Evaluation Of Thermal Properties Of Magnesium Fluoride Powders, Influence Of Mechanical Compression, Powder Composition And Gaseous Conditions
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F Baillet, M Allibert & A Jourdan
In high temperature reactors, thermal dams are usually made from porous materials. It is often complex to evaluate their particular thermal properties using models that take into account physical or physico-chemical phenomena. The evaluation of these thermal properties that is usually done with small amount of materials and simple setting is now possible with non-stationary methods. They are helpful in building a model of the properties and for the thermal modeling of the reactor. In this study, we use two non stationary methods which have the peculiarity that only a small amount of materials is necessary to determine the thermal properties of powders. The first method used a plane and circular probe geometry representing a heating element etched on a Kapton® polymer. Considering the thermal equation obtained for this sensor geometry, its minimization gives the sample thermal diffusivity and conductivity. The second method is the Hot Disk system developed by Chalmers University (Sweden). In this experimental set-up, the sensor is composed of a double spiral (heating element and temperature sensor) assembled on a mica membrane. The basic principle of modeling is identical even if the thermal model is more complex due to the geometry of the sensor. This study presents the results obtained with different powder mixtures containing magnesium fluoride and uranium fluoride in several conditions. These mixtures are used in the Comurhex processes for magnesiothermie production of metallic uranium. The results are compared to the thermal properties calculated with models or reported in the literature. The main results show the difficulty to take into account all the phenomena that occur in this kind of materials.