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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.
51

NMR characterization of a diiron macrocycle and structural characterization of a diketo derivative

Brackett, Claudia Lindblom 01 January 2001 (has links)
The time-dependent visible spectra and the crystal structure of [Fe2(C20H24N8O2)(CH3CN)4]·PF6 (diketo-dimer) were studied. The spectra showed that the most significant chemistry occurred during the initial 1.5 hours of the synthetic reaction. The starting materials 343 nm peak shifted to a lower energy, at 360 nm, and a new shoulder appeared at 490 nm. This change suggests the formation of a new intermediate whose spectrum has an exceptional resemblance to the starting materials mixed valent species, [Fe2(TIED)(Cl)4]+1 (TIED = tetraiminethylene dimacrocycles). Two isosbestic points were found at 538 and 371 nm. The diketo-dimer's crystals appear to have individual colors, a physical characteristic called pleochroism. Pleochroism is a topic in the study of optical crystallography which is discussed and applied to the diketo-dimer. The extinction angle was estimated to be 14°, a value consistent for triclinic crystals. X-ray crystallography found that the diketo-dimer is triclinic, and has a space group of P-1. A noteworthy feature is the bond length, 1.406 Å, between the two linking bridgehead carbons. This bond length matches the value for partial double bonds of aromatic compounds. This argues for a delocalized electron circulating within the macrocycle. The NMR spectra of a diiron macrocycle, [Fe2(TIED)(CH3CN)4]4+, were examined. Temperature dependent, pH dependent, D+ substitution, selectively decoupled, and COSY 1H NMR experiments were performed. Two sets of structural equilibria were found. One set is temperature dependent, and the other is pH dependent. Of particular interest are the peaks centered at 9.7 ppm and assigned to the imine carbon protons H2. Its resonance indicates an imine proton in an extensively conjugated aromatic environment with an electron deficient metal.
52

Systematic syntheses of iron-triad (Fe,Ru,Os) tetranuclear clusters by redox condensation reactions of [Ru(3);CO(11)) and [Os(3);CO(11)] trinuclear carbonylates; co-crystallization of ruthenium-osmium clusters /

Siriwardane, Upali January 1985 (has links)
No description available.
53

The demagnetising factors for bonded neodymium iron boron (NdFeB) magnets

Wang, Zhiran January 2000 (has links)
No description available.
54

Brillouin Light Scattering studies of magnetic thin films and multilayers

Pugh, Peter Rupert Thomas January 2000 (has links)
No description available.
55

EXAFS structural analysis on metal binding sites in wood pulp and a brief study on chelation of metals in bleaching

Ow Yang, Giselle Bei 04 1900 (has links)
No description available.
56

Synthesis and characterization of LiNi0.6Mn0.35Co0.05O2 and Li2FeSiO4/C as electrodes for rechargeable lithium ion battery

Hong, Pengda., 洪鹏达. January 2011 (has links)
The rechargeable lithium ion batteries (LIB) are playing increasingly important roles in powering portal commercial electronic devices. They are also the potential power sources of electric mobile vehicles. The first kind of the cathode materials, LiXCoO2, was commercialized by Sony Company in 1980s, and it is still widely used today in LIB. However, the high cost of cobalt source, its environmental unfriendliness and the safety issue of LiXCoO2 have hindered its widespread usage today. Searching for alternative cathode materials with low cost of the precursors, being environmentally benign and more stable in usage has become a hot topic in LIB research and development. In the first part of this study, lithium nickel manganese cobalt oxide (LiNi0.6Mn0.35Co0.05O2) is studied as the electrode. The materials are synthesized at high temperatures by solid state reaction method. The effect of synthesis temperature on the electrochemical performance is investigated, where characterizations by, for example, X-ray diffraction (XRD) and scanning electron microscopy (SEM), for particle size distribution, specific surface area, and charge-discharge property, are done over samples prepared at different conditions for comparison. The electrochemical tests of the rechargeable Li ion batteries using LiNi0.6Mn0.35Co0.05 cathode prepared at optimum conditions are carried out in various voltage ranges, at different discharge rates and at high temperature. In another set of experiments, the material is adopted as anode with lithium foil as the cathode, and its capacitance is tested. In the second part of this study, the iron based cathode material is investigated. Lithium iron orthosilicate with carbon coating is synthesized at 700℃ by solid state reaction, which is assisted by high energy ball milling. Characterizations are done for discharge capacities of the samples with different carbon weight ratio coatings. / published_or_final_version / Physics / Master / Master of Philosophy
57

