Platinum heating coils

Lehmann and Brauer [25] and Brauer [26] investigated the Py-GC of polymethylmethacrylate (PMMA) at temperatures between 400 °C and 1100 °C utilising for the pyrolysis a silica boat surrounded by a platinum heating coil. 

Elias et al.43 observed that the heat liberated on a silver-coated platinum wire coil was about 10% higher than that expected from the known concentration of atomic oxygen in a discharge flow system, and they ascribed the effect to appreciable concentrations of 02(1A5) in the discharge products. It was then shown that some heat was released even after all the atomic oxygen had been removed by reaction with ethylene. 

Determination of the flow point is a method which has been suggested by Lillie (1952). The measurement is carried out under standard conditions so that a glass fibre (0.6—0.7 mm in diameter, about 8 cm in length) is suspended in a heating coil of platinum-rhodium which is then heated up to 1450 °C by switching on the current. The period of time from the switching on the coil until the fibre drops off is measured, that is the time required for its disruption by melting the healed section. The apparatus must be carefully calibrated in advance. 

The furnace heating coil is wound non-induc-tively to avoid magnetic interactions between the coil and the sample. Coils are made from various materials, such as nichrome (T < 1300 K), platinum (T > 1300 K), platinum-10% rhodium (T < 1800 K) and silicon carbide (T < 1800 K). The furnaces consisting of an infrared (IR) ray heater instead of a standard coil heater are also used. An IR furnace is routinely used up to 1800 K. Using an elliptical reflector or parabolic reflector, IR... 

Pellistors are used to detect flammable gases like CO, NH3, CH4 or natural gas. Some flammable gases, their upper and lower explosion limits and the corresponding self-ignition temperatures are listed in Tab. 5.1. This kind of gas sensor uses the exothermicity of gas combustion on a catalytic surface. As the combustion process is activated at higher temperatures, a pellistor is equipped with a heater coil which heats up the active catalytic surface to an operative temperature of about 500 °C. Usually a Platinum coil is used as heater, embedded in an inert support structure which itself is covered by the active catalyst (see Fig. 5.33). The most frequently used catalysts are platinum, palladium, iridium and rhodium. 

During the reaction of the hot catalyst surface with a flammable gas the temperature of the device increases. The Platinum coil itself serves at the same time as a resistance thermometer. The resistance increase of the coil then is a direct measure for the amount of combusted gas. Usually the amount of heat that develops during combustion is small and amounts to 800 kj/mol for methane, for example [8], Therefore the sensor is connected in a bridge circuit to a second resistor which shows the same setup as the pellistor but is catalytically inactive. The bridge voltage is then controlled by the temperature difference of the two sensors (see Fig. 5.34). 

Transmission of Hod through Thin Plates.—The bodies employed by Mellon were a Locatelli s lamp, fixed as1 at a in Fig, 10 a coil of platinum kept at incandescence by the flame of alcohol, as seen in Fig. 12 a blackened copper foil fixed to a stend, and heated with a spirit lamp to 752°, as represented in Fig, 13 j and a brass canister filled with water kept at 212 , as shown in Fig, 14, One or other... 

Sintered metal elements as a part of a flameproof enclosure are often used for gas warning detectors for combustible gases. As a cost effective gas sensor, an electrically heated platinum coil covered with a catalyst and as a part of a... 

A resistance-heated system (platinum ribbon or coil). 

Heated-filament pyrolyzers are often used to analyze lignins (Kratzl et al. 1965, Lindberg et al. 1982, Obst 1983, Gardner et al. 1985, Faix et al. 1987, 1991, Funazukuri et al. 1987, Salo et al. 1989). In this type of analyzer, electric current is passed through a resistance ribbon or coiled wire, both made of platinum. The dissipation of power increases the temperature of the conductor. Heat-up and pyrolysis times are selected from an instrument control. Characteristic parameters of this type of pyrolyzer have been described by Wells et al. (1980) and Wampler and Levy (1987). 

Fusion of an analytical sample. The sample is ground until it passes through a 100 pm sieve. A 0.250 g quantity is weighed and mixed with 4.0g of sodium tetraborate and 0.2g of sodium nitrate. The fusion occurs in a platinum-crucible either at 1350°C with a coil which is heated indue-... 

The thermometer and stirrer should be inserted with the thermometer carefully mounted in such a way that the sensing element (bulb of a mercury thermometer, resistance coil of a platinum resistance thermometer, or calibrated thermistor) is about halfway between the bottom of the test tube and the upper surface of the liquid and concentric with the tube so that the stirrer can easily pass around it. If the thermometer is too close to the bottom, a bridge of frozen solvent can easily form, which will conduct heat away from the thermometer and result in low readings. 

Several methods have been described for the preparation of silver-silver chloride electrodes a small sheet or short coil of platinum is first coated with silver by electrolysis of an argentocyanide solution, and this is partly converted into silver chloride by using it as an anode in a chloride solution. Alternatively, a spiral of platinum wire may be covered with a paste of silver oxide which is reduced to finely divided silver by heating... 

E. H. Griffiths sed electrical heating and took elaborate precautions to minimise errors (Fig. 1. VIIIL). The cylindrical calorimeter (8 cm. high and 8 cm. diam.) contained a coil of 33 cm. of platinum wire (0 01 cm. diam., resistance... 

Pyrolysis in the Presence of TMAH. A wide set of Fulvic Acids (FA), Humic Acids (HA) and related materials from different origins have been thus far studied using the TMAH/thermochemolysis procedure (9,15-17,22,24,25). The TMAH procedure has mainly been performed in pyroprobe units, in much the same way as the conventional flash pyrolysis using either quartz tubes and/or a platinum coil, by mixing the humic materii with a few drops of the reagent prior to heating. 

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