Requirements for a heating element

• It should have melting point greater than furnace temperature.
• It should not react with the atmosphere of the furnace. Commonly furnace atmospheres are oxidizing, reducing and may contain water vapour.
• It should be resistant to thermal and mechanical shock.
• It should have enough resistivity. Resistivity is the ability of a material to inhibit flow of current in presence of applied voltage.

Available Materials

Broadly speaking three different types of materials are available namely metallic, refractory metals and non-metallic ones.

Metallic:

Among metallic materials, Nickel chrome and iron-chrome-Al are commonly used. Nickel chrome can be used upto . Iron-chrome-Al commonly known as Kanthal can be used at temperatures  to . Pure platinum could be used uptown  whereas alloys platinum and rhodium can be used upto . Pt-Rh alloys can be used in reducing atmospheres.

Refractory metals:

Molybdenum and tungsten are used.  can be used upto  and  upto . Tungsten heating elements can be used in dry hydrogen atmosphere and under vacuum.