Electrical impedance spectroscopy and electrical response in metal/non-metal systems

A new analysis of the electrical response of a macroscopic solid state system to an arbitrary electrical voltage input is presented. The results indicate that with a small, sinusoidal voltage input within the classical frequency range (ω < 10¹⁰Hz), the electrical response in spatially homogeneous systems mirrors first of all the static, spatial distribution of the mobile charge carrier density through the local electrical conductivity relaxation time. This enables any system, inclusive interface and electrical contact regions to be modelled by a simple, passive R, C electrical network, where each of the network elements has a very direct physical meaning. Ultra pure, single crystal silicon, pure polycrystalline silicon and Al-Al₂O₃-Au metal-insulator-metal (MIM) structure are used as illustrative examples.     

Hydrogenation of phenylacetylene and 3-phenylpropyne using Rh(diene) complexes under homogeneous and heterogeneous conditions

Hydrogenation of phenylacetylene (PA) and 3-phenylpropyne (PP) was carried out using [Rh(diene)Cl]₂ complexes (diene is hexadiene (HD), cycloocta-1,5-diene (COD), norborna-2,5-diene (NBD)) in their immobilized forms and compared with hydrogenation in homogeneous arrangement. Immobilization brings significant increase of the catalytic activity and product selectivity in the step-wise hydrogenation to corresponding vinyl-resp. allyl-benzenes. Diene-ligand effect was apparent in PA hydrogenation; the product selectivity decreased in order Rh(HD) > Rh(NBD) > Rh(COD) and catalytic activity decreased in order Rh(HD) > Rh(COD) > Rh(NBD).     

Isothermal and adiabatic Young's moduli of alumina and zirconia ceramics at elevated temperatures

The elastic moduli (Young's moduli) of alumina and zirconia ceramics with porosities ranging from almost dense (2–3%) to highly porous (46–52%), the latter prepared with starch as a pore-forming agent, have been measured via impulse excitation and four-point bending tests from room temperature up to more than 1200 °C. It is shown that, independent of the temperature and the material, the porosity dependence of the Young's modulus is well predicted by our exponential relation and that, irrespective of porosity, the temperature dependence follows a master curve that is characteristic of the material (for alumina exhibiting a decrease with a gradually growing tangent slope and for zirconia exhibiting a steep decrease with an inflection point at moderately elevated temperatures below 400 °C). Differences between isothermal (static) and adiabatic (dynamic) values are negligible as long as the materials are purely elastic (i.e. at temperatures below approximately 1000 °C).     

Project Tocoen. The Fate of Selected Organic Compounds in the Environment. Part XXVIII. Levels of PAHs and Some Halogenated POPs in Ambient Air in Czech Republic

Abstract

Concentrations of polyaromatic hydrocarbons (PAHs), chlorinated pesticides, polychlorinated biphenyls, dibenzo-p-dioxins and dibenzo-p-furans (PCDDs/Fs) in ambient air in Ko?etice, a background locality in the South Bohemia, have been estimated in the period from July to December 1994. The 24-hours samples have been taken by the means of a high-volume sampler. Sample analysis involved Soxhlet extraction of polyurethane foam, extract preconcentration and chromatographic clean-up procedure followed by HPLC determination of PAHs with fluorescence detection, GC/ECD determination of chlorinated pollutants, and GC/MS determination of PCDDs/Fs. The results of this first detailed study undertaken in Czech Republic are compared with the data obtained by similar projects in industrial and/or urban areas in the Czech Republic and in rural or urban areas in other European countries.     

Influence of uncertainty in diffusion coefficients on moisture field during wood drying

The paper presents an experimental measurement of diffusion coefficients of wood and theoretical analysis (stochastic analysis) based on influence of uncertainty in these coefficients on moisture field during wood drying simulations. Experimental measurement was used to verify of analytic equations for calculation of diffusion coefficients, which were implemented in the numerical simulations. Histograms show on normal distribution, but stochastic analysis was used for uniform distribution as well. Mean value of diffusion coefficient in tangential direction was calculated as 1.016·10^?10 m² s^?1 and standard deviation as 0.153·10^?10 m² s^?1. Stochastic analysis is based on the Monte Carlo method. The analysis proves that final moisture field has a same probability distribution as the diffusion coefficient (normal or uniform distribution) and also depicts a character of course and distribution of uncertainty in lumber during drying.     

