Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the CrO-Cr2O3, CrO-Cr2O3-Al2O3, and CrO-Cr2O3-CaO systems

Available thermodynamic and phase diagram data have been critically assessed for all phases in the CrO-Cr₂O₃, CrO-Cr₂O₂-Al₂O₃, and CrO-Cr₂O₂-CaO systems from 298 K to above the liquidus temperatures and for oxygen partial pressures ranging from equilibrium with metallic Cr to equilibrium with air in the case of the first two systems and toP _{O 2} = 10^?3 atm for the CrO-Cr₂O₃-CaO system. All reliable data have been simultaneously optimized to obtain one set of model equations for the Gibbs energy of the liquid slag and all solid phases as functions of composition and temperature. The modified quasichemical model was used for the slag. The models permit phase equilibria to be calculated for regions of composition, temperature, and oxygen potential where data are not available.     

Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the CrO-Cr2O3-SiO2 and CrO-Cr2O3-SiO2-Al2O3 systems

Available thermodynamic and phase diagram data have been critically assessed for all phases in the CrO-Cr₂O₃-SiO₂ and CrO-Cr₂O₃-SiO₂-Al₂O₃ systems from 298 K to above the liquidus temperatures and for oxygen partial pressures ranging from equilibrium with metallic Cr to equilibrium with air. All reliable data have been simultaneously optimized to obtain one set of model equations for the Gibbs energy of the liquid slag and all solid phases as functions of composition and temperature. The modified quasi-chemical model was used for the slag. The models permit phase equilibria to be calculated for regions of composition, temperature, and oxygen potential where data are not available.     

Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the CrO-Cr2O3, CrO-Cr2O3-Al2O3, and CrO-Cr2O3-CaO systems

Available thermodynamic and phase diagram data have been critically assessed for all phases in the CrO-Cr₂O₃, CrO-Cr₂O₂-Al₂O₃, and CrO-Cr₂O₂-CaO systems from 298 K to above the liquidus temperatures and for oxygen partial pressures ranging from equilibrium with metallic Cr to equilibrium with air in the case of the first two systems and toP _{O 2} = 10⁻³ atm for the CrO-Cr₂O₃-CaO system. All reliable data have been simultaneously optimized to obtain one set of model equations for the Gibbs energy of the liquid slag and all solid phases as functions of composition and temperature. The modified quasichemical model was used for the slag. The models permit phase equilibria to be calculated for regions of composition, temperature, and oxygen potential where data are not available.     

Critical thermodynamic evaluation and optimization of the MgO-Al2O3, CaO-MgO-Al2O3, and MgO-Al2O3-SiO2 Systems

A complete literature review, critical evaluation, and thermodynamic modeling of the phase diagrams and thermodynamic properties of all oxide phases in the MgO-Al₂O₃, CaO-MgO-Al₂O₃, and MgO-Al₂O₃-SiO₂ systems at 1 bar total pressure are presented. Optimized model equations for the thermodynamic properties of all phases are obtained that reproduce all available thermodynamic and phase equilibrium data within experimental error limits from 25 °C to above the liquidus temperatures at all compositions. The database of the model parameters can be used along with software for Gibbs energy minimization to calculate all thermodynamic properties and any type of phase diagram section. The modified quasichemical model was used for the liquid slag phase and sublattice models, based upon the compound energy formalism, were used for the spinel, pyroxene, and monoxide solid solutions. The use of physically reasonable models means that the models can be used to predict thermodynamic properties and phase equilibria in composition and temperature regions where data are not available.     

Experimental Study and Thermodynamic Re-optimization of the FeO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> System

Phase equilibria and thermodynamic data in the FeO-Fe₂O₃-SiO₂ system were critically reviewed. New experiments were undertaken to resolve discrepancies found in previous data. The liquid oxide/slag phase was described using the modified quasichemical model. New optimized parameters of the thermodynamic models for the Gibbs energies of slag and other phases in the selected system were obtained. The new parameters reproduce all available phase equilibria and thermodynamic data within the experimental error limits from 298 K (25 °C) to above the liquidus temperatures at all compositions and oxygen partial pressures from metal saturation to 1 atm of O₂. This study was carried out as part of the development of a self-consistent thermodynamic database for the Al-Ca-Cu-Fe-Mg-Si-O-S multi-component system.     

