Search results for "Oxydes"
showing 8 items of 8 documents
Oxidative stress markers at birth: Analyses of a neonatal population
2015
In order to further understand neonatal stress and, thus, control it efficaciously, there is a need for more information on the manifestations of stress at the molecular level in the newborn, with particular regard to oxidants, and anti-oxidant and anti-stress mechanisms, including mitochondrial heat shock protein-chaperones such as Hsp60. We investigated patterns of anti-oxidants, biomarkers of oxidative stress, and Hsp60 levels in sera from newborns and found significant associations between glutathione (GSH) levels and gestational age, delivery modality, and lipid hydroperoxydes (LOOH) level. LOOH levels and spontaneous (vaginal) delivery were independently associated with increased GSH …
Study of the different polymorphs of alumina and transitional phases appearing in the first oxidation stage of aluminium : simulation at the atomic s…
2014
The goal of this work is to develop a new SMTB-Q potential in order to study the early stages of the oxidation of aluminium by molecular dynamics (MD).Our potential is able to model different alumina polymorphs as well as transitions from the amorphous state to a crystalline phase. Our approach couples a covalent term with the charge. It uses Rapp_ and Goddard scheme for the electrostatic part and the model of alternating network developed by C. Noguera for the covalent part.The SMTB-Q potential was validated with a Monte Carlo approach. This study shows that the potential SMTB-Q gives satisfactory results for the Al-O bonding in different atomic configurations. The bonding results from the…
Les matériaux pour capteurs chimiques
2002
National audience; A chemical sensor is composed of one part supplying chemical reco gnition coupled to one transducingsystem. At the recognition origin, interaction with the target chemical species is oftwo types, either electronicexchange, or ionic exchange. Two large classes of materials that can supply recognition proceed: metals andsemiconductors giving rise to electronic exchange and ionic conducting materials giving rise to ionic exchan-ge. This paper is structured in tw o large parts, emphasizing on materi als inducing specific interactions:semiconductor materials (metallic oxides and molecular semiconductors) and ionic conductor materials.In each part will be presented nature of ma…
Influences of atomization process and precursor material on the compaction mechanisms and metallurgical properties of parts developed by HIP
2022
Hot Isostatic pressing process is based on the densification of metals powders to near net shape parts with higher mechanicals properties than forged chemical equivalent. The precursor material can influence the parts properties. Thus the aims of this these is to understand the influence of the powder properties on the HIP parts. The particles characterization and the elements and compound monitoring during the HIP cycle allowed to understand the different oxidations phenomenons and their impact on the mechanical properties of parts. The comparison of differents powders batches with identical particles size repartition or identical chemical composition showed that the chemical composition a…
Structure et croissance de nanophases supportées d'oxyde de tungstène
2010
Tungsten trioxide nanorods can be elaborated on muscovite mica substrate through simple vapor deposition method. Growth of rods seems to follow a Stranski-Krastanov model. Their crystallography was investigated by TEM and reveals the presence of hexagonal phase. Such a metastable structure occurs from an interfacial hexagonal tungsten bronze which grows epitaxially on the substrate. This bronze phase contains potassium atoms coming from mica. Concerning the thickest rods, a monoclinic phase grows on the top of the hexagonal one. The hexagonal structure is thermally very stable: after annealing at 600°C, this phase is still detected whereas the rod morphology is destroyed. This point seems t…
Development of the microwave transduction applied to ammonia detection : from nanomaterials to broadband sensor, understanding of the mechanisms and …
2017
The main objective of this thesis is to propose an analysis of the microwave transduction specificities in the framework of ammonia sensing applications. The two main features of this transduction are its broadband characterization (1 to 8 GHz) as well as its sensitive materials (dielectrics). This transduction method is based on the interaction between a polluting gas and a sensitive material deposited on the surface of a microwave-specific propagating structure. The response of the sensor is not directly induced by the dielectric properties of the gaseous target molecule, but rather by those of the target species adsorbed on the surface of the sensitive material. This adsorption causes a …
Ab initio study of tungsten trioxide WO3 in volume and surface area
2012
The structure and stability of different crystallographic phases of tungstentrioxide and the effect of potassium doping have been studied using ab initiocalcuations, both in the bulk and at the surface. The study was motivatedby experimental works on the growth of WO3 nanorods on a mica substrate.The nanorods adopt a hexagonal phase, which is metastable in bulk WO3.The first part of the manuscript reports the study of bulk WO3. For thehexagonal and monoclinique phase, the atomic structure is deterimined andcompared with different models that have been proposed in the experimentalliterature. The relative stability of the two phases is calculated as a functionof potassium doping. From this an…
Contribution to the development of 100% bio-based composites : synthesis of bio-based polyepoxides, supercritical CO2 treatment of hemp fibers and im…
2018
This thesis contributes to the development of 100% bio-based hemp/epoxy composites. Current environmental issues favor the emergence of materials derived from renewable resources such as plant fibres and a wide range of bio-based building-blocks, source of epoxy prepolymers in particular. An intensive investigation of the two constituents (hemp fibres and polyepoxidic matrix) is carried out before the composites manufacturing. Supercritical CO2 treatment is applied to hemp fibres used as reinforcement in composite materials. This treatment, not optimized, leads to better individualization as well as a decrease in the hygroscopic power of the fibres. These aspects, which are essential in ord…