Disorder-order phase transformations and electrical resistivity of nonstoichiometric titanium carbide

Phase transformations of the disorder-order type in the homogeneity region of nonstoichiometric titanium carbide TiC_y (0.5<y<1.0) have been studied. It has been established that, depending on the actual composition of TiC_y, there may form in it for T<980–1000 K a cubic or a trigonal ordered Ti₂C phase (space groups Fd3m and , respectively) and a rhombic ordered Ti₃C₂ phase (space group C222₁). The effect of ordering on the electrical resistivity of the nonstoichiometric carbide TiC_y was studied, and the temperatures of the reversible disorder-order equilibrium transitions determined. The ordering in titanium carbide is shown to be a first-order phase transition. Fiz. Tverd. Tela (St. Petersburg) 40, 1332–1340 (July 1998)     

Structural features of composite protein-polysaccharide hydrogel in the presence of a carbon nanomaterial

Russian Chemical Bulletin - The structures of a protein-polysaccharide composite hydrogel and its modifications prepared using carbon nanotubes (CNTs) were studied by small-angle X-ray scattering...     

Formation Mechanism of Argon Clathrates with Carbon Dendrites

The formation mechanism of argon clathrates with carbon dendrites obtained in the plasma of an atmospheric-pressure gas discharge has been studied. It has been shown that the formation of these clathrates is due to the difference between characteristic times: the lifetime of molecules surrounding argon atoms and the time of C–C bonding. It has been noted that argon clathrates with carbon dendrites can form only if a number of conditions are met: formation of molecular traps in the discharge, provision of a sufficiently low temperature at the center of the arc discharge, and the presence of active carbon particles arising from plasma decomposition of hydrocarbon precursors. Whether or not these conditions are met depends primarily on the composition of the initial hydrocarbon mixture and discharge current density, as follows from experimental data.     

Complexes of CuII with nitroxides and their magnetochemical behavior

The synthesis, structures, and magnetochemical data for the heterospin chain polymer complexes Cu(hfac)₂L^All and Cu(hfac)₂L^Bu·0.5Solv, where hfac is the hexafluoroacetylacetonate anion, L^All and L^Bu are 2-(1-allyl-1H-pyrazol-4-yl)- and 2-(1-butyl-1H-pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyls, respectively, Solv is isopropylbenzene or tert-butylbenzene, were described. These polycrystalline solids were found to exhibit similar magnetic anomalies. Thus, the effective magnetic moment first decreases and then increases with temperature, resulting in the specific minimum in the curve μ_eff(T). The study of the magneto-structural correlations showed that the appearance of the minimum is attributed to different factors. For Cu(hfac)₂L^All, this is the phase transition accompanied by the structural rearrangement of the exchange cluster >N—·O—Cu^II—O·—N<, which leads to a change in the energy of the exchange interaction between the unpaired electrons of the paramagnetic centers. By contrast, for Cu(hfac)₂L^Bu·0.5PrⁱPh and Cu(hfac)₂L^Bu·0.5Bu^tPh, the appearance of the minimum is a consequence of the coexistence of exchange interaction energies with opposite signs, while the structure of the solid phase remains unchanged.     

Effect of the Solvent Composition on the Content of the Crystalline Phase and Melting Temperature of Paraffin Waxes

Russian Journal of Applied Chemistry - The results of a study of melting the commercial waxes in the composition of asphaltene-resin-paraffin deposits and for comparison of petroleum waxes in...     

Collimation of atomic beams by resonant laser radiation pressure

The application of the resonant light pressure created by an axially symmetrical light field for collimating atomic beams has been considered. As an example, consideration is given to the possibility of collimating an atomic beam by the light field produced by the reflection of a plane wave from the internal surface of a metal cone. It has been shown that the radiation pressure can reduce the atomic-beam transverse velocities to the value of the order of 100 cm/s which corresponds to effective temperature of about 10^–3 K. A method for producing collimated beams of cold atoms based on simultaneous deceleration and collimation of atomic beams by resonant laser radiation pressure is proposed.     

Physical Interpretation of the Electronegativity

An additivity scheme of electronegativities of univalent substituents has been proposed on the basis on the Van Vleck orbital model of valence states of atoms. The electronegativity of any organic or heteroelement-containing substituent can be calculated from the orbital electronegativities and hardnesses of atoms constituting that substituent. The proposed additivity scheme is the most consistent among those currently available for calculation of orbital electronegativities of univalent substituents. The scheme was substantiated with the aid of quantum-chemical scale of group electronegativities.