Electrical heating elements

Protective-Atmosphere Furnaces. These furnaces are used where the work caimot tolerate oxidation or where the atmosphere must provide a chemical or metallurgical reaction with the work. In some cases, mainly in high temperature appHcations, the atmosphere is required to protect the electric heating element from oxidation. 

Silicon carbide has very high thermal conductivity and can withstand thermal shock cycling without damage. It also is an electrical conductor and is used for electrical heating elements. Other carbides have relatively poor oxidation resistance. Under neutral or reducing conditions, several carbides have potential usehilness as technical ceramics in aerospace appHcation, eg, the carbides (qv) of B, Nb, Hf, Ta, Zr, Ti, V, Mo, and Cr. Ba, Be, Ca, and Sr carbides are hydrolyzed by water vapor. 

Borides and Silicides. These materials do not show good resistance to oxidation. Some siUcides, however, form Si02 coatings upon heating which retards further oxidation. Molybdenum disiUcide [1317-33-5] MoSi2, is used widely, primarily as an electrical heating element. 

Electronic conductivity Flexible conductor of electricity heating elements (resistance heating), shielding of electromagnetic radiation field flattening (high-voltage cables), materials with antistatic capability... 

Heating mantles. These consist of a flexible knitted fibre glass sheath which fits snugly around a flask and contains an electrical heating element which operates at black heat. The mantle may be supported in an aluminium case which stands on the bench, but for use with suspended vessels the mantle is supplied without a case. Electric power is supplied to the heating element through a control unit which may be either a continuously variable transformer or a thyristor controller, and so the operating temperature of the mantle can be smoothly adjusted... 

For many years, gas was the primary source of heat in the laboratory. Today, although electric heaters have become more common, gas still has some advantages sometimes overlooked. It is a quick source of heat and very fast to regulate. A gas burner can be pulled away in a fraction of a second should a distillation or a reflux operation get out of hand. In case of a spill, a gas burner is quickly dismantled and cleaned, whereas an electric heating element may have to be replaced. Another advantage is the lower cost of the gas burners. 

An electrically heated element of surface area 12 cm2 is completely immersed in a fluidised bed. The resistance of the element is measured as a function of the voltage applied to it giving the following data ... 

Armaou and Christofides (1999) present a two-electrode design for the deposition of 500-A films on an 8-cm wafer, which sits on top of the lower electrode, as shown in Fig. 10.4-2. The reactor is fed with 10% SiEE (silane) in He at 1 torr through a showerhead. An RF power source, at 13.56 MHz frequency, is used to generate the plasma, which is transported by convection and diffusion to the surface of the wafer where reaction occurs to deposit amorphous silicon. Electrical heating elements are positioned below the wafer and along the walls to achieve a uniform temperature of the plasma and wafer at 500 K. 

Heat transfer coefficients for a number of gas-solids systems were measured by Richardson and Shakiri 112 using an electrically heated element 25 mm square over a range of pressures from sub-atmospheric (0.03 MN/m2) to elevated pressures (up to 1.5 MN/m2). The measuring technique was essentially similar to that employed earlier for liquid-solids systems, as described in Section 6.5.2. 

The other forms of blackbody sources are adaptations of those used widely in conventional laboratory-style IR instruments, which feature exposed electrically heated elements. Various designs have been used, with metal filaments, made from Kanthral and Nichrome, being simple solutions in lower cost laboratory... 

Electric heating elements. These should also be available in your lab. They are sometimes the only heating device capable of producing higher temperatures. 

Metallurgical Applications, Structural Graphite Shapes, Electrical Heating Elements, Carbon and Graphite Powder and Particles)... 

The gel block (Figure 3) consists of an aluminum casting 48 inches long by 4 inches wide by 1 inch deep with electrical heating elements at one end and facilities for water cooling, if required, at the other end. The block is lagged and is fitted with... 

Thermal conductivity cell. A chamber in which an electrically heated element will reflect changes in thermal conductivity within the chamber atmosphere. The measurement is possible because of the change in resistance of the element. 

In addilion to ferrous ulluys, chromium also is added to cupper, vanadium, zirconium, and other metals to form several hundred chromium-bearing alloys. Nickel-chromium-iron alloys have high electrical resistance and are used widely as electrical heating elements. Niclirttme and ChromeI are examples. 

A thermoplastic material is, usually as a granulate, brought into a cylinder, which is kept at a constant temperature by electric heating elements. With the simplest type of machine the material is molten by heat transfer from the cylinder wall. Since plastics are poor heat conductors, such a heating process takes a considerable time, so that the risk is run of degradation at the wall. 

Carborundum, Glowbar Silicon Carbide Electric Heating Elements , Form A-7038, Rev. 3-92, The Carborundum Company, Niagara Falls, NY, p.10 (1992). 

Cross section of the electrolyzer, 1 — Outer box of the electrolyzer with electrical heating and circulation of hot air, — Electric heating elements, 3 — Eloctrolyzer vessel. 4 — Electro lyzor cover, 5 — Graphite anode, H — Electron diaphragm, C — Cathodo of perforated silver plate, some 1.5 mm thick, fixed to silver frame. 

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