Vibrational control of crystal growth from liquid phase

Modeling and numerical simulations of the convective flows induced by the vibration of the monocrystal during crystal growth have been performed for two configurations simulating the Cz and FZ methods. This permitted to emphasize the role of different vibrational mechanisms in the formation of the average flows. It is shown that an appropriate combination of these mechanisms can be used to counteract the usual convective flows (buoyancy- and/or thermocapillary-driven) inherent to crystal growth processes from the liquid phase. While vibrational convection is rather complex due to these identified mechanisms, the new modeling used in the present paper opens up very promising perspectives to efficiently control heat and mass transfer during real industrial applications of crystal growth from the liquid phase.     

Quantum-Chemical Calculations of Ruthenium Nitrosyl Complexes with Tetradentate Macrocyclic Ligands

The geometric structure of the ground state and of metastable isomers of nitrosyl complexes trans-[Ru(P)(NO)(Cl)] (P = porphinate dianion) and trans-[Ru(NO)(salen)(X)]^q [salen = N,N'-ethylenebis(salicylideniminate) dianion; X = Cl^- (q = 0), H₂O (q = +1)] was optimized within the framework of the density functional method (SVWN/LanL2DZ+6-31G). The local minima corresponding to metastable isomers with a linear NO coordination through the oxygen atom and with a side ² NO coordination were found on the potential energy surfaces of these compounds. The second metastable states of all the three complexes have a lower energy. The difference in energies between the stable and metastable isomers is the least in the case of the complex trans-[Ru(NO)(salen)(Cl)].     

Alkylation of difluoronitroethanol by epichlorohydrin

Conclusions The reaction of 2,2-difluoro-2-nitroethanol with epichlorohydrin in alkaline medium gives 2,2-difluoro-2-nitroethyl glycidyl ether, whose yield is raised to 70% upon carrying out the reaction in the presence of formaldehyde.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2865–2868, December, 1988.     

A Spectral Study of the Complexation between the Hybrid Spiropyran Molecules and Metal Ions

Russian Journal of General Chemistry - The absorption and fluorescent, as well as photochromic properties exhibited by hybrid spiropyran during formation of complexes between its molecules with...     

Numerical modelling of three-dimensional thermo- and solutocapillary-induced flows in a floating zone during crystal growth

Numerical modeling of temperature distribution, velocity and dopant concentration in crystal growth by the floating zone method in microgravity conditions is carried out taking into account thermocapillary and solutocapillary effects. The deformations of free surface and the curvature of crystallization and melting fronts are neglected. Non-stationary three-dimensional problem is solved by finite differences method. The establishing of stationary axisymmetrical regimes as well as the development of non-stationary three-dimensional regimes are observed.     

Stationary convection of a viscoplastic liquid in a vertical layer

A study is made of plane-parallel convective motion of a viscoplastic liquid between parallel vertical planes on which different temperatures are maintained. In contrast to [1], the yield shear stress ₀ is not a constant but is assumed to be a function of the temperature; moreover, above a certain critical temperature T_* the yield shear stress vanishes, so that for T > T_* the liquid is purely Newtonian. The structure of the regions of quasirigid and viscoplastic flow is studied in its dependence on the Theological parameters. The velocity profiles corresponding to the different flow regimes are found, and the boundaries between the regimes and the longitudinal heat flux are determined.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 118–123, March–April, 1980.We thank G. Z. Gershuni and A. A. Nepomnyashchii for a helpful discussion of the work.     

Synthesis and spectrophotometry study of the acid-base properties of nitro-substituted 5-phenyl-β-octaalkylporphines

10,15-Dinitro-5-phenyl-2,3,7,8,12,13,17,18-octamethylporphine, 10,15,20-trinitro-5-phenyl-2,3,7,8,12,13,17,18-octamethylporphine, and 10,15,20-trinitro-5-(4-nitrophenyl)-2,3,7,8,12,13,17,18-octamethylporphine were synthesized and identified by electronic absorption, IR, and ¹Н NMR spectroscopy. The acid–base properties of the synthesized compounds were studied by spectrophotometric titration in HClO₄–acetonitrile and 1,8-diazabicyclo[5.4.0]undec-7-ene–acetonitrile systems at 298 K. Parameters of the electronic absorption spectra and concentration ranges of existence of the mono- and diprotonated, as well as mono- and dideprotonated forms of the corresponding ligands and the acid and base dissociation constants of the latter were determined. Comparative analysis of the effect of nitro groups on the reactivity of the synthesized compounds was performed.