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.     

Determination of 1600° and 1700°C. Liquidus Lines in CaO-2Al2O3 and AI2O3 Stability Fields of the System CaO—Al2O3—SiO2

The 1600° and 1700°C. liquidus lines in the CaO·2Al₂O₃ and A1₂O₃ stability fields of the system CaO-Al₂O₃-SiO₂ are determined from the chemical analyses of saturated slags at these temperatures.     

Reactions in the System PbO-Ta2O5

Subsolidus phase relations in the binary system PbO-Ta₂O₅ were investigated by the quenching method. The following compounds were identified by X-ray diffraction patterns: PbO -2Ta2O₅, PbO Ta₂O₆, 3PbO 2Ta₂P₅, 2PbO Ta₂O₆, 5PbO -2Ta₂O₅, and 3PbOTa₂O₅ The 1:1 compound has rhombohedral symmetry when it is prepared below 1150°C. Above this temperature, it yields an orthorhombic phase. Compounds with the same ratio of lead oxide to pentoxide exist in the systems PbO-Ta₂O₆ and PbO-Nb₂O₅.     

Phase Equilibrium Relationships in a Portion of the System MgO–Al2O3–2CaO·SiO2

The system MgO–Al₂O₃–2CaO·SiO₂ comprises a plane through the tetrahedron CaO–MgO–Al₂O₃–SiO₂. A total of 108 compositions were prepared having an alumina content below the line joining 2CaO·Al₂O₃SiO₂ (gehlenite) and MgO·Al₂O₃ (spinel). Quenching experiments were carried out on 96 of these compositions at temperatures up to 1590°C. Three binary eutectic systems and two ternary eutectic systems are described. Compositions on this plane are of significance in an investigation of the constitution of basic refractory clinkers made from Canadian dolomitic magnesites. They also concern the compositions of certain blast furnace slags.     

Studies in Lithium Oxide Systems: VII, Li2O–B2O2–SiO2

Phase relations in the system Li₂O–B₂O₃–SiO₂ were studied by quenching and solid-state reactions. No ternary compounds were detected in the portion of the system containing less than 53% Li₂O. Compatibility triangles were formed from the binary borate and silicate compounds. Liquidus data obtained by quenching are reported for four joins, Li₂O·2SiO₂–Li₂O·2B₂O₃, Li₂O·SiO₂-Li₂O·2B₂O₃, Li₂O·SiO₂-Li₂O·B₂O₃, and Li₂O·2B₂O₃-SiO₂. The last join cuts across the two-liquid region and is not a true binary system. Some probable ternary invariant points were located in the portion of the system which was quenchable to glass and adjacent to the two-liquid region. Further data on the previously reported immiscible liquid formation are given and the significance is discussed. Data on the thermal expansion behavior of certain glasses are presented.     

The Binary System CaO–Nb2O5

The binary system CaO-Nb₂O₅ has been shown to include three compounds: CaO·Nb₂O₅, which melts congruently at 1560°C; 2CaO·Nb₂O₅, which melts congruently at 1576°C; and 3CaO·-Nb₂O₅, which melts incongruently at 1560°C. Three eutectic compositions occur at 6% CaO (1362°C), 23% CaO (1492°C), and 34% CaO (1535°C). These results were obtained by the cone-fusion technique. The compound 3CaO-Nb₂O₅ has been shown to exist in two forms: type I, face-centered cubic with a = 7.978 A, having a superlattice with a = 23.934 A, and type II, orthorhombic (pseudotetragonal, distorted cubic) with a = 11.51 A, b = 11.10 A, c = 15.98 A, having a pseudocell with a = 5.754 A, b = 5.551 A, and c = 7.990 A. The conditions controlling the formation of these two forms were not determinable from the experiments conducted.     

The System Iron Oxide-TiO2-SiO2 in Air

Phase relations at liquidus temperatures in the system iron oxide-TiO₂-SiO₂ have been determined in air. The equilibrium existence of the crystalline phases magnetite (ss), hematite (ss), pseudobrookite(ss), rutile(ss), and silica (tridy-mite or cristobalite) has been established. Three isobaric eutectic points are formed by the intersections of quaternary liquidus univariant lines of the system Fe-Ti-Si-O and the 0.21 atmosphere isobaric surface. The liquid misci-bility gaps present in the bounding "binary" systems iron oxide-Si0₂ and TiO₂-SiO₂ extend across the composition triangle representing the "ternary" system iron oxide-TiO₂-SiO₂. Liquidus temperatures decrease within the two-liquid region from approximately l <57Q^a C. in the system iron oxide-SiO₂ and 1780°C. in the system Ti(VSiO₂ to 1540°C. at the cristobalite-rutile(ss) boundary curve which bisects the two-liquid region. Paths of equilibrium crystallization of representative mixtures are discussed with reference to a simplified projection into the plane FeOFe₂O₃-TiO₂-SiO₂ as well as in terms of the tetrahedron representing the system FeO-Fe₂O₃-TiO₂-SiO₂.     

