Synthesis and Physicochemical Properties of Nanopowders and Ceramics in a CeO<Subscript>2</Subscript>–Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> System

Nanopowders with a composition of (СeO₂)_1–x(Gd₂O₃)_x (x = 0.03, 0.05, 0.07, and 0.10) are synthesized by the coprecipitation method using cryotechnologies. The coherent scattering region (CSR) of the powders is 10–14 nm and the specific surface area is 70–81 m²/g. Based on the powders, ceramic nanosized materials with CRS of 64–71 nm are obtained. The dependence of the phase composition, microstructure, and electrical transport properties of the obtained samples on the Gd₂O₃ content is established. In a CeO₂–Gd₂O₃ system, a solid solution with the composition of (CeO₂)_0.90(Gd₂O₃)_0.10 has the highest ionic conductivity with the transfer number of ions of t_i = 0.74 at a temperature of 700°C. It is shown that ceramics of this composition can be used as a solid electrolyte of intermediate-temperature fuel cells due to their physicochemical characteristics.     

Effect of temperature on the synthesis of nanoparticles with different morphology in the system MgO–SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>–H<Subscript>2</Subscript>O under hydrothermal conditions

Nanoparticles with different morphology have been obtained by hydrothermal method in the system MgO–SiO₂–TiO₂–H₂O. It has been found that in the investigated temperature–time interval the formation of nanotubes of hydrosilicate with the structure of chrysotile with a small amount of impurity phases predominantly takes place.     

Mechanical,Structural and Thermal Properties of Transparent Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZnO–TeO<Subscript>2</Subscript> Glass System

Oxide based optical glass materials has important potential material in many applications from fiber optic to sensor due to the high transparency and amourphous structures. The objective of this study is to synthesize the novel optical glass materials based on the bismuth and aluminum contents to be able to determine the physical, chemical and mechanical properties by considering the systematic experimental steps. In this study, Bi₂O₃–Al₂O₃ based tellurite optical glasses have been prepared by using conventional melt quenching method as a function of the both Bi₂O₃ and Al₂O₃ compositions. There is a strong interactions between the glass former and modifier ions that might effect on the structure and mechanical properties. During the experimental steps, thermal, structural and mechanical properties of the prepared glass materials have been determined considering the DTA/DSC, FT-IR spectroscopy, SEM and Vicker’s hardness techniques, respectively. Thermal parameters, like glass transition, T_g, onset, T_x, crystallization, T_p, and melting, T_m, temperatures were obtained by using DTA scan.     

Structural and thermal degradation studies on thin films of the nanocomposite system PVP–Ce(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>·4H<Subscript>2</Subscript>O

Newly prepared and well-characterized nanocomposite thin films of polyvinylpyrrolidone (PVP) containing 2, 5, 10, and 15 wt% cerium (IV) sulfate have been subjected to structural and thermal stability investigations using the transmission electron microscopy (TEM), atomic force microscope (AFM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The nanostructural nature of the investigated films was confirmed from the estimated average size of the particles. Better crystallinity was achieved with the addition of 15 wt% cerium disulfate to PVP. The thermograms of DSC and its derivative for the investigated composites indicated the development of a new endothermic peak of decomposition nature, and the values of peak position and associated enthalpy were found to be composition dependent, indicating a decrease in thermal stability of PVP with the increase of dopant concentration. Thermograms of TGA and its derivative revealed that the weight loss in the composite samples is composition dependent, and two main steps of degradation were clearly evident, the first assigned mainly to dehydration processes at relatively lower temperature range (30–200 °C) and the second at higher temperatures up to 400 °C attributed to decomposition processes. Thermodynamic parameters, such as activation energy, entropy, enthalpy, and Gibbs free energy, were also determined on the basis of thermogravimetric data.     

Homogeneous and Heterogeneous Crystal Nucleation in Glass of the Li<Subscript>2</Subscript>O–SiO<Subscript>2</Subscript> System

The results of studying the kinetics of homogeneous (spontaneous) and heterogeneous (catalyzed) crystal nucleation in silicate glass is presented for glasses in the Li₂O–SiO₂ system. Nucleation is catalyzed via the photosensitive mechanism by adding poorly soluble impurities, shifting the glass composition towards the higher content of one of the components (autocatalysis), and by passing steam through the glass melt. The fundamental characteristics of crystal nucleation are obtained. The composition ranges with the maximum and minimum steady-state crystal nucleation rates are identified.     

