Optical properties of the Cr<Subscript>5</Subscript>S<Subscript>6</Subscript> single crystal

Results of the investigation of optical density spectra of Cr₅S₆ single crystals in the infrared region have been presented. A comparative analysis of the temperature dependences of the magnetization and the light absorption has been performed. Physical mechanisms to explain the specific features of the spectral and temperature dependences of the optical density have been proposed.     

A statistical analysis of the kinetics of chain-branching chemical reactions with quadratic chain termination

Analytical and numerical simulations of stochastic phenomena in the kinetics of chain-branching reactions with linear and quadratic chain termination during fast changes in external conditions that cause sharp transitions of the governing parameter through the critical point were studied. A statistical analysis was performed based on nonlinear stochastic differential equations of Langevin type for the concentration of active species and on the corresponding Fokker-Planck equations for the probability distribution function of the concentration of these species. An expression for the statistical distribution of the induction period of the reaction and its mean and variance were calculated from an approximate analytical solution. The time evolution of the probability density function of the concentration of active species was presented graphically.     

Ferrite and high-temperature superconductor targets for sputtering

A method is described of preparing targets for sputtering, which involves the use of plasma deposition of respective powders onto a cooled metal plate. It is demonstrated that the use of plasma technology enables one to produce, in a controlled atmosphere, intricately shaped ceramic targets characterized by a highly uniform composition and by reliable mechanical and thermal contact of the resultant coating with the holder plate. Experiments are performed on the sputtering of targets to prepare polycrystalline ferrite films for magnetooptical applications and epitaxial films of high-temperature superconductors.     

Adsorption properties of carbon nanotubes depending on the temperature of their synthesis and subsequent treatment

A correlation between the temperature of the synthesis of carbon nanotubes (CNT) by method of catalytic pyrolysis from ethanol on a nickel catalyst and their ability for the modification of oxidation under various conditions and also their adsorption capacity to a number of metal ions is demonstrated. The study of infrared spectra in correlation with the total acidity of the CNT synthesized and modified under various conditions has shown that the samples synthesized at 400°C possess the maximum ability for modification. This can be explained by the higher deficiency of their structures at low synthesis temperatures. Adsorption isotherms of silver, copper, lead, cadmium, zinc, iron, and magnesium ions under batch and dynamic modes were studied, depending on pH and element concentration in the solution. It was found that CNT synthesized at 400°C and treated with conc. HNO₃ in an autoclave at 110–120°C possess the maximum adsorption capacity of all the studied elements, which exceeds the capacity of active coal, traditionally used for these purposes, by several times. The attained adsorption capacity is 5–10 times higher than that reported in the literature for carbon nanotubes in relation to the same elements. Prospects of using CNT as collectors for the preconcentration of trace impurities in spectroscopic methods of analysis are considered.     

Determination of Mercury by Nondispersive Atomic Fluorescence Spectrometry

A nondispersive atomic fluorescence spectrometer for the determination of mercury by the cold-vapor technique has been developed. The conditions for mercury vapor generation in a hydride generator (the concentration and volume of the reagents, reaction and purge times, and argon flow rate) are optimized for fluorescence measurements. An algorithm is proposed for the calculation of the analytical signal that leads to an increase in the signal-to-noise ratio by a factor of 3 as compared to the conventional procedure. On the basis of the results obtained, procedures for the determination of mercury in soil and semolina samples are developed with a detection limit of 60 pg and RSD = 10%. The accuracy of the determinations is verified by an analysis of standard reference samples of soil and semolina.