Добірка наукової літератури з теми "Molybdate Glass"

ABSTRACTAlkaline earth aluminosilicate glasses (AeAS) with different MoO3 additions have been produced and assessed. MoO3 solubility increases with the equimolar substitution of smaller to larger alkaline earths and reaches 5.34 mol% in magnesium aluminosilicate glass (MAS). All visibly homogeneous glasses are X-ray amorphous, while the partially crystallised glasses exhibit some small X-ray diffraction peaks which are probably due to corresponding molybdates. The addition of MoO3 decreases glass transition and crystallisation temperatures and creates two broad Raman bands which are assigned to vibrations of MoO42‒ tetrahedra. The intensities of these bands increase along with MoO3 incorporation until the maximum solubility is reached. Electron microscopy shows that these separated particles are spherical, with sub-micron diameters and are randomly dispersed within glass. The separated phases are formed through liquid-liquid separation and thereafter crystallisation. Overall AeAS glasses look quite promising for molybdate immobilisation with MAS glasses being particularly attractive.

Lithium molybdate doped tungsten trioxide electrochromic films were prepared from tungsten trioxide precursor and lithium molybdate powder by sol-gel and dip coating methods on fluorine doped tin oxide glass. The films, which synthesized were flat and amorphous structure, which confirmed by x-ray diffraction patterns. From UV-vis transmittance spectra within the wavelength from 400 to 800 nm. and cyclic voltammogram at the applying a potential of 1.0 V (bleached state) to -1.0 V (colored state) in sulfuric acid 0.5 M solution. The doping lithium molybdate 10 mol% films showed good result in terms of transmittance modulation, high diffusion coefficient and optimal surface area. Therefore, doping lithium molybdate 10 mol% has better outcome when compared to undoped lithium molybdate.

ABSTRACTSodium carbonate is currently being considered as a wash-out reagent for the removal of the settled solids in the unagitated Highly Active Liquor (HAL) storage tanks at Sellafield. As the settled solids are expected to comprise mainly zirconium molybdate (ZM), this will result in a challenging feed to the Waste Vitrification Plant (WVP) containing high concentrations of both molybdenum and sodium.In previous studies, it was shown that at high wash-out waste loadings, i.e. 10 – 12 wt% MoO3 incorporation, there was very little tolerance in ‘Ca/Zn’ base glass for extra sodium before the formation of significant separated sodium molybdate salt phase. However, higher amounts of sodium can be accommodated in borosilicate glasses if the wash-out waste loading is reduced. Further studies have now been carried out to investigate the vitrification of more representative calcined waste feeds. Both pure zirconium molybdate (ZM) and blended ZM-reprocessing waste calcines were produced from the appropriate liquor feeds. The maximum waste incorporations of these two calcines in ‘Ca/Zn’ base glass have been determined, along with a complete product quality assessment. This assessment included measuring the bulk density, degree of crystallinity, heat treatment, durability (Soxhlet and PCT), glass transition temperature, and viscosity.

