Determination of diffusion and activity coefficients in the gallium-indium system by the contact-melting method

The concentration profile in the liquid layer and the rate of contact melting are derived. These characteristics are found as functions of the self-diffusion coefficients D_A and D_B of the components and of the activity coefficients in the regular-solution approximation. Comparison of these equations with the experimental concentration profile and with the experimental contact-melting rate allows calculation of D_A, D_B, and the factork in the expression for Inf in the Ga-In system.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 53–57, April, 1971.     

Single crystalline YAG:Ce phosphor for powerful solid-state sources of white light. The influence of production conditions on luminescence properties and lighting characteristics

It is shown that the spectral properties and spatial distribution of LED radiation with a YAG:Ce single crystalline luminescent converter significantly depend on the morphology of the converter surface. The variation of surface roughness enables one to obtain a light source with a wide range of color characteristics. As a result of optimization of converter parameters we demonstrate a possibility of creating a white light LED with correlated color temperature Т_CC ~ 5000–6500 K and color rendering index CRI ≈ 60–70.     

Preparation, structural analysis and dielectric properties of Bi x La1−x FeO3 perovskite

Rare earth element substituted bismuth ferrites (BiFeO₃) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi _x La_1−x FeO₃ (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz). All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity as well as ε′ are found to be maximum for the sample x=0.2 at room temperature.     

New chelating sorbents for noble metals

The properties of the new ehelate-forming “POLYORGS” sorbents for concentration of noble metals are discussed. POLYORGS are made from different polymeric matrices (polystyrene, copolymers of styréne with divinylbenzene, fibrous materials). They contain heterocyclic amine and amidoxime groups, and are selective for noble metals. Some methods of noble metal determination after preliminary concentration of POLYORGS sorbents are given.     

Spectrophotometric Methods for Determining Noble Metals

The main trends of the development of spectrophotometric methods for determining noble metals (NMs) are considered. One of these trends is the synthesis and study of new, highly sensitive and selective organic reagents for determining NMs in solutions and in solid phase. Another trend is the search for and development of new methodological approaches (techniques) and color reactions, including those that involve modified and immobilized reagents. The third trend includes the improvement of equipment and automation in FIA, CFA, derivative, rapid-scanning, and multiwavelength spectrophotometry. It also implies a new generation of instruments measuring the absorbance and reflectance of solid materials modified with organic reagents and with their NM complexes; microwave energy sources for the dissolution of samples, preparation of test solutions, and activation of photometric reactions; and multioperational analytical moduli for autoclave sample preparation with resistive heating. The present-day spectrophotometry can provide the determination of NMs in samples with concentrations from several to 10^–4% (photometry and differential photometry) and down to 10^–7% (test and sorption–spectroscopic methods based on photometry and diffuse-reflectance spectroscopy, including the use of chromaticity functions).     

Lanthanum complexation with reagents of the arsenazo III group on the solid phase of fibrous ion exchangers

Color reactions of lanthanum with reagents of the arsenazo III group on the solid phase of fibrous materials filled with an ion exchanger are studied. Substrates and reagents of various types, sorption and complexation conditions, and effects of some concomitant components are investigated. The most pronounced analytical effect is observed upon lanthanum sorption on disks with an anion exchanger containing iminodiacetate ANKB-50 groups followed by complexation on the solid phase with arsenazo III or arsenazo M in 0.05 M HCl. The reaction with arsenazo III is characterized by the lowest detection limit (5 ng/mL), and the reaction with arsenazo M is most selective.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 4, 2005, pp. 378–383.Original Russian Text Copyright © 2005 by Savvin, Shvoeva, Dedkova.     

Sorption-spectrometric determination of thorium(IV) and uranium(VI) with the reagent Arsenazo III on the solid phase of a fibrous material filled with a cation exchanger

The possibility of the use of organic reagents of the Arsenazo III group for the sorption-spectrometric determination of elements on fibrous cation-exchange materials was examined. The conditions of the sorption of Arsenazo III with the use of diphenylguanidinium chloride on the strongly acidic fibrous cation exchanger PANV-KU-2 were found. Procedures for the determination on the solid phase were developed for thorium in 7 M HNO₃ in the presence of 30-fold amounts of uranium with the detection limit of thorium of 0.005 μg/mL and for uranium in 0.05 M HCl in the presence of fivefold amounts of thorium with a detection limit of uranium of 0.05 μg/mL. The conditions were found for the selective preconcentration of thorium and uranium in the presence of each other, and a procedure was developed for their separate sorption-spectrometric determination.     

Effect of pulses from a high-power ytterbium fiber laser on a material with a nonuniform refractive index. II. Production and parameters of Nd:Y2O3 nanopowders

The laser ablation of the Nd:Y₂O₃ target with substantially nonuniform refractive index leads to the formation of a needle-shaped surface with a needle height of 6–8 mm. An increase in the displacement velocity of the laser beam on the surface to 80 cm/s and an increase in the diameter of the laser spot at the central part of the beam waist to 430 μm lead to a more uniform relief of the target surface and an increase in the nanopowder yield and production rate to 22% and 23 g/h, respectively. In addition, an excess of the mole content of the low-melting Nd₂O₃ in the powder decreases from 174 to 11% in comparison with the target. At an air pressure in the evaporation chamber of 0.8 bar, the mean sizes of nanoparticles (13–14 nm) are virtually independent of the displacement velocity of the beam on the surface (7–81 cm/s) and the rate of air flow above the target (13–70 m/s) in spite of significantly different nanopowder production rates.     

Anionic Lead Complexes on the Solid Phase of Fibrous Filled Materials in the Reaction with 4(2-Pyridylazo)resorcinol

The influence of the nature of anions (iodide, bromide, thiosulfate, pyrophosphate, tartrate, and acetate) in the anionic lead complex adsorbed on a solid phase of a fibrous sorbent filled with the AV-17 anion exchanger on the color reaction between lead and 4-(2-pyridylazo)resorcinol (PAR) was studied by diffuse reflectance spectrometry. The influence of anions on the complexation of lead with PAR on the solid phase was discussed for different types of the color reaction. It was demonstrated that the reactions with iodide at pH 5–10 and with thiosulfate at pH 10 are significant in the determination of lead as three-component complexes on the support. In the presence of other anions, lead ions do not react with PAR on the AV-17 solid phase.     

Selective Sorption–Spectrometric Determination of Nanogram Amounts of Vanadium(IV) and Vanadium(V)

Conditions of the selective sorption–spectrometric determination of vanadium(IV) and vanadium(V) using sulfonitrophenol M were found. The determination of vanadium (visual test (RSD = 30%) using a reference color scale or quantitative determination (RSD < 10%) by diffuse reflectance spectra is performed immediately after the dynamic-mode sorption of its colored complexes with sulfonitrophenol M at pH 3.5 (vanadium(IV)) or with sulfonitrophenol M and hydroxylamine at pH 1.5 (vanadium(V), 650 nm) at the surface of polyamide membrane disks (d= 1 cm, l= 0.1 mm, m= 2.7 mg). The flow rate is 10–20 mL/min. The detection limit is 5–7 ng of vanadium in the support zone or 0.2–0.5 ng/mL. The determination of 0.5–5 ng/mL vanadium(V) at pH 1.5 does not interfere with 20-fold amounts of V(IV) and 1000-fold amounts of Ni, Zn, Cd, Mg, Co, Cr(III), Mn, PO^3- ₄, and F^–.