What material is silicon nitride?

Silicon nitride, an inorganic compound with the chemical formula Si3N4, appears as a light off-white material. It is produced by heating silicon powder in a nitrogen atmosphere or by reacting silicon halide with ammonia. This compound is notable for its exceptional corrosion resistance, remaining inert to most inorganic acids except hydrofluoric acid. Additionally, it withstands oxidation even at elevated temperatures.

Silicon nitride represents a cutting-edge material in modern technology. Alongside it, various other ferroalloys are available, including ferrosilicon nitride, ferrochrome nitride, and silicon manganese nitride.

Physical and Chemical Properties of Silicon Nitride

Chemical Composition %

Features of Silicon Nitride Powder

Silicon nitride powder is an essential material in the production of silicon nitride ceramics. Its properties significantly influence the shaping, sintering process, density, and mechanical characteristics of the resulting ceramic products.

Key Characteristics:

1. Corrosion Resistance and Thermal Stability: Silicon nitride powder offers excellent resistance to corrosion and thermal shock, making it suitable for applications at temperatures up to 1900 degrees Celsius. Its durability under extreme conditions ensures reliability in demanding environments.

2. Superior Mechanical Properties: With exceptional split endurance and wear resistance, silicon nitride powder contributes to the production of high-strength ceramics. The powder's stable chemical composition and efficient thermal conductivity further enhance the mechanical properties of the final products.

3. Low Expansion and High Conductivity: The nitrides present in silicon nitride powder endow it with a low expansion rate and high thermal conductivity. This combination ensures that the material retains its structural integrity and strength, even under high temperatures, with minimal shrinkage when heated.

4. High-Temperature Oxidation Resistance: Silicon nitride powder demonstrates outstanding resistance to oxidation at high temperatures. During prolonged use, a protective oxide film forms on the surface, safeguarding the underlying material from chemical reactions and extending the lifespan of the ceramic products.

Silicon nitride powder is integral to producing advanced ceramics with high density, strength, and thermal stability. Its unique properties make it indispensable in various high-temperature and high-stress applications.

Supplier of Silicon Nitride Powder

CG Metal offers premium ceramic-grade silicon nitride powder that stands out due to its exceptional qualities. Our silicon nitride powder is characterized by a high content of the alpha phase, superior purity, consistent grain size distribution, and excellent sintering activity.

Key features include:

• Exceptional Purity: The powder contains minimal impurities, typically less than 200 ppm, ensuring high purity.
• Optimal Dispersibility: The powder exhibits excellent dispersibility with a uniform and well-controlled particle size distribution, contributing to stable performance.
• High Alpha Phase Content: The high α phase content enhances the powder’s sintering activity, making it highly suitable for demanding applications.
• Ideal for High-Performance Products: This powder is particularly well-suited for manufacturing products that require superior sintering performance, such as silicon nitride cutting tools and bearing balls.

Utilization of Silicon Nitride

Silicon nitride finds diverse applications across various industries, particularly in steelmaking, refractory materials, and sealing abrasives, demonstrating its versatility and effectiveness in multiple contexts.

Steel Production Sector In the steelmaking industry, silicon nitride plays a pivotal role in mitigating oxidation and burnout issues encountered during the heat treatment of billets. Research outcomes underscore the remarkable efficacy of nano-silicate anti-oxidation coatings in reducing oxide scale formation. For instance, the application of such coatings has shown a significant reduction from 3%-5% to merely 0.1%-0.8% in oxide scale formation, consequently enhancing the quality of stainless steel hot-rolled plates. Moreover, silicon nitride serves as a key component in tap hole mud formulations, enhancing sintering activation, corrosion resistance, and crack prevention. This mud, when employed in furnace sealing applications, ensures stable sealing of blast furnace mouths with enhanced breakage properties.

Enhanced Steel Bar Production Silicon nitride contributes to the production of HRB400 hot-rolled steel bars, where it serves as a nitrogen enhancer alongside FeV to produce V microalloyed grade III steel bars. The incorporation of silicon nitride in this alloying process results in steel bars with superior and consistent performance characteristics, marking a significant advancement in the production of HRB400 grade III steel bars.

