Probing the mystery of Liesegang band formation: revealing the origin of self-organized dual-frequency micro and nanoparticle arrays

Periodic precipitation processes in gels can result in impressive micro- and nanostructured patterns known as periodic precipitation (or Liesegang bands). Under certain conditions, the silver nitrate–chromium(VI) system exhibits the coexistence of two kinds of Liesegang bands with different frequencies. We now present that the two kinds of bands form independently on different time scales and the pH-dependent chromate(VI)–dichromate(VI) equilibrium controls the formation of the precipitates. We determined the spatial distribution and constitution of the particles in the bands using focused ion beam-scanning electron microscopy (FIB-SEM) and scanning transmission X-ray spectromicroscopy (STXM) measurements. This provided the necessary empirical input data to formulate a model for the pattern formation; a model that quantitatively reproduces the experimental observations. Understanding the pattern-forming process at the molecular level enables us to tailor the size and the shape of the bands, which, in turn, can lead to new functional architectures for a range of applications

High-spectral-resolution Fabry-Perot interferometers overcome fundamental limitations of present volcanic gas remote sensing techniques

Remote sensing (RS) of volcanic gases has become a central tool for studying volcanic activity. For instance, ultraviolet (UV) skylight spectroscopy with grating spectrographs (GS) enables SO2 (and, under favourable conditions, BrO) quantification in volcanic plumes from autonomous platforms at safe distances. These measurements can serve volcanic monitoring and they cover all stages of volcanic activity in long measurement time series, which substantially contributes to the refinement of theories on volcanic degassing. Infrared (IR) remote sensing techniques are able to measure further volcanic gases (e.g., HF, HCl, CO2, CO). However, the employed Fourier transform spectrometers (FTSs) are intrinsically intricate and, due to limited resolving power or light throughput, mostly rely on either lamps, direct sun, or hot lava as light source, usually limiting measurements to individual field campaigns. We show that many limitations of grating spectrographs and Fourier transform spectrometer measurements can be overcome by Fabry-Perot interferometer (FPI) based spectrograph implementations. Compared to grating spectrographs and Fourier transform spectrometers, Fabry-Perot interferometer spectrographs reach a 1-3 orders of magnitude higher spectral resolution and superior light throughput with compact and stable set-ups. This leads to 1) enhanced sensitivity and selectivity of the spectral trace gas detection, 2) enables the measurement of so far undetected volcanic plume constituents [e.g., hydroxyl (OH) or sulfanyl (SH)], and 3) extends the range of gases that can be measured continuously using the sky as light source. Here, we present measurements with a shoe-box-size Fabry-Perot interferometer spectrograph (resolving power of ca. 150000), performed in the crater of Nyiragongo volcano. By analysing the light of a ultraviolet light emitting diode that is sent through the hot gas emission of an active lava flow, we reach an OH detection limit of about 20 ppb, which is orders of magnitude lower than the mixing ratios predicted by high-temperature chemical models. Furthermore, we introduce example calculations that demonstrate the feasibility of skylight-based remote sensing of HF and HCl in the short-wave infrared with Fabry-Perot interferometer spectrographs, which opens the path to continuous monitoring and data acquisition during all stages of volcanic activity. This is only one among many further potential applications of remote sensing of volcanic gases with high spectral resolution

Small-scale spatial variability of soil CO2 flux: Implication for monitoring strategy

