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Abstract The results of a study of the rheological properties (shrinkage on heating, viscosity) of porous glasses (PGs) obtained as a result of through acid leaching of two-phase sodium borosilicate glass doped with small additives of P2O5 and fluoride ions, as well as bismuth-containing PGs and quartzoid glasses based on them, depending on the temperature of the heat treatment of the PG and in comparison with the characteristics of the samples obtained from sodium borosilicate glass without additives, are presented. It is found that doping glass with the indicated impurities leads to a decrease in the thermal resistance of the obtained PGs and bismuth-containing PGs. The introduction of bismuth nitrate into PG in the case of the low-temperature treatment (at 120°C) lowers the temperature for the same viscosity values of quartzoid glasses by 15–20°C, in contrast to samples without additives, as well as from higher-temperature treatment (at 650°C) PGs with additives.

This paper presents the method and features of determining the chemical composition of boron-containing glass by the method of quadrupole mass spectrometry with inductively coupled plasma and laser ablation (LA-Q-ICP-MS). A number of glasses of systems Na2O–B2O3–GeO2–SiO2 and Na2O–B2O3–GeO2 with the boron content ranging from 2.2 to 16.1 wt % are studied. The analysis used the international standard NIST SRM-610 and SRM-612 samples, as well as natural crystals of danburite and datolite as the control reference samples. A correlation is established when comparing the results of the content of sodium, boron, germanium, and silicon in glassy samples with the data of X-ray spectral microanalysis (electron probe macro analyzer (EPMA). It is shown that the optimal conditions for determining the chemical composition by the LA-Q-ICP-MS method are when the maximum laser beam size does not exceed 40 μm, the ablation energy is above 20–22 J/cm2, and natural borosilicate crystals are used as the external standard for boron. The regularities of boron losses during the synthesis of glasses by the standard method of melt quenching are determined, which for the studied systems vary from 13.5 to 32 rel. %.

We investigated the effects of the flame-ablation treatment on the inner surface of borosilicate glass vials and the adhesion of fluorinated diamond-like carbon coating to glass vials. Transmission electron microscopy with energy-dispersive X-ray spectroscopy analysis show that the flame-ablation treatment removed the less durable layers that contained sodium borate, which might cause elution and delamination in an aqueous solution, and formed a flat surface. The outermost surface of the flame-ablated inner wall of the vials formed a microcrystal layer containing Na and K. In addition, the flame-ablation treatment improved the adhesion of the coating to the glass vials. The EDX maps show that F derived from the F-DLC coating and Na and K derived from the glass were mixed and formed an interface layer between the F-DLC coating and the glass vial. This result indicates that the flame-ablation treatment is a promising method to improve the adhesion of the coating to borosilicate glass vials.

The Raman spectra of borosilicate glass containing 35, 40, and 45 mol % of alkali-earth metal oxide (SrO and BaO) are studied. The structural changes taking place at a gradual substitution of boron oxide by silica are determined. At a high boron oxide content, transformations among borate structural units are predominant because the main part of the modifying oxide reacts with the borate network. When boron is replaced by silicon, the appearance of borosilicate ring structures is observed in alkali-earth borosilicate glass. At the ratio of SiO2/B2O3 > 0.5, a part of the triborate groups and borate structural units containing nonbridging oxygen atoms decreases gradually. When SiO2/B2O3 > 1, the character of the transformations among the Q n structural units changes.

The article presents the results of a study of the biological activity of porous high-silica glass obtained based on two-phase alkali borosilicate glass. The test results show that the toxicity of the investigated porous glass (PG) in relation to Paramecium caudatum varies depending on the concentration and time of contact of the finely dispersed PG powder with water. It is assumed that the revealed pattern is related to, first of all, the extraction of alkaline ions into an aqueous solution.