Crystallization and properties of some CaO-Al2O3-SiO2 system glass-ceramics with Y2O3 addition

The crystallization behavior and mechanical properties of CaO-Al2O3-SiO2 （CAS） system glass-ceramics with addition of Y2O3 were investigated. The optimal sintering temperatures of all heat-treated glasses were altered and the crystallization was accelerated with Y2O3 addition, and only wollastonite as a main crystalline phase was precipitated. The volume fraction of crystalline phase and density were increased with Y2O3 addition. The results suggest that the CAS glass-ceramics would get the lowest sintering temperature and optimal microstructure with the addition of Y2O3 by 3.25 %. The bending strength has a maximum due to the oriented and interlocked wollastonite crystal, which causes crack divert or blunts to limit the further development of the flaw size and increases the surface energy of fracture.     

Optimum composition of blast furnace slag as deduced from liquidus data for the quaternary system CaO-MgO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript>

On the basis of liquidus measurements in the system CaO-MgO-Al₂O₃-SiO₂ and previously published data, diagrams have been constructed at 5 pct Al₂O₃ intervals from 5 to 35 pct Al₂O₃. Liquidus temperatures and primary phase fields are shown. The optimum composition of a blast furnace slag for a given alumina content is indicated. At the optimum point, ordinary slags will be entirely liquid and will have maximum desulphurization potential and minimum viscosity. The relation of optimum composition of slags to the “plateau region” of the liquidus surface, and the application of these data on synthetic quaternary slags to actual slag compositions are discussed. Index of refraction of glasses is given as well as composition, temperature, and phase data for each mixture.     

The quaternary system B2O3-PbO-SiO2-ZnO: Thermodynamics and phase diagram

We evaluated the six binary phase diagrams, B₂O₃-PbO, B₂O₃-SiO₂, B₂O₃-ZnO, PbO-SiO2, PbO-ZnO, and SiO₂-ZnO, to obtain a consistent picture for the quaternary system B₂O₃-PbO-SiO₂-ZnO. We used all the available thermodynamic data: enthalpies of mixing, activity data, complete phase diagrams, and miscibility gaps. The agreement between the various sets of data is good. We also calculated the enthalpy of formation of the ternary compound 5PbO-B₂O₃-SiO₂. Δ_fH/R of 1/8 [5PbO-B₂O₃-SiO₂] =-(2.104 ± 0.057) kK.     

Primary study of the isothermal phase diagram of the Cu2O-Al2O3-SiO2 ternary system at 1150℃ in air

The isothermal phase diagram of the Cu2O-Al2O3-SiO2 ternary system at 1150℃ was reported for the samples which were prepared from sol-gel method and quenched by water after being heated at 1150℃ for 12 h. Based on the conventional X-ray powder diffraction （XRD） and in situ high-temperature XRD quantitative analysis,in addition to scanning electron microscopy measurement,the phase identification was achieved. Combining the deduction from the component phase diagrams of the binary systems using the phase equilibrium theorem,the primary isothermal phase diagram was plotted over the composition area Cu2O-mullite-SiO2. In this area,the approximate composition areas of two two-phase regions and one three-phase region,（L2＋Cr）,（L2＋M）,and （L1＋L2＋Tr）,were determined. Moreover,the precise composition areas of both of the three-phase regions （L2＋Cr＋M） and （L2＋M＋A） were determined according to the results of conventional and in situ high-temperature XRD quantitative analysis by Rietveld method.     