Les verres nucléaires sont synthétisés par réactions chimiques à haute température entre un précurseur vitreux (fritte de verre) et un déchet calciné (calcinat) dans un procédé de calcination-vitrification. Le déchet est d'abord séché et dénitré (calcination) avant d'être mélangé à la fritte de verre (vitrification). Une succession de processus physico-chimiques d'imprégnation, diffusion, cristallisation et dissolution, est mise en jeu afin d'intégrer les éléments présents dans le calcinat au sein du réseau vitreux. Ces réactions, dépendantes de la composition des précurseurs et des conditions d'élaboration, doivent être complètes afin d'assurer l'homogénéité du verre et garantir son comportement à long terme. Ce travail a pour objectif de déterminer les réactions chimiques entre les précurseurs et de quantifier les cinétiques réactionnelles afin d'identifier in fine les processus responsables de leur limitation. Un système simplifié constitué d'une fritte de verre de type alumino-borosilicate de sodium et d'un calcinat contenant du nitrate de sodium et de l'oxyde d'aluminium (composés majeurs présents dans les calcinats complexes) est complexifié progressivement afin de déterminer l'influence des éléments de faible solubilité, présents initialement dans les solutions de produits de fission à vitrifier. Les cas des oxydes de molybdène et de néodyme sont en particulier étudiés. Les conditions de formation (temps, température) des phases cristallines de type molybdates (sodium, calcium) et aluminates (sodium, néodyme) ainsi que leur domaine de stabilité dans les calcinats sont déterminés. Les cinétiques de dissolution de ces phases dans la fritte de verre sont modélisées. Il est montré que la dissolution du molybdène, mis en évidence sous forme Na2MoO4, est contrôlée d'une part par la solubilité thermodynamique du MoO3 dans le verre, indépendamment de la dissolution des aluminates de sodium. D'autre part, les cinétiques de dissolution de Na2MoO4 et des aluminates présentent un comportement arrhénien avec la température dont les valeurs des énergies d'activation sont proches de celles de la viscosité du verre. Ces travaux décrivent également les mécanismes de formation d'intermédiaires réactionnels à l'origine de la cristallisation de la " yellow phase " (riche en oxydes de molybdène, d'alcalins et d'alcalinoterreux) pouvant se former dans des verres plus complexes
Nuclear waste glasses are produced by chemical reactions between a solid waste (calcine) and a glassy precursor (glass frit) through a high-temperature vitrification process. The waste is first dried and calcined (to lose water and nitrogen respectively), then mixed with the glass frit. A succession of physicochemical processes of impregnation, diffusion, crystallization and dissolution is involved in order to incorporate the radioactive elements within the glassy network. These reactions, which are dependent on the precursor composition and the synthesis conditions, must be complete to ensure the homogeneity of the glass and to guarantee its long-term behavior. The aim of this work is to determine the chemical reactions between the precursors and to quantify the reaction kinetics in order to identify the processes responsible for their limitation. A simplified system consisting of a sodium-aluminum borosilicate glass frit and a calcine containing sodium nitrate and aluminum oxide (the principal oxides present in complex calcines) is progressively complexified to determine the influence of low solubility elements initially present in the fission product solutions to be vitrified. The cases of molybdenum and neodymium oxides are the focus of attention. The formation conditions (time, temperature) of crystalline molybdates (sodium, calcium) and aluminates (sodium, neodymium) and their range of stability in the calcines are determined. The dissolution kinetics of these phases in the glass frit is modeled. It is shown that the dissolution of molybdenum, as Na2MoO4, is controlled by the thermodynamic solubility of MoO3 in the glass. It is independent of the sodium aluminate dissolution. For both, Na2MoO4 and sodium aluminates, dissolution reactions present an Arrhenian behaviour and the activation energies are close to that of the viscous flow. This work also describes the formation mechanisms of intermediate phases which can lead to the crystallization of the "yellow phase" (enriched in molybdenum, alkali and alkaline-earth oxides) that can form in more complex glasses

Après dissolution du combustible et séparation des différents éléments par le procédé PUREX, la majeure partie des produits de fission et des actinides mineurs est calcinée puis vitrifiée dans des verres de conditionnement des déchets nucléaires. Parmi ces produits de fission, certains précipitent et ne sont pas immobilisés dans la phase vitreuse dédiée aux déchets de haute activité à vie longue. Les éléments platinoïdes Pd-Rh-Ru sont insolubles dans le verre nucléaire. En fonction du potentiel d'oxygène imposé par la fritte de verre, ils précipitent sous la forme de phases oxydes complexes ou de composés intermétalliques principalement alliés aux éléments chalcogènes Te et Se. Au contraire, le molybdène reste oxydé lors des dernières étapes du procédé de vitrification. Très réactif vis-à-vis des oxydes constitutifs de la fonte verrière, il forme majoritairement des molybdates. Au cours de cette thèse, la thermodynamique des systèmes chimiques contenant le molybdène (Mo), les éléments platinoïdes Pd-Rh-Ru et les chalcogènes Se-Te ont été étudiés expérimentalement. En parallèle, la thermodynamique de ces systèmes chimiques est également modélisée par la méthode Calphad. L'objectif de cette modélisation est de prédire les phénomènes de cristallisation du molybdène et des platinoïdes observés au cours des étapes de vitrification en fonction de la composition et de la température. Ces modélisations permettent d'effectuer des calculs d'applications en lien avec le procédé industriel de vitrification
After the dissolution of the used fuel and the separation of several elements by the PUREX process, the high level nuclear wastes composed of fission products and minor actinides are reprocessed and vitrified in nuclear glasses at AREVA La Hague plant. Some of the fission products precipitate : they are not solubilized in the glass matrix. On the one hand, platinoids Pd-Ru-Rh are not soluble in the nuclear glasses. Depending on the oxygen potential, they form complex solid oxyde phases or intermetallic compounds containing chalcogen elements such as selenium and tellurium. On the other hand, the molybdenum forms only oxide phases during the vitrification process. It reacts strongly with the oxide phases present in the glass melt to form mainly molybdate phases. Some of these phases are only temporary formed but other are more stable and can precipitate in the glass matrix when a large amount of molybdenum is supplied. In this thesis, the thermodynamics of the chemical systems containing molybdenum, the platinoid elements Pd-Rh-Ru and the chalcogen elements Se and Te were experimentally investigated. At the same time, these chemical systems were modeled with the Calphad method so as to be able to predict the crystallization phenomena of molybdenum and the platinoids occurring during the vitrification as a function of the composition and the temperature. These modelings are useful to perform application calculations in relation with the vitrification process

