Silicon nitride (Si3N4) is a non-oxidizing high-temperature structural ceramic material

Overview of Silicon Nitride Si3N4 Powder

Silicon nitride Si3N4 powder is an inorganic substance with a chemical formula of Si3N4. It is an important structural ceramic material with high hardness, inherent lubricity, wear resistance, atomic crystal, and high temperature oxidation resistance.

Silicon nitride powder is the main raw material for silicon nitride ceramics and related products. At present, the main preparation methods include direct nitridation of silicon powder, carbothermic reduction method, thermal decomposition method, sol-gel method, chemical vapor deposition and self-propagation Law and so on.

Six commonly used preparation methods for silicon nitride powder

(1) Direct nitridation of silicon powder

The direct nitridation of silicon powder is the earliest method used to prepare silicon nitride powder, and it is still widely used in China. The method is relatively simple and low in cost. The metal silicon powder is heated in an atmosphere of nitrogen or ammonia gas, and the metal silicon powder and the nitrogen source directly react to form silicon nitride powder. The reaction equation is as follows:

3Si+2N2(g)=Si3N4 (1)

3Si+4NH3(g)=Si3N4+6H2(g) (2)

This method has low cost and low equipment requirements. However, the nitridation reaction of metal silicon powder is an exothermic reaction. If the heat cannot be released in time during the nitriding process, it will cause the nearby metal silicon powder to melt and cause serious problems. The effect of nitriding reaction. Therefore, this process must strictly control the nitriding temperature, nitriding speed, the particle size of the raw materials, and the concentration of the diluent. The synthesized silicon nitride is a non-uniform block, therefore, it needs to be prepared into silicon nitride powder by ball milling or other methods, which is not efficient, and it is easy to introduce impurities in the process;

(2) Carbothermal reduction method

Carbothermal reduction method is to reduce SiO2 powder with carbon under high temperature nitrogen environment. SiO2 is first reduced to gas phase SiO. Gas phase SiO reacts with nitrogen in the atmosphere to form silicon nitride. The overall reaction equation is as follows:

3SiO2(s)+6C(s)+2N2(g)=Si3N4(s)+6CO(g) (3)

The cost of raw materials used in the carbothermic reduction method is low, the particle size of the prepared powder product is small, the reaction speed is fast, and the content of α-Si3N4 is high, which is suitable for large-scale production. However, the silicon nitride powder prepared by this method often contains residual carbon or silicon carbide, so the purity of the prepared powder is not high, which affects the quality and application of the product.

(3) Thermal decomposition method

This method uses SiCl4 at low temperature to react with ammonia gas to obtain solid imino silicon (Si(NH2) or amino silicon (Si(NH2)4). These two silicides can be decomposed at high temperature to obtain nitridation. Silicon powder. This method has high reaction efficiency and can prepare a large amount of high-purity silicon nitride powder in a short time. The silicon nitride powder prepared by this method has uniform particle size and high purity, which is suitable for preparing high-quality nitride The process used for silicon powder. At present, this method has become the most important method used for commercial production of high-purity and high-quality silicon nitride powder;

(4) Sol-gel method

The sol-gel method is a method for preparing uniform and high-quality silicon nitride powder. It usually uses a highly active silicon source as a precursor. In the presence of a liquid phase, the raw materials are uniformly mixed to form a stable The coagulation of the sol. After aging, it slowly polymerizes into a gel, and then is dried and sintered to prepare nano-level silicon nitride powder. This method overcomes the shortcomings of other methods of uneven mixing and large particle size distribution.

(5) Chemical gas phase reaction method

High-temperature chemical vapor reaction (CVD) is a method of using gaseous silicon sources, such as SiCl4 and SiH4, to react with gaseous nitrogen sources such as NH3 to prepare high-purity, ultra-fine silicon nitride powder. The reaction equation is as follows :

3SiCl4(g)+16NH3(g)=Si3N4(s)+12NH4Cl(g) (4)

3SiH4(g)+4NH3(g)=Si3N4(S)+12H2(g) (5)

Since the reaction process is a gas phase reaction process, the mixing is uniform and the reaction process speed is very fast. It is easy to control the progress of the reaction by controlling the flow of the gas phase;

(6) Self-propagating high-temperature synthesis method

Self-propagating high-temperature synthesis, also known as SHS, is a synthesis technology that uses the heat released by a chemical reaction as a heat source to heat neighboring reactants so that the reaction can continue and conduct. Once the reaction starts, no external energy is needed, and the reaction continues on its own exotherm until the reaction is completely over.

Since the nitridation of silicon powder is a large amount of exothermic reaction, silicon nitride can be prepared by self-propagating synthesis. The production equipment and process are relatively simple, and the reaction speed is fast. The purity of silicon nitride powder prepared in this way High, good sintering activity. However, this process needs to control the diffusion of heat. If the diffusion is not good, it is easy to cause the phenomenon of silicon melting and prevent the nitridation reaction.

Application of Silicon Nitride Si3N4 Powder

Silicon nitride Si3N4 powder is used as high-grade refractory material. For example, SI3N4-SIC refractory materials and sic are used in blast furnace bodies and other parts, and SI3N4-BN materials and BN are used in horizontal continuous casting separation rings. Continuous casting separation ring is a fine structure ceramic material with uniform structure, high mechanical strength, good thermal shock resistance, and will not be wetted by molten steel, which meets the requirements of continuous casting process.

Silicon nitride Si3N4 powder ceramic material has excellent properties such as high thermal stability, strong oxidation resistance, and high product dimensional accuracy. Since silicon nitride is a covalent compound with high bonding strength, it can form an oxide protective film in the air, so it has good chemical stability and will not be oxidized below 1200°C. The protective film formed at 1200~1600°C can prevent It is further oxidized and will not be infiltrated by many molten metals or alloys such as aluminum, lead, tin, silver, brass, and nickel. Or corrosion, but it can be corroded by molten magnesium, nickel-chromium alloys, stainless steel and other melts.

Silicon nitride Si3N4 powder ceramic materials can be used for high-temperature engineering parts, advanced refractories in the metallurgical industry, corrosion-resistant parts and seals in the chemical industry, tools and knives in the machining industry, etc. It can form a strong bond with silicon carbide, aluminum oxide, thorium dioxide, boron nitride, etc., so it can be used as a bonding material for different proportions of modification.

In addition, silicon nitride can also be applied to solar cells. After the silicon nitride film is coated by the PECVD method, it can not only be used as an anti-reflection film to reduce the reflection of incident light, but also in the deposition process of the silicon nitride film, the hydrogen atoms of the reaction product enter the silicon nitride film and the silicon wafer passivation Defects. The ratio of the number of silicon nitride to silicon atoms here is not strictly 4:3, but depends on the process conditions within a certain range. Internal fluctuations, different atomic ratios correspond to different physical properties of the film.

Used in ultra-high temperature gas turbines, aircraft engines, electric furnaces, etc.

Silicon nitride Si3N4 powder price

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Silicon Nitride Si3N4 Powder Supplier

As a global silicon nitride Si3N4 powder supplier, Tanki New Materials Co., Ltd. has extensive experience in the performance, application and cost-effective manufacturing of advanced engineering materials. The company has successfully developed a series of powder materials (titanium nitride, silicon nitride, titanium nitride, etc.) high-purity targets, functional ceramics and structural devices, and provides OEM services.

Chemical Composition of Silicon Nitride Si3N4 Powder