CN102060544B - Quick crystallization method for realizing amorphous silicon nitride powder by taking silica powder as additive - Google Patents

Abstract

The invention belongs to the technical field of preparation of ultrafine silicon nitride powder, and relates to a rapid crystallization method of amorphous silicon nitride powder by using silicon powder as an additive, which can produce high-purity and high-alpha phase in batches under high temperature and normal pressure Silicon nitride ultrafine powder. The method includes a raw material mixing system, a raw material screening system, a raw material drying system and a raw material crystallization heat treatment system. The use of silicon powder as a crystallization additive can effectively promote the crystallization process of amorphous silicon nitride powder, greatly shorten the crystallization time, and at the same time complete the nitriding of silicon powder itself, and the product is high-quality high-α-phase silicon nitride powder. Compared with the existing amorphous silicon nitride crystallization process, this method has the advantages of high production efficiency, simple equipment, convenient operation, fast energy saving, mass production and high product purity, and is especially suitable for crystallization of amorphous silicon nitride powder Mass production of high-quality silicon nitride powder with high α-phase content.

Description

A method for rapid crystallization of amorphous silicon nitride powder using silicon powder as an additive

technical field

The invention belongs to the technical field of preparation of ultrafine silicon nitride powder, and relates to a rapid crystallization method of amorphous silicon nitride powder by using silicon powder as an additive, which can produce high-purity and high-alpha phase in batches under high temperature and normal pressure Silicon nitride ultrafine powder.

Background technique

Among various ceramic materials, silicon nitride (Si ₃ N ₄ ) ceramics is a new engineering material with the most development potential and application market. Because of its advantages such as high specific strength, high specific modulus, high temperature resistance, oxidation resistance and wear resistance, and high thermal shock resistance, silicon nitride ceramics have special applications in working environments with high temperature, high speed, and strong corrosive media. value.

The preparation of high-quality Si ₃ N ₄ ceramic products requires the use of high-quality Si ₃ N ₄ powder. There are many known preparation methods of silicon nitride powder, the most researched are the following: silicon powder direct nitriding method, carbothermal reduction of silicon dioxide method, thermal decomposition method, chemical vapor deposition method, self-propagating high temperature synthesis and sol-gel methods. Judging from the current research and application at home and abroad, the direct nitridation of silicon powder is a relatively mature process, but it requires a long time at high temperature to complete the reaction, consumes more energy, and the conversion rate and product purity are also low. The thermal decomposition method has developed rapidly in recent years, and industrial-scale silicon nitride powder production lines have been established abroad, but there are still some technical problems in general and the production cost needs to be further reduced. Although various chemical vapor deposition methods can obtain products with high purity, their production costs are relatively high, and the production scale is relatively small, so they are only suitable for application in some special fields. Self-propagating high-temperature synthesis has a faster reaction rate, shorter time required to complete the reaction, less energy consumption, and a simple production process, but the reaction temperature is not easy to control, the local sintering quality of the product is unstable, and subsequent grinding is required, which increases the production cost.

Silicon nitride powder on the market is mainly divided into amorphous phase, α phase and β phase. Because α-Si ₃ N ₄ has good sinterability, it is a common raw material for preparing high-performance Si ₃ N ₄ ceramics. At present, domestic and foreign research focuses on the preparation of high α-phase Si ₃ N ₄ powder.

“A method for preparing high α-Si ₃ N ₄ ” (US Patent US5032370) invented by Russia Merzhanov et al. needs to complete the synthesis reaction under a relatively high nitrogen pressure (4-30Mpa), and the requirements for equipment are more stringent, and the accident The probability of occurrence increases, and at the same time, a large amount of ammonia salt containing Cl and F needs to be added, which seriously corrodes the equipment and increases the cost. These reasons are not conducive to large-scale production. Chen Kexin of Tsinghua University and others invented "a method of low-pressure combustion to synthesize high-α-phase silicon nitride powder" (Chinese Patent Publication No. CN1362358A). This method requires pretreatment of silicon powder, including pickling, ultrasonic treatment, High-speed ball milling, followed by adding active agent, diluent and additives, and then milling the above powder on a ball mill for a long time, requires a lot of time for pretreatment. Gao Liwen and others invented the "Preparation Method of High α-Si ₃ N ₄ Phase Silicon Nitride" (Chinese Patent Publication No. CN101269803A). High α-phase silicon nitride powder is produced in large quantities, but due to the need for segmental heating and pressure control, the operation is complicated and difficult to control. Qi Longhao of Tsinghua University and others invented the "Plasma Chemical Vapor Phase Process for Batch Production of Silicon Nitride Powder Phase Inversion Process and System" (Chinese Patent Publication No. CN1397487A), which realizes the amorphous nitriding process produced by plasma chemical vapor phase The process of batch crystallization of silicon to obtain high-α-phase silicon nitride, but because the phase transformation process is slow, usually takes more than 3 hours, so the efficiency is low and the cost is still high.

