RESUMEN
Emanation thermal analysis (ETA), differential thermal analysis (DTA), thermogravimetry (TG), evolved gas analysis with mass spectrometric detection (EGA-MS), and X-ray diffraction (XRD) were used to investigate the formation of perovskite type lanthanum ruthenates on heating their hydroxide precursor in argon from 20 to 1200 degrees C. The co-precipitated lanthanum-ruthenium mixed hydroxide containing a small amount of carbonates was used as a precursor. The mass loss corresponding to the release of water and CO(2) from the precursor was determined by TG and EGA (MS), respectively. The ETA characterized the exposure of sample surface after release of water and CO(2), as well as microstructure development corresponding to the crystallization and structure ordering of LaRuO(3) and La(3.5)Ru(4.0)O(13) perovskite phases. The obtained information on formation of phases and their transformation is useful for optimizing their synthesis protocols for achieving the desired physical properties, and to estimate the thermal stability of these materials to be used as catalysts.
RESUMEN
This paper describes a unique phenomenon occurred during the calcination of ZnO powders, i.e., the ZnO particles self-assembled to form prismatic aggregates with a clear edges and faces. Field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were used to characterize the particle morphology and crystal structure of the calcined sample. The emanation thermal analysis (ETA) technique was used to monitor the changes of ZnO particle surface and subsurface microstructure irregularities and the occurrence of interparticle compaction phenomena under in situ conditions of heating and cooling. It was assumed from the ETA results that the driven force of the self-assembly of ZnO particles towards prismatic aggregates originated from the solid state diffusion and migration of grain boundaries. The photocatalytic tests indicated that the prismatic aggregates of ZnO calcined at 800 degrees C demonstrated a highest photocatalytic activity for acetaldehyde decomposition because of the enhancement of the surface-exposed high-active crystal face of (101 0).
RESUMEN
Thermogravimetry (TG) and differential thermal analysis (DTA) were used to investigate the oxidation behavior of Ru/TiO2 and metallic Ru fine particles during heating in air in the range 20-1000 degrees C. Temperature ranges of the oxidation for two samples of Ru/TiO2 with the compositions (92 wt% Ru, 8 wt% TiO2) and (75 wt% Ru, 25 wt% TiO2) and for pure metallic Ru fine particle agglomerates were determined. It was assumed that after the partial oxidation of Ru in the sample containing 75 wt% Ru and 25 wt% TiO2 and in the pure metallic Ru a diffusion barrier was formed, preventing further oxidation of Ru in Ru/RuO2 and Ru/RuO2/TiO2 matrices. XRD and TEM were used for the sample characterization.
RESUMEN
Emanation thermal analysis (ETA), thermogravimetry (TG), differential thermal analysis (DTA), X-ray diffraction analysis (XRD), and transmission electron microscopy (TEM) were used for the characterization of thermal behavior of hydrous oxides (RuO(2))(x)-(TiO(2))(1-x).nH(2)O and dehydrated oxides (RuO(2)) (x)-(TiO(2))(1-x), respectively (x=1, 0.9, and 0.7) on heating in argon and argon +10% hydrogen, respectively. The samples were heated in the range 20-600 degrees C at the constant heating rate 6 K/min. From the TG and DTA results the temperature intervals of dehydration and/or reduction of ruthenium dioxide into Ru metal were determined. ETA (based on the measurement of radon previously incorporated into the sample) brought about the information about surface area development and microstructure changes in the near surface layers up to 80 nm under in situ conditions of the heating. The temperature intervals of the annealing of near surface and structure defects serving as diffusion paths for radon were determined from the ETA results.
