G. A. Sycheva

Formation of the bubble structure in the 26Li2O · 74SiO2 glass

The formation of a bubble structure in the glass of composition 26Li2O · 74SiO2 is investigated. The stable reproducible characteristics of the bubble structure are obtained, namely, dependences of the number of bubbles on the conditions of glass synthesis, i.e., the synthesis temperature, the synthesis time, and the type of initial reagents. It is shown that the number of bubbles decreases with an increase in the height of the sample (glass melt in the crucible), as well as with an increase in the synthesis temperature at a fixed synthesis time or with an increase in the synthesis time for each specific temperature. The bubble size distribution curves are obtained for all synthesis conditions. The reproducible bubble structure is determined for each layer of the glass sample, which is subsequently used in studying the kinetics of heterogeneous nucleation.

Influence of the presence of bubbles on the parameters of crystal nucleation in the 26Li2O · 74SiO2 glass

The crystal nucleation in the glass of composition (mol %) 26Li2O · 74SiO2 has been investigated in the cases of homogeneous and heterogeneous nucleation. Parameters of homogeneous nucleation, such as the stationary nucleation rate Ist, the time of nonstationary nucleation τ, and the crystal growth rate U, have been determined. The temperature dependences of these parameters have been constructed. The surface energy σ at the nucleus-glass melt interface has been determined, and its temperature dependence has been obtained. The surface energy σ has been evaluated using the graphical method for solving the transcendental equation derived by transforming the relationships for the stationary crystal nucleation rate and the time of nonstationary crystal nucleation. The critical nucleus sizes r* and the free energy of formation of the critical nucleus Φ* have been determined. The heterogeneous nucleation on bubbles specially produced in the glass has been studied. It has been demonstrated that the presence of bubbles in the initial glass does not affect the crystal growth rate and substantially changes the nonstationary nucleation rate. The largest contribution to the change in the nucleation rate is made by “active” bubbles (filled by water vapor) formed in the glasses synthesized with the use of hydrated silicon dioxide.

Volume nucleation of crystals in glass based on blast-furnace slag

The nucleation of crystals in glass obtained by blending metallurgical slag with silicon dioxide has been studied. The type of crystallization (homogeneous or heterogeneous, volume or surface) is revealed for each of nine compositions of synthesized glass. It is shown that the first crystalline phase in a volume-crystallizing glass is perovskite (CaO · SiO2); in this phase a nucleation of the main phase occurs: melilite (solid solution of gehlinite 2CaO · Al2O3 · SiO2 in akermanite 2CaO · MgO · 2SiO2). The fundamental characteristics of homogeneous (for a catalizing phase, perovskite) and heterogeneous (for a catalyzed phase, melilite) of crystallization are determined: the steady-state nucleation rate Ist, time of unsteady-state nucleation τ, crystal growth rate U, and activation energy of frictional flow. The temperature dependences of Ist, τ, and U are obtained. Practical recommendations are presented for the use of blast-furnace slag as a raw material for the synthesis of glass and their further utilization.

Sol-gel synthesis of photostructured gold-containing lithium silicate glasses

A sol-gel method has been proposed for preparing the batch used in the synthesis of a photostructured gold-containing glass of the composition 33.56Li2O · 66.5SiO2. It has been found that the main crystalline phase in the glass of this composition is lithium disilicate Li2O · 2SiO2. The temperature-time dependences of the nucleation rate of lithium disilicate crystals with a gold impurity have been investigated under conditions of X-ray irradiation of the initial glass and without irradiation. It has been shown that, in the absence of X-ray irradiation, the gold impurities do not affect the nucleation of lithium disilicate crystals. It has been established that the use of the sol-gel method for the preparation of the batch for synthesizing photostructured gold-containing glasses leads to a more uniform spatial distribution of gold microimpurities in the bulk of the glass.

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.

Determination of the size of the critical nucleus of crystals in lithium and sodium silicate glass

Sizes r* of critical nuclei of lithium and sodium di- and metasilicates arising in lithium and sodium silicate glass were determined. The experimentally found data on the stationary nucleation rate and the induction period, the calculated values of the surface energy, and the data in the literature on the differences in the free energies of the glass and the crystal were used to find r*. The values of the surface energy on the nucleus-glass interface were determined by transformation of the equations for the nucleation rate and its induction period into a transcendental equation and solving it by the graphical method.

Features of the anomalous scattering of light in two-phase sodium borosilicate glass

This paper is devoted to the study of light scattering in inhomogeneous glasses. The spectral behavior of the extinction coefficient of the initial sodium borosilicate glass and two glasses obtained by heat treatment is experimentally studied. It is established that the extinction coefficient of heat-treated glasses in the visible region is determined by the scattering of light. Experimental data on the anomalous spectral dependence of the extinction coefficient of the glass subjected to more prolonged heat treatment are compared with the results of calculations carried out in terms of various scattering models based on literature data on the structure of this glass, which consists of liquation spherical particles in a matrix. It is shown that the ordering effects observed earlier in the relative position of the particles play an important role in the light scattering. It is pointed out that, to theoretically describe the scattering properties of a system of polydisperse particles, it is necessary to know the pairwise correlation function of the particles, which depends on the size of the particles in the pair.

Effect of X-rays on crystal nucleation in photostructured glasses of a lithium-silicate system

Crystal nucleation parameters have been determined in a wide range of compositions of photo-structured glasses of the lithium-silicate system (23.40–45.00 mol % Li2O) for homogeneous and heterogeneous nucleation. The homogeneous nucleation occurred in glasses without photosensitive additives and with photosensitive gold-silver additives (0.05 wt % above 100%) without irradiation; the heterogeneous nucleation occurred in glasses with photosensitive gold-silver additives under X-ray irradiation. The ranges of the compositions are reported in which the effect of catalyzing irradiation is reversed (suppressing crystallization according to the autocatalytic mechanism) under certain conditions.

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.

Nucleation and morphology of crystals in simple and complex silicate glasses R′2O-SiO2, R′2O-R″O-SiO2, (R′ = Li, Na, K; R″ = Ca, Mg) synthesized by the sol-gel method

Sol-gel technology is a promising method not only to obtain the batch of the main composition but also to include low additives in glass. In this work, the batches obtained via the sol-gel method have been used to synthesize silicate glass based on the Li2O-SiO2 system with the additives of R′2O and R″O, (R′ = Na, K; R″ = Ca, Mg). The Li2O-SiO2 system without the additives R′ and R″ has been studied by us most completely. It has been determined that the main crystal phase in the glass of Li2O-SiO2 system with Li2O content up to 33 mol % is lithium disilicate, Li2O · 2SiO2. In the range of compositions from 33.8 to 40.7 mol % Li2O, solid solutions based on lithium disilicate are formed; and, starting from 40.7 mol % Li2O, solid solutions based on lithium metasilicate. The kinetic dependences of the number of nucleating lithium disilicate crystals from the time of heat treatment have been obtained at various temperatures of heat treatment. The temperature dependences of the stationary rate of nucleation of crystals have been studied. The results have been compared for the glass prepared with the use of the conventional and sol-gel method. It has been determined that the complication of the composition of glass based on 26Li2O · 74SiO2 (mol %) by the addition of R′ = Na, K; R″ = Ca, Mg affects the morphology of lithium disilicate crystals. The use of the sol-gel method of synthesis of glass leads to a more homogeneous spatial arrangement of crystals in bulk glass, the measure of which (distribution) is the dispersion of the number of traces of crystals per unit area of the section.