CN100415641C - A method for synthesizing homogeneous silicon nitride powder by layered cloth combustion - Google Patents

Abstract

The invention provides a method for synthesizing homogeneous silicon nitride powder by burning layered cloth, which belongs to the field of inorganic non-metallic materials. Grind and mix silicon powder and silicon nitride powder in different proportions to obtain a required reaction mixture with different component ratios. After drying, place it in a combustion synthesis reaction device in the form of layered cloth, and fill it with 1-20MPa The nitrogen-containing gas is ignited to induce a combustion synthesis reaction, so that the reaction mixture is combusted and synthesized into a homogeneous silicon nitride powder. The invention solves the problem of inhomogeneous phase composition and microscopic appearance in different parts of the synthetic product when the silicon nitride powder is prepared by the conventional combustion synthesis method, especially under industrial scale production conditions. It also realizes energy saving, simple equipment, low cost, easy operation, high production efficiency, high purity of the synthesized silicon nitride powder, high α phase content, uniform phase composition, uniform and fine particle size.

Description

A method for synthesizing homogeneous silicon nitride powder by layered cloth combustion

technical field

The invention belongs to the field of inorganic non-metallic materials, and in particular provides a method for layered cloth combustion synthesis (Combustion Synthesis, CS) homogeneous silicon nitride powder.

Background technique

Silicon nitride is a synthetic non-oxide ceramic. It has the characteristics of low density, low specific gravity, high hardness, high strength, corrosion resistance, oxidation resistance, wear resistance, high elastic modulus, high temperature resistance, small thermal expansion coefficient, large thermal conductivity, thermal shock resistance and good electrical insulation performance. , its mechanical properties and thermal properties are significantly better than general oxide ceramics. Silicon nitride ceramic products and silicon nitride-based composite ceramic products manufactured by different sintering processes can be widely used in cutting tools, bearings, engine parts, as well as chemical industry, metallurgy, machinery, petroleum, electronics, military industry, aerospace, nuclear energy and All kinds of wear-resistant, heat-resistant, corrosion-resistant parts and shielding materials, armor materials, etc. required by light industry are recognized as one of the most important and most potential engineering ceramic materials for heat resistance, high strength, wear resistance and corrosion resistance. one.

The preparation methods of silicon nitride powder researched and developed at home and abroad mainly include silicon powder direct nitriding method, carbothermal reduction nitriding method, chemical vapor phase synthesis method, plasma method and combustion synthesis method. The direct nitriding method is to place the silicon powder in a nitrogen (or nitrogen/hydrogen) flowing atmosphere, hold it for a long time in several stages, and fully nitride it to obtain the silicon nitride powder. This method has a long production cycle (more than 40 hours), high energy consumption, requires secondary nitriding, and requires high purity of raw materials. In addition, strict control of process parameters such as reaction temperature and nitrogen flow rate is required. German Starck Company and Japanese Denka Company use this method to produce various brands of silicon nitride powder. The carbothermal reduction method has the disadvantages of slow reaction speed, complicated reaction process, and long production cycle. At the same time, it also has problems such as high energy consumption, low efficiency, and high content of impurities such as carbon and oxygen in the product. Because the chemical vapor phase synthesis method is a gas phase reaction, the reaction The air flow is easy to control, the product has high purity and fine particle size. This method can produce silicon nitride powder with an α-phase content of up to 98%, which is currently recognized as the best commercial silicon nitride powder, represented by the powder produced by Japan UBE Company. However, the process is complex, the cost is high, and there are corrosion problems in the production process and the disadvantages of high chlorine content in the product. The plasma method is to pass the plasma working gas (such as N ₂ -H ₂ -Ar, etc.) into the plasma generator, and inject nitrogen-containing raw materials (such as NH ₃ , N _{2 ,} etc.) Si-containing raw materials (such as SiH ₄ , SiCl _{4 ,} etc.) undergo a chemical vapor phase reaction to prepare silicon nitride powder. Most of the silicon nitride directly prepared by the plasma method is amorphous silicon nitride powder, and contains ammonium chloride impurities. It needs to go through the removal of ammonium chloride impurities above 500°C and high temperature phase inversion treatment above 1400°C to obtain α-phase nitrogen. Silicon powder. The plasma method also has disadvantages such as complex equipment and cumbersome process, and also requires large energy consumption.