Various glass compositions (x = 0.0, 0.1, 0.3, 0.5 and 0.7) in the system 55[(PbxCa1 – x)O · TiO2] · 44[2SiO2 · B2O3] · 1V2O5 were synthesized by employing melt–quenching technique. Subsequently, their glass ceramics were obtained by given suitable heat treatment schedule. The X-ray diffractometer technique was used to identify the phase and crystal structure along with assessment of the cell parameters. The scanning electron microscope was used to study the surface morphology of the synthesized GC samples. The detailed electrical study of three GC samples, with x = 0.0, 0.3 and 0.7 was carried out using LCR meter. The lead free GC sample, x = 0.0 possesses highest dielectric constant, 19 127 at 50 Hz and 500°C due to space charge polarization.

A number of new solid solutions Ca3 − 1.5xErx□0.5xB2SiO8 (x = 0–0.4) based on borosilicate Ca3B2SiO8 are synthesized: homogeneous solid solutions with х = 0–0.125 are structurally similar to the low-temperature monoclinic polymorphic modification of β-Сa3B2SiO8; and at 0.16 < х < 0.25, to the high-temperature orthorhombic polymorph α-Сa3B2SiO8. High-temperature X-ray powder diffraction and high-temperature Raman spectroscopy (20–1000°C) are used to study the monoclinic-orthorhombic transition of solid solutions through the two-phase region (0.125 < х

The effect of the treatment of borosilicate glass with hydrofluoric acid (HF), Caro’s acid, and concentrated hydrogen peroxide solution on their hydrophilic-hydrophobic properties and surface morphology is studied by the method of the measurement of the contact angle and calculation of the total, polar, and dispersion parts of the surface energy. It is shown that the most significant and stable hydrophilization of the glass surface, together with the maximum increase in the surface energy, is reached at the subsequent treatment with Caro’s acid and HF.

The article studies the adsorption of iron ions from solutions of iron(III) chloride with a concentration of 10–4–10–3 M at pH 3 on micro- and macroporous glass, as well as on microporous glass heat-treated at 750°C, obtained from two-phase sodium borosilicate glass. It is found that the adsorption values at a constant concentration of the iron chloride solution are a function of the structural parameters of the porous glass (PG). It is shown that the Freindlich and Langmuir adsorption isotherms can be used to analyze the experimental data and the constants of these isotherms are found. In the systems studied, adsorption mainly occurs via the monolayer mechanism.

The interaction of water vapor with borosilicate (BS) glass (Corning 7740) at a temperature of 97°C is studied by the method of secondary-ion mass spectrometry. Hydration experiments are carried out over a time period from one day to six months. The profiles of hydrogen distribution in glass are determined by a layer-by-layer analysis using a time-of-flight mass spectrometer. It is experimentally shown in this study that the hydrogenated layer on the surface of soda borosilicate glass growths linearly with time during the first two weeks of hydration (the hydration temperature used in the work) and the thickness of the hydrogenated layer increases in accordance with the parabolic law, i.e., in proportion to the square root of the processing time, starting from the fourth week of the treatment.

Thermal conductivity and electrical conductivity of borosilicate and alumophosphate glass containing imitators of highly active waste (HAW) from the processing of spent nuclear fuel VVER-440 are studied by the methods of coaxial cylinders and impedance spectroscopy from room temperature to 1200°С. For all glass samples, their thermal conductivity increases with temperature growth; however, the thermal conductivity of phosphate glass increases above the glass transition point more significantly to 2.0 W/m K at 1200°С. The thermal conductivity of borosilicate glass containing HAW imitators ranges within 1.40–1.65 W/m K in the temperature range 600–1200°С. The electrical conductivity of alumophosphate and borosilicate glass changes mainly with the concentration of sodium oxide and changes significantly with temperature. The influence of the concentration of the components of HAW imitators on the electrical conductivity of the melts is small in the studied range.

Shrinkage during the sintering of porous glass (PG) of different backgrounds and the viscosity of quartz-like glass (QG) sintered until the pores collapse are measured. The samples are obtained as a result of acid leaching of phase-separated sodium borosilicate glass. The initial PG and the samples that are doped with bismuth nitrate from a water-salt solution are studied. It is found that the heat treatment of the matrices at 750°C leads to an increase in their thermal stability. The viscosity of the matrices sintered at 870°C is practically independent of their pretreatment temperature. The viscosity of bismuth-containing quartz-like glass (BQG) decreases with an increase in the matrices’ treatment temperature.

