Silicon Carbide (SiC) Heating Element
A Silicon Carbide (SiC) Heating Element is typically an extruded tubular rod or cylinder made from high-purity grains of silicon carbide that are fused together by either a reaction-bonding process or a recrystallization process at temperatures in excess of 3900°F (2150°C). The result is a chemically stable material with a low thermal-expansion coefficient and little tendency to deform.
Recrystallization forms fine grains of silicon carbide that act as "bridges" or connection points between larger grains, thus forming conductive pathways. The number of bridges formed dictates the materials resistance - the greater the number, the lower the resistance. The secret to the creation of a good heating element is controlling this formation process within the material so as to develop a consistent electrical resistance.
The factors that influence the life of a silicon carbide heating element include the type of furnace atmosphere, watt density, operating temperature, type of service (continuous or intermittent) and maintenance. Furnace type, design and loading play an important role as well. Transformers used for silicon carbide heating elements have multiple secondary taps in anticipation of a change in resistance of the elements over time. Silicon carbide heating elements, being 20-30% porous, oxidize or otherwise react with the furnace atmosphere and increase in resistance during their operational life. Oxidation causes a reduction in the cross-sectional area of the bridges, resulting in greater resistance to electrical flow.
Working temperature up to 1550°C.