Influence of thermal stability on dielectric properties of SiO<Subscript>2</Subscript>–K<Subscript>2</Subscript>O–CaO–MgO glasses

Compositions of 55SiO₂–10K₂O–(35–x)CaO–xMgO are prepared by melt and quench technique. Thermal parameters of the as-prepared glasses are studied using the differential thermal analyzer under non-isothermal conditions. Kissinger, Augis–Bennett and Lasocka models are employed to investigate the kinetics of crystallization and thermal stability of these glasses. Based on this, it is concluded that CM-15 glass exhibits highest thermal stability. Raman spectroscopy is used to reveal the structural units of the glasses. Dielectric properties are observed through impedance spectroscopy. All the glasses are phase separated. The ratio of CaO/MgO influences the thermal stability, which leads to affect the dielectric properties. The highest dielectric permittivity is observed ~22 at room temperature and 100 Hz for CM-15 glass, where CaO/MgO ratio is ~1.33.     

Thermal characterisation of raw aluminosilicate glazes in SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–CaO–K<Subscript>2</Subscript>O–Na<Subscript>2</Subscript>O–ZnO system with variable content of ZnO

Thermal properties of raw aluminosilicate ceramic glazes in the multicomponent system of SiO₂–Al₂O₃–CaO–K₂O–Na₂O–ZnO modified by ZnO addition were studied by differential thermal analysis (DTA), dilatometry (DIL), hot-stage microscopy (HSM), X-ray diffraction and fourier transform infrared spectroscopy (FTIR). Using the method of differential thermal analysis, the ways in which zinc oxides affect the temperature of transition (T _g), crystallisation (T _c) were determined. An analysis of the DTA data obtained during thermal tests showed that an increase in ZnO content results in decreasing the T _g value. Also, the influence of ZnO on characteristic temperatures and viscosity of glazes was checked. The introduction of zinc oxide (ZnO) into the glaze composition contributes to the decrease in viscosity of such glazes. An increasing ZnO content in the glazes also causes the reduction in softening (T _s), half-sphere (T _half-sphere) and fusion (T _fusion) temperatures. The mid-infrared spectroscopy showed that the thermal properties of glazes in SiO₂–Al₂O₃–CaO–K₂O–Na₂O–ZnO system modified by addition of ZnO can be associated with the depolymerising influence of zinc ions on the structure of the tested glazes.     

Synthesis and photophysical properties of semiconductor molecules of D<Subscript>1</Subscript>–A–D<Subscript>2</Subscript>–A–D<Subscript>1</Subscript> structure on the basis of quinoxaline and dithienosilole derivatives for organic solar cells

new DTS(FCT₂)₂ organic semiconductor of the D₁–A–D₂–A–D₁ structure containing dithienosilole and quinoxaline chromophores as electron-donating and electron-accepting moieties, respectively, has been synthesized. The study of optical and electrochemical properties shows that the material absorbs light in a wide range of the solar spectrum through 700 nm and has an appropriate arrangement of energy levels for the efficient dissociation of excitons. The obtained results demonstrate that this approach to the design of semiconductor molecules of the D₁–A–D₂–A–D₁ structure is promising for high-performance organic solar cells.     

3D model of the <Emphasis Type="Italic">T–x–y</Emphasis> diagram of the Bi–In–Sn system for designing microstructure of alloys

The published experimental and calculated data (binary systems, x–y projection of the liquidus, table of invariant reactions with the liquid phase, and one isothermal and two polythermal sections) were used for constructing a spatial computer model of the T–x–y diagram of the Bi–In–Sn system that was supplemented with the regions of the decomposition of the compound Bi_mIn_n and the polymorphic transformation of tin. It was determined that the T–x–y diagram comprises 173 surfaces and 74 phase regions. Using the model for analyzing the material balances of phases and their microstructural components at all the stages of crystallization was demonstrated.     

