Examinando por Autor "Bueno, Salvador"
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Ítem Design and processing of Al2O3–Al2TiO5 layered structures(Elsevier, 2005) Bueno, Salvador; Moreno-Botella, Rodrigo; Baudín, CarmenAl2O3-Al2TiO5 layered composites were manufactured by a colloidal route from aqueous Al2O3 and TiO2 suspensions with 50vol.% solids. The mechanical behaviours of individual monolithic composite materials were combined and taken as basis for the design of the layered structures. Residual stresses which are likely to occur due to processing and thermally introduced misfits were calculated and considered for the manufacture of the laminates. Monoliths with 10, 30 and 40 vol.% of second phase showed that increasing proportions of aluminium titanate decrease strength and increase the non-linear behaviour. In order to obtain the desired combination of mechanical behaviours of the layers, two laminate designs with external and central layers of one composition and the alternating internal layer of the other composition were chosen taking into account chemical compatibility and development of residual stresses. In the system AA10, external and central layers of monophase Al2O3 with high strength were combined with intermediate layers of Al2O3 with 10vol.% of Al2TiO5. The system A10A40 was selected to combine low strength and energy absorbing intermediate layers of Al2O3 with 40vol.% of Al2TiO5 and sufficient strength provided by external layers of Al2O3 with 10vol.% of Al2TiO5. The stress-strain behaviour of the laminates was linear up to their failure stresses, with apparent strain for zero load after fracture larger than that corresponding the monoliths of the same composition as that of the external layers. Moreover, the stress drop of the laminate samples occurred in step-like form thus suggesting the occurrence of additional energy consuming processes during fracture.Ítem Energy, Environmental and Technical Assessment for the Incorporatión of EAF Stainless Steel Slag in Ceramic Building Materials(Elsevier, 2017) Galán-Arboledas, Rosendo; Álvarez-de-Diego, Javier; Dondi, Michele; Bueno, SalvadorThe paper studies the addition of electric arc furnace stainless steel (EAF-SS) slag to clay raw materials for ceramic brick manufacturing in order to get more sustainable materials without compromising their final properties. Different amounts (10 wt%, 20 wt% and 30 wt%) of EAF-SS slag were added to a reference clay material. The samples were processed by extrusion and the main technological properties were deter-mined to characterize the behavior of the materials during the shaping and drying processes (working moisture, drying linear shrinkage and modulus of rupture) and the final properties of sintered materials (bulk density, linear shrinkage, water absorption and modulus of rupture) at five maximum temperatures (850, 900, 950, 1000 and 1050 C). The environmental impact was evaluated by qualitatively analyzing gaseous emissions during firing and by leaching tests on laboratory specimens. Furthermore, energy demand and fuel (natural gas) required to produce the formulated compositions, according to a standard industrial scale, was calculated in both the dryer and the kiln. Calculation of CO2 emissions during such theoretical industrial processing was also performed. Results show that the incorporation of EAF-SS leads in general to adequate technological properties and causes a potential saving of up to 17% of natural gas consumption and a reduction in CO2 emissions of up to 24% during manufacturing materials with 30 wt%of EAF-SS slag at 950 C. However, in these materials the higher metals leaching potential would restrain the EAF-SS slag incorporation to a content of about 10 wt% or less and to sintering temperatures >950 C. Therefore, clay ceramics incorporating EAF-SS slag in their composition can be technologically feasible and environment-friendly depending on both sintering temperature and amount of waste addition.Ítem Evaluation of spent diatomite incorporation in clay based materials for light-weight bricks processing(Elsevier, 2017) Galán-Arboledas, Rosendo J.; Cotes Palomino, María Teresa; Bueno, Salvador; Martínez García, CarmenIn this study, diatomaceous earth residues from two industrial processes, refining of vegetable oils and brewing, have been used as raw materials for brick making. The aim has been to substitute part of the clay traditionally used for the manufacturing of bricks, between 3 and 10 wt.