Combustion Synthesis (Combustion Synthesis, abbreviated as CS) is a new technology for material synthesis and preparation that has been widely studied and applied in recent years. Combustion synthesis is also called self-propagating high-temperature synthesis (Self-propagating High-temperature Synthesis, abbreviated as SHS). The basic characteristics of combustion synthesis technology are: using externally provided necessary energy to induce a local chemical reaction in a highly exothermic chemical reaction system (this process is called ignition), forming a front of the combustion reaction (that is, a combustion wave), after which the combustion reaction emits With the support of heat, the reaction is self-sustaining (that is, self-propagating), showing that the combustion wave spreads throughout the reaction system. During the process of the combustion wave spreading and advancing, the reactants are transformed into synthetic materials. The most prominent advantages of combustion synthesis technology are rapid reaction, energy saving, low cost, simple equipment, and high purity of synthetic products. So far, more than 500 products have been produced by combustion synthesis technology. For the combustion synthesis of nitrogen-silicon system, since the reaction system between nitrogen and solid-phase silicon powder is a highly exothermic system (743.5KJ/mol), silicon nitride powder can be rapidly synthesized in a short time. Moreover, due to the low price of raw materials, easy availability, short production cycle, and simple follow-up treatment of products, the preparation of silicon nitride powder by combustion synthesis technology has been highly valued and extensively studied by material researchers at home and abroad since the 1990s. .

Domestic and foreign patents related to combustion synthesis of silicon nitride powder have their own focus and limitations. Such as the "preparation method of silicon nitride with high α-phase content" (US Patent No. US5032370) invented by AGMerzhanov of Russia, etc., the nitrogen pressure required for the combustion and synthesis of silicon nitride powder is too high (up to 30MPa), and the ammonium salt is added The amount is too high (up to 60% of the weight of silicon powder). In addition, different contents of amorphous silicon or silicon imide are added to the silicon powder raw materials used, which increases the cost of raw materials. U.S. JB Holt et al. invented "synthesis of fine-grained α-phase silicon nitride by combustion method" _{(U.S. Patent No. US4944930), which uses alkali metal superimposed products (such as NaN 3 etc.} ) 50% of the reactant silicon powder), is not suitable for the large-scale production of large-scale samples. "A method for low-pressure combustion synthesis of high-α-phase silicon nitride powder" (Chinese patent application number is 02100183.9) invented by Chen Kexin, etc. Using the technology of suspending silicon nitride powder, high α-phase silicon nitride powder can be synthesized under lower nitrogen pressure. However, different contents of amorphous silicon or silicon imine are also added to the silicon powder raw materials used. Moreover, the production equipment and technological process are relatively complicated, the production cycle is long, the energy consumption is large, and the production process control is difficult, which ultimately leads to excessive production costs. Most of the above patents use different additives and processes (such as reducing nitrogen pressure, etc.), focusing on Increasing the content of α-phase silicon nitride in the combustion synthesis product does not involve the uniformity of the structure and composition of the combustion synthesis product, especially the uniformity of the combustion synthesis powder in terms of phase composition, impurity content, microstructure and grain size .

For the combustion synthesis of silicon nitride powder, the problem of uniformity in the structure and composition of the combustion synthesis product is not so prominent in the case of a small amount of charge in a single furnace (less than 1Kg), but there are also stratification or sandwich phenomena. That is to say, overburning is caused by the high internal combustion temperature of the powder body, which eventually leads to the problem that the phase composition of the synthetic product is quite different from that of the external product. Under the condition of large-scale production (single furnace charge is greater than 4Kg), due to the large amount of charge each time, the heat transfer conditions and nitrogen supply conditions of the inside and outside of the reactant powder blank are different when the combustion synthesis self-reaction occurs. It is very different, mainly because the outer layer of the reactant powder has a large contact area with nitrogen, and the nitrogen permeability is good, so the nitriding reaction is rapid, and the main reason is that the outer layer of the reactant powder has good heat dissipation conditions and the combustion temperature is lower. It is suitable for the formation of α-phase silicon nitride. If the control is not good, there will be incomplete combustion, and there will be a certain amount of free silicon. However, the contact area of the reactant powder with nitrogen is small, and the nitrogen permeability is poor, so the nitriding reaction is relatively slow, and post-nitridation is prone to occur. In addition, the heat dissipation conditions inside the reactant powder are poor, and the heat released by the reaction cannot be quickly dissipated. As a result, the internal combustion temperature of the reactant powder is higher, so that the high-temperature stable β-phase silicon nitride is easier to form. The α-phase silicon nitride that has been formed is also prone to phase transformation and transformation into β-phase silicon nitride at high temperature. What's more important is that due to high-temperature over-burning, dense hard lumps that are difficult to break often appear inside the reactants, and the sintering performance of the over-burned powder is relatively poor. In a word, the inhomogeneity of the heat distribution in the process of combustion synthesis reaction caused by too much charge can easily lead to the inhomogeneity of the synthesis product, which is mainly reflected in the phase composition, impurity content, microstructure and grain of the combustion product inside and outside. There is greater inhomogeneity in size. The inhomogeneity of the synthetic product often occurs in the process of combustion synthesis of silicon nitride powder, which greatly affects the production efficiency and product purity of combustion synthesis silicon nitride powder, and also increases the difficulty of subsequent separation and treatment, seriously Limit the large-scale industrial production and application of burning and synthesizing silicon nitride powder.

