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.
| 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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