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- 3DOM ceria ecoceramics from sustainable cork templates for solar thermochemical CO2 splittingPublication . Pullar, Robert C.; Novais, Rui M.; Caetano, Ana P. F.; Barreiros, M. Alexandra; Abanades, Stéphane; Almeida Costa Oliveira, Fernando
- A review of solar thermochemical CO2 splitting using ceria-based ceramics with designed morphologies and microstructuresPublication . Pullar, Robert C.; Novais, Rui M.; Caetano, Ana P. F.; Barreiros, M. Alexandra; Abanades, Stéphane; Oliveira, Fernando Almeida CostaABSTRACT: This review explores the advances in the synthesis of ceria materials with specific morphologies or porous macro- and microstructures for the solar-driven production of carbon monoxide (CO) from carbon dioxide (CO2). As the demand for renewable energy and fuels continues to grow, there is a great deal of interest in solar thermochemical fuel production (STFP), with the use of concentrated solar light to power the splitting of carbon dioxide. This can be achieved in a two-step cycle, involving the reduction of CeO2 at high temperatures, followed by oxidation at lower temperatures with CO2, splitting it to produce CO, driven by concentrated solar radiation obtained with concentrating solar technologies (CST) to provide the high reaction temperatures of typically up to 1,500 degrees C. Since cerium oxide was first explored as a solar-driven redox material in 2006, and to specifically split CO2 in 2010, there has been an increasing interest in this material. The solar-to-fuel conversion efficiency is influenced by the material composition itself, but also by the material morphology that mostly determines the available surface area for solid/gas reactions (the material oxidation mechanism is mainly governed by surface reaction). The diffusion length and specific surface area affect, respectively, the reduction and oxidation steps. They both depend on the reactive material morphology that also substantially affects the reaction kinetics and heat and mass transport in the material. Accordingly, the main relevant options for materials shaping are summarized. We explore the effects of microstructure and porosity, and the exploitation of designed structures such as fibers, 3-DOM (three-dimensionally ordered macroporous) materials, reticulated and replicated foams, and the new area of biomimetic/biomorphous porous ceria redox materials produced from natural and sustainable templates such as wood or cork, also known as ecoceramics.
- Manufacture of cordierite foams by direct foamingPublication . Silva, Elisabete Ribeiro; Correia, N.; Silva, J. M.; Oliveira, Fernando Almeida Costa; Ribeiro, F. R. M. C.; Bordalo, J. C.; Ribeiro, M. F.Open cell cordiereti fosms were prepared by a direct foaming two-component polyurethane (PUR)/ceramic system. Throught optimization of several experimental parameters such as contents of catalysts and ceramic cordiereti precursor, as well as plasticizer presence, foams with porosites 85-95&% and densities ranging from 130-410 kg/m3 were obtained. Thse foams characteristics make them attractive to be used as catalyst supports. The new two-component PUR/ceramics system developped allows the high solid's loading (higher than 40 wt. %). Finer ceramic particles in this system provide better particles packaged and cohesion upon sintering, favouring the cordiereti foam stability.
- Novel two-step processing route combining mechanical alloying and microwave hybrid sintering to fabricate dense La9.33Si2Ge4O26 for SOFCsPublication . Santos, Mário João dos; Alves, Cátia; Oliveira, Fernando Almeida Costa; Marcelo, Teresa; Mascarenhas, João; Cavaleiro, A.; Trindade, B.In this work, microwave hybrid sintering at 1300 and 1350 °C was carried out for densification of La9.33Si2Ge4O26 mechanically alloyed powder with apatite structure. The pellets sintered at these two temperatures present the same structure (apatite) with relative densities of 92 and 96%, respectively. Mechanical analysis performed on sintered materials revealed the following results: hardness of 7.1 and 8.0 GPa, Young's modulus of 122 and 133 GPa, yield strength of 1807 and 2073 MPa and fracture toughness of 1.5 and 1.0 MPa m1/2, respectively.
- Synthesis of Non-Cubic Nitride Phases of Va-Group Metals (V, Nb, and Ta) from Metal Powders in Stream of NH3 Gas under Concentrated Solar RadiationPublication . Shohoji, Nobumitsu; Oliveira, Fernando Almeida Costa; Galindo, José; Rodriguez, Jose; Cañadas, Inmaculada; Fernandes, Jorge Cruz; Rosa, Luís GuerraABSTRACT: Using a high-flux solar furnace, loosely compacted powders of Va-group transition metal (V, Nb, and Ta) were reacted with stream of NH3 gas (uncracked NH3 gas) being heated by concentrated solar beam to a temperature (T) range between 600 and 1000 degrees C. From V, sub-nitride V2N (gamma phase) and hypo-stoichiometric mono-nitride VN possessing fcc (face-centered cubic) crystal lattice structure (delta phase) were synthesized. On the other hand, in the reaction product from Nb and Ta, hexagonal mono-nitride phase with N/M atom ratio close to 1 (epsilon phase) was detected. The reaction duration was normalized to be 60 min. In a conventional industrial or laboratory electric furnace, the synthesis of mono-nitride phase with high degree of crystallinity that yield sharp XRD peaks for Va-group metal might take a quite long duration even at T exceeding 1000 degrees C. In contrast, mono-nitride phase MN of Va-group metal was synthesized for a relatively short duration of 60 min at T lower than 1000 degrees C being co-existed with lower nitride phases.