Thermodynamic Database for the Al-Ca-Co-Cr-Fe-Mg-Mn-Ni-Si-O-P-S System and Applications in Ferrous Process Metallurgy

Computerized thermodynamic databases for solid and liquid metals, slag, and solid oxide phases in the Al₂O₃-CaO-CoO-CrO-Cr₂O₃-FeO-Fe₂O₃-MgO-MnO-NiO-SiO₂ system (with dissolved S and P) have been developed by critical evaluation/optimization of various available phase equilibrium and thermodynamic data. The databases contain parameters of models specifically developed for molten slags, liquid steel, and solid oxide solutions such as spinel, pyroxenes, olivine, monoxide (wustite, periclase, lime), corundum, etc. By means of the optimization process, model parameters are found which reproduce various thermodynamic and phase equilibrium data within experimental error limits. Furthermore, the models permit extrapolation into regions of temperature and composition where data are not available. The databases are automatically accessed by user-friendly software that calculates complex equilibria involving slag, metals, refractories, and gases simultaneously, for systems with many components, over wide ranges of temperature, oxygen potential, and pressure. A short review of the available databases is presented. The critical evaluation/optimization procedure is outlined using the Al₂O₃-CaO-FeO-Fe₂O₃-MgO-SiO₂ and Al₂O₃-CaO-MnO-SiO₂ systems as examples. Several applications of the databases to deoxidation, dehydrogenation, and dephosphorization of iron and to inclusion control in steel are discussed.     

Phase relationships in the systems RE2O3-Al2O3-SiO2 (RE = rare earth element, Y, and Sc)

A literature survey and recent results on phase relationships in the quasi-ternary systems RE₂O₃-Al₂O₃-SiO₂ are given. The investigated systems exhibit extended ternary solid solutions, RE_9.33+2x(Si_{1_x}Al_xO₄)₆O₂ (withx up to ~0.33) and/or RE₄Al_{2(1_X)}Si_2xO_9+x (withx up to ~0.3), which are based on the quasi-binary phases RE_9.33(SiO₄)₆O₂ and RE₄A1₂O₉, respectively. The former is encountered only in systems with laige RE³⁺ ions (e.g., La³⁺), whereas the latter is found in systems with small RE³⁺ ions (e.g., Yb³⁺); in systems with medium-sized KE³⁺ ions (e.g., Gd³⁺) both types exist Quasi-ternary compounds are known only in the La, Ce, and Sc systems. Severe discrepancies in reported ternary eutectic temperatures led to a need for their accurate redeteimination.     

Chromium distribution between liquid iron and molten basic slags

An equilibrium study was made of the distribution of chromium and oxygen between liquid iron, containing less than 1 pct Cr, and simple slags of the CaO(MgO)-SiO₂-FeO-Cr₂O₃ type in the temperature range 1526° to 1734°C The effects of slag oxidation, temperature, and basicity were observed.     

Phase diagram of the Ba2YCu3O6-Ba2YCu3O7 system below 400°C

X-ray diffraction analysis and transmission electron microscopy have been used to study the low-temperature decomposition of the nonstoichiometric (in oxygen) HTSC compound Ba₂YCu₃O_{7 ? δ}. The phase diagram of the Ba₂YCu₃O₆-Ba₂YCu₃O₇ system below ≤400°C has been constructed. The temperature range corresponding to phase separation has been found to be divided into two portions. At T > 250°C, two orthorhombic phases characterized by different oxygen contents are formed; at the higher temperatures, the phase separation of the compound into a tetragonal and an orthorhombic phase takes place. The separation was also found to observe at T = 100°C; this indicates the possibility of natural aging for the Ba₂YCu₃O_{7 ? δ} compound at room temperature.     

