Jérôme Adrien

Particle redistribution and structural defect development during ice templating

The freezing of colloidal suspensions is encountered in many natural and engineering processes. It can be harnessed, through a process known as ice templating, to produce porous materials and composites exhibiting unique functional properties. The phenomenon by itself appears simple: a solidification interface propagates through a colloidal suspension. We are nevertheless still far from a complete understanding and control of the phenomenon. Such lack of control is reflected in the very large scattering of mechanical properties reported for ice-templated ceramics, largely due to the formation of structural defects. Through systematic in situ investigations, we demonstrate here the role of suspension composition and the role of particle-particle electrostatic interactions on defect formation during ice templating. Flocculation can occur in the intercrystal space, leading to a destabilization of the solid-liquid interface and triggering the growth of crystals perpendicular to the main ice growth direction. This mechanism contributes significantly to the formation of structural defects and largely explains the scattering of compressive strength values reported in the literature.

Ice shaping properties, similar to that of antifreeze proteins, of a zirconium acetate complex.

The control of the growth morphologies of ice crystals is a critical issue in fields as diverse as biomineralization, medicine, biology, civil or food engineering. Such control can be achieved through the ice-shaping properties of specific compounds. The development of synthetic ice-shaping compounds is inspired by the natural occurrence of such properties exhibited by antifreeze proteins. We reveal how a particular zirconium acetate complex is exhibiting ice-shaping properties very similar to that of antifreeze proteins, albeit being a radically different compound. We use these properties as a bioinspired approach to template unique faceted pores in cellular materials. These results suggest that ice-structuring properties are not exclusive to long organic molecules and should broaden the field of investigations and applications of such substances.

Time-lapse, three-dimensional in situ imaging of ice crystal growth in a colloidal silica suspension

Abstract The freezing of colloidal suspensions is encountered in many natural and engineering processes such as the freezing of soils, food engineering and cryobiology. It can also be used as a bio-inspired, versatile and environmentally friendly processing route for porous materials and composites. Yet, it is still a puzzling phenomenon with many unexplained features, owing to the complexity of the system and the space and time scales at which the process should be investigated. This study demonstrates the interest in fast X-ray computed tomography for providing time-lapse, three-dimensional, in situ imaging of ice crystal growth in a colloidal silica suspension. The experimental measurements show that the local increase in colloid concentration does not affect the growth kinetics of the crystals until the colloidal particles become closely packed. For particles much smaller than ice crystals, the concentrated colloidal suspension is equivalent to a simple liquid phase with higher viscosity and a freezing point determined by the concentration of colloidal particles.

Ice-Templating of Alumina Suspensions: Effect of Supercooling and Crystal Growth During the Initial Freezing Regime

We investigate the ice-templating behaviour of alumina suspensions by in-situ X-rays radiography and tomography. We focus here on the formation and structure of the transitional zone, which takes place during the initials instants of freezing. For many applications, this part is undesirable since the resulting porosity is heterogeneous, in size, morphology and orientation. We investigate the influence of the composition of alumina suspensions on the formation of the transitional zone. Alumina particles are dispersed by three different dispersants, in various quantities, or by chlorhydric acid. We show that the height and the morphology of the transitional zone are determined by the growth of large dendritic ice-crystals growing in a supercooled state, and growing much faster than the cellular freezing front. When the freezing temperature decreases, the degree of supercooling increases. This results in a faster freezing front velocity and increases the dimensions of the transitional zone. It is therefore possible to adjust the dimensions of the transitional zone by changing the composition of alumina suspensions. The counter-ion Na+ has the most dramatic influence on the freezing temperature of suspensions, yielding a predominance of cellular ice crystals instead of the usual lamellar crystals.

Fast in-situ X-ray micro tomography characterisation of microstructural evolution and strain-induced damage in alloys at various temperatures

Abstract Fast in-situ X-ray tomography has been used at ESRF Grenoble to characterise the microstructural evolution and the formation of strain-induced damage in various materials during different thermomechanical treatments. Materials are both light alloys (Al and Mg based alloys) and steels. The thermomechanical treatments include tensile deformation both in the solid state at room and high temperatures and in the semi-solid state together with thermal treatments above the solidus temperature. Melting and solidification of Al-alloys are also considered in this paper.

Iron ore sinter porosity characterisation with application of 3D X-ray tomography

Abstract X-ray tomography has been applied for the estimation of iron ore sinter porosity. Procedures to distinguish open and closed pores and to estimate the volume and the equivalent diameter of each pore were developed, providing the possibility to calculate the amount of porosity considering open and closed pores separately. The effect of the sinter mixture composition on the porosity parameters was investigated, and a comparison with a mercury intrusion measurement is also presented. Reducibility tests were performed for the samples, the porosity of which had been previously identified by tomography. The fact that samples with a premeasured porosity could be analysed with other characterisation methods opens new possibilities to understand the effect of the porosity on the properties of the sinter.

