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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Studies of metal substituted alumino-phosphates and other related systems

Franklin, Ilona Louise January 2005 (has links)
The research within this thesis has concentrated around the identification and catalytic understanding of the acid and redox properties of a series of metal substituted aluminophosphates, silicoaluminophosphates and polyoxometalates. The aim being to understand how the active metal sites were co-ordinated, to what degree of substitution had been successfully achieved and finally the direct relation this information had in understanding the degree of reaction for the various catalytic processes. In most part hydrothermal synthesis was employed, the exception being in the case of the polyoxometalate and polyoxometalate layered double hydroxide synthesis. Characterisation was achieved through the use of many analytical techniques predominantly X-ray diffraction (XRD) and extended X-ray spectroscopy (XAS). In total, four commercially important reactions were studied. Firstly, the shape selective and redox properties associated with (a) the substitution of different metal ions within the same aluminophosphate framework and (b) the substitution of the same metal ion within different aluminophosphate frameworks were characterised and investigated for the methanol to olefin (MTO) reaction to demonstrate the activity and selectivity of different frameworks in the production of a range of olefins. Secondly, several transition metal ion-exchanged zeolites and aluminophosphates were synthesised, characterised and subsequently analysed for the hydroxylation of phenol. Here temperature effects were also investigated to see what, if any effect it had upon the final conversion of phenol. Thirdly, a series of bifunctional platinum impregnated silicoaluminophosphate (Pt/SAPO) and metal substituted aluminophosphate (Pt/MeAlPO) catalysts were synthesised, characterised then investigated to understand how their acidic nature effected the catalytic activity and selectivity for the hydroisomerisation of n-heptane. Finally, the properties of several cobalt-substituted polyoxometalates (POM's) and polyoxometalate pillared layered double hydroxides (POM-LDH's) were studied and investigated for their catalytic activity for the oxidation of cyclohexane with molecular oxygen in the presence of TBHP.
2

Studies in the benefication of low grade phosphate rock

Zafar, Zafar Iqbal January 1998 (has links)
No description available.
3

Synthèse et caractérisation de verres d’oxyde d’argent : évolution sous rayonnements ionisants et structuration multi-échelle par laser femtoseconde / Synthesis and characterization of silver-containing glasses : evolution under ionizing irradiation and femtosecond laser multiscale structuring

Desmoulin, Jean-Charles 02 December 2016 (has links)
Les verres de phosphates de zinc et gallium contenant de l’argent ont permis des développements originauxau travers de la structuration d’architectures photoniques multi-échelles innovantes en volume, en surfaceou sur fibre, et également à travers l’ingénierie de composition chimique du matériau. Un taux accru d’oxyded’argent permet de maximiser la quantité de paires au sein de la matrice vitreuse lors de la synthèse dumatériau. Ce dimère favorise les processus d’agrégation conduisant à la formation d’espèces lors del’interaction locale entre le verre et le laser femtoseconde infrarouge. Une étude par spectroscopie RPEmenée sur des échantillons irradiés par des sources ionisantes a permis de montrer que le débit de dose estprépondérant quant au contrôle des processus chimiques. Des centres à électron et à trou sont les espècesmajoritairement stabilisées à faible débit de dose, alors que la formation d’agrégats d’argent luminescentsintervient pour des puissances crête élevées typiques des lasers ultra-courts. Le caractère local de lastructuration par Direct Laser Writing a permis de créer des objets 3D originaux. L’analyse fine de ladistribution chimique au sein d’objets fluorescents a permis de montrer clairement une zone de déplétion enions argent au centre. Les effets de migration d’ions depuis le centre du faisceau laser vers le bord externea ainsi été mis en évidence. Le dopage des verres photosensibles par des ions europium a permis de montrerdes effets de synergie entre agrégats d’argent photo-inscrits et lanthanides trivalent. En effet, une exaltationde l’émission de luminescence de ces derniers à l’endroit des structurations laser a été mesurée. / The silver-containing phosphate glasses allowed original developments throughout the microstructuring ofarchitectures for innovative photonic in the volume, at the surface or in the fibered material. The chemicalengineering of the material plays an important role from this point of view. An increasing silver oxide ratioleads to an important quantity of pairs in the pristine glass matrix. This dimer in favor of the aggregationprocess bringing to the production of species during the interaction between the glass and the infraredfemtosecond laser. A study conducted by EPR spectroscopy on irradiated samples (ionizing sources)demonstrated that the dose rate is predominant for the control of the involved chemical process. Mainly,electron and holes are stabilized at low dose rate whereas the formation of luminescent silver clusters occursfor high peak power typical of ultra-short lasers. The Direct Laser Writing process allows local structuring ofthe matter and resulted in original tridimensional patterns. The fine chemical distribution analysis insideannular fluorescent objects clearly showed a depletion zone of the silver concentration in the center. Ionicmigration effects from the center towards the edges of the laser beam are then highlighted. The Eu3+-dopedphotosensitive glasses emphasized a synergy between photo-induced silver clusters and trivalentlanthanides. Indeed, a luminescence exaltation associated to the europium emission is measured.

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