In-Flight Spheroidization of Alumina Powders in Ar–H<Subscript>2</Subscript> and Ar–N<Subscript>2</Subscript> Induction Plasmas

In-flight spheroidization of alumina powders in Ar–H₂ (H₂–7.6%, vol/vol) and Ar–N₂ (N₂–13.0%, vol/vol) RF induction plasmas was investigated numerically and experimentally. The mathematical model for the plasma flows incorporates the k– turbulence model, and that for particles is the Particle-Source-in-Cell (PSI-Cell) model. Experimental results demonstrate that spheroidized alumina particles are produced in both Ar–H₂ and Ar–N₂ RF plasmas, with different particle size distributions and crystal phases. Agreement between the predicted and measured particle size distributions is satisfactory under high particle feed rate conditions, while the results obtained for the Ar–H₂ plasma are better than those for the Ar–N₂ plasma. The discrepancy occurring in low feed rate conditions suggests that particle evaporation is an important factor affecting the plasma–particle heat transfer.     

On the Control of Plasma Parameters and Active Species Kinetics in CF<Subscript>4</Subscript> + O<Subscript>2</Subscript> + Ar Gas Mixture by CF<Subscript>4</Subscript>/O<Subscript>2</Subscript> and O<Subscript>2</Subscript>/Ar Mixing Ratios

The effects of both CF₄/O₂ and Ar/O₂ mixing ratios in three-component CF₄ + O₂ + Ar mixture on plasma parameters, densities and fluxes of active species determining the dry etching kinetics were analyzed. The investigation combined plasma diagnostics by Langmuir probes and zero-dimensional plasma modeling. It was found that the substitution of CF₄ for O₂ at constant fraction of Ar in a feed gas produces the non-monotonic change in F atom density, as it was repeatedly reported for the binary CF₄/O₂ gas mixtures. At the same time, the substitution of Ar for O₂ at constant fraction of CF₄ results in the monotonic increase in F atom density toward more oxygenated plasmas. The natures of these phenomena as well as theirs possible impacts on the etching/polymerization kinetics were discussed in details.     

Dissociation enthalpies and phase equilibrium for TBAB semi-clathrate hydrates of N<Subscript>2</Subscript>, CO<Subscript>2</Subscript>, N<Subscript>2</Subscript> + CO<Subscript>2</Subscript> and CH<Subscript>4</Subscript> + CO<Subscript>2</Subscript>

Tetra-n-butyl ammonium bromide (TBAB) semi-clathrate (sc) hydrates of gas are of prime importance in the secondary refrigeration domain and in the separation of gas molecules by molecular size. However, there is a scarcity of dissociation enthalpies under pressure of pure gases and gases mixtures for such systems. In addition, the phase equilibrium of TBAB sc hydrates of several pure gases is not well defined yet as a function of the TBAB concentration and as a function of the pressure. In this paper, dissociation enthalpies and the phase equilibrium of TBAB sc hydrates of gas have been investigated by differential scanning calorimetry (DSC) under pressure. Pure gases such as N₂ and CO₂ and gases mixtures such as N₂ +  CO₂ and CH₄ +  CO₂ were studied. To our knowledge, we present the first phase diagram of TBAB sc hydrates of N₂ for different pressures of gas in the TBAB concentration range from 0.170 to 0.350 wt. Enthalpies of dissociation of TBAB sc hydrates of pure gases and gases mixtures were determined as a function of the presssure for a compound with a congruent melting point whose hydration number corresponds to 26.     

Solubility and Ionic Interaction of the CaF<Subscript>2</Subscript>–CaSO<Subscript>4</Subscript>–H<Subscript>2</Subscript>O System at 298.1 K

Solubility isotherms of the sparingly soluble salts CaF_2(s) and CaSO₄·2H₂O_(s) in their mixed aqueous solutions have been measured at 298.1 K. It was found that the CaF_2(s) solubility decreases with increasing CaSO₄ concentration in the solution and reaches about 1/3 of the CaF_2(s) solubility in pure water in the CaSO₄·2H₂O_(S) saturated solution. A thermodynamic model was developed to predict the CaF_2(s) solubility isotherm in this system, in which the short range interactions of the species in the aqueous solution are represented by ion-association constants reported in literature, and the long range interaction, i.e., the electrostatic term, is represented by the well known Davies equation. The predicted solubility isotherm reasonably agrees with the experimental results. The contributions of the long-range term and the short-range term to the calculated solubility isotherm were investigated. It was concluded that the ionic association combining with the Davies equation is sufficient to represent the excess interaction of the CaF₂ + CaSO₄ aqueous solution at 298.15 K. This model approach could be applicable for other dilute mixed electrolyte systems in which component activity coefficients are lacking and model parameters are difficult to determine.     