The structure of borosilicate glasses is studied with 11B and 29Si NMR spectroscopy in order to investigate the influence of replacement of Na2O by oxides of alkali earth metals on their local structure. The quantitative data are analyzed with respect to their correspondence to the criterion of the average charge of the structural unit. The reasons for the deviation between the experimental results and this criterion are considered. It is shown that, in the case of glass devoid of borate structural units with nonbridging oxygen atoms, the corrected contents of these units are consistent with the predictions of thermodynamic modeling of the structure and properties of oxide glasses.

Adsorption of iron ions from diluted solutions (10−5–10−4 mol/L) of iron(III) chloride on macroporous glass (average pore radius 14.5 ± 0.6 nm) produced from sodium borosilicate glass is investigated. It is shown that the adsorption isotherm in the studied concentration range is in compliance with the Langmuir type. The limiting adsorption in the monomolecular layer and the adsorption equilibrium constant are determined.

The results of studying the thermal behavior of natural boron albite–reedmergnerite NaBSi3O8 and aqueous boricilicate–searlesite NaBSi2O5(OH)2 obtained by the method of hydrothermal synthesis are presented. In the investigated temperature range, reedmergnerite (30–780°C) does not undergo phase transformations. Thermal expansion is sharply anisotropic, which is a characteristic feature of the expansion of feldspars. Aqueous borosilicate searlesite (25–750°C) is amorphized above 400°C as a result of dehydration and cristobalite crystallizes from the amorphous phase. The expansion of searlesite is relatively isotropic.

New solid solutions Ca3B2 + x Si1–x O8–x/2 based on monoclinic borosilicate β-Ca3B2SiO8 are prepared using crystallization from a melt. The homogeneity range of solid solutions (0 < х ≤ 0.86) is determined and the thermal behavior of solid solution Ca3B2.4Si0.6O7.8 is studied using high-temperature X-ray powder diffraction: a reversible β ↔ α polymorphic transition is discovered in the solid solution (х = 0.4) at 550°C, decomposition begins in the solid state above 940°C with the formation of CaSiO3. The thermal expansion of both modifications is anisotropic: 20–540°C (α11 = 17, α22 = 16, α33 = 0, α V = 32 × 10−6°C−1) and 560–900°C (α11 = 15, α22 = 24, α33 = 3, and α V = 42 × 10−6°C−1).

The effect of the relative volume of the conducting phase on the electroconductivity of phase-separated glasses in the ternary system Na2O–B2O3–SiO2, whose compositions are on the same glass transition isotherm at 550°C, is investigated. It is demonstrated that the electroconductivity of phase-separated sodium borosilicate glasses does not depend on the relative volume of the conducting phase (within the limits from 0.3 to 0.9) under the condition that its composition invariable.

The local structure of cesium-borosilicate glasses with various Cs2O and B2O3 proportions and constant SiO2 content (50 mol %) is studied with 11B, 29Si, and 133Cs MAS NMR spectroscopy. The portions of three- and four-fold Si atoms are determined, as well as the concentrations of various silicate Q n units. Our experimental data are compared with the predictions of Dell’s model and thermodynamic modeling for sodium–borosilicate analogs of the glasses studied.

Borosilicate glasses of two compositions are synthesized and investigated with the aim of preparing glass microspheres from them. Using the Appen and Okhotin additive methods, the physicochemical properties of the glasses and melts are calculated, their crystallization ability and water stability are experimentally studied, their intrinsic temperatures are determined using dilatometry and differential scanning calorimetry, and their TLCE values are obtained.

