Raman Spectra and the Structure of Melts in the Na2O–P2O5–SiO2System

Raman spectra of melts in the Na₂O–P₂O₅–SiO₂system are measured at high temperatures. The differences between the Raman spectra of melts and glasses with identical compositions are considered. It is demonstrated that the structural inhomogeneity of the system slightly increases with a decrease in temperature and vitrification of the melt.     

Citrate-Nitrate Synthesis and the Electrophysical Properties of Ceramics in the K2O–TiO2–Fe2O3 System

Glass Physics and Chemistry - This paper presents a study of the electrically conductive properties of ceramics based on phases crystallizing in the K2O–Fe2O3–TiO2 system, when using...     

Liquid–Liquid Equilibrium And Extraction Capacity of the PPG 425–NaNO3–H2O System

Theoretical Foundations of Chemical Engineering - In this work, we study the liquid–liquid phase equilibrium for a new extraction system with polypropylene glycol 425 (PPG 425) and sodium...     

Critical evaluation and thermodynamic optimization of the Na2O–FeO–Fe2O3–Al2O3–SiO2 system

A critical assessment and thermodynamic optimization of phase diagrams and thermodynamic properties of the entire Na₂O–FeO–Fe₂O₃–Al₂O₃–SiO₂ system were carried out at 1 atm total pressure. A set of optimized model parameters obtained for all phases present in this system reproduces available and reliable thermodynamic property and phase equilibrium data within experimental error limits from 298 K to above liquidus temperatures for all compositions and oxygen partial pressures from metallic Fe saturation to 1 atm. The Gibbs energy of liquid solution was described based on the Modified Quasichemical Model considering the possible formation of NaAlO₂ and NaFeO₂ associates in the liquid state. The solid solutions wüstite, spinel, feldspar, nepheline, carnegieite, mullite, corundum, clino-pyroxene, meta-oxides and Na-β″-alumina were treated within the framework of Compound Energy Formalism. The database of model parameters can be used to calculate any thermodynamic property and phase diagram section of the present system.     

On the Possibility of Forming Complexes with the Participation of O2– Ions in Melts and Glasses of the Na2O–SiO2–Cu2O System

The structural role of copper ions in melts (glasses) of the Na₂O–SiO₂–Cu₂O–CuO system is analyzed in the framework of the acid–base concept with due regard for the geometric (the radius ratio for Cu²⁽¹⁾⁺ and O^2– ions) and energy (the mean enthalpies of the Cu²⁽¹⁾⁺–O bonds) factors. It is demonstrated that copper ions in the structure fulfill the function of modifier cations. In these melts, the Cu¹⁺–Cu²⁺ redox equilibrium can be described without regard for the formation of [Cu²⁽¹⁾⁺O_4/2]^2(3)– ionic complexes (which could be incorporated into the structure of silicon–oxygen anions) and [Cu²⁺O _b/k ]^{2 – b/k} polyhedra providing the interaction between Cu²⁺ ions and anions. The influence of the formation of these polyhedra on the redox equilibrium is considered within the formalism of chemical thermodynamics. The composition dependence of the oxygen ion exponent pO is measured by an electromotive force (emf) technique. The ratio between the numbers of copper atoms with different valences is determined by chemical analysis. The experimental data obtained are in agreement with the theoretical inferences.     

Phase Equilibriums in the Al2O3–SiO2–ZrO2 System: Calculation and Experiment

Glass Physics and Chemistry - The phase equilibria in the Al2O3–SiO2–ZrO2 system up to a temperature of 2550.15 K, calculated using the Nuclea database, are considered in comparison...     

On the Nature of Current Carriers in Glasses of the NaF–Na2O–B2O3 System

Glasses in the Na₂O–B₂O₃, NaF–Na₂O–B₂O₃, and NaF–B₂O₃ systems have been synthesized. The nature of current carriers and their transport numbers in these glasses are determined by the Hittorf and Tubandt techniques. The concentration dependences of the electrical conductivity and the transport numbers are investigated. It is demonstrated that the electricity transport in glasses in the NaF–B₂O₃ system is provided by sodium and fluorine ions. The results obtained are interpreted in terms of the microinhomogeneous glass structure.     

Production of Chemically Pure Zirconia-Based Nanoceramics in the ZrO2(Y2O3)–Al2O3 System for Restorative Dentistry

Theoretical Foundations of Chemical Engineering - The synthesis technology of a chemically pure nanodisperse precursor powder (10–12 nm) based on a tetragonal solid zirconia (t-ZrO2) solution...     

Thermal shock resistance of Cr2O3–Al2O3–ZrO2 bricks with the microstructure of Cr2O3 aggregates coated by ZrO2

Zirconia-coated Cr₂O₃ aggregates synthesized by mixing ZrO₂ powders and Cr₂O₃ aggregates with a phenolic resin binder followed by thermosetting treatment were employed as modified Cr₂O₃ aggregates to obtain Cr₂O₃–Al₂O₃–ZrO₂ bricks (high-chromia bricks). The elastic modulus (E) and cold modulus of rupture (CMOR) of these high-chromia bricks before and after thermal shock cycles were systematically investigated, and the residual ratios of CMOR and E were calculated. The thermal shock resistance of the high-chromia bricks was significantly improved by the factor of modification of Cr₂O₃ aggregates. The mechanism of the improved thermal shock resistance of these high-chromia bricks was studied via microstructure analysis, and the crack propagation behavior was analyzed by scanning electron microscopy (SEM). The fracture work (γ_WOF), thermal shock damage factor (R′′′′), and thermal stress crack stability parameter (R_st) were measured and calculated using the wedge splitting test (WST). The results indicate that the porous ZrO₂ coating layer wrapped the Cr₂O₃ aggregates, forming modified Cr₂O₃ aggregates that can increase crack deflection, free path of crack propagation, and fracture work, thus improving the thermal shock resistance of high-chromia bricks. The thermal shock resistance of the fabricated high-chromia bricks was highly correlated with the thickness of the ZrO₂ coating layer surrounding the Cr₂O₃ aggregates. The variation trend of R_st is well consistent with the experimental results, which is suitable to evaluate the thermal shock resistance of high-chromia bricks.     

