CN110790245A

CN110790245A - Method for preparing silicon oxynitride nano powder by thermal explosion synthesis-gravity separation

Info

Publication number: CN110790245A
Application number: CN201911197640.5A
Authority: CN
Inventors: 尹传强; 周浪; 李晓敏; 魏秀琴; 兰宇
Original assignee: Lattice Power Jiangxi Corp
Current assignee: Lattice Power Jiangxi Corp; Nanchang University
Priority date: 2019-11-29
Filing date: 2019-11-29
Publication date: 2020-02-14

Abstract

The invention discloses a method for preparing silicon oxynitride nano powder by thermal explosion synthesis-gravity separation. The method comprises the steps of proportionally mixing silicon powder and silicon dioxide serving as raw materials, and carrying out thermal explosion synthesis to obtain a synthetic product which mainly comprises a silicon oxynitride phase and contains a small amount of residual silicon dioxide and a silicon nitride byproduct phase. And finally, obtaining the silicon oxynitride nano powder by utilizing the particle size difference between the silicon oxynitride particles and the impurity phase particles in a gravity separation mode. The invention also relates to the technical improvement of the invention patent of CN104891459A 'a method for preparing silicon oxynitride powder by normal pressure thermal explosion synthesis'. Compared with the CN104891459A patent, the method optimizes the grain diameter and the proportion of the raw materials, and optimizes the time of thermal explosion synthesis and gravity selection, thereby being capable of preparing and obtaining the nano-grade silicon oxynitride powder with high purity, uniform grain diameter distribution and product yield of more than 90 percent.

Description

Method for preparing silicon oxynitride nano powder by thermal explosion synthesis-gravity separation

Technical Field

The invention relates to the technical field of preparation of inorganic nonmetal nano powder materials, in particular to a method for preparing silicon oxynitride nano powder by thermal explosion synthesis-gravity separation.

Background

Silicon oxynitride (Si)₂N₂O) has similar physical and chemical properties with silicon nitride, and is widely applied to high-temperature structural materials and refractory materials due to better thermal shock resistance, high-temperature strength, high-temperature oxidation resistance and lower thermal expansion coefficient. Meanwhile, the silicon oxynitride material has the characteristics of high bulk resistance, metal diffusion resistance, excellent dielectric property, optical property and the like, and can be used as an antireflection film of a semiconductor film, a Rugate filter and the like; the silicon oxynitride material with neutron radiation resistance can be used as a nuclear reactor speed reducer, a reflecting material and the like, and is a high-performance material with great economic prospect and value.

At present, there are many methods for synthesizing silicon oxynitride powder, mainly including the following processes. The inorganic solid phase reaction of sintering the mixed powder of silicon dioxide and silicon nitride at 1700 ℃, the process has high reaction temperature and large energy consumption, and simultaneously, silicon dioxide and silicon nitride phases which do not participate in the reaction inevitably remain, and in addition, the silicon nitride raw material is relatively expensive, so the wide application of the silicon nitride raw material is limited; the process is simple and convenient, the raw material source is economic and convenient, but a plurality of side reactions can occur in a reaction system, a pure silicon oxynitride product is not easy to obtain, and the product has certain carbon pollution; nitriding silicon dioxide powder in ammonia gas, wherein the process is limited to synthesizing amorphous silicon oxynitride powder and the reaction time is as long as about 40 hours; the direct nitrogen oxidation reaction of silicon powder in nitrogen and oxygen mixed gas or the direct nitrogen oxidation reaction of silicon powder is adopted, the process needs to strictly control the oxygen partial pressure and the competitive reaction of nitrogen and oxygen, so that the yield of nitrogen oxide products is lower; the method adopts the nitridation reaction of the mixed powder of silicon and silicon dioxide, has simple process method and economic and convenient raw material sources, needs high-temperature and long-time process conditions under the conditions of high pressure or normal pressure, and the synthesized product often contains a certain amount of by-product silicon nitride and/or residual raw materials, so that the pure-phase silicon oxynitride powder is difficult to obtain.

