ME - Comunicações em actas de encontros científicos internacionais
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- Advanced cyclic accelerated aging testing of solar reflector materialsPublication . Wette, Johannes; Sutter, Florian; Tu, Mai; Fernández-Garcia, Aránzazu; Buendia, Francisco; Carvalho, Maria João; Cunha Diamantino, TeresaABSTRACT: Lifetime prediction methods for the components of concentrated solar power (CSP) plants have been in the focus of interest of manufacturers and plant developers for the past years. Recently, an accelerated aging standard for solar mirrors was published by the Spanish AENOR committee [1]. This standard allows performing comparative testing but it is not suited to derive meaningful life-time estimations. Firstly, the testing defined in the standard is not aggressive enough to produce significant degradation on most of the materials and secondly, it has been shown that the passing of these tests does not guarantee a high durability during outdoor exposure [2]. These findings have proven the need for the investigation of more realistic procedures. To provoke the mechanisms that are detected during outdoor exposure, a more realistic application of environmental stresses is being investigated. In this work a series of tests is conducted in which several weathering stresses are combined and applied in a cyclic manner. Some of these cycles have shown to correlate better with real outdoor behavior.
- Analysis of a stand-alone residential PEMFC Power system with sodium borohydride as hydrogen sourcePublication . Pinto, P.J.R.; Fernandes, Vitor; Pinto, A. M. F. R.; Rangel, C. M.Catalytic hydrolysis of sodium borohydride (NaBH4) has been investigated as a method to generate hydrogen for fuel cell applications. The high purity of the generated hydrogen makes this process an ideal source of hydrogen for polymer electrolyte membrane fuel cells (PEMFCs). In this paper, the possibility of using a NaBH4-based hydrogen generator with a PEMFC for stand-alone residential use is examined. A complete model of the system is developed, based on models taken from literature with appropriate modifications and improvements. Supervisory control strategies are also developed to manage the hydrogen generation and storage and the power flow. The operation and performance of the integrated system over a one-week period under real loading conditions is analyzed through simulation. Finally, results of the analysis are summarized and the limitations/further scope are indicated.
- Batch solid sodium borohydride hydrolysis for hydrogen generation : the role of reactor bottom shapePublication . Ferreira, M. J. F.; Rangel, C. M.; Pinto, A. M. F. R.The present study reports original experimental work on generation of hydrogen, by hydrolysis of solid sodium borohydride with stoichiometric amount of distilled water (H2O/NaBH4: 2, 2.84 and 3 mol/mol), in the presence of a powder unsupported Ni-Ru based catalyst, reused about 320 times. The experiments, performed in two batch reactors with equal internal volume but with different bottom shapes (flat and conical), revealed - for the conical bottom shape with any excess of water - 8.1 H2 wt% and 92 kg H2/m3 (materials-only basis), and a H2 rate of 87.4 L(H2) min-1g-1 catalyst. The role of reactor bottom geometry on the solid NaBH4 hydrolysis - with any excess of water - is, as the authors are aware, for the first time here referred.
- Battery recycling by hydrometallurgy : evaluation of simultaneous treatment of several cell systemsPublication . Nogueira, Carlos; Margarido, F.A research work has being carried out aiming at evaluating the possibility of treating simultaneously several electrochemical systems of spent batteries using the same process, in order to overcome the high costs and difficulties of selective collection and sorting. Zn-MnO2 systems, representing more than 75% of portable battery market, shall be treated in dedicated processes. The treatment assessment using a single hydrometallurgical process of the other major systems (NiCd, NiMH and Li-ion), having Ni and Co as main metals, was the aim of the research work here reported. Sulfuric acid leaching was demonstrated to be adequate for dissolving more than 90% of the metals of interest contained in batteries. The subsequent separation of metals by solvent extraction, using organophosphorous extractants like DEHPA and Cyanex 272, allowed the production of pure solutions of rare earths, cadmium/manganese, cobalt, nickel and lithium, enabling their further recovering
- Can small additions of an organic polymer or surfactant to sodium borohydride show the way to high hydrogen storage systems for portable applications?Publication . Ferreira, M. J. F.; Gales, L.; Fernandes, Vitor; Rangel, C. M.; Pinto, A. M. F. R.