Comparative Study of Powders Based on the ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–СeO<Subscript>2</Subscript> System Obtained by Various Liquid Phase Methods of Synthesis

Using the liquid-phase methods of synthesis—the coprecipitation of hydroxides and the hydrothermal method—mesoporous xerogels are obtained based on the ZrО₂–Y₂О₃–CeО₂ system with 5–8-nm particles and powders (after the heat treatment of xerogels at 600°C) with a coherent scattering region (CSR) size of 9 to 10 nm and S_sp = 96–156 m²/g. After calcination at 1400°C, the powders are transformed into tetragonal solid solutions with a CSR size of 65 nm in the synthesis by the coprecipitation method, and they are transformed into solid solutions with a CSR size of 84 nm with a high degree of tetragonality of c/a = 1.438–1.431 in the synthesis by the hydrothermal method.     

Migration processes in the glass forming melts of the Na<Subscript>2</Subscript>O–BaO–Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system

The specific conductivity and tracer of diffusion of sodium and barium ions have been determined and the values of the transport numbers and correlation factor for diffusion have been calculated in two melts of the Na₂O–BaO–Ga₂O₃–SiO₂ system.     

Structural heterogeneity of SiO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glass

It is shown that the phase heterogeneity of SiO₂–Na₂O–Al₂O₃ glass has a liquation and crystallization nature, the balance between which is determined by the conditions of their synthesis. An increase in the aluminum oxide content decreases the number of liquation and crystallization sites, and also the linear sizes of the crystalline formations without eliminating the phase separation due to the liquation. The area of metastable immiscibility in the SiO₂–Na₂O–Al₂O₃ system, which is determined by scanning electron microscopy, is probably wider than the area detected by the optical methods.     

Effect of the relative volume of the conducting phase on the electroconductivity of glasses in the Na<Subscript>2</Subscript>O–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system

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.     

Analysis of a gas-phase Br<Subscript>2</Subscript>–H<Subscript>2</Subscript> redox flow battery

The operation of a gas-phase Br₂–H₂ flow battery is analyzed via a mathematical model and compared to experimental data. The model predicts the operating conditions of the cell in both fuel-cell (i.e., discharge) and electrolysis (i.e., charge) mode as a function of current, inlet gas composition, flow rate, and pressure differential across the membrane. The analysis reveals that gas-phase Br₂/HBr reactants significantly enhance mass transfer, which enables higher currents densities to be achieved compared to a liquid-fed system. A key feature of the model is water transport across the membrane, which determines membrane conductivity, reactant concentration and undesired condensation. The model is used to provide insight into cell operation, including operating conditions needed to avoid water condensation.     

Vapor–Liquid Equilibrium of Binary Components of the BrCF<Subscript>2</Subscript>COOCH<Subscript>3</Subscript>–CF<Subscript>3</Subscript>COOH–BrCF<Subscript>2</Subscript>COOH–CF<Subscript>3</Subscript>COOCH<Subscript>3</Subscript> Quaternary System

Vapor–liquid equilibria of binary components of the BrCF₂COOCH₃–CF₃COOH–BrCF₂COOH–CF₃COOCH₃ quaternary system have been studied experimentally at constant pressure. The experiments have been carried out on a modified Sventoslavskii ebulliometer. Using the Aspen Plus software package, the appropriate models have been selected and the vapor–liquid equilibria for six binary systems have been simulated.     

The Use of the [H<Subscript>2</Subscript>O–CO<Subscript>2</Subscript>] Arbitrary Decomposition Assumption to Predict the Performance of Condensed High Explosives

The plate dent test is one of the simplest tools for fast determination of the detonation pressure. The test is based on the observation that the detonation pressure correlates with the depth of the dent produced by a detonating explosive on a metal witness plate. The present study is aimed at developing a model for estimating the dent depth, which is used not only to obtain the detonation pressure, but also to evaluate the brisance relative to a reference explosive. It is shown that the experimental dent depth values for CHNO and CHNOClF explosives can be successfully reproduced by a model based on few parameters, namely: loading density, number of moles of gaseous detonation products per gram of the explosive, and average molecular weight of the gaseous products, where the number of moles and the mean molecular weight of the gaseous products are calculated according to the [H₂O–CO₂] arbitrary decomposition assumption. Furthermore, the predicted values of the dent depth and the Kamlet–Jacobs method are used to estimate the detonation pressure for 37 explosives. The results show that the pressures obtained on the basis of the dent depth values are in better agreement with experimental/thermochemical code data than the predictions of the Kamlet–Jacobs method.     

Synthesis of the study of solid solutions based on the ZrO<Subscript>2</Subscript>–HfO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>(CeO<Subscript>2</Subscript>) system

The results of the studies of the conditions of the liquid-phase synthesis of highly dispersed xerogels with a low degree of agglomeration and precursor nanopowders (~10–12 nm) based on zirconium dioxide in the ZrO₂–HfO₂–Y₂O₃(CeO₂) system are presented. The thermal decomposition of xerogels and formation of crystalline solid solutions with the structure of fluorite are investigated. The optimal conditions for the solidification of nanodispersed powders for fabricating compact ceramics based on solid solutions of ZrO₂ and the physical–chemical properties of these ceramics are studied.