Etudes effectuees en vue de preciser la nature des electrons qui participent ala conduction et au magnetisme de ces composes. Les composes, caracterises par la presence d'amas tetraedriques des ions metalliques mo et nb dans les bas etats d'oxydation, revelent des proprietes de magnetisme itinerant repondant au modele de stoner-wohlfarth avec les densites d'etats les plus elevees observees dans des composes intermetalliques 3d ou 4d. La rpe a confirme que les raies observees correspondant aux ions metalliques dans un etat s = 3/2 (ions mo**(3+) et nb**(3+)); leur elargissement est d'origine dipolaire retrecie par echange et les valeurs des integrales d'echange obtenues sont en bon accord avec celles obtenues a partir des temperatures de curie

La construction d’un NSOM, dans ce manuscrit de thèse, est décrite en détail. Lacombinaison du système NSOM construit avec un interféromètre est proposée afin d’accéderà des mesures de phase, à la fois de ultra-haute sensibilité mais également de très granderésolution spatiale. Le nom de l’instrument développé est un interferomètre optique àbalayage en champ proche (NSOI, pour l’acronyme en anglais). Le principe est basé surl’utilisation d’un diapason accordable en cristal de quartz, sur lequel se trouve une pointe,afin de sonder le matériau étudié. La mesure de la force de cisaillement de la pointe sondeau voisinage de la surface permet d’assurer la régulation et la stabilité de la distance depositionnement de la pointe par rapport à la surface considérée. Le dispositif est construit encombinant différents éléments électroniques pilotés par un logiciel développé en langageLab-VIEW. Le bruit de la mesure en NSOI est supprimé par un calcul simple basé sur lathéorie de l’optique ondulatoire et des interférences associées. Le système permet deréaliser des mesures optiques en champ proche ainsi que la détermination en hauterésolution de la phase du champ optique. L’échantillon SNG01 (l’un des réseaux utilisés pourcaractériser notre microscope à balayage en champ proche), ainsi que des disques optiques(CD, DVD and disques blu-ray) ont été utilisés pour tester la faisabilité et les performancesde notre système.Dans ce manuscrit de thèse, le graphène et les monocouches de MoS2 sont étudiés. Nous montrons qu’une épaisseur à l’échelle atomique peut être résolue par notresystème NSOI, avec l’utilisation de l’algorithme de suppression du bruit de mesure. Lesjoints de grain du graphène sont observés à grande échelle, via la technique d’imagerie parcollection en champ proche et par la réalisation de cartographies de phase. En particulier,les tensions internes à une couche de graphène sont observées, uniquement dans le casd’une imagerie de phase
In this thesis, near-field scanning optical interferometry (NSOI), which combinesNSOM with interferometer, is proposed for the phase measurement. The shear-forcedetection scheme is applied for distance regulation. The hardware of the systemis constructed by combining various electronic devices, and the operating softwareis coded by LabVIEW. Unwanted background signal is removed by simple calculationbased on interference theory. By using this, the near-field optical measurementand the ultra-sensitive phase investigation of nano-materials are performed. 2D materialssuch as graphene and monolayer MoS2 are investigated. It is shown thatatomic-scale thickness can be resolved by the NSOI. Especially, the grain boundariesof graphene and the seed of MoS2 can be found by phase detection. In addition,direct laser writing (DLW) on silver-containing glass is observed by using NSOM,and NSOI. For the first time, the writing threshold is correlatively observed in thefluorescence imaging and the near-field phase image

