Phase stability and equilibria in the La2O3–TiO2 system

XRD, electron probe wavelength and energy dispersive X-ray analyses were used to reexamine the phase relations in the La₂O₃–TiO₂ system. The diagram was redrawn to include the compound La₄Ti₃O₁₂ in addition to La₄Ti₉O₂₄, La₂Ti₂O₇ and La₂TiO₅. Above 1455°C a cation deficient perovskite La_2/3TiO₃ is stabilized by a small number of Ti³⁺ ions and remains stable on cooling in air. The proposed diagram represents a section through the system at the normal oxygen pressure in air at 1 atm, compositions being expressed in terms of the oxide components stable at room temperature.     

Phase equilibria in the La2O3-Y2O3-Nd2O3 system at 1500 °C

The phase equilibria in the ternary La₂O₃-Y₂O₃-Nd₂O₃ system at 1500 °C were studied by X-ray diffraction, petrography, and electron microscopy in the overall concentration range. The samples of different compositions have been prepared from nitrate acid solutions by evaporation, drying, and calcination at 1100 and 1500 °C. The solid solutions based on various polymorphous forms of source components and ordered phase of LaYO₃ were revealed in the system. The isothermal section of the phase diagram for the La₂O₃-Y₂O₃-Nd₂O₃ system has been developed. It was established that in the ternary La₂O₃-Y₂O₃-Nd₂O₃ system there exist fields of solid solutions based on hexagonal (A) and monoclinic (B) modifications of La₂O₃ and Nd₂O₃, cubic (C) modification of Y₂O₃, as well as perovskite-type structure of LaYO₃ (R) with rhombic distortions. The systematic study that covered the whole composition range excluded the formation of new phases. The refined lattice parameter of the unit cell and the boundaries of the homogeneity fields for solid solutions were determined.     

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.     

Phase equilibria and microwave dielectric properties in the ternary La2O3–TiO2–Nb2O5 system

High-temperature phase relations in the La₂O₃–TiO₂–Nb₂O₅ ternary system were investigated at 1290 °C using SEM, EDS and XRD, and a subsolidus phase equilibrium diagram was constructed. It was demonstrated that the addition of the La_1/3NbO₃ to the La₂O₃:3TiO₂ mixture completely stabilizes a perovskite-La_2/3TiO₃ compound, which is otherwise not stable at stoichiometric composition. On the other hand, a mixture La₂O₃:TiO₂ =1:3 dissolves in La_1/3NbO₃ up to 15 mol% TiO₂. Moreover, a newly defined composition of compound La₃₀Ti₁₆Nb₄O₈₇ formed in the La₂O₃-rich part of the system and a solid solution La₃Ti₅Nb₁₀O_39.5–La₂Ti₂Nb₈O₂₇ were proposed. In the binary subsystem LaTiNbO₆-La_0.462Ti_0.386Nb_0.614O₃, the components exhibit opposite temperature dependence of resonant frequency in the microwave frequency range. Thus, the dielectric properties of the prepared ceramics can be tailored by varying the component concentration and thermally stable dielectric properties can be achieved for a composition with a LaTiNbO₆/La_0.462Ti_0.386Nb_0.614O₃ molar ratio of 0.27.     

Phase equilibria in the CaO·SiO2Na2O·SiO2Na2O·Al2O3·6SiO2 system

Equilibrium phase relations in the system CaO·SiO₂Na₂O·SiO₂Na₂O·Al₂O₃·6SiO₂ at 40–80 wt% Na₂O·Al₂O₃·6SiO₂ composition range have been experimentally studied at temperatures between 800 °C and 1200 °C. The liquidus temperature was determined with differential scanning calorimetry. The equilibrated samples were quenched with pressurized nitrogen, and examined with electron probe X-ray microanalysis and X-ray diffraction for identification of microstructure and phase relations. Five primary phase fields, CaO·SiO₂, Na₂O·SiO₂, Na₂O·2CaO·3SiO₂, 2Na₂O·CaO·3SiO₂ and Na₂O·Al₂O₃·6SiO₂ were established. The ternary eutectic point of CaO·SiO₂, Na₂O·2CaO·3SiO₂ and Na₂O·Al₂O₃·6SiO₂ was determined to be at 1030 °C with the composition of 29.0 wt% CaO·SiO₂, 12.0 wt% Na₂O·SiO₂ and 59.0 wt% Na₂O·Al₂O₃·6SiO₂. Peritectic reaction of Na₂O·2CaO·3SiO₂, 2Na₂O·CaO·3SiO₂ and Na₂O·Al₂O₃·6SiO₂ occurred at 930 °C with the composition of 13.0 wt% CaO·SiO₂, 29.0 wt% Na₂O·SiO₂ and 58.0 wt% Na₂O·Al₂O₃·6SiO₂. The liquidus surface projection of the ternary system has been constructed in the composition region important for the bottom ash application.     