Single crystals of the β-Ca3B2SiO8 new monoclinic modification have been obtained by cooling the melt of a stoichiometric composition. The crystal structure has been determined from the single crystal X-ray diffraction data and refined with R = 0.059 (wR = 0.069) in the monoclinic space group P21/m. The thermal behavior of the synthetic borosilicate has been studied. At 472 ± 5°С, a reversible phase transition of the first order occurs, leading to the formation of the orthorhombic α-Ca3B2SiO8 modification. The thermal expansion of α- and β-modifications of Ca3B2SiO8 is anisotropic: (α11 = 15, α22 = 16, α33 =–1, α V = 30 × 10–6°С–1) and α11 = 9, α22 = 28, α33 = 1, α V = 38 × 10–6°C–1, respectively.

The results of studying the iron oxide-containing two-phase sodium borosilicate glass and porous glass based on it using the method of optical spectroscopy in the visible and infrared regions are presented. Decoding the transmittance spectra of this glass in these spectral ranges using the literary data and their comparative analysis with two-phase sodium borosilicate glass that does not contain iron were carried out.

The oxidation states and coordination environment of iron ions in borosilicate glass used for the immobilization of iron-containing radioactive waste are studied by the methods of Mossbauer and Fourier transform IR spectroscopies. In homogeneous glass, containing no more than 50 wt % of waste oxides, iron is present in the form of Fe3+ and Fe2+ ions in octahedral coordination with oxygen. The phase of a iron-containing spinel, in which iron atoms with an oxidation number of +3 in the magnetically ordered state surrounded tetrahedrally by oxygen atoms (Fe3+O4) and iron in the two- and trivalent states in the octahedral oxygen environment (Fe3+O6 + Fe2+O6) are present, is precipitated at higher waste concentrations. Both the Mossbauer and IR spectra of glass crystalline materials are combinations of the corresponding individual spectra. The quantitative ratio of the doubly- and triply-charged iron ions in samples depends on the synthesis conditions. The maximum fraction of iron in the glass phase (about 28%) and, at the same time, the maximum fraction of the Fe3+ ions (91.3%) are observed in the sample prepared in a crucible by heating in a laboratory furnace in the air environment and subsequent quenching on a metal sheet.

Longitudinal and shear wave velocities were measured in borosilicate glasses containing V2O5 using the pulse echo technique. Measurements were carried out at 4 MHz frequency and at room temperature. The density was measured by the conventional Archimedes method. Elastic moduli and some other physical parameters such as Debye temperature and softening temperature were calculated. Results indicated that these parameters depend upon the V2O5 content in glass composition.

The electrokinetic properties of the particles of microporous borosilicate glass powder containing the magnetite phase in its composition on the background of an indifferent electrolyte (NaCl) have been studied. It is found that the modification of two-phase sodium borosilicate glass with iron oxide leads to a shift in the position of the isoelectric point from pH 0.5 for alkali borosilicate (ABS) porous glass (PG) to pH 4.1 ± 0.1 for iron-containing ABS PG. The observed changes in the behavior of modified PG open up new prospects for their practical application.

The influence of the acid leaching conditions (duration, HCl concentration) of phase-separated alkali borosilicate glass with composition 7.6Na2O · 20.4B2O3 · 71.9SiO2 · 0.1Al2O3 on the porous glass (PG) structure formation has been studied with diagnostics of meso- and micropores. The morphology of the PG pores has been investigated with the use of the equilibrium and kinetic adsorption-desorption methods at low, medium, and high relative pressures. It has been established that all PG samples under study were characterized by a polymodal pore size distribution with micropore sizes ranging from 0.45 to 0.70 nm (up to 3 modes) and mesopores (from 2 to 4 modes, with a dominant bimodal distribution). At the end of the acid leaching process and with an increasing duration of treatment and acid concentration, the secondary silica structuring in the liquation channels takes place. In addition, the fraction of liquation channels free of secondary silica particles decreased, the width of the second peak attributed to mesopores increased, with a modification of their shape and packing. The fraction of micropores in the total volume of accessible pores decreased from 7.5 by up to 5.5%.

