LTCC active oxygen getter module for hermetic packaging applications

LTCC and thick-film technologies constitute excellent platforms for hermetic and controlled-atmosphere packaging, for applications in MEMS, space, micro/nanofabrication and biological fields. This work presents an active oxygen getter module, based on an integrated LTCC micro-hotplate coated with an oxygen-reactive metal in thick-film form. Gettering is activated by heating the platform, and getter consumption is monitored by the increase of its electrical resistance. Different reactive metals, ceramics or polymers may be used in order to getter / control other gases such as nitrogen, vapour, etc. This technique is a simple way to sense / react with oxygen in integrated packages, which does not require a vacuum environment and heating up the whole package. Also, the sensing / getter material can be tailored for reactivity with other gases, a specific oxygen pressure (buffer), etc. Also, gettering and reactivity may be controlled by setting the temperature of operation. terial

A coupled experimental, numerical and statistical homogenization approach towards an accurate feedback relationship between porosity and diffusive properties of model cementitious materials in the field of reactive transport modelling

Au vu de leurs différentes propriétés, les matériaux cimentaires sont largement considérés dans les différents projets de gestion de déchets radioactifs. Leurs propriétés mécaniques, leurs faibles coefficients de transport ainsi que leur capacité à fixer les principaux radionucléides sont les principaux avantages qui en font un des meilleurs choix pour la conception des barrières ouvragées.Pour les études de sûreté, leur durabilité est capitale. Au cours de la vie d’un tel dépôt,via l’infiltration d’eau ou les interfaces chimiquement agressives avec les argiles, les différents matériaux vont subir des perturbations physicochimiques qui vont altérer leurs structures et potentiellement compromettre leurs fonctions de sûreté. L’étendue de ces perturbations, fondamentale pour l’étude de sûreté, est contrôlée par les propriétés de transport de ces matériaux.Pour modéliser proprement ces phénomènes, il faut pouvoir coupler les évolutions géochimiques des matériaux tout en évaluant le transport à travers ceux-ci. C’est le but de différents codes de transport réactif, qui utilisent une loi de rétroaction pour modifier les propriétés de transport lors d’une modification de microstructure. Le problème est qu’il n’existe pas de loi de rétroaction adaptée aux matériaux cimentaires, qui possèdent une structure poreuse complexe du nanomètre jusqu’à plusieurs micromètres. En général, des lois empiriques de type Archie sont utilisées. Toutefois, même l’utilisation de lois plus sophistiquées ne permet pas de reproduire sensiblement les évolutions liées à la structure porale. Cette loi de rétroaction est probablement la principale raison pour laquelle les résultats de simulation ont du mal à reproduire lesrésultats expérimentaux. Le but de cette thèse est de proposer une meilleure loi de rétroaction et de l’intégrer dans un code de transport réactif.Pour ce faire, trois approches complémentaires ont été mises en oeuvre. La première, expérimentale,consiste en la réalisation des matériaux cimentaires les plus simples possibles :des phases C-S-H pures et une pâte de ciment modèle. Ces matériaux sont ensuite caractérisés finement :leurs propriétés de transport sont évaluées et une description fine de leur microstructure est obtenue. L’approche expérimentale consiste ensuite en la dégradation (par lixiviation et carbonatation sous eau) de la pâte de ciment modèle, afin de comprendre l’impact de ces dégradations sur la microstructure et les propriétés de transport.La deuxième partie, numérique, consiste en l’obtention d’un volume élémentaire représentatif de la pâte de ciment modèle, basée sur les caractérisations expérimentales. Différentes analyses de sensibilité et de propriétés de transport permettent de comprendre les liens entre les différents paramètres et les propriétés effectives. Ensuite, l’approche numérique modélise les dégradations.Ces approches numériques démontrent pourquoi les approches empiriques fonctionnent dans certains cas, et pas dans d’autres.La dernière partie dédiée à la modélisation mathématique développe une approche d’homogénéisation statistique de la diffusion, basée sur une description du phénomène à l’échelle du pore. Cette étude met en évidence des paramètres clés qui contrôlent les propriétés effectives de diffusion.C’est ce pour quoi il est démontré que cette approche, en plus d’être très adaptée aux matériaux cimentaires, est applicable à un large spectre de microstructures. Les paramètres mis en évidences ont intrinsèquement sensibles aux propriétés de percolation et de connectivités de la structure poreuse, qui sont centrales pour la compréhension des propriétés effectives de transport ainsi que l’impact des dégradations. La finalité de la thèse consiste en le couplage de ces différentes approches et en l’incorporation de celles-ci dans un code de transport réactif. Les résultats obtenus en utilisant différentes lois de rétroaction sont comparés entre eux. L’utilisation de lois de rétroaction basée sur l’étude tri-dimensionnelle de la microstructure améliore la comparaison aux résultats expérimentaux.Doctorat en Sciences de l'ingénieur et technologieinfo:eu-repo/semantics/nonPublishe

