Silicon Nitride

Silicon Nitride

Silicon nitride, a light grayish-white substance, is an inorganic non-metallic material composed of nitrogen and silicon elements. It finds excellent applications in steel and iron smelting, and re...

Description of Silicon Nitride

Silicon nitride, a light grayish-white substance, is an inorganic non-metallic material composed of nitrogen and silicon elements. It finds excellent applications in steel and iron smelting, and refractory materials and is widely used in wear-resistant rubber, plastics, ceramics, and both room-temperature and high-temperature sealing abrasives.

Silicon Nitride

Silicon Nitride Lumps

Specification of Silicon Nitride

Si N C S P Al
56-61 35-38 ≤0.3 ≤0.03 ≤0.03 ≤0.5

Advantages of Silicon Nitride:

Silicon Nitride Granules

Silicon Nitride Granules

• High Hardness: Silicon nitride exhibits remarkable hardness and strength, surpassing many traditional materials such as steel and ceramics.

• High-Temperature Resistance: It boasts outstanding resistance to high temperatures, allowing for stable operation in elevated temperature environments, typically enduring temperatures up to 1700 degrees Celsius.

• Corrosion Resistance: Silicon nitride demonstrates strong resistance to most chemicals, including acids, alkalis, and solvents.

• Excellent Insulating Properties: Silicon nitride is an excellent insulating material with high insulation performance against electricity and heat, making it suitable for applications in high-voltage and high-temperature environments.

• Good Thermal Conductivity: Despite being an insulating material, silicon nitride possesses high thermal conductivity, making it suitable for use as a high-temperature heat-dissipating material.

Methods for Preparing Silicon Nitride:

• Thermal Decomposition Method: Silicon materials react with ammonia gas at high temperatures to produce silicon nitride.

• Chemical Vapor Deposition (CVD) Method: Silicon and ammonia react in the vapor phase, resulting in the deposition of a silicon nitride film.

• Reaction Sintering Method: Silicon powder and ammonia are combined and react at high temperatures to produce silicon nitride in block form.

• Usage of Silicon Nitride Products:

Silicon Nitride POWDER

Silicon Nitride Powder

1. In the non-ferrous industry, silicon nitride is widely used due to its excellent corrosion resistance and wetting properties.

2. In the steel industry:

• Silicon nitride coatings effectively address the issue of oxidation during the heat treatment of steel billets. Experimental results show that nano-silicate anti-oxidation coatings significantly reduce the oxidation scale from 3%-5% to 0.1%-0.8% for ordinary hot-rolled plates and from 1%-3% to below 0.2% for stainless steel hot-rolled plates.

• Silicon nitride gunning mix. Gunning mixes containing silicon nitride play an effective role in sintering activation, corrosion resistance, and anti-splitting. When applied in furnaces or electric furnaces, they help stabilize the furnace mouth of blast furnaces more effectively and are easily cut.

• Silicon nitride has excellent applications in HRB400 high-strength hot-rolled steel bars. Si3N4, as a nitrogen-increasing agent, combined with FeV, is used to produce V micro-alloyed Grade III steel bars. The steel bars exhibit excellent and stable performance, representing a new alloying process for producing HRB400 Grade III steel bars.

• Silicon nitride, second only to boron nitride in nitrogen content per unit weight, is cost-effective, making it highly competitive in nitrogen-increasing applications.

Production Process of Silicon Nitride Products:

The manufacturing process of silicon nitride products involves various techniques, including reaction sintering, hot pressing, pressureless sintering, equal channel angular pressing (ECAP) sintering, and reaction re-sintering. Among these methods, reaction sintering is commonly used in the production of silicon nitride refractory products.

In the reaction sintering method, silicon powder is finely ground (typically with a particle size less than 80 μm) and then shaped by mechanical or equal channel angular pressing. The formed body is dried and subsequently heated to a temperature of 1350 to 1400°C in a nitrogen atmosphere. During the sintering process, nitrogenation occurs simultaneously, resulting in the formation of silicon nitride products. Factors such as raw material conditions, sintering process, and atmospheric conditions have a significant impact on product performance in this production method.

Silicon powder contains various impurities such as Fe, Ca, Al, Ti, etc. Fe is considered a catalyst in the reaction process, promoting the diffusion of silicon but may also lead to defects such as pores. The main role of Fe as an additive is to act as a catalyst, facilitating the formation of SiO2 oxide film on the product surface. Additionally, in the formation process of iron-silicon melt, nitrogen dissolves in liquid FeSi2, promoting the formation of β-Si3N4. However, excessive or large iron particles can cause defects like pores, thereby reducing overall performance. Typically, the addition of iron ranges from 0% to 5%. Impurities like Al, Ca, and Ti easily form eutectics with silicon. Adding these impurities appropriately can enhance sintering and improve product performance.

The finer the particle size and the larger the surface area of silicon powder, the lower the sintering temperature. Compared to coarser silicon powder, finer particles result in higher α-Si3N4 content in the product. Reducing the particle size of silicon powder helps decrease the size of micropores in the product. An appropriate particle size distribution can enhance product density.

Temperature significantly affects the nitrogenation rate. Nitridation reaction begins around 970-1000°C, with the reaction rate increasing at around 1250°C. At high temperatures, if the temperature rapidly exceeds the melting point of silicon (1420°C), the exothermic reaction makes silicon prone to flow, leading to the collapse of silicon powder.

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