Studying the structural features of radiation-induced centers in glass obtained based on sodium borosilicate glass subjected to various stages of treatment (thermal treatment, leaching, and sintering) has been carried out using electron paramagnetic resonance (EPR) and electron spectra of absorption (ESA). Relative changes in the spectra of EPR and ESP are traced depending on the presence in glass of structural groups of the type of boron oxygen hole center and boron electron center found in these objects for the first time. It is shown that the structural groups remain in the matrix of glass at various stages of its treatment.

The process of the formation of microregions (MRs) in the volume of alkaline-borosilicate glasses using the method which includes the production of porous glass (PG) by leaching two-phase alkaline-borosilicate glass in acid and the action on PG of laser radiation of a wavelength practically not absorbed by glass has been studied. The optical properties of MRs and the possibility of their preservation after PG sintering in a furnace to obtain a quartzoid glass are studied.

Using the technique of high-temperature Raman scattering spectroscopy, we studied the structure of glasses and melts of the systems Na2O-B2O3-SiO2, K2O-B2O3-SiO2, and Cs2O-B2O3-SiO2 with the relations $${{X_{M_2 O} } \mathord{\left/ {\vphantom {{X_{M_2 O} } X}} \right. \kern-\nulldelimiterspace} X}_{B_2 O_3 } = 1$$ (M = Na, K, Cs) and $${{X_{SiO_2 } } \mathord{\left/ {\vphantom {{X_{SiO_2 } } X}} \right. \kern-\nulldelimiterspace} X}_{B_2 O_3 } = 3$$ and 4/3. Based on the analysis of the registered spectra, we have shown that, at a high content of SiO2, the disordered network of glasses is composed of the Q 4, Q 3, [BO4/2]− tetrahedrons and BO3/2 triangles. When the content of SiO2 reduces, asymmetric borate triangles BO2/2O− are formed in the structure in addition. A substantial part of borate tetrahedrons are included into the content of mixed borosilicate rings composed of two silicon-oxygen and two boron-oxygen tetrahedrons. The amount of borate structural units joined into purely borate superstructural groups increases with a decrease of the silicon oxide content, depends on the alkali kation type, and grows in the direction from Cs to Na. An increase in the temperature causes a decrease of various types of rings and growth of the concentration of asymmetric triangles. Both in glasses and melts, the fraction of the BO2/2O− triangles depends on the alkali cation type and increases in the succession Cs → K → Na. The results obtained present the basis to suggest that there is some differentiation in the mechanisms of structural reconstruction of the glasses under study by their heating depending on the modifying oxide.

Various glass samples were prepared in the system [(PbxSr1 − x)O · TiO2]-[2SiO2 · B2O3]-[K2O]-[BaO]-[Nb2O5] (0.5 ≤ x ≤ 1) by melt quench method. Donor dopant Nb2O5 has been found to play an important role in the crystallization of the parent glasses. X-ray diffraction studies indicated that perovskite lead titanate (PT) or perovskite (Pb, Sr)TiO3 (PST) crystallize as a major phase followed by secondary phases of PbTi3O7, PbB2O4 and TiO2 (Rutile). Scanning electron microscopy (SEM) shows the uniform and well-interconnected morphology of the crystallites. Energy dispersive X-ray analysis (EDAX) confirms the formation of perovskite PT/PST solid solution as major phase.

The temperature dependences of the density and intensity of SAXRS of a variety of sodium borosilicate glasses in equilibrium states below vitrification temperature are obtained. The existence of a transition of the investigated supercooled liquids in a solid noncrystalline state was discovered that is similar to the one observed in the study of vitreous boron oxide and alkali-borate glasses. The temperature of the transition of supercooled liquids of the investigated compositions to a solid noncrystalline state is about 50°C below the vitrification temperatures determined by the SAXRS data. Thus, the transition occurs at a viscosity of 1014 P in borate and sodium borosilicate glasses.

