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ItemCompressive creep behavior of zirconia/nickel oxide composites(International Committee on Composite Materials, 2017) Huamán Mamani, Fredy; Jiménez Melendo, ManuelNickel oxide/zirconia composites with different NiO contensts have been fabricated by mechanical mixing of nickel oxide and zirconia powders and sintering at 1500 ºC for 10 h in air. The resulting microstructures have been characterized by scanning and transmission electron microscopy. The mechanical behaviour of the composites has been characterized by compressive tests at high temperatures between 1100 and 1350 ºC. For NiO contents above the percolation limit, the softer phase was found to be rate-controlling in oxidizing atmospheres, achieving extended steady states of deformation without macroscopic failure. By contrast, the overall creep strength of the composites decreased severely in reducing conditions. © 2017 International Committee on Composite Materials. All rights reserved. ItemCreep properties of polycrystalline Al2O3 – Based ceramic composites(International Committee on Composite Materials, 2017) Huamán Mamani, Fredy; Jiménez Melendo, ManuelThree-phase Al2O3 - ZrO2 - Er2O3 composites with the ternary eutectic composition were fabricated by a conventional solid-state reaction route starting from commercial powders of alumina, erbia and monoclinic zirconia. Bulk composites with relative densities higher than 98% were obtained after calcining at 1400 ºC for 10 h in air and sintering at 1500 °C in air for 10 h. X-ray diffraction and energy-dispersive X-ray spectroscopy showed the presence of the three expected phases: alumina, EAG and zirconia. The composites exhibit a homogeneous microstructure with equiaxed grains of about 1 µm in size. Mechanical tests were carried out in compression at temperatures between 1300 – 1450 °C in air. Extended steady states of deformation were attained without macroscopic damage. The stress exponent in such experimental conditions was close to 2, suggesting that grain boundary sliding is the main deformation mechanism, as found in other fine-grained ceramics. © 2017 International Committee on Composite Materials. All rights reserved. ItemStudy of the Equilibrium, Kinetics, and Thermodynamics of Boron Removal from Waters with Commercial Magnesium Oxide(Hindawi Limited, 2018) Montalvo Andia, Javier; Yokoyama, Lidia; Cesar Teixeira, Luiz AlbertoIn the present work, the equilibrium, thermodynamics, and kinetics of boron removal from aqueous solutions by the adsorption on commercial magnesium oxide powder were studied in a batch reactor. The adsorption efficiency of boron removal increases with temperature from 25°C to 50°C. The experimental results were fitted to the Langmuir, Freundlich, and Dubinin-Radushkevich (DR) adsorption isotherm models. The Freundlich model provided the best fitting, and the maximum monolayer adsorption capacity of MgO was 36.11 mg·g-1. In addition, experimental kinetic data interpretations were attempted for the pseudo-first-order kinetic model and pseudo-second-order kinetic model. The results show that the pseudo-second-order kinetic model provides the best fit. Such result suggests that the adsorption process seems to occur in two stages due to the two straight slopes obtained through the application of the pseudo-first-order kinetic model, which is confirmed by the adjustment of the results to the pseudo-second-order model. The calculated activation energy (Ea) was 45.5 kJ·mol-1, and the values calculated for ?G°, ?H°, and ?S° were -4.16 kJ·mol-1, 21.7 kJ·mol-1, and 87.3 kJ·mol-1, respectively. These values confirm the spontaneous and endothermic nature of the adsorption process and indicated that the disorder increased at the solid-liquid interface. The results indicate that the controlling step of boron adsorption process on MgO is of a physical nature. © 2018 Javier Paul Montalvo Andia et al. ItemFabrication and evaluation of the mechanical behavior of geopolymer compounds using waste from the mining and construction industry(IOP Publishing Ltd, 2021) Huamán-Mamani, F. A.; Mayta-Ponce, D. L.; Rodríguez-Guillén, G. P.Geopolymers are lately being considered a group of revolutionary materials, due to their good mechanical properties, chemical stability, fire resistance and diversity of applications where they can be used. For the synthesis of geopolymers, a great variety of types of natural and artificial raw materials (residues from other industries) can be used, which allows obtaining materials with very specific applications. Two of the most important industries in Peru are also those that generate greater environmental degradation, mainly due to the waste they generate. The mining industry has a negative impact on the environment, generating a large amount of inorganic