Up-scaling a Sol-Gel Process for the Production of a Multi-Component Xerogel Powder

A sol-gel process for the synthesis of a multi-component oxide material from the system SiO2-ZrO2-Al2O3underwent optimization and up-scaling. Initially, on a laboratory scale, components including precursors, catalysts, and additives were methodically evaluated to ensure a safe and efficient transition to larger volumes. Subsequently, the equipment for the whole setup of the sol-gel process was strategically selected. Leveraging insights from these optimizations, the process was successfully scaled-up to pilot-scale operation, conducting hydrolysis, condensation reactions, gelation, aging, and drying within a single, integrated conical dryer system for an 80 L batch. A visual test and FTIR spectroscopy were applied for process control and monitoring

Impact of composite structure and morphology on electronic and ionic conductivity of carbon contained LiCoO2 cathode

Cathodes in lithium ion batteries consist of an ionic conductor, an electronic conductor and a binder in order to make a composite that is both electronically and ionically conductive. The carbon coating on the cathode material plays a critical role for the electrochemical properties of lithium ion batteries due to the increased electronic conductivity. We explain the relationship between the electrochemical properties and the characteristics of composites prepared using the ball-milling process in this report. We investigated two types of carbonaceous materials (graphite and carbon black) in LiCoO₂ electrodes. These selected carbon materials have different characteristics and structure upon ball-milling with LiCoO₂. The composite prepared by ball-milling for 5 min leads to better mixing of carbon and LiCoO₂, an intimate contact of carbon on LiCoO₂, a higher lithium ion diffusion (DLi) than non ball-milled and longer ball-milled composites. On the other hand, a longer time of ball-milling (30 and 60 min) decreases the electronic and ionic conductivity due to an increase of disordered structure of carbon and a thick and dense carbon coating layer on LiCoO₂ particles, preventing the diffusion of lithium ions, respectively

Kinetics of the chrysotile and brucite dehydroxylation reaction: a combined non-isothermal/isothermal thermogravimetric analysis and high-temperature X-ray powder diffraction study

The dehydroxylation reactions of chrysotile Mg3Si2O5(OH)4 and brucite Mg(OH)2 were studied under inert nitrogen atmosphere using isothermal and non-isothermal approaches. The brucite decomposition was additionally studied under CO2 in order to check the influence of a competing dehydroxylation/carbonation/decarbonisation reaction on the reaction kinetics. Isothermal experiments were conducted using in situ high-temperature X-ray powder diffraction, whereas non-isothermal experiments were performed by thermogravimetric analyses. All data were treated by model-free, isoconversional approaches (‘time to a given fraction' and Friedman method) to avoid the influence of kinetic misinterpretation caused by model-fitting techniques. All examined reactions are characterised by a dynamic, non-constant reaction-progress-resolved (‘α'-resolved) course of the apparent activation energy E a and indicate, therefore, multi-step reaction scenarios in case of the three studied reactions. The dehydroxylation kinetics of chrysotile can be subdivided into three different stages characterised by a steadily increasing E a (α≤15%, 240-300kJ/mol), before coming down and forming a plateau (15%≤α≤60%, 300-260kJ/mol). The reaction ends with an increasing E a (α≥60%, 260-290kJ/mol). The dehydroxylation of brucite under nitrogen shows a less dynamic, but generally decreasing trend in E a versus α (160-110kJ/mol). In contrast to that, the decomposition of brucite under CO2 delivers a dynamic course with a much higher apparent E a characterised by an initial stage of around 290kJ/mol. Afterwards, the apparent E a comes down to around 250kJ/mol at α~65% before rising up to around 400kJ/mol. The delivered kinetic data have been investigated by the z(α) master plot and generalised time master plot methods in order to discriminate the reaction mechanism. Resulting data verify the multi-step reaction scenarios (reactions governed by more than one rate-determining step) already visible in E a versus α plots

Thermal characterization of ancient hearths from the cave of Les Fraux (Dordogne, France) by thermoluminescence and magnetic susceptibility measurements

International audienceNumerous sorts of evidence of fires were observed in the cave of Les Fraux (Dordogne, France) and in particular the effects of fire on sediment were studied for a better understanding of their use centuries ago. Our present objective is the evaluation of the firing intensity by determining the past temperature (paleotemperature) attained by the topmost sediment of the archaeological fires. The principle of paleotemperature determination is based on the thermoluminescence (TL) properties of quartz and the magnetic susceptibility of the sediment. By comparing the TL signal of anciently heated quartz to the TL signal of thermal references made in the laboratory, we were able to obtain a maximal equivalent temperature attained for each sample extracted from ancient fires. The magnetic susceptibility (previously measured on the hearth surface) could thus be estimated as a function of temperature. The main result of this study is the temperature mapping of the hearth which can be used as meaningful information about the ancient firing intensity

