Phase equilibria in the CaF2-Al2O3-CaO system

Computations of phase equilibria in the CaF₂-Al₂O₃-CaO system have been carried out on the basis of experimentally found thermodynamic properties of all intermediate phases and melts. Coordinates of the phase equilibrium boundaries were determined by solving a system of equations expressing equality of chemical potentials of the components in coexisting phases. The nature and quantity of the coexisting phases were established by a search for the Gibbs energy minimum of the system. All the phases of the CaF₂-Al₂O₃-CaO system were taken into consideration. Calculated phase diagrams of the CaO-CaF₂, CaO-Al₂O₃ and CaF₂-Al₂O₃ binary subsystems are in good agreement with the data available in the literature. Isotherms of the CaF₂-Al₂O₃-CaO system were calculated at 1600, 1650, 1723 and 1773 K. A wide region of liquid separation into two phases is observed in the system. One phase is composed of practically pure CaF₂ with additions of several mol% of CaO and Al₂O₃, and the other consists of 50 to 65 mol% of CaF₂ only. Eleven invariant points of the CaF₂-Al₂O₃-CaO system include seven ternary eutectics, two ternary peritectics and two points of four-phase monotectic transition. The primary fields of crystallization of all the phases are alongated toward the CaF₂ apex, the CaO field being the widest and the 3CaO·Al₂O₃ field the narrowest. Seven junctions of the CaF₂-Al₂O₃-CaO phase diagram were represented. Computed saturation lines of CaF₂-Al₂O₃-CaO melt with CaO, Al₂O₃, CaO·6Al₂O₃ and CaO·2Al₂O₃, and also the positions of a number of characteristic points, agree well with the experimental data available. The present calculations reveal a number of details and peculiarities of the constitution of the CaF₂-Al₂O₃-CaO phase diagram.     

Phase equilibria in the RuO2−Bi2O3−CdO−Nb2O5 system

Interactions between the conductive phase in thick-film resistor materials (RuO₂ and Bi₂Ru₂O₇) and TCR modifiers (CdO and Nb₂O₅) were studied. Phase equilibria in the RuO₂−Bi₂O₃−CdO, RuO₂−Bi₂O₃−Nb₂O₅ and RuO₂−CdO−Nb₂O₅ systems were examined. The lines in the systems were established. The existence of a solid solution of composition Bi _2−x Cd _x Ru₂O _7−x/2 was confirmed.     

Co-precipitated RuO2-Al2O3 catalysts: bulk and surface characterization

A series of co-precipitated RuO₂-Al₂O₃ samples was characterized by means of bulk and surface techniques such as X-ray diffraction (XRD), specific surface area measurements, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The existence of a substitutional solid solution of Al³⁺ ions in RuO₂ is suggested on the basis of XRD results. A more detailed study of such a phase was hindered by its thermal instability. XPS and AES quantitative data indicate a strong enrichment of Al on the surface. A simple model based on a reciprocal masking action of the particles of the two oxides with respect to the primary beam (X-rays or electrons) was found to fit the surface composition data well.     

Reaction mechanism of the hydrothermally treated CaO-SiO2-Al2O3 and CaO-SiO2-Al2O3-CaSO4 systems

Mixtures of CaO, amorphous SiO₂ and kaolinite in the presence or absence of SO ₄ ^2– ions (added as CaSO₄·2H₂O) were treated in suspension under hydrothermal conditions at temperatures of 80–200 °C. Kaolinite was added to replace 3 and 10% of the total weight of the dry mix with the overall CaO/SiO₂ mole ratio being 0.83. The hydration products were investigated by XRD, IR spectroscopy and DTA techniques in order to elucidate their phase compositions. The results indicate that the presence of SO ₄ ^2– ions leads to a marked increase in the reaction rate at all temperatures investigated. In the C-S-A system, the detected hydration products are calcium silicate hydrate which is then transformed into 1.13 nm aluminium-substituted tobermorite and -C₂SH by increasing the autoclaving temperature. In the C-S-A-C¯s system the hydrated products are calcium silicate hydrate, ettringite and monosulpho-alumirtate. On increasing the hydrothermal temperature they decompose, recrystallize and 1.13 nm aluminium-substituted tobermorite, -C₂SH and anhydrite II are formed. In both systems the excess Al₂O₃ appeared as a hydrogarnet phase, C₃ASH₄.Cement Notations used are C CaO - S SiO₂ - A Al₂O₃ - H H₂O - CH Ca(OH)₂ - C¯s CaSO₄     

