I. G. Polyakova

Volumetric nucleation of crystals catalyzed by Cr2O3 in glass based on furnace slags

The features of the volumetric nucleation of crystals in glass obtained by melting furnace slags with the additive of SiO2, chromium sesquioxide Cr2O3, are studied by the methods of differential thermal and Xray phase analysis and optical microscopy. Upon the introduction of Cr2O3 as the catalytic additive, two phases are sequentially formed in the glass: magnesiochromite (MgO · Cr2O3) and diopside (CaO · MgO · 2SiO2). The characteristics of homogeneous and heterogeneous crystallization are determined: the stationary nucleation rate, nonstationary nucleation time, crystal growth rate, and their temperature dependences are obtained. Practical recommendations on the use of the obtained glass are given.

Physicochemical properties of glasses of the Na2O-B2O3-SiO2-Fe2O3 system in the 8Na2O/70SiO2 section

Glasses of the 8Na2O-(22-x)B2O3-70SiO2-xFe2O3 system, where x varies from 0.3 to 10 mol %, have been studied by dilatometry, X-ray powder diffractometry (XRPD), and transmission electron microscopy (TEM). The glasses were heat treated at temperatures of 550, 650, and 700°C for 144, 10, and 2 h, respectively. When comparing the data of dilatometry and electron microscopy, we conclude that phase-separated glasses have a difference between the onset deformation temperature and the glass transition temperature of more than 100°C, while for single-phase glasses, the difference is less than 65°C. According to XRPD, it is shown that in the glasses containing from 4 to 8 mol % of Fe2O3, cristobalite is formed after exposure at 700°C for 2 hours, whose reversible α-β-transition is fixed in the subsequent dilatometry as a sharp jump in the thermal expansion in the temperature interval of 190–210°C. Starting from 3 mol % of Fe2O3, magnetite is formed in the glasses whose content increases with an increase in the content of iron oxide.

Surface crystallization of glass based on blast furnace slags

Using differential thermal analysis, X-ray phase analysis, electron microscopy, and optical microscopy, surface nucleation of crystals in glass, obtained from metallurgical slags with the addition of SiO2, is studied. It is shown that the main phases, crystallized from the surface of the samples are melilite (solid solution of gehlenite 2СаО · Al2O3 · SiO2 in akermanite 2СаО · МgO · 2SiO2) and diopside (CaO · МgO · 2SiO2). The kinetics of the crystallization of glass is studied and the rates of the surface crystal growth are determined in the glass of nine compositions. The influence of the degree of dispersion of the particles of the original glass on the deposition order of the crystalline phases and the degree of crystallinity of the glass is studied.

Synthesis and comparative studies of xerogels, aerogels, and powders based on the ZrO2–Y2O3–СeO2 system

The technology of liquid-phase synthesis of mesoporous xerogels and aerogels based on ZrO2–Y2O3–CeO2 is developed. Xerogels are obtained by the coprecipitation of hydroxides, while aerogels are obtained in accordance with the sol–gel technology: the average pore size is 1.5–17.2 nm and the specific surface area is 120–878 m2/g. Aerogels are characterized by a high degree of porosity: the pore volume attains 1–4 cm3/g. Based on precursor xerogels, nanopowders of a tetragonal solid solution of the (ZrО2)0.92(Y2О3)0.03(CeО2)0.05 composition with a particle size of 5–9 nm and Sspec = 74 m2/g were fabricated. Due to the high values of their specific surface area, the synthesized xerogels and aerogels are promising as sorbents, catalysts, or catalyst supports.

Neodymium nickelate—A cathode material for fuel cells

Nanocrystals of the neodymium nickelate (Nd2NiO4) compound have been synthesized using the method of the combined crystallization of nitrates’ solutions and its electrophysical properties have been investigated. It has been established that Nd2NiO4 is characterized with rather high specific conductivity of the metallic type (∼200 S cm–1) in the temperature range 500–900°C and the thermal expansion coefficient comparable with that of solid solutions based on ZrO2.

Phase separation in the glasses of the (8–x)Na2O · xFe2O3 · 22B2O3 · 70SiO2 system

Glasses with the (8–x)Na2O · xFe2O3 ∙ 22B2O3 ∙ 70SiO2 compositions, where the Fe2O3 content varies from 2 to 6 mol %, which were heat-treated at the temperatures of 550 and 700°С for 144 and 2 h, respectively, have been studied by dilatometry, electron microscopy, and X-ray powder diffractometry. It has been shown that, with an increase in the total concentration of Fe2O3 in the glass, there is a trend to the transition from an interconnected to a droplet-matrix phase-separated structure. The crystal line phases of Fe3O4, FeSiO3, and β-Fe2O3 are formed depending on composition, while the latter is observed only in the glass with the equivalent contents of Na2O and Fe2O3. There is a minimum on the glass transition temperature dependence of the composition at equimolar (4 mol %) contents of Na2O and Fe2O3.

Synthesis and study of film-forming composites based on silica sols and dispersed oxides for the fabrication of glass ceramic electro-insulating coatings

The physical-chemical and technological factors determining the selection of initial components for film-forming sol-gel composites obtained by mixing silica sols containing different dopants and dispersed oxides has been discussed on specific examples. Their effect on phase composition, structure, and the electrophysical properties of the fabricated electro-insulating glass ceramic coatings has been analyzed. The fabricated coatings serve to be applied in electrical engineering, in particular, for the protection of glass bulbs of X-ray tubes operated at high voltage (up to 160 kV).

Phase-separated structure and properties of glasses in the (16–x)Na2O–14B2O3–70SiO2–xFe2O3 system

The effect of Fe2O3 on the structure, glass transition temperature, viscosity, and electric resistance of glasses in the (16–x)Na2O–14B2O3–70SiO2–xFe2O3 (x changes from 2 to 10 mol %) system is investigated. It is demonstrated that at a Fe2O3 concentration up to and including 4 mol % glasses are single-phased and X-ray-amorphous. When the Fe2O3 content is higher than 6 mol %, glasses are characterized with a phase-separated structure with magnetite inclusions. The addition of Fe2O3 up to 4 mol % (inclusive) decreases the viscosity and glass transition temperature. Along with the decrease of the Fe2O3 content in glasses under study, the electric resistance decreases for all heat treatment conditions by 1–2 orders of magnitude, and the calculated activation energy values are similar to those of sodium-borosilicate glasses without iron.

Effect of the thermal treatment on the phase composition of the surface of coatings based on Si–B–ZrB2 and modified with ZrO2 fibers

Coatings on graphite that are stable to oxidation and based on the silicon–boron–zirconium boride composite containing from 5 to 50% of fibrous zirconium dioxide as a modifying dopant have been produced by the suspension–annealing method. A nonporous layer is formed at the zirconium dioxide content ranging from 5 to 15%, while a porous layer is formed at its 50% content. A glass-forming melt, as well as zirconium dioxide and silicate, is formed during thermal treatment as a result of the chemical reactions with the oxygen in air. The zirconium silicate content increases, along with the modifier’s concentration and temperature.

The smallest structural elements of glass determining its properties according to vibrational spectroscopy data

The brief review of the results of the studies of the structural elements of a medium-range order of oxide glass is given based on the approaches to the processing of the vibrational spectra of glass by means of chemometrics, which were suggested by us at the beginning of the 1980s. It has been shown that it is possible to receive information on the stoichiometry and concentrations of stable molecular groups of constant composition formed in glass within the suggested approach and interpret and calculate their properties based on this, as well as predict the compositions corresponding to the optimal characteristics of glass that is of practical value.