In recent decades, soil CO2 flux measurements have been often used in both volcanic and seismically active areas to investigate the interconnections between temporal and spatial anomalies in degassing and telluric activities. In this study, we focus on a narrow degassing area of the Piton de la Fournaise volcano, that has been chosen for its proximity and link with the frequently active volcanic area. Our aim is to constrain the degassing in this narrow area and identify the potential processes involved in both spatial and temporal soil CO2 variations in order to provide an enhanced monitoring strategy for soil CO2 flux. We performed a geophysical survey (self-potential measurements: SP; electrical resistivity tomography: ERT) to provide a high-resolution description of the subsurface. We identified one main SP negative anomaly dividing the area in two zones. Based on these results, we set ten control points, from the site of the main SP negative anomaly up to 230 m away, where soil CO2 fluxes were weekly measured during one year of intense eruptive activity at Piton de la Fournaise. Our findings show that lateral and vertical soil heterogeneities and structures exert a strong control on the degassing pattern. We find that temporal soil CO2 flux series at control points close to the main SP negative anomaly better record variations linked to the volcanic activity. We also show that the synchronicity between the increase of soil CO2 flux and deep seismicity can be best explained by a pulsed process pushing out the CO2 already stored and fractionated in the system. Importantly, our findings show that low soil CO2 fluxes and low carbon isotopic signature are able to track variations of volcanic activity in the same way as high fluxes and high carbon isotopic signature do. This result gives important insights in terms of monitoring strategy of volcanic and seismotectonic areas in geodynamics contexts characterized by difficult environmental operational conditions as commonly met in tropical areaPublished13-264A. Oceanografia e climaJCR Journa

Self-assembled photonic mesostructures for water splitting photoanodes

Solar water splitting is a relevant principle for the production of green hydrogen fuel. A wealth of different designs has been envisioned to produce hydrogen using sunlight. Among those designs photoelectrochemical water splitting offers possible advantages regarding components integration and costs. This technology requires blending many materials requirements in a single component, such as solar light absorption, high electric conductivity, resistance to photocorrosion, and electrocatalytic properties. To achieve this goal it is necessary to build materials with emerging properties by discovering complex architectures at the micrometric and nanometric scales that can overcome bulk material limitations. Materials of interest for application as photoanode for photoelectrochemical water splitting are metal oxides because of their resistance to corrosion. In this thesis I focused on two of these oxides, namely hematite (alpha-Fe2O3) and monoclinic tungsten oxide (mWO3) since these materials have a relatively narrow band gap allowing absorption of a significant part of sun's irradiance. In a photoanode they were implemented as thin films on a conductive substrate. I proposed to investigate inexpensive and upscalable structuration processes for the formation of such photoanodes thin films with a controlled microstructure and studied the impact of such structures on the film photoelectrochemical performance. Self-assembly strategies are bottom-up approaches which allow to grow structures with original morphologies at a low cost compared to top-down techniques such as lithography. I was particularly interested in strategies that would grant a fine control of the feature sizes. Two different processing techniques were implemented, a polymer templated sol-gel route and electrohydrodynamic lithography. Both techniques allowed to obtain metal oxides structures at the meso- to nanoscale. The polymer templated sol-gel route was the most successful strategy. It allowed to produce microspheroids with a tungsten oxide core and a hematite nanometric overlayer with control on the structure dimensions. In addition to an in depth understanding of the different bottom-up approaches investigated, I proposed a complete description of the relationship between form and function in the film composed of tungsten oxide / hematite microspheroids. These films have significant photonic features linked to their original morphology and I discussed how their photoactivity is influenced by light trapping in these films

Architecture and dynamics of magma systems linked to basaltic volcanoes : the case of Piton de la Fournaise