Phase equilibria in the Nd2O3–BaO–Fe2O3 system: Crystal structure,oxygen content,and properties of intermediate oxides

The phase equilibria in the ½Nd₂O₃–BaO–½Fe₂O₃ system were systematically studied at 1373 K in air and presented in the form of a phase diagram. By X-ray diffraction (XRD) analysis of quenched samples, the homogeneity ranges and crystal structure were determined for the following intermediate oxides: Nd_1-xBa_xFeO_3-δ with 0.0 ≤ x ≤ 0.05 (space group (SG) Pnma) and with 0.6 ≤ x ≤ 0.7 (SG Pm-3m), Ba_6+yNd_2-yFe₄O_15-δ with 0.0 ≤ y ≤ 0.4 (SG P6₃mc), and Ba_1.1Nd_1.9Fe₂O_7-δ (SG P4₂/mnm). The structural parameters of single-phase oxides were refined by the Rietveld method. The changes in oxygen content for Nd_1-xBa_xFeO_3-δ (0.6 ≤ x ≤ 0.7), Ba₆Nd₂Fe₄O_15-δ, and Ba_1.1Nd_1.9Fe₂O_7-δ versus temperature in air were determined by thermogravimetric analysis. Gradual substitution of neodymium by barium in the Nd_1-xBa_xFeO_3-δ (0.6 ≤ x ≤ 0.7) oxides leads to a decrease of oxygen content. Partial ordering via formation of separate domains with a_p × a_p × 5a_p superstructure in Nd_0.4Ba_0.6FeO_3-δ, which cannot be detected by XRD, noticeably influence its thermal expansion and electrical conductivity.     

Phase equilibria in the calcium nitrate–water–isopropyl alcohol system

Results of an investigation of the solubility of the components of the water–isopropyl alcohol system in the temperature range of 253–268 K are given. Using fractional fusion, the concentrations of twocomponent water–isopropyl alcohol system have been determined, where fusion occurs more homogeneously. Phase diagrams of the calcium nitrate–water–isopropyl alcohol systems have been plotted at temperatures of 253, 263, and 268 K. The working area where compositions can be chosen for preparing the process liquid with a low freezing point has been determined.     

Phase equilibria in the ZrO2-YO1.5-TaO2.5 system at 1250 °C

The phase relationships in the ZrO₂-YO_1.5-TaO_2.5 (ZYTO) system at 1250?°C—a temperature of interest for thermal barrier coatings applications—were investigated using precursor-derived powders. The system is bisected by a quasi-binary joining the tetragonal (t) ZrO₂ and monoclinic (M’) YTaO₄ solid solutions. The mutual solubility limits for these phases differ significantly depending on whether the third phase in equilibrium with t and M’ is fluorite or the orthorhombic (O) Zr₆Ta₂O₁₇. More importantly, the tetragonal phase in equilibrium with fluorite is non-transformable to the monoclinic form upon cooling, whereas that in equilibrium with O, which has lower stabilizer content, is transformable. The behavior contrasts with that previously observed for the equilibrium at 1500?°C, wherein the t phase on both sides of the quasi-binary is non-transformable. The fluorite solid solution extends from the ZrO₂-YO_1.5 binary to the YO_1.5-TaO_2.5 binary at 1250?°C, as previously shown for 1500?°C.     

Phase equilibria studies in the CaO–SiO2–Al2O3–MgO system with CaO/SiO2 ratio of 0.9

Phase equilibria and liquidus temperatures in the CaO–SiO₂–Al₂O₃–MgO system at a CaO/SiO₂ weight ratio of 0.9 in the liquid phase have been experimentally determined employing high-temperature equilibration and quenching technique followed by electron probe X-ray microanalysis. Isotherms at 1573, 1623, 1673, and 1773 K were determined and the primary phase fields of wollastonite, melilite, olivine, periclase, spinel, and corundum have been located. Compositions of the olivine and melilite solid solutions were analyzed and discussed. Comparisons between the newly constructed diagram, existing data, and FactSage predicted phase diagrams were performed and differences were discussed. The present study will be useful for guidance of industrial practices and further development of thermodynamic modeling.     

