SILICON NITRIDE (Si3N4) THERMOCOUPLE PROTECTION TUBES
Precise and reliable temperature measurement is a critical requirement in any casting process. For example, the automotive industry increasingly requires suppliers to limit temperature deviations to no more than five degrees Celsius from the specified values. Thermocouples must therefore be protected by a material with a high thermal conductivity, high strength and good thermal shock resistance. EKatherm® silicon nitride provides all these material properties. The material has such high strength that the wall thickness of the thermocouple protection tubes can be minimized. This is essential to detect even tiny temperature differences and permit an effective automatic control loop.
All these advantages make ESK’s EKatherm® silicon nitride (Si3N4) the material of choice for thermocouple protection tubes, riser tubes, as well as for a whole range of other products that come into contact with liquid aluminum.
| Silicon Nitride | |||
| Material properties | Norm | Symbol/Unit | EKatherm® |
| Density | DIN EN 623-2 | ρ [g/cm3] | >3.24 |
| Porosity | DIN EN 623-2 | P [%] | <0.5 |
| Mean grain size | [μm] | <2 | |
| Aspect ratio (L/D) | 3-5 | ||
| Phase composition | β-Si3N4, Oxide | ||
| Vickers hardness | DIN EN 843-4 | HV 1 [GPa] | 15 |
| Knoop hardness | DIN EN 843-4 | HK 0.1 [GPa] | 15 |
| Young's modulus | DIN EN 843-2 | E [GPa] | 300 |
| Weibull modulus | DIN EN 843-5 | m | 15 |
| Flexural strength, 4-pt bending | DIN EN 843-1 | σB [MPa] | 700 |
| Compressive strength | DIN 51104 | σD [MPa] | >2500 |
| Poisson ratio | DIN EN 843-2 | ν | 0.28 |
| Fracture toughness (SENB) | Klc [MPa·m0,5] | 7 | |
| Coefficient of thermal expansion | DIN EN 821-1 | ||
| 25°C - 500°C | α [10-6/K] | 2.5 | |
| 500°C - 1000°C | α [10-6/K] | 3.9 | |
| Specific heat at 25°C | DIN EN 821-3 | cp [J/g K] | 0.65 |
| Thermal conductivity at 25°C | DIN EN 821-2 | λ [W/m K] | 27 |
| Thermal stress parameters | calculated | ||
| R1 = σB·(1-ν) / (α·E) | [K] | 672 | |
| R2 = R1·λ | [W/mm] | 18 | |
| Specific electrical resistance at 25°C |
DIN EN 50359 | ρ [Ω cm] | >1011 |
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