Neo Materials / Materials / Silicon Carbide

Silicon Carbide

SiC · 9.5 Mohs · Chemically Inert · 1600°C Continuous Service · Zero Oxygen Reactivity

Silicon Carbide's covalent Si–C tetrahedral bonds (bond energy 435 kJ/mol) make it impervious to virtually all chemical attack. From hydrofluoric acid to molten metals, SiC forms a self-healing SiO₂ passivation layer that renders it effectively immortal in oxidising environments. The only material on Earth combining ceramic hardness with semiconductor-grade purity.

9.5
Mohs
1600°C
Max Temp
435 kJ/mol
Bond Energy
Inert
O₂ Reactivity
Request Sample Enter Lab ↓
CHEMICAL INERTNESS LABORATORY

Silicon Carbide: A PhD-Level Tour

10 interactive modules — from atomic bonding to corrosion resistance in the harshest environments.

Wurtzite / Zinc-Blende Crystal
SiC crystallises in over 250 polytypes sharing the same tetrahedral Si–C bond (1.89 Å) but differing stacking sequences. The 4H-SiC wurtzite polytype dominates power electronics; 3C-SiC (zinc-blende) is used for abrasives.
Bond length Si–C1.89 Å
Lattice constant a3.073 Å (4H)
Lattice constant c10.053 Å (4H)
Space groupP6₃mc (4H)
Coordination number4 (tetrahedral)
Density3210 kg/m³
Polytypes known>250
A B C B Si C 4H-SiC stacking: ABCB…
sp³ Covalent Bond Network
Each silicon atom forms 4 equivalent tetrahedral covalent bonds with carbon atoms (and vice versa). Bond energy 435 kJ/mol — comparable to diamond (C–C: 346 kJ/mol). The high electronegativity difference (Si: 1.9, C: 2.5) introduces 12% ionic character, further strengthening the lattice.
Bond typesp³ covalent + 12% ionic
Bond energy435 kJ/mol
Bond angle109.5° (tetrahedral)
Electronegativity ΔX0.6 (Si→C)
Ionic character12%
Young's modulus410 GPa

The sp³ network is 3D-isotropic — meaning bond strength is identical in every direction. There is no weak cleavage plane (unlike graphite or mica), which explains both the extreme hardness and the lack of easy fracture pathways.

Si C C C C 109.5° Si–C bond energy: 435 kJ/mol C–C diamond bond: 346 kJ/mol
Chemical Inertness: Acid & Alkali Resistance
SiC resists virtually all chemical attack at room temperature. Its dense covalent network leaves no reactive surface sites for acid or alkali ions to attack. The table below shows reaction rates with common aggressive chemicals.
SiC HCl H₂SO₄ NaOH HF HNO₃ ⟵ All chemical species repelled ⟶ CHEMICAL CONCENTRATION TEMP CORROSION RATE HCl (hydrochloric)37%RT0.00 mm/yr H₂SO₄ (sulfuric) 98%100°C0.00 mm/yr NaOH (caustic soda) 50%RT0.00 mm/yr HF (hydrofluoric) 48%RT0.01 mm/yr HNO₃ + HF (aqua) Mixed80°C0.03 mm/yr
Immune
vs Strong Acids
Immune
vs Bases (RT)
Immune
vs Organic Solvents
Inert
vs Molten Metals
Self-Healing SiO₂ Passivation
When SiC contacts oxygen at elevated temperatures, a nanometric SiO₂ layer (amorphous silica glass) forms instantly. This layer is impermeable to further O₂ diffusion — the reaction is self-terminating. No spallation, no growth beyond ~200 nm.
ReactionSiC + O₂ → SiO₂ + CO
Onset temp~800°C
SiO₂ layer thickness50–200 nm
O₂ diffusivity in SiO₂10⁻²³ m²/s
Max service temp (air)1600°C
Spallation onset>1700°C

The SiO₂ passivation mechanism is fundamentally different from iron oxide (rust): SiO₂ is dense, amorphous, and adherent. Rust is porous and non-adherent — exposing fresh metal. SiC's oxide is its own shield.

