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Systematic studies were carried out on the oxidation behaviour of uranium dicarbide in air in the temperature range 25 ~ to 700 ~ employing thermogravlmetry, evolved gas detection Xray diffraction and chemical analysis. The mechanistic aspects were investigated and the oxidation was found to proceed through reaction processes involving oxidation of uranium to ct-UO3 with release of chemically bound carbon, reaction of released carbon leading to the formation of CO 2 which gets liberated stepwise, decomposition of ~-UO 3 to U3Os and oxidation of free carbon to CO2. Examination of the thermoanalytical behaviour of sintered graphite, UO3, mixtures of graphite with UO 3 and with U3Os supported the above findings. John Wiley & Sons, Limited, ChichesterAkad$miai Kiadr, Budapest

The use of reaction calorimetry in the chemical industry is constantly growing. Its use aims at the assessment and subsequent reductions of the risks arising from reaction thermal runaways in the event of cooling system malfunction or agitation failure and at optimum process design.A reaction calorimeter is a small-scale automated jacketed reactor equipped with a precise temperature controller, which is capable of heat balancing. The reactor contents may be heated or cooled by heat-transfer oil and they are continuously agitated. A powerful thermostatic bath allows rapid adjustment of jacket temperature to maintain the desired reactor temperature-profile. The reactor and jacket temperatures as well as a number of other quantities are continuously measured. A heat balance, based on a number of assumptions, is used for the evaluation of the heat of reaction and its global kinetics. The evaluation of the overall heat transfer coefficient and the accumulated heat are achieved by means of calibrations. Their measurement is, in the main, long. Also it is very often lacking sufficient accuracy.In the present approach, a simple method for the accurate evaluation of the overall heat transfer coefficient is presented. It is also shown how the analysis of the heatbalance equations in different stages can be used for the simultaneous evaluation of a number of quantities and constants of the reaction calorimeter using a single set of calibration experiments.