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Radiant heater tubes, Silicon nitride (Si3N4)


The aluminum processing industry employs various technologies for heating melts or keeping them hot. The most effective of these employs immersion heaters. This technology heats the melt from the inside and makes optimum use of the energy. Dross is greatly reduced since immersion heaters do not cause the overheating of the bath surface typically caused by overhead heaters or gas burners.

EKatherm® silicon nitride radiant heater tubes are deal for use as immersion heaters since their high thermal conductivity and excellent heat transfer coefficients ensure optimum utilization of the energy. They are easy to maintain because they are not wetted by aluminum, and have extremely long lives because of their extreme chemical resistance to aluminum, their alloying elements, chlorine and all kinds of salts.

EKatherm® silicon nitride from ESK is the ideal material for cost-efficient heating of molten 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