Contraindre l'architecture et la dynamique des systèmes magmatiques est d’une importance capitale dans la compréhension des phénomènes volcaniques. Les principaux objectifs de cette thèse sont (1) de contraindre l'architecture du système magmatique du Piton de la Fournaise dans son ensemble, et (2) d'étudier l’évolution des magmas et les transferts associés en son sein. En couplant l'étude pétro-géochimique des magmas et du dégazage de CO2 à travers le sol, nous développons une approche intégrée, focalisée sur le flanc ouest de l'édifice. Cette zone témoigne d'une activité éruptive récente très peu étudiée, traçant potentiellement des processus magmatiques profonds. Nos résultats permettent de valider l'hypothèse du caractère décentré de la plomberie magmatique profonde du Piton de la Fournaise sous le flanc ouest de l'édifice. Nous démontrons que les magmas stockés dans la partie profonde de la plomberie magmatique préservent une certaine variabilité géochimique, principalement liée à de légères hétérogénéités de source et à des processus polybariques de cristallisation et d'assimilation. Nous montrons également que les flux de CO2 à travers le sol du flanc ouest de l'édifice enregistrent le dégazage précoce des magmas au sein du manteau lithosphérique. Nous soulignons ici que les variations temporelles des flux de CO2 à travers le sol peuvent être utilisées pour détecter les recharges du système magmatique central via des transferts magmatiques profonds.Nos résultats ouvrent des perspectives prometteuses quant à la surveillance des processus magmatiques profonds sous les édifices volcaniques, même en conditions tropicales.Constraining the architecture and dynamics of magma systems is fundamental in volcanology. The main objectives of this study are to (1) constrain the architecture of the whole plumbing system of Piton de la Fournaise, and (2) study magma evolution and transfers from the deepest roots of the plumbing system. Coupling magma petrogeochemistry and diffusive soil degassing, we develop an integrated approach, focused on the western flank of the volcano. This zone shows evidences of a recent eruptive activity, poorly documented, but potentially related to deep magma processes. Our results allow to confirm the offset of the deep part of the Piton de la Fournaise plumbing system beneath the western flank of the volcano. We demonstrate that magma stored in the deepest roots of the plumbing system display a geochemical variability, mainly related to minor mantle source heterogeneities and to polybaric crystallization and assimilation processes. We show that soil CO2 fluxes on the western flank of the volcano record early magma degassing in the lithospheric mantle. We highlight that temporal variations of soil CO2 flux may be used to detect magma replenishement of the central magmatic system by deep magma transfers, hardly detectable by the geophysical network.Our results opens exciting prospects to improve the monitoring of deep magma processes below volcanoes, even in tropical conditions

Architecture et dynamique des systèmes magmatiques associés aux volcans basaltiques : exemple du Piton de la Fournaise

Constraining the architecture and dynamics of magma systems is fundamental in volcanology. The main objectives of this study are to (1) constrain the architecture of the whole plumbing system of Piton de la Fournaise, and (2) study magma evolution and transfers from the deepest roots of the plumbing system. Coupling magma petrogeochemistry and diffusive soil degassing, we develop an integrated approach, focused on the western flank of the volcano. This zone shows evidences of a recent eruptive activity, poorly documented, but potentially related to deep magma processes. Our results allow to confirm the offset of the deep part of the Piton de la Fournaise plumbing system beneath the western flank of the volcano. We demonstrate that magma stored in the deepest roots of the plumbing system display a geochemical variability, mainly related to minor mantle source heterogeneities and to polybaric crystallization and assimilation processes. We show that soil CO2 fluxes on the western flank of the volcano record early magma degassing in the lithospheric mantle. We highlight that temporal variations of soil CO2 flux may be used to detect magma replenishement of the central magmatic system by deep magma transfers, hardly detectable by the geophysical network.Our results opens exciting prospects to improve the monitoring of deep magma processes below volcanoes, even in tropical conditions.Contraindre l'architecture et la dynamique des systèmes magmatiques est d’une importance capitale dans la compréhension des phénomènes volcaniques. Les principaux objectifs de cette thèse sont (1) de contraindre l'architecture du système magmatique du Piton de la Fournaise dans son ensemble, et (2) d'étudier l’évolution des magmas et les transferts associés en son sein. En couplant l'étude pétro-géochimique des magmas et du dégazage de CO2 à travers le sol, nous développons une approche intégrée, focalisée sur le flanc ouest de l'édifice. Cette zone témoigne d'une activité éruptive récente très peu étudiée, traçant potentiellement des processus magmatiques profonds. Nos résultats permettent de valider l'hypothèse du caractère décentré de la plomberie magmatique profonde du Piton de la Fournaise sous le flanc ouest de l'édifice. Nous démontrons que les magmas stockés dans la partie profonde de la plomberie magmatique préservent une certaine variabilité géochimique, principalement liée à de légères hétérogénéités de source et à des processus polybariques de cristallisation et d'assimilation. Nous montrons également que les flux de CO2 à travers le sol du flanc ouest de l'édifice enregistrent le dégazage précoce des magmas au sein du manteau lithosphérique. Nous soulignons ici que les variations temporelles des flux de CO2 à travers le sol peuvent être utilisées pour détecter les recharges du système magmatique central via des transferts magmatiques profonds.Nos résultats ouvrent des perspectives prometteuses quant à la surveillance des processus magmatiques profonds sous les édifices volcaniques, même en conditions tropicales

