Silicon Carbide‑Bonded Silicon Nitride Special Shaped Bricks
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Main Types of Silicon Nitride Refractory Bricks
Silicon nitride refractory bricks are mainly divided into three categories based on differences in production processes and performance: reaction‑bonded silicon nitride ( RBSN, hot‑pressed silicon nitride (HPSN), and sintered silicon nitride (SSN). RBSN is produced by directly nitriding silicon powder and has a relatively low density (about 2.5 g/cm³); HPSN and SSN boast higher densities (up to 3.2 g/cm³) and superior physical properties. In addition, there are composite products such as Sialon (silicon aluminum oxynitride)–bonded silicon carbide bricks and β-SiC–bonded silicon carbide bricks, where performance is optimized by adjusting the bonding phase (such as Si₃N₄, Si₂ON₂, etc.).
Production Process
The core process in the production of silicon nitride refractory bricks is the nitridation reaction of silicon powder. Taking silicon nitride‑bonded silicon carbide bricks as an example, after silicon carbide particles are mixed with silicon powder and formed, Sintering is carried out in a nitrogen atmosphere at 1300–1400°C, where silicon reacts with nitrogen to form the Si₃N₄ bonding phase (reaction equation: 3Si + 2N₂ → Si₃N₄). Key process controls include silicon powder particle size (fine silicon powder is used for the low‑temperature zone, while coarse silicon powder is used for the high‑temperature zone), nitrogen purity (≥99.999%), and stepwise temperature ramping (e.g., holding at 1150°C, 1250°C, and 1400°C in successive stages). For composite materials (such as Sialon‑bonded products), additives like Al₂O₃ must be added to form solid solution phases.
Application Scenarios
Silicon nitride refractory bricks are widely used in extreme high‑temperature and corrosive environments:
- Metallurgical Industry: Blast furnace belly and side lining of aluminum electrolytic cells, resistant to molten iron erosion and cryolite molten salt corrosion.
- Ceramic and Glass Industry: Kiln furniture and shelf boards with high-temperature deformation resistance;
- Chemical Industry: Linings for Oil and Gas Cracking Furnaces;
- Energy and Environmental Protection: Waste incineration furnaces and nuclear reactor components, leveraging their radiation resistance.
- Aerospace: Rocket nozzle vanes, subjected to high‑temperature gas impingement.
Performance Advantages
The advantages of silicon nitride refractory bricks are as follows: 1) High-Temperature Stability: With a melting point of 1900°C, it remains stable even at temperatures between 1450–1550°C; 2) Mechanical Properties: It exhibits a flexural strength of 400–800 MPa, and its hot‑pressed silicon nitride boasts a hardness close to that of diamond; 3) Thermal Shock Resistance: Its low coefficient of thermal expansion (3 × 10⁻⁶/°C) helps minimize thermal stress and cracking; 4) Chemical Inertness: It is resistant to corrosion by acids, alkalis, and molten metals (e.g., it exhibits a large wetting angle with aluminum melt); 5) Wear Resistance: With a high hardness (Mohs scale 9), it is ideally suited for areas subject to abrasive wear. Compared with traditional high‑alumina bricks, its high‑temperature strength is improved by more than 40%.
Physicochemical Indicators
The physicochemical properties of typical silicon nitride‑bonded silicon carbide bricks include:
- Chemical composition: SiC ≥ 50%, Si₃N₄ bonding phase 20–40%, impurities (Fe₂O₃ + TiO₂) < 1.5%;
- Physical Properties: Bulk Density 2.5–3.2 g/cm³, apparent porosity of 12–18%;
- High-temperature performance: Refractoriness ≥ 1790°C, softening temperature under load ≥ 1650°C, thermal shock stability (water quenching at 1100°C) ≥ 25 cycles;
- Electrical Properties: Resistivity at Room Temperature 10¹⁵–10¹⁶ Ω·cm, dielectric constant 9.4–9.5. Special‑purpose products such as Sialon‑bonded bricks must also meet specific Al₂O₃ content requirements (5–15%).
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Silicon Carbide‑Bonded Silicon Nitride Special Shaped Bricks
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