Heating element
Encyclopedia
A heating element converts electricity into heat through the process of Joule heating
. Electric current
through the element encounters resistance
, resulting in heating of the element.
Most heating elements use Nichrome
80/20 (80% nickel
, 20% chromium
) wire, ribbon, or strip. 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. Material beneath the wire will not oxidize, preventing the wire from breaking or burning out.
Heating elements for high-temperature furnace
s are often made of exotic materials, including platinum
, molybdenum disilicide, molybdenum
(vacuum furnace
s) and silicon carbide
. Silicon carbide igniters are common in gas ovens.
Joule heating
Joule heating, also known as ohmic heating and resistive heating, is the process by which the passage of an electric current through a conductor releases heat. It was first studied by James Prescott Joule in 1841. Joule immersed a length of wire in a fixed mass of water and measured the temperature...
. Electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
through the element encounters resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
, resulting in heating of the element.
Most heating elements use Nichrome
Nichrome
Nichrome is a non-magnetic alloy of nickel, chromium, and often iron, usually used as a resistance wire. Patented in 1905, it is the oldest documented form of resistance heating alloy. A common alloy is 80% nickel and 20% chromium, by mass, but there are many others to accommodate various...
80/20 (80% nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
, 20% chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
) wire, ribbon, or strip. 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. Material beneath the wire will not oxidize, preventing the wire from breaking or burning out.
- Resistance wire: may be wire or ribbon, straight or coiled. Used in common items such as toasterToasterThe toaster is typically a small electric kitchen appliance designed to toast multiple types of bread products. A typical modern two-slice toaster draws anywhere between 600 and 1200 W and makes toast in 1 to 3 minutes...
s and hair dryerBlowdryerA blowdryer or hairdryer is an electromechanical device designed to blow cool or hot air over wet or damp hair, in order to accelerate the evaporation of water particles and dry the hair. Blowdryers allow to better control the shape and style of hair, by accelerating and controlling the formation...
s, furnaces for industrial heating, floor heating, roof heating, pathway heating to melt snow, dryers etc. Most common wires are from the following classes
- KanthalKanthalKanthal is the trademark for a family of iron-chromium-aluminium alloys used in a wide range of resistance and high-temperature applications. Kanthal FeCrAl alloys consist of mainly iron, chromium and aluminium . The first Kanthal FeCrAl alloy was developed by Hans von Kantzow in Hallstahammar,...
(FeCrAl) wires - Nichrome 80/20 wire and strip
- CupronickelCupronickelCupronickel or copper-nickel or "cupernickel" is an alloy of copper that contains nickel and strengthening elements, such as iron and manganese. Cupronickel is highly resistant to corrosion in seawater, because its electrode potential is adjusted to be neutral with regard to seawater...
(CuNi) alloys for low temperature heating
- Molybdenum disilicide (MoSi2, molybdenum silicide, or MOSI2), an intermetallic compound, a silicide of molybdenum, is a refractory ceramic with primary use in heating elements. It has moderate density, melting point 2030 °C, and is electrically conductive. At high temperatures it forms a passivation layer of silicon dioxide, protecting it from further oxidation. Application area is Glass Industry, Ceramic sintering, heat treatment furnaces, semiconductorSemiconductorA semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
diffusion furnaceFurnaceA furnace is a device used for heating. The name derives from Latin fornax, oven.In American English and Canadian English, the term furnace on its own is generally used to describe household heating systems based on a central furnace , and sometimes as a synonym for kiln, a device used in the...
- Molybdenum disilicide doped with Al or Mo(Si,Al)2, an intermetallic compound, a silicide of molybdenum, is a refractory ceramic with primary use in heating elements. At high temperatures it forms a passivation layer of alumina (Al2O3) protecting it from corrosion or further oxidation. Application area is Glass Industry, Ceramic sintering, heat treatmentHeat treatmentHeat treating is a group of industrial and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass...
furnaces, semiconductorSemiconductorA semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
diffusion furnace. Working 300 oC higher in reducing atmospheres than MoSi2.
- Screen-printed metal–ceramic tracks deposited on ceramic insulated metal (generally steel) plates. These elements have found widespread application for kettles and other domestic appliances since the mid 1990s.
- 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. These elements are commonly found in precision heating applications such as Medical Diagnostics, Satellite, and Aerospace.