Contents of the invention

The purpose of the present invention is to use the promotion effect of silicon powder in the crystallization process of amorphous silicon nitride to solve the problems of long time and high cost in the crystallization process of amorphous silicon nitride, and to realize the use of amorphous silicon nitride in batches A method for large-scale production of α-phase silicon nitride powder by crystallization.

A method of using silicon powder as an additive to realize rapid crystallization of amorphous silicon nitride powder, the present invention is to use amorphous silicon nitride powder and silicon powder as an additive according to silicon nitride powder: silicon powder=(98～70) : (2 to 30) mass ratio is fully mixed, and then sieved and dried to meet the particle size range of 0.01 μm to 200 μm, and then placed in a high-temperature nitrogen furnace for crystallization of amorphous silicon nitride. The additive silicon powder not only effectively shortens the crystallization time of amorphous silicon nitride, but also undergoes a combustion synthesis reaction with nitrogen to generate α-phase silicon nitride. The final product is high α-phase silicon nitride powder, and the silicon content in the product is below 0.1%.

The main feature of the present invention is to make full use of the promotion effect of silicon powder on the phase transformation process of amorphous silicon nitride, to realize rapid crystallization of amorphous silicon nitride powder in a short time, and to complete the silicon powder nitriding process at the same time to obtain high-purity, High-quality α-phase silicon nitride powder, and there is no residual amorphous phase in the product, and the silicon content is extremely low.

The crystallization product described in the present invention is high α-phase silicon nitride superfine powder or α/β-phase composite silicon nitride powder; silicon nitride powder with different crystal phases can be obtained by changing the process conditions. When the nitriding temperature is 1400-1500°C, the product is mainly α-phase silicon nitride. When the nitriding temperature is 1500-1650°C, a small amount of β-phase silicon nitride will appear in the product, and the content of β-phase will gradually increase with the prolongation of heat treatment time.

The invention relates to a method for realizing rapid crystallization of amorphous silicon nitride powder and producing high alpha phase silicon nitride powder under high temperature and normal pressure conditions. Using silicon powder as a phase transformation additive can effectively promote the phase transformation process of amorphous silicon nitride powder, greatly shorten the crystallization time, and at the same time complete its own nitriding, so it has the advantages of fast speed, energy saving, mass production and high product purity. The method is particularly suitable for batch production of high-quality silicon nitride powder with high α-phase content by using the amorphous silicon nitride powder.

The crystallization method of amorphous silicon nitride powder of the present invention has the following advantages:

1. The crystallization method of ordinary amorphous silicon nitride powder usually takes 3-4 hours or even longer (including 1-2 hours of heat treatment in the early stage), and the conversion efficiency is low. It is not suitable for mass production of high-α-phase silicon nitride powder. The inventive method can greatly shorten the crystallization time of amorphous silicon nitride powder (within 30 minutes), thereby improving production efficiency and being suitable for large-scale application;

2. Silicon powder is added to the amorphous silicon nitride powder, which effectively shortens the crystallization time and at the same time completes the silicon powder nitriding process, that is, completes the two processes of amorphous silicon nitride crystallization and silicon powder nitriding at the same time , so that the yield of the product α-phase silicon nitride powder is much higher than the crystallization method of pure amorphous silicon nitride powder;

3. The amount of silicon powder added is controllable (2-30%), and the application can be flexibly controlled according to the actual production situation.

Description of drawings

Figure 1 is a schematic diagram of a powder screening device. 1 is the powder to be screened, 2 is the stirring motor, 3 is the inverted T-shaped stirring rod, 4 is the main body of the screening device, 5 is the vibration motor, 6 is the screen, 7 is the funnel-shaped collection channel, and 8 is the filling material device.