Long-Term Evolution of Uranium Mobility within Sulfated Mill Tailings in Arid Regions: A Reactive Transport Study

Management of mill tailings is an important part of mining operations that aims at preventing environmental dispersion of contaminants of concern. To this end, geochemical models and reactive transport modeling provide a quantitative assessment of the mobility of the main contaminants. In arid regions with limited rainfall and intense evaporation, solutes transport may significantly differ from the usual gravity-driven vertical flow. In the uranium tailings of the Cominak mine (Niger), these evaporative processes resulted in the crystallization of gypsum, and to a lesser extent jarosite, and in the formation of surface levels of sulfated gypcrete, locally enriched in uranium. We present a fully coupled reactive transport modeling approach using HYTEC, encompassing evaporation, to quantitatively reproduce the complex sequence of observed coupled hydrogeochemical processes. The sulfated gypcrete formation, porosity evolution and solid uranium content were successfully reproduced at the surface and paleosurfaces of the tailing deposit. Simulations confirm that high solubility uranyl-sulfate phase may form at the atmospheric boundary where evaporation takes place, which would then be transformed into uranyl-phosphate phases after being watered or buried under fresh tailings. As these phases usually exhibit a lower solubility, this transition is beneficial for mine operators and tailings management

On the scales of dynamic topography in whole-mantle convection models

Mantle convection shapes Earth\u27s surface by generating dynamic topography. Observational constraints and regional convection models suggest that surface topography could be sensitive to mantle flow for wavelengths as short as 1,000 and 250 km, respectively. At these spatial scales, surface processes including sedimentation and relative sea‐level change occur on million‐year timescales. However, time‐dependent global mantle flow models do not predict small‐scale dynamic topography yet. Here we present 2‐D spherical annulus numerical models of mantle convection with large radial and lateral viscosity contrasts. We first identify the range of Rayleigh number, internal heat production rate and yield stress for which models generate plate‐like behavior, surface heat flow, surface velocities, and topography distribution comparable to Earth\u27s. These models produce both whole‐mantle convection and small‐scale convection in the upper mantle, which results in small‐scale (km) to large‐scale (\u3e104 km) dynamic topography, with a spectral power for intermediate scales (500 to 104 km) comparable to estimates of present‐day residual topography. Timescales of convection and the associated dynamic topography vary from five to several hundreds of millions of years. For a Rayleigh number of 107, we investigate how lithosphere yield stress variations (10-50 MPa) and the presence of deep thermochemical heterogeneities favor small‐scale (200-500 km) and intermediate‐scale (500-104 km) dynamic topography by controlling the formation of small‐scale convection and the number and distribution of subduction zones, respectively. The interplay between mantle convection and lithosphere dynamics generates a complex spatial and temporal pattern of dynamic topography consistent with constraints for Earth

On the scales of dynamic topography in whole-mantle convection models - preprint version