Study of the NaF–NaBr–Na<Subscript>2</Subscript>SO<Subscript>4</Subscript> system

The NaBr–D (Na₃FSO₄) quasi-binary system and the NaF–NaBr–Na₂SO₄ ternary system were studied by differential thermal analysis. The melting points and compositions of eutectic mixtures were determined, and in-, mono-, and divariant equilibrium states were described.     

Effect of acid–base characteristics of ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript> on catalytic properties in carboxylation of methanol

We have established that the calcination temperature for ZrO₂–Y₂O₃ catalysts changes their acid–base spectrum, which determines the direction of the conversions in the mixture MeOH + CO₂. For samples with predominance of acid sites, the major product is dimethyl ether. As the content of base sites increases, methyl formate is formed. Activity in dimethyl carbonate synthesis is exhibited only by samples in which the basicity is higher than the acidity or close to it.     

Photocatalytic Conversion of a FeCl<Subscript>3</Subscript>–CCl<Subscript>4</Subscript>–ROH System

The photocatalytic transformations of carbon tetrachloride and aliphatic primary alcohols in the presence of iron trichloride and a molar ratio of components FeCl₃: CCl₄: ROH = 1: 300: 2550 were studied. CCl₄ is transformed into chloroform and hexachloroethane after exposure to a mercury lamp (250 W) to the FeCl₃–CCl₄–ROH system at 20°C, whereas the primary ROH alcohols are selectively oxidized into acetals (1,1-dialkoxyalkanes). The maximum conversion of CCl₄ reaches 80%. The kinetics and mechanism of the photocatalytic conversion of the FeCl₃–CCl₄–ROH system are considered.     

Thermodynamic properties of complex fluoride in KF–NaF–ThF<Subscript>4</Subscript> system

The coolant salt mixture: KF–NaF–ThF₄ has been identified as a breeding blanket for the molten salt reactor. KF–NaF–ThF₄ system is characterized with single quaternary fluoride, KNaThF₆(s) which was synthesized by solution route. The heat capacity and Gibbs energy formation of KNaThF₆(s) have been experimentally measured by differential scanning calorimeter and solid electrolyte Galvanic cell, respectively. The thermodynamic functions for KNaThF₆(s) have been determined from measured data in this study along with required data of the literature.     

Thermodynamic analysis of the structure of aqueous solutions of C<Subscript>12</Subscript>–C<Subscript>18</Subscript> hydrocarbons

Thermodynamic cycles including the increments \(\Delta G_{CH_2 }^0 , \Delta H_{CH_2 }^0 \), and \(T\Delta S_{CH_2 }^0 \) were constructed for dissolution, evaporation, hydrophobic hydration of C₅–C₉ hydrocarbons, and transfer from vapor (\(\Delta G_{CH_2 }^0 \) = ?0.7 kJ·mol^?1, \(\Delta H_{CH_2 }^0 \) = 2.9 kJ·mol^?1, \(T\Delta S_{CH_2 }^0 \) = 3.6 kJ·mol^?1) and water (\(\Delta G_{CH_2 }^0 \) = ?1.4 kJ·mol^?1, \(\Delta H_{CH_2 }^0 \) = 5.8 kJ·mol^?1, \(T\Delta S_{CH_2 }^0 \) = 7.2 kJ·mol^?1) to micelles of C₁₂–C₁₈ hydrocarbons. The formation of bistable hydrated micelles of C₁₂–C₁₈ is explained by a transition between the order-disorder states in an assembly of small (nano) systems of water. The extensive parameters of small systems and critical phenomena predicted by fluctuation theory are discussed.     

Phase Diagram of Quaternary System NaBr–KBr–CaBr<Subscript>2</Subscript>–H<Subscript>2</Subscript>O at 323 K

The phase equilibria in the system NaBr–KBr–CaBr₂–H₂O at 323 K were studied using the isothermal dissolution equilibrium method. Using the experimental solubilities of salts data, phase diagram was constructed. The phase diagram have two invariant points, five univariant curves, and four crystallization fields. The equilibrium solid phases in the system are NaBr, NaBr · 2H₂O, KBr, and CaBr₂ · 4H₂O. The solubilities of salts in the system at 323 K were calculated by Pitzer’s equation. There is shown that the calculated solubilities agree well with experimental data.     