- Characterisation and performance studies of a LiFePO4 cathode material synthesized by microwave heatingPublication . Plancha, Maria João; Paiva Luís, Teresa; Rangel, C. M.Lithium iron phosphate with incorporated carbon, LiFePO4-C, was synthesized by the microwave-assisted method. X-ray diffraction analyses showed higher crystallization degrees for samples submitted to higher irradiation times. A particle-agglomerated morphology was associated as revealed by scanning electron microscopy. The electrochemical character-istics of a composite cathode containing the synthesized product were evaluated. The two-phase electrochemical process between FePO4 and LiFePO4 was evidenced in the cycling voltammogram profile and its reversibility and stability were demonstrated. An additional redox reversible reaction was revealed and assigned to another phosphate present in the synthesized product. The charge/discharge performance study indicated a good capacity retention after the initial cy-cles where capacity fading was associated to the resistance of a SEI film that forms and grows on the cathode’s surface. Results obtained by electrochemical impedance analysis before and after cell’s cycling are discussed.
- Characterisation of automotive shredder residuePublication . Margarido, F.; Nogueira, CarlosThe autofluff residue of a Portuguese shredding facility was characterised aiming at identifying the presence of heavy metals in several constituents of these residues, in order to propose possible valorising solutions. Particle size analysis showed that average characteristic diameter (d50) was 6.5 mm, the coarser fractions (> 11 mm, representing 40% of weight) being essentially composed of plastic pieces, rubber, foams and textiles, particles in the range 2-11 mm being composed of mixed materials, while in particles below 2 mm (referred as fines) the presence of glass, ceramics and other inorganic materials became very frequent, in spite of a very fine foam was also detected in the very fine fractions. XRD analysis of fines allowed detecting the crystalline phases quartz, calcite, rutile and magnetite. Elemental analysis by EDXRF was carried out on several fractions in the particle size range 0.02-2.0 mm, showing the presence of practically all the elements detected in all fractions, namely Fe, Zn, Cu, Pb, Ba, Sn, and also traces of Cd, Sb, Mo and Sr. Some of these metals are hazardous and can be problematic in what concerns the possible valorisation of the residue.
- Characterization of Cu2ZnSn(SSe)4 monograin powders by FE-SEMPublication . Neves, Filipe; Livramento, Vanessa; Martins, Isabel M.; Esperto, Luís; Santos, Mário J. G.; Correia, J.B.; Muska, K.; Holopainen, T.The design and synthesis of high-efficiency materials to convert solar to electrical energy is an increasingly important research field. Within the photovoltaic technologies, crystalline Si have an 80% share while the remaining 20% are mostly thin film solar cells based on Cu(In,Ga)(S,Se)2 (CIGSSe) and CdTe [1,2].
- Characterization of smart MARFOS NiTi shape memory alloysPublication . Neves, Filipe; Fernandes, F. M. Braz; Martins, J.; Correia, J.B.; Oliveira, M.; Gaffet, E.; Wang, T. Y.; Lattemann, M.; Suffner, J.; Hahn, H.In the present study, structural characterization of NiTi smart shape memory al-loys (SMAs), produced by an alternative powder metallurgy approach named mechanically ac-tivated reactive forging (MARFOS), was carried out by means of transmission electron micros-copy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was observed that MARFOS materials had a multiphase nanocrystalline structure. In addition, the transformation behaviour associated with the shape memory effect of the MARFOS aged mate-rials was studied with differential scanning calorimetry (DSC). Multiple-step martensitic trans-formations could be observed in aged materials.
- Comparison of processes for lithium recovery from lepidolite by H2SO4 digestion or HCl leachingPublication . Nogueira, Carlos; Margarido, F.; Vieceli, N.; Durão, F.; Guimarães, C.Lithium is becoming a strategic metal due to its important applications in secondary battery electrodes used in electronic appliances and also in electric traction vehicles. Lithium primary resources are brines and rock minerals, the former being nowadays almost exclusively used in the production of lithium commodities. With the expected increase in lithium demand, the development of competitive technologies for recovery lithium from ores like pegmatites is getting imperative. The high energy and reagents consumption in processing minerals is an issue that should be considered. This paper presents some results on the comparison of two acid treatment routes for lepidolite, the H2SO4 digestion and HCl leaching. Before both chemical treatments, lepidolite was calcined at 800oC and was transformed in a more reactive species, ƒÀ-spodumene. The H2SO4 digestion at 175oC (followed by water leaching) allowed 88% Li recovery into the solution in 30 min. By the contrary, the HCl leaching process carried out at 90oC also achieved similar yields but only after 4 h of reaction. In both cases, an acid excess was used, but clearly higher for the essays with HCl. The H2SO4 digestion process was also advantageous in what concerns to selectivity over other contained metals. Al, Mn and Fe concentrations in solutions were substantially higher in the hydrochloric acid leaching. These results showed that the digestion with sulphuric acid can be a more efficient and competitive process.