Thermal Expansion of Melts and Glasses in the As–Se System

The bulk thermal expansion coefficients of glasses and melts in the As–Se system are measured in the temperature range 298–1200 K. In glass-forming melts containing 40–60 mol % As, an increase in the density is found at temperatures above 1000 K, which is assumed to be associated with changes in the structure and character of the chemical bonding.     

The Viscosity of Molten Material in Pores and Capillary Channels of the Matrix Phase of High-Alumina Castables Employed in Thermal Power Units of Ferrous Metallurgy. 1. Viscosity Analysis of Melts in the CaO – Al2O3 –FeO – Fe2O3 – SiO2 System

A new approach to the viscosity analysis of high-alumina, low-calcium melts of the CaO – Al₂O₃ – FeO – Fe₂O₃ – SiO₂ system is used. A mathematical formalism for handling experimental viscosity data on the CaO – FeO – Fe₂O₃ – SiO₂ system is proposed that allows viscosity of the system to be evaluated within _av = 0.004 Pa · sec in the temperature range of 1500 – 1700°C at concentrations (mol.%) of CaO = 15.3 – 50.3, Fe_xO_y = 2.3 – 38.5, and SiO₂ = 17.7 – 57.7. An equation describing viscosity as a function of temperature is derived. Using this equation, the viscosity of model melts compositionally analogous to the products of interaction between molten slag and the glassy matrix phase of castables employed in thermal power units of ferrous metallurgy is considered.     

A Study of the Acid–Base Properties of Melts in the Na2O–B2O3–SiO2System: I. Composition Joins with a Na2O Content of Less Than 20 mol %

Three composition joins in the Na₂O–B₂O₃–SiO₂system at constant Na₂O contents of 5, 10, and 15 mol % are studied by the high-temperature method of determining oxygen ion exponents pO for oxide melts. It is found that the basicity of melts increases in going from the binary sodium borate system to the sodium silicate system. The acid–base properties of ternary melts are simulated under the assumption that their basicity is determined by the interaction in pseudobinary systems. It is shown that the basicity of the studied melts is governed, to a large extent, by the formation of the Na₂O · B₂O₃· 2SiO₂ternary compound.     

Glass Formation in the MgO–B2O3–SiO2 System

Silicon - The glass formation region in the MgO–B2O3–SiO2 system was determined by the conventional melt-quenching technique at 1450 °C. The homogeneous transparent...     

Crystallization of Glasses in the K2O–Nb2O5–SiO2System

The changes in the structure and phase composition of glasses in the K₂O–Nb₂O₅–SiO₂system upon their heat treatment in the temperature range 700–800°C are studied by the small-angle X-ray scattering (SAXS) technique and X-ray powder diffraction. It is demonstrated that the crystallization is the primary process giving rise to microinhomogeneities in glasses due to heat treatment. Nanocrystals of an unidentified niobium-containing phase precipitate in glasses with the formation of regions with a decreased content of potassium and niobium oxides. An increase in the duration of heat treatment at the studied temperatures results in an increase in the size of nanocrystals without change in their phase composition. This is accompanied by the disappearance of diffusion zones, which leads to a decrease in the SAXS intensity in the range of small scattering angles and, correspondingly, to a decrease in the light scattering intensity.     

Phase equilibria and stability of intermediate phases in the Sm2O3–BaO–Fe2O3 system

Phase equilibria in the ½ Sm₂O₃–BaO–½ Fe₂O₃ system were systematically studied at 1100°C in air. Two individual compounds: Sm_1.875Ba_3.125Fe₅O_15-δ and Ba₃SmFe₂O_7.5+δ have been detected in the studied system at 1100°C in air. One more complex oxide with double perovskite structure SmBaFe₂O_5+w has been obtained under reduced oxygen partial pressure. Thermodynamic stability of SmBaFe₂O_5+w and its thermal stability in metastable state in air were determined. The subsolidus phase diagram for the ½ Sm₂O₃ – BaO – ½ Fe₂O₃ system at 1100°C in air has been constructed.     

Thermal conductivity of single- and multi-phase compositions in the ZrO2–Y2O3–Ta2O5 system

Compositions in the ZrO₂–Y₂O₃–Ta₂O₅ system are of interest as low thermal conductivity, fracture resistant oxides for the next generation thermal barrier coatings (TBC). Multiple phases occur in the system offering the opportunity to compare the thermal properties of single, two-phase, and three-phase materials. Despite rather large variations in compositions almost all the solid solution compounds had rather similar thermal conductivities and, furthermore, exhibited only relatively small variations with temperature up to 1000 °C. These characteristics are attributed to the extensive mass disorder in all the compounds and, in turn, small interfacial Kapitza (thermal) resistances. More complicated behavior, associated with the transformation from the tetragonal to monoclinic phase, occurs on long-term annealing in air of some of the compositions. However, the phases in two of the compositional regions do not change with annealing in air and their thermal conductivities remain unchanged suggesting they may be suitable for further exploration as thermally stable TBC overcoats.