Requirement of Heating Material:
Resistance of conducting element varies with the temperature; this variation should be small in case of an element.
Otherwise when switched ON from room temperature to go upto say 1200˚C, the low resistance at initial stage will draw excessively high currents at the same operating voltage.
If temperature is negative the element will draw more current when hot.
A higher current means more voltage, a higher temperature or a still lower resistance, which can instability of operation.
Its melting point should be sufficiently higher than its operating temperature. Otherwise a small rise in the operating voltage will destroy the element.
The resistivity of the material used for making element should be high.
This will require small lengths and shall give convenient size.
Its oxidizing temperature should higher than its operating temperature.
To have convenient shapes and sizes, the material used should have high ductility and flexibility.
It should not be brittle and fragile.
In most industrial process quite strong vibrations are produced.
Some furnaces have to open or rock while hot. The element material should withstand the vibrations while hot and should not break open.
The material used should have sufficient mechanical strength of its own.