Ionic mobility and electrophysical properties of solid solutions in PbF<Subscript>2</Subscript>–SbF<Subscript>3</Subscript> and PbF<Subscript>2</Subscript>–SnF<Subscript>2</Subscript>–SbF<Subscript>3</Subscript> systems

Ionic mobility and electrical conductivity of solid solutions with fluorite structure, obtained with solid-state approach in PbF₂–SbF₃ and PbF₂–SnF₂–SbF₃ systems, are studied by 19F NMR and electrochemical impedance spectroscopy methods. The 19F NMR spectra parameters, types of ion motions in the fluoride sublattice, and the ionic conductivity magnitude are shown to be determined by the temperature and fluoride concentration in the solid solutions. The solid solution specific conductivity in the PbF₂–SbF₃ and PbF₂–SnF₂–SbF₃ systems at 420–450 K is as high as ~10^–2 S/cm, which allows accounting the solid solutions as a base for preparation of functional materials.     

Oxidation of Iodo- and Bromo-Substituted Polymethylbenzenes in the System PbO<Subscript>2</Subscript>–CF<Subscript>3</Subscript>COOH–CH<Subscript>2</Subscript>Cl<Subscript>2</Subscript>

The oxidation of mono- and diiodo- and -bromo-substituted polymethylbenzenes (mesitylene and durene) in the system PbO₂–CF₃COOH–CH₂Cl₂ at room temperature (2–70 h) leads mainly to the formation of iodo- and bromobenzyl alcohols as result of oxidation of methyl group. The reaction involves intermediate formation of haloarene radical cations. ESR study of these radical cations made it possible to determine the structure of their singly occupied molecular orbitals a₂ or b₁ and interpret their reactivity.     

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.     

Distribution of niobium and lanthanum between two immiscible melts in the system LaPO<Subscript>4</Subscript>–SiO<Subscript>2</Subscript>–NaF–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

The system LaPO₄–SiO₂–NaF–Nb₂O₅–Fe₂O₃ is characterized by immiscibility fields in the liquid state region. Addition of iron expands fields of immiscibility of melts and decreases the temperature of their coexistence. A fraction of 87–90% of niobium is extracted into iron silicate melt, and 92–98% of lanthanum is extracted into phosphate salt melt.     

Structure and Crystallization of Glasses in the MnNbOF<Subscript>5</Subscript>–BaF<Subscript>2</Subscript>–InF<Subscript>3</Subscript> System

Glasses of the MnNbOF₅–BaF₂–InF₃ system were prepared. The structure, thermal behavior, and crystallization of these glasses were studied by IR and Raman spectroscopy, differential scanning calorimetry (DSC), X-ray powder diffraction, and microscopy. The \(\rm{NbO}_2\rm{F}_4^{3-}\) and \(\rm{InF}_6^{3-}\) ions form a mixed glass network. Glass crystallization occurs in one or two steps depending on the component ratio. The major crystal phases are Ba₃In₂F₁₂ and BaNbOF₅. The obtainability of transparent crystal-glass samples in MnNbOF₅–BaF₂–InF₃ glasses via heat treatment is shown.     

Phase transformations in the systems Ti<Subscript>2</Subscript>Fe–H<Subscript>2</Subscript> and Ti<Subscript>2</Subscript>Fe–NH<Subscript>3</Subscript>

The interactions of two-phase alloy Ti₂Fe with hydrogen and ammonia at 100–500°C were studied, the compositions of the products were found, and the conditions for producing hydride and nitride phases were determined. The potential of using the two-phase alloy in a metal hydride hydrogen accumulator operating at 20–600°C was considered.     

