Phase Equilibria in the Alkali Fluoride-Uranium Tetrafluoride Fused Salt Systems: III, The System NaF–LiF–UF4

The phase equilibrium diagram of the ternary system NaF–LiF–UF₄ described in this paper is based on evidence from thermal analysis and from microscopic and X-ray analyses of samples obtained from thermal gradient quenching experiments. Temperature-composition relations were established through the temperature interval between the liquidus and a lower limit of about 300°C. All the stable compounds in the binary systems LiF–UF₄ and NaF-UF₄, (including the subsolidus compound NaF·2UF₄) display primary phase fields in the ternary system. No ternary compounds of NaF–LiF–UF₄ occur. The following eutectics are to be found in the ternary system: 60 NaF, 21 LiF, 19 mole % UF₄, 480°C.; 35 NaF, 37 LiF, 28 mole % UF₄, 480°C.; 24.3 NaF, 43.5 LiF, 32.2 mole % UF₄, 445°C.; and 24.5 NaF, 29 LiF, 46.5 mole % UF₄, 602°C. The compounds 7NaF · 6UF₄ and 7LiF · 6UF₄ display limited solubility in each other. The exact limits of the miscibility gap in the 7NaF · 6UF₄-7LiF · 6UF₄ join have not been determined.     

Phase Equilibria in the Systems UF4-ThF4 and Li F-UF4-ThF4

As part of a study of materials potentially useful as fluid fuels for high-temperature reactors, equilibrium diagrams for the condensed systems UF₄–ThF₄ and LiF-UF₄–ThF₄ have been determined. Both thermal analysis and quenching techniques were used with phase identification accomplished by microscopic and X-ray dsraction analyses. A complete series of solid solutions without maximum or minimum is formed by UF₄ and ThF₄. Within the system LiF-UF₄–ThF, there occur three invariant points and seven primary phases of which four are ternary solid solutions. Optical properties for all the solid solutions, fractionation paths for the ternary solid solutions, and compatibility triangles for the ternary invariant points have been determined.     

Phase Equilibria in the System NaF-ThF4-UF4

Phase equilibria in the condensed system NaF-ThF₄-UF₄ were determined by cooling-curve and thermal-gradient quenching experiments from the liquidus to ∼450°C. A phase diagram of the ternary system was constructed, showing three singular points and eleven invariant points, including two eutectics, occurring in association with the primary phases of ten solid solutions and two pure solids. The eutectic mixture having the composition 75.5NaF-10.5ThF₄-14UF₄ (mole %) melts at 575°C, the lowest liquidus temperature in the system. Except for NaF, NaF-ThF₄, and ThF₄-UF₄ solid solutions, phases crystallizing from molten NaF-ThF₄-UF₄ mixtures are solid solutions formed by interchange of U⁴⁺ and Th⁴⁺ ions in NaF-ThF₄ and NaF-UF₄ compounds. No ternary compounds were found. Phase diagrams of the systems NaF-ThF₄ and NaF-UF₄, revised in the course of this study to include the newly identified phases, 7NaF.2ThF₄ and 7NaF.2UF₄, are presented. X-ray diffraction and optical data are given for the pure crystal phases, 4NaF.ThF₄, 7NaF.2ThF₄, 7NaF.2UF₄, 3NaF.UF₄, and for 3NaF.2ThF₄-5NaF.3UF₄ solid solutions. The system is unique among the fluoride systems reported in containing so wide a variety of substitutional solid solutions and in containing a continuous solid solution formed of binary compound pairs 3NaF.2ThF₄ and 5NaF.3UF₄ which are isomorphous but of different stoichiometry.     

Phase Equilibria in the Ternary Fused-Salt System LiF-BeF2,-UF4

The phase diagram for the ternary fused-salt system LiF-BeF₂-UF₄ was determined from 300°C to the liquidus by differential thermal analysis, thermal-gradient quenching studies, and high-temperature filtration techniques. The samples prepared by quenching were examined by polarized-light microscopy and X-ray diffraction techniques. The experimental methods are described. The primary-phase fields for the compounds LiF, 7LiF·6UF₄, LiF·4UF₄, and UF₄ covered most of the liquidus surface. Small areas of the liquidus surface were covered by the compounds BeF₂, 2LiF·BeF₂, and 4LiF·UF₄. The compound 4LiF·UF₄, which was stable at the binary liquidus temperature, decomposed in the ternary system when the liquidus temperature decreased below 480°C. No ternary compounds or solid solutions were observed. Two ternary eutectics were found. The first, containing 48 mole % LiF, 51.5 mole % BeF₂, and 0.5 mole % UF₄, melted at 350°C. The second, containing 69.5 mole % LiF, 22.5 mole % BeF₂, and 8 mole % UF₄, melted at 427°C.     