Na2SO4-lnduced Corrosion of Si3N4 Coated with Chemically Vapor Deposited Ta2O5

Hot isostatically pressed Si₃N₄ was coated with chemically vapor-deposited Ta₂O₅, and subjected to oxidative and corrosive environments to determine the feasibility of using a Ta₂O₅ coating for protecting Si₃N₄ from hot corrosion. The coated structure was relatively stable at 1000^deg;C in pure O₂. However, the Ta₂O₅-Si₃N₄ system became unstable in an environment containing Na₂SO₄ and O₂ at 1000^deg;C because (1) Ta₂O₅ and Na₂SO₄ reacted rapidly to form NaTaO₃ and (2) subsequently NaTaO₃ interacted destructively with the underlying Si₃N₄ substrate to form a molten phase.     

Subsolidus Equilibria in the System ZrO2-WO3-P2O5

The existence of stable and metastable forms of 2ZrO₂·P₂O₅ and the subsolidus phase relations in the system ZrO₂-ZrP₂O₇ were confirmed before investigation of the ternary system. The synthesis and thermal behavior of ZrW₂O₈ were reinvestigated, and the system WO₃-P₂O₅ was examined cursorily. A ternary compound, 2ZrO₂·WO₃·P₂O₅, was found, and compatibility triangles for the system between 1105° and 1150°C were established. The ternary compound is compatible with ZrO₂, WO₃, and three binary compounds, giving rise to five composition triangles. In addition, ZrP₂O₇, WO₃, and "W₂O₃(PO₄)₂" were compatible.     

The High-Silica Liquidus Surface of the System Na2O-B2O3-SiO2

The liquidus surface for the high silica (>60 wt%) portion of the ternary system Na₂O-B₂O₃-SiO₂ is presented. Determinations were made by quench runs and solubility studies. The compound, reedmergnerite, NaBSi₃O₈ was not observed. Tridymite is the major primary phase .     

Ordered Fluorite-Related Phases in the Systems ZrO2(HfO2)-MgO-Nb2O5 (Ta2O5)

New phases in the ternary systems ZrO₂ (HfO₂)-MgO-Nb₂O₅ (Ta₂O_s) were identified. These M₇O₁₂ compositions have fluorite superstructures isomorphous with the rhombohedral Y₆UO₁₂ type.     

Formation of Metastable Fluorite Phase by Rapid Quenching of Melts in the Y2O3-Ta2O5 System

Melts of x mol% Ta₂O₅–Y₂O₃ (x = 0–32.5) were rapidly quenched to investigate the formation of metastable fluorite solid solutions. C-type Y₂O₃, fluorite, and fergusonite phases existed in the compositional regions of 0 x 16, 8 x 32.5, and 27.5 x 32.5, respectively. Their lattice parameters were precisely measured through either Rietveld analysis or a least-squares fit of the individual X-ray diffraction peak positions. The lattice parameter of the fluorite phase decreased linearly with increasing Ta₂O₅ content, strongly suggesting the formation of compositionally homogeneous metastable solid solutions. Ta₂O₅ was almost insoluble into Y₂O₃ at 1700°C in the equilibrium state.     

The System CaO-Al2O3-H2O

Phase equilibria have been determined in the system CaO-Al₂O₃-H₂O in the temperature range 100° to 1000°C. under water pressures of up to 3000 atmospheres. Only three hydrated phases are formed stably in the system: Ca(OH)₂, 3CaO·Al₂O₃·6H₂O, and 4CaO·3Al₂O₃-3H₂O. Pressure-temperature curves delineating the equilibrium decomposition of each of these phases have been determined, and some ther-mochemical data have been deduced therefrom. It has been established that both the compounds CaO·Al₂O₃ and 3CaO·Al₂O₃ have a minimum temperature of stability which is above 1000°C. The relevance of the new data to some aspects of cement chemistry is discussed.     

Studies in Lithium Oxide Systems: XII, Li2O-B2O3-Al2O3

Tentative phase relations in the binary system BnOa-A1₂O₃ are presented as a prerequisite to the understanding of the system Li₂O-B₂O₃-Al₂O₃. Two binary compounds, 2A1₂O₃.B₂O₃ and 9A1₂O₃.-2B₂O₃, melted incongruently at 1030° f 7°C and about 144°C, respectively. Two ternary compounds were isolated, 2Li₂O.A1₂O₃.B₂O₃ and 2Li₂O. 2AI₂O₃. 3B₂0₃. The 2:1:1 compound gave a melting reaction by differential thermal analysis at 870°± 20° C, but the exact nature of the melting behavior was not determined. The 2:2:-3 compound melted at 790°± 20° C to Li_zO.-5Al₂O₃ and liquid. X-ray diffraction data for the compounds are presented and compatibility triangles are shown.     

Phase Transformations in the High-Temperature Form of Pure and TiO2-Stabilized Ta2O5

The high-temperature forms of undoped tantalum pentoxide (H-100Ta₂O₅) and TiO₂–modified Ta₂O₅ (H-92Ta₂O₅–8TiO₂) were investigated by in situ synchrotron X-ray diffraction and Raman scattering measurements. Two unquenchable and reversible phase transformations were observed in pure H-Ta₂O₅, while only one was detected for TiO₂-stabilized H-Ta₂O₅. Diffraction studies were consistent with displasive transformations, but hot-stage Raman spectroscopy indicated the existence of transient intermediate forms during the transformations. Use of complementary techniques enabled the reinterpretation of phase transformations in light of a newly proposed crystal structure model for H-Ta₂O₅, ¹ and emphasized the structural contributions of the oxygen sublattice.     

