Resistance-heating elements

Advanced Structural and Heating Materials. Molybdenum siHcide [12136-78-6] and composites of MoSi2 and siHcon carbide, SiC, have properties that allow use as high temperature stmctural materials that are stable in oxidizing environments (see Composite materials Metal-matrix composites). Molybdenum disiHcide also finds use in resistance heating elements (87,88). 

For a large number of applications involving ceramic materials, electrical conduction behavior is dorninant. In certain oxides, borides (see Boron compounds), nitrides (qv), and carbides (qv), metallic or fast ionic conduction may occur, making these materials useful in thick-film pastes, in fuel cell apphcations (see Fuel cells), or as electrodes for use over a wide temperature range. Superconductivity is also found in special ceramic oxides, and these materials are undergoing intensive research. Other classes of ceramic materials may behave as semiconductors (qv). These materials are used in many specialized apphcations including resistance heating elements and in devices such as rectifiers, photocells, varistors, and thermistors. 

Nonferrous alloys account for only about 2 wt % of the total chromium used ia the United States. Nonetheless, some of these appHcations are unique and constitute a vital role for chromium. Eor example, ia high temperature materials, chromium ia amounts of 15—30 wt % confers corrosion and oxidation resistance on the nickel-base and cobalt-base superaHoys used ia jet engines the familiar electrical resistance heating elements are made of Ni-Cr alloy and a variety of Ee-Ni and Ni-based alloys used ia a diverse array of appHcations, especially for nuclear reactors, depend on chromium for oxidation and corrosion resistance. Evaporated, amorphous, thin-film resistors based on Ni-Cr with A1 additions have the advantageous property of a near-2ero temperature coefficient of resistance (58). 

Electrical resistance boilers use banks of fixed, immersion-type, resistance heating elements (typically sheathed in seamless copper, Incoloy 800, or 316SS) to provide an energy source that is contained within a carbon-steel pressure vessel. The vessel is provided with a sight glass and all normal boiler controls, valves, and regulators necessary for automatic operation. The vessel is generally well insulated and housed within an enameled metal cabinet. Various electrical supply options are available. 

Insulating substrate in ribbon heaters in combination with a pyrolytic graphite resistance heating element. 

Silver is employed for low resistance electrical contacts and conductors, and in silver cell batteries. Antimony is used in lead add storage batteries to improve the workability of the lead and lead oxides. Copper and copper alloy wires, connectors, cables, switches, printed drcuit boards, and transistor and rectifier bases are common throughout the industry. Nickel is used in high resistance heating elements, glass-to-metal seals, batteries, and spedalty steels for power generation equipment Household appliances employ stainless and electroplated steel containing nickel. 

Alternating current works just as well as direct current for generating heat from resistance heating elements, since as long as the electrons are moving and impacting, they need not drift in a consistent direction. 

For cryogenic temperature measurements, furnaces consist of thermally conductive jackets filled with liquid nitrogen (boiling point 77.35 K) or liquid helium (boiling point 4.215 K). The heat dissipation from resistance heating elements competes with the cooling effects of these fluids to permit stable temperature control down to near absolute zero [10]. 

Heating of the specimen can also be accomplished in several ways including resistance heating elements and direct radiation methods such as quartz lamps. Each of these methods will provide the necessary temperature, but care must be exercised to ensure that thermal gradients and time variations are minimized. The absolute temperature must be measured to provide the necessary control of the test temperature. Temperature measurement, discussed in more detail later, can be accomplished by a number of methods. The... 

Both metals are inert to oxygen at ordinary temperatures, but at red heat they combine with it readily to give the trioxides. They both combine with chlorine when heated, but even at room temperature they are attacked by fluorine, yielding the hexafluorides. The metals also react on heating with B, N, and Si. Molybdenum disilicide (MoSi2) is used in resistance heating elements, and WC is used to tip cutting tools. 

A 40-cm-loiig, 800-W electric resistance heating element with diameter 0.5 cm and surface temperature 120°C is immersed in 75 kg of water initially at 20°C. Determine how long it will take for Ihis heater to raise the water temperature to 80°C. Also, determine the convection heat transfer coefficients at the beginning and at the end of the hearing process. 

For continuous melting of domestic and technical glass, small electric furnaces have been developed a longitudinal cross section of one such type is shown in Fig. 102. At the working end, the temperature is controlled by resistance heating elements. The direction of melt flow is shown by the arrow. All-electric furnaces have to be heated up by auxiliary gas burners since the cold batch does not conduct electrically. 

Indirect Sintering. A schematic view of a furnace with resistance-heating elements is presented in Fig. 5.34. A modem industrial aggregate is shown in Fig. 5.35. The green compacts (no presintering necessary) are placed inside a cylindrical or basketlike heating element of the furnace (constmcted of Mo or preferably W). In a radial direction to the outside, the furnace is adapted with radiation shields (inner shields made of W, outer sheets made of Mo), which protect the furnace wall and concentrate the heat to... 

The filter temperature can be raised by direct heating with a burner, placed in front of the filter, or by equipping the filter with resistive heating elements. 

As resistive heating elements of this electrothermic interface thin film platinum resistors and surface mount technology (SMT) resistors are used (Richter et al. 2003, 2009a). The hydrogel components can be heated and cooled also by Peltier elements (Yu et al. 2003b Luo et al. 2003a). 

Gottschlich et al. [134] developed a microfluidic system that integrated enzymatic reactions, electrophoretic separation of the reactants from the products, and postseparation labeling of the proteins and peptides prior to fluorescence detection (see Fig. 12). Tryptic digestion of oxidized insulin p-chain was performed in 15 min under stopped flow conditions in a heated channel serving as the reactor, and the separation was completed in 60 s. Localized thermal control of the reaction channel was achieved using a resistive heating element. The separated reaction products were then labeled with naphthalene-2,3-dicarboxaldehyde (NDA) and detected by fluorescence detection. 

The top lid also carries stainless steel cooling coils, through which air may be circulated, to control top temperatures and prevent loss of ZrCU vapor in gases discharged from the furnace. The furnace is provided with three external electric resistance heating elements to provide the heat of sublimation of ZrCLi and control temperature distribution. 

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