Analytical Model for Pulsed-Laser Induced Mode-Mismatched Dual-Beam Thermal Lens Spectroscopy in Liquids.

Analytical models are very important to understand physical, chemical, and biological phenomena. In many cases, obtaining an analytical model is a complex, even an impossible task. In this work, an analytical model for thermal lens spectroscopy has been developed. The model considers light absorbing liquids, a laser pulsed beam as the heat source, timescale thermal regime, and small phase change produced by heating. A simplification for low-absorption samples is obtained. A complete theoretical study of their utilization is shown. Measurements of the thermal diffusivity of water-ethanol sample mixtures in the liquid phase are analyzed. These values for pure substances are in good agreement with those reported in the literature. Our methodology could be very useful in the analysis of the optical and thermal properties of liquids.

Evidence of a Thermal Diffusivity Gap in Sintered Li-Co-Sb-O Solid Solutions.

In this work, the thermal properties of ternary Li3x Co7-4x Sb2+x O12 solid solutions are studied for different concentrations in the range 0 ≤ x ≤ 0.7. Samples are elaborated at four different sintering temperatures: 1100, 1150, 1200 and 1250 °C. The effect of increasing the content of Li+ and Sb5+, accompanied by the reduction of Co2+, on the thermal properties is studied. It is shown that a thermal diffusivity gap, which is more pronounced for low values of x, can be triggered at a certain threshold sintering temperature (around 1150 °C in this study). This effect is explained by the increase of contact area between adjacent grains. Nevertheless, this effect is found to be less pronounced in the thermal conductivity. Moreover, a new framework for heat diffusion in solids is presented that establishes that both the heat flux and the thermal energy (or heat) satisfy a diffusion equation and therefore highlights the importance of thermal diffusivity in transient heat conduction phenomena.

Photoacoustic monitoring of sedimentation of micro-particles in low viscosity fluids.

In this work, the potential of photoacoustic technique in the study of the sedimentation process of particles in liquids is explored. Experiments were performed using zirconia particles of 50 and 100 µm in three different low viscosity liquids, water, citronella, and ethylene glycol. It is shown that the evolution of the PA signal depends not only on the kind of liquids used but also on the size of the particles. An effective thermal model is developed in order to study the process and to infer the evolution of the thermal conductivity of the sedimented layer when it behaves as thermally thin, or the thermal effusivity if it behaves as thermally thick. It is shown that based on these results, the time evolution of the volume fraction of particles, in the region in which the sediment is deposited, can be obtained. These results can be useful in establishing a methodology for the photoacoustic monitoring of the process of sedimentation in more complex systems.