Figure 2 is a schematic diagram of a powder mixing device. 9 is a mixed material, 10 is a stirring motor, 11 is a spiral stirring rod, 12 is a mixing device main body, and 13 is a vibrating motor. When mixing materials, first put the two materials into the main body of the mixing device, and then start the stirring motor and the vibration motor. Under the combined action of the stirring rod and vibration, the ultrafine powders are fully mixed with each other and evenly distributed to achieve two or more Mixing of powder materials.

Fig. 3 is a schematic diagram of a heat treatment device for crystallization. The device mainly includes a preheating chamber, a high-temperature nitrogen furnace, a cooling chamber, and a gas circulation system. 14 is the feeding bin door of the preheating chamber, 15 is the preheating chamber, 16 is the front airtight passage, 17 is the high temperature nitrogen furnace, 18 is the rear airtight passage, 19 is the cooling chamber, 20 is the discharge door, 21 is the nitrogen furnace heating Layer, 22 is a nitrogen furnace insulation layer, and P is a pressure gauge.

Fig. 4 is a schematic diagram of the crystallization process of amorphous silicon nitride powder. The raw material powder goes through processes such as screening, mixing, drying, charging, ventilation preheating, high-temperature crystallization and nitriding, and cooling in order to complete the two processes of amorphous silicon nitride powder crystallization and silicon powder nitriding, and finally The product high α-phase silicon nitride powder is obtained.

detailed description

The invention mainly includes several process steps of powder screening, mixing, drying and heat treatment, involving the following main devices.

Powder screening device: when screening materials, first put the materials into the main body of the screening device, then start the stirring motor and vibration motor, under the joint action of the stirring rod and vibration, the ultra-fine powder passes through the sieve and passes through the funnel The material-shaped channel enters the container to realize the screening process.

Powder mixing device: when mixing materials, first put the two materials into the main body of the mixing device, then start the stirring motor and vibration motor, under the joint action of the stirring rod and vibration, the ultrafine powders are fully mixed with each other and evenly distributed to achieve Mixing of two or more powder materials.

Crystallization heat treatment device: the device mainly includes a preheating chamber, a high temperature nitrogen furnace, a cooling chamber, a gas circulation system, etc. During heat treatment, the mixed material is first heated by high-temperature nitrogen in the preheating chamber, and then enters the nitrogen furnace to complete the crystallization of silicon nitride powder and the nitriding process of silicon powder, and then it is cooled in the cooling chamber and discharged to become the final product . During the heat treatment process, always ensure that the high-temperature nitrogen furnace is a nitrogen atmosphere (or nitrogen and hydrogen mixed atmosphere), and it is slightly positive pressure, with a gauge pressure of 0-0.02MPa; the conversion temperature is controlled at 1400-1650°C depending on the specific process conditions between.

Realize the concrete technological process of the present invention as follows:

a. Raw material mixing and crushing and agglomeration treatment

Fully mix amorphous silicon nitride powder and silicon powder as an additive in the raw material mixing system according to the mass ratio of silicon nitride powder: silicon powder = (98-70): (2-30), so that the two raw materials are evenly distributed ;Sieve the mixed material in the screening system, so that the particle size range of amorphous silicon nitride powder and silicon powder as an additive is 0.01 μm to 200 μm, to ensure the removal of large particle powder; the mixed material in the drying system Carry out drying treatment in the middle, the drying temperature is 80-120 ℃, the drying time is 1-8 hours, and the water adsorbed in the powder is removed.

b. Raw material preheating and feeding to nitriding furnace

The dried and screened mixed material is loosely packed into a crucible container and sent into a preheating chamber, and preheated for 1 to 10 minutes under a nitrogen atmosphere.

c. Crystallization of amorphous silicon nitride powder and nitriding process of additive silicon powder

The material entering the high-temperature nitrogen furnace is rapidly heated to a certain temperature in the range of 1400-1650°C in a nitrogen atmosphere, and the amorphous silicon nitride powder crystallizes at this temperature to form α-phase silicon nitride powder; at the same time The silicon powder used as an additive is combusted and synthesized with nitrogen to generate α-phase silicon nitride powder. While the combustion reaction between silicon powder and nitrogen gas occurs, the crystallization process of amorphous silicon nitride is effectively promoted, and its crystallization rate is greatly accelerated. During the whole nitriding process, the pressure inside the nitrogen furnace has been kept slightly positive, and the gauge pressure is 0-0.02MPa.

d. Cooling process of crystallized product

After the mixed material completes the phase inversion and nitriding process, it enters the cooling chamber and is cooled by high-purity nitrogen at room temperature.

e. Discharging process

The cooled product is taken out from the crucible, and the product is collected.