Phase relation studies in the CeO2–La2O3–Er2O3 system at 1500°C

Materials based on CeO₂–La₂O₃–Er₂O₃ system are promising candidates for a wide of applications, but the phase relationship has not been studied systematically previously. To address this challenge, the isothermal section of the phase diagram for 1500 °C was investigated. The phase relations in the CeO₂–La₂O₃–Er₂O₃ ternary system at 1500 °C were studied by X-ray diffraction and scanning electron microscopy in the overall concentration range. To study phase relationships at 1500 °C the as-repared samples were thermally treated in two stages: at 1100 °C (for 300 in air) and then at 1500 °C (for 70 h in air) in the furnaces with heating elements based on Fecral (H23U5T) and Superkanthal (MoSi2), respectively. The solid solutions based on various polymorphous forms of constituent phases and with perovskite-type structure of LaErO₃ (R) with orthorhombic distortions were revealed in the system. No new phases were found. The isothermal section of the phase diagram for the CeO₂–La₂O₃–Er₂O₃ system has been constructed. It was established that in the ternary CeO₂–La₂O₃–Er₂O₃ system there exist fields of solid solutions based on hexagonal (A) modification of La₂O₃, cubic modification of CeO₂ with fluorite-type structure (F), cubic modification Er₂O₃ and with perovskite-type structure of LaErO₃ (R) with orthorhombic distortions. The maximal solubility of ceria in LaErO₃ was found to be around ∼ 2 mol% CeO₂ along the section CeO₂–(50 mol % La₂O₃ –50 mol% Er₂O₃).     

Phase equilibria study of K–O–Si system in equilibrium with air

The binary phase diagram in the silica rich corner of K–O–Si system in equilibrium with air has been studied at temperatures between 770 °C and 1500 °C. Equilibration at high temperature in an appropriate containment material of pure silica, followed by rapid quenching and measurement of phase structures and assemblages using SEM-EDS confirmed by an electron probe X-ray microanalysis technique, was carried out to obtain the phase composition data at equilibrium. The results are in good agreement with previous experimental data and close to the earlier assessed phase equilibria at silica saturation.     

Phase evaluation during high temperature long heat treatments in the Y2O3–Al2O3–SiO2 system

The effect of high temperature long heat treatments on the microstructure of the eutectic glass composition in the Y₂O₃–Al₂O₃–SiO₂ system was examined. The qualitative and quantitative phase analyses were conducted by using scanning electron microscopy combined with energy dispersive analysis and electron microprobe. Simultaneous thermal analyses were carried out to determine the transition temperatures and enthalpies. The crystallization behavior of these glasses was monitored with X-ray powder diffraction. A needle like X-phase was observed in the structure of this eutectic composition after long heat treatment at 1350 °C.     

Experimental phase equilibria study and thermodynamic modelling of the PbO-“FeO”-SiO2-ZnO,PbO-“FeO”-SiO2-Al2O3 and PbO-“FeO”-SiO2-MgO systems in equilibrium with metallic Pb and Fe

Phase equilibria of the PbO-“FeO”-SiO₂-ZnO, PbO-“FeO”-SiO₂-Al₂O₃ and PbO-“FeO”-SiO₂-MgO slags with liquid Pb metal, solid or liquid Fe metal and solid oxides (cristobalite and tridymite SiO₂, willemite (Zn,Fe)₂SiO₄, wustite (Fe,Al)O_1+x, spinel (Fe,Al)₃O₄, olivine Fe₂SiO₄, corundum (Al,Fe)₂O₃, mullite Al₆Si₂O₁₃ and pyroxene (Mg,Fe)SiO₃) were investigated at 1125–1670 °C. These conditions correspond to the minimum solubility of PbO in slag in presence of Pb and Fe metals at reducing conditions and represent the limit of lead smelting and slag cleaning process. High-temperature equilibration on silica, corundum or iron foil substrates, followed by quenching and direct measurement of Pb, Fe, Si, Zn, Al and Mg concentrations in the liquid and solid phases with the electron probe X-ray microanalysis (EPMA) was used. Present data can be used to improve the thermodynamic models for all phases in this system.     

