Internal Oxidation of an Ag–1.3 at.% Te Alloy

The internal oxidation of Ag–1.3 at.% Te was studied at 750, 800, and 830°C in pure oxygen (1 atm). The internal oxidation under such high oxygen pressure resulted in formation of two different types of oxide particles and two different fronts of internal oxidation in the internal oxidation zone. The coarser Ag₂TeO₃ particles were formed through the in situ internal oxidation of Ag₂Te particles and the tiny oxide precipitates (most probably also Ag₂TeO₃) were formed through internal oxidation of tellurium from solid solution. Considering the mechanism of internal oxidation, both diffusionless and diffusive modes were found to be present simultaneously in the oxidation of Ag–1.3 at.% Te alloy. These results were examined with regard to the solubility of tellurium in silver, which was found to be 0.1 at.% Te at 750°C and 0.26 at.% Te at 830°C, as well as the presence and dissolution of Ag₂Te particles.     

Anomalous dilatation-temperature curves of PZT-ZrO2 composites

The dilatation-temperature curves of the PZT-ZrO₂ composites, containing 1.3–13.2 vol% ZrO₂ were studied. The course of martensitic transformation (MT) of dispersed ZrO₂ particles in the PZT matrix was followed. Upon cooling, a spontaneous microcrack formation occurred during the MT from tetragonal to monoclinic crystal phase of ZrO₂. The phenomenon of intensive shrinkage above 800 °C upon heating is explained as a process of microcrack healing in the presence of the PbO-rich liquid phase.     

Lattice Dynamics and Phase Transitions in KNbO3 and K0.5Na0.5NbO3 Ceramics

Phonons in both ceramic samples KNbO₃ (KN) and K_0.5Na_0.5NbO₃ (KNN-50) were investigated from 10 to 900 K by means of Raman, infrared, and THz spectroscopy. First-order transitions from cubic to tetragonal phases were detected at about 755 K (in KN) and 710 K (in KNN-50), where the first component of the polarization appears. Transitions from the tetragonal to the orthorhombic phases take place around 510 and 475 K, respectively. The last transitions from orthorhombic to rhombohedral phases are strongly first-order type. T_C is shifted from 200 K in KN to about 90 K in KNN-50. All Raman active modes below 200 cm^-1. disappear in KN but not in KNN-50. The overdamped soft mode present at high temperatures in the THz range changes its dielectric strength at each phase transition (when the corresponding component jumps to higher frequencies) and abruptly disappears from THz spectra in the rhombohedral phase, because it stiffens up to 200 cm^-1. This mode has lower frequency and higher dielectric strength in KNN-50.     

On activated sintering and electrical properties of NaKNbO3

Sintering of Na_0.5K_0.5NbO₃ may be activated by slight excess of Nb⁵⁺ ions or by incorporation of Mg²⁺ ions into crystal lattice. By this means, high density samples (97% TD) were prepared by conventional sintering technique. Mg-doped sintered samples exhibit increase in k_p, some lowering in ε and large increase in resistivity after prolonged sintering.     

A simple synthesis method for studying thermally integrated distillation sequences

In this paper an improved method for studying processes for separation of multicomponent mixtures is presented. A thermodynamically oriented procedure was developed for the analysis and synthesis of the best heat‐integrated distillation system. Systematic ranking of possible schemes was used in order to verify the best structure of a heat‐integrated distillation system. An integrability criterion was introduced for the selection of the most promising heat‐integrated sequences. Distillation columns were studied according to their ability for heat integration. The proposed selection of possible distillation columns sequences using rising integrability criteria gave a good approximation of the best heat‐integrated distillation column sequences according to their total annual cost. Computational simulation of the process and pinch analysis were used for thermodynamic optimization of energy consumption. The method is illustrated with five‐ and six‐component example problems.     

Subsolidus phase equilibria in the RuO2-Bi2O3-ZrO2 system

Subsolidus equilibria in air in the RuO₂-Bi₂O₃-ZrO₂ system were studied with the aim of obtaining information on possible interactions between a Bi₂Ru₂O₇-based cathode and a ZrO₂-based solid electrolyte in solid-oxide fuel cells (SOFCs). No ternary compound was found in the system. The tie lines are between Bi₂Ru₂O₇ and ZrO₂, and between Bi₂Ru₂O₇ and gamma-Bi₂O₃—the ZrO₂ stabilised Bi₂O₃ phase, stable at temperatures over 710 °C.     

Electrochemical impedance spectroscopy of pure copper exposed in bentonite under oxic conditions

The corrosion rate of pure copper has been followed by thin electrical resistance (ER) sensors placed in a test package containing an oxic bentonite/saline groundwater environment at room temperature for a period of more than three years. Potential measurements have verified oxic conditions in the test package. A series of electrochemical impedance spectroscopy (EIS) measurements has also been performed on the ER sensors and results from one of the sensors are presented.The impedance spectra for copper in the oxic bentonite/saline groundwater environment changed considerably with time of exposure. The impedance increased over the whole frequency range. Three methods were applied to estimate the corrosion rate from the EIS spectra.The EIS measurements have revealed decreasing but measurable corrosion rates all through the exposure period. The former reveals a desired behaviour of copper in the environment. After three-year exposure the estimated corrosion rate from the EIS measurements fell in the range 0.4–0.7 μm/year, which is somewhat lower than the value of 1.0 μm/year, obtained from the ER measurements. Gravimetric data from six years exposure in the Äspö Hard Rock Laboratory showed an average corrosion rate of 0.5 μm/year. The corrosion resistance of copper is improved by the presence of bentonite.     

Higher thyroid hormone levels in neonatal life result in reduced testis volume in postpubertal bulls

Thyroid hormones appear to determine adult testis size in rodents by regulating the period of Sertoli cell proliferation in the neonatal period. In the present study, the correlation between neonatal thyroid hormone levels (T3 and thyroxin, T4) and postpubertal testis size in Simental bulls was examined. T3 and T4 levels were measured in blood plasma from 35 calves immediately after their arrival at the AI centre at age 3-6 months. Testis size (height and width) was measured at 12 months of age in the same live animals. A significant negative correlation (r = -0.55; p < or = 0.001) was found between T4 and calculated testicular volume using either the Pearson correlation test or linear regression analysis, while the levels of T3 and testis volume showed a negative correlation, although this did not reach statistical significance (r = -0.20, p < or = 0.05). The results of this study suggest, therefore, that neonatal thyroid hormone levels might have the same effect on testicular size in cattle as they do in rodents.     

Water–based synthesis of La0,5Sr0,5CoO3 (LSCO) electrodes for ferroelectric thin films

Abstract

La_0,5Sr_0,5CoO₃ (LSCO) thin films were prepared from water solutions of lanthanum nitrate La(NO₃)₃x6H₂O, strontium nitrate Sr(NO₃)₂ and cobalt nitrate Co(NO₃)₂x6H₂O with different amounts of polyvinylalcohol (PVA). Thin films were deposited on platinum coated and thermally oxidized silicon substrates. The influence of the amount of PVA on the thermal decomposition of LSCO precursors, the surface wetting and the microstructure of LSCO thin films were investigated. The effort was also focused on the optimization of the thermal treatment to obtain dense LSCO thin films.