Optimisation de l'écoulement granulaire dans une machine de pesage et d'ensachage de matériau en vrac à alimentation gravitaire

RÉSUMÉ: L'entreprise, dont nous tairons le nom pour des raisons de propriété intellectuelle, travaille entre autres à la réalisation de systèmes de pesage et d'ensachage de grains en vrac. Le projet porte sur l'optimisation de l'écoulement de grains d'une de leurs machines en vue d'améliorer la vitesse et/ou la précision de l'ensemble du cycle de pesage et d'ensachage. L'étude se concentrera sur deux organes essentiels de la machine à savoir la chute de transition qui dirige la matière pesée vers la bouche d'ensachage ainsi que sur le module d'alimentation qui alimente la balance jusqu'au poids consigne. Le sujet traite donc de l'écoulement de matière granulaire en régime dense. La littérature nous permet d'identifier certains aspects de ce type d'écoulement. Cependant, leur comportement spécial et nos connaissances limitées vont nous orienter vers une optimisation basée sur l'expérimentation. Nous avons décidé d'utiliser un logiciel spécialisé en écoulement de matériaux granulaires: EDEM de la compagnie DEM Solutions pour modéliser notre système. Nous commencerons par une phase d'essais et de calibration du logiciel pour vérifier la pertinence de l'outil. Nous établirons une technique d'optimisation efficace des paramètres du logiciël qui varient selon le matériau employé puis nous testerons le logiciel pour vérifier ses capacités (mesure de débit, caractère erratique de l'écoulement, etc.). Une fois notre modèle de simulation prêt, nous l'appliquerons à l'optimisation de la chute de transition. Un jeu de courbes nous permettra d'analyser le comportement de la matière lors de la décharge et d'améliorer notre compréhension du phénomène. Nous poursuivrons l'analyse en comparant les résultats d'écoulement dans divers modèles et géométries. Malheureusement, aucune géométrie plus performante ne pourra être identifiée. L'optimisation portera ensuite sur le module d'alimentation et sur la précision de pesage. Lors d'un cycle de pesée, on peut assez bien contrôler l'apport de matière, mais l'imprécision apparaît au moment de la fermeture. En effet, il reste toujours une certaine quantité dans les airs et la précision est liée à la capacité de prévoir cette quantité. Nous chercherons alors à optimiser le module dans le but de donner un débit le plus constant possible à l'écoulement et donc à la fenneture . Cela se traduira par l'étude de différentes géométries et par la création de prototypes pour les solutions les plus prometteuses. Nous construirons un système à 2 portes, mais qui se révèlera finalement moins précis qu'escompté. Les résultats montreront toutefois une bonne amélioration de la précision. -- ABSTRACT: The company we are working for pro vides weighing and bagging solutions for granular materials. The project is to improve the bagging speed or/and the accuracy of the entire system. We are going to focus on two key components : the transition hopper which directs the grain from the scale to the bagging spout and the feeder which controls the granular flow to the scale. Dense granular flow is the main topic. We can find sorne aspects and properties of this type of flow in scientific literature. However because of their very particular behaviour and our limited knowledge on the subject, we are going to optimize the machine by studying experimental results. We acquired a software able to simulate granular flows simulations. Acquiring a new software means it needs to be calibrated. We also develop a method that gives us the material properties. Finally we study sorne of the software's abilities (flow measurement, erratic comportment of the grains, etc.). Once the software is checked and calibrated, we use it for transition hopper optimisation by comparing the flow of particles in the actual hopper to other types. Unfortunately we could not find a better hopper but we have improved the understanding of granular flow. Conclusions are finally presented and they show sorne tips for transition hoppers design. For the feeder, we focus on the weighing accuracy. During a weighing cycle, we can control the feeding flow of particles in the scale but when we close the door a small quantity of grain is still in the air. The accuracy is linked to the capacity of knowing this exact quantity. A method is developed in order to compare the models with the same unit and check the real improvement. We simulate different models of feeders and check their flows accuracy. The most hopeful models are realized and tested as prototypes. Finally the results show a good accuracy gain depending the speed or model chosen