Caractérisation thermique de foyers de l'âge du Bronze de la grotte des Fraux (Dordogne)

International audienceThe Les Fraux cave (Dordogne, France) was occupied during the Bronze Age. It contained numerous hearth features. The questions related to the function of the cave and more particularly of the hearth features involved a multidisciplinary study of these remains. The aim of this paper is to present the methods applied for the study of the hearths. The analysis combined thermoluminescence (TL) of the quartz grains and magnetic susceptibility principally registered by the iron oxides contained in the sediments (whether heated or not). For each sample, the TL permits to obtain the corresponding temperature (palaeotemperature) by comparison between the TL curves of the samples and those of the thermal references. The relationship established between the palaeotemperature and the magnetic susceptibility allows converting magnetic susceptibility to palaeotemperatures reached by the sediment on a larger surface. This permits to characterize the intensity of heat attained in these hearths and to contribute to the determination of the function of this site through the comparison with experimental firesLa grotte des Fraux (Dordogne, France), occupée à l'âge du Bronze, présente de nombreuses structures de combustion. Les questions relatives à la fonction du site et plus particulièrement des foyers, ont entrainé la mise en place d'une étude pluridisciplinaire de ces structures. L'objet de cet article est de présenter la méthodologie mise en oeuvre pour l'étude de ces foyers. Elle s'appuie sur un couplage entre la thermoluminescence (TL) des grains de quartz et la susceptibilité magnétique principalement portée par les oxydes de fer contenus dans les sédiments (chauffés ou non). Pour chaque prélèvement, la TL permet d'obtenir une température équivalente (paléotempérature) par comparaison entre les courbes TL correspondantes et celles de références thermiques. La relation établie entre la paléotempérature et la susceptibilité magnétique permet de traduire la carte de susceptibilité magnétique en paléotempératures atteintes par le sédiment sur une surface étendue. L'objectif est de caractériser l'intensité de chauffe de ces foyers et, par une comparaison avec des feux expérimentaux, de contribuer à préciser la fonction de ce site

Melt-spun nanocomposite fibers reinforced with aligned tunicate nanocrystals

The fabrication of nanocomposite films and fibers based on cellulose nanocrystals (P-tCNCs) and a thermoplastic polyurethane (PU) elastomer is reported. High-aspect-ratio P-tCNCs were isolated from tunicates using phosphoric acid hydrolysis, which is a process that affords nanocrystals displaying high thermal stability. Nanocomposites were produced by solvent casting (films) or melt-mixing in a twin-screw extruder and subsequent melt-spinning (fibers). The processing protocols were found to affect the orientation of both PU hard segments and the P-tCNCs within the PU matrix and therefore the mechanical properties. While the films were isotropic, both the polymer matrix and the P-tCNCs proved to be aligned along the fiber direction in the fibers, as shown using SAXS/WAXS, angle-dependent Raman spectroscopy, and birefringence analysis. Tensile tests reveal that fibers and films, at similar P-tCNC contents, display Young’s moduli and strain-at-break that are within the same order of magnitude, but the stress-at-break was found to be ten-times higher for fibers, conferring them a superior toughness over films

Materials science at Swiss universities of applied sciences

Copyright ©Swiss Chemical Society: CHIMIA, Volume 73, Numbers 7-8, August 2019, pp. 645-655(11)In the Swiss Universities of Applied Sciences, several research institutes are involved in Materials Science, with different approaches and applications fields. A few examples of recent projects from different groups of the University of Applied Sciences and Arts Western Switzerland (HES-SO), the Zurich University of Applied Sciences (ZHAW) and the University of Applied Sciences and Arts Northwestern Switzerland (FHNW) are given

Simulation of an experimental fire in an underground limestone quarry for the study of Paleolithic fires

International audienceNumerous fire marks occur on the walls of the Chauvet-Pont d’Arc cave. Dating indicated that some of the fires were contemporary to the Aurignacian. Violent thermal shocks were observed in surprisingly narrow areas of the cave. This raises numerous archaeological questions about the function of the fires; the answers depend on the location of the hearths, and the intensity of the fires. Numerical simulation was used here to provide information about the behaviour of fires in such confined spaces. An underground non-archaeological site, in a limestone quarry, was equipped to monitor fires in an environment similar to that of the Megaceros gallery of the Chauvet-Pont d’Arc cave. The fire and the movement of heat and smoke in the quarry were simulated by the open source code “Fire Dynamics Simulator (FDS)”. Results were validated on wall temperatures recorded behind and above the fire. The thermo-mechanical impact of the fire on the rock was simulated with CAST3M software, providing the most probable zones for limestone spalling due to thermal gradients. The validated approach will, in a forthcoming study, be applied to the Chauvet-Pont d’Arc cave, in which coupled simulations in the air and in the rock should indicate the location of the hearths and the intensity of the fires that generated the marks