Contents of the invention

The purpose of the present invention is to provide a method for the combustion synthesis of homogeneous silicon nitride powder in layered cloth, which solves the problems of phase composition, impurity content, microstructure and grain size of the internal and external combustion products of the conventional combustion synthesis method. There is a problem of large inhomogeneity, so that the phase composition of the prepared silicon nitride powder product is uniform, the sintering activity is good, the powder particles are fine and uniform, the impurity content is low, and the operation is convenient, the equipment is simple, and the production efficiency is high.

The invention uses silicon powder and silicon nitride powder as an inert diluent as raw materials. After grinding, mixing and drying, a group of reaction mixtures with different component ratios are prepared to obtain a group of reaction mixtures with different component ratios, and layered cloth is carried out in a porous reaction container. , the distributing method is to divide the reaction mixture into 2 to 5 layers, each layer uses a reaction mixture with different component ratios, and the ratio of the weight of silicon powder in each adjacent layer to the weight of silicon nitride powder as an inert diluent is different. The number of layers is different, and the silicon powder and inert diluent silicon nitride components vary from 1 to 50%. Then the porous reaction vessel after the cloth is placed in the combustion synthesis reaction device, and the reaction device is vacuumed and filled with nitrogen. Or the mixed gas of ammonia or nitrogen and other gases (ammonia, argon, hydrogen fluoride, hydrogen chloride, hydrogen bromide, hydrogen iodide, hydrogen, etc.), so that the gas pressure in the combustion synthesis reaction device is controlled within the pressure range of 1 ~ 20MPa Then, the ignition agent is ignited to induce the reaction mixture to carry out the combustion synthesis reaction. After the reaction is completed, the product is supplemented with post-treatment processes such as fine grinding to obtain a homogeneous silicon nitride powder.

It mainly includes the following steps:

1. Configure raw materials of different components:

40% to 90% of silicon powder and 10% to 60% of inert diluent silicon nitride are mixed in different proportions by weight to obtain a set of reaction mixtures with different component ratios;

The silicon powder described herein has a purity of 95-99.99%, preferably a purity of more than 97%, and a particle size range of 0.1-90 μm, preferably a particle size of 0.1-30 μm;

Wherein, the inert diluent silicon nitride can be prepared by combustion synthesis method or other traditional methods, the purity is 90-99.9%, preferably 95%-99.9%; the particle size range is 0.05-50 μm, preferably 0.05 ~10μm; oxygen content is 0.01-10%, preferably 0.01-3%; α-phase content is 80-99.9%, preferably α-phase content is more than 90%;

2. Grinding and mixing of raw materials:

Grinding and mixing a group of reaction mixtures with different component ratios prepared according to step 1 on the grinding equipment; wherein the grinding and mixing can be wet grinding or dry grinding under air atmosphere, nitrogen atmosphere or ammonia atmosphere Grinding; wherein the wet grinding medium can be one of methanol, ethanol, isobutanol, acetone, water, liquid nitrogen, etc.;

3. Dry the reaction mixture:

Drying a group of reaction mixtures with different component ratios after grinding and mixing according to step 2 on the drying equipment, the drying temperature is between 30°C and 90°C;

Wherein said drying can be carried out under air atmosphere or nitrogen atmosphere or vacuum condition;