Thus, to satisfy different processes and achieve a diversity of different products, a suitable process may be selected. For the technological research of the nitridation reaction of the mixed powder of silicon and silicon dioxide, in the invention patent of CN104891459A 'a method for preparing silicon oxynitride powder by normal pressure thermal explosion synthesis', a method for preparing silicon oxynitride powder by normal pressure thermal explosion synthesis under high purity nitrogen atmosphere by using silicon powder with the particle size of less than 2 microns and quartz powder with the particle size of more than 10 microns as raw materials is provided. The thermal explosion synthesis process has the advantages of simple method, no need of any catalyst and diluent in the process, low price of raw materials and the like, but the problems of low silicon oxynitride powder yield and wide powder particle size distribution are caused by the problems of low mass ratio of silicon powder, large quartz powder particles, short ultrasonic time in the gravity separation stage and the like. Therefore, it is also necessary to find a better thermal explosion synthesis process.

Disclosure of Invention

On the basis of overcoming the defects of the prior art, the invention provides a method for preparing silicon oxynitride nano powder by thermal explosion synthesis-gravity separation, in particular to a method for preparing single-phase high-dispersion nano silicon oxynitride powder by taking small-particle silicon powder and large-particle silicon dioxide powder with proper mass ratio as raw materials, performing thermal explosion synthesis under the condition of high-purity nitrogen atmosphere, and then performing gravity separation. The invention improves the raw materials to the process on the basis of CN104891459A 'a method for preparing silicon oxynitride powder by normal pressure thermal explosion synthesis', and the finally prepared nitrogen oxide has high purity and high yield, and the process is simplified.

In order to realize the purpose, the technical scheme is as follows:

on the one hand, the method for preparing the silicon oxynitride nano powder by thermal explosion synthesis-gravity separation comprises the following steps:

(1) preparing materials: silicon powder and silicon dioxide powder are mixed according to the following proportion:

silicon powder: 46 to 55 percent of the weight percentage,

silicon dioxide powder: 45 to 54 percent of the weight percentage;

(2) mixing: mixing the batch materials obtained in the step 1 in a mixer for 2-8 h to ensure that the batch materials are fully and uniformly mixed;

(3) thermal explosion synthesis reaction: loosely loading the uniformly mixed powder obtained in the step 2 into a ceramic sagger, and placing the sagger at the low-temperature end of an atmosphere furnace; exhausting gas at the flow rate of 100mL/min of high-purity nitrogen for 20-60 min, and rapidly heating the furnace body to a certain high temperature; after the nitrogen flow is increased to be more than or equal to 1L/min, the ceramic sagger at the low temperature end is quickly pushed into the high temperature area of the hearth to carry out thermal explosion reaction for 5 min-20 min; pushing the ceramic sagger to a low-temperature end after thermal explosion reaction, cooling and discharging to obtain a white and soft block silicon oxynitride synthetic product;

(4) gravity separation: and (3) ultrasonically dispersing the silicon oxynitride synthetic product obtained in the step (3) in a solution medium, standing, and filtering and drying the suspension to obtain a finished product of silicon oxynitride powder.

Furthermore, the average powder particle diameter of the silicon powder in the step 1 is 0.5-2 μm.

Furthermore, the average powder particle size of the silicon dioxide powder in the step 1 is 5-10 μm.

Further, the silicon dioxide powder in the step 1 is crystalline silicon dioxide powder, and the crystalline silicon dioxide powder comprises quartz powder and cristobalite powder.

Furthermore, in the step 3, the furnace body is quickly heated to a certain high temperature, the temperature is 1380-1500 ℃, and the temperature of the atmosphere furnace can be quickly heated.

Further, in the step 4, the solution medium is pure water, ethanol and acetone, the ultrasonic dispersion time is 10-30 min, and the standing time is 2-8 min.

Further, the suspension in the step 4 can be filtered by adopting solid-liquid separation methods such as vacuum filtration, filter pressing, centrifugal separation and the like.

In another aspect, a silicon oxynitride nanopowder prepared by the above preparation method is provided.

