Browsing by Issue Date, starting with "2007-04"
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- Deep Submarine Giant Scours in northern Gulf of Cadiz (offshore SW Iberia) : a singular case of sedimentary and tectonic couplingPublication . Duarte, João C.; Rosas, Filipe M.; Terrinha, Pedro; Valadares, Vasco; Taborda, Rui; Matias, Luís; Roque, Ana Cristina; Magalhães, Vítor Hugo; Henriet, Jean-Pierre; Pinheiro, Luís M.
- Complex pattern of Heinrich events in the mid-latitudes of the North-east Atlantic explained by oceanic and atmospheric mechanismsPublication . Naughton, Filipa; Sánchez Goñi, María Fernanda; Duprat, Josette; Cortijo, Elsa; Malaizé, Bruno; Joly, C.; Bard, Edouard; Rostek, Franke; Turon, Jean-Louis
- Strain partitioning and westwards migration of deformation in NW Gulf of Cadiz (Africa-Iberia plate boundary)Publication . Rosas, Filipe M.; Duarte, João C.; Terrinha, Pedro; Vicente, J.; Matias, Luís; Valadares, Vasco; Duarte, Henrique; Roque, Ana Cristina
- Effects of NaBH4 additions on hydrogen absorption by nanostuctured FeTi powdersPublication . Marques, Sofia Figueiredo; Correia, J.B.; Shohoji, Nobumitsu; Rangel, C. M.; Paiva Luís, TeresaHydrogen is nowadays considered as one of the most promising fuels for the future transportation market, since it is highly energetic and its combustion products are non-toxic. There are however some inherent problems related to its handling and storage that makes its implementation difficult in the energy market [1]. One way of storing hydrogen is in form of intermetallic hydrides. Some intermetallics can store large amounts of hydrogen in their interstitial sites and, in some cases, reversible equilibrium absorption/desorption cycles might be realized near ambient temperature and normal pressure. FeTi is an intermetallic compound that is being widely studied for hydrogen storage purposes. This system has one of the highest volumetric storage capacities and can be produced at low cost [2,3]. However, the FeTi alloy prepared through conventional metallurgical process requires activation treatments at elevated temperature. It has been shown previously that the nanostructured FeTi can be activated at room temperature with the mechanical alloying of pure metallic constituents, Fe and Ti, with NaBH4 [4]. In this work nanostructured FeTi based powders were produced by mechanical alloying, and the effects of adding different amounts of NaBH4 on the hydrogen absorption capacity and on the agglomeration of the powders were studied. The effect of handling powders in a glovebox with oxygen free atmosphere or in atmospheric ambient condition was also examined. Several parameters of the as-milled powders were controlled. Among the characterization performed are phase identification and crystallite size determinations by X-ray diffraction, micro hardness measurements, scanning electron microscopy and absorption isotherms determinations.
- PEM fuel cells: materials ageing mechanisms and performance impactPublication . Rangel, C. M.; Silva, R. A.; Paiva Luís, TeresaPolymer exchange membrane (PEM) fuel cells are considered promising power sources, with a vast application domain that includes consumer electronics, automotive and residential applications. As the technology matures, durability, reliability and cost are amongst the most critical issues, so creating the need for a more comprehensive knowledge of material’s ageing mechanism. In this work, the Membrane-Electrode Assembly, MEA, is considered a key component subject to material’s ageing with considerable impact on fuel cell performance. As it contains the polymer electrolyte membrane, the active catalysts and the gas diffusion layers (GDL), the mechanisms of degradation are complex. Furthermore, performance is also link to components such as gas distributor plates, since the used design and flow channels dimensions (channel width, channel depth, rib width) allow minimization of the diffusion pathway for gases. Effective oxidant supply and water management is greatly affected by cell geometry and materials. In-situ and ex-situ evaluation of MEA degradation were conducted after fuel cell ageing in extreme testing conditions. Humidified and dry gas feeds were also examined and the effect on cell performance and membrane conductivity examined. Variations of membrane conductivity with temperature and water content were considered critical: drying during operation as a result of dragging of water by protons or over saturated conditions cause condensation at the electrodes causing flooding with the consequent voltage degradation. Electrochemical Impedance Spectroscopy was found instrumental in the identification of flooding conditions using an equivalent circuit to model the interfaces at critical current densities, according to the location of identified irreversibility’s in the voltage-current domain of the fuel cell. Electrocatalyst surface area loss due to growth of catalyst particle size and particle agglomeration with the number of load cycles is suggested when using cyclic voltammetry of electrodes, this is thought to be due to a mechanism involving catalyst dissolution/precipitation. Cross sections of the membrane catalyst layers and GDLμs were examined under a FEG-SEM indicating that cathode thickness is considerably reduced as a result of ageing. Catalyst particles were found to migrate outwards and located on carbon backings. Fluoride release was considered as an early predictor of membrane degradation, quantified using an ion selective at gases outlet. MEA degradation mechanisms are discussed together with contributions that might aid design and operating strategies in PEM fuel Cells.