Sintese e caracterizacao de nanoparticulas magneticas de oxidos mistos de MnFesub(2)Osub(4) recobertas comm quitosona. Estudos da influencia na dopagem com Gdsup(3+) nas propriedades estruturais e magneticas / Synthesis and characterization of magnetic nanoparticles of mixing oxides of MnFe2O4 recovered with chitosan. Studies of the dopade influence with Gd3+ in properties structural and magnetic

RIBEIRO, THATIANA G.D. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:52:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:48Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
58

Sintese e caracterizacao de nanoparticulas magneticas de oxidos mistos de MnFesub(2)Osub(4) recobertas comm quitosona. Estudos da influencia na dopagem com Gdsup(3+) nas propriedades estruturais e magneticas / Synthesis and characterization of magnetic nanoparticles of mixing oxides of MnFe2O4 recovered with chitosan. Studies of the dopade influence with Gd3+ in properties structural and magnetic

RIBEIRO, THATIANA G.D. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:52:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:48Z (GMT). No. of bitstreams: 0 / Neste trabalho sintetizou-se e caracterizou-se nanopartículas magnéticas de ferritas de manganês, utilizando-se algumas variáveis, como: pH de precipitação (11, 12 e 13), tipo de base (NH4OH, KOH, LiOH e NaOH), concentração molar da base NaOH (1, 5 e 10 mol.L-1), tempo de aquecimento (0, 1 e 2 horas), a adição do surfactante Tween 80, a dopagem com európio (1% molar) e a dopagem com gadolínio (1, 3, 5, 7 e 10% molar) para aplicação em biotecnologia. As nanopartículas magnéticas de ferrita de manganês, ferrita de manganês dopadas foram sintetizadas pelo método de co-precipitação partindose de soluções de cloreto dos metais (ferro (III), manganês (II), európio (III) e gadolínio (III)), utilizando-se como agente de precipitação hidróxidos. As nanopartículas magnéticas foram caracterizadas por microscopia eletrônica de varredura, espectroscopia de infravermelho, difratograma de raios-X, curvas de magnetização e análise térmica. A maioria das partículas de ferrita de manganês obtidas apresentaram comportamento superparamagnético. Após as caracterizações verificou-se que a amostra de ferrita de manganês não dopada sintetizada em condições de pH de precipitação 12, com a base NaOH (5 mol.L-1), com o tempo de aquecimento de 1 hora, sem adição de surfactante é a que apresenta maior resposta e magnetização induzida por um campo externo enquanto que, dentre as amostras dopadas a 7% molar de gadolínio é a melhor. Por isso essas duas amostras foram encapsuladas por uma camada polimérica de quitosana (pelo método de microemulsão), resultando na partícula magnética. Foram utilizadas varias técnicas para caracterização destes materiais tais como difração de raios X, espectro na região do infravermelho, curvas de magnetização e análise térmica. As resinas magnéticas foram sintetizadas objetivando-se futuras aplicações na separação de materiais biológicos. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
59

Evaluation of iron valence state alterations in thermally processed liquid model systems

Trayner, Elizabeth Lois January 1984 (has links)
A glucose glycine liquid model system fortified with 24 ppm of iron as either ferrous sulfate, ferric orthophosphate or ferric orthophosphate + 110 ppm ascorbic acid was thermally processed as 240, 250 and 260°F for 3, 6, 9, 12 and 15 minutes. Levels of elemental, nonelemental, soluble, total ionic and ferrous iron were measured for the model systems at each processing parameter. Data from the iron profiles were evaluated for the effect of iron salt; ascorbic acid; glucose and glycine, and processing temperature and time on changes in the iron chemistry during processing. The ferrous sulfate model system resulted in significantly higher levels of soluble and ferrous iron. Soluble iron from the ferric orthophosphate model system increased significantly with the addition of ascorbic acid. The presence of glucose and glycine prevented formation of insoluble iron hydroxides during processing of the ferrous sulfate system, promoted solubilization and ionization of iron for the ferric orthophosphate system and restricted the enhancing effect of ascorbic acid on the ferric orthophosphate profile. The interaction of the iron salt with the model system was stimulated by the application of heat. The insignificant correlation between process lethality values and the iron profile for each iron salt indicated that changes in the iron profile were time and temperature dependent. Kinetic parameters were calculated for all three model systems. The ferric orthophosphate iron profile was less sensitive to temperature change than either of the other two model systems. Evaluation of samples at sequential time intervals during the processing treatment allowed for a better understanding of the reaction mechanisms that occurred during processing which brought about a change in the iron profile of each model system. / Master of Science
60

Neutron studies of amorphous solids

Stone, Cora Emma January 2001 (has links)
No description available.

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