The invention has the following positive effects:

the invention is based on a large amount of system experimental research of the inventor on the preparation of the silicon oxynitride nano powder. By utilizing the particle size difference of silicon and silicon dioxide, a synthetic product which mainly comprises a silicon oxynitride phase and contains a small amount of residual silicon dioxide and a silicon nitride byproduct phase is synthesized by thermal explosion. Because the silicon nitride and cristobalite byproduct phases can be agglomerated into micron-sized particles in a micro-sintered state during synthesis, residual silicon dioxide powder is still in micron-sized large particles after surface reaction, and silicon oxynitride synthesized by thermal explosion falls off in the form of nano-sized fragments to form nano-sized silicon oxynitride particles, the high-purity single-phase silicon oxynitride nano-powder can be obtained by utilizing the particle size difference between the silicon oxynitride particles and the impure-phase particles in a gravity separation mode. The thermal explosion synthesis process is a self-propagating high-temperature synthesis method which heats a reaction system to a certain temperature to initiate the whole combustion of the reaction system. The method can effectively solve the problem of high energy consumption of the conventional high-temperature synthesis process and avoid the additional requirement of equipment caused by high-pressure nitriding atmosphere required by the conventional self-propagating high-temperature synthesis process. The invention can be suitable for the thermal explosion combustion synthesis process of large-scale continuous production, not only can greatly reduce the preparation cost of the silicon oxynitride powder, but also can improve the purity of the product. The product of the invention can be used as raw material powder of silicon oxynitride ceramic products, coating materials of photovoltaic polysilicon ingot casting crucibles, and the like.

Besides the beneficial effects, the invention is also a technical improvement of the invention patent of CN104891459A 'a method for preparing silicon oxynitride powder by normal pressure thermal explosion synthesis'. Compared with the patent of CN104891459A, the invention also has the following beneficial effects.

(1) The yield of the silicon oxynitride powder obtained by the invention is obviously improved. The raw material selection and the mass ratio of the silicon powder and the silicon dioxide powder are optimized and improved. The proportion of the silicon powder is greatly increased to 46 to 55 percent by mass, and the particle size of the silicon oxide is reduced to 5 to 10 mu m. The technical scheme of the invention aims to ensure that silicon and silicon oxide fully react and improve the yield of the silicon oxynitride nano powder under the condition of ensuring the purity of the product. In the thermal explosion synthesis process, the product of the invention is inevitably mixed with a small amount of silicon nitride, cristobalite and other by-product phases. However, the silicon nitride and the cristobalite form micron-sized large particles due to the bonding and agglomeration of the particles at high temperature, and meanwhile, the silicon oxynitride nucleates and grows into nano-sized micro particles under the condition of short-time thermal explosion, and most of the silicon oxynitride is separated from the surfaces of the silicon dioxide particles in the form of fragments. Therefore, the silicon oxynitride nanopowder can be separated by gravity according to the large difference in particle size. Compared with patent CN104891459A, the silicon oxynitride powder with higher yield can be obtained.

(2) The silicon oxynitride powder obtained by the invention has uniform particle size distribution and is nano-scale particles. By optimizing the reaction conditions of thermal explosion synthesis, the growth of coarse silicon oxynitride crystals is avoided. Meanwhile, the ultrasonic dispersion time in the gravity separation stage is properly prolonged, so that large-particle by-products and residual silicon dioxide can be fully settled. Compared with patent CN104891459A, the nanometer silicon oxynitride powder with uniform particle size distribution can be obtained.

(3) According to the invention, the particle size and the mass ratio of the silicon powder and the silicon dioxide powder are optimized, and the raw material powder is uniformly mixed and loosely loaded into the ceramic sagger, so that the sufficient void ratio of the raw material stacking body is ensured. Realizes the loosening property of the thermal explosion synthesized product, and can effectively solve the problem that the product is hard and needs to be broken in industrial production.

(4) The thermal explosion synthesized product can be directly subjected to gravity separation without removing samples at the edge. One process step in the production of the product is omitted, and the yield of the product can be correspondingly improved.

