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Riser tubes, silicon nitride (Si3N4)

SILICON NITRIDE (Si3N4) RISER TUBES

EKatherm® silicon nitride ceramics offer the best price/performance available in aluminum, low-pressure casting.

The differences can be explained by comparing lifetimes and costs. At first glance, EKatherm® is the most expensive material. However, it has a greatly superior lifetime of one and a half years on average. Once that is brought into the equation, silicon carbide, for example, is almost 50 percent more expensive, since its lifetime is only about six weeks. Aluminum titanate shows a similar balance sheet. With a lifetime of only 12 weeks, its costs are a good half higher. In the comparison of these two factors, other materials fare much worse still. These analyses do not even take into account the outlay for installation and removal of the tubes, production downtime and shorter intervals between cleaning.

The microstructure of EKatherm® is responsible for the particularly high mechanical strength, thermal shock resistance and gas tightness. It also provides chemical inertness and prevents dross formation. EKatherm® also does not dissolve in aluminum and does not show aging or fatigue.

According to these comparisons, EKatherm® silicon nitride is demonstrably the ideal material for riser tubes.

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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