may react with the raw materials at high temperatures, introducing oxygen impurities. Summary of the Invention

[0005] This application addresses the technical problems of low purity and yield of existing silicon nitride magnesium powder by providing a novel stepwise gas pressure self-propagating preparation method that can effectively improve reaction uniformity, significantly suppress magnesium volatilization, and obtain high-purity, low-oxygen-content silicon nitride magnesium powder.

[0006] The objective of this application can be achieved through the following technical solutions.

[0007] In a first aspect of this application, a stepwise gas-pressure self-propagating preparation method for silicon magnesium nitride powder is provided, characterized by comprising the following steps:

[0008] Magnesium powder, silicon nitride powder and inorganic salt powder are provided and mixed to obtain a mixed powder.

[0009] The mixed powder was placed in a self-propagating reaction system and subjected to multi-point low-pressure ignition under a first pressure P1, followed by a high-pressure reaction under a second pressure P2 to obtain silicon magnesium nitride composite powder.

[0010] The silicon nitride magnesium composite powder is sequentially cleaned and heat-treated to obtain the silicon nitride magnesium powder; wherein, P2:P1=(3.75-10):1.

[0011] Preferably, the multi-point low-pressure ignition has 2 to 3 ignition points, which are distributed on three adjacent walls or two opposite walls of the square material frame; the gas introduced for the multi-point low-pressure ignition is argon, and the gas introduced for the high-pressure reaction is nitrogen.

[0012] This application utilizes multi-point low-pressure ignition to initiate multiple reaction wavefronts, allowing them to superimpose and ensuring more complete reaction propagation within the billet, thus reducing unreacted zones. In the stepwise gas pressure self-propagating preparation method, the low-pressure argon atmosphere primarily acts during the reaction initiation stage, providing an inert environment to prevent magnesium powder from being oxidized or undergoing abnormal combustion during ignition, while ensuring the mild and controllable initiation of the self-propagating reaction. Subsequently, the high-pressure nitrogen atmosphere acts as the reaction driver, significantly suppressing the volatilization loss of magnesium powder at high temperatures by increasing the system pressure, forcing more magnesium powder to participate in the reaction in a condensed state. Based on gas dissolution and diffusion, the high-pressure environment significantly increases the solubility of nitrogen in molten magnesium and accelerates the diffusion of nitrogen atoms, thereby efficiently promoting the formation of magnesium nitride and obtaining high-purity magnesium silicon nitride powder.

[0013] More preferably, the pressure range of the first pressure P1 is 0.5MPa to 0.8MPa, and the pressure range of the second pressure P2 is 3MPa to 5MPa.

[0014] The first pressure P1 of this application is a low-pressure range, which can eliminate air interference and make the reaction temperature controllable; the second pressure P2 is a high-pressure range, which can significantly increase the partial pressure of nitrogen. Based on the principle of gas dissolution and diffusion, high pressure can ensure that magnesium powder is fully nitrided and improve the conversion rate and purity of the final product.

[0015] The inorganic salt powder includes potassium chloride and / or sodium chloride.

[0016] The inorganic salt powder described in this application is a diluent that absorbs a large amount of reaction heat when it melts or vaporizes at high temperatures, effectively suppressing the system temperature and preventing the product from sintering and agglomerating. At the same time, the molten salt surrounds the newly formed particles to form a physical barrier, which plays an isolation role, thereby controlling the particle size and morphology of the final product.

[0017] This application introduces a specific mass fraction of inorganic salt as a diluent to suppress the sintering and agglomeration of magnesium silicon nitride particles at high temperatures and excessive grain growth, thereby obtaining powder with fine particle size and uniform distribution.

[0018] Furthermore, the cleaning process includes multiple cleaning steps, and the heat treatment includes low-temperature annealing under a nitrogen atmosphere.

[0019] Preferably, the multi-step cleaning includes deionized water cleaning and acid washing; the low-temperature annealing treatment has a temperature range of 800℃~1000℃ and a time of 1h~4h.

[0020] The multi-step cleaning process described in this application removes various impurities: water washing dissolves inorganic salts, while acid washing dissolves unreacted metallic magnesium or its oxides. Low-temperature annealing under nitrogen provides heat to the powder, promoting atomic migration to repair lattice defects and improve crystallinity, while simultaneously preventing oxidation of the powder at high temperatures. Through this multi-step cleaning process, grain perfection and growth are effectively promoted, thereby significantly improving the crystallinity of the final product and resulting in an extremely low oxygen content.

[0021] Preferably, the mixing method is high-energy ball milling; more preferably, the high-energy ball milling speed is 200 rpm to 300 rpm and the time is 6 h to 24 h.