4. Layered fabric:

A group of reaction mixtures with different component ratios after fully grinding and drying according to steps 2 and 3 are distributed in layers according to the size and shape of the porous reaction vessel. The distributing method is to divide the reaction material into 2 to 5 layers, each layer uses a reaction mixture with different component ratios, and the reactant powder after distributing can be in various shapes such as cylindrical and semi-cylindrical according to the shape of the porous reaction container. . The ratio of the weight of silicon powder to the weight of inert diluent silicon nitride powder in each adjacent layer is different, and the variation range of each component is between 1% and 50% according to the number of layers used;

A group of reaction mixtures with different component proportions described therein means that the weight ratio of silicon powder and inert diluent silicon nitride powder in each part of reaction mixture is different;

Wherein the porous reaction vessel can be a reaction vessel of any shape made of carbon felt, paper material, asbestos cloth, porous graphite, porous ceramics, etc.;

The shape of the porous reaction vessel and the reactant powder base can be one of any shape such as cylinder, semi-cylindrical, disc, rectangle, circle, etc.;

5. Combustion synthesis reaction:

Put the porous reaction container after the layered cloth according to step 4 into the combustion synthesis reaction device, after vacuuming, fill it with nitrogen or ammonia or nitrogen and other gases (ammonia, argon, hydrogen fluoride, hydrogen chloride, hydrogen bromide , hydrogen iodide, hydrogen, etc.) to control the gas pressure in the combustion synthesis reaction device within a suitable pressure range (1 to 20 MPa), and then ignite the ignition agent to induce the reaction mixture to carry out the combustion synthesis reaction by an appropriate ignition method. The combustion synthesis reaction lasts for tens of minutes and is completed. After cooling to room temperature and releasing the pressure in the reactor, a powder or loose block product can be obtained, and a homogeneous silicon nitride powder can be obtained after post-treatment processes such as grinding and classification. ;

Wherein said combustion synthesis reaction device refers to the high-temperature-resistant high-pressure container made of materials such as stainless steel, and its volume is 1～60 liters;

When using a mixture of nitrogen and other gases, the other gases mentioned are one or a combination of ammonia, argon, hydrogen fluoride, hydrogen chloride, hydrogen bromide, hydrogen iodide, hydrogen, etc., and other gases account for the volume of nitrogen 1~50% of

Wherein said gas pressure range is between 1～20MPa, preferably between 2～15MPa;

The ignition method described herein may be one of ignition methods such as electric spark, arc discharge, tungsten wire, laser, microwave, and infrared heat source;

The igniter mentioned therein may be one of Ti, Ti+C, Fe ₃ O ₄ +Al and other igniters.

The layered fabric mentioned therein means that the reaction materials are divided into 2 to 5 layers, and each layer adopts a reaction mixture with different component ratios.

The ratio of silicon powder weight and inert diluent silicon nitride powder weight in each adjacent layer described therein is different, and can be a kind of in the following composition change:

(1) The weight ratio of silicon powder in the reaction material from the center layer of the reaction material to the middle layer and then to the outer layers gradually increases by 1 to 50%, and the weight ratio of the inert diluent silicon nitride powder remains unchanged;

(2) The weight ratio of silicon powder in the reaction material from the center layer of the reaction material to the middle layer and then to the outer layers remains unchanged, and the weight ratio of the inert diluent silicon nitride powder gradually decreases by 1 to 50%;

(3) The weight proportion of silicon powder in the reaction material from the central layer of the reaction material to the middle layer and then to the outer layers gradually increases by 1-50%, and the weight proportion of the inert diluent silicon nitride powder gradually decreases by 1-50%.

The method of layered cloth combustion synthesis of homogeneous silicon nitride powder proposed by the present invention solves the problem of uneven temperature field distribution in various parts of the reaction mixture system caused by the different conditions of heat loss and heat accumulation in the conventional combustion synthesis method. The problem is to overcome the problem of inhomogeneity in the composition and microscopic morphology of the synthetic product existing in the conventional combustion synthesis method, especially the problem that the internal phase composition, impurity content, grain size and grain shape of the synthetic product are quite different. In view of the uneven distribution of temperature field in different parts of the reaction mixture system, through the composition design and layered distribution of the reaction mixture system, the promotion effect of the inert diluent in the process of combustion synthesis reaction, such as heat absorption and cooling, is fully utilized to achieve both The purpose of reducing the maximum combustion temperature and controlling the temperature field distribution of each part of the reaction mixture system. Finally, the reaction temperature of each part of the reaction mixture system can be kept at the same level. Adding a certain amount of silicon nitride as an inert diluent in the reaction mixture system can prevent the melting and agglomeration of silicon during the reaction, thereby increasing the permeability of nitrogen gas, reducing the combustion temperature, and promoting the nitriding of silicon powder as a seed crystal.

