No description available.

Les oxydes mixtes à base de cérium-nickel et zirconium ou aluminium permettent de stocker de grande quantités d'hydrogène. Afin de déterminer la nature, la réactivité et les propriétés des espèces hydrogène (diffusion, désorption directe ... ), les solides ont été étudiés par différentes techniques physico-chimiques à l'état séché. calciné et partiellement réduit: DRX, porosité, ATG, TPR, TPA, TPD, dosage chimique et diffusion de neutrons (INS), Les solides sont majoritairement mésoporeux avec un diamètre de pore commun à 4 nm. Ils sont constitués d'une phase CeO2, de solution solide Ce-Ni ou Ce-Ni-Zr et de Ni(OH)2 à l'état séché et NiO à l'état calciné. Les espèces Ni se trouvent. dans différents environnements et les interactions fortes entre les cations en solution solide et aux interfaces des différentes particules influencent leur réductibilité et la création de lacunes anioniques. L'activation sous H2 en température est déterminante pour le stockage de l'hydrogène dans le solide alors que l'étape de calcination n'est pas nécessaire. Les analyses par INS mettent en évidence que les espèces hydrogène insérées lors du traitement sous H2 sont des espèces H+ (OH-), hydrures H- et H* (nickel métallique), présentes dans différents environnements chimiques, en particulier pour les hydrures. Toutes les espèces hydrogène participent à la réaction lors du dosage chimique en accord avec le mécanisme d'hydrogénation proposé. L'étude de l'adsorption d'hydrogène montre que celle-ci est rapide et en quantité du même ordre de grandeur que celle mesurée par dosage chimique, La désorption directe de l'hydrogène sous forme H2 est très faible, liés a la présence d'hydrogène en interaction avec le nickel métallique,(H*). Un dégagement d'eau est observé en parallèle, correspondant à l'élimination de groupements hydroxyles, Les especes hydrures quant a elles ne sont pas desorbees. Ces différentes observations ont permis de relier les propriétés des espèces hydrogène à leur localisation dans la structure et de modéliser des sites actifs / The mixed oxides based on cerium-nickel and zirconium or aluminium are able to store large quantities of hydrogen, To determiine nature, reactivity and properties of hydrogen species (spill-over, direct desorption), the solid were studied by different physicochemical techniques in the dried, calcined and partially reduced states: XRD, porosity, TGA, TPR, TPA, TPD, chemical titration and inelastic neutron scattering (INS). Solids are mainly mesoporous with a common pore size at 4 nm, They are constituted of CeO2 phase, Ce-Ni or Ce-Ni-Zr solid solution and of Ni(OH)2 in the dried state and NiO in the calcined state. The Ni species are in various environments and the strong interactions between the cations in solid solution and at different particles interface influence their reducibility and the creation of anionic vacancies. Activation in H2 in temperature is determining for hydrogen storage in the solid while calcination step is not necessary. INS Analyses evidence that the hydrogen species inserted during treatment in H2 are H+( OH-), hydride H- and H* (metallic nickel) species, present in various chemical environments, in particular for hydride species. All kinds of hydrogen species participate to the reaction during the chemical titration in agreement with the proposed hydrogenation mechanism. The study of the adsorption of hydrogen shows that this step is fast and in quantity of the same order as that measured by chemical titration. The direct desorption of H2 is very low, linked to the presence of hydrogen in interaction with metallic nickel (H*-·). Desorption of water is also observed, in parallel, corresponding to the elimination of groups. The hydride species are not desorbed. These various observations allow connecting hydrogen species properties with their localization in the structure and to model active sites.

LD2668 .T4 1950 B33 / Master of Science

M.Tech. / The study into the effect of additives used in nickel powder precipitation by sodium hypophosphite has been carried out. Reduction experiments were conducted in a 10 L stainless steel batch reactor fitted with 3 baffles, 4-bladed axial impeller, heating element, thermocouple and thermostat. Nickel seed was used to initiate the reduction process, sodium hypophosphite was used as a reducing agent, and ammonia solution was used to adjust pH, poly(ethylene-comaleic anhydride) (EMA) was used as the first additive and poly(acrylic acid) (PA) as the second additive. Reduction experiments were conducted at a temperature between 60oC to 70oC, pH around 8 and a reaction time of 3 min. Synthetic nickel sulfate solution and sodium hypophosphite solutions at concentration of 0.5 g/L were used as nickel feed solution and reducing agent, respectively. Additives were investigated at high and low concentrations of 5 mg/L and 10 mg/L. The effect of additives on reduction behavior of nickel was investigated by studying the evolution of the volume distribution, moments, specific surface area, and rate of reduction and purity of the powder product. EMA was found to be a growth promoter and PA was found to be a growth inhibitor. The highest reduction rate was observed in the presence of EMA and the lowest in the presence of PA. The SEM micrographs of the powder obtained in the presence of EMA and PA showed that the powder was spherical shaped, open, dentritic and more porous compared with that of the seed particles. Both additives were found to increase the pore size of the powder particles. The presence of particle fragments observed in the scanning electron micrographs confirmed breakage as one of the major particulate process. The addition of additives significantly affected the volume distribution at lower concentrations of 5 mg/L. The extent of aggregation increased with increasing dosages of PA and decreased with increasing dosages of EMA. The highest specific surface area was obtained in the presence of 5 mg/L of EMA.

