Estudos de moagem de alta energia e sinterização de cerâmicas de Al2O3+Ta2O5 para uso em reatores de geração de energia com recirculação química

Abstract

Due to the global warming effects on weather, the use of substances to capture CO2 and hydrogen generation technologies may contribute to the reduction and emission of pollutants and, consequently, renewal generation of clean and alternative energy. In this regard, the use of materials, which can be reduced and, in a subsequent stage, be oxidized, provide an opportunity to use it as power generation reactors of "chemical looping combustion-CLC (CO2 and water generation)" and "chemical looping reforming-CLR (generation of CO and H2). Typically the use of ceramic nanoparticles is required to ensure a high surface area. This ceramic is prepared by conventional techniques of solution and precipitation. The high energy milling has been used for the preparation of different ceramic materials with higher value of fracture toughness. Thus, the present work aims at evaluating physicochemical properties of ceramics of Al2O3 + Ta2O5 (molar ratio of 50:50 and 95:5) prepared by high energy milling and subsequent sintering. The milling process was conducted in Fritsch P-5 planetary ball mill using vessels (225 mL) and balls (10 mm diameter) of silicon nitride, speed at 300 rpm and a mass ratio 10:1. To verify the effect of milling on possible phase transformations, powders mixtures Al2O3 + Ta2O5 were processed at different times: 0, 120, 300 and 600 minutes. As a result, powders were compressed in form of cylinders by axial loading (187 MPa), which were heated in air at 900-1200°C during 4 hours. As-milled powder and sintered samples were characterized by using x-ray diffraction techniques, BET analysis, Helium pycnometry and thermal analyses (DSC/TG). To evaluate selectivity of multiple reactions and the potential to use in CLC system or CLR, the prepared ceramics were rendered in reactors to evaluate their characteristics of reduction and oxidation. Results indicates that high-energy ball milling and subsequent sintering have contributed to form the AlTaO4 compound and Al2O3+AlTaO4 composite from the 50mol%Al2O3+50mol%Ta2O5 and 95mol%Al2O3+5mol%Ta2O5, respectively. However, the as-milled powder presents low surface area, which has even been more reduced after sintering the compacted samples. Evaluated materials (sintered samples) present no tendency of oxidation and reduction when exposed in reducing and oxidizing atmosphere, accordingly, due to their low surface areas and/or high chemical stability of AlTaO4.