waste, while the construction industry does the same, generating large amounts of demolition waste. Both, mining and demolition waste, constitute a serious environmental problem, since currently they are only deposited without any alternative use. Therefore, our research proposes the use of geopolymeric technology for the use of mining and demolition waste in the manufacture of geopolymeric concrete with mechanical strengths similar to that of Portland cement concrete. © 2021 Institute of Physics Publishing. All rights reserved. ItemFabrication and creep properties of eutectic-composition Al2O3/YAG/YSZ sintered composites(Elsevier Ltd, 2021) Huamán-Mamani, F.A.; Jiménez-Holgado, C.; Jiménez-Melendo, M."Three-phase alumina/YAG/yttria-stabilized cubic zirconia (YSZ) composites were fabricated by a solid-state reaction route starting from commercial powders of Al2O3, Y2O3 and monoclinic ZrO2. The final phases Al2O3, YAG and YSZ were obtained after calcination of the powder mixtures at 1400 °C. Dense bulk composites were obtained after sintering, with a homogeneous microstructure of fine and equiaxed grains with sizes of 1 μm. Compressive mechanical tests were performed at 1300–1450 °C in air at constant load and at constant initial strain rate. A brittle-to-ductile transition was found with increasing temperature. Grain boundary sliding is the main deformation mechanism in the ductile regime, characterized by a stress exponent of 2 and by the absence of dislocation activity and changes in grain morphology. Alumina seems to be the rate-controlling phase owing to the improvement in creep resistance by the presence of yttrium and zirconium of the other two phases." ItemFabrication, microstructure and high-temperature plastic deformation of three-phase Al2O3/Er3Al5O12/ZrO2 sintered ceramics(Elsevier Ltd, 2021) Huamán-Mamani, F.A.; Jiménez-Holgado, C.; Jiménez-Melendo, M."The fabrication, microstructure and high-temperature creep behavior of chemically compatible, three-phase alumina/erbium aluminum garnet (Er3Al5O12, EAG)/erbia fully-stabilized cubic ZrO2 (ESZ) particulate composites with the ternary eutectic composition is investigated. The composites were fabricated by a solid-state reaction route of α-Al2O3, Er2O3 and monoclinic ZrO2 powders. The final phases α-Al2O3, EAG and ESZ were obtained after calcination of the powder mixtures at 1400 °C. High dense bulk composites were obtained after sintering at 1500 °C in air for 10 h, with a homogeneous microstructure formed by fine and equiaxed grains of the three phases with average sizes of 1 μm. The composites were tested in compression at temperatures between 1250 and 1450 °C in air at constant load and at constant strain rate. As the temperature increases, a gradual brittle-to-ductile transition was found. Extended steady states of deformation were attained without signs of creep damage in the ductile region, characterized by a stress exponent of nearly 2 and by the lack of dislocation activity and modifications in grain size and shape. The main deformation mechanism in steady state is grain boundary sliding, as found in superplastic metals and ceramics. In the semibrittle region, microcavities developed along grain boundaries; these flaws, however, did not grow and coalescence into macrocracks, resulting in a flaw-tolerant material. Alumina is the creep-controlling phase in the composite because of the grain boundary strengthening caused by the (unavoidable) Er3+- and Zr4+-doping provided by the other two phases. © 2021" ItemMechanical characterization of new geopolymeric materials based on mining tailings and rice husk ash(IOP Publishing Ltd, 2021) Huamán-Mamani, F. A.; Mayta-Ponce, D. L.; Rodríguez-Guillén, G. P."This work presents the results of the thermomechanical evaluation of geopolymeric concrete fabricated from mining tailings, rice husk ash and fine sand. Ten types of geopolymeric concrete were studied and the relationship between the initial volumetric concentrations of the components in the mixtures and the maximum resistance in uniaxial compression under conditions of variable temperature (between ambient and 600 ºC) was analyzed. The results revealed that increases in the concentration of mining tailings and fine sand lead to an increase in the value of the maximum mechanical resistance, in contrast, the increase in the concentration of rice husk ash led to a reduction in the value of the maximum mechanical resistance. Furthermore, increases in test temperature, up to 500 °C, led to systematic increases in maximum mechanical strength. Finally, the geopolymeric concretes presented a brittle-ductile transition between 500 and 600 °C showing only a ductile behavior when tested at 600 °C and only brittle up to test temperatures of 500 °C. © 2021 Institute of Physics Publishing. All rights reserved."