Ternary System Al2O3—MgO—CaO: Part II, Phase Relationships in the Subsystem Al2O3—MgAl2O4—CaAl4O7

Solid-state compatibility and melting relationships in the subsystem Al₂O₃—MgAl₂O₄—CaAl₄O₇ were studied by firing and quenching selected samples located in the isopletal section (CaO·MgO)—Al₂O₃. The samples then were examined using X-ray diffractomtery, optical microscopy, and scanning and transmission electron microscopies with wavelength- and energy-dispersive spectroscopies, respectively. The temperature, composition, and character of the ternary invariant points of the subsystem were established. The existence of two new ternary phases (Ca₂Mg₂Al₂₈O₄₆ and CaMg₂Al₁₆O₂₇) was confirmed, and the composition, temperature, and peritectic character of their melting points were determined. The isothermal sections at 1650°, 1750°, and 1840°C of this subsystem were plotted, and the solid-solution ranges of CaAl₄O₇, CaAl₁₂O₁₉, MgAl₂O₄, Ca₂Mg₂Al₂₈O₄₆, and CaMg₂Al₁₆O₂₇ were determined at various temperatures. The experimental data obtained in this investigation, those reported in Part I of this work, and those found in the literature were used to establish the projection of the liquidus surface of the ternary system Al₂O₃—MgO—CaO.     

The System Al2O3-Cr2O3-Sio2

Liquidus phase equilibrium data are presented for the system Al₂O₃-Cr₂O₃-SiO₂. The liquidus diagram is dominated by a large, high-temperature, two-liquid region overlying the primary phase field of corundum solid solution. Other important features are a narrow field for mullite solid solution, a very small cristobalite field, and a ternary eutectic at 1580°C. The eutectic liquid (6Al₂O₃-ICr₂O₃-93SiO₂) coexists with a mullite solid solution (61Al₂O₃-10Cr₂O₃-29SiO₂), a corundum solid solution (19Al₂O₃-81Cr₂O₃), and cristobalite (SO₂). Diagrams are presented to show courses of fractional crystallization, courses of equilibrium crystallization, and phase relations on isothermal planes at 1800°, 1700°, and 1575°C. Tie lines were sketched to indicate the composition of coexisting mullite and corundum solid solution phases.     

Crystallization of Beta NaFeO2 from a Glass Along the Na2SiO3-Fe2O3 Join

Fine-particle beta sodium ferrite (β-NaFeO₂), rather than α-Fe₂O₃, may be responsible for superparamagnetic behavior in a glass of composition (in mole fractions) 0.37Na₂O-0.26Fe₂O₃-0.37SiO₂. The 700°C isothermal section of the phase diagram of the Na₂O-Fe₂O₃-SiO₂ system is given, showing a three-phase field bounded by Na₂SiO₃-NaFeO₂-Fe₂O₃; there is no evidence for the existence (at 700°C) of compounds of molar composition 6Na₂O-4Fe₂O₃-5SiO₂ or 2Na₂O-Fe₂O₃-SiO₂. The Moessbauer spectrum of β-NaFeO₂ has an internal magnetic field of 487 kOe at room temperature.     

Phase Equilibria and Ionic Conductivity in the System ZrO2−Yb2O3−Y2O3

The phase equilibria in the zirconia-rich part of the system ZrO₂−Yb₂O₃−Y₂O₃ were determined at 1200°, 1400°, and 1650°C. The stabilizing effects of Yb₂O₃ and Y₂O₃ were found to be quite similar with <10 mol% of either being necessary to fully stabilize the cubic fluorite-structure phase at 1200°C. The two binary ordered phases, Zr₃Yb₄O₁₂ and Zr₃Y₄O₁₂, are completely miscible at 1200°C. These were the only binary or ternary phases detected. The ionic conductivities of ternary specimens in this system were measured using the complex impedance analysis technique. For a given level of total dopant, the substitution of Yb₂O₃ for Y₂O₃ gives only minor increases in specimen conductivity.     

Formation and Transformation of Solid Solutions in the System Nb2O5–Ta2O5

In the system Nb₂O₅–Ta₂O₅, a continuous series of δ-Nb₂O₅ (δ-Ta₂O₅) solid solutions with a hexagonal cell is formed while heating amorphous materials prepared by the simultaneous hydrolysis of niobium and tantalum alkoxides. The lattice parameters a and c change linearly with increasing Ta₂O₅ content; the former value increases from 0.3604 to 0.3620 nm, and the latter value decreases from 0.3923 to 0.3883 nm. They transform to γ-Nb₂O₅ (β-Ta₂O₅) solid solutions with an orthorhombic cell at higher temperatures. The changes in lattice parameters a and c as functions of composition are the same as those of hexagonal solid solutions, whereas parameter b is relatively constant.