Wire furnaces

Because most enamels contain not more than 30% solids, 70% of the enamel is bulk that does not contribute to the final product. Instead, it adds to the cost of transportation and handling, and at the site of application the solvent is evaporated. Because of the low solvent concentration in the hot exhaust fumes formed in wire furnaces, it is not economical to recover the solvents by condensation. Long before our present concern with protection of the environment, it became common practice to incinerate the solvent vapors prior to release into the atmosphere. 

Special furnaces iridium and timgsten wire furnaces, high-frequency heating furnaces, cathode ray ovens, arc furnaces, etc. 

Mad] Thermal analysis, light microscopy, chemical analysis of layers. Armko Fe and electrolitic Cu. The alloys were melted in a vertical molybdenum-wire furnace in an atmosphere of cracked ammonia. Alloys with 50 mass% Cu and Fe and fiom 0.05 to 2.0 mass% C. Stable C-Cu-Fe diagram, miscibiUty gap, the compositions of two Uquid layers at 1150°C (invariant monotectic equiUbrium), temperature and constitution of critical point on the miscibiUty curve. 

Starting materials were electrolyte Fe (99.998%), graphite (99.94%) and eiystallized boron (99.8%). Alloys were melted in a high frequeney or Tammann fumaee. The B and C eontent of the alloys was eonlrolled by wet ehemieal methods. Isothermal reactions were determined on alloys (50 g each) heated in a Mo-wire furnace to preset temperature under argon in Fe- or C-cmeibles. 

The furnace and thermostatic mortar. For heating the tube packing, a small electric furnace N has been found to be more satisfactory than a row of gas burners. The type used consists of a silica tube (I s cm. in diameter and 25 cm. long) wound with nichrome wire and contained in an asbestos cylinder, the annular space being lagged the ends of the asbestos cylinder being closed by asbestos semi-circles built round the porcelain furnace tube. The furnace is controlled by a Simmerstat that has been calibrated at 680 against a bimetal pyrometer, and the furnace temperature is checked by this method from time to time. The furnace is equipped with a small steel bar attached to the asbestos and is thus mounted on an ordinary laboratory stand the Simmerstat may then be placed immediately underneath it on the baseplate of this stand, or alternatively the furnace may be built on to the top of the Simmerstat box. 

At the end of the sweeping out, the tap Ti is first closed, and then the taps T3, T4, Ts and Tj in this order. The tubes R and S are then detached from the beak of the combustion tube, the guard tube V is then detached from them and replaced on the combustion tube beak. The furnace and thermostatic mortar are then switched off and the combustion tube allowed to cool with the tap to the oxygen supply open. The bung J is removed, and the boat withdrawn by means of a piece of rigid copper wire with a small hook in the end that fits into the small hole in the lip at the back of the boat the bung is then replaced and the boat transferred to its block in the desiccator. 

The temporary filling of the combustion tube D is now inserted this is in part replaced after every combustion. Sufficient wire-form copper oxide is added so that it just emerges to the left of the furnace E when the tube (not including the beak) is protruding 10-15 mm. at the beak end this constitutes the main oxidative packing of the tube. This is followed by 25 mm. of M.A.R. powder-form" copper oxide, followed by the sample suspended in more copper oxide, and backed by an oxidised copper spiral, 50 mm. in length. 

Co, by weight, is an extremely powerful magnet that offers a B-H (max) almost twice that of Alnico V. Platinum resistance wires are used for constructing high-temperature electric furnaces. 

Since detailed chemical structure information is not usually required from isotope ratio measurements, it is possible to vaporize samples by simply pyrolyzing them. For this purpose, the sample can be placed on a tungsten, rhenium, or platinum wire and heated strongly in vacuum by passing an electric current through the wire. This is thermal or surface ionization (TI). Alternatively, a small electric furnace can be used when removal of solvent from a dilute solution is desirable before vaporization of residual solute. Again, a wide variety of mass analyzers can be used to measure m/z values of atomic ions and their relative abundances. 

Because of its small size and portabiHty, the hot-wire anemometer is ideally suited to measure gas velocities either continuously or on a troubleshooting basis in systems where excess pressure drop cannot be tolerated. Furnaces, smokestacks, electrostatic precipitators, and air ducts are typical areas of appHcation. Its fast response to velocity or temperature fluctuations in the surrounding gas makes it particularly useful in studying the turbulence characteristics and rapidity of mixing in gas streams. The constant current mode of operation has a wide frequency response and relatively lower noise level, provided a sufficiently small wire can be used. Where a more mgged wire is required, the constant temperature mode is employed because of its insensitivity to sensor heat capacity. In Hquids, hot-film sensors are employed instead of wires. The sensor consists of a thin metallic film mounted on the surface of a thermally and electrically insulated probe. 

Incandescent Lamps, Electronic Tubes, and Resistance Elements. Articles fashioned in any form from molybdenum and tungsten usually fall within the bounds of powder metallurgy. These metals normally are first produced as a powder. Both molybdenum and tungsten are used as targets in x-ray tubes, for stmctural shapes such as lead and grid wires in electron tubes, and as resistance elements in furnaces. 

The same properties that make molybdenum metal effective in high temperature furnace appHcations make it useful as support wires for tungsten filaments in incandescent light bulbs and as targets in x-ray tubes. 

Platinum has many uses in dentistry. Pure platinum foil serves as the matrix in the constmction of fused-porcelain restorations. Platinum foil may be laminated with gold foil for cold-welded foil restorations. Platinum wire has found use as retention posts and pins in crown and bridge restorations. Heating elements and thermocouples in high-fusing porcelain furnaces are usually made of platinum or its alloys (see Platinum-GROUP metals). 

Radiation differs from conduction and convection not only in mathematical structure but in its much higher sensitivity to temperature. It is of dominating importance in furnaces because of their temperature, and in ciyogenic insulation because of the vacuum existing between particles. The temperature at which it accounts for roughly half of the total heat loss from a surface in air depends on such factors as surface emissivity and the convection coefficient. For pipes in free convection, this is room temperature for fine wires of low emissivity it is above red heat. Gases at combustion-chamber temperatures lose more than 90 percent of their energy by radiation from the carbon dioxide, water vapor, and particulate matter. 

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