Hygrothermal performance study of an innovative interior thermal insulation system

An innovative interior thermal insulation system on the basis of hydrophilic mineral wool which can serve as an alternative solution to the commonly used systems with water vapor barrier is presented in the paper. At first, the process of materials design is described. Then, the hygrothermal performance of the designed insulation system is tested in the difference climate conditions that correspond to the winter climate in Middle Europe. In the experiment, the profiles of temperature, relative humidity and liquid moisture content are monitored. Measured temperature profiles demonstrate the proper thermal insulation function of the system. The hygric function can also be considered very good as no water condensation during the whole testing period of five months appears in the insulation layer. Therefore, the basic requirements for the successful application of the system in building practice are met.     

Quartz Tuning Fork: Thermometer, Pressure- and Viscometer for Helium Liquids

Commercial quartz oscillators of the tuning-fork type with a resonant frequency of ∼ 32 kHz have been investigated in helium liquids. The oscillators are found to have at best Q values in the range 10⁵–10⁶, when measured in vacuum below 1.5 K. However, the variability is large and for very low temperature operation the sensor has to be preselected. We explore their properties in the regime of linear viscous hydrodynamic response in normal and superfluid ³He and ⁴He, by comparing measurements to the hydrodynamic model of the sensor. Dedicated to former JLTP editor Frank Pobell.     

Elemental analysis of instant soups and seasoning mixtures by ICP–OES

A method for the determination of Na, K, Ca, Mg, P, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn levels in high saline food products (instant soups and seasoning mixtures) using ICP–OES was developed. The results of the direct determination with multi-elemental water standards were compared with the internal standardisation, the standard addition methods and the allowable limits of the above mentioned elements in food. The method was shown to be sensitive with limits of detection: Na 1.50, K 12, Ca 0.32, Mg 0.13, P 1.1, Cd 0.16, Cr 0.21, Cu 0.32, Fe 0.30, Mn 0.17, Ni 0.42, Pb 2.1 and Zn 0.21 (in mg kg⁻¹). The method exhibited RSD 2–8%.     

Prototype of highly efficient liquid electrode pulsating corona plasma reactor for degradation of organics in water

Prototype of atmospheric pressure non-thermal corona plasma reactor, developed for degradation of organics in water, operates at significantly higher frequency than other reactors for that purpose, and without sparks. Its construction provides the umbrella shaped, sustained pulsating corona discharge, with defined discharge oscillations on a given pulse frequency above the water surface. Dye degradation rate decreases with the decrease of discharge current density. Plasmaformed H_2O_2 is consumed in dye degradation. The energy yield of dye degradation is 2.45 g k Wh~(-1) for 50 ppm solution, which is higher than in other publications for comparable experimental conditions.     

ZnO nanorods-PANI heterojunction dielectric,electrochemical properties,and photodegradation study of organic pollutant under solar light

In the last years, the development of photocatalysts has gained a growing interest in the photoelectrochemical conversion. Here, we report a hetero-junction organic/inorganic (Polyaniline (PANI)) on n type Silicon substrate prepared by electrophoretic deposition (EPD). ZnO nanorods (NRs) are grown by chemical bath deposition (CBD) on seed layer of ZnO prepared by dip coating onto the PANI layer. The relief and morphological properties are investigated by both atomic force microscope (AFM) and scanning electron microscopy (SEM). The forbidden bands (E_g) of 1.12 and 3.26 eV are obtained for PANI and ZnO_NRS respectively. The optical and dielectric constants are determined by the diffuse reflectance where the extinction coefficient (k), the refractive index (n), optical conductivity, dissipation factor and relaxation time are extracted. The semi conductivity is highlighted by the capacitance measurement; a flat band potential (E_fb = 0.541 V) for ZnO_NRs-PANI is deduced from the Mott-Schottky plot. The contributions of the bulk and grain boundaries of the electrode are evidenced from the electrochemical impedance spectroscopy (EIS). The as-fabricated samples show improved photoactivity compared to PANI and ZnO_NRs. Indeed, the hetero-junction exhibits a high stability and recyclability for the photodegradation of Orange II (OII) after six cycling runs. The current research offers a new understanding of designing a high performance of the photocatalyst under solar light based on PANI for the wastewater treatment.