Phase equilibria and ordering in the system HfO2-Yb2O3

The system HfO₂-Yb₂O₃ was investigated in the 0 to 100 mol % Yb₂O₃ range using X-ray diffraction analysis, linear thermal expansion measurements and melting point studies. At high temperatures, the system is dominated by wide regions of solid solutions based on HfO₂ and Yb₂O₃ separated by a two-phase field which appears to extend to the solidus. The extent of the cubic hafnia and ytterbia C-type solid solution fields was established using the precision lattice parameter method. At low temperature (< 1800° C) two ordered phases were found in the system, one at 40 mol % ytterbia with ideal formula Yb₄Hf₃O₁₂, and another at 70 mol % ytterbia with formula Yb₆HfO₁₁. Four eutectoid reactions and a peritectic reaction cubic ytterbia solid solution cubic hafnia solid solution + liquid at 67 mol % and 2380° C have been established in the system. By incorporating the known tetragonal-cubic hafnia and C-type-hexagonal ytterbia transition temperatures, and the melting points data in the system, a tentative phase diagram is given for the system HfO₂-Yb₂O₃.     

Phase equilibria in the pseudo-binary In2O3–SnO2 system

The pseudo-binary In₂O₃–SnO₂ phase diagram has been determined in the range of 1000–1650 °C using electron probe microanalysis (EPMA) and x-ray diffraction (XRD) analysis of solid-state sintered samples. The solubility of SnO₂ in In₂O₃ was found to range from 1.3 mol% at 1000 °C to a maximum of 13.1 mol% at 1650 °C, indicating that commercial SnO₂-doped In₂O₃ thin films are thermodynamically metastable. In₂O₃ was found to have negligible solubility in SnO₂ throughout the temperatures examined. In this study two intermediate compounds, In₄Sn₃O₁₂ and In₂SnO_5, were found. Each phase was found to be stable only at high temperatures, decomposing eutectoidally at 1325 and 1575 °C, respectively. This is believed to be the first report of the high temperature phase In₂SnO₅, which is attractive for future research as a transparent conducting oxide.     

Phase changes at abraded surfaces of ZrO2-Sc2O3-Al2O3 solid electrolyte

Diamond grinding drastically lowered the surface monoclinic concentration in a ZrO₂-Sc₂O₃-Al₂O₃ solid electrolyte and caused asymmetric broadening of the X-ray diffraction peaks. Annealing in air eliminated the broadening and partly restored the monoclinic concentration, in a manner which suggests that the grinding had converted surface monoclinic to a metastable tetragonal structure.     

Phase equilibria in the system CdO-ZnO-B2O3 at 850°C

Phase equilibria in the system CdO-ZnO-B₂O₃ were investigated at 850 °C using quenching and X-ray powder diffraction techniques. The binary phases reported previously were confirmed. The ternary phase diagram was solved and a new phase postulated: 3CdO · 3ZnO · 2B₂O₃. X-ray powder data are given for this. Solid solution effects were investigated for the primary and binary phases by comparison of patterns; none were detected. These results are compared with those of a previous determination and the differences discussed.     

Phase equilibria in the system CaO-ZnO-B2O3 at 850°C

Phase equilibria in the system CaO-ZnO-B₂O₃ were investigated at 850°C using X-ray powder diffraction techniques. The binary phases reported previously were confirmed, but no ternary phases were found. Solid solution effects were investigated for the binary phases by comparison of the patterns, whereas for calcium oxide and zinc oxide, accurate lattice parameters were compared. No solid solutions were detected.