Phase Relations in the Systems SrO-Y2O3-CuO-O2 and CaO-Y2O3-CuO-O2 at 1173 K

Phase relations in the systems SrO-Y₂O₃-CuO-O₂ and CaO-Y₂O₃-CuO-O₂ at 1173 K were estab-lished by equilibrating different compositions in flowing oxygen gas at a pressure of 1.01 × 10⁵ Pa. The quenched samples were examined by optical microscopy, X-ray diffraction (XRD), energy dis-persive analysis of X-rays (EDAX), and electron spin resonance (ESR). In the system SrO-Y₂O₃-CuO-O₂, except for the limited substitution of Y₃+ for Sr₂+ ions in the ternary oxide Sr₁₄ Cu₂₄O₄₁, no new quaternary phase was found to be stable. The compositions corresponding to the solid solution Sr_14-xY_xCu₂₄O₄₁ and the compound SrCuO₂+δ lie above the plane containing SrO, Y₂O₃, and CuO, displaced towards the oxygen apex. However, in the system CaO-Y₂O₃-CuO-O₂ at 1173 K, all the condensed phases lie on the plane containing CaO, Y₂O₃, and CuO, and a new quaternary oxide YCa₂Cu₃O_6.5 is present. The quaternary phase has a composition that lies at the center of the non-stoichiometric field of the analogous phase YBa₂Cu₃O_7-δ in the BaO-Y₂O₃-CuO-O₂ system. The com-pound YCa₂Cu₃O_6.5 has the tetragonal structure and does not become superconducting at low temperature. Surprisingly, phase relations in the three systems CaO-Y₂O₃-CuO-O₂, SrO-Y₂O₃-CuO-O₂, and BaO-Y₂O₃-CuO-O₂ are found to be quite different.     

Composition-Property Correlation in B2O3-SiO2 Preform Rods Produced Using Modified Chemical Vapor Deposition Technique

Due to unique optical properties of high birefringent (Hi-Bi) fibers for sensing and coherent optical communications, there is a strong interest in process optimization at preform fabrication and fiber drawing stages. Boron-doped silica cladding acts as stress-applying part resulting in polarization properties of Hi-Bi fibers that are strongly dependent on chemical composition. Using modified chemical vapor deposition (MCVD) technique, B₂O₃-doped silica preform rods were synthesized under different precursor gas flow conditions. Qualitative information about B₂O₃-SiO₂ system composition was derived from etching behavior in nonbuffered HF solution and subsequent microstructural examination using scanning electron microscope. Significant degree of B₂O₃ incorporation was seen in case of high BCl₃:SiCl₄ ratio and mild oxygen-deficient processing conditions. Increasing the B₂O₃ content to ~26 mol% led to a corresponding increase in coefficient of thermal expansion (CTE) to a maximum value of 2.35 ppm/K. The value of refractive index (RI), on the other hand, was found to decrease with increased B₂O₃ incorporation. A qualitative correlation between B₂O₃ and SiO₂ system composition and physical properties such as CTE and RI was established.     

Phase relations in the Ta2O5-WO3-SiO2 system

Subsolidus relations and liquidus boundaries in the Ta₂O₃-WO₃-SiO₂ system at temperatures ranging from 1200 °C to 1500 °C were investigated. Phase diagrams were constructed. Compounds with stoichiometries of Ta₂₂W₄O₆₇, Ta₂WO₈ and Ta₁₆W₁₈O₉₄ formed in the Ta₂O₅-WO₃ subsystem at 1200 °C. SiO₂ was compatible with each of the compounds. A solid solution with a formula of (1 − x) Ta₂O₅·xWO₃ formed on the Ta₂O₅-WO₃ line in the compositional range of Ta₂O₅:WO₃ > 11:4. SiO₂ had a maximum solubility of 25% SiO₂ in the solid solution. Liquid phase first appeared in the WO₃-rich corner at 1300 °C. As the temperature was increased up to 1500 °C, the liquidus area boundary gradually expanded towards the SiO₂- and the Ta₂O₅-rich corners.     

Gibbs Energy of Formation of Ca3Ti8Al12O37 and Phase Relations and Chemical Potentials in the System Al2O3-TiO2-CaO

The quaternary oxide in the system Al₂O₃-CaO-TiO₂ is found to have the composition Ca₃Ti₈Al₁₂O₃₇ rather than CaTi₃Al₈O₁₉ as reported in the literature. The standard Gibbs energy of formation of Ca₃Ti₈Al₁₂O₃₇ from component binary oxides is measured in the temperature range from 900 to 1250?K using a solid-state electrochemical cell incorporating single crystal CaF₂ as the solid electrolyte. The results can be represented by the equation: $$ \Updelta G_{\text{f(ox)}}^{\text{o}} ( \pm 70)/{\text{J}}\,{\text{mol}}^{ - 1} = - 248474 - 15.706(T/{\text{K}}). $$ Combining this information with thermodynamic data on calcium aluminates and titanates available in the literature, subsolidus phase relations in the pseudo-ternary system Al₂O₃-CaO-TiO₂ are computed and presented as isothermal sections. The evolution of phase relations with temperature is highlighted. Chemical potential diagrams are computed at 1200?K, showing the stability domains of the various phases in the chemical potential-composition space. In each chemical potential diagram, chemical potential of one component is plotted against the cationic fraction of the other two components. The diagrams are valid at relatively high oxygen potentials where Ti is present in its four-valent state in all the oxide phases.     

