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- Characterization of a Functionally Gradient Ceramic Based on CaZrO3 – MgOPublication . Babo, Débora Rafaela Telha de; Nunes-Pereira, João; Silva, Pedro D.; Pena, Pilar; Baudin, Carmen; Pereira Silva, AIn the case, where the structure is exposed to severe conditions of operation, such as high strength, wear and high-temperature gradients (e.g. engine components, insulation system, thermal barrier and thermal shield) must be applied. In this work, it was developed and characterized a functional gradient ceramic coating. A ceramic composite based in CaZrO3 – MgO was used in order to design a material with successive layers of molar composition 2:3, 1:1 and 1:3 of CaZrO3:MgO, respectively. A dense material was obtained by sintering assisted reaction (Figure 1). Thermal conductivity at room temperature, hardness, fracture toughness, surface energy, and microstructure were characterized.The results show for monolithic specimens of 2:3 CZ, 1:1 CZ and 1:3 CZ a H of 9,9 GPa, 9,8 GPa and 10,1GPa; a Kc of 1,6 MPa.m1/2, 1,7 MPa.m1/ and 2,1 MPa.m1/2; a k of 0,59 W/mK; 0,76 W/mK and 0,79 W/mK; and a surface energy (SE) of 43,27 mN/m, 51,39 mN/m and 46,55 mN/m, respectively. The functional gradient ceramic shows a H of 10,7 GPa, a Kc of 1,97 MPa.m1/2; a k of 0,82 W/mK and SE of 53,98 mN/m. The individual composition and the functional gradient ceramic show a similar relative density of 4,3 g/cm3 and a porosity of 0,2%. This design methodology has the advantage of allowing the properties of the same material to suit different substrates.
- Development and characterization of ceramic composites based on CaZrO3-MgOPublication . Nunes-Pereira, João; Pena, Pilar; Baudin, Carmen; Pereira Silva, AAdvanced materials for severe environment conditions, such as high temperature, wear and high erosion and corrosion, are of growing interest, namely for transport and energy industries. Particularly, in aerospace industry the increase of working temperature of engines and turbines combined with weight reduction will give rise to higher thrust and lower fuel consumption and consequently less emissions. In this sense, new ceramic multiphasic composites based on calcium zirconate (CaZrO3) and magnesium oxide (MgO) are being proposed with suitable thermal, mechanical and chemical properties for severe conditions application. In the present work, an equimolar composition of CaZrO3-MgO, processed from easily and accessible synthetic raw materials, have been developed and the particle size distribution optimized by milling under controlled conditions. CaZrO3-MgO ceramic composites uniaxially pressed disks have been produced by rate controlled sintering during 2 hours at 1400, 1450 and 1500 ºC, respectively. The physical, microstructural and mechanical properties, have been assessed to evaluate the performance and suitability of the processed materials for high responsibility applications. A homogeneous microstructure was obtained for all sintering temperature samples with porosities ranging between ~10 %, for samples sintered at 1400 ºC, to ~100 % theoretical density for samples sintered at 1500 ºC. Diametral compression strength follows the Weibull distribution with characteristic strengths between ~50 and 170 MPa, Vickers hardness reach values above 8 GPa, while the facture toughness present values between 2 and 3 MPa.m1/2, for 1400 and 1500 ºC respectively. These results show that the ceramic composites based on CaZrO3-MgO sintering at 1500 ºC proved to be a suitable alternative to high responsibility applications.
- Design and Thermal Conductivity Characterization of a Functionally Gradient Ceramic Based on CaZrO3 – MgO CompositionPublication . Babo, Débora Rafaela Telha de; Nunes-Pereira, João; Pereira Silva, A; Pena, Pilar; Baudin, CarmenSpace exploration involves the use of state-of-the-art technologies such as satellite production, propulsion systems, avionics, aerodynamics, research and development of materials, etc. In the particular case of human spaceflight, the insulation system of the spacecraft is also required in order to ensure crew safety in re-entry of the atmosphere and, if possible, the spacecraft re-use. In the case, where the structure is exposed to high temperature gradients, among other systems a thermal barrier must be used for the structure in order to protect it from critical damage. Based on this concept, in this work it was developed and characterized a design of a functional gradient ceramic coating. Recently, several studies have proposed the stoichiometric composition of calcium zirconate (CaZrO3) as a viable alternative for harsh environments subjected to high temperatures, corrosion and wear, and the mechanical properties of this compound can be improved through a solid solution ion order to obtain a CaZrO3-MgO multiphase ceramic composites. In this work, a functional gradient material was produced with successive layers with variation in its molar composition (1:3, 1:1 and 2:3 of CaZrO3:MgO) and its thermal conductivity characterized.
- Advanced CaZrO3-MgO Ceramic Compositions for High Responsability ApplicationsPublication . Nunes-Pereira, João; Pereira Silva, A; Pena, Pilar; Baudin, CarmenThe development of new advanced materials for harsh environment operation conditions, such as high temperature, wear and severe erosion and corrosion, is of growing interest, namely for transport and energy industries, due to the ecological and energetic current concerns on a global scale. Particularly, in aerospace industry the increase of working temperature of engines and turbines combined with weight reduction will give rise to higher thrust and lower fuel consumption and consequently less emissions. [...]
- Young’s modulus and hardness of multiphase CaZrO3 -MgO ceramics by micro and nanoindentationPublication . Silva, Abílio P.; Booth, Fernando; Garrido, Liliana; Aglietti, Esteban; Pena, Pilar; Baudin, CarmenThe aim of this work is to determine the values of the hardness and elastic modulus of the phases present in CaZrO3-MgO-ZrO2 composites and to analyse their contribution to the composite properties. Two materials previously developed with the same major phases (CaZrO3, MgO and c-ZrO2) present in different volume fractions and grain size have been analysed. The hardness and Young´s modulus of each phase determined by nanoindentation are independent from the specific composite and coincident with nanoindentation values for single phase bulk materials. The contribution of the individual phases to Young´s modulus of the multiphase materials is in agreement with calculations using the nanoindentation values and the Voight upper limit of the “rule of mixtures”. Scale dependence due to microcracking has been observed for microhardness values of the composites and differences between calculations and experimental values are related to this effect.