Uncertainty Assessment for Very High Temperature Thermal Diffusivity Measurements on Molybdenum, Tungsten and Isotropic Graphite

The French National Metrology Institute LNE has improved its homemade laser flash apparatus in order to perform accurate and reliable measurements of thermal diffusivity of homogeneous solid materials at very high temperature. The inductive furnace and the associated infrared (IR) detection systems have been modified and a specific procedure for the in situ calibration of the used radiation thermometers has been developed. This new configuration of the LNE’s diffusivimeter has been then applied for measuring the thermal diffusivity of molybdenum up to 2200 °C, tungsten up to 2400 °C and isotropic graphite up to 3000 °C. Uncertainties associated with these high temperature thermal diffusivity measurements have been assessed for the first time according to the principles of the “Guide to the Expression of Uncertainty in Measurement” (GUM). Detailed uncertainty budgets are here presented in the case of the isotropic graphite for measurements performed at 1000 °C, 2000 °C and 3000 °C. The relative expanded uncertainty (coverage factor k = 2) of the thermal diffusivity measurement is estimated to be between 3 % and 5 % in the whole temperature range for the three investigated refractory materials.

Quantifying Uncertainty in Pulsed Thermographic Inspection by Analysing the Thermal Diffusivity Measurements of Metals and Composites

Pulsed thermography has been used significantly over the years to detect near and sub-surface damage in both metals and composites. Where most of the research has been in either improving the detectability and/or its applicability to specific parts and scenarios, efforts to analyse and establish the level of uncertainty in the measurements have been very limited. This paper presents the analysis of multiple uncertainties associated with thermographic measurements under multiple scenarios such as the choice of post-processing algorithms; multiple flash power settings; and repeat tests on four materials, i.e., aluminium, steel, carbon-fibre reinforced plastics (CFRP) and glass-fibre reinforced plastics (GFRP). Thermal diffusivity measurement has been used as the parameter to determine the uncertainty associated with all the above categories. The results have been computed and represented in the form of a relative standard deviation (RSD) ratio in all cases, where the RSD is the ratio of standard deviation to the mean. The results clearly indicate that the thermal diffusivity measurements show a large RSD due to the post-processing algorithms in the case of steel and a large variability when it comes to assessing the GFRP laminates.

Lipid tracking at kilohertz sampling rates on live cell membranes through Interferometric Scattering microscopy

The lateral dynamics of lipids on the cellular membranes are one of the most challenging topics to study in membrane biophysics, needing simultaneously high spatial and temporal resolution. In this study, we have employed Interferometric scattering Microscopy (ISCAT) to explore the dynamics of a biotinylated lipid analogue labelled with streptavidin-coated gold nanoparticles (20 and 40nm in diameter) at 2kHz sampling rate. We developed a statistics-driven analysis pipeline to analyse both ensemble average and single trajectory Mean Squared Displacements from each dataset, and to discern the most likely diffusion mode. We found that the use of larger tags slows down the target motion without affecting the diffusion mode. Moreover, we determined from our statistical analysis that the prevalent diffusion mode of the tracked gold-labelled lipids is compartmentalized diffusion. This model describes the motion of particles diffusing on a corralled surface, with a certain probability of changing compartment. This is compatible with the picket-fence model of membrane structure, already observed by similar studies. Through our analysis, we could determine significant physical parameters, such as average compartment size, dynamic localization uncertainty, and the intra- and inter-compartmental diffusion rates. We then simulated diffusion in an environment compatible with the experimentally-derived parameters and model. The closeness of the results from the analysis of experimental and simulated trajectories validates our analysis and the proposed description of the cell membrane. Finally, we introduce the confinement strength metric to compare diffusivity measurements across techniques and experimental conditions, which we used to successfully compare the present results with other related studies.

Numerical Simulation of Thermal Diffusivity Measurements with the Laser-Flash-Method to Evaluate the Effective Property of Composite Materials

Laser Flash Method (LFM) is commonly used to measure the thermal diffusivity of homogeneous and isotropic materials, but it can be also applied to macroscopically inhomogeneous materials, such as composites. When composites present thermal anisotropy, as fiber-reinforced, LFM can be used to measure the effective thermal diffusivity (aeff) in the direction of heat flux. In the present work, the thermal behavior of composites during thermal diffusivity measurements with the LFM was simulated with a Finite Element Model (FEM) using commercial software. Three composite structures were considered: sandwich layered (layers arranged in series or parallel); fiber-reinforced composites; particle composite (spheres). Numerical data were processed through a non-linear least-square fitting (NL-LSF) to obtain the effective thermal diffusivity of the composite. This value has the meaning of "dynamic effective thermal diffusivity". Afterward, the effective thermal conductivity (?eff) is calculated from the dynamic effective thermal diffusivity, equivalent heat capacity and density of the composite. The results of this methodology are compared with the analytically calculated values of the same quantity, which assume the meaning of "static effective thermophysical property". The comparison of the dynamic and static property values is so related to the inhomogeneity of the samples, a deviation of the temperature vs time trend from the solution for the perfectly homogeneous sample gives information about the sample's lack of uniformity.

Improvement of the photoacoustic response in thermal diffusivity measurements

An alternative photoacoustic cell configuration for the determination of the thermal diffusivity (α), at room temperature, for solid materials is presented. The method is based on the use of two identical photoacoustic chambers, inside both of them, a metallic foil thermally thin is used to transform the light energy to heat energy. A Reference material placed parallel to a study material allows to relate the thermal properties of the materials used as support in the photoacoustic chambers of the experimental arrangement presented here. The ratio between experimental and theoretical photoacoustic amplitudes is realized to validate a proposed mathematical model.

Asthenosphere dynamics based on the H2O dependence of element diffusivity in olivine

The oceanic asthenosphere shows two enigmatic features: low viscosity and high electrical conductivity. Their origins gather wide attention, but remain unsolved. Recent self-diffusivity measurements as a function of H2O content in olivine demonstrated that the H2O-incorporation in olivine cannot soften the asthenosphere, but it enhances the ionic conductivity, and causes the high-conductivity anomaly.