Tribological performance of fluoroalkylsilane modification of sol–gel TiO<Subscript>2</Subscript> coating

This paper explores the possibility of making coatings with super friction-reducing and wear protection properties by using both sol–gel and self-assembling techniques. The thin film of TiO₂ was firstly prepared on glass substrates via a sol–gel method, followed by sintering at 480°C. The self-assembled monolayer of Fluoroalkylsilane (FAS) were then prepared on TiO₂ thin film to obtain TiO₂–FAS dual-layer film. The contact angle measurement and X-ray photoelectron spectroscopy were used to determine the wetting behavior and chemical structure of films, respectively. The friction behavior of films sliding against a steel ball was examined on a macro friction and wear tester. It is shown that FAS is strongly adsorbed on sol–gel derived TiO₂ thin film, making it strongly hydrophobic. Good friction-reducing and wear protection behavior is observed for the glass substrate after duplex surface-modification with sol–gel TiO₂ and top layer of FAS.     

Electrochemistry of praseodymium in LiF–CaF<Subscript>2</Subscript>

The electrochemical behaviour of PrF₃ was studied in the LiF–CaF₂ (79/21 molar ratio) at 1,213 K. Inert (W) and reactive (Ni) electrodes were used. Pr(III) ions are reduced in a single, three electron exchange. The redox potential of the Pr(III)/Pr couple at the inert electrode was observed very close to the decomposition potential of the LiF–CaF₂ melt. Experiments using reactive working electrode were done. The results show the potential shift connected to the alloying reactions of Pr and Ni. Deposition of Pr–Ni layer was confirmed by SEM-EDX analysis. Conclusions for the Pr separation possibilities from spent nuclear fuel were done.     

Production of HfB<Subscript>2</Subscript>–SiC (10–65 vol % SiC) Ultra-High-Temperature Ceramics by Hot Pressing of HfB<Subscript>2</Subscript>–(SiO<Subscript>2</Subscript>–C) Composite Powder Synthesized by the Sol–Gel Method

The formation of HfB₂–SiC (10–65 vol % SiC) ultra-high-temperature ceramics by hot pressing of HfB₂–(SiO₂–C) composite powder synthesized by the sol–gel method was studied. By the example of HfB₂–30 vol % SiC ceramic, it was shown that the synthesis of nanocrystalline silicon carbide is completed at temperatures of as low as ≥1700°C (crystallite size 35–39 nm). The production of the composite materials with various contents of fine silicon carbide at 1800°C demonstrated that the samples of the composition HfB₂–SiC (20–30 vol % SiC) are characterized by the formation of SiC crystallites of the minimum sizes (36–38 nm), by the highest density (89%), and by higher oxidation resistance during heating in an air flow to 1400°C.     

Numerical Simulation of pH Measurement in Dilute Solutions of the System H<Subscript>2</Subscript>O–KCl–HCl

Potentiometric pH measurements on cells with liquid junctions are known to be biased with respect to the notional pH in dilute acid solutions, but detailed evaluation of the problem is obstructed by experimental difficulties. In this work, pH measurements are simulated numerically on a kind of the Harned cell with a free-diffusion junction between the saturated solution of KCl and dilute solutions of HCl + KCl with ionic strength and acid concentration varying from 0.0001 to 0.1 in terms of molarity. The pH is standardized against the solution 0.0001 M HCl + 0.05 M KCl, and the simulations are based on known solution properties (transport numbers, activity coefficients and diffusion coefficients). The bias is found to range from ?0.012 to 0.056 in the composition range studied. The cell response is nearly linear in the notional pH in solutions with varying acid concentration, but no such relation is found in solutions with varying ionic strength at fixed acid concentration. It is shown that the Henderson equation underestimates the residual liquid-junction effect in very dilute solutions, largely due to failure to account for activity coefficients varying along the junction.     