[0022] Further, the molar ratio of the magnesium powder to the silicon nitride powder is (1.1~1.2):1; the mass fraction of the inorganic salt powder in the mixed powder is 10wt.%~20wt.%; the particle size of the magnesium powder is 10μm~100μm; and the particle size of the silicon nitride powder is 20nm~100nm.

[0023] The magnesium powder used in this application is added in excess of 10% to 20% to compensate for its volatilization loss at high temperatures, ensuring complete and sufficient reaction of silicon nitride. The amount of inorganic salt added within this range effectively dilutes and controls the temperature, avoiding ineffective reaction due to insufficient addition or reaction-inhibiting reaction due to excessive addition.

[0024] In a second aspect, this application provides a silicon-magnesium nitride powder obtained by the above-described stepwise gas pressure self-propagating preparation method, wherein the silicon-magnesium nitride powder has a particle size of 1.2 μm to 2.5 μm and a specific surface area of ​​2.0 m². 2 / g~8.0m 2 / g; In the silicon nitride magnesium powder, the molar content of magnesium is 25%~45%, the molar content of silicon nitride is 55%~75%, and the oxygen content is <0.2wt.%.

[0025] In a third aspect, this application provides the application of the aforementioned magnesium silicon nitride powder in sintering aids, refractory material components, metal / ceramic reinforcing phases, high thermal conductivity ceramic substrates for electronic packaging, or circuit substrates.

[0026] The beneficial effects of the method described in this application include: by adopting a stepwise gas pressure control strategy of low-pressure ignition-high-pressure reaction, combined with multi-point low-pressure ignition, it ensures that the self-propagating reaction wave can propagate uniformly and completely, effectively reducing the unreacted zone, thereby significantly improving the stability of batch reaction and the consistency of products. Based on the self-propagating high-temperature synthesis technology, the reaction itself has the advantages of low energy consumption and rapid reaction. Attached Figure Description

[0027] Figure 1 Here is a morphology image of the magnesium silicon nitride powder prepared in Example 1;

[0028] Figure 2 Here is a morphology image of the magnesium silicon nitride powder prepared in Example 2;

[0029] Figure 3 Here is a morphology image of the magnesium silicon nitride powder prepared in Example 3;

[0030] Figure 4 These are the XRD patterns of magnesium silicon nitride prepared in Examples 1-3. Detailed Implementation

[0031] The following detailed description, with appropriate reference to the accompanying drawings, discloses an embodiment of magnesium silicon nitride powder, its stepwise gas pressure self-propagating preparation method, and its application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0032] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. The range defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range.

[0033] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0034] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0035] Existing technologies often employ a single atmospheric or constant pressure for self-propagating synthesis. During the reaction, a large amount of magnesium powder is lost due to volatilization at high temperatures, and the driving force of nitrogen penetration is insufficient, resulting in unreacted magnesium or silicon nitride remaining in the product, leading to low phase purity. Furthermore, the product is prone to severe sintering due to local overheating, resulting in poor particle size uniformity. Therefore, this application designs a stepwise pressure self-propagating preparation method that can effectively suppress magnesium volatilization, promote complete reaction, and obtain high-purity, fine-particle magnesium silicon nitride powder.

[0036] The stepwise gas pressure self-propagating preparation method of silicon nitride magnesium powder in this application includes the following steps:

[0037] Magnesium powder, silicon nitride powder and inorganic salt powder are provided and mixed to obtain a mixed powder.

[0038] The mixed powder was placed in a self-propagating reaction system and subjected to multi-point low-pressure ignition under a first pressure P1, followed by a high-pressure reaction under a second pressure P2 to obtain silicon magnesium nitride composite powder.

[0039] The silicon nitride magnesium composite powder is sequentially cleaned and heat-treated to obtain the silicon nitride magnesium powder; wherein, P2:P1 = (3.75-10):1.

[0040] The multi-point low-pressure ignition has 2 to 3 ignition points, which are distributed on three adjacent walls or two opposite walls of the square material frame; the gas introduced for the multi-point low-pressure ignition is argon, and the gas introduced for the high-pressure reaction is nitrogen.

[0041] The pressure range of the first pressure P1 is 0.5MPa to 0.8MPa, and the pressure range of the second pressure P2 is 3MPa to 5MPa.

[0042] The inorganic salt powder includes potassium chloride and / or sodium chloride.

[0043] The cleaning process includes multiple steps, and the heat treatment includes low-temperature annealing under a nitrogen atmosphere.