Advantage of the present invention compared with prior art:

1) The present invention realizes the complete nitriding of silicon powder under the nearly isothermal mode of the whole reactant through the component design and layered distribution of the reaction mixture system, and improves the uniformity of silicon nitride powder in the combustion synthesis product. The synthesized The silicon nitride powder has high purity, consistent phase content and high sintering activity.

2) The present invention solves the problem of incomplete reaction or uneven composition and microscopic appearance of the synthetic product due to excessive reaction temperature or uneven temperature field distribution of the reaction mixture system in the conventional combustion synthesis process, especially overcomes the problem of incomplete synthesis The product has the problems of delamination and sandwich phenomenon. Through the composition design and layered distribution of the reaction mixture system, the temperature field distribution of the entire reaction mixture system is regulated from the perspective of raw material formula, and the combustion synthesis reaction process and reaction temperature are effectively controlled, so as to achieve the control of the microscopic morphology and composition of the combustion products. The purpose of uniformity is to finally make the different parts of the combustion-synthesized silicon nitride powder have the characteristics of uniform phase composition and uniform and fine particle size.

3) The present invention improves the output rate and output qualification rate of silicon nitride powder through the composition design and layered distribution of the reaction mixture system, and avoids the non-uniform composition and microscopic appearance of the synthetic product during the conventional combustion synthesis process. The added follow-up separation and purification process can stably synthesize silicon nitride powder with high purity, consistent phase content and uniform particle size distribution.

4) The energy consumption is small and the production cost is low. In addition to the need to add energy to heat and ignite the ignition agent to induce the reaction, the combustion synthesis of homogeneous silicon nitride powder depends on the thermal effect of the reaction itself. Therefore, the method has advantages in reducing energy consumption and production cost.

5) The reaction time is short and the production efficiency is high. The entire combustion synthesis reaction process is rapid, and the reaction time is generally several minutes to tens of minutes according to the weight and proportion of raw materials. The production cycle is short and the production process time can be saved.

The method for combusting and synthesizing homogeneous silicon nitride powder with layered cloth proposed by the present invention has no special restrictions on the combustion synthesis reaction device and the process, and the size of the combustion synthesis reaction device is determined according to the production capacity.

Description of drawings

Figure 1 is a schematic diagram of the layered cloth reactant powder used in Example 1, wherein 1 is the outer layer, 2 is the middle layer, and 3 is the center layer.

2 is a schematic diagram of the layered cloth reactant powder used in Example 2, wherein 1 is the upper surface layer, 2 is the middle layer, and 3 is the lower surface layer.

3 is a schematic diagram of the layered cloth reactant powder used in Example 3, wherein 1 is the upper surface layer, 2 is the middle layer, and 3 is the lower surface layer.

4 is a schematic diagram of the layered cloth reactant powder used in Example 4, wherein 1 is the middle layer, and 2 is the outer layer.

Fig. 5 is a scanning electron microscope microscopic analysis diagram of the silicon nitride powder sampled from the center of the combustion synthesis product in Example 1.

6 is an X-ray diffraction pattern of silicon nitride powder sampled from the center of the combustion synthesis product in Example 1.

7 is a scanning electron microscope microscopic analysis diagram of the silicon nitride powder sampled from the surface region of the combustion synthesis product in Example 1.

Fig. 8 is an X-ray diffraction pattern of silicon nitride powder sampled from the surface region of the combustion synthesis product in Example 1.