The first observations of CO2 and CO2/SO2 degassing variations recorded at Mt. Etna during the 2018 eruptions followed by three strong earthquakes

International audienceMount Etna volcano is well-known for its frequent eruptions and high degassing rates from its summit craters and flanks. The geochemical monitoring network on Mt. Etna that measures soil CO2 flux and in-plume CO2/SO2 ratio recorded very important degassing variations from the flank and the summit craters during the second half of 2018. In this area several significant volcanic events occurred in October and December 2018 and in January 2019. Past observations have distinguished a tendency for wide variations in degassing rates, marked by a sharp increase preceding the onset of volcanic activity. However, this is the first time that three earthquakes of magnitude M>4 have been registered since the inception of the geochemical network in January 2001. Of particular interest is the CO2/SO2 ratio in plumes recorded by the monitoring station sited at the summit crater of Voragine showed very significant degassing variations, which were comparable with those recorded for the soil CO2 flux. This paper focuses on the combination of events occurring on Mt. Etna and their relationship with degassing rates. The most remarkable results can be summarized as follow: i) the networks recorded high variations of soil CO2 flux and CO2/SO2 ratio, which assisted in identifying distinctive phases of pressurization of Mt. Etna plumbing system and ii) all earthquakes occurred during phases of minimum gas rate, which in turn followed stages of pressurization involving different portions of the plumbing system. The 2018 period of high volcanic activity and the corresponding seismic episodes provided an invaluable case study for Mt. Etna, which allowed to combine seismic events and geochemical signal variations

Recommendations and Protocols for the Use of the Isotope RatioInfrared Spectrometer (Delta Ray) to Measure StableIsotopes from CO2: An Application to Volcanic Emissions atMount Etna and Stromboli (Sicily, Italy)

Co-auteur étrangerInternational audienceAmong major volatiles released from the Earth’s interior, CO2 is an important target for the international community. The interestis keenly motivated by the contribution of CO2 in the Earth’s carbon budget and its role on past, current, and future climatedynamics. In particular, the isotopic signature of CO2 is fundamental to characterize the source of this gas and its evolution upto the atmosphere. The recent development of new laser-based techniques has marked an important milestone for the scientificcommunity by favoring both high-frequency and in situ stable isotope measurements. Among them, the Delta Ray IRIS(Thermo Scientific Inc., Waltham, USA) is one of the most promising instruments thanks to its high precision, its limitedinterferences with other gaseous species (such as H2S and/or SO2), and its internal calibration procedure. These characteristicsand the relative easiness to transport the Delta Ray IRIS have encouraged its use on the field to analyze volcanic CO2 emissionsin recent years but often with distinct customized protocols of measurements. In this study, various tests in the laboratory andon the field have been performed to study the dependence of CO2 isotope measurements on analytical, instrumental, andenvironmental conditions. We emphasize the exceptional ability of the Delta Ray IRIS to perform isotope measurements for alarge range of CO2 concentration (200 ppm–100%) thanks to a dilution system and to get a reliable estimation of the real CO2content from the diluted one. These tests lead to point out major recommendations on the use of Delta Ray IRIS and allow thedevelopment of adapted protocols to analyze CO2 emissions like in volcanic environments

Combining parallel pattern generation of electrohydrodynamic lithography with serial addressing

Electrohydrodynamic lithography (EHDL) is a parallel patterning process which typically makes use of topographically structured electrodes to guide pattern formation along areas of higher electrical field strength. The main driving force for pattern formation is an electrostatic pressure acting on a thin film polymer surface caused by a voltage applied between a top and bottom electrode. We here demonstrate that the principle can be applied using an addressable electrode composed of interdigitated fingers. Depending on the applied voltages, line patterns with different periodicities were fabricated. Our proof-of-concept experiments pave the way for a parallel pattern replication process where a serially addressed master is used. We complement the experiments by modelling the potentials across the electrodes and electrostatic forces acting on the polymer surface using different addressing schemes. Numerical simulations of the experimental setup pointed to some critical issues we experienced during the design of the experiments