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Electrochemical Aspects of Miniaturized Analytical PlatformsKlett, Oliver January 2003 (has links)
<p>This thesis ties some electrochemical aspects of development and fabrication of an analytical system on a microchip together. These aspects develop through the fundamentals of amperometric detection in microsystems and microfabrication via the interaction of electrochemical detection and electrophoretic separation finally to the interfacing of a microsystem to the macro world.</p><p>Paper <b>I</b> deals with amperometric detection in microscale systems and describes the fabrication of the necessary on-chip microelectrodes together with fluidic channels in silicon. It was furthermore studied, if the interelectrode distance of some μm could be used to improve the sensitivity in amperometric detection by employing redox cycling. </p><p>Papers <b>II</b>, <b>III</b> and <b>IV</b> deal with the effect of a high voltage field on amperometric detection. In analytical microdevices typically an electrophoretic separation step (e.g. capillary electrophoresis, CE) precedes the detection. The interference of the CE high voltage with the amperometric detection potential is often considered one of the main hindrances for an effective combination of these techniques. In paper <b>II</b> one reason for the observed disturbing potential shift was elucidated. It was shown that positioning of working electrode and reference electrode on an equipotiental surface eliminates this problem. Paper <b>III</b> reports an application of this technique. In paper <b>IV</b> it could be shown that this approach could further be used to significantly reduce the instrumental requirements for amperometric detection in CE.</p><p>Papers <b>V</b>, <b>VI</b>, <b>VII</b>, finally discuss the interfacing of low volumetric flows that typically occur on microanalytical devices to other techniques. Both, interfacing from liquid to liquid phase (μLC to CE in paper <b>V</b>) and from liquid to gas phase (CE to MS in paper <b>VI</b> and <b>VII</b>) were discussed. Electrochemical methods are used in this context to evaluate the stability and, in paper <b>VI</b> and <b>VII</b>, to increase the understanding of underlying processes of corrosion.</p>
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Electrochemical Aspects of Miniaturized Analytical PlatformsKlett, Oliver January 2003 (has links)
This thesis ties some electrochemical aspects of development and fabrication of an analytical system on a microchip together. These aspects develop through the fundamentals of amperometric detection in microsystems and microfabrication via the interaction of electrochemical detection and electrophoretic separation finally to the interfacing of a microsystem to the macro world. Paper I deals with amperometric detection in microscale systems and describes the fabrication of the necessary on-chip microelectrodes together with fluidic channels in silicon. It was furthermore studied, if the interelectrode distance of some μm could be used to improve the sensitivity in amperometric detection by employing redox cycling. Papers II, III and IV deal with the effect of a high voltage field on amperometric detection. In analytical microdevices typically an electrophoretic separation step (e.g. capillary electrophoresis, CE) precedes the detection. The interference of the CE high voltage with the amperometric detection potential is often considered one of the main hindrances for an effective combination of these techniques. In paper II one reason for the observed disturbing potential shift was elucidated. It was shown that positioning of working electrode and reference electrode on an equipotiental surface eliminates this problem. Paper III reports an application of this technique. In paper IV it could be shown that this approach could further be used to significantly reduce the instrumental requirements for amperometric detection in CE. Papers V, VI, VII, finally discuss the interfacing of low volumetric flows that typically occur on microanalytical devices to other techniques. Both, interfacing from liquid to liquid phase (μLC to CE in paper V) and from liquid to gas phase (CE to MS in paper VI and VII) were discussed. Electrochemical methods are used in this context to evaluate the stability and, in paper VI and VII, to increase the understanding of underlying processes of corrosion.
