Том 42, № 2 (2016)

The results of study of mechanical losses by dynamic methods for silicate, borate, and chalcogenide glasses, metallic glass and glycerol at heating in the glass transition region were analyzed. Essential differences between the dynamic viscosity values η* calculated by means of the Maxwell equation based on the relaxation time at the maximum of losses (ωτ = 1) for labile states of glass, and the experimental values of η for the metastable liquid at the same temperature were revealed. The ratio η*/η was systematized in the framework of kinetic theory of glass transition and thermodynamics. An interpretation of the regularities was proposed based on the theory of dynamic properties of liquids. It was shown that different widths of spectra of relaxation times were the most probable reason of the difference between η* and η. The width of spectrum is determined by the degree of ordering of states of compared metastable liquid and glass at the same temperature; it depends on the thermal prehistory of each state. A wider spectrum of relaxation times corresponds to a more ordered state. For the considered glasses, the ratio of the temperature corresponding to viscosity value η* of the metastable liquid to the temperature of α-relaxation maximum (T_α) is 1.03 ± 0.01 at T_α variation from 190 to 1550 K. It is the evidence that all the relaxation frequencies, constituting both “narrow” and “broad” spectrum are associated with one and the same molecular mechanism. Mechanical losses in the metastable supercooled glycerol are described by the Maxwell equation with high precision for η values from 10¹³ to 10⁵ Pa s.

Mixed alkali alkaline earth oxide borate glasses of the composition (25 – x)Li₂O–xK₂O–12.5BaO–12.5MgO–49B₂O₃–1CuO (x = 0, 5, 10, 15 and 20 mol %) were prepared by the melt quenching technique. The X-ray diffractograms of all the glass samples were recorded at room temperature. Peak free X-ray spectra revealed the amorphous nature of all the prepared glasses. Modulated differential scanning calorimetry (MDSC) was used to determine the glass-transition temperature (T_g). The probable mixed alkali effect was investigated using experimental techniques like density, molar volume, MDSC, electron paramagnetic resonance (EPR), and optical absorption studies. From the EPR spectra the spin-Hamiltonian parameters were evaluated. The spin-Hamiltonian parameter values indicated that the ground state of \(C{u^{2 + }}is{\kern 1pt} {d_{{x^2} - {y^2}}}\) orbital (²B_1g) and the site symmetry around Cu² is tetragonally distorted octahedral. The variation of g_|| and A_|| as a function of Li₂O content was found to be nonlinear. A broad optical absorption band was observed in all the glasses containing Cu² ions corresponding to ²B_1g → ²B_2g transition. From the optical absorption studies the values of the optical band gap (E_opt) for indirect, direct transitions and Urbarch energy (ΔE) have been evaluated. By co-relating the EPR and optical absorption data, bonding parameters α², β² and β₁² were evaluated.

The influence of the treatment temperature of KU-1 quartz glass on the value of the elastic recovery of the microindentation imprint of a Vickers diamond tetrahedral pyramid is studied. It is found that the value of the elastic recovery of the imprint’s diagonal and the fracture resistance of quartz glass upon microindentation varies depending on the preliminary thermal treatment. The obtained experimental results are compared with the data reported by other authors.

The two-electron exchange between neutral and doubly ionized U^– tin centers in the partially compensated Pb_0.96Sn_0.02Na_0.01Tl_0.01S hole solid solutions in the temperature range of 80–900 K and in the partially compensated Pb_0.965Sn_0.015Na_0.01Tl_0.01Se hole solid solutions in the temperature range of 80–600 K was studied by ^119mmSn(^119mSn) Mössbauer spectroscopy. The activation energy of this process for the Pb_0.96Sn_0.02Na_0.01Tl_0.01S solid solutions is comparable with the depth of the tin energy levels in the PbS band gap and amounts to 0.11(2) eV, while in the Pb_0.965Sn_0.015Na_0.01Tl_0.01Se solid solutions it is comparable with the correlation energy of the donor U^– tin centers in PbSe and amounts to 0.05(1) eV. It is established that the exchange is implemented by the simultaneous transfer of two electrons with the valence band states involved. In the glass-like (As₂Se₃)_0.3(GeSe)_0.6(SnSe)_0.1 alloy containing quadruply charged six-coordinated tin (singly ionized donor center) and doubly charged three-coordinated tin (singly ionized acceptor center), no traces of the electronic exchange between differently charged tin states was observed up to a temperature of 480 K, which is explained by the fact that the doubly charged and quadruply charged tin centers are in different coordination states.

Ring-shaped carbon nanotubes have been simulated as macromolecular coils in the context of the fractal physical chemistry of polymer solutions k]The dependence of the interfacial adhesion level in polymer/carbon nanotube nanocomposites on the structure of the above composites k]characterized by its fractal dimension k]has been shown k]The validity of this interpretation has been confirmed via a description of the degree of reinforcement of nanocomposites within the reinforcement molecular model.

Bioactive glass 46S6 has been elaborated by melting method at high temperature. “In vitro” experiments of 46S6 glass were carried out by soaking in a simulated body fluid for different times. The kinetics of chemical reactivity and the bioactivity of this biomaterial was investigated by X-ray diffraction and elucidated by using an original structural analysis method based on solid-state MAS-NMR. After in vitro assays, X-ray diffraction confirmed the high bioactivity of bioglass 46S6. The ²⁹Si MAS-NMR spectra showed the emergence of two new species: Q_Si³ (OH) Q_Si⁴ and which are characteristic of the dissolution of vitreous network of 46S6 glass while the ³¹P MAS-NMR spectra highlighted the formation of new component attributed to hydroxycarbonate apatite. The bioglass 46S6 have presented the rapid formation of a biological active hydroxycarbonate apatite layer after soaking in simulated body fluid fluid.

Iron oxoborate Fe₃O₂(BO₄) has been first produced in solid-phase chemical reactions. Its thermal behavior in the temperature range 20–900°C is studied with the use in-situ high-temperature powder X-ray diffraction. It is shown that Fe₃O₂(BO₄) begins decomposing with the formation of Fe₂O₃ in the temperature range 660–900°C. Thermal expansion is sharply anisotropic at room temperature (α_max/α_min = 7) and becomes more isotropic with an increase in the temperature (α_max/α_min = 1.2). The degree of oxidation of Fe³⁺ has been confirmed by Mössbauer spectroscopy (at a room temperature), and two nonequivalent positions in the structure have been detected, which are occupied by iron atoms with the octahedral environment of the oxygen atoms.

The spectrophotometric differential kinetic method of determination of silicon and germanium based on a difference in the kinetic parameters in the presence of each other the same analytical form in GeO₂–SiO₂ systems is described. The possibility of the development of analytical techniques taking into account the revealed limitations of the proposed kinetic scheme is shown. The studies of the model solutions show that the margin of analytical error does not exceed the acceptable limit for the applied method.