Silicon carbide ceramics are widely used in semiconductor, high-temperature, and corrosive industrial environments. Among them, Reaction-Bonded Silicon Carbide (SiSiC) and Pressureless Sintered Silicon Carbide (SSiC) represent two fundamentally different material systems. Although both are based on SiC, their composition, microstructure, performance limits, and cost structure differ significantly.
Material Composition
SiSiC (Reaction-Bonded Silicon Carbide)
SiSiC is produced by infiltrating molten silicon into a porous carbon or SiC–carbon preform. During infiltration, silicon reacts with carbon to form secondary SiC, while a portion of free silicon remains in the final structure.
Typical composition (by weight):
SiC: ≥ 83%
Free Si: ≤ 16%
The presence of free silicon improves densification and dimensional stability but defines the upper temperature and corrosion limits of the material.
SSiC (Pressureless Sintered Silicon Carbide)
SSiC is manufactured from high-purity SiC powder and densified by solid-state sintering without external pressure. The resulting microstructure is nearly 100% SiC, with clean grain boundaries and no free silicon phase.
Typical purity:
SiC content: ≈ 99%
Physical and Mechanical Properties
Density and Porosity
SiSiC: Density ≥ 3.02 g/cm³, porosity ≤ 0.3%
SSiC: Density ≈ 3.15 g/cm³, near-zero open porosity
Higher density and purity give SSiC superior mechanical reliability under extreme conditions.
Strength and Elastic Properties
| Property | SiSiC | SSiC |
| Flexural strength (20 °C) | ≥ 250 MPa | ≈ 450 MPa |
| Flexural strength (1200 °C) | ≥ 280 MPa | Maintains high strength |
| Elastic modulus | ≥ 300 GPa | ≈ 430 GPa |
| Fracture toughness | — | ≈ 4 MPa·m¹ᐟ² |
| Poisson’s ratio | — | 0.14 |
Thermal Performance
| Property | SiSiC | SSiC |
| Thermal conductivity (25 °C) | ≥ 140 W/m·K | ≈ 110 W/m·K |
| Coefficient of thermal expansion | (4.5 ± 0.5) ×10⁻⁶ /K | ≈ 4.0 ×10⁻⁶ /K |
| Maximum service temperature | ~1350 °C | >1600 °C |
| Melting point | — | ~2800 °C |
| Specific heat | — | 0.8 J/g·K |
Electrical Properties
| Property | SSiC |
| Dielectric constant (1 MHz) | ≈ 10 |
| Dielectric loss (1 MHz) | ≈ 0.001 |
| Dielectric strength | ~1 × 10⁶ V/cm |
| Electrical resistivity | 10⁷–10⁹ Ω·cm |
Typical Application
SiSiC Applications
Semiconductor susceptors and support plates
Kiln furniture and roller components
Heat exchangers
Large structural parts
SSiC Applications
High-end mechanical seals
High-temperature semiconductor process components
Strongly corrosive chemical environments
Aerospace and high-reliability systems
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