Metal block, heated

Other thermal zones which should be thermostated separately from the column oven include the Injector and detector ovens. These are generally insulted metal blocks heated by cartridge heaters controlled by sensors located in a feedback loop with the power supply. Detector blocks are usually maintained at a temperature selected to minimize detector contamination from condensation of column bleed or sample components and to optimize the response of the detector to the sample. The requirements for i injectors may be different depending on the injector design and may include provision for temperature program operation. 

Finally, a method that is used to determine pitch volatility (ASTM D-4893) might also be used, on occasion, to determine the nonvolatility of mineral oil. In the method, an aluminum dish containing about 15 g of accurately weighed sample is introduced into the cavity of a metal block heated and maintained at 350°C (662°F). After 30 min, during which the volatiles are swept away from the surface of the sample by preheated nitrogen, the residual sample is taken out and allowed to cool down in the desiccator. Nonvolatility is determined by the sample weight remaining and reported as % w/w residue. 

System is the metal block + heat engine (closed)... 

All calorimeters consist of the calorimeter proper and its surround. This surround, which may be a jacket or a batii, is used to control tlie temperature of the calorimeter and the rate of heat leak to the environment. For temperatures not too far removed from room temperature, the jacket or bath usually contains a stirred liquid at a controlled temperature. For measurements at extreme temperatures, the jacket usually consists of a metal block containing a heater to control the temperature. With non-isothemial calorimeters (calorimeters where the temperature either increases or decreases as the reaction proceeds), if the jacket is kept at a constant temperature there will be some heat leak to the jacket when the temperature of the calorimeter changes. 

In this microcalorimeter, the heat sink is not a massive metal block but is divided into several parts which are mobile with respect to each other. Each thermoelectric element (E) and a cell guide (D) are affixed to a fluxmeter holder (C). The holder (C) is mobile with respect to a massive arm (B) which, in turn, rotates around a vertical axle (A). All parts of the heat sink are made of brass. Surfaces in contact are lubricated by silicone grease. Four thermoelectric elements (E) are mounted in this fashion. They enclose two parallelepipedic calorimetric cells, which can be made of glass (cells for the spectrography of liquids are particularly convenient) or of metal (in this case, the electrical insulation is provided by a very thin sheet of mica). The thermoelectric elements surrounding both cells are connected differentially, the Petit microcalorimeter being thus a twin differential calorimeter. 

The measurement of an enthalpy change is based either on the law of conservation of energy or on the Newton and Stefan-Boltzmann laws for the rate of heat transfer. In the latter case, the heat flow between a sample and a heat sink maintained at isothermal conditions is measured. Most of these isoperibol heat flux calorimeters are of the twin type with two sample chambers, each surrounded by a thermopile linking it to a constant temperature metal block or another type of heat reservoir. A reaction is initiated in one sample chamber after obtaining a stable stationary state defining the baseline from the thermopiles. The other sample chamber acts as a reference. As the reaction proceeds, the thermopile measures the temperature difference between the sample chamber and the reference cell. The rate of heat flow between the calorimeter and its surroundings is proportional to the temperature difference between the sample and the heat sink and the total heat effect is proportional to the integrated area under the calorimetric peak. A calibration is thus... 

Never use a wet rag or sponge to quickly cool off the heating block. This might permanently warp the block. You can use a cold metal block to cool it if you re in a hurry. Careful. If you slip, you may burn yourself. 

With the Thiele tube (Fig. 39) you use hot oil to transfer heat evenly to your sample in a melting point capillary, just like the metal block of the Mel-Temp apparatus does. You heat the oil in the sidearm and it expands. The hot oil goes up the sidearm, warming your sample and thermometer as it touches them. Now, the oil is cooler and it falls to the bottom of the tube where it is heated again by a burner. This cycle goes on automatically as you do the melting point experiment in the Thiele tube. 

Heating is most often achieved using electrical resistive devices to heat a relatively massive metal block. This ensures that the temperature... 

Modern heat flow microcalorimeters employ a diversity of heat sinks and cells, depending on the applications for which they were designed. The heat sinks can be water baths, kept at a constant temperature ( 5 x 10-4 K) and typically operating in the range of 20-80 °C, or metal blocks, allowing much wider temperature ranges (e.g., -196°C to 200°C, 20°C to 1000°C). In some cases it is possible to scan the temperature at a predetermined rate (see chapter 12). 

The connecting tubing should be as short and narrow as possible. The volume of a 20 cm x 0.5 mm i.d. tube is 39.3 p. That of a 20 cm x 0.25 mm i.d. tube is 9.8 /A, and that of a 20 cm x 0.125 mm i.d. tube is 2.5 [A. Some detectors are equipped with a heat exchanger that consists of a metal block containing a capillary tube. The volume of this tube also affects the theoretical plate number. If highly sensitive operation is not required, the heat exchanger can be removed or bypassed. 

In order to extract small fluid samples from the reaction cell at high temperatures, a capillary with a tip of sintered alumina, can be introduced sidewise into the center of the reaction cell. The samples pass into a section of stainless steel capillary between two high pressure valves mounted on a heated metal block. The capillary section serves as a pipette from which liquid and gaseous components can be extracted for analysis. Another method is, to use a small spindle press. By turning it back very slowly, samples can be sucked out steadily from the reaction cell. 

In the table which. follows are listed the temps in °C which were detd in the USA by means of apparatus similar to the one described in Ref 28. The values are taken from PATR 1740, Rev (1958) and from the table entitled "Military Explosives compiled at PicArsn. The temps detd in Russia for some expls and reported in Ref 24, p 29 and Ref 25, pp 326-27 are given here for comparison Most of the apparatuses used in foreign countries employ heated baths either filled with Wood s metal or with. some liquid of high bp, such as in apparatus of Kostevitch (Refs 5 24). Exceptions are the apparatus of Lang-hans, briefly described in Ref 4, which employs a metal block and the apparatus of Belgrano (Ref 18) which employs an iron plate and is of very simple construction... 

Essentially, all of these devices consist of a metallic block or bar heated either by gas (as in the Maquenne Block) or by an electric heater. The test may be conducted by placing a few small grains of explosive on the preheated block and noting the temperature at which the sample ignites, deflagrates or explodes by means of a thermometer installed inside the block... 

Pa, catalog (1970), p 640] another is Ma-quenne Block (electrically heated metal block with. holes for capillary tubes thermometer)... 

N 28.74% greenish-brown crysts, mp — explodes on heating to 198—202° or when dropped on metallic block preheated to 220—25 does not explode from impact. It can be prepd by dissolving Cu azide in trim ethyl pyridine soln, or hv addj> NaN to the Cu" "" " salt of tri-... 

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