Preparation and bioevaluation of <Superscript>99m</Superscript>Tc–carbonyl complex of guanine

The aim of this study is to prepare radiolabeled guanine with ^99mTc(CO)₃⁺ core. For this purpose, guanine has been radiolabeled with ^99mTc(CO)₃⁺ core. Quality control study of radiolabeled guanine molecule with ^99mTc(CO)₃⁺ core was performed by thin layer radio chromatography (TLRC) and high performance liquid radio chromatography (HPLRC). The results showed that the radiolabeling yield was quite high (94 ± 3%). Beside that ^99mTc(CO)₃–Gua complex has showed good in vitro stability during the 24 h period. Radiopharmaceutical potential of this complex was evaluated in Wistar Albino Rats. It was concluded that ^99mTc(CO)₃–Gua could be used as a nucleotide radiopharmaceutical for in vivo applications.     

Structure and thermal properties of the fritted glazes in SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–CaO–MgO–Na<Subscript>2</Subscript>O–K<Subscript>2</Subscript>O–ZnO system

In this work, the structure and thermal properties of aluminosilicate fritted glazes in SiO₂–Al₂O₃–CaO–MgO–Na₂O–K₂O–ZnO system with (4.0 mol%) and without addition of ZnO were examined by GIXRD, FTIR, MAS-NMR and thermal methods (DTA, DIL). It has been found that the all experimental glazes are amorphous material (transparent glazes). On the base of spectroscopic investigations, it was found that zinc ions exist in the network glazes in the octahedral coordination—Zn²⁺ ions play a network modifier role in structure of glazes. An analysis of the data obtained from thermal tests showed that addition of ZnO into chemical composition results in decrease in glass transition temperature value (T _g) for all glazes (DTA, DIL). The coefficient of thermal expansion (α) is decreased as the whole measurement range for one series of fritted glazes.     

Effect of ionic conductivity of a PAN–PC–LiClO<Subscript>4</Subscript> solid polymeric electrolyte on the performance of a TiO<Subscript>2</Subscript> photoelectrochemical cell

A nanoparticle TiO₂ solid-state photoelectrochemical cell has been fabricated. The effect of ionic conductivity of a solid electrolyte of polyacrylonitrile (PAN)–propylene carbonate (PC)–lithium perchlorate (LiClO₄) on the performance of a photoelectrochemical cell of indium tin oxide (ITO)/TiO₂/PAN–PC–LiClO₄/graphite has been investigated. A nanoparticle TiO₂ film was deposited onto ITO-covered glass substrate by controlled hydrolysis technique. A solid electrolyte of PAN–LiClO₄ with PC plasticizer prepared by solution casting technique was used as a redox couple medium. The room temperature conductivity of the electrolyte was determined by AC impedance spectroscopy technique. A graphite electrode was prepared onto a glass slide by electron beam evaporation technique. The device shows a photovoltaic effect under illumination. The short-circuit current density, J _sc, and open-circuit voltage, V _oc, vary with the conductivity of the electrolyte. The highest J _sc of 2.82 μA cm⁻² and V _oc of 0.56 V were obtained at the conductivity of 4.2 × 10⁻⁴ Scm⁻¹ and at the intensity of 100 mW cm⁻².     

Retention of phosphates from aqueous solutions with in sol–gel-derived amorphous CaO–MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system as a model of blast furnace slag

The article proposes new possibilities for the estimation of the maximum phosphate retention capacities (PRC) in blast furnace slags using their modeling. The amorphous blast furnace slag model (BFS–SG) and slag samples along the joining of the CaO:SiO₂ = 1 and (CaO + MgO):SiO₂ = 1 of the CaO–MgO–Al₂O₃–SiO₂ phase diagram were prepared by the sol–gel method. The surface analysis of BFS–SG was performed and the results were compared with real BFS. Batch adsorption experiments were performed to evaluate the phosphate removal of slags. SEM analysis and Raman spectroscopy were used to identify phosphate adsorbed forms. Phosphate retention is realized by the surface reactions of hydration products resulting in a nanostructured Ca-hydroxyapatite. The acid–base properties of the model samples in the selected cross-sections were characterized by the values of the optical basicity. An excellent linear relation between the phosphorus retention capacity (PRC) and the optical basicity of the model samples was found, which allows an estimation of slag retention capacities and the forms of adsorbed phosphorus.     

