Development of NaNO2–O2 system as an oxidant at uranium leaching processes

A process of ferrous ion oxidation by sodium nitrite in sulfate uranium in situ leaching solutions was investigated. Kinetic, spectrophotometric, and heat effect studies have been made in order to investigate the chemistry of the oxidation process. As a result the method of ferrous ion oxidation in uranium in situ leaching solution was developed that makes possible to decrease sodium nitrite consumption by 20?C30 times comparing with traditional oxidation technique. It was founded also that process of ferrous ion oxidation can be conducted with partial sodium nitrite recirculation.     

Photonics of liquid-crystal structures: A review

The original results of studies of the electro-optical and laser effects which have been performed at the Laboratory of Liquid Crystals of the Institute of Crystallography, Russian Academy of Sciences, over the last few years are reviewed. Cholesteric liquid crystals as vivid representatives of photonic structures and their behavior in an electric field are considered in detail. The formation of higher harmonics in the periodic distribution of the director field in a helical liquid crystal structure and, correspondingly, the new (anharmonic) mode of electro-optical effects are discussed. Another group of studies is devoted to bistable light switching by an electric field in chiral nematics. Polarization diffraction gratings controlled by an electric field are also considered. The results of studies devoted to microlasers on various photonic structures with cholesteric and nematic liquid crystals are considered in detail. Particular attention is given to the new regime: leaky-mode lasing. Designs of liquid crystal light amplifiers and their polarization, field, and spectral characteristics are considered in the last section.     

Calculation of the NQR frequency dependence on the length of a chain of saturated bonds

It is shown that the periodic dependence on n of the NQR signal frequency observed for molecules of -dichloroparaffins Cl-(CH₂)n-Cl for n>3 can be explained by assuming partial delocalization of the C-C bonds. From the calculation, using the MO LCAO approximation, it follows that, with n>3, the negative charge on the chlorine atoms is somewhat greater for even n than for odd n.     

Estimation of the london intermolecular forces in conjugated systems from the dispersions of the Hartree-Fock energy

It has been shown that the intermolecular interaction energy found from the dispersion of the Hartree-Fock -electron energy of a molecular complex is proportional, in the wide range of distances, to the energy calculated from the total-configuration-interaction (TCI) approach. This result makes it possible to obtain reliable estimates for intermolecular forces in large conjugated systems where the application of the TCI approach is impracticable.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 2, pp. 133–136, March–April, 1992.     

Thermodynamics and kinetics of initial gas phase reactions in chemical vapor deposition of titanium nitride. Theoretical study of TiCl4 ammonolysis

Thermodynamic equilibrium and kinetics of the gas‐phase reaction between TiCl₄ and NH₃ have been studied computationally using results from recent quantum mechanical calculations of titanium tetrachloride ammonolysis. 1 These calculations were based upon the transition state theory for the direct reactions and RRKM theory for the reactions proceeding via intermediate complex. Rate constants for the barrierless reactions were expressed through the thermodynamic characteristics of the reagents and products using a semiempirical variational method. The kinetic simulation of the gas‐phase steps of CVD was performed within a model of a well‐stirred reactor at temperatures 300–1200 K and residence times between 0.1–2 s. At temperatures below 450 K formation of donor–acceptor complexes between TiCl₄ and NH₃ is the dominating process. At higher temperatures sequential direct ammonolysis takes place. At typical LPCVD conditions the only product of the first step of ammonolysis, TiCl₃NH₂, is formed in substantial amount. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1366–1376, 2001     

Mathematical model of compensation for dispersion of light polarization states in electrooptical systems based on chiral liquid crystals

Spectral dispersion of the polarization states occurs after passage of linearly polarized light through a thin layer of a chiral nematic crystal along the helical axis. It is clearly pronounced for crystals with a high optical anisotropy and a helical pitch somewhat larger than the light wavelength. The results of numerical analysis of the spectral dependence of polarization states at the output of the liquid crystal layer and the method for compensating for the dispersion are presented for the first time. It is shown that polarization dispersion can be eliminated using phase plates of two types, one of which should have a high anomalous birefringence dispersion. The possibility of developing fast light modulators operating in a wide spectral range is discussed.     

Mechanism and kinetics of thin zirconium and hafnium oxide film growth in an ALD reactor

A mechanism of HfO₂ and ZrO₂ film growth in an ALD reactor from metal chlorides and water vapor is proposed to explain the experimentally observed features of the process: the formation of less than one monolayer per cycle and the dependence of the film growth rate (mass or thickness increment per cycle) and the residual chorine concentration on the process temperature. Energy parameters of the relevant gas-surface reactions are estimated from quantum-chemical density functional theory calculations. The rate constants of the elementary reactions are calculated using RRKM theory. ALD process simulations, based on the proposed mechanism and a transient plug-flow reactor model, are consistent with the available experimental data, indicating a decrease in deposition rate with increasing temperature. The reduction in deposition rate is attributed to the increased dehydroxylation of the film surface as the temperature is increased. The H₂O adsorption energy was found to increase with increasing dehydroxylation from 33 to 53 kcal/mol for ZrO₂ and from 35 to 51 kcal/mol for HfO₂. A kinetic Monte Carlo model of film growth, based on the proposed mechanism, describes the observed temperature dependence of the residual chlorine concentration in the film in terms of the steric repulsion between chemisorbed surface groups and adsorbed MCl₄ molecules (M=Zr, Hf).