E. G. Vovkotrub

Synthesis of dense ceramics of single-phase mayenite (Ca12Al14O32)O

The nanoporous material mayenite was synthesized by two methods: solid-phase and self-propagating high-temperature (combusting) (SHS) syntheses. The structure of the materials was determined by the X-ray diffraction analysis and IR and Raman spectroscopy.

Raman scattering and luminescence of yttria nanopowders and ceramics

We have studied Raman scattering in yttria nanopowders and ceramics that was excited by radiation at wavelengths of 514.5 and 632.8 nm. We show that, in undoped nanopowders and cubic phase of doped yttria ceramics, only the Raman scattering by phonons is observed, with no other Raman scattering centers having been revealed. In nanopowders of the monoclinic phase, we have observed an additional Raman line with a Raman shift of 1093 ± 4 cm−1. If all the objects under investigation are excited by the radiation at a wavelength of 514.5 nm, their spectra exhibit four series of photoluminescence lines, two of which (at λ = 521–523 and 538–564 nm) are emitted by Er3+ ions, “impurity” dopants, while the other two lines (at λ = 607–635 and 644–684 nm) are emitted by intrinsic centers. Under excitation by the radiation at a wavelength of 632.8 nm, only a series of bands at λ = 644–684 nm is emitted. In addition to these photoluminescence bands, neodymium-doped ceramics show photoluminescence bands of Nd3+ ions. We have shown that intrinsic luminescence centers, which occur in all the examined specimens, are capable of acting as acceptors with respect to neodymium ions excited to the upper laser level.

Conditions of hydrochemical synthesis, composition, and structure of tellurium films

Conditions of the hydrochemical synthesis of thin tellurium fi lms by reduction of an aqueous solution of tellurous acid with hydrazine were determined. The redox potentials of tellurous acid and hydrazine and their difference in relation to pH of the medium and concentration of tellurite ions were calculated. The kinetics of tellurium layer growth on glass-ceramic substrates and the structure, composition, and morphology of the layers were studied.

Antifriction properties of oils with thickeners based on modified fluoroalkyl-containing silica particles

Covalently modified silica particles were prepared by the sol-gel process from tetraethoxysilane in the presence of (2-iodo-4,4,5,5,6,6,7,7,7-nonafluoroheptyloxy)methyloxirane under the conditions of base catalysis. The friction coefficients of formulations of petroleum oil with thickeners based on modified SiO2 particles (5 and 10 wt %) at loads of 10, 20, 30, and 60 N were determined. The formulation with the lowest thickener content under the conditions of low loads demonstrates the most pronounced decrease in the friction coefficient. The probable mechanism of the improvement of antifriction properties is the formation of friction layers based on iron compounds.

Raman spectroscopy study of products of reactions of zirconium and hafnium tetrachlorides with indium and thallium monochlorides

Reactions of ZrCl4 and HfCl4 with InCl and TlCl accompanied by formation of several solid complex compounds were studied by the Raman spectroscopy method.

Luminescence of oxygen molecular ion in neodymium-doped yttria

Pulsed cathodoluminescence spectra of Nd3+:Y2O3 compacts registered after their annealing in air at a temperature above 950°C exhibit a structured band in the range 610–660 nm with four well-resolved components located at wavelengths of 620.6, 630.6, 645.3, and 655.6 nm. At the same time, the lattice parameter of the cubic yttria increases, and the color of samples changes from light blue to yellowish. In addition, the nearly complete absorption of the intrinsic luminescence band of yttria is observed in the range of 380–600 nm with a center at λ = 485 nm. We assume that these effects are caused by oxygen molecular ions O2−, which are formed in cubic yttria due to the penetration of oxygen into natural anion vacancies. The frequencies of vibrations of the ground and excited states of the oxygen molecular ion has been determined.

Synthesis, Structure, and Thermal Properties of Ca 5 Ga 6 O 14

Calcium gallate Ca5Ga6O14 is synthesized by solid-phase means. Its melting point is 1325 ± 2°C. A phase transition of the second kind is observed in the temperature interval of 750–800°C. The temperature dependence of a thermal linear expansion coefficient within 200–900°C is given. Vibrational spectroscopy data confirm that Ca5Ga6O14 contains not only GaO4 tetrahedra but also GaO6 octahedra.

Luminescence of oxide ceramics in the Bi2O3-Er2O3-CeO2 system

The method of pulse high-current cathode luminescence is used to study the Bi2O3-Er2O3-CeO2 system at room temperature in air. New luminescence centers associated presumably with cation vacancies and an anion vacancy are determined in systems containing CeO2. The luminescence parameters are shown to behave nonmonotonically with variation of the composition of the system. It is assumed that an abrupt change in these parameters at a certain composition of the substance corresponds to a phase transformation.

The Investigation of Interaction PCl5 with LnCl3 (Ln - Rare Earth Elements)

Abstract The data about possibility of the interaction between chlorides phosphorus and earth metals in science literature are absent.