Thermal expansion of glasses in the SrO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

The linear thermal expansion coefficients below and above the glass transition range and the glass transition temperatures in the SrO-B₂O₃-SiO₂ system are determined using a quartz dilatometer.     

Density and microhardness of glasses in the SrO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

The density d at a temperature of 25°C is measured by the hydrostatic weighing method, the Vickers microhardness H _V is determined, and the fluctuation free volume fraction f _g is calculated for glasses in the SrO-B₂O₃-SiO₂ system with a constant strontium oxide content in the range from 35 to 45 mol %. It is demonstrated that the quantities H _V and f _g decrease and the density d increases with an increase in the SrO content.     

Crystallization of glasses in the SrO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The crystallization of strontium borate glasses containing 16.7–43.0 mol % SrO is investigated. New crystalline compounds of the hypothetical compositions 2SrO · 3B₂O₃ (metastable) and SrO · 5B₂O₃ (stable below 750°C), as well as the metastable diborate modification β-SrO · 2B₂O₃, are revealed, and their X-ray powder diffraction data are obtained. It is demonstrated that, with a deficit of strontium oxide, the 4SrO · 7B₂O₃ compound forms solid solutions. Strontium triborate SrO · 3B₂O₃, which was previously prepared only through the dehydration of crystal hydrates, is produced using crystallization of glasses. The thermal stability of this compound is studied. The influence of the dispersity on the stability of different crystalline phases is discussed. Variants of the phase diagram for the SrO · B₂O₃-B₂O₃ system in the case of monolithic and dispersed samples are proposed from analyzing the experimental results and the data available in the literature.     

On the structure of glasses in the BaO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

The structure of single-phase glasses in the BaO-B₂O₃-SiO₂ system has been studied by the large- and small-angle X-ray scattering techniques. The glasses containing 40 mol % BaO upon equimolar replacement of B₂O₃ by SiO₂ have been investigated. It has been demonstrated that the incorporation of barium ions into structural groupings fixes their position and provides ordering in the distribution of barium ions at interatomic distances up to at least 5 Å. The glasses under investigation are homogeneous, and their inhomogeneity is determined by thermal density fluctuations and fluctuations of the concentration of a part of barium ions distributed in a statistically random manner in the volume of the glass. The observed ordering in the distribution of barium ions is not reduced to the formation of local clusters with an increased concentration of barium ions but is most likely a characteristic feature of the bulk glass structure. The glass structure is consistent with the model of ideal associated solutions.     

Viscosity of glass melts in the SrO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

The temperature dependences of the viscosity are investigated for three series of glass melts in the SrO-B₂O₃-SiO₂ system with a constant strontium oxide content equal to 35, 40, or 45 mol % in the viscosity range from 10¹⁰ to 10¹³ P.     

Glass formation region and order of formation of crystalline phases in the SrO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

The glass formation region in the SrO-B₂O₃-SiO₂ system has been refined. The order of formation of crystalline phases in the system has been investigated at SrO contents of 50–75 mol %. It has been demonstrated that, at low temperatures, the 2SrO · SiO₂ and 3SrO · B₂O₃ phases crystallize first irrespective of the composition. The congruent melting temperature of the 3SrO · B₂O₃ · SiO₂ compound is determined to be 1180 ± 10°C. The triangulation previously performed for the SrO-B₂O₃-SiO₂ system in the concentration range 50–75 mol % SrO has been confirmed.     

Europium(II) in glasses of the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript>-MnO-Eu<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Triply and doubly charged states of europium are revealed by ¹⁵¹Eu Mössbauer spectroscopy in the structure of glasses of the composition (mol %) 19.5Al₂O₃, 31.5SiO₂, 26.5MnO, and 22.5Eu₂O₃. The isomer shifts in the Mössbauer spectra of Eu³⁺ and Eu²⁺ ions in the structure of glasses differ from the isomer shifts in the spectra of the Eu₂O₃ and EuO compounds. This difference is explained by the fact that the electron density at ¹⁵¹Eu nuclei is affected by the manganese and aluminum atoms, which are not bound directly to the europium atoms. The broadening of the spectra of the Eu²⁺ ions in glasses is caused by the nonuniform isomer shift.     

