Silicon nitride is an inorganic substance with the chemical formula Si3N4. It presents a light off-white color. Silicon nitride can be made by heating silicon powder in nitrogen or reacting silicon halide with ammonia. Except for hydrofluoric acid, it does not react with other inorganic acids. It has strong corrosion resistance and is resistant to oxidation at high temperatures.
Physical and chemical indexes of silicon nitride
Chemical Composition %
Features of silicon nitride powder
Silicon nitride powder is a key raw material for the preparation of silicon nitride ceramics, and its performance is a key factor affecting the formation and sintering of silicon nitride bodies and has an important influence on the density and mechanical properties of the final silicon nitride ceramic products.
- It has good corrosion resistance, thermal shock, and abrasion resistance. It can be used at temperatures below 1900 degrees Celsius.
- It has excellent split endurance, very stable chemical composition, and thermal conductivity.
- The product contains nitrides, which have the characteristics of low expansion rate, high thermal conductivity, and high strength, and almost no shrinkage when heated.
- High strength and wear resistance.
- High-temperature oxidation resistance. An oxide film will be formed on the surface after long-term use, and the internal materials can be protected from chemical reactions.
Silicon nitride powder supplier
The prepared ceramic-grade silicon nitride powder Zhenxin supplies have the advantages of high alpha phase content, high powder purity, narrow grain size distribution, and high sintering activity.
- The purity is high with very small impurity content which is generally less than 200ppm.
- The powder has good dispersibility, uniform and reasonable particle size distribution, and stable performance.
- The high content of α phase and high sintering activity.
- It is suitable for products that require high sintering performance, such as silicon nitride cutting tools and bearing balls.
Application of Silicon nitride
Silicon nitride has very good applications in steel smelting, refractory materials such as reciprocating engine components, bearings, metal processing, etc. It is also widely used in normal temperature and high temperature sealing abrasives such as wear-resistant rubber, plastics, and ceramics.
- Silicon nitride coatings can effectively solve the problem of oxidation and burnout during the heat treatment of billets. The experimental results show that the anti-oxidation effect of the nano-silicate anti-oxidation coating is obvious, which can reduce the 3%-5% of the oxide scale produced by the original ordinary hot-rolled plate to 0.1%-0.8% so that the stainless steel hot-rolled plate produced oxide scale of 1%-3% is reduced to less than 0.2%.
- Silicon nitride as tap hole mud. The tap hole mud containing silicon nitride will play an effective role in sintering activation, corrosion resistance, and crack resistance. It can be used in the furnace body or electric furnace to seal the blast furnace mouth more stably and easy to break.
- Silicon nitride has very good applications in HRB400 hot-rolled steel bars. Si3N4 is used as a nitrogen enhancer and FeV is used to produce V microalloyed grade III steel bars. The performance of the steel bars is excellent and stable. It is a new alloying process of HRB400 grade III steel bars.
- Silicon nitride is second only to boron nitride in the unit mass nitrogen content, and the price is lower. It is very cost-effective in terms of nitrogen increase.
Silicon nitride can be used as a high-duty refractory in high-temperature engineering components, metallurgical industry, etc.
In the metallurgical industry, due to the high-temperature resistance of silicon nitride, the low friction coefficient, and the self-lubricating property, it is stable to most metal alloy solutions. Therefore, it can be used to make tools and molds for metal material processing, such as the core rod, extrusion wire drawing molds, rolls, conveyor roller, heating element fixture, thermocouple sleeve, metal heat treatment support, the crucible, aluminum liquid guide, aluminum ladle lining, etc.
Combined with sic as SI3N4-SIC refractory materials used in blast furnace shafts and other parts. when in cooperation with BN, SI3N4-BN materials are used for horizontal continuous casting separation rings. SI3N4-BN series horizontal continuous casting separation ring is a fine-structure ceramic material with a uniform structure and high mechanical strength. It has good thermal shock resistance and will not be wetted by molten steel, which meets the process requirements of continuous casting.
silicon nitride ceramics are used as bearing balls, roller, ball seats, molds, new ceramic cutting tools, pump plunger, spindle sealing material, etc.
silicon nitride ceramics are used as wear-resistant and corrosion-resistant parts such as ball valve, pump body, combustion vaporizer, filter, etc.
Silicon nitride ceramic materials are also widely used in the electronics, military, and nuclear industries.
The production process of Silicon nitride
According to the fabrication process, silicon nitride products can be divided into reaction sintered products, hot-pressed products, atmospheric sintered products, isostatic pressure sintered products, and reactive re-fired products. Among them, reaction sintering is a commonly used method for producing silicon nitride refractory products.
The reaction sintering method to produce silicon nitride products is to make finely ground silicon powder (with a particle size generally less than 80μm) and form it by machine or isostatic pressing. After the green body is dried, it is heated to 1350～1400℃ in nitrogen. During the sintering process, it is made by nitriding at the same time. With this production method, the raw material conditions, calcination process, and atmosphere conditions greatly influence the performance of the product.
Silicon powder contains many impurities, such as Fe, Ca, Aì, Ti, and so on. Fe is considered to be the catalyst in the reaction process. It can promote the diffusion of silicon, but at the same time, it will also cause defects such as pores. The main function of Fe as an additive: It can be used as a catalyst in the reaction process to promote the formation of SiO2 oxide film on the surface of the product; to form the iron-silicon melt system, nitrogen is dissolved in liquid FeSi2 and promotes the formation of β-Si3N4. However, if the iron particles are too large or the content is too high, defects such as pores will also appear in the product, which reduces the performance. Generally, the amount of iron added is 0-5%. Impurities such as Al, Ca, and Ti can easily form eutectic with silicon. Appropriate addition can promote sintering and improve the performance of products.
The finer the particle size of the silicon powder and the larger the specific surface area, the lower the sintering temperature can be. Compared with silica fume with coarser particle size, the content of α-Si3N4 in the product is higher for the finer particle size silicon powder. Reducing the particle size of silicon powder can reduce the size of the microscopic pores of the product. Proper particle size ratio can increase product density.
The temperature has a great influence on the nitriding rate. The nitridation reaction starts at 970-1000°C, and the reaction rate increases at around 1250°C. In the high-temperature stage, if the temperature quickly exceeds the melting point of silicon (1420°C), the flow of silicon will easily occur due to the exothermic reaction, which will cause the silicon powder body to melt and collapse.