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Fluorine Partitioning Between Nominally Anhydrous Minerals (Olivine, Clinopyroxene, and Plagioclase) and Silicate Melt using Secondary Ion Mass Spectrometry and Newly Synthesized Basaltic Fluorine Microanalytical Glass StandardsJanuary 2012 (has links)
abstract: Fluorine (F) is a volatile constituent of magmas and hydrous mantle minerals. Compared to other volatile species, F is highly soluble in silicate melts, allowing F to remain in the melt during magma differentiation and rendering F less subject to disturbance during degassing upon magma ascent. Hence, the association between fluorine in basalts and fluorine in the mantle source region is more robust than for other volatile species. The ionic radius of F- is similar to that of OH- and O2-, and F may substitute for hydroxyl and oxygen in silicate minerals and melt. Fluorine is also incorporated at trace levels within nominally anhydrous minerals (NAMs) such as olivine, clinopyroxene, and plagioclase. Investigating the geochemical behavior of F in NAMs provides a means to estimate the pre-eruptive F contents of degassed magmas and to better understand the degassing behavior of H. The partition coefficients of F were determined for clinopyroxene, olivine, plagioclase, and hornblende within melts of olivine-minette, augite-minette, basaltic andesite, and latite compositions. The samples analyzed were run products from previously-published phase-equilibria experiments. Fluorine was measured by secondary ion mass spectrometry (SIMS) using an 16O- primary beam and detection of negative secondary ions (19F-, 18O-, 28Si-). SIMS ion intensities are converted to concentrations by analyzing matrix-matched microanalytical reference materials and constructing calibration curves. For robust F calibration standards, five basaltic glasses (termed Fba glasses) were synthesized in-house using a natural tholeiite mixed with variable amounts of CaF2. The Fba glasses were characterized for F content and homogeneity, using both SIMS and electron-probe microanalysis (EPMA), and used as F standards. The partition coefficients for clinopyroxene (0.04-028) and olivine (0.01-0.16) varied with melt composition such that DF (olivine-minette) < DF (augite-minette) < DF (basaltic andesite) < DF (latite). Crystal chemical controls were found to influence the incorporation of F into clinopyroxene, but none were found that affected olivine. Fluorine partitioning was compared with that of OH within clinopyroxenes, and the alumina content of clinopyroxene was shown to be a strong influence on the incorporation of both anions. Fluorine substitution into both olivine and clinopyroxene was found to be strongly controlled by melt viscosity and degree of melt polymerization. / Dissertation/Thesis / Ph.D. Geological Sciences 2012
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[en] ARCHAEOMETALLURGY STUDY OF METALLIC ARTIFACTS RECOVERED FROM HISTORICALS SITES IN RIO DE JANEIRO / [pt] ESTUDO ARQUEOMETALÚRGICO DE OBJETOS METÁLICOS RESGATADOS DE SÍTIOS HISTÓRICOS DO RIO DE JANEIROGUADALUPE DO NASCIMENTO CAMPOS 03 March 2006 (has links)
[pt] Este trabalho tem como objetivo efetuar um estudo
arqueometalúrgico de
objetos ferrosos e não-ferrosos resgatados de sítios
históricos do Rio de
janeiro. A pesquisa experimental desenvolveu uma
metodologia de análise
utilizando-se de técnicas destrutivas como Microscopia
Ótica (MO),
Microscopia Eletrônica de Varredura (MEV), Microscopia
Eletrônica de
Transmissão e não destrutivas como Fluorescência de Raio X
(FRX) e Emissão
de Raios-X por Indução de Partículas (PIXE). Os objetos
foram analisados com
o intuito de caracterizar sua composição, estrutura e
método de elaboração.
Estes correspondem a seis artefatos de natureza metálica
não-ferrosa e um de
natureza metálica ferrosa. O objeto metálico ferroso
corresponde a uma
enxada. As características microestruturais dos objetos
estão correlacionadas
com a função que esses desempenhavam na época e indicativa
de que a
enxada possa ter sido feita no Brasil por escravos
africanos. A análise da
enxada permite concluir que é constituída de um ferro
pudlado e que foi
processada por fundição e forjamento. Quanto aos objetos
não-ferrosos, o
rosário é constituído de um latão monofásico mais rico em
cobre. Com relação
à fabricação do rosário pode-se concluir de que seja de
origem européia, sendo
decorrente de um minério pirítico. As medalhas são de
procedência européia
constituídas de latão. Historicamente, pode-se deduzir que
são referentes ao
século XVIII. Conclui-se que as duas moedas do Sítio
Rochedo sejam
originárias de fontes diferentes, constatado pelas
análises químicas. Porém, as
concentrações químicas da moeda de 1821 são próximas a uma
das moedas
de 40 réis. A presente tese permitiu evidenciar a
importância da sistemática de
trabalho experimental de caracterização, a partir de
técnicas destrutivas e nãodestrutivas
de materiais, de objetos arqueológicos para estabelecer seu
contexto histórico. / [en] This work undertakes an archeometallurgical study of
ferrous and non-ferrous
artifacts recovered from historical sites of Rio de
Janeiro. The experimental
research developed an analytical methodology based on
destructive techniques,
such as Optical Microscopy (OM), Scanning Electronic
Microscopy (SEM) and
Transmission Electronic Microscopy (TEM); as well as non-
destructive
techniques, namely X-Ray Fluorescence (XRF) and Particle
Induction X-Ray
Emission (PIXE). These artifacts were analyzed in order to
characterize their
composition, structure and elaboration/processing methods.
There are six
artifacts with a non-ferrous metallic nature and one with
a ferrous metallic nature.
The ferrous metallic artifact was a hoe. The
microstructure characteristics is
related to the usage of this object at that time, and
indicates that the hoe could
have been made in Brazil by African slaves. The analysis
of the hoe indicates
that it was elaborated from puddle iron and that it had
been processed by foundry
and forging. The rosary, one of the non-ferrous artifacts,
is formed by singlephase
brass riche in copper; and according to historical
research it is of
European origin, deriving from pyrite ore. The medals are
also of European origin
and are based on brass. Historically one can deduce that
they are dated from the
18th century. The two coins from the Rochedo site most
probably came from
distinct sources, as validated by the chemical analysis.
However, the chemical
composition of the 1821 coin is close to that of the 40
réis coin. The present
thesis has shown the importance of a systematic
methodology to characterize
ancient objects combining both destructive and non-
destructive techniques.
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