- Tubular (sealed element, often known by the trademark "Calrod"): a fine coil of Nickel chrome wire in a ceramic insulating binder (MgO, alumina powder), sealed inside a tube made of stainless steel or brass. These can be a straight rod (as in toaster ovens) or curved to span an area to be heated (such as in electric stoveStoveA stove is an enclosed heated space. The term is commonly taken to mean an enclosed space in which fuel is burned to provide heating, either to heat the space in which the stove is situated or to heat the stove itself, and items placed on it...
s, ovenOvenAn oven is a thermally insulated chamber used for the heating, baking or drying of a substance. It is most commonly used for cooking. Kilns, and furnaces are special-purpose ovens...
s, and coffee makers).
- Heat lamp: a high-powered incandescent lamp usually run at less than maximum power to radiate mostly infraredInfraredInfrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
instead of visible lightVisible spectrumThe visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of...
. These are usually found in radiant space heatersRadiant heatingRadiant heating is a technology for heating indoor and outdoor areas. Heating by radiant energy is observed everyday, the warmth of the sunshine being probably the most commonly observed example. Radiant heating as a technology is typically more narrowly defined...
and food warmers, taking either a long, tubular form or an R40 reflector-lamp form. The reflector lamp style is often tinted red to minimize the visible light produced; the tubular form is always clear.
- PTC ceramicCeramicA ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
: This material is named for its Positive Thermal Coefficient of resistance. Most ceramics have a negative coefficient; most metals, a positive one. While metals do become slightly more resistant at higher temperatures, this class of ceramics (often barium titanateBarium titanateBarium titanate is the inorganic compound with the chemical formula BaTiO3. Barium titanate is a white powder and transparent as larger crystals...
and lead titanateLead titanateLead titanate is an inorganic compound with the chemical formula PbTiO3. It is the lead salt of titanic acid. Lead titanate is a yellow powder that is insoluble in water....
compositesComposite materialComposite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...
) has a highly nonlinear thermal response, so that it becomes extremely resistant above a composition-dependent threshold temperature. This behavior causes the material to act as its own thermostatThermostatA thermostat is the component of a control system which regulates the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature. The thermostat does this by switching heating or cooling devices on or off, or regulating the flow of a heat transfer...
, since current passes when it is cool, and does not when it is hot. Thin filmThin filmA thin film is a layer of material ranging from fractions of a nanometer to several micrometers in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction....
s of this material are used in automotive rear-window defrost heaters, and honeycomb-shaped elements are used in more expensive hair dryersBlowdryerA blowdryer or hairdryer is an electromechanical device designed to blow cool or hot air over wet or damp hair, in order to accelerate the evaporation of water particles and dry the hair. Blowdryers allow to better control the shape and style of hair, by accelerating and controlling the formation...
and space heatersSpace heatingA space heater is a self-contained device for heating an enclosed area. Space heating is generally employed to warm a small space, and is usually held in contrast with central heating, which warms many connected spaces at once...
.
- Thick film technologyThick film technologyThick film technology is used to produce electronic devices such as surface mount devices, hybrid integrated circuits and sensors.Thick film circuits are widely used, in automotive industry, both in sensors ex...
:
Heating elements for high-temperature furnace
Furnace
A furnace is a device used for heating. The name derives from Latin fornax, oven.In American English and Canadian English, the term furnace on its own is generally used to describe household heating systems based on a central furnace , and sometimes as a synonym for kiln, a device used in the...
s are often made of exotic materials, including platinum
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
, molybdenum disilicide, molybdenum
Molybdenum
Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...
(vacuum furnace
Vacuum furnace
A vacuum furnace is a type of furnace that can heat materials, typically metals, to very high temperatures and carry out processes such as brazing, sintering and heat treatment with high consistency and low contamination....
s) and silicon carbide
Silicon carbide
Silicon carbide , also known as carborundum, is a compound of silicon and carbon with chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive...
. Silicon carbide igniters are common in gas ovens.
See also
- Thermoelectric effectThermoelectric effectThe thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice-versa. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely, when a voltage is applied to it, it creates a temperature difference...
- Positive temperature coefficient
- Heated hoseHeated hoseHeated hoses are used in bonding technology , filling and dosing systems, medical technology, chemical, pharmaceutical and food industry, extruder applications, and research & development. The heated hoses are used wherever a liquid, viscous or melted medium has to be transported from one place to...
- Heating mantleHeating mantleHeating mantle or isomantle is a term for certain pieces of laboratory equipment used to apply heat to containers, as an alternative to other forms of heated bath...
- Molybdenum disilicide