The Systems PbF2-AlF3 and CaF2-AlF3

The compound Pb₃Al₂FI₁₂ is reported in the system PbF₂-AIF₃. It is tetragonal, I 4/m, d₀ = 14.23 å, c_o = 7.20 Å. A phase diagram for the system is presented on the basis of DTA and X-ray Powder Patterns. The compound melts incongruently at 649°C. Solid solubility of AlF₃ in PbF₂ occurs with up to 15 mol% AlF₃. Data for the system CaF₂-A1F₃ is compared with previous reports.     

Phase Equilibria in the System CaF2-AlF3-Na3AlF6 and Part of the System CaF2-AlF3-Na3AlF6-Al2O3

The complete phase-equilibrium diagram of the system CaF₂-AlF₃-Na₃AlF₆ and the subsolidus portion of the system CaF₂-AlF₃-Na₃AlF₆-Al₂O₃ were established from microscopic, powder X-ray diffraction, quench, and DTA data obtained from samples encapsulated in sealed tubes and either reacted in the solid state or melted and recrystallized. The system Na₃AlF₆-CaF₂ contains a simple eutectic with no compound formation or solid solution. The system CaF₂-AlF₃-Na₃AlF₆ contains two ternary compounds, NaCaAlF₆ and NaCaAl₂F₉, which melt incongruently at 735° and 712°C, respectively; NaCaAlF₆ exists in three polymorphic forms with transitions at 610° and 722°C and NaCaAl₂F₉ is body-centered cubic with a₀= 10.765 Å. The three binary and two ternary compounds divide the system into eight compatibility triangles. Along the NaCaAlF₆-Na₃AlF₆ join, 7 mol% NaCaAlF₆ is soluble in α-cryolite at 525° and 42% in β-cryolite at 731°C. The quaternary system Na₃AlF₆-AlF₃-CaF₂-Al₂O₃ contains eight compatibility tetrahedra.     

Interdiffusion in the CaF2-YF3 System

An electron microprobe interdiffusion study was made in single crystals between 1200° and 1331°C over the solid-solution compositional range 0 to 20 mol% YF₃ in CaF₂. At constant temperature, the value of δ , the interdiffusion coefficient, increased approximately exponentially with increasing YF₃ content. As YF₃ content increased, the temperature dependence of δ decreased. Extrapolation of δ to 0% YF₃ combined with consideration of the defect formation mechanism at mite dilution allowed estimation of the impurity diffusion coefficient for Y in essentially pure CaF₂.     

Phase Equilibria in the System MgO-B2O3

Phase equilibria in the system MgO-B₂O₃ were investigated using DTA and quenching techniques. The system contains 4 invariant points. The compounds MgO·2B₂O₃ and 2MgO·B₂O₃ melt incongruently at 995° and 1312°C, respectively, whereas 3MgO·B₂O₃ melts congruently at 1410°C. A eutectic occurs at 1333°C and 71% MgO.     

Phase Equilibria in the System CaO-Yb2O3

Phase equilibrium relations in the system CaO-Yb₂O₃ were studied. Results of this work demonstrated the existence of four crystalline phases: Yb₂O₃.3CaO, Yb₂O₃.2CaO, Yb₂O₃°CaO, and 2Yb₂O₃°CaO. The 2Yb₂O₃°CaO phase is metastable at all temperatures and was obtained only by rapid quenching from the melt. The crystalline solubility limit of Yb_aO₃ in CaO at 1850°C is slightly greater than 8 mole %, whereas no solubility of CaO in Yb₂O₃ was detected. All four compounds have subsolidus minimums of stability and dissociate into the component oxides below 1800°C. Data are also presented for the systems CaO-Gd₂O₃ and CaO-La₂O₃.     

Phase Equilibria in Subsystems of the Quaternary Reciprocal System Na2O-SiO2-Al2O3-NaF-SiF4-AlF3

The phase relations in the pseudobinary system sodium fluoride-mullite have been investigated as a model system for fluoride attack on fire clay refractories in aluminum electrolysis cells. The phase composition below the solidus temperature 857°C changes from sodium fluoride, cryolite, nepheline, and ß-alumina to cryolite, albite, silica, and α-alumina with increasing oxide content. Albite was not observed to crystallize and an increasing amount of glass was observed with increasing mullite content. The phase diagram of the ternary system sodium fluoride-cryolite-nepheline was also measured in order to describe the composition of the most stable melt along the sodium fluoride-mullite composition join. The present findings are discussed in relation to the deterioration mechanism of fire clay refractories during fluoride attack. The formation of viscous albite-based melts is suggested to increase the resistance toward fluoride attack due to the reduced diffusion rate of fluorides.     

Phase Equilibria in the System CaO-PbO-SiO2

Phase relations in the ternary system were determined by solid- state reaction, quenching, and electron microscopy of the immiscible liquid region. The limits of the stable 2-liquid region and the approximate limits of the metastable 2-liquid region were determined. Relations in the region of homogeneous glass formation in the system, which included the joins CaSiO₃-PbSiO₃ and CaSiO₃-Pb₂SiO₄, were determined by quenching. Two new compounds were discovered, 3CaO-PbO.SiO₂ and 2CaO.3PbO.SiO₂, and extensive solid-state trials permitted the compatibility triangles to be established. The accumulated data were assembled in the form of an equilibrium diagram for the system including joins, boundary lines, and isotherms.     