Developing efficient, fast performing and thermally stable AgI-Ag2O-MoO3glasses are of great interest for Resistive Random Access Memory (RRAM) applications; however there many challenges such as metallization in bulk, behavior of Vth profile over composition and corrosion reactions. In this thesis work, fast ion conducting (FIC) AgI-Ag2O-MoO3 glasses have been investigated with an idea to solve some technical challenges such as thermal stability, corrosion etc. with the help of deep understanding of the material. Employing various experimental and characterization techniques, this research work aims to identify the links between various material and technical aspects and how to tune these aspects to solve the challenges envisaged. Bulk AgI-Ag2O-MoO3 (50:25:25) glasses have been prepared by melt quenching method (Microwave heating and quenched between two heavy steel plates). The electrical switching experiments have been carried out using a Keithley Source Meter (model 2410) controlled by Lab VIEW 6i, on samples of thicknesses (d) 0.1, 0.2 and 0.3 mm at different ON state currents (Imax) (3 mA, 2 mA, 1 mA, 0.6 mA, 0.4 mA and 0.25 mA); It has been found that these samples exhibit fast near ideal memory switching. The power dissipation (P) increases with both d and Imax. It is also found that the threshold voltage (Vth) increases with d; and for a given thickness, the Vth decreases with increasing Imax. A sample of d = 0.1 mm exhibits near ideal memory switching with the least P for Imax = 0.25 mA. These samples can be used for fast switching applications with minimum power dissipation. Further, the electrical switching behavior of bulk, FIC (AgI)50+x-(Ag2O)25-(MoO3)25-x, for 10 ≤ x ≤ -10 glasses has been investigated, in order to understand the switching mechanism of bulk samples with the inert electrodes. It is found that by using inert electrodes, the switching becomes irreversible, memory type. In these samples, the switching mechanism is an electrochemical metallization process. The inert electrodes restrain ionic mass transfer; however exhibit a low barrier to electron transfer allowing the cathodic metallization reaction to reach Nernst equilibrium faster. The cations involved in this process transport thorough the free volume within the glass structure and follows Mott-Gurney (MG) model for electric field driven thermally activated ion hopping conductivity. This model along with the thermal stability profile provide a narrow region within composition with better switching performance based on swiftness to reach Vth and less power loss. It is found that traces of anionic contribution to metallization are absent. Moreover, anodic oxidation involves reactions that cause bubble formation and corrosion which becomes evident from SEM (Scanning electron Microscope) micrographs of the switched and un-switched parts of the sample. Rigidity percolation phenomena in (AgI)50+x-(Ag2O)25-(MoO3)25-x, for 5 ≤ x ≤ -12.5 has been observed by performing calorimetry (ADSC) and photoelectron spectroscopy experiments (XPS). The temperature dependence of heat capacity (normalized Cp) at glass transition temperature (Tg), exhibits fluctuations for samples with higher AgI concentration indicating the fragile nature of the glass. The composition range chosen in the present study, accommodates both the fragile and strong glasses, and the fragility threshold. Cp (absolute) values, at Tg, exhibits abrupt sign shift at this threshold. The negative Cp is identified as a thermodynamic behavior of nanoclusters. The XPS study shows the formation of covalent structural units, [‒Mo‒O‒Ag‒O‒] and complex molybdenum oxides in the positive Cp region. Finally, the non-reversing enthalpy profile, exhibits square well minima, sandwiched between floppy and stress rigid region, which has been identified to be the intermediate phase, within the range 32.25 ≤ MoO3 concentration ≤ 35. Electrochemical Impedance Spectroscopy (EIS) and Raman studies have been performed on this glass, over a wide range of composition ((AgI)50+x-(Ag2O)25-(MoO3)25-x, for 3.75 ≤ x ≤ -10.5) to understand the features of structure, ion migration and their correlation. These features essentially involve diffusion and relaxation. The coefficients associated with diffusion process, especially, the diffusion coefficient, diffusion length and relaxation time has been determined by applying Nguyen-Breitkopf method. Besides, by tuning the concentration of the constituents, it is possible to obtain samples which exhibit two important structural characteristics, namely fragility and polymeric phase formation. The present study essentially addresses these issues and endeavors to figure out the corroboration among them. The relaxation behavior, when scrutinized in the light of Diffusion Controlled Relaxation (DCR) model, ascertains the fragility threshold which is also identified as the margin between the two types of polymeric phases. Simultaneously, it fathoms into the equivalent circuitry, its elements and their behavioral changes with above mentioned features. The power law behavior of A.C. conductivity exhibits three different non-Jonscher type dispersive regimes along with a high frequency plateau. The sub-linearity and super-linearity remain significantly below and above the Jonscher’s carrier transport limit, 0.5 ≤ n ≤ 0.9. Finally, by observing the behavior of the crossover between these sun-linear and super-linear (SLPL) regime, an intuitive suggestion has been proposed for the appearance of SLPL: oxygen vacancy formation.