[0044] The multi-step cleaning includes deionized water cleaning and acid washing; the low-temperature annealing treatment has a temperature range of 800℃~1000℃ and a time range of 1h~4h.

[0045] The mixing method is high-energy ball milling.

[0046] The molar ratio of magnesium powder to silicon nitride powder is (1.1~1.2):1, the mass fraction of inorganic salt powder in the mixed powder is 10wt.%~20wt.%, the particle size of magnesium powder is 10μm~100μm, and the particle size of silicon nitride powder is 20nm~100nm.

[0047] Example 1

[0048] The silicon nitride magnesium raw material composition of this embodiment is: magnesium powder, silicon nitride powder, and potassium chloride powder; the particle size of the magnesium powder is 50μm~100μm, the particle size of the silicon nitride powder is 20nm~50nm, and the molar ratio of magnesium powder to silicon nitride powder is 1.15:1; the potassium chloride powder accounts for 15 wt.% of the total mass of the above mixed powders, and the potassium chloride powder is used as an inorganic salt diluent.

[0049] S1. Magnesium powder, silicon nitride powder and potassium chloride powder are placed in a planetary ball mill and mechanically mixed at a speed of 250 rpm for 12 hours to obtain a uniformly mixed powder.

[0050] S2. Load the above mixed powder into a self-propagating high-temperature synthesis reaction apparatus and seal the reaction chamber. First, introduce high-purity argon gas into the reaction chamber to replace the air, and then adjust and maintain the gas pressure in the chamber at 0.6 MPa.

[0051] Under the low-pressure argon atmosphere, a multi-point ignition device is used to ignite the mixed powder at three adjacent walls of the square material frame simultaneously, thereby initiating a self-propagating reaction.

[0052] After the reaction wave has stabilized and propagated, the gas in the reaction chamber is quickly switched to high-purity nitrogen, and the gas pressure is rapidly increased to 4.0 MPa. The reaction is maintained under this high-pressure nitrogen atmosphere until completion. After natural cooling, blocky silicon magnesium nitride composite powder is obtained.

[0053] S3. The resulting blocky composite powder is first washed multiple times with deionized water to completely remove soluble potassium chloride. Then, it is acid-washed with a 0.5 mol / L dilute hydrochloric acid solution for 30 minutes to dissolve unreacted magnesium metal and any magnesium oxide that may be present on its surface. After acid washing, it is repeatedly rinsed with deionized water until neutral, and finally dried in an oven at 80℃ for 12 hours.

[0054] S4. Place the cleaned and dried powder in a tube furnace and heat it to 900°C at a heating rate of 5°C / min under the protection of flowing high-purity nitrogen. Hold it at this temperature for 2 hours for annealing treatment, and then cool it to room temperature with the furnace to obtain the final high-purity silicon magnesium nitride powder.

[0055] The silicon-magnesium nitride powder prepared by the method in this embodiment has a grain size of 1.5 μm-2.5 μm. Figure 1 The purity was 99.75%, the yield reached 96.63%, the oxygen content was as low as 0.09 wt.%, and the specific surface area was 4.87 m². 2 / g (specific data for each indicator are shown in Table 1); this powder exhibits high purity, low oxygen content, and suitable specific surface area; XRD pattern ( Figure 4 The results show that the product has good crystallization and very few impurity phase peaks.

[0056] Example 2

[0057] The silicon nitride magnesium raw material composition of this embodiment is: magnesium powder, silicon nitride powder, and sodium chloride powder; the particle size of the magnesium powder is 80μm~100μm, the particle size of the silicon nitride powder is 20nm~100nm, and the molar ratio of magnesium powder to silicon nitride powder is 1.2:1; the sodium chloride powder accounts for 10 wt.% of the total mass of the above mixed powder, and the potassium chloride powder is used as an inorganic salt diluent.

[0058] S1. Magnesium powder, silicon nitride powder and sodium chloride powder are placed in a planetary ball mill and mechanically mixed at a speed of 300 rpm for 15 hours to obtain a uniformly mixed powder.

[0059] S2. Load the above mixed powder into a self-propagating high-temperature synthesis reaction apparatus and seal the reaction chamber. First, introduce high-purity argon gas into the reaction chamber to replace the air, and then adjust and maintain the gas pressure in the chamber at 0.8 MPa.

[0060] Under the low-pressure argon atmosphere, a multi-point ignition device is used to ignite the mixed powder at three adjacent walls of the square material frame simultaneously, thereby initiating a self-propagating reaction.

[0061] After the reaction wave has stabilized and propagated, the gas in the reaction chamber is quickly switched to high-purity nitrogen, and the gas pressure is rapidly increased to 6.0 MPa. The reaction is maintained under this high-pressure nitrogen atmosphere until completion. After natural cooling, blocky silicon magnesium nitride composite powder is obtained.

