Tag: 3D microstructure

The shape of snow: New insights could help climate models

The shape of snow: New insights could help climate models

Scientists from the Institut des Géosciences de l’Environnement of Grenoble, the Centre d’Etudes de la Neige and the Groupe de Météorologie Expérimentale et Instrumentale have developed a new approach for measuring the interaction between snow and sunlight. This methodology is important to improve the accuracy of climate models. They did X-ray tomography experiments at ESRF ID19 beamline. The results are published in Nature Communications.

Once deposited on the ground, snow is a material composed of air and ice crystals, whose shape and arrangement vary greatly at the micrometre scale. This is known as the microstructure of snow. This “skeleton” of ice and air governs the propagation of light within the snowpack through optical phenomena such as refraction and internal reflections in the ice phase.

However, despite its extreme complexity and irregularity, natural snow is still represented in a simplistic manner in almost all optical models, including those implemented in climate models. These models typically depict snow as a collection of ice particles with perfect geometric shapes, mainly spheres. Among the many implications for the energy balance of snow, this simplification leads to significant uncertainties in climate modelling, with potential impacts of up to 1.2°C on global air temperature.

In this new study, the authors from the Institut des Géosciences de l’Environnement of Grenoble (IGE / CNRS – INRAE – IRD – UGA – Grenoble INP-UGA), the Centre d’Etudes de la Neige (CEN / CNRM / Météo-France – CNRS) and the Groupe de Météorologie Expérimentale et Instrumentale (GMEI / CNRM / Météo-France – CNRS) have accurately simulated the light propagation in a collection of 3D images of snow microstructure obtained by X-ray tomography, using a ray-tracing model. Very different snow types were investigated, from fresh snow (PP) to refrozen melt-freeze forms (MF). Some images were obtained at the 3SR-Lab. Several snow microstructures required higher resolution and were acquired at ESRF beamline ID19.

Read more on the ESRF website

Image: Snow microstructure: This is what fresh snow looks like at the micrometre scale

X-ray nanotomography reveals 3D microstructure of graphite anodes for lithium-ion batteries

X-ray nanotomography reveals 3D microstructure of graphite anodes for lithium-ion batteries

The optimisation of battery electrode architecture is a key aspect of improving battery performance, provided that precise characterisation of the complex battery microstructure is possible. In this work, X-ray nanotomography [1] was used at beamline ID16B [2] to obtain high-resolution images of the microstructure of graphite battery electrodes, providing 3D analysis and thorough quantification of the electrode/particle inner structure and porosity at the nanoscale.

A crucial step in the production of battery-grade natural graphite for lithium-ion batteries is the spheroidisation process: the morphological change that occurs in the electrode material during cycling or charging/discharging cycles. However, the low yield (30-50%) of this process results in a large quantity of wasted graphite fines that are not suitable for use in lithium-ion batteries due to their small particle size [3]. A method was devised to recycle waste graphite fines via a re-agglomeration process followed by a petroleum pitch coating in order to obtain aggregated graphite particles with sound mechanical strength and battery-suitable size to be used for electrode preparation. A compression step called ‘calendering’ was applied to the electrode’s coating to reduce its thickness and consequently increase its volumetric capacity.

X-ray nanotomography measurements carried out at beamline ID16B provided important microstructural details of the electrode-representative volumes (128 × 128 × 108 µm3 with 50 nm voxel size), along with statistical analysis of ~500 particles imaged in a single measurement. Data acquired on non-calendered and calendered pristine electrodes show that higher electrode density could be reached by calendering the electrode, without considerably affecting the active material accessibility through diffusion in the pore network. Despite the considerable morphological changes, no clear agglomerate fractures were observed, and particle integrity was preserved as individual agglomerate particles could still be distinguished. This highlights the fact that structural integrity is maintained from the electrode scale down to the particle level, and that the calendering process does not compromise the electrochemical performance.

Read more on ESRF website

Image: lectrode and particle porosity evolution with calendering in terms of (a) pore volume fraction and (b-e) microstructure. 3D rendering views of the (b) non-calendered and (c) calendered electrodes and (d,e) corresponding isolated graphite aggregated particles (with cross-section images).