The ternary system cerium-rhodium-silicon

Phase relations have been established in the ternary system Ce-Rh-Si for the isothermal section at 800 °C based on X-ray powder diffraction and EPMA on about 80 alloys, which were prepared by arc melting under argon or by powder reaction sintering. From the 25 ternary compounds observed at 800 °C 13 phases have been reported earlier. Based on XPD Rietveld refinements the crystal structures for 9 new ternary phases were assigned to known structure types. Structural chemistry of these compounds follows the characteristics already outlined for their prototype structures: τ₇—Ce₃RhSi₃, (Ba₃Al₂Ge₂-type), τ₈—Ce₂Rh_3−xSi_3+x (Ce₂Rh_1.35Ge_4.65-type), τ₁₀—Ce₃Rh_4−xSi_4+x (U₃Ni₄Si₄-type), τ₁₁—CeRh₆Si₄ (LiCo₆P₄-type), τ₁₃—Ce₆Rh₃₀Si_19.3 (U₆Co₃₀Si₁₉-type), τ₁₈—Ce₄Rh₄Si₃ (Sm₄Pd₄Si₃-type), τ₂₁—CeRh₂Si (CeIr₂Si-type), τ₂₂—Ce₂Rh_3+xSi_1−x (Y₂Rh₃Ge-type) and τ₂₄—Ce₈(Rh_1−xSi_x)₂₄Si (Ce₈Pd₂₄Sb-type). For τ₂₅—Ce₄(Rh_1−xSi_x)₁₂Si a novel bcc structure was proposed from Rietveld analysis. Detailed crystal structure data were derived for τ₃—CeRhSi₂ (CeNiSi₂-type) and τ₆—Ce₂Rh₃Si₅ (U₂Co₃Si₅-type) by X-ray single crystal experiments, confirming the structure types. The crystal structures of τ₄—Ce₂₂Rh₂₂Si₅₆, τ₅—Ce₂₀Rh₂₇Si₅₃ and τ₂₃—Ce_33.3Rh_58.2−55.2Si_8.5−11.5 are unknown. High temperature compounds with compositions Ce₁₀Rh₅₁Si₃₃ (U₁₀Co₅₁Si₃₃-type) and CeRhSi (LaIrSi-type) have been observed in as-cast alloys but these phases do not participate in the phase equilibria at 800 °C.     

X-ray structural study of intermetallic alloys RT2Si and RTSi2 (R=rare earth, T=noble metal)

Two series of intermetallic alloys, RT₂Si and RTSi₂, have been synthesized from stoichiometric compositions. The crystal structures of EuPt_1+xSi_2−x (CeNiSi₂-type), CeIr₂Si (new structure type), YbPd₂Si and YbPt₂Si (both YPd₂Si-type) have been elucidated from X-ray single crystal CCD data, which were confirmed by XPD experiments. The crystal structures of LaRh₂Si and LaIr₂Si (CeIr₂Si-type), {La,Ce,Pr,Nd}AgSi₂ (all TbFeSi₂-type), and EuPt₂Si (inverse CeNiSi₂-type) were characterized by XPD data. RT₂Si/RTSi₂ compounds were neither detected in as-cast alloys Sc₂₅Pt₅₀Si₂₅, Eu₂₅Os₂₅Si₅₀ and Eu₂₅Rh₂₅Si₅₀ nor after annealing at 900 °C. Instead, X-ray single crystal data prompted Eu₂Os₃Si₅ (Sc₂Fe₃Si₅-type) and EuRh_2+xSi_2−x (x=0.04, ThCr₂Si₂-type) as well as a new structure type for Sc₂Pt₃Si₂ (own type).     

Thermochemistry of lignin

Thermochemical reactions occurring in various stages of structural transformations of native lignin in its thermal treatment in a wide temperature range are considered and classified. Attention is given to the initial state of lignin in its primary isolation without heating. The terminology of lignin products, used in the literature, is put in order to a certain extent. The thermochemical reactions in which lignins are transformed in processing of raw wood materials and the structure of isolated lignins undergoes changes in the course of the target thermal treatment are differentiated. The applied aspect of the directed thermochemical synthesis of new lignin-based low- and high-molecular-mass compounds is discussed.     

The study of polystyrene-fullerene solid-phase composites

Polystyrene-based films containing from 0 to 45 mol % of C₆₀ fullerene are investigated. It is found that the introduction of fullerene increases the molecular packing density of polystyrene chains, thus affecting the transport of small molecules through the polymer films. Gas diffusion through the composite films is slower than through the polystyrene films, while the gas-distributing properties of the composites are higher. The dielectric relaxation method shows that the solution-grown films retain the cluster state of fullerene. When the films containing more than 0.15 mol % of fullerene are heated above the glass transition temperature of polystyrene away from air, the relaxation time of the α transition in polystyrene is found to increase. This effect is associated with strong chain interaction via fullerene molecules incorporated into polystyrene-C₆₀ complexes. The NMR spectroscopy method allows us to observe the typical changes in the composites.     

Influence of Allotropic Forms of Carbon on Formation and Cross-Linking of Heat-Resistant Polymer Binders

The thermochemical reactions of polyimide binder with various allotropic forms of carbon, fullerene C₆₀ and ultradispersed artificial diamonds, were studied by thermal and spectral analyses.     

Physicochemical properties of Water-Soluble Fullerene C60-Carbohydrate Composites

Water-soluble composites of fullerene C60 with carbohydrates (saccharose, fructose, and dextrans) prepared by the mechanochemical procedure were analyzed by electronic absorption and ¹³C NMR spectroscopy, thin-layer chromatography, and differential scanning calorimetry.     

Addition Polymerization of 5-Ethylidene-2-Norbornene in the Presence of Pd N-Heterocyclic Carbene Complexes

New high-performance catalytic systems based on Pd N-heterocyclic carbene complexes for the selective addition polymerization of 5-ethylidene-2-norbornene (ENB) were proposed. With these catalysts, polymerization can be conducted at unprecedentedly high monomer/catalyst ratio (up to 5 × 10⁵/1) and gives high-molecular-weight soluble polymers with good film-forming properties. Varying the polymerization conditions (reaction temperature, monomer and catalyst concentrations, monomer/Pd ratio) makes it possible to prepare soluble ENB-based addition polymers with specified molecular weights in reasonable yields.     

Composites of lignin and polyacrylonitrile as carbon precursors

Films of polyacrylonitrile and lignin cast from dimethylformamide were studied by dynamic thermal analysis in a self-generated atmosphere and in a vacuum. The occurrence of a thermochemical reaction of the components on heating was demonstrated. The optimal conditions of the reaction between polyacrylonitrile and lignin were determined.