[0062] S3. Perform deionized water cleaning and dilute hydrochloric acid pickling in sequence; anneal the powder at 850℃ under nitrogen atmosphere for 3 hours.

[0063] The silicon magnesium nitride powder prepared by the method in this embodiment has a grain size of 1.5μm-2.0μm. Figure 2 The purity is as high as 99.84%, the yield is 95.91%, the oxygen content is 0.13 wt.%, and the specific surface area reaches 7.39 m². 2 / g (specific data for each indicator are shown in Table 1); the powder has a uniform particle size distribution and regular morphology; XRD pattern ( Figure 4 The results show that the product has good crystallization and very few impurity phase peaks.

[0064] Example 3

[0065] The silicon nitride magnesium raw material composition of this embodiment is: magnesium powder, silicon nitride powder, sodium chloride, and potassium chloride powder; the particle size of the magnesium powder is 10μm~50μm, the particle size of the silicon nitride powder is 20nm~80nm, and the molar ratio of magnesium powder to silicon nitride powder is 1.1:1; an inorganic salt diluent with a total mass of 20 wt.% of the mixed powder is added to the above raw material powder, and the diluent is composed of potassium chloride and sodium chloride mixed in a mass ratio of 1:1.

[0066] S1. Place the mixed powder in a high-energy ball mill and ball mill at 220 rpm for 18 hours to ensure uniform mixing.

[0067] S2. Magnesium powder, silicon nitride powder, sodium chloride powder and potassium chloride powder are placed in a planetary ball mill and mechanically mixed at a speed of 280 rpm for 24 hours to obtain a uniformly mixed powder.

[0068] S3. Load the above mixed powder into a self-propagating high-temperature synthesis reaction apparatus and seal the reaction chamber. First, introduce high-purity argon gas into the reaction chamber to replace the air, and then adjust and maintain the gas pressure in the chamber at 0.5 MPa.

[0069] Under the low-pressure argon atmosphere, a multi-point ignition device is used to ignite the mixed powder simultaneously on two adjacent opposite walls of the square material frame, thus initiating a self-propagating reaction.

[0070] After the reaction wave has stabilized and propagated, the gas in the reaction chamber is quickly switched to high-purity nitrogen, and the gas pressure is rapidly increased to 7.0 MPa. The reaction is maintained under this high-pressure nitrogen atmosphere until completion. After natural cooling, blocky silicon magnesium nitride composite powder is obtained.

[0071] S4. Perform deionized water cleaning and dilute hydrochloric acid pickling in sequence; anneal the powder at 1000℃ under nitrogen atmosphere for 1 hour.

[0072] The silicon-magnesium nitride powder prepared by the method in this embodiment has a grain size of 1.4 μm-2.0 μm (see [reference]). Figure 3 The purity reached 99.94%, the yield was 94.57%, the oxygen content was 0.16 wt.%, and the specific surface area was 7.11 m². 2 / g (Specific data for each indicator are shown in Table 1). XRD pattern ( Figure 4 The results show that the product has good crystallization and very few impurity phase peaks.

[0073] Comparative Example 1

[0074] This comparative example does not use stepwise pressure; the entire reaction is carried out in a nitrogen atmosphere of 4.0 MPa. A single ignition source is used for ignition from one direction. The remaining steps are the same as in Example 1.

[0075] The product obtained by this comparative method had a yield of only 70.25%, an oxygen content as high as 1.8 wt.%, and a relatively low specific surface area of ​​2.76 m². 2 / g (specific data for each indicator are shown in Table 1). The presence of a large number of unreacted areas and severe sintering agglomeration in the product indicates that the single high pressure and single-point ignition led to uneven reaction and severe magnesium volatilization, resulting in performance significantly inferior to the embodiments of the present invention.

[0076] Comparative Example 2

[0077] This comparative example does not add any inorganic salt powder, and the remaining steps are exactly the same as in Example 1.

[0078] The product obtained by this comparative method had a yield of 78.54%, an oxygen content of 1.1 wt.%, and a specific surface area of ​​3.91 m². 2 / g (specific data for each indicator are shown in Table 1). The product has uneven particle size and obvious hard agglomeration, proving that the lack of inorganic salt diluent cannot effectively control the reaction temperature and inhibit particle sintering.

[0079] Comparative Example 3

[0080] After the mixed powder is loaded into the reaction apparatus, without introducing an inert gas for protection, it is directly ignited in air (at normal pressure) at multiple points; after the reaction is initiated, nitrogen gas is quickly introduced and the pressure is increased to 4.0 MPa; the remaining steps are the same as in Example 1.