Detailed ways

Example 1

Silicon powder with an average particle diameter of 25 μm (purity greater than 98.5%) and silicon nitride powder with an average particle diameter of 2.2 μm (purity greater than 96%, α-phase content of about 93%), respectively, according to different weight ratios (in this embodiment For three batching ratios) after the batching, ball milling in the ball mill tank of the roller ball mill for 72 hours was ground and mixed to obtain three parts of reaction mixtures with different component distribution ratios, i.e. reaction mixture A (the batching ratio is Si: Si ₃ N ₄ =45: 55), reaction mixture B (ingredient ratio is Si: Si ₃ N ₄ =47.5: 52.5) and reaction mixture C (ingredient ratio is Si: Si ₃ N ₄ = 50: 50), reaction mixture A, B, C total weight 4.8 kg. The reaction mixtures A, B, and C were respectively placed in an electric oven for drying at 70°C. Then these three parts of reaction mixtures with different component ratios are layered in a cylindrical porous graphite crucible as shown in Figure 1, that is, the central layer of the cylindrical reactant powder adopts the reaction mixture A, and the central layer adopts the reaction mixture B, while the outer layer uses reaction mixture C. Put the powdered cylindrical porous graphite crucible into a 60-liter combustion synthesis reaction device, and place a spirally wound tungsten wire at one end of the cylindrical reactant powder as an ignition source. After vacuuming, nitrogen is filled inside the combustion synthesis reaction device until the nitrogen pressure reaches 9MPa. A pulse current is applied to the helical tungsten wire to ignite the igniter to induce the reaction mixture to carry out the combustion synthesis reaction. The igniter is titanium powder. Induce the combustion of raw material powder, after the combustion reaction is completed, cool to room temperature, release the nitrogen gas in the combustion synthesis reaction device, and the obtained combustion synthesis product has uniform color and luster, without layering and sandwiching, supplemented by post-treatment processes such as fine grinding That is, a homogeneous silicon nitride powder body with a purity of 98.5%, an α-phase silicon nitride content of 96 wt%, a free silicon content of 0.06 wt%, and an average particle size of 0.8 μm was obtained.

In this embodiment, the silicon nitride powder sampled from the central part of the combustion synthesis product without fine grinding and other post-treatment processes is analyzed by X-ray fluorescence analysis and its chemical composition is: Si (59.53wt%), N (39.03%), Fe (0.0352wt%), Ca (0.045wt%), Al (0.0343wt%), C (0.16wt%), O (1.16wt%). The content of α-phase silicon nitride was quantitatively calculated by X-ray diffraction analysis method to be 96.52wt%. See accompanying drawings 5 and 6 for its scanning electron microscope microanalysis diagram and X-ray diffraction diagram. The silicon nitride powder body sampled in the surface area is analyzed by X-ray fluorescence analysis method and its chemical composition is: Si (59.47wt%), N (38.96%), Fe (0.0448wt%), Ca (0.049wt%), Al ( 0.0292wt%), C (0.1wt%), O (1.34wt%). The content of α-phase silicon nitride was quantitatively calculated by X-ray diffraction analysis method to be 96.62wt%. See accompanying drawings 7 and 8 for its scanning electron microscope microscopic analysis diagram and X-ray diffraction diagram. From the above analysis results, it can be seen that the chemical composition of the silicon nitride powder sampled in the center and surface area of the combustion synthesis product in this example is the same, the phase composition is the same, the content of α-phase silicon nitride is close, and the particle size and microscopic appearance are similar , with the characteristics of homogeneous silicon nitride powder.