Characterization of porosity, structure, and mechanical properties of electrospun SiOC fiber mats

In this study, silicon oxycarbide (SiOC) ceramic fiber mats obtained by electrospinning of two different preceramic polymers (MK and H44 resin) were evaluated in terms of their total porosity and other structural characteristics using three different characterization tools. The tensile strength and the permeability of the fiber mats were also investigated. The results indicated that the porosity could be easily calculated based on the apparent density and true density of the fiber mats obtained by gas pycnometry. A modified mercury intrusion porosimetry, in which the bulk volume of the fiber mats was calculated based on its independently measured bulk density, also allowed for an accurate evaluation of the porosity and the pore size distribution of the fiber mats. X-ray computed tomography was able to provide various structural characteristics of the 3D morphology of the fiber mats, but it was less effective in the determination of the total porosity due to resolution limits. All results showed that the MK-derived SiOC fiber mats possessed a higher porosity than the H44-derived SiOC fiber mats, resulting in a higher gas permeability. The ceramic fiber mats possessed a suitable permeability for filtration applications in harsh environments.

Multiscale morphological characterization of process induced heterogeneities in blended positive electrodes for lithium-ion batteries

The 3D morphology of LiNi1/3Mn1/3Co1/3O2 (NMC), LiFePO4 (LFP), and blended NMC/LFP electrodes envisioned for electric vehicles Li–ion batteries is characterized by both synchrotron X-ray tomography and FIB/SEM tomography. The size distribution of the active materials, the carbon phase and the pores, the specific surface area of the different solid phases, the concentration variations of the various phases through the total electrode thickness (X-ray tomography) or in smaller volumes (FIB/SEM tomography) are quantified. Results are assessed in relationship with the electrode composition and with their typical slurry rheological properties. Several heterogeneities are evidenced as the fingerprint of phenomena associated with the different processing steps of the electrodes.

On the Potential of Bulk Metallic Glasses for Dental Implantology: Case Study on Ti40Zr10Cu36Pd14

Ti40Zr10Cu36Pd14 Bulk Metallic Glass (BMG) appears very attractive for future biomedical applications thanks to its high glass forming ability, the absence of toxic elements such as Ni, Al or Be and its good mechanical properties. For the first time, a complete and exhaustive characterization of a unique batch of this glassy alloy was performed, together with ISO standard mechanical tests on machined implant-abutment assemblies. The results were compared to the benchmark Ti-6Al-4V ELI (Extra-Low-Interstitial) to assess its potential in dental implantology. The thermal stability, corrosion and sterilization resistance, cytocompatibility and mechanical properties were measured on samples with a simple geometry, but also on implant-abutment assemblies’ prototypes. Results show that the glassy alloy exhibits a quite high thermal stability, with a temperature range of 38 °C between the glass transition and crystallization, a compressive strength of 2 GPa, a certain plastic deformation (0.7%), a hardness of 5.5 GPa and a toughness of 56 MPa.√m. Moreover, the alloy shows a relatively lower Young’s modulus (96 GPa) than the Ti-6Al-4V alloy (110–115 GPa), which is beneficial to limit bone stress shielding. The BMG shows a satisfactory cytocompatibility, a high resistance to sterilization and a good corrosion resistance (corrosion potential of −0.07 V/SCE and corrosion current density of 6.0 nA/cm2), which may ensure its use as a biomaterial. Tests on dental implants reveal a load to failure 1.5-times higher than that of Ti-6Al-4V and a comparable fatigue limit. Moreover, implants could be machined and sandblasted by methods usually conducted for titanium implants, without significant degradation of their amorphous nature. All these properties place this metallic glass among a promising class of materials for mechanically-challenging applications such as dental implants.

X Ray Tomography Study of Cellular Materials: Experiments and Modelling

This paper summarizes different results obtained by the authors applying X-ray tomography to the study of cellular materials (metals, ceramics and polymers). From the 3D images, three different kinds of analysis are carried out. The first is image processing to retrieve the morphological characteristics (density, size, tortuosity) of the studied materials. The second is the analysis of the deformation modes using in situ or ex situ mechanical tests (tension, compression, fatigue). The third is devoted to FE calculations in which models are produced to represent as exactly as possible the architecture of these materials as seen in tomography. These different points are successively presented and exemplified in the present paper.