- Nanoscale layered double hydroxide materials for corrosion resistancePublication . Rangel, C. M.; Travassos, Maria AntóniaLayered Double Hydroxides (LDHμs), represented by the general formula [MII (1-x)MIIIx(OH)2[An-x/n].zH2O or [MIMIII2(OH)6[An-1/n].zH2O], where MI, MII, MIII are mono-, di- and tri-valent metal cations, are being researched as anion-exchange materials which interesting intercalation chemistry that accommodate a wide range of applications from heterogeneous catalysis to storage and subsequent controlled release of bioactive agents. In this work, layered double hydroxides containing a monovalent (Li+) and trivalent (Al3+) matrix cations, have been synthesized and characterised using X-ray diffraction, FTIR and SEM. LDHμs were prepared by a simple co-precipitation method using metal hydroxides and metal salts in an alkaline solution. Hybrid systems are produced by intercalation which involves a guest molecule introduced into the host structure replacing the existing interlayer ion, without affecting the host structure opening new applications according to desired functionalities namely as thin films in corrosion protection. Li based conversion coatings are easily formed under open circuit conditions on Al surfaces [1-3]. Formation of LDHμs on the metal surface of copper-rich Al alloys were attempted with excellent results. Pitting corrosion was inhibited on Aluminium 2024-T3 with an extensive capability to withstand the presence of high concentrations of chloride ions. Intergranular corrosion was found to be inhibited in Al-Li 8090 alloy by action on copper containing T-phases located at the grain and sub-grain boundaries. The formation of DHLμs is thought to be responsible for inhibition which is demonstrated to be under diffusion control. The action of DLHμs on copper is demonstrated in separated experiments using pure copper samples in similar experimental conditions as for the alloy, in an extensive electrochemical study.
- Materials for solar hydrogen production with simultaneous mineralization of ethanolPublication . Rangel, C. M.; Silva, R. A.; Paiva Luís, Teresa; Charasse, B.The photo-catalytic production of hydrogen by means of irradiation of a suspension of semiconductor oxides presents attractive features over other methods with higher cost such as water electrolysis. In this work, photocatalytic hydrogen production from water is studied, using ethanol as sacrificial agent. New nanostructured multifunctionalised semiconductor materials based on titanium dioxide, with effective photo-catalytic properties under UV illumination were synthesized using sol-gel technology and characterised by X-Ray diffraction and scanning electron microscopy. Aqueous suspensions of the semiconductor powders were used and the effect of solution pH and temperature (20-70ºC) as well as the effect of concentration of ethanol on hydrogen production were studied, for fixed concentrations of the catalyst. Comparison is made with doped Degussa-P25 TiO2 titanium dioxide. The need to decrease the electron-hole recombination rate was accounted for by metal doping [1] with the ethanol molecule acting as a hole trap. An increase in the hydrogen production rate was found as a result of the percentage of metal on doped titania and optimisation of experimental conditions with rate values being superior to recently published literature data [2]. Particle size, reactive surface area, structure and crystallinity of the semiconductor were found to be determinant in the production of highly photoactive titanium dioxide. Research in progress includes development of catalyst that allows effective utilization of visible light and design of an experimental reactor
- Return mobility of scientists and knowledge circulation : an exploratory approach to scientists attitudes and perspectivesPublication . Fontes, MargaridaThe paper addresses the international mobility and return of scientists and its implications for regions/countries with weaker scientific and technological systems. It focuses on the “return dilemma” and, using the Portuguese case as empirical setting, discusses the conditions for return, the “diaspora” alternative and the role of policies in minimising the impacts of mobility flows. Despite the growing importance assumed by scientific mobility, our understanding of mobility flows, in particular of return mobility, is still deficient. Data about the level of mobility and mobility paths is scarce and difficult to obtain and the knowledge about expatriate scientists’ motivations and strategies, namely their attitudes towards the home country and their perspectives concerning career and return mobility, remains limited. The research presented in this paper is a preliminary contribution to attend to some of these issues. A method is proposed to address some methodological problems in empirical research on scientific mobility. It permits to delimit a sample of “scientifically productive” expatriate scientists in specific fields, to locate these scientists and to trace their professional trajectories, thus making possible to collect information on their mobility behaviour as well as to gain some preliminary insights on their attitudes and perspectives. This methodology is experimentally applied to the Portuguese case. Notwithstanding its exploratory nature, the empirical research provides some insights into the behaviour of a younger generation of “scientifically productive scientists” in a field with a strong international mobility pattern (biotechnology), which can be relevant for policy making
- Aplicações desenvolvidas no ambito da metrologia eléctrica e de vibração no INETIPublication . Ribeiro, Luís; Godinho, Maria Isabel; Cabral, Alexandre Pereira; Oliveira, Vitor; Nunes, Mário Constanzo; Rebordão, José ManuelSão apresentados diversos módulos desenvolvidos em ambiente LabView, para controlo de instrumentação, processamento e tratamento estatístico de dados e determinação de incertezas, aplicados aos domínios da Metrologia Eléctrica e de Vibração no INETI. É efectuada uma breve síntese do contexto técnico em que cada uma das aplicações se insere assim como uma descrição dos principais aspectos associados a cada módulo.