Characteristics and Applications of Recrystallized Silicon Carbide (R-SiC)

I. Characteristics of Recrystallized Silicon Carbide

1. High Purity

   • Contains no metallic or oxide sintering aids, with a composition of nearly pure SiC (purity > 99%), making it suitable for chemically demanding environments.

2. Excellent High-Temperature Performance

   • Melting point up to 2700°C, capable of long-term use above 1600°C. It exhibits high strength and thermal shock resistance (due to the absence of a glass phase and low thermal expansion coefficient).

3. Outstanding Corrosion Resistance

   • Resistant to acids, alkalis, molten metals, and high-temperature oxidation, particularly in harsh environments such as strong acids (e.g., HF), strong alkalis (e.g., NaOH), and salt spray.

4. Superior Wear Resistance

   • High hardness (Mohs hardness 9.2), with wear resistance close to that of diamond, making it ideal for high-friction and erosive conditions.

5. Porous Structure

   • No volume shrinkage during sintering, resulting in approximately 10%-20% open porosity. This allows controllable permeability but reduces mechanical strength compared to reaction-bonded or pressureless-sintered SiC.

6. Low Thermal Conductivity & Electrical Insulation

   • Porosity lowers thermal conductivity, making it suitable for thermal insulation. Pure SiC provides electrical insulation (unlike conductive reaction-bonded SiC).

II. Applications of Recrystallized Silicon Carbide

1. High-Temperature Industrial Furnace Components

   • Kiln Furniture (shelves, rollers): Used in ceramic and electronic component sintering, enduring repeated thermal cycles.

   • Thermocouple protection tubes: Operates stably in molten metals or corrosive gases for extended periods.

2. Chemical & Environmental Protection

   • Corrosion-resistant filters: Used in high-temperature flue gas filtration (e.g., waste incinerators) and chemical slurry filtration.

   • Catalyst supports: Porous structure provides high surface area, resistant to acid/alkali erosion.

3. Semiconductor & Photovoltaic Industries

   • Wafer carriers (boats, paddles): High purity prevents contamination of silicon wafers, resistant to corrosive gases (e.g., Cl₂, HF) in semiconductor processes.

   • Components for polysilicon casting furnaces: Withstands temperatures above 1600°C with long service life.

4. Wear & Sealing Components

   • Sandblasting nozzles, mechanical seal rings: High hardness extends component lifespan.

   • Bearings & bushings: Used in rotating equipment exposed to corrosive media.

5. New Energy & Scientific Research

   • Nuclear reactor materials: Low neutron absorption cross-section, radiation-resistant.

   • Spacecraft thermal protection: Resists extreme high-temperature gas erosion.

6. Other Fields

   • Porous burners: Uniform permeability enables efficient, low-emission combustion.

   • Biomedical implants (research stage): Utilizes bio-inertness, though porosity-related strength issues need addressing.

III. Comparison with Other Silicon Carbide Ceramics

IV. Limitations

• Lower Mechanical Strength: Due to porosity, not suitable for high-load applications.

• Difficult Machining: Extreme hardness requires diamond grinding or laser processing.

Recrystallized silicon carbide, with its unique combination of high-temperature resistance, corrosion resistance, and permeability, is irreplaceable in extreme environments. Its future potential in high-end fields such as new energy and semiconductors remains vast.