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Silicon nitride (Si3N4) tubes and reaction-bonded silicon carbide (RBSiC/SiSiC) tubes differ mainly in thermal shock resistance, thermal conductivity, strength/density balance, and oxidation limits; Si3N4 emphasizes thermal shock and reliability, while RBSiC emphasizes heat flow, wear, and stiffness at temperature.
Comparison table
Aspect | Silicon Nitride (Si3N4) Tube | Reaction-Bonded Silicon Carbide (RBSiC/SiSiC) Tube |
Composition & process | Non-oxide ceramic; common tube grades are GPSN/HPSN/HIP-SN; dense, low porosity; multiple routes incl. RBSN exist, but tubes often GPSN for strength and reliability | SiC matrix with infiltrated free Si (<~12% typical); reaction-bonded route yields near-net shapes with very low porosity and high thermal conductivity |
Density | ~3.2 g/cm³ for dense GPSN tubes | ~3.0–3.2 g/cm³ typical for RBSiC |
Flexural strength (room T) | Up to ~800 MPa (GPSN data) | >250 MPa typical; varies by grade, often 250–400+ MPa |
Elastic modulus | ~320 GPa (GPSN) | ~300–490 GPa range for SiC ceramics; RBSiC ~300–370+ GPa |
Fracture toughness | ~6.5 MPa·m^1/2 (GPSN) | ~3.4–4.6 MPa·m^1/2 typical for SiC classes; RBSiC in this band |
Hardness | ~16 GPa Vickers (GPSN) | ~21 GPa Vickers (HV0.5) typical for RBSiC |
Thermal conductivity | Low–moderate: ~28 W/m·K at 20°C; ~16 W/m·K at 1000°C | High: ~45 W/m·K at 1200°C; many RBSiC grades 120–170 W/m·K at lower T (broader SiC range) |
Thermal expansion | Low: ~2–3.5 µm/m·K depending on range | Higher than Si3N4: ~4.0–4.5 µm/m·K typical |
Thermal shock resistance | Excellent; high tolerance to rapid temperature swings due to microstructure; high R-parameters | Good to moderate; less tolerant than Si3N4 though still capable in many cycling uses |
Max use temperature in air | ~1100°C (GPSN tubes) | Up to ~1380°C cited for RBSiC; depends on grade and environment |
Oxidation/creep resistance | Superior oxidation and creep resistance for Si3N4 in air up to its limit | Very good oxidation resistance; performance tied to free-Si content and environment |
Electrical resistivity | High insulating: ~10^12 Ω·cm at 20°C | Lower than Si3N4; SiC ranges ~10^−1–10^2 Ω·m order; RBSiC is more semiconductive |
Wear/erosion resistance | Very good; not as hard as SiC | Excellent; higher hardness favors abrasion/erosion resistance |
Typical advantages | Best-in-class thermal shock, high strength-to-weight, reliability under mechanical shock/thermal cycling | High thermal conductivity for heat transfer, high stiffness at temperature, great wear/corrosion resistance, shape versatility |
Common tube applications | Thermocouple protection in molten metal, degassing lances, high-cycling thermal environments, corrosive atmospheres requiring reliability | Radiant heater tubes, kiln furniture/fixtures, burners, wear-exposed process tubes needing heat flux and stiffness |
Practical selection notes
- Choose Si3N4 when frequent thermal cycling, thermal gradients, or mechanical shock are dominant risks; it maintains integrity with low thermal expansion and good toughness.
- Choose RBSiC when heat transfer, high-temperature stiffness, and abrasion resistance take priority; high conductivity and hardness are key benefits, with higher service temperature in air than common GPSN tubes.
- Author:QDSIC
- URL:https://blog.qdsic.com/article/Silicon-Nitride-vs-Reaction-Bonded-Silicon-Carbide-Tubes
- Copyright:All articles in this blog, except for special statements, adopt BY-NC-SA agreement. Please indicate the source!
