While most ceramics have a negative coefficient, these materials (often barium titanate and lead titanate composites) have a highly nonlinear thermal response, so that above a composition-dependent threshold temperature their resistance increases rapidly. PTC ceramic elements: PTC ceramic materials are named for their positive thermal coefficient of resistance (i.e., resistance increases upon heating).Such heating element or glow plug reach a maximum temperature of 1400 ☌ and are quick to ignite gas, diesel or kerosene. New generation hot surface igniter for gas furnace and diesel engine glow plug are made of silicon nitride material. Silicon nitride, see silicon nitride in automotive industry.Silicon carbide, see silicon carbide § heating elements.The application area includes glass industry, ceramic sintering, heat treatment furnaces and semiconductor diffusion furnaces. At high temperatures it forms a passivation layer of silicon dioxide, protecting it from further oxidation. It has moderate density, melting point 2030 ☌ (3686 ☏) and is electrically conductive. Molybdenum disilicide (MoSi 2) an intermetallic compound, a silicide of molybdenum, is a refractory ceramic primarily used in heating elements.These elements are commonly found in precision heating applications like medical diagnostics and aerospace. Etched foil: Etched foil elements are generally made from the same alloys as resistance wire elements, but are produced with a subtractive photo-etching process that starts with a continuous sheet of metal foil and ends with a complex resistance pattern.Cupronickel (CuNi) alloys for low temperature heating.Material beneath this layer will not oxidize, preventing the wire from breaking or burning out. Nichrome 80/20 is an ideal material, because it has relatively high resistance and forms an adherent layer of chromium oxide when it is heated for the first time. Nichrome: Most resistance wire heating elements usually use nichrome 80/20 (80% Nickel, 20% Chromium) wire, ribbon, or strip.The most common classes of materials used include:
They are used in common heating devices like toasters and hair dryers, furnaces for industrial heating, floor heating, roof heating, pathway heating to melt snow, dryers, etc.
Resistance wire: Metallic resistance heating elements may be wire or ribbon, straight or coiled. A coiled heating element from an electric toaster Metal