Combustion calorimeters conventional

Conventional combustion calorimeters operate on a macro scale, that is, they require samples of 0.5-1.0 g per experiment. Unfortunately, many interesting compounds are available only in much smaller amounts. In the case of oxygen combustion calorimetry, however, several combustion microcalori-meters that only demand 2-50 mg samples have been developed in recent years. The achievements and trends in this area through 1999 have been reviewed [7-10], and interested readers are directed to these publications. Since then, a few new apparatus have been reported [11-17], Nevertheless, it should be pointed out that the general principles and techniques used to study compounds at the micro scale are not greatly different from those used in macro combustion calorimetry. 

Chemists always need to know bond energies, often for unusual combinations of elements, for which bomb combustion calorimetry experiments have never been done, partly because the appetite of conventional bomb combustion calorimeters for large samples is not easily met for rare compounds. Thus there is a need for future micro rotating-bomb calorimeters. 

However, it is often criticized that multi-ton quantities cannot be reduced representatively to 1 g samples burnt in conventional bombs and that milling MSW to 2 mm particles alters the composition. To check this criticism a - compared with the usual instruments - huge combustion calorimeter was constructed at the National Institute of Standards and Techniques in Gaithersburg, MD/USA [144]. With a combuster of about 0.2 m volume in a calorimeter of 1.33 m outer diame-... 

The Cone Calorimeter was equipped with a conveyor belt (Figure 16.13) to allow for continuous supply of small samples to pass under the cone heater for testing this is called RCC. Similar to a conventional Cone [35], the combustion products (smoke, CO, C02, etc.) are analyzed with the primary measurement being the amount of 02 consumed while burning. The operation procedure of the RCC and the conventional cone (ASTM 1354) are quite different as the RCC uses significantly smaller specimens and the test is continuous. In these studies, both the RCC and conventional cone were operated at a heat flux of 35 kW/m2. The absolute values for the RCC and conventional cone are not identical, since the sample masses are different, but the result... 

Gas densitometers can measure, continuonsly and indirectly, the calorific value of natural gas, can accnrately control the calorific value of send-out town gas and can accurately monitor process gas. Comparison with conventional combustion-type calorimeters, based on actual experience at the works, reveals the tendencies shown in Table 5. 

The experimental determination of the heat of formation of an organic compound will usually require the investigator to measure the heat of combustion of the compound in a suitable calorimeter. If the compound is a gas, or volatile liquid at room temperature, the flame calorimeter 141) offers itself as a suitable instrument but for most liquid or solid compounds, the bomb calorimeter is the obvious choice. There are, however, decided limitations to the usefulness of conventional calorimeters when organo-metallic compounds are under investigation. 

The difficulties stem from the fact that the metallic component rarely burns completely, so that the solid inorganic residue resulting from combustion consists of a mixture of products which may be complex. In this event, the measured combustion heat refers to a process which can only be properly defined if the products of combustion are accurately analyzed. The problem is not merely analytical, because the solid products are deposited in the crucible, and on the walls of the bomb, and the composition of the deposit varies from one part of the bomb to another. A striking example, quoted by Good and Scott (65), is provided by Knowlton s study of the combustion of tetraethyllead in a conventional bomb calorimeter the solid product was found to contain PbO, Pb02, PbC03, and Pb(N03)2 admixed with unburned Pb, but the interpretation of the measured heat of combustion with respect to these products led to a value for the heat of formation of tetraethyllead which was in error by no less than 40 kcal/mole This is, perhaps, an extreme example, but the fact remains that conventional... 

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