Heat operation

Copper and silver combined with refractory metals, such as tungsten, tungsten carbide, and molybdenum, are the principal materials for electrical contacts. A mixture of the powders is pressed and sintered, or a previously pressed and sintered refractory matrix is infiltrated with molten copper or silver in a separate heating operation. The composition is controlled by the porosity of the refractory matrix. Copper—tungsten contacts are used primarily in power-circuit breakers and transformer-tap charges. They are confined to an oil bath because of the rapid oxidation of copper in air. Copper—tungsten carbide compositions are used where greater mechanical wear resistance is necessary. 

The conveyor and collector parts are thoroughly insulated to reduce heat losses in diying and other heating operations. Operating control is maintained usually by control of the exit-gas temperature, with the inlet-gas temperature varied to compensate for changing feed conditions. A constant solids feed rate must be maintained. 

Cascade coating The cascade coating technique is used extensively for the external coating of metal pipes with polyethylene to convey natural gas throughout Europe. There are several ways of using this technique but in all cases the pipe is evenly heated to a surface temperature of 250-350°C. Powder is then poured from above, cascaded , onto the rotating pipe. A second heating operation may be necessary to completely fuse the powder. 

Microwave ovens. These also find application for drying and heating operations. They are particularly useful for determining the moisture content of materials since the elimination of water takes place very rapidly on exposure to microwave radiation. 

The coalescence of Au microcrystal in the islet film occurs during thermal annealing, as well as when the metal concentration is increased. It is probably the coalescence that does determine the above-mentioned loss of Au/ZnO-sensor sensitivity during high-temperature heating operations. 

The efficiency of the heating operation with the chosen fuel. A costly fuel with a high efficiency ultimately is cheaper than a cheap fuel at a poor efficiency... 

It will be some time before fuel cells become available as a realistic commercial alternative for power generation applications. In order to compete with modem gas turbines/combined-cycle equipment, fuel cell plants will have to produce high-temperature waste heat, operate at an electrical efficiency of... 

Another requirement is a reduction in the generation of heat. Operation of any membrane under 90°C, even at 8 kA m-2, is very much desired for safety reasons and to prolong the life of the cell, piping or any other facilities subjected to high temperature. The ohmic drop beyond the membrane has been previously lowered by the narrowed gap separating the electrodes. This leaves further reduction of the ohmic resistance of the membrane to be achieved. 

Rate-of-rise Alarm System One of the systems installed for detecting fire by an abnormal rate of increase of heat operates when a normal amount of air in a pneumatic tube expands rapidly when heated and exerts pressure on diaphragms. 

Minor decomposition of p-toluenesulfinic acid is observed at temperatures above 55°C. For this reason, the water bath of the rotary evaporator and all subsequent heating operations should be kept at temperatures below 35-40°C to obtain best results. 

An explosion involving ethyl isocyanide has been reported.2 For this reason, prudence dictates the use of adequate shielding in all heating operations. 

Delayed tack adhesives. These are usually heat activated to achieve the tacky state, after which they can be affixed to any item without a heat source. Most frequently the heating operation plus pressure of application are applied simultaneously, however. The tacky state remains for some time after the source of heat is removed. These are more versatile than the instant tack type, particularly in their application to bottles, tinplate, and plastics, either coated or laminated. Speeds of around 600 per min can be achieved. 

After drying (removal of water), the extract is quantitatively transferred into a Kudema-Danish flask equipped with a concentrator tube and a Snyder column for sample concentration. The apparatus is placed in a water bath and ether is evaporated out. Use boiling chips in all heating operations. The volume of the extract is concentrated down to 1 to 2 mL. 

Radioactive aerosols Aerosols containing radionuclides are called radioactive aerosols. They have natural and artificial origin. Artificial radioactive aerosols are formed during nuclear explosions, in accelerator tunnels during operation, and during heating operation of activated metals. 

Avicenna, another great Sage, says that "natural heat operating in humid bodies first causes blackness, and finally causes whiteness, as may be seen in calyx." "Coction," says Alze, "causes the substance to become first black, then white, then red, all by the separation of waters. The waters being divided, cook the matter and the vapor until coagulation takes place, and there is made a White Stone."... 

The heating operation is hampered by the low heat conductivity of the material and by its sensitivity to heat degradation during long exposure times. Sheets up to 3 mm can be heated from one side with thicker ones both sides should be heated. The use of a liquid bath, e.g. glycol, is, when possible, the best method. 

Because of these potential dangers, heating operations should be done within a fume hood. The windows of the fume hood should have tempered glass and/or plastic film coatings. The door of the fume hood should always be closed as low as possible, especially when in use. Place your hands underneath the door to work while protecting your face behind the window. However, do not use the fume hood door in place of eye protection—use both. 

The abdomen of the anesthetized rat is shaved, the rat is then fixed in dorsal position on the heated operating table (thermostat set to 37 °C) and the abdomen is disinfected with a commercial skin disinfectant. 

This method for the stability testing of propellants was proposed by Vieille in 1896. The sample is heated at 110 °C (230 °F) in the presence of a strip of litmus paper, and is then exposed to air at room temperature overnight, after which the cycle is repeated. This treatment is continued until the litmus paper turns red within one hour. The overall duration of the heating operations thus performed is a measure of the stability. 

Accurately weigh approximately 28 mg of extractive- and moisture-free wood meal into the autoclave and add two small stainless steel balls. For each 28 mg of wood meal, 1ml of reagent is added. The autoclave is sealed, shaken manually for about 5 min, then heated at 180 1—2°C for 4h. The autoclave is shaken continuously throughout the heating operation. 

The nitration is carried out in pitchpine vats of about 2500-liter capacity. They are equipped with good hoods (see Fig. 56, page 376) and last over a year. All parts of the equipment which come in contact with the vapors driven off during the heating operations should be covered with wooden boards held in place by wooden pegs. 

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