[0081] The product obtained by this comparative method had a yield as low as 69.41%, a severely excessive oxygen content (8.0 wt.%), and an abnormally high specific surface area of ​​10.32 m². 2 / g (specific data for each indicator are shown in Table 1). The product was severely oxidized due to ignition in air, resulting in the formation of a large number of impurity phases, which completely fails to meet the requirements for high-purity powder.

[0082] Comparative Example 4

[0083] The composite powder obtained in this comparative reaction was simply washed with deionized water until no chloride ions were detected, and then dried. No acid washing or subsequent low-temperature annealing was performed. The remaining steps were the same as in Example 1.

[0084] The product obtained by this comparative method had a yield of 85.32%, but the oxygen content was still as high as 2.86 wt.%, and the specific surface area was relatively low at 2.90 m². 2 / g (specific data for each indicator are shown in Table 1). Due to the lack of pickling and annealing, unreacted magnesium and its oxides remain in the powder, and the crystallinity is poor, which affects the purity and final performance of the powder.

[0085] Table 1 Performance characterization data of the comparative examples

[0086]

[0087] The embodiments herein do not exhaustively cover the points not covered by the technical scope claimed in this application, and new technical solutions formed by equivalent substitutions of one or more technical features in the technical solutions of the embodiments are also within the scope of protection claimed in this application. At the same time, in all the listed or unlisted embodiments of the solution in this application, each parameter in the same embodiment merely represents an instance of its technical solution (i.e., a feasible solution), and there is no strict matching or limiting relationship between the parameters. The parameters can be substituted for each other without violating axioms and the claims of this application, unless otherwise stated.

[0088] The technical means disclosed in this application are not limited to those described above, but also include technical solutions composed of any combination of the above technical features. The above descriptions are specific embodiments of this application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered within the scope of protection of this application.

[0089] The specific embodiments described herein are merely illustrative examples of the spirit of this application. Those skilled in the art to which this application pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of this application or exceeding the scope defined by the appended claims.

Claims

1. A stepwise gas pressure self-propagating preparation method for silicon magnesium nitride powder, characterized in that, Includes the following steps: Magnesium powder, silicon nitride powder and inorganic salt powder are provided and mixed to obtain a mixed powder. The mixed powder is placed in a self-propagating reaction system, and multi-point low-pressure ignition is performed under a first pressure P1, followed by high-pressure reaction under a second pressure P2 to obtain silicon magnesium nitride composite powder. The gas introduced for the multi-point low-pressure ignition is argon, and the gas introduced for the high-pressure reaction is nitrogen. The silicon nitride magnesium composite powder is sequentially cleaned and heat-treated to obtain the silicon nitride magnesium powder; wherein, P2:P1=(3.75-10):1, the pressure range of the first pressure P1 is 0.5MPa~0.8MPa, and the pressure range of the second pressure P2 is 3MPa~5MPa.

2. The stepwise gas pressure self-propagating preparation method of silicon magnesium nitride powder according to claim 1, characterized in that: The multi-point low-pressure ignition has 2 to 3 ignition points, which are distributed on three adjacent walls or two opposite walls of the square material frame.

3. The stepwise gas pressure self-propagating preparation method of silicon magnesium nitride powder according to claim 1, characterized in that: The inorganic salt powder includes potassium chloride and / or sodium chloride.

4. The stepwise gas pressure self-propagating preparation method of silicon magnesium nitride powder according to claim 1, characterized in that: The cleaning process includes multiple cleaning steps, and the heat treatment includes low-temperature annealing under a nitrogen atmosphere, with the temperature range of the low-temperature annealing process being 800℃~1000℃.

5. The stepwise gas pressure self-propagating preparation method of silicon magnesium nitride powder according to claim 4, characterized in that: The multi-step cleaning process includes deionized water cleaning and acid washing; the low-temperature annealing treatment takes 1 to 4 hours.

6. The stepwise gas pressure self-propagating preparation method of silicon magnesium nitride powder according to claim 1, characterized in that: The mixing method is high-energy ball milling.

7. The stepwise gas pressure self-propagating preparation method of silicon magnesium nitride powder according to claim 1, characterized in that: The molar ratio of the magnesium powder to the silicon nitride powder is (1.1~1.2):1, and the mass fraction of the inorganic salt powder in the mixed powder is 10wt.%~20wt.%; and / or, The magnesium powder has a particle size of 10μm to 100μm, and the silicon nitride powder has a particle size of 20nm to 100nm.

Images