Thermodynamics and phase diagrams in the binary systems Na2O-SiO2, Na2O-GeO2, Na2O-B2O3, Li2O-B2O3, CaO-B2O3, SrO-B2O3, and BaO-B2O3

We applied our model to the enthalpy of mixing data of the binary systems Na₂O-SiO₂, Na₂O-GeO₂, Na₂O-B₂O₃, Li₂O-B₂O₃, CaO-B₂O₃, SrO-B₂O₃, and BaO-B₂O₃. The most stable composition in the liquid, that is where the enthalpy of mixing is most negative, is with a metal-oxygen ratio of 4 to 3, for monovalent metals (Na and Li) and 3 to 4 for divalent metals (Ba and Ca) in liquid silicates or borates. The same applies to the CaO-SiO₂, CaO-Al₂O₃, PbO-B₂O₃, PbO-SiO₂, ZnO-B₂O₃, and ZnO-SiO₂ systems. The oxygen to metal ratio, its constant value in various types of systems, reflects and describes the structure of the liquid. Using the analyzed enthalpies of mixing data and the available phase diagrams, we calculated the enthalpies of formation of the various binary compounds. The results are in excellent agreement with data in the literature that were obtained from direct solid-solid calorimetry.     

Lu2O3-SiO2-ZrO2 Coatings for Environmental Barrier Application by Solution Precursor Plasma Spraying and Influence of Precursor Chemistry

As environmental barrier coatings are subjected to thermal stress in gas turbine engines, the introduction of a secondary phase as zircon (ZrSiO₄) is likely to increase the stress resistance of Lu₂Si₂O₇ coatings generated by induction plasma spraying using liquid precursors. In a first step, precursor chemistry effect is investigated by the synthesis of ZrO₂-SiO₂ nanopowders by induction plasma nanopowder synthesis technique. Tetraethyl orthosilicate (TEOS) as silicon precursor and zirconium oxynitrate and zirconium ethoxide as zirconium precursors are mixed in ethanol and produce a mixture of tetragonal zirconia and amorphous silica nanoparticles. The use of zirconium ethoxide precursor results in zirconia particles with diameter below 50 nm because of exothermic thermal decomposition of the ethoxide and its high boiling point with respect to solvent, while larger particles are formed when zirconium oxynitrate is employed. The formation temperature of zircon from zirconia and silica oxides is found at 1425 °C. Second, coatings are synthesized in Lu₂O₃-ZrO₂-SiO₂ system. After heat treatment, the doping effect of lutetium on zirconia grains totally inhibits the zircon formation. Dense coatings are obtained with the use of zirconium ethoxide because denser particles with a homogeneous diameter distribution constitute the coating.     

The quaternary system B2O3-PbO-SiO2-ZnO: Thermodynamics and phase diagram

We evaluated the six binary phase diagrams, B₂O₃-PbO, B₂O₃-SiO₂, B₂O₃-ZnO, PbO-SiO2, PbO-ZnO, and SiO₂-ZnO, to obtain a consistent picture for the quaternary system B₂O₃-PbO-SiO₂-ZnO. We used all the available thermodynamic data: enthalpies of mixing, activity data, complete phase diagrams, and miscibility gaps. The agreement between the various sets of data is good. We also calculated the enthalpy of formation of the ternary compound 5PbO-B₂O₃-SiO₂. Δ_fH/R of 1/8 [5PbO-B₂O₃-SiO₂] =-(2.104 ± 0.057) kK.