Studies in Germanium Oxide Systems: II, Phase Equilibria in the System Na2O—GeO2

Phase equilibrium relations in the system Na₂O-GeO₂ have been determined using standard quenching techniques supplemented by differential thermal analysis. Two congruently melting compounds, Na₂O·GeO₂ and 2Na₂O·9GeO₂, exist; the melting points are 1103°± 15°C and 1073°± 3°C, respectively. The eutectic temperature between GeO₂ and 2Na₂O·9GeO₂ is 950°±f 10°C at 94.5 wt GeO₂. The eutectic temperature between 2Na₂O · 9GeO₂ and Na₂O·GeO₂ is 790° f 10°C at about 75 wt% GeO₂. Both the refractive index and the density of glasses in the system Na₂O-GeO₂ exhibit maximum values at about 16 to 18 mole % Na₂O. The Ge-O-Ge absorption band at 890 cm⁻¹ shifts toward lower wave numbers with the addition of Na₂O.     

Phase Equilibria in the Systems CaO–CuO and CaO-Bi2O3

New data are presented on the phase equilibria of the binary systems CaO-CuO and CaO-Bi₂O₃. Corrected compositions are reported for Ca.Bi₆O₁₃ and Ca₂Bi₂O₅ and a new metastable high-temperature phase is reported for a composition near Ca₆Bi₇O_16.5. The composition and decomposition temperatures for Ca_1–x.CuO₂ are given for both air and 1 atm of oxygen at 755 ± 5° and 835 ± 5°C, respectively.     

Phase Equilibria in the System MgO—MgCr2O4

The liquidus, solidus, and subsolidus in the system MgO-MgCrz04 were redetermined. Petro-graphic studies indicated that 47 wt% Cr203 could enter into the periclase lattice at about 235OO C. X-ray and optical data showed that the solid solution decreased to 32 wt% Cr202 at 2165OC, 11 wt% at 1600°C, 5 wt% at 1400°C, 2.5 wt% at 1200°C, and 0 wt% at 1000°C. Petro-graphic studies also suggested that picrochromite could contain about 5 wt% MgO in solid solution. The liquidus was much higher than has been indicated on previously published phase equilibrium diagrams.     

Copper ⇌ Alkali Ion Exchange of Alkali Aluminosilicate Glasses in Copper-Containing Molten Salt: II, Divalent Copper Salts, CuCl2 and CuSO4

The ion-exchange mechanism between copper and alkali ions, when 20R₂O · 10Al₂O₃· 70SiO₂ (R = Li, Na, and K) glasses are immersed in divalent copper-containing molten salts in air and nitrogen at 550°C, has been investigated. In molten CuCl₂, the ion-exchange behavior in both air and nitrogen was very close to that in molten CuCl in air reported previously. This is explained by assuming that CuCl₂ decomposes into CuCl and Cl₂ at 550°C and the Cu⁺ ions thus formed mainly diffuse in glasses to replace alkali ions, where Cl₂ acts as an oxidizing agent just like oxygen. In the case of molten CuSO₄─₂SO₄, a small amount of Cu⁺ which is present in the molten state plays a primary role in the Cu ⇌ R⁺ ion exchange process, although the contribution of direct Cu²⁺⇌ 2R⁺ ion exchange cannot be ignored.     

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.     

Phase Equilibria in the Systems SrO-CuO and SrO-1/2Bi2O3

The phase equilibria of the systems SrO-CuO and SrO-1/2Bi₂O₃ were studied by X-ray diffraction analysis of quenched powder samples. The compounds SrCuO₂ and Sr₂CuO₃ melt incongruently at 1085° and 1225°C, respectively. The newly found compound Sr₆Bi₂O₉ decomposes at 965°C into SrO and Sr₃Bi₂O₆ melts incongruently into SrO and liquid at 1210°C. SrBi₂O₄ undergoes a phase transition at ∼825°C, and although both are nonstoichiometric, the low-temperature phase is slightly poorer in SrO with 33.5 mol% SrO than the high-temperature phase.     

Equilibria in KAlF4-Containing Systems

Stability relations in the systems KF-AlF₃, KAlF₄-RbAlF₄, and KAlF₄-RbAlF₄-KBF₄ were established using DTA, direct observational analysis, and quenching techniques. Two KF-AlF₃ compounds, K₃AlF₆ and KAlF₄, are stable and, on cooling, cubic KAlF₄ inverts (between -23° and +50°C) to an orthorhombic modification. On heating, the cubic form is stable to the congruent melting temperature of 574°± 1°C. Melting points of K₃AlF₆, and AlF₃ are 985° and 990°C, respectively. The compounds KAlF₄ and RbAlF₄ form a complete solid solution with a relatively narrow solidus-liquidus interval. As little as 5 mole % RbAlF₄ in the KAlF₄ lattice greatly affects the low-temperature inversion, causing it to occur below the temperature of liquid nitrogen (−196°C).     

Phase Equilibria in the System CaF2-AlF3

The phase diagram of the system CaF₂-AlF₃ was established from microscopic, powder X-ray diffraction, quench, and DTA data obtained from samples encapsulated in sealed Pt tubes and either reacted in the solid state or melted. Two compounds, CaAlF₅ and Ca₂AlF₇, melted incongruently at 873^°° 3^° and 845^°°3^°C, respectively. Previously unreported Ca₂AlF₇ was successfully indexed as orthorhombic with α₀= 18.22 Å, b ₀=9.06 Å, and c ₀= 7.11 Å. The only eutectic in the system exists at 836^°° 3^°C and 37.5 mol% AlF₃.     

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.