GC–ICP–MS determination of dimethylselenide in human breath after ingestion of <Superscript>77</Superscript>Se-enriched selenite: monitoring of in-vivo methylation of selenium

The amount of volatile dimethylselenide (DMSe) in breath has been monitored after ingestion of sub-toxic amounts of selenium (300 μg ⁷⁷Se, as selenite) by a healthy male volunteer. The breath samples were collected in Tedlar bags every hour in the first 12 h and then at longer intervals for the next 10 days. The samples were subjected to speciation analysis for volatile selenium compounds by use of cryotrapping–cryofocussing–GC–ICP–MS. Simultaneously, all urine was collected and subjected to total selenium determination by use of ICP–MS. By monitoring m/z 82 and 77, background or dietary selenium and selenium from the administered selenite were simultaneously determined in the urine and in the breath—dietary selenium only was measured by monitoring m/z 82 whereas the amount of spiked ⁷⁷Se (99.1% [enriched spike]) and naturally occurring selenium (7.6% [natural abundance]) were measured by monitoring m/z 77. Quantification of DMSe was performed by using DMSe gas samples prepared in Tedlar bags (linear range 10–300 pg, R ²=0.996, detection limit of Se as DMSe was 10 pg Se, or 0.02 ng L⁻¹, when 0.5 L gas was collected). Dimethylselenide was the only selenium species detected in breath samples before and after the ingestion of ⁷⁷Se-enriched selenite. Additional DM⁷⁷Se was identified as early as 15 min after ingestion of the isotopically-labelled selenite. Although the maximum concentration of ⁷⁷Se in DMSe was recorded 90 min after ingestion, the natural isotope ratio for selenium in DMSe (77/82) was not reached after 20 days. The concentration of DMSe correlated with the total Se concentration in the urine during the experiment (R ²=0.80). Furthermore, the sub-toxic dose of 300 μg selenium led to a significant increase of DMSe and renal excretion of background selenium, confirming that selenium ingested as selenite is homeostatically controlled by excretion. The maximum concentration of DMSe resulting from the spiked selenite was 1.4 ng Se L⁻¹ whereas the dietary background level was less than 0.4 ng Se L⁻¹. Overall excretion as DMSe was calculated to be 11.2% from the ingested selenite within the first 10 days whereas urinary excretion accounts for nearly 18.5%.     

Synthesis of nanopowders and physicochemical properties of ceramic matrices of the LaPO<Subscript>4</Subscript>–YPO<Subscript>4</Subscript>–(H<Subscript>2</Subscript>O) and LaPO<Subscript>4</Subscript>–HoPO<Subscript>4</Subscript>–(H<Subscript>2</Subscript>O) systems

Sol-gel method was used to synthesize nanosize powders in the LaPO₄–YPO₄–(H₂O) and LaPO₄–HoPO₄–(H₂O) systems. Dense ceramic samples with high microhardness (up to 25 GPa) were formed from these powders by sintering at temperatures of up to 1600°C. The isomorphic capacity of the monoclinic LaPO₄ matrix for the second component (yttrium or holmium) simulating radioactive nuclides of the actinide-rare-earth fraction was found to be high. The composites are stable in aqueous solutions, which is indicated by the low concentration of lanthanum and yttrium ions during leaching test (~10^–7 g L^–1). The results obtained in the study can be used to develop new high-efficiency ceramic matrices for solidification of the actinide-rare-earth fraction of liquid wastes formed in processing of the spent nuclear fuel.