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Electrochemical impedance spectroscopy investigation of the electrochemical behaviour of copper coated with artificial patina layers and submitted to wet and dry cycles

HERNANDEZ, R. del P. B.; AOKI, I. V.; TRIBOLLET, B.; MELO, H. G. de
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.5%
Due to rain events historical monuments exposed to the atmosphere are frequently submitted to wet and dry cycles. During drying periods wetness is maintained in some confined regions and the corrosion product layer, generally denominated patinas, builds up and gets thicker. The aim of this study is to use electrochemical impedance spectroscopy (EIS) to investigate the electrochemical behaviour of pure copper coated with two artificial patina layers and submitted either to continuous or to intermittent immersion tests, this latter aiming to simulate wet and dry cycles. The experiments were performed in 0.1 mol dm(-3) NaCl solution and in artificial rainwater containing the most significant pollutants of the city of Sao Paulo. The results of the continuous immersion tests in the NaCl solution have shown that the coated samples behave like a porous electrode with finite pore length. On the other hand, in the intermittent tests a porous electrode response with semi-infinite pore length can be developed. The results were interpreted based on the model of de Levie and a critical comparison with previous interpretations reported in the literature for similar systems is presented. (C) 2011 Elsevier Ltd. All rights reserved.; CNPq

Local electrochemical investigation of copper patina

Mennucci, Marina Martins; Sanchez-Moreno, M.; Aoki, Idalina Vieira; Bernard, M-C.; Melo, Hercilio Gomes de; Joiret, S.; Vivier, Vincent
Fonte: SPRINGER; NEW YORK Publicador: SPRINGER; NEW YORK
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
26.16%
The patination of copper is known for its complexity and heterogeneous formation. For a deeper investigation, a locally resolved surface analysis was considered. An exact determination of the accessed area and a potentiostatic control in a three-electrode configuration was reached with the use of the electrochemical microcell technique, which enables local electrochemical measurement such as local electrochemical impedance spectroscopy and cyclic voltammetry. Such a technique provides a unique way for performing the investigation of heterogeneities on electrode surfaces. The local electrochemical measurements on the artificially patinated surface have allowed distinguishing areas of different reactivity even when the analysis of the surface revealed a homogenous chemical composition of patina. Local measurements with the electrochemical microcell showed the presence of small defects on the patina layer that can be modelled by considering a hemispherical diffusion process at small active areas surrounded by larger less reactive domains.; CAPES; Spanish Education Ministry

Estudo e caracterização de pátinas em cobre e bronze com técnicas PIXE e ED-XRF; Patina Study and Characterization on Copper and Bronze with PIXE and ED-XRF Techniques.

Campos, Pedro Herzilio Ottoni Viviani de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 09/04/2010 PT
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27.08%
No acervo que compõem o patrimônio cultural, há muitos utensílios, obras de arte, monumentos, etc., que são feitos de metais. Mas dentre os diversos metais existentes, o cobre possui uma posição de destaque na história, pois este foi o primeiro utilizado pela humanidade. Os metais quando expostos à atmosfera podem sofrer processos de corrosão, o que pode comprometer um artefato histórico. No cobre e suas ligas, o produto dos processos de corrosão é denominado pátina. O estudo das pátinas e das ligas que compõe a matriz, no qual a pátina se forma, é de fundamental importância para a compreensão dos processos de corrosão. Com esta informação, puderam-se determinar as melhores técnicas de conservação e restauração que devem ser aplicadas. No presente estudo utilizou-se pátinas artificiais, que já são amplamente conhecidas, e possibilitam a simulação de pátinas naturais, além de ser possível utilizá-las na recolocação de pátinas que fora removidas e/ou perdidas de peças metálicas. Em um estudo anterior foram produzidas pátinas artificiais a partir de três soluções utilizando dois procedimentos de preparação e a análise foi realizada através das técnicas: EIS (Espectroscopia por Impedância Eletroquímica)...

A multianalytical approach to investigate stone biodeterioration at a UNESCO world heritage site: the volcanic rock-hewn churches of Lalibela, Northern Ethiopia.