Cost-Effective Nitrogen Enhancement Notably, silicon nitride boasts a nitrogen content second only to boron nitride on a unit mass basis, yet at a more economical price point. This cost-effectiveness, coupled with its ability to increase nitrogen content, renders silicon nitride a highly desirable option for nitrogen enhancement in various industrial processes.

The widespread utilization of silicon nitride across steel smelting, refractory materials, and sealing abrasives underscores its indispensability and cost-effectiveness in enhancing product quality and performance across diverse industrial applications.

Metallurgical Industry

In the realm of metallurgical applications, silicon nitride emerges as a stalwart refractory material, boasting remarkable resilience in high-temperature environments. Its low friction coefficient and inherent self-lubricating qualities render it steadfast in the face of various metal alloy solutions. Consequently, it finds extensive utility in crafting an array of tools and molds pivotal for metal processing endeavors. These include but are not limited to core rods, extrusion wire drawing molds, rolls, conveyor rollers, heating element fixtures, thermocouple sleeves, metal heat treatment supports, crucibles, guides for molten aluminum, and linings for aluminum ladles.

Moreover, when amalgamated with silicon carbide (SiC), silicon nitride forms SI3N4-SiC refractory compounds that find application in critical components of blast furnaces and other pertinent segments of metallurgical infrastructure. Collaborating with boron nitride (BN) yields SI3N4-BN materials, specifically tailored for horizontal continuous casting separation rings. Distinguished by their intricate microstructure and robust mechanical strength, SI3N4-BN series rings exhibit exceptional thermal shock resistance and remain impervious to molten steel, aligning seamlessly with the exacting demands of continuous casting processes.

In the mechanical domain, silicon nitride ceramics reign supreme as pivotal components in a myriad of applications. Bearing balls, rollers, ball seats, molds, cutting-edge ceramic tools, pump plungers, and spindle sealing materials all benefit from the exceptional properties of silicon nitride.

Transitioning to the chemical sphere, silicon nitride ceramics emerge as indispensable players in combating wear and corrosion. From ball valves to pump bodies, combustion vaporizers, and filtration systems, these ceramics stand as stalwart guardians against the deleterious effects of chemical exposure.

Beyond these realms, silicon nitride ceramic materials carve a ubiquitous presence across diverse sectors, spanning electronics, military, and nuclear industries, underscoring their versatility and indispensability in contemporary technological landscapes.

The Manufacturing Process of Silicon Nitride

Silicon nitride products undergo various fabrication processes, including reaction sintering, hot pressing, atmospheric sintering, isostatic pressure sintering, and reactive re-firing. Among these methods, reaction sintering stands out as a commonly employed technique for producing silicon nitride refractory products.

In the reaction sintering process, finely ground silicon powder (typically with a particle size less than 80μm) is molded using machinery or isostatic pressing. Once the green body is formed, it undergoes drying before being heated to temperatures ranging from 1350 to 1400°C in a nitrogen environment. Nitridation occurs simultaneously during the sintering process. The quality and performance of the product are heavily influenced by factors such as raw material conditions, calcination processes, and atmospheric conditions.

Silicon powder inherently contains impurities such as Fe, Ca, Al, and Ti. Fe, acting as a catalyst in the reaction process, facilitates silicon diffusion but can also lead to defects like pores. Its primary roles include catalyzing the formation of SiO2 oxide film on product surfaces and promoting the formation of β-Si3N4 within the iron-silicon melt system. However, excessive iron content or large iron particles can result in defects, diminishing product performance. Typically, iron is added in quantities ranging from 0 to 5%. Impurities like Al, Ca, and Ti readily form eutectics with silicon, aiding in sintering and enhancing product performance when added appropriately.

The finer the particle size of the silicon powder and the larger its specific surface area, the lower the sintering temperature required. Finer particle size silicon powder yields higher α-Si3N4 content in the product compared to coarser silica fume. Reduction in silicon powder particle size leads to smaller microscopic pores in the product, while an optimal particle size ratio increases product density.

Temperature significantly influences the nitriding rate, with the reaction commencing around 970-1000°C and accelerating at approximately 1250°C. In the high-temperature stage, exceeding the melting point of silicon (1420°C) can cause silicon flow due to the exothermic reaction, resulting in melting and collapse of the silicon powder body. Thus, precise temperature control is crucial throughout the nitridation process.