%, with the aforementioned residues, so obtaining ceramic pieces at three firing temperatures: 850, 950 and 1050 C. The studied properties were compared with those of conventional materials (100% clay), and the results show that these alternative raw materials can be considered technological ‘‘nutrients” whose addition improves the behaviour of the materials in the drying process. The incorporation of these materials also increases the open porosity of the fired pieces and reduces the bulk density by up to 10%. The increase in porosity is greater in materials that incorporate diatomites from oil filtration, reaching the maximum value (37 vol.%). These results are confirmed from the microstructure observed by SEM. With regard to mechanical properties, increasing the content of both residues generally decreases the bending strength to values exceeding 10 MPa, thus resulting admissible for use in construction. Moreover, the energy release from the residues during the firing stage is greater than the energy demand required for drying, while the ther-mal conductivity values of the final materials decreases with the amount of residue, which confers ther-mal insulating properties to the ceramic pieces and thus can reduce the energy consumption of buildingsÍtem Fracture behaviour of microcrack-free alumina-aluminium titanate ceramics with second phase nanoparticles at alumina grain boundaries(Elsevier, 2008) Bueno, Salvador; M. Helene, Berger; Moreno, RodrigoÍtem Improved wear behaviour of alumina-aluminium titanate laminates with low residual stresses and large grained interfaces(Elsevier, 2011) Bueno, Salvador; Micele, Lorenzo; Melandri, Cesare; Baudín, Carmen; de-Portu, GoffredoThe wear behaviour of a monolithic alumina and an alumina–aluminium titanate laminated structure was studied. The laminate, containing surface fine grained alumina layers and internal composite layers with 10 vol.% of aluminium titanate, showed relatively low (∼=20 MPa) compressive residual stresses at the surface. Interfaces between layers were constituted by large alumina grains (up to =50 m) that promoted toughening due to crack deflection and branching. Wear tests were performed on square specimens (30 mm × 30 mm × 6 mm) using the pin-on-disc method. The laminates showed higher wear resistance than the monolithic alumina. The analysis of the results together with SEM-EDX observations was performed to identify possible wear mechanisms. The wear resistance improvements are discussed in terms of the residual stresses in the laminate and the properties provided by the special microstructure of the interfaces.Ítem Layered materials with high strength and flaw tolerance based on alumina and aluminium titanate(Elsevier, 2007) Bueno, Salvador; Baudín, CarmenLaminates in which high strength external layers and flaw tolerant internal layers with similar compositions are combined, can provide improved mechanical behavior in relation to that of monolithic materials with the same composition as the layers. The limitation of this design, in which no residual stresses are present, is the difficulty that involves the co-sintering of layers with large microstructural differences in the green state. This work describes a new method to obtain laminates constituted by layers with large differences in terms of grain size starting from green bodies with similar microstructures. The approach is based on the effect of small amounts of titania as agents for alumina grain growth enhancement. Starting from fine grained green bodies that combined alumina layers with composite layers made of mixtures of alumina and titania, additional "in situ" formed layers constituted by large (≅20-30µm) alumina grains were found after sintering contiguous to the composite layers. The thickness of the "in situ" formed layers reached up to 200 µm, depending on the thermal treatment (1450-1550ºC). The fracture behaviour of the laminates and the monoliths was studied, using stable SEVNB (Single Edge V Notched Beam) tests, in terms of work of fracture and the critical stress intensity factor in mode I, KIC. The large grain sized alumina layers reinforced the laminates by crack branching and bridging.Ítem Non-destructive characterization of alumina/aluminium titanate composites using a micromechanical model and ultrasonic determinations. Part I. Evaluation of the effective elastic constants of aluminium titanate.