Phase Relations in the System Na2O-TiO2-SiO2

Liǵuid us and subsolidus phase relations were studied using the quenching technique. The system contains four ternary compounds stable to liquidus temperatures: Na₂TiSi₄O₁₁, Na₂TiSi₂O₇, Na₂TiSiO₅, and Na₂Ti₂Si₂O₉. Six eutectics, eight peritecties, and eight thermal maxima were located and a region of liquid immiscibility was delineated. X-ray powder data are given for the stable and metastable crystalline phases. Glass-transition temperatures were determined by thermal analysis. The relation between physical properties of melts and glasses and the configuration of the liquidus is discussed.     

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 Diagram of Na2O-B2O3-SiO2 System

The binary isopleth Na₂O.B₂O₃-SiO₂ of the Na₂O-B₂O₃ SiO₂ ternary system has been investigated. A phase diagram is presented based upon data from differential thermal analysis studies of prepared glasses and direct observation of the melting behavior using solid-state video imaging. Phase equilibria relations in the Na₂O-B₂O₃-SiO₂ ternary system have been reassessed by combining information from this study with existing data from the literature. A revised liquidus surface for the ternary is presented in which the form of the isotherms is updated.     

Phase Equilibria in the System Li2O-Cr2O3-SiO2

The system Li₂O-Cr₂O₃–SiO₂ contains one previously reported ternary compound, LiCrSi₂O₆. Six subsolidus compatibility triangles and six ternary invariant points were located. The highest solidus, temperature is 1283°C, but liquidus temperatures are much higher for many compositions.     

Phase Equilibria at Liquidus Temperatures in the System MgO-FeO-Fe2O3-SiO2

Liquidus temperatures are presented for mixtures in the system MgO-FeO-Fe₂O₃-SiO₂. The standard quenching technique was modified for work under controlled atmospheres of varying O₂ pressures. Data were obtained for the temperature range 1159° to 1775°C., and with O₂ pressures ranging from 1 to 10^-8.⁹ atm. Approximate compositions of crystalline phases were determined, and paths of equilibrium crystallization were derived for selected mixtures under idealized conditions. Application of the phase diagrams to steel-plant refractories problems is indicated.     

Phase Equilibria in the System Na2SiO3-Li2SiO3

Phase equilibria were studied for the system Na₂SiO_:rLi₂SiO₃. The 2 end-member metasilicates show limited mutual solid solubility with the (Na_2-χLi_χ)SiO₃ solid solutions being particularly extensive at solidus temperatures (0 x 1.06). Ordering of the latter solid solution occurs at the NaLiSiO_;) composition with a_supercellx= 6a_subcell During cooling of the solid solutions, metastable phase transformations occur; a twinned monoclinic metastable phase, low (Na, Li)₂SiO₃, has been characterized.     

Phase Equilibria in the System MnO-"FeO"-ZrO2-SiO2

Phase equilibrium relations in the liquidus temperature region of the system MnO-"FeO"-ZrO₂-SiO₂ and of its bounding systems MnO-ZrO₂, MnO-ZrO₂-SiO₂, and MnO-"FeO"-ZrO₂ were determined by the quenching technique. The equilibrations were carried out at sufficiently low O₂ pressures to keep most of the Mn and Fe in divalent states. The results obtained were combined with literature data for the other bounding binary and ternary systems to present phase diagrams showing liquidus surfaces and interrelations between coexisting liquid and solid-solution phases. Applications of the data to refractory problems are discussed.     

Phase Equilibria and Crystallization of Melts in the System Na2O-BaO-SiO2

Phase-equilibrium studies of the liquidus surface of the Na₂O-BaO-SiO₂ system are presented. The system contains 5 ternary compounds, Na₂Ba₄Si₁₀O₂₅, Na₂Ba₄Si₂O₆, Na₂Ba₂Si₂O₇, X (probably Na₂Ba₁₈Si₂₈O₇₅), and Y (probably Na₂Ba₄₅Si₇₃O₁₉₂), all of which melt incongruently. Twenty-three liquidus invariant points, including 13 peritectics, 4 eutectics, and 6 thermal maxima, were located. Metastable crystallization reactions are commonly encountered, and some of the metastable equilibria are described.     

Phase Equilibria in the System Na3AlF6−AlF3

The phase diagram for the system Na₃AlF₆−AlF₃ was determined by quenching and microscopy supplemented with DTA and X-ray powder diffraction. Primary crystallization fields for cryolite, chiolite, and aluminum fluoride are defined. Liquid containing 30 wt% AlF₃ is in peritectic equilibrium with solid cryolite and chiolite at 741°C; solid chiolite and aluminum fluoride are in equilibrium with liquid at the eutectic composition 39 wt% AlF₃ and 694°C.     

