Browsing by Author "Nunes, A."
Now showing 1 - 5 of 5
Results Per Page
Sort Options
- Bedding mortars from medieval ceramic flooring from the Alcobaça Monastery in PortugalPublication . Carvalho, Fernanda; Nunes, A.; Pagará, A.; Costeira, I.; Silva, Teresa; Leal, Nuno; Simão, J.; Galhano, Carlos; Águas, Hugo; Lima, M.M.R.A.; Veiga, JPABSTRACT: Bedding mortars are fundamental materials to ensure the stability of titles, especially in the case of flooring which withstand the impact of people circulation. In a church, the quality of mortars, tiles pieces and their maintenance over time can be decisive for pavement durability. Inside the church of Santa Maria de Alcobaça Monastery, stone slabs are currently the main and the most applied type of paving in terms of covered area.
- Corrosion protection of PVD and paint coatings for selective solar absorber surfacesPublication . Nunes, A.; Carvalho, Maria João; Cunha Diamantino, Teresa; Fernandes, J. C. S.The selective solar absorber surface is a fundamental part of a solar thermal collector, as it is responsible for the solar radiation absorption and for reduction of radiation heat losses. The surface’s optical properties, the solar absorption (á) and the emittance (å), have great impact on the solar thermal collector efficiency. In this work, two coatings types were studied: coatings obtained by physical vapor deposition (PVDs) and coatings obtained by projection with different paints (PCs) on aluminum substrates. The most common industrial high performing solar selective absorbers are nowadays produced by vacuum deposition methods, showing some disadvantages, such as lower durability, lower resistance to corrosion, adhesion and scratch, higher cost and complex production techniques. Currently, spectrally selective paints are a potential alternative for absorbing surfaces in low temperature applications, with attractive features such as ease of processing, durability and commercial availability with low cost. Solar absorber surfaces were submitted to accelerated ageing tests, specified in ISO 22975-3. This standard is applicable to the evaluation of the long term behavior and service life of selective solar absorbers for solar collectors working under typical domestic hot water system conditions. The studied coatings have, in the case of PVDs solar absorptions between 0.93 and 0.96 and emittance between 0.07 and 0.10, and in the case of PCs, solar absorptions between 0.91 and 0.93 and emittance between 0.40 and 0.60. In addition to evaluating long term behavior based on artificial ageing tests, it is also important to know the degradation mechanism of different coatings that are currently in the market. Electrochemical impedance spectroscopy (EIS) allows for the assessment of mechanistic information concerning the degradation processes, providing quantitative data as output, which can easily relate to the kinetic parameters of the system. EIS measures were carried out on Gamry FAS2 Femostat coupled with a PCL4 Controller. Two electrolytes were used, 0.5 M NaCl and 0.5 M Na2SO4, and the surfaces were tested at different immersion times up to 4 weeks. The following types of specimens have been tested: Aluminium with/without surface treatment, 3 selective paint coatings (one with a poly(urethane) binder and two with silicone binders) and 2 PVD coatings. Based on the behaviour of the specimens throughout the 4 weeks of immersion, it is possible to conclude that the coating showing the best protective properties corresponds to the selective paint coating with a polyurethane resin followed by the other paint coatings, whereas both the PVD coatings do not confer any protection to the substrate, having a deleterious effect as compared to the untreated aluminium reference.
- Historical lime-based flooring mortars from the Church of Santa Maria de Alcobaça monastery (12th century), Portugal: A multi-analytical approachPublication . Carvalho, Fernanda; Nunes, A.; Pagará, A.; Costeira, I.; Silva, Teresa; Lima, M.M.R.A.; Veiga, JPABSTRACT: The Monastery of Alcobaça houses in reserve the ceramic tiles that adorned the floor of the church's apse. These tiles were removed during rehabilitation works and many preserve part of their original fixing mortars. A comprehensive analysis of 21 samples was conducted using a multi-analytical approach (X-ray fluorescence, X-ray diffraction, scanning electron microscopy–energy-dispersive X-ray spectroscopy, μ-Raman spectroscopy, thermogravimetry–differential thermal analysis, optical microscopy, and colorimetry). Results suggest compositional variations in the samples from the back and sides of the ceramic tiles; however, the mineralogy and general characteristics of the aggregates remained consistent between the samples and are coherent with the local geology, suggesting a shared historical origin.
- Mortars from the Monastery of Santa Maria de Alcobaça, in Portugal: characteristics and functionsPublication . Carvalho, Fernanda; Lima, M.M.R.A.; Silva, Teresa; Nunes, A.; Pagará, A.; Costeira, I.; Leal, Nuno; Simão, J.; Galhano, Carlos; Veiga, JP
- Portland cement clinker production using concentrated solar energy : a proof-of-concept approachPublication . Oliveira, Fernando Almeida Costa; Fernandes, Jorge Cruz; Galindo, José; Rodríguez, José; Cañadas, Inmaculada; Vermelhudo, V.; Nunes, A.; Rosa, Luís GuerraABSTRACT: The aim of this work was to demonstrate the feasibility of producing Portland cement clinker upon direct exposure of the raw materials under concentrated solar radiation using the PSA high concentration solar furnace SF40. For this purpose, a short thermal cycle ( < 40 min) was devised including 5 min dwell times at temperatures in the range 900-950 degrees C and 1250-1300 degrees C, followed by 10-15 min at 1500-1550 degrees C. The chemical and mineralogical data of the grey clinker produced are encouraging since values of 51.0 +/- 6.9% C3S, 22.7 +/- 5.3% C2S, 8.6 +/- 0.4% C(3)A and 10.8 +/- 0.7% C(4)AF are similar to those observed for conventional clinker used for the production of Portland cement in accordance to EN 197-1 standard. White clinker, in turn, could not be produced by direct irradiation in this setup conditions because of its low absorptance of solar energy.