Effect of Fe-zeolite on formation of N<Subscript>2</Subscript>O in selective reduction of NO by NH<Subscript>3</Subscript> over V<Subscript>2</Subscript>O<Subscript>5</Subscript>–WO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> catalyst

An approach for significantly suppressing N₂O formation in reduction of NO by NH₃ over V₂O₅–WO₃/TiO₂ (VWT) catalyst has been studied by coating different amounts of a Fe-exchanged zeolite (FeZ) onto the catalyst. FeZ-promoted VWT samples were characterized using N₂ sorption, X-ray diffraction (XRD) analysis, and NH₃ adsorption/desorption techniques to understand the primary role of FeZ in lowering N₂O production levels. At high temperatures (≥450 °C), VWT gave N₂O production with high concentrations, while N₂O formation was noticeably reduced when using FeZ-promoted catalysts, which also showed somewhat lower NO removal activities (<5 %) at all temperatures. N₂ sorption and XRD measurements revealed no perceptible physical or chemical alterations of each constituent, even in VWT catalysts after FeZ coating following high-temperature calcination. Adsorption of NH₃ on unpromoted and FeZ-promoted catalysts and subsequent desorption yielded very complicated spectra for N₂O that might primarily come from NH₃ oxidation, and the interaction between V–NO species at temperatures >580 °C. NO on neighboring sites seems to be produced via decomposition of N₂O generated at lower temperatures. The FeZ in the promoted VWT catalysts could be responsible for N₂O decomposition and N₂O reduction with unreacted NH₃ at temperatures >400 °C, thereby significantly lowering N₂O emission levels. This promotional effect bodes well for use in many industrial deNO _x applications.     

Structural characterisation and thermo-physical properties of glasses in the Li<Subscript>2</Subscript>O–SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–K<Subscript>2</Subscript>O system

This article aims to shed some light on the structure and thermo-physical properties of lithium disilicate glasses in the system Li₂O–SiO₂–Al₂O₃–K₂O. A glass with nominal composition 23Li₂O–77SiO₂ (mol%) (labelled as L₂₃S₇₇) and glasses containing Al₂O₃ and K₂O with SiO₂/Li₂O molar ratios (3.13–4.88) were produced by conventional melt-quenching technique in bulk and frit forms. The glass-ceramics (GCs) were obtained from nucleation and crystallisation of monolithic bulk glasses as well as via sintering and crystallisation of glass powder compacts. The structure of glasses as investigated by magic angle spinning-nuclear magnetic resonance (MAS-NMR) depict the role of Al₂O₃ as glass network former with four-fold coordination, i.e., Al(IV) species while silicon exists predominantly as a mixture of Q ³ and Q ⁴ (Si) structural units. The qualitative as well as quantitative crystalline phase evolution in glasses was followed by differential thermal analysis (DTA), X-ray diffraction (XRD) adjoined with Rietveld-reference intensity ratio (R.I.R.) method, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The possible correlation amongst structural features of glasses, phase composition and thermo-physical properties of GCs has been discussed.     

Etching Characteristics and Mechanisms of TiO<Subscript>2</Subscript> Thin Films in CF<Subscript>4</Subscript> + Ar,Cl<Subscript>2</Subscript> + Ar and HBr + Ar Inductively Coupled Plasmas

The comparative study of etching characteristics and mechanisms for TiO₂ thin films in CF₄ + Ar, Cl₂ + Ar and HBr + Ar inductively coupled plasmas was carried out. The etching rates for TiO₂, Si and photoresist were measured as functions of gas mixing ratios at fixed gas pressure (10 mTorr), input power (800 W) and bias power (300 W). It was found that the maximum TiO₂ etching rate of ~130 nm/min correspond to pure CF₄ plasma while an increase in Ar fraction in a feed gas results in the monotonic non-linear decrease in the TiO₂ etching rates in all three gas mixtures. Plasma diagnostics by Langmuir probes and 0-dimensional (global) plasma modeling supplied the data on the densities of plasma actives specie as well as on particle and energy fluxes to the etched surface. It was concluded that, under the given set of experimental conditions, the TiO₂ etching kinetics in all gas systems correspond to the ion-assisted chemical reaction with a domination of the chemical etching pathway. It was found also that the differences in the absolute TiO₂ etching rates correlate with the energy thresholds for TiO₂ + F, Cl or Br reaction, and the reaction probabilities for F, Cl and Br atoms exhibit the different changes with the ion energy flux according to the volatility of corresponding etching products.     

Effects of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> on the crystallization and structure of CaO–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> glass ceramics

Radiation-induced degradation of the weakly and strongly 4-vinylpyridine basic ion exchange resins by gamma radiolysis was investigated in the presence of air and liquid water. This study is focused on evaluating the radiolytic gases (H₂, CO, CO₂ and CH₄) and liquid products (water-solute TOC and NH₄ ⁺). The weakly basic resin yielded lower amounts of H₂ and CO and higher amounts of CO₂ than those of the strongly basic resin. Moreover, the strong basic resin tended to yield greater amounts of NH₄ ⁺. Resins were characterized by the FTIR spectroscopy technique and the results showed that the resins structures are relatively stable.     