Phase Equilibria in the System Si3N4-SiO2-BeO-Be3N2

The 1780°C isothermal section of the reciprocal quasiternary system Si₃N₄-SiO₂-BeO-Be₃N₂ was investigated by the X-ray analysis of hot-pressed samples. The equilibrium relations shown involve previously known compounds and 8 newly found compounds: Be₆Si³N₈, Be₁₁Si₅N₁₄, Be₅Si²N₆, Be₉Si₃N₁₀, Be₈SiO₄N₄, Be₆O₃N₂, Be₈O₅N₂, and Be₉O₆N₂. Large solid solubility occurs in β-Si₃N₄, BeSiN₂, Be₉Si₃N₁₀, Be₄SiN₄, and β-Be₃N₂. Solid solubility in β-Si₃N₄ extends toward Be₂SiO₄ and decreases with increasing temperature from 19 mol% at 1770°C to 11.5 mol% Be₂SiO₄ at 1880°C. A 4-phase isotherm, liquid +β-Si₃N₄ ( ss )Si₂ON₂+ BeO, exists at 1770°C.     

Reinvestigation of the System Na3AlF6-Li3AlF6

A partial phase diagram for the system Na₃AlF₆-Li₃AlF₆ was constructed from DTA and X-ray diffraction measurements. A region of solid solution extends from Na₃AlF₆ to the limiting composition Na₂LiAlF₆. At compositions between Na_1.5Li_1.5AlF₆ and NaLi₂AlF₆ a cubic phase resembling the mineral cryolithionite is stable over a narrow range of temperatures, which shifts progressively to higher temperatures with increasing lithium content. A single phase can be quenched from samples annealed within this range except near the ideal cryolithionite composition (Na_1.5Li_1.5AlF₆) where the upper temperature limit is too low to permit recombination of two solid phases to cryolithionite even with prolonged annealing. Cryolithionite precipitated from aqueous solution, a sample of the mineral, and the solid solutions containing from 53 to 65 mole % Li₃AlF₆ have identical powder patterns except for differences of lattice constants. Solid solubility of Na₃AlF₆ in Li₃AlF₆ reaches 30 mole % at the eutectic temperature.     

Phase Equilibria in the System Na2O – Nb2O5

Phase equilibria data, obtained both by differential thermal analysis and by quenching, are presented for the system Na₂O-Nb₂O₅. Five compounds corresponding to the formulas 3Na₂O.1Nb₂0₆, lNa₂O. 1Nb₂O₅, lNa₂O 4Nb₂O₆, lNa_zO.7Nb₂O₅, and lNa₂O. 10Nb₂O₆ have been found. The compound 3Na_z0.lNb₂O₅ melts congruently at 992°C. The compounds 1Na₂O. 4Nb₂O₆, lNa₂O.7Nb₂O, and 1Na₂O. 1Onb₂O₅ melt incongruently at 1265°, 1275°, and 1290°C., respectively. The well-known perovskite structure phase NaNbO₃ was found to melt congruently at 1412°C. The transition temperatures in NaNbO₅ were checked by thermal analysis and only the major structural changes at 368° and 640°C. could be detected. A new disordered form of NaNbO₃ could be preserved to room temperature by very rapid quenching.     

Preliminary Study of the Phase Equilibria Diagram of Tho2-SiO2

A preliminary study of the system Tho₂-SiO₂ supported the premise that the system CaF₂ BeF₂ is a model for this silicate system. The only compound present was the monoclinic form of ThSiO₄ (huttonite), which melted incongruently to Tho₂ and liquid at 1975° f 50° C. as determined from a series of powder X-ray spectrometer patterns. The eutectic temperature as tentatively determined is 1700°± 10°C. at a composition of greater than 95% by weight of Sio². No solid-solution areas were observed. The quenching samples were fired in a modified oxygen-acetylene furnace which was developed to insure accurate temperature readings and to retain the effects of heating the samples in air.     

Effects of MoO3, on Phase Separation of Na2O-B2O3-SiO2 Glasses

Immiscibility temperatures of Na₂O-B₂O₃-SiO glasses, with andwithout 1 mol% MoO₃, additions, were determined and the effect of MoO₃ additions on the 65O°C immiscibility isotherms was established. In addition, immiscibility temperature and phase-separation morphology of an Na₂O-B₂O₃-SiO₂ glass with progressive additions of MoO₃, were investigated. It was found that the addition of small amounts of MoO₃ extends the immiscibility boundary of the system and raises the immiscibility temperature by ∼l8°C for each mol % MoO₃, addition. Analysis of phase-separation morphology suggests that the MoO₃, additions do not significantly alter the tie lines of phase separation in the system, although such additions cause a lowering of the viscosities and the glass-transition temperatures of these glasses.     

Property-Composition-Substructure Relations in Na2O-TiO2-SiO2 Glasses

Published data on optical properties and specific volumes of Na₂O-TiO₂-SiO₂ glasses located in 7 primary phase fields are represented quantitatively in terms of linear mole fraction equations. These equations are used to calculate a primary phase diagram of this system. The fidelity of the representation of experimental data is compared with that obtained using the Huggins-Sun method.     

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.