Phase Equilibria in the System SrO-PbO-SiO2

Phase relations in the ternary system were determined by solid-state reaction, quenching, and electron microscopy of the immiscible liquid region. The limits of the stable 2-liquid region and the approximate limits of the metastable 2-liquid region were determined. Relations in the region of homogeneous glass formation in the system, which included the joins SrSiO₃-PbSiO₃, SrSiO₃-Pb₂SiO₄, and SrSiO₃-Pb₄SiO₆, were determined by quenching. The solid-solution limits of SrSiO₃ in Pb₂SiO₄ and Pb₄SiO₆ and of PbSiO₃ in SrSiO₃ were established. Two new compounds were discovered, 3SrO.2PbO.SiO₂ and 2SrO.3PbO.SiO₂, and extensive solid-state trials permitted the compatibility triangles to be established. The accumulated data were assembled in the form of an equilibrium diagram for the system, including joins, boundary lines, and isotherms.     

Solid-State Phase Equilibria in the ZnS-Ga2S3 System

The ZnS-Ga₂S₃ equilibrium phase diagram has been determined to 50 mol% over the temperature range 700° to 900°C. Samples of various compositions were prepared via solid-state diffusion starting from powders of the pure components. The identification of the phases was determined by X-ray diffraction methods. The principal feature of the phase equilibria is the eutectoid transformation at 818 ± 5°C of hexagonal wurtzite containing 16 ± 1 mol% Ga₂S₃ to cubic ZnS and tetragonal ZnGa₂S₄. ZnGa₂S₄ is the equilibrium compound at 50 mol% Ga_zS₃, but it exists over a considerable range of stoichiometry. The solubility of Ga₂S₃ in ZnS increases with increasing temperature to a maximum of 9 ± 1 mol% at the eutectoid temperature.     

Phase Equilibria in the System MgO-Cr2O3-SiO2

Studies of phase equilibria by the method of quenching show that there are no ternary compounds at liquidus temperatures in the system MgO-Cr₂O₃-SiO₂. There is an extensive two-liquid region, and the stability fields of periclase, picrochromite, and chromic oxide extend across most of the diagram. Temperatures of liquid formation are sufficiently high that a number of different compositions can be suggested for refractory purposes. Fundamental explanations are brought out for the improvement of chromite and chromite-forsterite refractories by the addition of MgO and for the improvement of chromite-silica refractories by the addition of chromic oxide or some other high-chromium compound.     

Phase Equilibria in the System Li2O-BeO-SiO2

The equilibrium phase diagram for the system Li₂O-BeO-SiO₂ contains only one ternary compound, Li₂BeSi0₄. Liquidus relations for compositions containing 33 mol% SiO₂ were determined; 10 liquidus invariant points were located and 7 subsolidus compatibility triangles. The most refractory compositions lie on the join BeO-Li₂BeSiO₄, with a solidus temperature of 1320°C. Metastable phases observed were a high-quartz phase, Li_2x(Si₁-_xBe_x)O₂, x 0.33; phase X which is probably a metastable orthosilicate between Li₂BeSiO₄ and Be₂SiO₄; and phase Y which lies on the join Li₂BeSiO₄-SiO₂. The crystal chemistry and glass network-forming properties of BeO are discussed.     

Phase Equilibria in the System Li2O-CaO-SiO2

Phase relations in the system Li₂O-CaO-SiO₂ were studied by the quenching method. Four stable ternary compounds were found (Li₂Ca₃Si₆O_l6, Li₂Ca₄Si₄O₁₃, Li₂Ca₂Si₂O₇, and Li₂CaSiO₄) as well as phase Y , which is probably a metastable orthosilicate fairly close to Ca₂SiO₄ in composition. X-ray powder data are given for the new phases. Eleven subsolidus compatibility triangles and thirteen liquidus invariant points were located. Melting relations were determined for that part of the system bounded by Li₂SiO₃, Li₂CaSiO₄, Ca₂SiO₄, and SiO₂. The join Li₂SiO₃-CaSiO₃ is binary.     

Subsolidus Phase Equilibria in the System SrO-B2O3-SiO2

The subsolidus compatibility relations in the system SrO-B₂O₃- SiO₂ were determined by solid-state reaction techniques and X-ray powder diffraction methods. The system was found to contain 11 subsolidus compatibility relations, one stable ternary compound (Sr₃B₂SiO₈), and one metastable ternary compound with a probable composition SrB₂Si₂O₈.     

Phase Equilibria in the Ga2O3In2O3 System

Subsolidus phase relationships in the Ga₂O₃–In₂O₃ system were studied by X-ray diffraction and electron probe microanalysis (EPMA) for the temperature range of 800°–1400°C. The solubility limit of In₂O₃ in the β-gallia structure decreases with increasing temperature from 44.1 ± 0.5 mol% at 1000°C to 41.4 ± 0.5 mol% at 1400°C. The solubility limit of Ga₂O₃ in cubic In₂O₃ increases with temperature from 4.X ± 0.5 mol% at 1000°C to 10.0 ± 0.5 mol% at 1400°C. The previously reported transparent conducting oxide phase in the Ga-In-O system cannot be GaInO₃, which is not stable, but is likely the In-doped β-Ga₂O₃ solid solution.