Solid-Liquid Equilibria in the Quaternary Systems KCl–MgCl<Subscript>2</Subscript>–SrCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O and NaCl–KCl–SrCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O at 348 K

Solid-liquid equilibria in the quaternary systems KCl–MgCl₂–SrCl₂–H₂O and NaCl–KCl–SrCl₂–H₂O at 348 K were measured by the isothermal solution saturation method. The composition of the equilibrium solid phase, solubilities of salts, and densities of saturated solution in the two systems were determined. Phase diagrams, water content diagrams and solution density diagrams of quaternary systems were plotted according to experimental data. The phase diagram of the quaternary system NaCl–KCl–SrCl₂–H₂O has one invariant point, three univariant curves as the boundary of NaCl, KCl and SrCl₂ · 2H₂O. This phase diagrams were simple co-saturation type without complex salt and solid solution. For the quaternary system KCl–MgCl₂–SrCl₂–H₂O, one complex salt KCl · MgCl₂ · 6H₂O (Car) had been found in this system, consisted of five univariant curves, two invariant points and four crystallization regions of MgCl₂ · 6H₂O (Bis), KCl, SrCl₂ · 2H₂O and KCl · MgCl₂ · 6H₂O. And the densities transformation rules were simply discussed. Simultaneously, the solubilities and densities data in invariant point of the quaternary system NaCl–KCl–SrCl₂–H₂O had been compared with the experimental data of previous researchers.     

Formation of solid solutions of multiferroics in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The sequence of phases appearance during the formation of Bi_1–xNd_xFeO₃ solid solutions in powder oxides mixtures of bismuth, neodymium, and iron has been determined. It has been shown that the closeness of the reaction mixture composition to that of the individual compound (BiFeO₃ or NdFeO₃) is essential for the realization of the series of phase transformations yielding solid solutions of multiferroics Bi_1–xNd_xFeO₃ as the final product, due to the prevalence of various interphase contacts in the starting reaction zone.     

Formation of nanocrystals in the ZrO<Subscript>2</Subscript>–H<Subscript>2</Subscript>O system

Formation of zirconia nanocrystals in the course of thermal treatment of an X-ray amorphous zirconium oxyhydroxide was studied. It was shown that the formation of tetragonal and monoclinic polymorphs of ZrO₂ in the temperature range from 500 to 700°C occurs owing to dehydration and crystallization of amorphous hydroxide. An increase of the temperature up to 800°C and higher activates mass transfer processes and, as a result, activates the nanoparticle growth and increases the fraction of the phase based on monoclinic modification of ZrO₂ due to mass transfer from the nanoparticles with the non-equilibrium tetragonal structure. Herewith, formed ZrO₂ nanocrystals with monoclinic structure have a broad size distribution of crystallites, and the average crystallite size after thermal treatment at 1200°C for 20 min is about 42 nm.     

Phase equilibria in the Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>–CdO system and the thermal stability of Cd<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>7</Subscript> and CdNb<Subscript>2</Subscript>O<Subscript>6</Subscript>

Phase equilibria were studied in the Nb₂O₅–CdO system in the Nb₂O₅-rich region including CdNb₂O₆ and Cd₂Nb₂O₇. It was determined that CdNb₂O₆ and Cd₂Nb₂O₇ in air are stable to 1150 and 1120°C, respectively, and that, above these temperatures, there is solid-phase decomposition of niobates with CdO release in the gas phase. Along with the cadmium oxide evaporation, the Cd₂Nb₂O₇ decomposition is accompanied by the formation of cadmium metaniobate CdNb₂O₆ and the CdNb₂O₆ decomposition results in the formation of niobium oxide Nb₂O₅. No thermal events were observed in the differential thermal analysis curve for a 1: 1 CdNb₂O₆–Cd₂Nb₂O₇ mixture heated to 1100°C in air, which suggests that there are neither phase transformations in cadmium niobates, nor a eutectic within this temperature and concentration ranges. A study of the morphology of compacted samples of niobates determined specific conditions for producing dense composite ceramics, a mixture of niobates, that is suitable for using as a dielectric material.