The product is silicon nitride superfine powder with high α phase content or α/β phase composite silicon nitride powder.

Example 1:

Put the amorphous silicon nitride powder with an average particle size of 0.2 μm and the silicon powder with 10 μm into the sieving device and sieve to remove large particles formed due to agglomeration and other reasons. Then put the two powders into the powder material mixing device according to the mass ratio of silicon nitride powder: silicon powder = 95:5 and mix them thoroughly, then put the mixed raw materials into a vacuum drying oven, and dry them at 90°C for 8 hours. Put the dried raw materials into the sieving device to sieve again to further remove the large-sized agglomerated powder, and then put it into the crystallization heat treatment device, after ventilation, heat treatment in a nitrogen atmosphere at 1450°C for 30 minutes, and cool it out of the furnace to obtain super Fine silicon nitride powder. According to X-ray diffraction analysis, the content of α-phase silicon nitride in the product is more than 80%, the content of uncrystallized amorphous silicon nitride is less than 20%, the content of residual silicon is less than 0.5%, and no β-phase silicon nitride is produced.

Example 2:

Put the amorphous silicon nitride powder with an average particle size of 0.2 μm and the silicon powder with 10 μm into the sieving device and sieve to remove large particles formed due to agglomeration and other reasons. Then put the two powders into the powder material mixing device according to the mass ratio of silicon nitride powder: silicon powder = 70:30 and mix them thoroughly, then put the mixed raw materials into a vacuum drying oven, and dry them at 90°C for 8 hours. Put the dried raw materials into the sieving device to sieve again to further remove the large-sized agglomerated powder, and then put it into the crystallization heat treatment device. After ventilation, heat treatment in a nitrogen atmosphere at 1450°C for 20 minutes, and then cool it out of the furnace to obtain super Fine silicon nitride powder. According to X-ray diffraction analysis, the content of α-phase silicon nitride in the product is more than 90%, the content of uncrystallized amorphous silicon nitride is less than 5%, the content of residual silicon is less than 5%, and no β-phase silicon nitride is produced.

Claims (3)

1. one kind realizes the method for amorphous silicon nitride powder rapid crystallization as additive with silica flour, it is characterized in that using amorphous silicon nitride powder and as the silica flour of additive according to silicon nitride powder: silica flour=(98 ~ 70): the mass ratio of (2 ~ 30) fully mixes, again through screening, drying process with after meeting particle size range and being 0.01 μm ~ 200 μm, load the crystallization of carrying out amorphous silicon nitride in high temperature nitrogen steam stove; Additive silica flour is while effectively shortening amorphous silicon nitride crystallization time, and generate α phase silicon nitride with nitrogen generation combustion synthesis reaction, the finished product are alpha-phase silicon nitride powder, and in product, silicone content is below 0.1%.

2. the method realizing amorphous silicon nitride powder rapid crystallization with silica flour as additive as claimed in claim 1, is characterized in that: the method comprises the crystallization and thermal treatment system of raw material mixing system, material screening system, raw material drying system and raw material;

Concrete technology step is:

(1) using amorphous silicon nitride powder and as the silica flour of additive according to silicon nitride powder: silica flour=(98 ~ 70): the mass ratio of (2 ~ 30) fully mixes in raw material mixing system, make two kinds of raw materials be uniformly distributed;

(2) mixture is carried out in screening system screening process, make amorphous silicon nitride powder and be 0.01 μm ~ 200 μm as the particle size range of the silica flour of additive, guarantee removing macrobead powder;

(3) mixture is carried out drying treatment in dehumidification system, drying temperature is 80 ~ 120 DEG C, and time of drying is 1 ~ 8 hour, removes the water adsorbed in powder;

(4) mixture is sent in crystallization and thermal treatment system, in a nitrogen atmosphere, successively through warm, crystallization and nitridation process, process of cooling, complete whole thermal treatment process, obtain ultrafine powder of silicon nitride or the α/β phase composite nitride silica flour of high α phase content.

3. the method realizing amorphous silicon nitride powder rapid crystallization with silica flour as additive as claimed in claim 2, it is characterized in that in processing step (4) crystallization and nitridation process, nitrogen furnace internal pressure keeps pressure-fired always, and gauge pressure is 0 ~ 0.02MPa.