Oxygen diffusion in nanostructured perovskites

Nonstoichiometric perovskite-related oxides (such as ferrites and cobaltites, etc.) are characterized by fast oxygen transport at ambient temperatures, which relates to the microstructural texturing of these materials, consisting wholly of nanoscale microdomains. We have developed an inhomogeneous diffusion model to describe the kinetics of oxygen incorporation into nanostructured oxides. Nanodomain boundaries are assumed to be the high diffusivity paths for oxygen transport whereas diffusion into the domains proceeds much slower. Using Laplace transform methods, an exact solution is found for a ramped stepwise potential, allowing fitting of the experimental data to theoretical curves (in Laplace transforms). A further model generalization is considered by introducing additional parameters for the size distribution of domains and particles. The model has been applied for qualitative evaluation of oxygen diffusion parameters from the data on wet electrochemical oxidation of nano-structured perovskite SrCo_0.5Fe_0.2Ta_0.3O_{3-y} samples.Comment: Submitted for ICCMR-7 conference (Italy). Latex (elsart.cls), 15 pages, 7 figure

Distortion in a 7xxx aluminum alloy during liquid phase sintering

The distortion in a sintered 7xxx aluminum alloy, Al-7Zn-2.5Mg-1Cu (wt. pct), has been investigated by sintering three rectangular bars in each batch at 893 K (620 °C) for 0 to 40 minutes in nitrogen, followed by air or furnace cooling. They were placed parallel to each other, equally spaced apart at 2 mm, with their long axes being perpendicular to the incoming nitrogen flow. Pore evolution in each sample during isothermal sintering was examined metallographically. The compositional changes across sample mid-cross section and surface layers were analyzed using energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy depth profiling, respectively. The two outer samples bent toward the middle one, while the middle sample was essentially distortion free after sintering. The distortion in the outer samples was a result of differential shrinkage between their outer and inner surfaces during isothermal sintering. The porous outer surface showed an enrichment of oxygen around the large pores as well as lower magnesium and zinc contents than the interior and inner surface of the same sample, while the inner surface was distinguished by the presence of AlN. The differential shrinkage was caused by different oxygen contents in local sintering atmosphere and unbalanced loss of magnesium and zinc between the outer and inner surfaces

ТЕРМОДИНАМИЧЕСКОЕ МОДЕЛИРОВАНИЕ ВЗАИМОДЕЙСТВИЯ Y2O3 С РАСПЛАВАМИ НА ОСНОВЕ Nb–Si

The thermodynamic modeling of interaction of yttrium ceramic with Nb–Si based molten alloys alloyed with Ti, Cr, Hf, Al has been performed. Formation of solid HfO2 oxide is shown to be the result of such interaction, and other elements are not involved practically in the chemical interaction. It is found in the course of modeling that yttrium reduction due to ceramic dissolution in the molten metallic solution is the main mechanism of interaction. The Y content in the solution depends on the temperature, metallic phase composition, and quantity.Проведено термодинамическое моделирование взаимодействия иттриевой керамики с расплавами на основе Nb–Si, легированными Ti, Cr, Hf и Al. Показано, что результатом их химического взаимодействия является образование твердого оксида гафния (HfO2), а остальные элементы в нем практически не участвуют. В ходе моделирования выявлено, что основным механизмом взаимодействия является восстановление иттрия при его переходе из керамики в металлический раствор, в котором содержание Y зависит от температуры, состава и количества металлической фазы

The potential to encode sex, age, and individual identity in the alarm calls of three species of Marmotinae

In addition to encoding referential information and information about the sender’s motivation, mammalian alarm calls may encode information about other attributes of the sender, providing the potential for recognition among kin, mates, and neighbors. Here, we examined 96 speckled ground squirrels (Spermophilus suslicus), 100 yellow ground squirrels (Spermophilus fulvus) and 85 yellow-bellied marmots (Marmota flaviventris) to determine whether their alarm calls differed between species in their ability to encode information about the caller’s sex, age, and identity. Alarm calls were elicited by approaching individually identified animals in live-traps. We assume this experimental design modeled a naturally occurring predatory event, when receivers should acquire information about attributes of a caller from a single bout of alarm calls. In each species, variation that allows identification of the caller’s identity was greater than variation allowing identification of age or sex. We discuss these results in relation to each species’ biology and sociality