Mantle convection shapes Earth's surface by generating dynamic topography. Observational constraints and regional convection models suggest that surface topography could be sensitive to mantle flow for wavelengths as short as 1,000 km and 250 km, respectively. At these spatial scales, surface processes including sedimentation and relative sea-level change occur on million year timescales. However, time dependent global mantle flow models do not predict small-scale dynamic topography yet. Here, we present 2D-spherical annulus numerical models of mantle convection with large radial and lateral viscosity contrasts. We first identify the range of Rayleigh number, internal heat production rate and yield stress for which models generate plate-like behaviour, surface heat flow, surface velocities and topography distribution comparable to Earth's. These models produce both whole mantle convection and small-scale convection in the upper mantle, which results in small- (< 500 km) to large-scale (> 10^4 km) dynamic topography, with a spectral power for intermediate scales (500 to 10^4 km) comparable to estimates of present-day residual topography. Timescales of convection and the associated dynamic topography vary from five to several hundreds of millions of years. For a Rayleigh number of 10^7, we investigate how lithosphere yield stress variations (10-50 MPa) and the presence of deep thermochemical heterogeneities favour small-scale (200-500 km) and intermediate scale (500-10^4 km) dynamic topography by controlling the formation of small scale convection and the number and distribution of subduction zones, respectively. The interplay between mantle convection and lithosphere dynamics generates a complex spatial and temporal pattern of dynamic topography consistent with constraints for Earth

A compositional global implicit approach for modeling coupled multicomponent reactive transport

International audienc

Reactive Transport in Evolving Porous Media

International audienc

Recoupling flow and chemistry in variably saturated reactive transport modelling - An algorithm to accurately couple the feedback of chemistry on water consumption, variable porosity and flow

International audienceMost reactive transport codes and algorithms decouple the flow from the reactive transport calculations. In some cases, geochemical reactions lead to significant modifications of porosity or water-content, which can have an impact on the flow. The flow problem is based on the continuity equation and is described in terms of pressure. However, most reactive transport codes do not model the pressure-evolution through mineral reactions. The aim of this study is to recouple the reactive transport and the flow, by providing an accurate description of the evolution of both the porosity and the water in the reactive system. We discuss a formulation of the geochemical solver, based on a mole-conservation, which allows an accurate computation of the volume and masses of all phases. This allows for a water and pore volume computation at the scale of the REV which can impact the fluid-pressure, hence the flow. Additionally, solving the geochemical equilibrium in terms of moles instead of concentrations is more accurate for problems involving important mineral reactions. Finally, this method is suited to saturated, unsaturated and two-phase flow. This method is easy to implement and can be used in different reactive transport simulators, regardless of their numerical approaches. We also test the numerical efficiency of this approach and apply it to fully-coupled problems involving variable porosity, variable saturation, water production/consumption

Mine Waste Rock: Insights for Sustainable Hydrogeochemical Management

International audienceMismanagement of mine waste rock can mobilize acidity, metal (loid)s, and other contaminants, and thereby negatively affect downstream environments. Hence, strategic long-term planning is required to prevent and mitigate deleterious environmental impacts. Technical frameworks to support waste-rock management have existed for decades and typically combine static and kinetic testing, field-scale experiments, and sometimes reactive-transport models. Yet, the design and implementation of robust long-term solutions remains challenging to date, due to site-specificity in the generated waste rock and local weathering conditions, physicochemical heterogeneity in large-scale systems, and the intricate coupling between chemical kinetics and mass- and heat-transfer processes. This work reviews recent advances in our understanding of the hydrogeochemical behavior of mine waste rock, including improved laboratory testing procedures, innovative analytical techniques, multi-scale field investigations, and reactive-transport modeling. Remaining knowledge-gaps pertaining to the processes involved in mine waste weathering and their parameterization are identified. Practical and sustainable waste-rock management decisions can to a large extent be informed by evidence-based simplification of complex waste-rock systems and through targeted quantification of a limited number of physicochemical parameters. Future research on the key (bio)geochemical processes and transport dynamics in waste-rock piles is essential to further optimize management and minimize potential negative environmental impacts

On coupling variable porosity and water activity with two-phase flow in reactive transport modelling

International audienc