Phase equilibria,structure, oxygen nonstoichiometry,and thermal expansion of oxides in the 1/2Y2O3–SrO–1/2Fe2O3 system

Phase equilibria in the 1/2Y₂O₃–SrO–1/2Fe₂O₃ system were systematically studied at 1373 K in air. The homogeneity ranges and crystal structure of the solid solutions Sr_1−xY_xFeO_3−δ with 0.875 ≤ x ≤ 1 (sp. gr. Pnma) and 0.05 ≤ x ≤ 0.25 (sp. gr. Pm3 m) and Sr_3−zY_zFe₂O_7−δ with 0 ≤ z ≤ 0.25 (sp. gr. I4/mmm) were determined by X-ray diffraction analysis of quenched samples. The structural parameters of the single-phase oxides were refined by the Rietveld profile method. The isothermal-isobaric phase diagram for the 1/2Y₂O₃–SrO–1/2Fe₂O₃ system at 1373 K in air is presented. The changes of oxygen content in the solid solutions Sr_1−xY_xFeO_3−δ (0.05 ≤ x ≤ 0.25) and Sr_3−zY_zFe₂O_7−δ with 0 ≤ z ≤ 0.25 vs temperature in air were determined by the thermogravimetric analysis. Oxygen content was also calculated from the iodometric titration results. The gradual substitution of strontium by yttrium in Sr_1−xY_xFeO_3−δ (0.05 ≤ x ≤ 0.25) leads to a decrease in the oxygen content and the mean oxidation state of iron. The average thermal expansion coefficients for Sr_1−xY_xFeO_3−δ (0.875 ≤ x ≤ 1 and 0.05 ≤ x ≤ 0.25) and Sr_3−zY_zFe₂O_7−δ (0 ≤ z ≤ 0.25) were calculated within the temperature range 298-1373 K in air.     

Phase relations and microstructure of molten specimens in the Al2O3-ZrO2—Mullite system

An installation for radiant heating and methods of x-ray phase analysis and microstructure investigation are used to study the phase relations and microstructure of molten cast specimens of the Al₂O₃ - ZrO₂ - mullite subsystem as a function of the melt's crystallization rate. The data obtained by thermal analysis are used to construct the liquidus and to refine the coordinates of invariant points in the given subsystem. The effect of Y₂O₃ and Na₂O on the phase composition and structure of the refractories and the optimal amounts of these admixtures for to manufacturing molten cast refractories under conditions of radiant heating are determined.Translated from Ogneupory, No. 6, pp. 19 – 22, June, 1994.     

Phase relation studies in the CeO2-Eu2O3 system at 1500 to 600 °C in air

Materials based on CeO₂-Eu₂O₃ system are promising candidates for a wide range of applications, but the phase relationship has not been studied systematically previously. To address this challenge, the subsection of the phase diagram for 600, 1100 and 1500 °C has been elucidated. Samples of different compositions have been prepared from nitrate acid solutions using conventional ceramic techniques; evaporation, drying, and calcinations. The phase relations in the binary CeO₂-Eu₂O₃ system at 600–1500 °C in air were studied from the heat treated samples using X-ray diffraction analysis, polarized light microscopy investigation and scanning electron microscopy in the overall concentration range. It was established that in the binary CeO₂-Eu₂O₃ system there exist fields of solid solutions based on monoclinic (B) modification of Eu₂O₃, cubic (C) modification of Eu₂O₃ and cubic modification of CeO₂ with fluorite-type structure (F). The systematic study that covered whole composition range excluded formation of new phases. The refined lattice parameters of the unit cells and the boundaries of the homogeneity fields for solid solutions were determined.     

Phase compositions and equilibria in the CaO–Al2O3–Fe2O3–SO3 system,for assemblages containing ye'elimite and ferrite Ca2(Al,Fe)O5

Phase equilibria in the CaO–Al₂O₃–Fe₂O₃–SO₃ system have been studied, mainly at 1325 °C. In particular the solid solution compositions of ye'elimite Ca₄(Al₆O₁₂)SO₄ and brownmillerite (C₂(A,F)) phases have been analysed and used to estimate the composition boundaries of these phases in their co-existence with liquid at 1325 °C. Sulfate and iron oxide facilitate the formation of a liquid phase, whose amount increases with overall Fe₂O₃ content. However, the solubility of sulfate in this liquid phase is very low and liquid formation tends to lead to the volatilisation of sulfate in unsealed samples.