Influence of pressure on the refractive index and relative density of glasses in the CaO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

The pressure dependences of the refractive index for aluminosilicate glasses of the compositions 0.167CaO · 0.167Al₂O₃ · 0.666SiO₂ and 0.157CaO · 0.177Al₂O₃ · 0.666SiO₂ at pressures up to 6.0 GPa are determined using a polarizing interference microscope and an apparatus with diamond anvils. The compressibilities of the glasses are calculated from the measured refractive indices within the framework of the theory of photoelasticity. The structural-chemical parameters NBO/T (where NBO is the number of gram-ions of nonbridging oxygen atoms and T is the total number of gram-ions of network formers) are calculated for the glasses under investigation with allowance made for the formation of triclusters and highly coordinated aluminum.     

Raman spectra and surface structure of CaO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> glass leached in potassium hydroxide solutions

It is difficult to research on the surface structure of amorphous phase in fly ash during leaching reaction due to crystalline phase and complex structure. In the present work, in order to reveal the effects of leaching reaction on the surface structure of amorphous phase in fly ash, the modelling CaO-Fe₂O₃-Al₂O₃-SiO₂ glass was prepared by the traditional melting methods. The leaching reaction of CaO-Fe₂O₃-Al₂O₃-SiO₂ glass with 7.5 M KOH was investigated by spectroscopy, spectrophotometer and wet chemical method. The results show that the content of Q ¹, Q ², Q ³ and Q ⁴ of glass without corrosion was 4.21, 9.51, 23.03 and 52.55%, respectively, which shows that the network polymerization of glass is compact. The leaching reaction of glass can be described by the following equation: dS/dt = k/(r + S ₀). Leaching in KOH for various times induces the content of Q ⁴ and Q ¹ to be decreased, and Q ² and Q ³ increased, resulted in the depolymerization of network and the surface glass dissolved in alkaline solution to form a gel phase. In stage one of leaching reaction, the rate of iron ion leached from glass surface was slow, which resulted in the small slope of straight-line relationship of leaching curve. In the following stage, the leaching rate of iron ion increased with the prolongation of time.     

Corrosion-resistant ceramics and polymer composites based on the BaO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

This paper reports on the results of investigations aimed at synthesizing ceramic materials with a high mechanical strength, as well as with high thermal and chemical resistances to corrosive media. The methods used for one-stage preparation of barite-based ceramic and polymer composites with these properties are considered.     

Synthetic spinels of the system MgO-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Synthetic spinels of the system MgO-Cr₂O₃-Al₂O₃-Fe₂O₃ are considered and the desirability of organizing their production for the refractory industry is demonstrated. Translated from Novye Ogneupory, No. 6, pp. 32–35, June 2008.     

Local crystallization of glasses in the La<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-GeO<Subscript>2</Subscript> system under laser irradiation

A method is proposed for local crystallization of glasses under laser irradiation. This method makes it possible to nucleate and grow microcrystals with a size distribution similar to a monodisperse distribution for several fractions of a second in any glass region chosen in advance. It is demonstrated using glasses in the La₂O₃-B₂O₃-GeO₂ system as an example that the crystallization of the stillwellite-like phase LaBGeO₅ with the composition close to the composition of the initial glass is observed in the glass under irradiation with the copper vapor laser operating in the high-speed pulse modulation mode. Strips (up to ～300 μm) produced at a specified depth from the glass surface contain extended regions consisting of uniformly distributed crystals, which have almost identical sizes, exhibit a pronounced faceting, and are identified using X-ray diffraction. The size and the number of crystals can be changed over a wide range by varying laser treatment conditions. This opens up the way to the design of new glass-ceramic materials in which the location of the crystalline phase in the glass bulk is controlled by a developer.     

Structure and crystallization of ZnO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Structure and crystalline behavior of the ternary system ZnO-B₂O₃-P₂O₅ glasses were investigated by means of X-ray diffraction (XRD) and infrared Raman spectra. The research showed that number of the planar [BO₃] units increases with the increase of B₂O₃ content. When the B₂O₃ content is above ≥10 mol %, the relative content of planar [BO₃] units increases rapidly and causes weakening of the glass structure and decrease in the chemical stability. In the crystallized glasses the predominant crystal phase Zn₂P₂O₇ decreases with the increase of B₂O₃ content, while the crystal phase BPO₄ increases with it, which cause the declining of chemical stability and the decrease of thermal coefficients of expansion.     