(5) The by-product of the lower layer sedimentation in the gravity separation stage of the invention consists of a quartz phase, a small amount of silicon oxynitride phase, a cristobalite phase and a silicon nitride phase. The quartz and the cristobalite are the raw material powder, and because the temperature at the moment of thermal explosion reaction is extremely high, a small amount of silicon nitride in the raw material can directly react with silicon oxide to generate silicon oxynitride. However, the particle size of the byproduct powder is too small to completely adopt the method of grading the byproduct and silicon to carry out thermal explosion synthesis reaction-gravity separation to obtain pure silicon oxynitride nano powder. However, the silica powder can be replaced by 0 to 20 percent of the raw material composition, thereby achieving the purpose of the invention. Therefore, the by-product of the lower layer sedimentation in the gravity separation stage can be used as raw material powder, and the resource utilization of the by-product is realized.

(6) The preparation method has simple process and low cost, and is easy to realize large-scale industrial production.

Drawings

Fig. 1 is an XRD spectrum of silicon oxynitride powder of example 1.

FIG. 2 is an SEM image of the silicon oxynitride powder of example 1.

Fig. 3 is an analysis of the oxygen content of the silicon oxynitride powder of example 1.

Fig. 4 is an XRD spectrum of the silicon oxynitride powder of comparative example 1.

Fig. 5 is an SEM topography of the silicon oxynitride powder of comparative example 1.

Fig. 6 is an analysis of the oxygen content of the silicon oxynitride powder of comparative example 1.

Fig. 7 is an XRD spectrum of the silicon oxynitride powder of comparative example 2.

Fig. 8 is an SEM topography of the silicon oxynitride powder of comparative example 2.

Fig. 9 is an analysis of the oxygen content of the silicon oxynitride powder of comparative example 2.

Figure 10 is the XRD pattern of the thermally exploded synthetic product of example 1 prior to gravity sorting.

FIG. 11 is an SEM topography of example 1 prior to gravity sorting of the thermally exploded synthesis product.

Figure 12 is the XRD pattern of the product of the thermal explosion synthesis of comparative example 1 before gravity sorting.

FIG. 13 is an SEM topography prior to gravity sorting of the thermally exploded synthesis product of comparative example 1.

Figure 14 is an XRD pattern of the furnace oxynitrided synthesized product of comparative example 2 prior to gravity sorting.

Fig. 15 is an SEM topography of the furnace oxynitrided synthesized product of comparative example 2 before gravity sorting.

Fig. 16 is an XRD pattern of the thermal explosion synthesized edge product of comparative example 1.

Fig. 17 is an XRD pattern of the furnace oxynitrided synthesized side product of comparative example 2.

Figure 18 is a photograph of the gravity sorting stage of example 1.

Figure 19 is the gravity sorted lower sediment XRD pattern of example 1.

Detailed Description

The present invention is further described in the following examples, which should not be construed as limiting the scope of the invention, but rather as providing the following examples which are set forth to illustrate and not limit the scope of the invention.

Example 1

Mixing silicon powder with the average grain diameter of 1.52 mu m and quartz powder with the average grain diameter of 8.49 mu m according to the weight percentage of 50 percent to 50 percent, and then putting the mixture into a mixer to be mixed for 5 hours to ensure that the mixture is fully and uniformly mixed. The mixed powder was then loosely packed in a ceramic sagger and placed at the low temperature end of an atmosphere furnace and vented for 20 minutes at a flow rate of 100mL/min of high purity nitrogen. And (3) rapidly heating the furnace body to 1380 ℃, adjusting the nitrogen flow to 1.5L/min, rapidly pushing the sagger at the low-temperature end into a high-temperature area of the hearth for thermal explosion synthesis, and reacting for 20 minutes. And pushing the sagger to a low-temperature end after thermal explosion reaction, and cooling and discharging to obtain a silicon oxynitride synthetic product. And (3) ultrasonically dispersing the product after the thermal explosion reaction in pure water for 10 minutes, standing for 5 minutes, and carrying out vacuum filtration and drying on the suspension to obtain the finished product of the silicon oxynitride powder.

