Advances in Science and Technology Vol. 46

Abstract: Formation of diffusion zone morphologies periodic in time and space during metalceramic reactions is considered as a manifestation of the Kirkendall effect. In a diffusion-controlled interaction, the Kirkendall marker plane can bifurcate, which is attributed to diverging vacancies fluxes in the reaction zone. When the Kirkendall plane is present in a phase layer, it attracts in situproduced inclusions of “secondary-formed phase”, which, in turn, can result in a highly patterned microstructure.

Abstract: Single phase TiO2 thin films of anatase structure have been prepared by reactive electron beam evaporation. Epitaxial (012)- and (001)-oriented anatase films were successfully obtained on (110)- and (100)-oriented SrTiO3 substrates, respectively. X-ray diffraction and cross section transmission electron microscopy investigations revealed a good epitaxial quality of the anatase films grown on the SrTiO3 substrates.

Abstract: Magnesium alloys are extremely attractive candidates for hydrogen storage applications since they can potentially absorb hydrogen between 3 and 8 wt.%. The purpose of this work is to understand the microstructural and the magnetic properties for 3d-transition metal and magnesium alloys with the difficult to alloy by the conventional method due to the positive value of mixing enthalpy. We successfully formed alloys of iron or cobalt, and magnesium powders with a wide range of compositions by mechanical alloying and characterized synthesized alloys with an X-ray diffractometer, a TEM, an SEM-EPMA and a vibration sample magnetometer. The obtained Fe-Mg alloys containing less than 25 at.% Mg were single phase bcc with expanded lattice parameter. The average powder particle size changes with Mg composition. The magnetization of the samples showed a linear dilution with content of Mg. The opposite variations in lattice parameter and the coercive force with Mg content were observed. On the other hand, we observed markedly broadened XRD lines from Co-Mg alloy compounds. The microstructure of these powders implies that the alloy could be partially amorphized or changed into a nanostructure as expected from microscopy and an XRD results.

Abstract: Different versions of thermoelectric unicouples composed of p-type Ca3Co4O9 (Co-349) and n-type LaNiO3 (Ni-113) or CaMnO3 (Mn-113) bulk materials were prepared. In the unicouples p- and n-type legs were connected with Ag electrodes using Ag paste including various oxide powders with various ratios. For the Co-349/Ni-113 unicouples, maximum output power (Pmax) reaches 177mW at a hot side temperature (TH) of 1073K and a temperature differential (ΔT) between TH and cold side temperature of 500K at 6wt% of Co-349 powder. On the other hand, the lowest internal resistance (RI) is observed in a Co-349/Mn-113 unicouple prepared using Ag paste including 3wt% of Mn-113 powder. Thermoelectric modules consisting of 8 pairs of oxide legs were fabricated using the same method with the unicouples. The open circuit voltage (VO) and Pmax increase with increasing TH and reach 0.392 V and 0.314 W, and 0.911 V and 0.233 W at a TH of 1273 K in air for the Co-349/Ni-113 and Co-349/Mn-113 modules, respectively.

Abstract: Bi2Te3 is the best compound for thermoelectric materials around the room temperature. If the temperature range is shifted to higher side, it is useful to obtain electrical energy from waste heat source which is abundant at the temperature around 500 K. In this experiment, Bi2Te3-GeTe pseudo binary compounds were investigated to shift the temperature range. The lattice thermal conductivity was remarkably decreased at 50 or 75 mol%GeTe by synergy effect of solid solution and grain boundaries. The peak temperature of figure of merit Z for Bi2Te3-GeTe pseudo binary compounds was higher than Bi2Te3.

Abstract: K2NiF4 type oxides have received considerable attention in recent years as possible mixed conducting membranes for technologically important applications such as solid oxide fuel cells and oxygen generators. Much of this interest has focused on the oxygen interstitial containing oxides such as La2NiO4+δ. This contribution will review some of the recent work on these and related materials and will present new data on the La2MO4+δ (M= Ni, Co or Mn) systems. In particular data on the oxide ion diffusivity of these systems, as determined by oxygen isotopic exchange and SIMS analysis highlighting the fast oxide ion diffusion (1 x 10-7 cm2s-1 at 750oC) present, will be discussed and the significance of these data evaluated in relation to solid oxide fuel cell systems. A further section of the presentation will consider the oxygen defect species present and discuss the nature of the mobile oxygen ions. Finally some preliminary data on the application of these materials as cathodes will be presented and the performance of the cathodes on intermediate temperature electrolytes discussed.

Abstract: Carbon-coated TiO2 photocatalysts were prepared by a simple heat treatment of the powder mixtures of anatase-type TiO2 with PVA at a temperature of 700 and 900 oC in a N2 atomosphere. Diffuse optical reflectance spectra for carbon-coated TiO2 showed the absorption edge for anatase structure clearly, overlapping with absorption due to coated carbon over whole range of wavelegth. These carbon-coated TiO2 photocatalysts had relatively high apparent BET surface area, from 50 to 170 m2/g, which suggested the formation of porous carbon layers, and showed relatively high adsorption of various pollutants, methylene blue (MB), reactive black (RB-5), phenol (Ph) and iminoctadine triacetate (IT), in water. Photocatalytic activity of carbon-coated TiO2 thus prepared was evaluated through the determination of the rate constant for the decomposition of different pollutants in water. Rate constant values were strongly depend on the pollutants, but their dependence on the crystallinity of TiO2 phase. The relations between adsorptivity and rate constant for four pollutants looked similar with each other, and the pollutants adsorbed in the larger amount was decomposed with the higher rate. Adsorptivity of carbon-coated TiO2 photocatlysts was determined and discussed on the relations to BET surface area, amount of carbon coated and also rate constant k for the decomposition of MB, RB5, Ph and IT. Adsorptivity of carbon-coated catalysts depends strongly on the adsorbate (pollutant) but also on the surface nature of carbon layer on TiO2 particles. The relations between adsorptivity and rate constant k for four pollutants looked similar, suggesting that the pollutant adsorbed in the larger amount being decomposed with the higher rate.

Abstract: We have presented general ideas to develop a theoretical methodology, based on Molecular simulation and Einstein equation aimed to describe the mechanism and behavior of chitosan-membrane ion conductivity and to obtain its magnitude for different ionic species. Atomistic molecular modelling has been utilized to construct an ionic-conducting polymer electrolyte system consisting of poly(chitosan), H O 2 molecules, and + H O 3 , − OH , 2− 4 SO ions, inside of the simulation cell. The COMPASS force field was used. The simulation allows describing the mechanism of ionic conductivity along the polymer matrix. The theoretical results obtained are compared with previously-reported experimental data for chitosan membranes. The present methodology can be considered as a first step towards understanding these complex problems of technological interest.