1. Product Overview
Core materials:
Silicon carbide (SiC) : Wide bandgap semiconductor (3.2eV), high-temperature resistant (≤1600℃), high thermal conductivity (120-490 W/m·K), and resistant to thermal shock.
Silicon nitride (Si₃N₄) : Ceramic insulator (band gap width 4.5eV), high mechanical strength (flexural strength > 800MPa), oxidation resistance (≤1400℃), and low coefficient of thermal expansion (3.2×10⁻⁶/℃).
Combined advantages: SiC serves as the sensitive element of the thermocouple, while Si₃N₄ acts as the protective sheath/insulating layer, jointly enhancing high-temperature stability and corrosion resistance.
2. Key performance parameters
Parameter index range test conditions
Temperature measurement range: -50℃ to 1800℃, long-term stable operation ≤1600℃
Accuracy grade ± 0.5%t or ±1.5℃, calibrated at 1000℃
Response time < 3 seconds (bare wire) / < 8 seconds (with sleeve) Step temperature change (500℃→600℃)
Thermoelectric potential output: 10-50 mV/℃, compatible with S-type and B-type thermocouples
Insulation resistance ≥100 MΩ (at 1000℃), test voltage 500VDC
The withstand voltage strength is ≥5 kV/mm, and the thickness of the Si₃N₄ casing is 1mm
3. Detailed Explanation of material Properties
Silicon carbide thermocouple element
Doping type: N-type (nitrogen-doped) or P-type (aluminum-doped), with a Seebeck coefficient that can reach 200-400 μV/K.
Corrosion resistance: Resistant to erosion by molten metals (Al, Cu) and acidic gases (SO₂, HCl).
Self-calibration characteristics: SiC has better lattice stability than metal thermocouples (e.g. K type) at high temperatures, with a drift rate of < 0.1%/1000h@1200 ° C.
Silicon nitride protective structure
Multi-layer design
Dense layer: 99.5% purity Si₃N₄, porosity < 0.5%, preventing slag penetration.
Porous layer: 20-30% porosity, alleviating thermal stress (thermal cycle times > 5,000 times).
Interface treatment: SiC-Si₃N₄ gradient transition layer to reduce microcracks caused by thermal expansion mismatch.
4. Product structure design
Standard model:
Bare wire type: Φ0.5-1.0mm SiC wire, directly exposed to the measurement environment (with inert atmosphere required).
Armored type: SiC wire + MgO insulation layer + Si₃N₄ sleeve (outer diameter Φ3-6mm), bable for installation.
Special variant:
Multi-point temperature measurement: A single tube integrates multiple pairs of SiC junctions, with a spatial resolution of ±2mm.
Wireless transmission: Built-in LoRa module, battery life > 3 years (in an environment below 800℃).
5. Advantages over traditional thermocouples
Characteristics: SiC/Si₃N₄ thermocouple - Metal thermocouple (such as Type B)
Maximum operating temperature: 1800℃ (short-term) - 1820℃ (platinum-rhodium is volatile)
Antioxidant property does not require protective gas (used in air), but needs H₂/Ar protection (> 1500℃)
Mechanical strength: Anti-bending (Si₃N₄ sleeve). Platinum wire is prone to breakage
The cost-benefit lifespan is over 2 years (for continuous temperature measurement of molten steel), and the platinum-rhodium couple needs to be replaced an average of 1.2 times per year