The theoretical and practical approaches to the formation of micro-optic elements (MOE) for the integrated optical communication on substrates made of different materials, including silicate glasses, have been reviewed. The applicability of high-silica porous glasses (PG) fabricated by a homogeneous acid leaching of two-phase alkali borosilicate glasses as basic matrices for laser formation of MOE of different types (microlenses and microchannels) has been discussed. It has been demonstrated that sintering laser-modified PGs at temperatures ensuring the collapse of the pore can be used to stabilize MOE optical properties. The results of choosing the time-temperature mode for sintering PG substrates with a planar MOE-strip waveguide (SW) providing the SW fixation on a completely sintered substrate were presented.

This paper reports on the constants of elasticity of xPbO-RNa2B4O7-(100 − R − x) CAS with 0 ≤ x ≤ 50, and 50 ≤ R ≤ 75 mol % glass system (CAS is calcium alumino silicate glasses). The constants of elasticity were calculated in terms of the bond compression model and Makishima-Mackenzie model. The average cross-link density, the number of network bonds per unit volume, the average stretching-force constant, and the ratio of the estimated bulk modulus (K bc ) to the experimentally determined (K e ), have been calculated and discussed in terms of the bond compression model to analyze the role of PbO. Young’s modulus, the packing density and dissociation energy have been calculated and analyzed according to the Makishima-Mackenzie model. The dimensionality of the glassy network has been calculated in terms of the d ratio (4C 44/C 12) and discussed in terms of the cross-link density of these glasses. C 12 = C 11−2C 44, C 11 and C 44 are the longitudinal and shear elastic constant. The results show good agreement between the experimental and theoretical data for the representation of the constants of elasticity of borosilicate glasses.

Phase composition and structure of the glass materials obtained by fusing calcined emulator of radioactive solid waste (RW) with glassforming additives , namely, sodium disilicate or sodium tetraborate, have been studied. Materials obtained by quenching the melts are mostly amorphous; upon slow cooling (annealing), melts crystallize with the formation of materials containing phases of nepheline, britholite, and spinel. Their quantitative ratio depends on the mass ratio of calcinate and glassforming additives. Changes in the structure of the anionic motif of the quenched glass materials with increasing content of RW and pre� cipitation of crystalline phases in the annealed materials have been studied by IR and Raman spectroscopy.

The transformation of the crystal structure by isomorphous K+-Cs+ substitutions in the non-tetrahedral positions leading to the phase transition has been studied in the series of K1 − xCsxBSi2O6 solid solutions. The samples have been crystallized from the glass at 850°C for 10 h. According to the data on the crystal structures refined by the Rietveld method, the compositions with 0 ≤ x ≤ 0.35 crystallize in space group \(I\bar 43d\), structural type KBSi2O6, and those with 0.37 ≤ x ≤ 1.0, crystallize in \(Ia\bar 3d\), structural type CsBSi2O6. The reversible cubic-cubic phase transition \(I\bar 43d \rightleftarrows Ia\bar 3d\) occurs in the composition range x = 0.35–0.37.

The results of the measurement of the electric conductivity of the quartz-like glass obtained on the basis of the porous high-silica alkali borosilicate (ABS) glass are presented. Porous glass has been impregnated with aqueous solutions containing cesium ions and then subjected to thermal treatment to the pore collapse. The values of the activation energy for the electric conductivity of the obtained quartz-like glass have been calculated.

The glass of the As2S3-Sb2S3-PbΓ2 system, where Γ = Cl, Br, and I, has been synthesized by welding in vacuum-treated quartz ampoules. The glass has been obtained by slow cooling in furnace. The effect of the type of halogen on vitrification has been shown; and the glass-transition temperatures have been determined.

A mathematical model for the calculation of the resistivity of oxide glasses as a function of their composition and temperature has been developed by the experimental statistical method. The root-meansquare deviation of the calculated values of log ρ [Ω cm] from the experimental data is equal to ±0.65. The model has been recommended to use in the design of electrically insulating silicate and borosilicate glasses and related coatings.

