Metallic molybdates are of great importance for their potential use as catalysts of selective nature. The synthesis of the β-NiMoO4 phase is not simple and has been approached employing different methods; however, combustion synthesis has never been proposed before. This work describes the synthesis of nanometric β-NiMoO4 powders from mixtures of Ni (II) and Mo (VI) acetylacetonates as cation precursors and urea as fuel. The characterization of the as-prepared combustion product showed that the combustion synthesis provides a straightforward method for the achievement of β-NiMoO4. This phase, prepared by this method, is stable at room temperature in the absence of NiO. The as-prepared powders are nanometric (∼6 nm as observed by TEM) and have a specific surface area of 31 ± 7 m2/g. Both parameters are crucial for an enhancement of its catalyst activity. As the β-NiMoO4 phase is not stable at room temperature its preparation is discussed taking into account its evolution with temperature and the synthesis conditions which promote metastable phases due to a high exothermic energy release followed by a rapid cooling. The electrical conductivity is determined in air as a function of temperature and discussed in relation with the phase transition that takes place promoted by temperature.

No abstract

No abstract

La(1 - x )Sr( x )PO4 materials are very stable at high temperature and water vapor partial pressure and they show protonic conductivity; thus, they could be used as electrolytes in HTPFCs (high-temperature protonic fuel cells), hydrogen sensors, and hydrogen separation technology. This work describes the combustion synthesis of La(1 - x )Sr( x )PO4 powders (x = 0, 0.025, 0.050) from mixtures of La(NO3)3·6H2O and Sr(NO3)2 as cation precursors, (NH4)2HPO4 as anion precursor, and urea as fuel. The characterization of the as-prepared combustion products showed that combustion synthesis provides a straightforward method for the achievement of solid solutions of these materials as nanometric powders. Furthermore, dilatometric studies reveal that dense ceramics can be obtained at low sintering temperature (1300 °C), in air, from the synthesized nanometric powders.

No abstract