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Vila Nova de Famalicão, Portugal

Kiersztyn I.,University of Porto | Neto L.,University of Porto | Carneiro A.,University of Porto | Carneiro A.,Center for Nanotechnology and Smart Materials | And 3 more authors.
Journal of Solid State Electrochemistry | Year: 2012

Poly[Cu(3-MeOsalpd)] films with good physical, chemical and electrochemical stability may be potentiodynamically electrodeposited with high deposition efficiency from acetonitrile solutions of the monomer. Comparative coulometric assays with the Ni-based analogue show that themetal in the salen motif does play a role in the electronic structure of the polymer, but that the electroactive response is ligand (not metal) based. The dynamics of redox switching are ultimately limited by coupled electron/counter ion diffusion, but this process is sufficiently rapid that it influences the voltammetric response only for thick films (Γ >420 nmol cm -2) at high scan rates. Redox cycling in monomer-free electrolyte shows a voltammetric signature that responds, via interaction with the pseudo-crown ether receptor sites, to the presence of Li +, K +, Mg 2+ and Ba 2+ ions in solution. The most prominent change is associated with the first anodic peak in the i-E signature. For each of the metal ions considered, this peak potential responds logarithmically to concentration in a manner that varies with individual complexed cation and film thickness and to an extent greater than predicted by the Nernst equation. The film characteristics offer some analytical promise, including a tradeoff between sensitivity and dynamic range and signal amplification, possibly due to supramolecular effects. © Springer-Verlag 2012. Source

Tansens P.,University of Porto | Rodal A.T.,University of Porto | Rodal A.T.,University of Santiago de Compostela | Machado C.M.M.,University of Porto | And 2 more authors.
Journal of Hazardous Materials | Year: 2011

Anodising industries use a concentrated caustic soda solution to remove aluminum from extruder matrixes. This procedure produces very alkaline effluents containing high amounts of aluminum. The work reported here was focussed on recycling aluminum, as aluminum hydroxide, from these effluents and regenerating an alkaline sodium hydroxide solution. Briefly, the method comprises a dilution step (necessary for reducing the viscosity of the effluent and allowing the subsequent filtration) followed by a filtration to eliminate a substantial amount of the insoluble iron. Then, sulphuric acid was added to neutralize the waste solution down to pH 12 and induce aluminum precipitation. The purity of the aluminum salt was improved after washing the precipitate with deionised water. The characterization of the solid recovered, performed by thermogravimetric analysis, Fourier transform infrared spectroscopy and X-ray diffraction, indicated characteristics typical of bayerite. The proposal method allowed recovering 82% of the aluminum present in the wastewater with high purity (99.5%). Additionally, a sufficiently concentrated caustic soda solution was also recovered, which can be reused in the anodising industries. This procedure can be easily implemented and ensures economy by recycling reagents (concentrated caustic soda solution) and by recovering commercial by-products (aluminum hydroxide), while avoiding environmental pollution. © 2011 Elsevier B.V. Source

Couto S.,University of Porto | Campos J.B.L.M.,University of Porto | Mayor T.S.,Center for Nanotechnology and Smart Materials
International Journal of Clothing Science and Technology | Year: 2011

Purpose: The purpose of this paper is to investigate the heat transfer on an alpine-climbing mitt featuring an electrical heating multilayer, in order to provide information for the optimization of its thermal performance. Design/methodology/approach: A numerical model was developed to simulate the heat transfer across an electrical-heated alpine mitt. The model was used to study the heat losses as a function of the environmental conditions, to optimise the positioning of the heating elements, to determine the optimal power input to the heating system, to estimate the battery capacity requirements and to assess the effect of low-emissivity surfaces. Findings: The results show that: the heating elements assure approximately constant temperatures across the skin provided they are not more than 6-7 mm apart; the use of low-emissivity surfaces facing the skin can reduce the total heat loss by 8-36 per cent (for air layer thicknesses in the range 10-3 to 10-2 m) and to increase the skin temperature during the transient operation of the heating multilayer; the heat losses from the mitt are practically independent of the chosen heating power; and a battery capacity of 4 A h assures active temperature regulation for more than 18-23 h. Practical implications: By enhancing the thermal performance of an electrical heating mitt, the use of low-emissivity surfaces (facing the skin) can favour the thermal comfort perception of its user. Originality/value: The influence of several parameters on the thermal performance of an electrical-heated mitt is analysed and discussed. The findings are relevant for improving the performance of existing electrical heating garments. © Emerald Group Publishing Limited. Source

Mayor T.S.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Couto S.,Center for Nanotechnology and Smart Materials | Psikuta A.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Rossi R.M.,Empa - Swiss Federal Laboratories for Materials Science and Technology
International Journal of Biometeorology | Year: 2015

The ability of clothing to provide protection against external environments is critical for wearer’s safety and thermal comfort. It is a function of several factors, such as external environmental conditions, clothing properties and activity level. These factors determine the characteristics of the different microclimates existing inside the clothing which, ultimately, have a key role in the transport processes occurring across clothing. As an effort to understand the effect of transport phenomena in clothing microclimates on the overall heat transport across clothing structures, a numerical approach was used to study the buoyancy-driven heat transfer across horizontal air layers trapped inside air impermeable clothing. The study included both the internal flow occurring inside the microclimate and the external flow occurring outside the clothing layer, in order to analyze the interdependency of these flows in the way heat is transported to/from the body. Two-dimensional simulations were conducted considering different values of microclimate thickness (8, 25 and 52 mm), external air temperature (10, 20 and 30 °C), external air velocity (0.5, 1 and 3 m s−1) and emissivity of the clothing inner surface (0.05 and 0.95), which implied Rayleigh numbers in the microclimate spanning 4 orders of magnitude (9 × 102–3 × 105). The convective heat transfer coefficients obtained along the clothing were found to strongly depend on the transport phenomena in the microclimate, in particular when natural convection is the most important transport mechanism. In such scenario, convective coefficients were found to vary in wavy-like manner, depending on the position of the flow vortices in the microclimate. These observations clearly differ from data in the literature for the case of air flow over flat-heated surfaces with constant temperature (which shows monotonic variations of the convective heat transfer coefficients, along the length of the surface). The flow patterns and temperature fields in the microclimates were found to strongly depend on the characteristics of the external boundary layer forming along the clothing and on the distribution of temperature in the clothing. The local heat transfer rates obtained in the microclimate are in marked contrast with those found in the literature for enclosures with constant-temperature active walls. These results stress the importance of coupling the calculation of the internal and the external flows and of the heat transfer convective and radiative components, when analyzing the way heat is transported to/from the body. © 2015 ISB Source

Pereira L.,University of Aveiro | Trindade A.J.,University of Aveiro | Santos M.G.,University of Aveiro | Gomes J.,Center for Nanotechnology and Smart Materials
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

One important key to improve the bulk-heterojunction photovoltaics (BHJs) is the fill-factor (FF). In this work, a study of the FF dependence factors on BHJs with an active layer of MEH-PPV / PCBM is made. The FF changes from 20% to 70%, depending on the current - voltage behavior and on the photovoltaic equivalent circuit parameters changes (parallel and series resistances, voltage open circuit, short circuit current and photocurrent). The efficiency changes from 1% to 5%. A theoretical simulation for FF optimization is made allowing a better understand of the physical process involved in the BHJ that modulates such parameter. © 2014 SPIE. Source

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