Browsing by Author "Dias, Diamantino"
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- Cerâmicos técnicos : materiais que vale a pena conhecerPublication . Dias, Diamantino; Almeida Costa Oliveira, FernandoRESUMO: São passadas em revista, de forma sucinta, as propriedades e as aplicações dos principais cerâmicos técnicos disponíveis no mercado.
- Fracture toughness of dense cordierite: sintering cycle effectPublication . Oliveira, Fernando Almeida Costa; Fernandes, Jorge Cruz; Schmitt, Julien; Rosa, Luís Guerra; Dias, DiamantinoThe aim of this work was to analyse the fracture behaviour of commercial dense cordierite bodies sintered in an electrical furnace in static air at 1250ºC, 1275ºC and 1300ºC for 30 min using different cycling schedules in order to obtain tougher materials at minimum energy costs. Using a stereomicroscope and a scanning electron microscope, fracture surfaces of as-sintered bars tested under four-point bending at room temperature were examined at different magnification levels in order to determine the origin of fracture in each sintered bar. Once the fracture origin was identified, it was possible to measure its size, and based on ASTM C1322-96a standard, we were able to estimate the fracture toughness of the sintered parts. Fracture toughness was found to increase with increasing of sintering temperature from 1.8 MPa·m½ to 3.1 MPa·m½ by rising the temperature from 1250ºC to 1300ºC as the fracture process is strongly influenced by the microstructure of the material.
- A New Insight into the Role of Silicate-Type Binders on the Crushing Strength of Alumina FoamsPublication . Oliveira, Fernando Almeida Costa; Pommier, Stéphane; Fernandes, Jorge Cruz; Dias, DiamantinoABSTRACT: Semi-closed cell macroporous alumina foams with relative densities ranging from 0.26 to 0.35 have been produced by the well-established replication method based on the coating of a polyurethane (PU) template foam by a ceramic slurry, followed by burnout of the PU template, and sintering of the ceramic skeleton. Collapse of the three-dimensional structure upon the volatilisation of the PU sponge can only be prevented using appropriate binders. Scarce data are available on the slurry formulations of commercial alumina foams. The aim of this study was to investigate the influence of silicate-type binders, namely kaolin and bentonite additives, on the crushing strength of alumina foams. The highest crushing strength of around 10 MPa was observed at a porosity of 66 +/- 2%. The open-cell model is inadequate to fit the crushing strength data of such semi-closed cell type structures. Both microscopic and macroscopic flaws resulting from the foam processing method contribute to the wide scatter of the strength, thereby explaining the Weibull modulus ranging from 4 to 7. Both flaw populations require further improvement to maximise the crushing strength of these foams with high potential for the design of structured catalyst carriers and molten aluminium filters.