Schiavon, N; De Caro, Tilde; Kiros, A; Caldeira, A Teresa; Parisi, I; Riccucci, C; Gigante, Giovanni
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
16.16%
A multianalytical approach combining Optical Microscopy (OM), Backscattered Variable Pressure Scanning Electron Microscopy + Energy Dispersive X-ray Spectroscopy (VP-BSEM + EDS), Powder X-ray Diffractometry (PXRD), Raman Spectroscopy, and Microbiological techniques has been applied to characterize decay products and processes occurring at the surface of two rockhewn churches (Bete Gyorgis and Bete Amanuel) at the UNESCO’s World Heritage site of Lalibela, Northern Ethiopia. The two churches were carved into volcanic scoria deposits of basaltic composition. In their geological history, the Lalibela volcanic rocks underwent late to post-magmatic hydrothermal alteration together with partial laterization and are therefore characterized by a decay-prone highly vesicular microtexture with late stage to post-magmatic precipitation of secondary mineral phases (calcite–zeolite–smectite). The main objective of the study was to gain a better insight into the weathering products and mechanisms affecting the surface of the stone monuments and to assess the relative contribution of natural “geological” weathering processes versus biological/salt attack in stone decay at this unique heritage site. Results indicate that while the main cause of bulk rock deterioration and structural failure could be related to the stone inherited “geological” features...

Astrobiological significance of minerals on Mars surface environment: UV-shielding properties of Fe (jarosite) vs. Ca (gypsum) sulphates

Amaral, Gabriel; Martinez-Frias, Jesus; Vazquez, Luis
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/12/2005
Relevância na Pesquisa
16.16%
The recent discovery of liquid water-related sulphates on Mars is of great astrobiological interest. UV radiation experiments, using natural Ca and Fe sulphates (gypsum, jarosite), coming from two selected areas of SE Spain (Jaroso Hydrothermal System and the Sorbas evaporitic basin), were performed using a Xe Lamp with an integrated output from 220 nm to 500 nm of 1.2 Wm-2. The results obtained demonstrate a large difference in the UV protection capabilities of both minerals and also confirm that the mineralogical composition of the Martian regolith is a crucial shielding factor. Whereas gypsum showed a much higher transmission percentage, jarosite samples, with a thickness of only 500 microns, prevented transmission. This result is extremely important for the search for life on Mars as: a) jarosite typically occurs on Earth as alteration crusts and patinas, and b) a very thin crust of jarosite on the surface of Mars would be sufficient to shield microorganisms from UV radiation.; Comment: 18 pages, 2 figures, submitted to Reviews in Environmental Science and Bio/Technology (invited paper), special issue "Extreme Life"

Alteraciones superficiales desarrolladas en rocas de ambientes urbanos y naturales

Ponce,María Beatriz
Fonte: Revista de la Asociación Geológica Argentina Publicador: Revista de la Asociación Geológica Argentina
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2010 ES
Relevância na Pesquisa
16.27%
En el presente trabajo, se investiga el desarrollo de costras y pátinas encontradas en algunas obras provenientes de sectores urbanos y otras de áreas naturales. En el primer caso se seleccionaron monumentos funerarios del cementerio de la Recoleta y el palacio del Congreso Nacional, en tanto que en el segundo el sector de Los Pizarrones en el Parque Nacional Talampaya. Para los estudios, se emplearon técnicas de microscopia óptica, difracción de rayos X y microscopia electrónica con análisis por microsonda. Los monumentos pertenecientes al ámbito de la Recoleta seleccionados para este trabajo, corresponden a Nicolás Avellaneda, Olivera de Pignetto y Luis María Campos. Las diferencias encontradas entre los monumentos radica en las condiciones de exposición (intemperie o resguardada) a las que contribuyen acciones biológicas, antropogénicas y de polución ambiental. De manera similar, el palacio del Congreso Nacional ubicado en el sector céntrico de la ciudad también revela que la caliza de sus fachadas, desarrolla costras como en los monumentos de Recoleta aunque con alguna variación de su composición mineral. La acción biológica se manifiesta en los contenidos encontrados de P, S y Si. El ejemplo de Los Pizarrones como área natural muestra el desarrollo de una pátina con importante acción biológica...