Silicon carbide and molybdenum disilicide heating elements for furnace temperatures above 1200 °C, where metallic wires cannot cope.
Also known as: SiC heating element · Silicon carbide heating element · MoSi2 heating element · Molybdenum disilicide heating element
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General Information
Metallic resistance wires cannot be used in furnace applications above 1200 °C; at these temperatures they oxidise rapidly and lose their mechanical strength. Ceramic heating elements are used instead. Silicon carbide (SiC) elements can operate up to 1600 °C, and molybdenum disilicide (MoSi₂) elements up to 1850 °C.
The behaviour of the two materials is fundamentally different. The resistance of SiC elements increases slowly over their service life — this is called ageing; the furnace control must have a voltage reserve to compensate for this increase. MoSi₂ elements do not age, but they are brittle at room temperature and soften and behave plastically at operating temperature; they are therefore always mounted hanging, in a vertical position.
Both elements operate in an oxidising atmosphere thanks to the protective silica layer they form on their surfaces. In reducing and vacuum atmospheres this layer cannot form and element life is seriously shortened; material selection must be assessed separately for such furnaces. If you share the furnace type, temperature, atmosphere and existing element dimensions, we will recommend the appropriate element type and arrangement.
Applications
- Ceramic kilns
- Glass furnaces
- Heat treatment furnaces
- Laboratory furnaces
- Sintering
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Frequently Asked Questions
Elements connected in parallel in the same furnace must have similar resistances; otherwise the element with lower resistance draws more current, overheats and breaks early. For this reason the elements are measured and supplied sorted into resistance groups.
Because the resistance of SiC elements increases with ageing, mixing a new element with old ones creates load imbalance. Where possible, all elements in the same zone should be replaced together. MoSi₂ does not have this problem; single replacement is possible.
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