Example 2

The raw materials used in this example are silicon powder with an average particle size of 17 μm (purity greater than 98.5%) and silicon nitride powder with an average particle size of 1.5 μm (purity greater than 98%, and α-phase content of about 95%). Batching was carried out according to different weight ratios and ground and mixed respectively to obtain three parts of reaction mixtures with different component distribution ratios, i.e. reaction mixture A (the batching ratio was Si:Si ₃ N ₄ =45:55), reaction mixture B (the batching ratio was Si :Si ₃ N ₄ =50:50) and reaction mixture C (the proportioning ratio is Si:Si ₃ N ₄ =55:45), and the total weight of reaction mixtures A, B, and C is 1.2 kg. The above-mentioned grinding and mixing of the three reaction mixtures is carried out in the following manner: first, the silicon powder is ground and mixed for 10 hours in the ball mill barrel of the agitating ball mill with absolute ethanol as the ball milling medium, and then the inert diluent silicon nitride powder is added Then grind and mix on a vibrating mill for 0.5 hours. Then dry it in an electric oven at 80°C. Then these three parts of reaction mixtures with different component ratios are carried out in a rectangular paper container according to the layered cloth shown in Figure 2, that is, the central layer of the rectangular reactant powder base adopts reaction mixture A, and the lower surface layer adopts reaction mixture B. Reaction mixture C was used for the upper skin layer. Put the rectangular paper container after powder distribution into a 10-liter combustion synthesis reaction device, and place a spirally wound tungsten wire at one end of the rectangular reactant powder blank as an ignition source. After evacuation, the interior of the combustion synthesis reaction device is filled with a mixture of nitrogen and hydrogen, wherein the proportion of hydrogen is 20vol%, until the gas pressure reaches 10MPa. A pulse current is applied to the helical tungsten wire to ignite the igniter to induce the reaction mixture to carry out the combustion synthesis reaction. The igniter is a mixture of titanium powder and carbon black. Induce the combustion of raw material powder, after the combustion reaction is completed, cool to room temperature, release the nitrogen gas in the combustion synthesis reaction device, and the obtained combustion synthesis product has uniform color and luster, without layering and sandwiching, supplemented by post-treatment processes such as fine grinding That is, a homogeneous silicon nitride powder body with a purity of 98%, an α-phase silicon nitride content of 97 wt%, a free silicon content of 0.07 wt%, and an average particle size of 1 μm was obtained.

Example 3

The raw materials used in this example are silicon powder with an average particle size of 5 μm (purity greater than 98.5%) and silicon nitride powder with an average particle size of 3 μm (purity greater than 96%, and α-phase content of about 90%). Batching was carried out according to different weight ratios and ground and mixed respectively to obtain three parts of reaction mixtures with different component distribution ratios, i.e. reaction mixture A (the batching ratio was Si:Si ₃ N ₄ =42.5:57.5), reaction mixture B (the batching ratio was Si :Si ₃ N ₄ =47.5:52.5) and reaction mixture C (the proportioning ratio is Si:Si ₃ N ₄ =52.5:47.5), the total weight of reaction mixtures A, B, and C is 5 kg. The above-mentioned grinding and mixing of the three reaction mixtures is carried out in the following manner: first, the silicon powder is ground and mixed for 6 hours in the ball mill barrel of the agitating ball mill with absolute ethanol as the ball milling medium, and then dried in a vacuum oven at 60°C . Then, the inert diluent silicon nitride powder was ground and mixed in the ball mill bucket of the agitating ball mill with acetone as the ball milling medium for 6 hours, and then dried in a vacuum oven at 40°C. Then mix the dried silicon powder and silicon nitride powder as an inert diluent, grind and mix on a vibrating mill for 2 hours. Then these three parts of reaction mixtures with different component ratios are layered in the circular carbon felt as shown in Figure 3, that is, the central layer of the circular reactant powder adopts the reaction mixture A, and the lower surface layer adopts the reaction mixture B , while the upper surface layer uses reaction mixture C. Put the circular carbon felt after powder distribution into a 60-liter combustion synthesis reaction device, and place a strip graphite sheet at one end of the circular reactant powder blank as an ignition source. After vacuuming, nitrogen is filled inside the combustion synthesis reaction device until the gas pressure reaches 8MPa. A pulse current is applied to the graphite sheet, and the igniter is ignited to induce the reaction mixture to carry out the combustion synthesis reaction, and the igniter is titanium powder. Induce the combustion of raw material powder, after the combustion reaction is completed, cool to room temperature, release the nitrogen gas in the combustion synthesis reaction device, and the obtained combustion synthesis product has uniform color and luster, without layering and sandwiching, supplemented by post-treatment processes such as fine grinding That is, a homogeneous silicon nitride powder body with a purity of 98%, an α-phase silicon nitride content of 93 wt%, a free silicon content of 0.1 wt%, and an average particle size of 1.2 μm was obtained.