(Elsevier, 2008) Bueno, Salvador; González-Hernández, Margarita; Sánchez-Martín, Teresa; Anaya-Velayos, José Javier; Baudín, CarmenA method to evaluate the elastic constants of aluminium titanate in alumina/aluminium titanate composites is described. Results are derived from a three-phase micromechanical model proposed to relate the velocity of propagation of ultrasounds in the materials with their microstructural characteristics and the elastic behaviour of the constituents. Dense and un-cracked alumina and alumina + 10 vol.% aluminium titanate specimens have been fabricated by colloidal processing and the longitudinal and transverse ultrasound velocities have been determined by the ultrasonic jointly pulse-echo and transmission ultrasound immersion techniques, employing a digital signal processing. In order to assure the adequacy of the proposed method, results for monophase alumina have been compared to those obtained from the resonance frequencies of high density alumina plates tested in flexure and shear. The values of elastic moduli obtained using the two methods were coincident, which assured the validity of the non destructive proposed method.Ítem Processing of alumina-coated tetragonal zirconia materials and their response to sliding wear(Elsevier, 2010) Bueno, Salvador; Ferrari, Begoña; Melandri, Cesare; de-Portu, Goffredo; Baudín, CarmenAlumina-coated tetragonal zirconia stabilised with 3 mol% of Y2O3 (YTZP) specimens (30 mm × 30 mm × 6 mm) have been obtained by dipping of pre-sintered YTZP compacts in alumina suspensions and subsequent sintering. The coated specimens present hardness values and a wear resistance similar to those of reference dense alumina specimens and significantly higher than those of the YTZP substrates. The optimisation of the processing parameters is described. First, YTZP compacts with different open porosity levels were fabricated by colloidal filtration and subsequent thermal treatment at temperatures ranging from 1100 to 1400 °C. Coated compacts were obtained by dipping the porous ones in alumina suspensions prepared in ethanol with two different solid loadings: 3 and 10 vol.%, during immersion times up to 40 min. Sintering (1500 °C–2 h) of the coated compacts was performed and microstructural analysis allowed the selection of the optimum porosity levels for the YTZP substrates and dipping conditions. For the optimised conditions, YTZP plates (30 mm × 30 mm × 6 mm) were coated and the thermal treatment to reach densification of the substrate and the coating was optimised. Relatively thick coatings (≅200 μm) were obtained. Hardness and wear resistance were evaluated for sintered monolithic and coated YTZP compacts and an alumina reference material and the wear damage of the tested specimens was analysed.Ítem Reaction sintered Al2O3/Al2TiO5 microcrack-free composites obtained by colloidal filtration(Elsevier, 2004) Bueno, Salvador; Moreno-Botella, Rodrigo; Baudín, CarmenDense and microcrack-free Al2O3 / Al2TiO5 composites (10, 30 and 40 vol. % of Al2TiO5) have been obtained by colloidal filtration and reaction sintering, using alumina and titania as starting powders. The processing of the composites has been studied focusing on the rheological behaviour of aqueous suspensions of each powder and of mixtures. Colloidal filtration of optimised suspensions, with a solid loading as high as 50 vol. %, and a thermal treatment at 1450ºC, lead to completely reacted and uncracked sintered materials with homogeneously distributed aluminium titanate contents up to 40 vol. % and high density. Thermal diffusivity values from 25 to 800ºC are coincident on heating and cooling for the three studied composites, and decrease with temperature and with aluminium titanate content.Ítem Reduced strength degradation of alumina-aluminium titanate composite subjected to low-velocity impact loading(Elsevier, 2008) Bueno, Salvador; Micele, Lorenzo; Baudín, Carmen; de-Portu, GoffredoThe impact behaviour of monophase alumina and alumina-aluminium titanate monolithic composite ceramics that present flaw tolerant behaviour was studied. Low-velocity impact loading tests were performed on bending bars and the residual strength after the impact was evaluated by 4-point bending tests. The impact tests were monitored using an instrumented drop-weight machine. During impact, the composites absorbed higher energy than the monophase material. The strength retention, in percentage, after the impact was significantly higher for the composite that presented damage tolerance for impact energy levels higher than monophase alumina. These results are discussed and fractographic analysis was used to identify the mechanisms responsible for the lower strength degradation of the composite.