- Heterogeneity along the Height in Disc Specimens of Graphite/Tungsten Powder Mixtures with Sub-Stoichiometric Carbon Atom Ratios Heated by Concentrated Solar Beam to 1600 CPublication . Shohoji, Nobumitsu; Magalhães, Teresa; Oliveira, Fernando Almeida Costa; Rosa, Luís Guerra; Fernandes, Jorge Cruz; Rodriguez, Jose; Cañadas, Inmaculada; Martinez, DiegoCompositional heterogeneity along the thickness of compacted disc specimens of graphite/tungsten powder mixtures with substoichiometric carbon atom ratios (0.35, 0.50 and 1.00) heated by concentrated solar beam to 1600 C was characterised by X-ray diffraction. Top surface of any examined test piece was consisted purely of mono-carbide WC while the bottom surface showed different constitution depending on the net initial C/W ratio of the test piece; almost pure metallicWfor the C/W ¼ 0:35 specimen, dominant metallicWassociated with small proportion ofW2C for the C/W ¼ 0:50 and dominantW2C with trivial proportion of WC for the C/W ¼ 1:0. In the intermediate zone between the top and the bottom layers, the constitution held virtually constant depending on the nominal C/W ratio of the starting material: co-existing metallicWandW2C for the C/W ¼ 0:35, pureW2C for the C/W ¼ 0:50 and predominant WC with traceW2C for the C/W ¼ 1:00. Unlike for the top surface of the C/W ¼ 0:35 test piece heated in a solar furnace to 1900 C reported earlier, no evidence of formation of nano-meter scale WC whisker was detected for the top surface in any sample heated to 1600 C in the present work.
- Mechanical properties of dense cordierite discs sintered by solar radiation heatingPublication . Oliveira, Fernando Almeida Costa; Shohoji, Nobumitsu; Martinez, Diego; Fernandes, Jorge Cruz; Rodriguez, Jose; Rosa, Luís Guerra; Cañadas, InmaculadaConsolidation of cordierite disc specimens was undertaken under concentrated solar beam in a solar furnace at PSA (Plataforma Solar de Almerıá). Satisfactory extent of densification was achieved by the present solar-sintering experiment. The mechanical properties measured for the solar-sintered cordierite test pieces were; density ¼ 2:45 0:02 g/cm3, Vickers microhardness HV ¼ 7:31 0:29 GPa, Young’s modulus E ¼ 97 5 GPa, shear modulus G ¼ 38 2 GPa, Poisson ratio ¼ 0:27 0:01, fracture toughness KIC ¼ 1:50 0:15 MPa m1=2 and modulus of rupture evaluated by ring-on-ring test MORROR ¼ 57:8 13:7 MPa which were comparable to those of the counterparts sintered by conventional industrial gas furnace.
- Desenho de experiências - estratégicasPublication . Domingues, Joaquim Resina; Oliveira, Fernando Almeida Costa; Esperto, LuísO desenvolvimento de produtos e processos pressupõe a realização de experiências que conduzam à sua optimização ao menor custo possível. As estratégias a utilizar na condução das experiências, bem como o tratamento estatístico dos resultados alcançados, deverão conduzir às melhores condições de realização dos ensaios necessários à prossecução deste objectivo. O método de Taguchi permite obter informação relevante, com um número reduzido de experiências, conforme se demonstra nos casos de estudo apresentados.
- Effect of particle size of starting oxide powders on the performance of doped-lanthanum oxyapatite produced by mechanical alloying followed by microwave sinteringPublication . Oliveira, Fernando Almeida Costa; Marcelo, Teresa; Alves, Cátia; Santos, Mário João dos; Mascarenhas, João; Trindade, B.La9.33Si2Ge4O26 oxyapatite powders were synthesized at room temperature through mechanical alloying of La2O3, GeO2 and SiO2 precursor powders with different particle sizes as well as crystal structure in the case of silica powder (crystalline/amorphous). The mechanical alloyed mixtures were subsequently sintered by microwave heating at 1350 C for 1 h in order to obtain dense and homogeneous materials. All sintered materials consisted of the target apatite phase although minor amounts of secondary phases (e.g.La4GeO8) were also present only in samples obtained from micrometric SiO2 powders with a crystalline structure. The microstructure of the materials obtained from nanometric SiO2 with an amorphous structure was found to be more homogenous than the ones obtained from micrometric/crystalline silica. The mechanical behavior of the samples was slightly dependent on the particle size of the precursors and on the SiO2 crystallinity.
- Cork-derived ceria ecoceramics for solar fuel production via thermochemical redox process using concentrated solar energyPublication . Novais, Rui M.; Oliveira, Fernando Almeida Costa; Barreiros, M. Alexandra; Abanades, Stéphane; Caetano, Ana P. F.; Pullar, Robert C.