Influence of Thermal Aging Phenomena on Thermoelectric Properties of Al-Substituted ZnO

The thermoelectric properties and stability of Al-substituted ZnO as a potential high-temperature n-type material were studied in heating-cooling cycles. Zn1−x Al x O (x=0.02, 0.06) was prepared by soft chemistry and solid-state reaction synthesis methods. Cycling during the thermoelectric measurement leads to an increase of the electrical resistivity and Seebeck coefficient values. The reason for this aging phenomenon can be assigned to a change in composition due to oxygen uptake along with modification in the defect concentrations. The aging is enhanced if the cycling is performed in oxygen. ZT value of 0.21 is reached at 1275K for samples with 2% Al substitution made by soft chemistry synthesi

Microscopic investigation of soot and ash particulate matter derived from biofuel and diesel: implications for the reactivity of soot

Investigation of soot and ash particulate matter deposited in diesel particulate filters (DPFs) operating with biofuel (B100) and diesel (pure diesel: B0 and diesel80/biofuel20 blend: B20) by means of optical microscopy, scanning electron microscopy, and high resolution transmission electron microscopy (HRTEM) reveals the following: the rapeseed methyl ester biofuel used for this study contributes to ash production, mainly of Ca-S- and P-bearing compounds ranging in size between 50 and 300nm. Smaller ash particles are less common and build aggregates. Ash is deposited on the inlet DPF surface, the inlet channel walls, and in B100-DPF at the plugged ends of inlet channels. The presence of Fe-Cr-Ni fragments, down to tens of nanometers in size within the ash is attributed to engine wear. Pt particles (50-400nm large) within the ash indicate that the diesel oxidation catalyst (DOC) upstream of the DPF shows aging effects. Radial cracks on the coating layer of the DOC confirm this assumption. The B100-DPF contains significantly less soot than B20 and B0. Based on the generally accepted view that soot reactivity correlates with the nanostructure of its primary particles, the length and curvature of graphene sheets from biofuel- and diesel-derived soot were measured and computed on the basis of HRTEM images. The results show that biofuel-derived soot can be more easily oxidized than diesel soot, not only during early formation but also during and after considerable particle growth. Differences in the graphene sheet separation distance, degree of crystalline order and size of primary soot particles between the two fuel types are in line with this inferenc

Sensors on Textile Fibres Based on Ag/a-C:H:O Nanocomposite Coatings

In this contribution we present a study of the vacuum deposition process of metal/plasma polymer nanocomposite thin films monitored using plasma diagnostics (optical emission spectroscopy). We investigate the electrical properties of the nanocomposite structures suitable for their application as humidity sensors. Furthermore, the film microstructure is characterized by transmission electron microscopy and electron diffraction analysis. The amount of silver in the nanocomposite is evaluated using inductively coupled plasma optical emission spectrometry and the morphology of the structured system of metal electrodes and nanocomposite films on monofilament textile fibres is visualized using scanning electron microscopy. Ageing of nanocomposite coatings and the influence of an aqueous environment on their internal structure and properties are discussed

The influence of defects formed by Ca excess and thermal post-treatments on the persistent luminescence of CaTiO_3:Pr

Red emitting CaTiO3:Pr phosphors with a nominal composition of Ca0.998+xPr0.002TiO3+δ (0.02≤x≤0.04) were prepared by solid state reactions with different thermal post treatments and characterized by X-ray diffraction, transmission electron microscopy and photoluminescence. The Ca excess exhibited complete solubility up to 4% in the samples treated at 1400 °C but segregation in the form of Ruddlesden-Popper phases (Ca3Ti2O7 - Ca4Ti3O10) was observed in samples prepared at 1500 °C. The increase in temperature for stoichiometric samples showed a monotonic increase of decay time due to the reduction of non-radiative recombination defects. It was found that the Ca excess favored the formation of oxygen vacancies which are known to act as trap. In the samples treated at 1400 °C, 3% of Ca excess showed to be the best concentration to increase the decay time of persistent luminescence. For the samples treated at 1500 °C, the segregation of Ruddlesden-Popper phases left a constant amount of Ca soluble in all the CaTiO3 samples. This constant concentration of Ca caused the same density of defects and, consequently, the same decay time in all samples