Phase equilibria in the Ho<Subscript>2</Subscript>O<Subscript>3</Subscript>-SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript> system

The phase formation is investigated and the phase diagram of the Ho₂O₃-SrAl₂O₄ system is constructed. A ternary compound, namely, Ho₂SrAl₂O₇, is revealed. It is established that this compound undergoes incongruent melting.     

Synthesis and properties of flux-cast refractories in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MgO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Details are given of the synthesis and testing of flux-cast refractory materials in the alumina-rich region of the Al₂O₃-MgO-B₂O₃ system; XRD and petrography indicate that the main structure-forming phases are corundum and magnesian spinel. In subordinate amounts there are the boroaluminate 9Al₂O₃·2B₂O₃ and the previously unknown compound 4Al₂O₃·MgO·2B₂O₃, whose composition has been established by microprobe analysis. Corrosion tests showed that three-component systems containing magnesium and boron oxides at levels of 5–10% do not increase the corrosion resistance of refractories in molten sodium-calcium-silicate glass and electrovacuum borosilicate glass. __________ Translated from Novye Ogneupory, No. 3, pp. 161–163, March, 2008.     

Kinetics of early stages of phase separation in glasses of the PbO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Kinetics of changes in sizes of phase regions and volumes at the early stages of the phase separation of glasses in the PbO-B₂O₃ system has been studied using small-angle X-ray scattering (SAXS). The existence of the interval of heating durations in which the changes in the sizes of the phase regions and volumes are small so that it is possible to approximately consider that the structure is in a relatively stable state has been experimentally established. The relative phase volumes and compositions in glasses of the studied system are close to the equilibrium ones already for the sizes (radii) of the regions of the separated phase of about 15–20 Å and the Ostwald ripening (coalescence) stage begins. Maxima due to the interparticle interference have been observed in the angular dependences of the SAXS intensities. This indicates ordering in the distribution of the phase regions.     

Electrical conductivity and the nature of charge carriers in glasses of the Tl<Subscript>2</Subscript>O-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The concentration dependence of the electrical conductivity of glasses in the Tl₂O-B₂O₃ system is studied. The nature of charge carriers in this system is experimentally investigated for the first time. It is demonstrated using the Hittorf, Tubandt, and Hebb-Liang-Wagner techniques and the Faraday law that neither Tl⁺ ions nor electrons are involved in the electricity transport. The verification of the Faraday law does not reveal the presence of thallium in the amalgam of the cathode or a change in the sample weight after electrolysis, to within the experimental error. This allows one to make the inference that protons can be charge carriers in glasses of the Tl₂O-B₂O₃ system. It is shown using extended X-ray absorption fine structure (EXAFS) spectroscopy that Tl³⁺ ions and thallium Tl⁰ reduced to the metallic state are absent in the structure of the glasses under investigation. This means that thallium in glasses of the Tl₂O-B₂O₃ system occurs only in the form of Tl⁺ ions. The analysis of the IR spectroscopic data leads to only a qualitative conclusion that the water content in the glasses insignificantly increases with an increase in the thallium oxide content. An increase in the electrical conductivity of glasses in the Tl₂O-B₂O₃ system with an increase in the thallium oxide content is explained by the increase in the number of protons formed upon dissociation of H⁺[BO_4/2]^? structural-chemical units, because their concentration increases with increasing Tl₂O content. In the structure of boron oxide, impurity hydrogen enters predominantly into the composition of H⁺[O_2/2BO^?] structural-chemical units, for which the dissociation energy is higher than that for the H⁺[BO_4/2]^? structural-chemical units. The increase in the concentration of H⁺[BO_4/2]^? structural-chemical units is accompanied by the increase in the number of dissociated protons, which are charge carriers in glasses of the Tl₂O-B₂O₃ system.     

Interaction of O<Subscript>2</Subscript>, O<Subscript>3</Subscript>, and H<Subscript>2</Subscript>O<Subscript>2</Subscript> with an activated carbon

The results of the modification of AG-OV-1 activated carbon under various conditions (by atmospheric oxygen at elevated temperatures and by hydrogen peroxide or ozone) are given. The effect of the used modifier on changes in the porosity, surface state, and adsorption capacity of activated carbon is evaluated.