Vol 45, No 3 (2019)

The combinatorial-topological analysis and simulation of the self-assembly of the Rb₂₄Na₂₀₀Ga₆₉₆-oF920 (space group Fmmm, V = 17 837 ų) crystal structure are conducted by the computer-based methods (TOPOS program package). The number of options for the cluster representation of the 3D atomic framework with the number of structural units ranging from 4 to 12 came to 9565 variants. Two framework-forming icosahedral clusters—ico-K108 and ico-K44—are determined. The ico-K108 three-layer 108-atom nanocluster has the 0@12(Ga₁₂)@24(Na₁₂Ga₁₂)@72(Rb₄Na₈Ga₆₀) chemical composition of shells, a diameter of 17 Å, and symmetry g = mmm. The ico-K44 two-layer 44-atom nanocluster has the 0@12(Ga₁₂)@32(Na₂₀Ga₁₂) chemical composition of shells, a diameter of 11 Å, and symmetry g = 2/m. The symmetry and topological codes of the Rb₂₄Na₂₀₀Ga₆₉₆–oF920 3D structure’s self-assembly processes from the iсo-K108 and ico-K44 nanocluster precursors are reconstructed in the form primary chain → microlayer → microframework. The Rb spacer atoms and related groups of Ga atoms in the form of chains are located in the large voids of the 3D framework.

The density of the glass of the composition 32MgO ∙ 20Al₂O₃ ∙ 48B₂O₃ (mol %) (the glass transition temperature is 644°С) in the course of the stabilization process in the temperature range 635−580°С and the temperature dependence of the stabilized glass density d_s in the range 700–580°С are investigated. The study aims to examine the temperature dependence of the stabilized glass density at temperatures below the glass transition point. The density is measured upon quenching the samples at room temperature via hydrostatic weighing in kerosene with an accuracy of ±0.001 g/cm³. It is established that in the temperature range 650−610°С the density d_s increases linearly with the temperature decrease. Deviation from the linear dependence d_s(T) towards lower density values is observed in the temperature range 610−580°С. Therefore, for the stabilized glass of the composition mentioned above in the investigated range below T_g the density first increases linearly with decreasing temperature, after which its growth gradually slows.

X-ray spectra of glass of the sodium-borate system are obtained by the method of X-ray diffractometry. Using the proposed processing of these spectra, the smallest elements of the sodium–borate glass structure (constant stoichiometry groups, CSGs), which unambiguously determine their properties, are determined. The method for determining the smallest elements of the glass structure consists of comparing the glass contours with the known contour of a glass of a stoichiometric composition.

Total mass attenuation coefficient (μ_m), total photon interaction cross-section, effective atomic numbers (Z_eff) and electron densities (N_e) of 15ZnO(17.5 – x)Al₂O₃ · xFe₂O₃ · 67.5P₂O₅ glass system (x = 0, 7.5, 12.5, 17.5) and 15ZnO(25 – x)Al₂O₃ · xFe₂O₃ · 60P₂O₅ glass system (x = 0, 25) have been investigated at 59.54 keV energy photon emitted by 100 mCi ²⁴¹Am point source employing narrow beam transmission geometry. Experimental results have been compared with theoretically calculated values using WinXCOM (2001). Mixture rule is employed to calculated theoretical mass attenuation coefficient values for each sample. Good agreement has been observed between experimental and theoretical values within experimental uncertainties. The selected glass sample with maximum contribution of Fe₂O₃ with ZnO has maximum value of mass attenuation coefficient and effective atomic number. It is found that measured values are in agreement within 2% of theoretical results. The measurement of mm, Z_eff, interaction cross-section and N_e enhances the understanding of glass sample characteristics. The prepared glass samples are found to have potential applications in radiation shielding, as well as numerous applications in the fields of medicine and industry.

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.

The hyperbolic equation of mass transfer—the wave model of diffusion—is used to describe the corrosion kinetics in binary and multicomponent glass. The coefficients of the wave diffusion model—the effective diffusion coefficient and concentration relaxation time—are calculated based on the experimental data on the outcome of substance from glass into solution.

A method of obtaining nanoparticles of gadolinium oxide by the sol-gel method from a gadolinium nitrate solution is considered. The conditions of gadolinium oxide precipitation and the size of colloidal particles are determined. Using differential scanning calorimetry (DSC), the phase transitions of gadolinium hydroxide gel on cooling to a negative temperature followed by heating from –30 to 250°C and mass loss (88.4%) in the gel during the heating to 250°C are established. The dependence of the degree of conversion in the dehydration process on the temperature is found and the activation energy of this process is calculated (54.03 kJ/mol). The particle size after the gel calcination (8–16 nm) is estimated using the TEM method.

It is established by the method of standard porosimetry that glass with a porous structure is formed as a result of the \({\text{K}}_{{{\text{glass}}}}^{ + }~ \rightleftarrows ~{\text{Na}}_{{{\text{melt}}}}^{ \pm }\) ion exchange. Half of the porous glass structure volume is occupied by pores of 1 to 4 nm. The remaining volume is filled with pores and cracks of 0.4 to 3 μm. The porosity and specific surface area of meso- and macropores, as well as the average pore radius, are determined.