Kin Man Ho. / Thesis (M.Ph.)--Chinese University of Hong Kong, 1988. / Bibliography: leaves 61-65.

by Lam Ka. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 54-60). / Abstracts in English and Chinese. / ABSTRACT --- p.i / ACKNOWLEDGEMENT --- p.ii / TABLE OF CONTENT --- p.iii / LIST OF TABLES --- p.v / LIST OF FIGURES --- p.vii / Chapter CHAPTER ONE: --- INTRODUCTION --- p.1 / Chapter 1.1 --- Metal deposition --- p.1 / Chapter 1.2 --- Electroless Nickel Plating --- p.3 / Chapter 1.2.1 --- Historical Review and Applications --- p.3 / Chapter 1.2.2 --- General Chemical Principles --- p.5 / Chapter 1.2.3 --- Previous Studies --- p.7 / Chapter 1.3 --- Scope of Work --- p.12 / Chapter CHAPTER TWO: --- EXPERIMENTAL --- p.13 / Chapter 2.1 --- Bath Composition --- p.13 / Chapter 2.1.1 --- Theoretical Description --- p.13 / Chapter 2.2.2 --- Materials --- p.15 / Chapter 2.2 --- Procedure and Experimental Conditions --- p.17 / Chapter 2.3 --- Characterization of EN Coatings --- p.18 / Chapter 2.3.1 --- Theory --- p.18 / Chapter 2.3.1.1 --- Energy Dispersive X-ray Detection of Scanning Electron Microscopy --- p.18 / Chapter 2.3.1.2 --- Polycrystalline X-ray Diffraction --- p.18 / Chapter 2.3.1.3 --- X-ray Photoelectron Spectroscopy --- p.20 / Chapter 2.3.1.4 --- Microhardness --- p.22 / Chapter 2.3.1.5 --- Corrosion resistance --- p.23 / Chapter 2.3.1.6 --- Thickness Measurement --- p.23 / Chapter 2.4 --- Application --- p.24 / Chapter CHAPTER THREE: --- RESULTS AND DISCUSSION --- p.26 / Chapter 3.1 --- Appearance --- p.28 / Chapter 3.2 --- Microstructure --- p.30 / Chapter 3.2.1 --- Effect of Phosphorus Content --- p.30 / Chapter 3.2.2 --- Effect of heat treatment --- p.32 / Chapter 3.3 --- Corrosion Resistance --- p.37 / Chapter 3.3.1 --- Effect of Phosphorus Content --- p.37 / Chapter 3.3.2 --- Effect of Heat Treatment --- p.45 / Chapter 3.3.2.1 --- Temperature --- p.45 / Chapter 3.3.2.2 --- Cooling Rate --- p.47 / Chapter 3.4 --- Microhardness --- p.49 / Chapter 3.4.1 --- Effect of Phosphorus Content --- p.49 / Chapter 3.4.2 --- Effect of Heat Treatment --- p.49 / Chapter CHAPTER FOUR: --- CONCLUSION --- p.52 / REFERENCES --- p.54

No description available.

Thesis (M.S.)--Oregon State University, 1963. / Typescript. Includes bibliographical references (leaves 75-81). Also available on the World Wide Web.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Donald L. Sparks, Dept. of Plant & Soil Science. Includes bibliographical references.

As part of a strategic research initiative at UBC to design and evaluate integrated underground mining and mineral processing systems, work has been done to determine how to utilize the coarse rejects of pre-concentration in the underground environment. An amenability study for nine orebodies from four of Xstrata Nickel’s Ontario operations evaluated both processing and waste disposal methods. Metallurgically the orebodies showed amenability to dense media separation and conductivity sorting. The dense media results showed high mass rejections and high metal recoveries for all nine orebodies. Conductivity sorter results were not as consistent, but still showed good results. Dense media rejects were examined to determine the applicability of their use in rockfills and composite minefills. The geotechnical properties indicated that the rejects would provide a competent material for minefills. The mix designs were examined for both strength and rheological properties and showed that fills utilizing rejects were comparable to fills currently used by industry. Composite fills containing rejects had significantly lower void ratios, decreasing cement requirements for a given strength requirement. Conceptual designs for pre-concentration systems based on the metallurgical, reject characterization, and mix design were developed for each of the four mines in the study. The designs took into consideration the current mining plans.