Example 2

Silicon powder with the average grain diameter of 1.95 microns and quartz powder with the average grain diameter of 5.72 microns are mixed according to the weight percentage of 46 percent to 54 percent, and then are put into a mixer to be mixed for 8 hours, so that the silicon powder and the quartz powder are fully and uniformly mixed. The mixed powder was then loosely packed in a ceramic sagger and placed at the low temperature end of an atmosphere furnace and vented for 50 minutes at a flow rate of 100mL/min of high purity nitrogen. And (3) rapidly heating the furnace body to 1500 ℃, adjusting the nitrogen flow to 1L/min, rapidly pushing the sagger at the low-temperature end into a high-temperature area of the hearth for thermal explosion synthesis, and reacting for 15 minutes. And pushing the sagger to a low-temperature end after thermal explosion reaction, and cooling and discharging to obtain a silicon oxynitride synthetic product. And (3) performing ultrasonic dispersion on the white loose soft block serving as a product after the thermal explosion reaction in acetone for 30 minutes, standing for 2 minutes, and performing centrifugal separation and drying on the suspension to obtain a finished product of the silicon oxynitride powder.

Example 3

Mixing silicon powder with the average grain diameter of 0.59 mu m and quartz powder with the average grain diameter of 7.81 mu m according to the weight percentage of 48 percent to 52 percent, and then putting the mixture into a mixer to be mixed for 6 hours to ensure that the mixture is fully and uniformly mixed. The mixed powder was then loosely packed in a ceramic sagger and placed at the low temperature end of an atmosphere furnace and vented for 60 minutes at a flow rate of 100mL/min of high purity nitrogen. And (3) rapidly heating the furnace body to 1420 ℃, increasing the nitrogen flow to 1L/min, and rapidly pushing the sagger at the low-temperature end into a high-temperature area of the hearth for thermal explosion synthesis, wherein the reaction time is 10 minutes. And pushing the sagger to a low-temperature end after thermal explosion reaction, and cooling and discharging to obtain a silicon oxynitride synthetic product. And (3) performing ultrasonic dispersion on the white soft block serving as a product after the thermal explosion reaction in pure water for 15 minutes, standing for 8 minutes, and performing vacuum suction filtration and drying on the suspension to obtain a finished product of the silicon oxynitride powder.

Example 4

Mixing silicon powder with the average grain size of 0.94 mu m and quartz powder with the average grain size of 9.84 mu m according to the weight percentage of 52 percent to 48 percent, and then putting the mixture into a mixer to be mixed for 4 hours to ensure that the mixture is fully and uniformly mixed. The mixed powder was then loosely packed in a ceramic sagger and placed at the low temperature end of an atmosphere furnace and vented for 40 minutes at a flow rate of 100mL/min of high purity nitrogen. And (3) rapidly heating the furnace body to 1480 ℃, adjusting the nitrogen flow to 1.5L/min, rapidly pushing the sagger at the low-temperature end into a high-temperature area of the hearth for thermal explosion synthesis, and reacting for 8 minutes. And pushing the sagger to a low-temperature end after thermal explosion reaction, and cooling and discharging to obtain a silicon oxynitride synthetic product. And (3) performing ultrasonic dispersion on the white soft block serving as a product after the thermal explosion reaction in ethanol for 25 minutes, standing for 4 minutes, and performing filter pressing and drying on the suspension to obtain a finished product of the silicon oxynitride powder.

Example 5

Silicon powder with the average grain size of 1.15 mu m and quartz powder with the average grain size of 5.72 mu m are mixed according to the weight percentage of 55 percent to 45 percent and then are put into a mixer to be mixed for 2 hours, so that the silicon powder and the quartz powder are fully and uniformly mixed. The mixed powder was then loosely packed in a ceramic sagger and placed at the low temperature end of an atmosphere furnace, and vented for 30 minutes at a flow rate of 100mL/min of high purity nitrogen. And (3) rapidly heating the furnace body to 1450 ℃, regulating the flow of nitrogen to 2L/min, rapidly pushing the sagger at the low-temperature end into a high-temperature area of the hearth for thermal explosion synthesis, and reacting for 5 minutes. And pushing the sagger to a low-temperature end after thermal explosion reaction, and cooling and discharging to obtain a silicon oxynitride synthetic product. And (3) performing ultrasonic dispersion on the white soft block serving as a product after the thermal explosion reaction in ethanol for 20 minutes, standing for 6 minutes, and performing centrifugal separation and drying on the suspension to obtain a finished product of the silicon oxynitride powder.

Comparative example 1

The patent CN104891459A is adopted to disclose a method for preparing silicon oxynitride nano powder by thermal explosion synthesis-gravity separation.