The vitrification of a high-level waste surrogate with high concentrations of aluminum, sodium, and iron oxides in a “cold crucible” results in the formation of glassy materials with the phase composition and structure dependent on the ratio between waste oxides and borosilicate glass frit. With an increase in the waste content from ∼50 to ∼66 wt %, the degree of crystallinity of the materials increases from ∼5 to 50 vol %. The main crystalline phase is spinel, and the additional crystalline phase is nepheline. The amount of the nepheline increases with an increase in the waste content in glassy materials and with a decrease in the rate of their cooling in heat-insulated molds. The spinel is the main concentrator of transition elements (Cr, Mn, Fe, Ni, Cu, Zn). A considerable fraction of sodium, aluminum, and silicon transfers into the formed nepheline, which leads to the depletion of the glass phase in oxides of these elements and to a decrease in its chemical durability.

Alkali borosilicate glassy materials with high iron and aluminum oxide concentrations, which simulate vitrified high-level wastes from the Savannah River Site (United States) at their content ranging from 50 to 70 wt %, have been investigated using X-ray powder diffraction, optical and electron microscopy, and infrared spectroscopy. Quenched and slowly cooled samples containing 50 wt % wastes are glasses. Samples containing 60 and 70 wt % wastes, which were quenched on a metal slab, are predominantly glasses with an insignificant content of the spinel formed in a trevorite-magnetite solid solution. The slowly cooled samples also contain nepheline, and its amount increases with an increase in the waste content in the glassy materials.

The emission spectra were measured for the sol-gel glass 5.7Na2O · 19B2O3 · 75.35SiO2 with chemical composition prepared under different experimental conditions, and the characteristic features of emission spectra are discussed. The results show the broad visible (500–750 nm) and IR (850–1350 nm) emission with unique light-emitting properties were found in NBS solgel glass.

Solid solutions K1 − xCsxBSi2O6 (x (atomic fraction) = 0.00, 0.20, 0.30, 0.35, 0.40, 0.80, 0.90,1.00) have been prepared by solid-phase synthesis and crystallization of glasses in the KBSi2O6-CsBSi2O6 borosilicate series. The thermal behavior of the solid solutions has been investigated using the annealing and quenching techniques, dilatometry, and high-temperature X-ray powder diffraction. It has been shown that solid solutions with x = 0.00–0.35 and 0.40–1.00 correspond to space groups I\( \bar 4 \) 3d and Ia\( \bar 3 \)d, respectively. The cubic-cubic phase transition I\( \bar 4 \) 3d ai Ia\( \bar 3 \)d occurs in the composition range x = 0.35−0.40 at room temperature. In the series of solid solutions with x = 0−0.30, the reversible cubic-cubic polymorphic transition I\( \bar 4 \) 3d ai ia\( \bar 3 \)d with an increase in the temperature has been revealed, the temperature of the polymorphic transition has been determined, and the thermal expansion in both polymorphic modifications has been studied using high-temperature X-ray diffraction and dilatometry. The solid solutions belonging to the space group Ia\( \bar 3 \)d are characterized by a lower thermal expansion than the solid solution belonging to the space group I\( \bar 4 \) 3d. According to the calculations, the equivalents α/γ for the space groups I\( \bar 4 \) 3d and Ia\( \bar 3 \)d are 0.03 and 0.02 (in cesium atomic fractions per degree Celsius), respectively.

The pore structure and light transmission of high-silica porous glasses in the visible spectral range have been investigated as a function of the heat treatment temperature and the composition of the initial two-phase alkali borosilicate glass. The character of light transmission in porous glasses has been analyzed in the framework of the concepts of structural features of their pore space and the processes occurring in the porous glass during heating. It has been demonstrated that an increase in the temperature of heat treatment of porous glasses with different compositions leads to an increase in the pore size and a decrease in their specific surface area (with a nearly constant total porosity), which is associated with the processes of overcondensation of pores due to the rearrangement and the change in the packing density of secondary silica particles. It has been revealed that the introduction of phosphate and fluoride ions into the initial sodium borosilicate glass results in an increase in the light extinction coefficient of porous glasses due to the increase in the sizes of phase-separated inhomogeneity regions in the initial two-phase glasses, the formation of larger pores, and the presence of nanosized microcrystalline phases in porous glasses.