Daniel Sánchez-Rodríguez

Measuring thermal conductivity of powders with differential scanning calorimetry

AbstractThis paper simplifies a recently proposed method for measuring the thermal conductivity of powders using differential scanning calorimetry (DSC) (Sánchez-Rodríguez et al. in J Therm Anal Calorim 121:469–473, 2015). With this method, a crucible is filled with powder and a spherical metal reference is partially sunk into it. The thermal resistance between the metal and the crucible wall at the metal melting point is obtained from the DSC melting peak slope. In the simplified method outlined in this paper, a cylindrical pan is substituted for the original hemispherical crucible. The equivalence of both methods is demonstrated with alumina powder and commercial cylindrical crucibles of several sizes and aspect ratios.

Determination of thermal conductivity of powders in different atmospheres by differential scanning calorimetry

We have developed a new method to measure the thermal conductivity of powders by differential scanning calorimetry that works with masses in amounts as low as tens of mg. The method is based on that used by Camirand to determine the thermal conductivity of materials in the form of thin sheets but introducing a hemispherical pan to contain powders in such a way that the issue of heat transfer is reduced to a one-dimensional problem. The modification of the method was successfully validated on obtaining identical results in determining the thermal conductivity of a commercial silicone with both Camirand’s method and the modified method. We have also tested our method with materials that, in bulk, cover a wide range of thermal conductivities and have performed the experiments with several atmospheres and reference metals. The results are consistent with already published general trends in that they confirm that thermal conductivity of powders is mainly governed by thermal conduction through the surrounding gas.

Thermal Gradients in Thermal Analysis Experiments

The concept of “sample temperature” in non-isothermal thermal analysis experiments is analyzed. From the analysis of the heat balance inside the sample, it is shown that the existence of such sample temperature is restricted to experimental conditions, where the thermal gradients are negligible. Two different sources of thermal gradients are studied: the sample thermal inertia and the heat of reaction that is not quickly removed. The conditions to prevent the formation of thermal gradients as well as the condition for a thermal runaway to occur are deduced. Finally, it is shown that the aspect ratio is a crucial parameter for the formation of thermal gradients within the sample.

The effect of volatiles on the measurement of the reaction heat by differential scanning calorimetry

When gases evolve during a chemical reaction, a fraction of the reaction heat is lost with them. We have analyzed, both theoretically and experimentally, the deviations that this effect can produce on the determination of the reaction heat by differential scanning calorimetry (DSC). It is shown that, even in the absence of gas overheating, deviations related to variations in the sample heat capacity can be substantial in experiments involving very intense DSC peaks. However, experiments performed on thermal decomposition of metal organic salts and on evaporation of liquids have shown that deviations usually arise from gas overheating.