SiC BULK SiO₂ passivation layer (~150 nm) OXYGEN-RICH ATMOSPHERE O₂ O₂ O₂ O₂ ✓ O₂ BLOCKED — Cannot penetrate SiO₂ CO↑ Service range: RT → 1600°C
Thermal Stability & Conductivity
SiC's covalent bond network retains its mechanical properties to astonishing temperatures. Unlike metals which soften above 0.5Tm, SiC maintains 80% of room-temperature strength at 1400°C. Thermal conductivity (120 W/m·K) rivals copper, enabling rapid heat dissipation without degradation.
500 400 300 200 100 0 Flex Strength (MPa) RT 400°C 800°C 1200°C 1600°C SiC Steel Al₂O₃ Thermal conductivity: 120 W/m·K CTE: 4.0×10⁻⁶/°C Specific heat: 750 J/kg·K
1600°C
Max Service
120 W/m·K
Thermal Cond.
4.0 ppm/°C
CTE
80%
Strength @1400°C
Extreme Hardness: 9.5 Mohs
Silicon Carbide sits at 9.5 on the Mohs scale — between corundum (9) and diamond (10). Its Vickers hardness of 2800 HV is achieved through the dense 3D covalent network. SiC abrasive grits cut through hardened steel, tungsten carbide, and most ceramics.
Mohs hardness9.5
Vickers hardness2800 HV
Knoop hardness2480 KHN
Young's modulus410 GPa
Compressive strength3900 MPa
Flexural strength490 MPa
KIc (fracture tough.)3.5 MPa·m½
MOHS HARDNESS SCALE 1 — Talc 2 — Gypsum 3 — Calcite 4 — Fluorite 5 — Apatite 6 — Feldspar 7 — Quartz 8 — Topaz 9 — Corundum (Al₂O₃) 9.5 — SiC ← You are here 10 — Diamond VICKERS HARDNESS (HV) 800 Steel 1800 WC 2800 SiC 9000 Diamond
Sintering Process: From Powder to Dense Ceramic
SiC powder is consolidated through pressureless sintering (PLS), hot pressing (HP), or reaction bonding (RBSC). The process densifies SiC grains to >98% theoretical density while preserving chemical purity.
POWDER GREEN BODY SINTERING DENSIFIED FINISHED ~0.5 µm particles 60% density → Isostatically pressed 65% density → 2100°C Argon atmosphere Solid-state diffusion 2–4 hours → >98% density Grain: 2–5 µm → SiC PART Ra < 0.2 µm Net-shape
SiC Polytypes: 250+ Crystal Forms, One Formula
Same Si–C formula, radically different properties. The stacking sequence of Si–C bilayers determines bandgap, electron mobility, and thermal performance. This phenomenon (polytypism) is unique in inorganic chemistry.
3C-SiC
Zinc-blende (cubic) · ABC stacking
A B C
Bandgap2.36 eV
UseAbrasives, MEMs
4H-SiC ★
Hexagonal · ABCB stacking
A B C B
Bandgap3.26 eV
UsePower electronics
6H-SiC
Hexagonal · ABCACB stacking
Bandgap3.02 eV
UseSubstrates, wafers
Wide-Bandgap Semiconductor
4H-SiC (bandgap 3.26 eV vs Si 1.12 eV) enables power devices that operate at 3× higher voltages, 10× higher frequencies, and 175°C junction temperatures impossible with silicon. SiC MOSFETs are replacing Si IGBTs in EV inverters globally.
Bandgap (4H)3.26 eV
Breakdown field3.5 MV/cm
Electron mobility1000 cm²/V·s
Thermal cond.3.7 W/cm·K
Saturated drift vel.2×10⁷ cm/s
Max junction temp600°C (theoretical)

The Baliga's Figure of Merit for SiC vs Si is 340 — meaning SiC power devices produce 340× less conduction loss for the same breakdown voltage. This single metric is why every major automotive OEM (Tesla, BMW, Toyota) has shifted to SiC power modules.

Silicon (Si) 4H-SiC Conduction Band Eg = 1.12 eV Valence Band Conduction Band Eg = 3.26 eV 3× wider gap Valence Band SiC vs Si Power Device Advantages Voltage rating 3× higher Switching freq 10× higher On-resistance 100× lower Junction temp +175°C max System size 50% smaller Efficiency gain 3% in EVs
SiC vs Other Advanced Ceramics
Comprehensive performance matrix comparing SiC against alumina (Al₂O₃), silicon nitride (Si₃N₄), boron carbide (B₄C), and tungsten carbide (WC) across key engineering parameters.
Property SiC ★ Al₂O₃ Si₃N₄ B₄C WC
Density (kg/m³) 3210 3980 3185 2520 15600
Hardness (HV) 2800 1800 1700 3000 2200
Flexural Strength (MPa) 490 380 700 350 1800
Thermal Cond. (W/m·K) 120 25 35 30 84
Max Service Temp (°C) 1600 1700 1300 600 500
Chemical resist. (acids) Excellent Good Good Fair Poor
Young's Modulus (GPa) 410 380 310 450 690

SiC's unique combination of extreme hardness, high thermal conductivity, chemical inertness, and semiconductor capability makes it the only material simultaneously used in semiconductor wafers, bulletproof armour, EV power modules, and chemical reactor linings.

Specify Silicon Carbide for Your Application

Available as sintered discs, tubes, nozzles, custom shapes, and semiconductor-grade wafers. Neo Materials supplies both dense SSiC and reaction-bonded SiSiC grades.

Request Technical Datasheet