Example 4

The raw materials used in this example are silicon powder with an average particle size of 10 μm (purity greater than 98.5%) and silicon nitride powder with an average particle size of 1 μm (purity greater than 98%, and α-phase content of about 95%). Batching was carried out according to different weight ratios and ground and mixed to obtain 2 parts of reaction mixtures with different component ratios, i.e. reaction mixture A (the batching ratio was Si:Si ₃ N ₄ =46:54) and reaction mixture B (the batching ratio was Si : Si ₃ N ₄ =52:48), the total weight of the reaction mixtures A and B is 4 kg. The above-mentioned grinding and mixing of the two parts of the reaction mixture is carried out in the following manner: first, the silicon powder is ground and mixed for 12 hours in the ball mill barrel of the agitating ball mill with absolute ethanol as the ball milling medium, and then the inert diluent silicon nitride powder is added Afterwards, continue to mill for 3 hours in the ball mill barrel of the roller ball mill, and dry at 65° C. in an electric oven. Then these 2 parts of reaction mixtures with different component ratios are layered in the asbestos cloth as shown in Figure 4, that is, the middle layer of the reactant powder adopts the reaction mixture A, and the outer layer adopts the reaction mixture B. Put the powdered asbestos cloth into a 60-liter combustion synthesis reaction device, and place a spirally wound tungsten wire at one end of the reactant powder blank as an ignition source. After vacuuming, nitrogen gas is filled inside the combustion synthesis reaction device until the gas pressure reaches 10 MPa. A pulse current is applied to the spirally wound tungsten wire to ignite the igniting agent to induce the reaction mixture to carry out the combustion synthesis reaction. The igniting agent is titanium powder. Induce the combustion of raw material powder, after the combustion reaction is completed, cool to room temperature, release the nitrogen gas in the combustion synthesis reaction device, and the obtained combustion synthesis product has uniform color and luster, without layering and sandwiching, supplemented by post-treatment processes such as fine grinding That is, a homogeneous silicon nitride powder body with a purity of 98%, an α-phase silicon nitride content of 98 wt%, a free silicon content of 0.06 wt%, and an average particle size of 0.8 μm was obtained.

Although the present invention has been explained above with preferred embodiments, these embodiments are not intended to limit the scope of the present invention. Anyone who understands and is familiar with the technology described in the present invention may make some changes and modifications without departing from the spirit and scope of the present invention, so the protection scope of the present invention should be based on the content defined by the appended claims .

Claims (4)

1. A method for synthesizing homogeneous silicon nitride powder by layered cloth combustion, characterized in that: using silicon powder and inert diluent silicon nitride powder as raw materials, after grinding, mixing and drying, it is prepared according to the ratio of different components Obtain a set of reaction mixtures, and carry out layered distribution in a porous reaction container. The distribution method is to divide the reaction mixture into 2 to 5 layers, and use a reaction mixture with different component ratios in each layer. The weight of silicon powder in each adjacent layer Different from the weight ratio of the inert diluent silicon nitride powder, the ratio of the weight ratio of the silicon powder to the inert diluent silicon nitride component varies from 1 to 50% according to the number of layers used, and then the porous material after the cloth The reaction vessel is placed in a combustion synthesis reaction device, and the reaction device is vacuumized and filled with nitrogen or a mixed gas of nitrogen and hydrogen, wherein hydrogen accounts for 1 to 50% of the nitrogen volume in the mixed gas, so that the gas pressure in the combustion synthesis reaction device The pressure is controlled within the range of 1-20MPa, and then the ignition agent is ignited to induce the reaction mixture to carry out the combustion synthesis reaction. After the reaction is completed, the product is supplemented with fine grinding to obtain homogeneous silicon nitride powder. 2. The method according to claim 1, characterized in that: a group of reaction mixtures with different component ratios is mixed with 40% to 90% of silicon powder and 10% to 60% of silicon nitride as an inert diluent by weight , to obtain a group of reaction mixtures with different component ratios; wherein, the silicon powder has a purity of 95-99.99% and a particle size range of 0.1-90 μm; the inert diluent silicon nitride has a purity of 90-99.9% and a particle size range of 0.05-50 μm, the oxygen content is 0.01-10%, and the α-phase content is 80-99.9%. 3. method according to claim 1, is characterized in that: described porous reaction vessel is the reaction vessel that a kind of material in carbon felt, paper material, asbestos cloth, porous graphite or porous ceramics is made; The shape of the container and the reactant powder is one of cylindrical, semi-cylindrical or disc. 4. The method according to claim 1, characterized in that: said combustion synthesis reaction device is a high-temperature-resistant high-pressure vessel made of stainless steel, with a volume of 1 to 60 liters; said ignition adopts electric spark, One of the ignition methods of arc discharge, tungsten wire, laser, microwave or infrared heat source; the ignition agent is one of Ti, Ti+C or Fe ₃ O ₄ +Al ignition agent.

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