Mixing silicon powder with the average grain diameter of 1.52 mu m and quartz powder with the average grain diameter of 14.3 mu m according to the weight percentage of 45 percent to 55 percent, and then putting the mixture into a mixer to be mixed for 3 hours to ensure that the mixture is fully and uniformly mixed. The mixed powder was then loosely packed in a ceramic sagger and placed in the low temperature end of an atmosphere furnace and vented for about 30 minutes at a flow rate of 100mL/min of high purity nitrogen. And (3) rapidly heating the furnace body to 1380 ℃, adjusting the nitrogen flow to 1.5L/min, rapidly pushing the sagger at the low-temperature end into a high-temperature area of the hearth for thermal explosion synthesis, and reacting for 15 minutes. And pushing the sagger to a low-temperature end after thermal explosion reaction, and cooling and discharging to obtain a silicon oxynitride synthetic product. And (3) the product after the thermal explosion reaction is a white loose soft block, after removing a small amount of edge products, ultrasonically dispersing in pure water for 10 minutes, standing for 5 minutes, and carrying out vacuum filtration and drying on the suspension to obtain the finished product of the silicon oxynitride powder.

Comparative example 2

The thermal explosion synthesis step in example 1 was replaced by a furnace-associated oxynitridation reaction, that is, the mixed powder was placed in a uniform temperature zone of an atmosphere furnace, and an oxynitridation reaction was performed in the furnace.

Mixing silicon powder with the average grain diameter of 1.52 mu m and quartz powder with the average grain diameter of 8.49 mu m according to the weight percentage of 50 percent to 50 percent, and then putting the mixture into a mixer to be mixed for 5 hours to ensure that the mixture is fully and uniformly mixed. And then loosely loading the mixed powder in a ceramic sagger, placing the sagger in a uniform temperature zone of an atmosphere furnace, and exhausting gas for 20 minutes at the flow rate of high-purity nitrogen gas of 100 mL/min. The temperature is controlled to raise to 1380 ℃ according to the temperature program with the temperature rise speed of 5 ℃/min, then the nitrogen flow is increased to 1.5L/min, and the reaction time is 20 minutes. Cooling and discharging to obtain the silicon oxynitride synthetic product. And performing oxynitridation reaction along with the furnace to obtain a white soft block, performing ultrasonic dispersion in pure water for 10 minutes, standing for 5 minutes, and performing vacuum suction filtration and drying on the suspension to obtain a finished product of the silicon nitride oxide powder.

Example 6

1. Calculation result of yield of finished silicon oxynitride powder

For the silicon oxynitride powder finished products prepared in the embodiments 1 to 5 and the comparative examples 1 to 2, the silicon oxynitride content a in the sample before gravity separation is calculated and combined with the weight W of the sample before gravity separation₁And the weight W of the silicon oxynitride sample is obtained after gravity separation₂Calculating the yield of the finished product of the silicon oxynitride powder as W₂/(W₁A) 100%, the results are given in table 1.

TABLE 1 yield of silicon oxynitride powder product

	Yield of the product
		Example 1	92.0％
Example 2	90.0％
		Example 3	91.4％
Example 4	92.6％
		Example 5	90.5％
Comparative example 1	80.1％
		Comparative example 2	60.8％

As is clear from table 1, the yield of the silicon oxynitride powder obtained in examples 1 to 5 was 90% or more.

2. Purity result of silicon oxynitride powder finished product

XRD, SEM and oxygen content analysis were performed on the finished silicon oxynitride powders prepared in example 1 and comparative examples 1 to 2, and the results are shown in table 2.

TABLE 2 XRD, SEM and oxygen content analysis results of silicon oxynitride powder finished product

As can be seen from Table 2, the finished products of the silicon oxynitride powders prepared in the examples and the comparative examples have very high purity, but the particle size is controlled, the examples are all in a nanometer level, and the particle sizes are smaller and the distribution is more uniform; the examples are also preferred in terms of oxygen content.

3. Gravity separation stage method improvement process investigation

Compared with the comparative examples 1-2, the preparation method of the invention has the advantages that the yield and purity of the finished product of the nitrogen oxide powder are greatly improved, the process is improved, especially in the gravity separation stage, compared with the patent CN104891459A, the step of removing the edge product is not needed, the process is simplified, and certain loss of the produced finished product is reduced. This step of removing the edge product was omitted for the present invention and was verified from several points:

(1) XRD and SEM analyses were performed on the silicon oxynitride intermediate products after the thermal explosion synthesis reaction steps of example 1 and comparative examples 1 to 2, and the results are shown in table 3.

TABLE 3 XRD and SEM analysis results of silicon oxynitride intermediate products

As can be seen from table 3, the silicon oxynitride intermediate products after the thermal explosion synthesis reaction steps of example 1 and comparative examples 1 to 2 were: the intermediate nitrogen-containing oxide prepared in example 1 and comparative example 1 has a higher purity, while comparative example 2 has a lower purity; from the aspect of particle size control: example 1 is based on nano-sized nitrogen oxides, while the comparative example contains a large number of micro-sized particles, especially comparative example 2 also contains other large-sized impurities. It can be seen that the intermediate products obtained in comparative examples 1-2 require the removal of the edge product because they are less pure than the examples and contain large particles of micron size, resulting in the presence of the edge product; the intermediate product obtained in example 1 has high purity and small particle size, and the whole intermediate product is uniformly distributed, so that the process of removing edge products is not needed, and the process is simplified.

(2) XRD analysis of the edge products of comparative examples 1-2 gave the results shown in Table 4:

table 4 edge product XRD analysis results

As can be seen from table 4, in the preparation processes of comparative examples 1 to 2, after the thermal explosion synthesis reaction, the removed edge product contains many impurities, and also contains silicon oxynitride, which causes loss in the preparation of the final product.

(3) Further experiment was conducted on the gravity separation process of example 1, and it was observed that the silicon oxynitride intermediate after thermal explosion synthesis was placed in a beaker, ethanol was added for ultrasonic dispersion for 25 minutes, the resulting mixture was allowed to stand for 4 minutes, and the condition of particles in the beaker at this time was observed, and the experimental photograph is shown in fig. 18, and it can be seen from fig. 18 that after the silicon oxynitride intermediate was subjected to ultrasonic dispersion, nano-sized particles were suspended in the solution, and micro-sized particles were settled to the bottom. The bottom of the beaker was then collected and the sediment was XRD analyzed and the results are shown in figure 19. As can be seen from fig. 19, the deposits are mainly composed of residual quartz, a small amount of silicon oxynitride, and a small amount of cristobalite by-products.

In conclusion, compared with the patent CN104891459A, the method has the advantages that the process is simpler, the yield and the purity of the prepared nitrogen oxide are higher, the particle size control is better, the distribution range is narrower, and the finished product is silicon oxynitride nano powder.

Claims

1. A method for preparing silicon oxynitride nano powder by thermal explosion synthesis-gravity separation is characterized by comprising the following steps:

silicon powder: 46 to 55 percent of the weight percentage,

silicon dioxide powder: 45 to 54 percent of the weight percentage;

2. The preparation method according to claim 1, wherein the powder average particle size of the silicon powder in the step 1 is 0.5 to 2 μm.

3. The method according to claim 1, wherein the silica powder in step 1 has a powder average particle diameter of 5 to 10 μm.

4. The preparation method according to claim 1, wherein the silica powder in the step 1 is crystalline silica powder, and the crystalline silica powder comprises quartz powder and cristobalite powder.

5. The preparation method according to claim 1, wherein in the step 3, the furnace body is rapidly heated to a certain high temperature, the temperature is 1380-1500 ℃, and the temperature can be raised at the fastest speed by the atmosphere furnace program.

6. The preparation method according to claim 1, wherein the solution medium in the step 4 is one of pure water, ethanol or acetone, the ultrasonic dispersion time is 10min to 30min, and the standing time is 2min to 8 min.

7. The preparation method according to claim 1, wherein the suspension in the step 4 is filtered by a solid-liquid separation method such as vacuum filtration, pressure filtration, centrifugal separation and the like.

8. A silicon oxynitride nanopowder prepared by the method of any one of claims 1 to 7.