Phase Relations in the System MgO-V2O3-VO2 at 1200°C

Phase relations in the quasi-ternary system MgO-V₂O₃-VO₂ at 1200°C were studied using the quenching technique under controlled O₂ atmospheres. A new phase of a type z VO _y Mg_{2− x} V_{1+ x} O₄ (0< x <1, y ≥1.5, z >0) was found with a compositional region along the MgV₂O₄-Mg₂VO₄ join. Equilibrium P _{O 2} observed for Mg_{2− x} V_{1+ x} O₄ is quite different from that for V _n O_{2 n -1} with an equal ratio of V³⁺/V⁴⁺, corresponding to the V³⁺ stabilities in two types of compounds. Thus, the phase relations in the ternary system were constructed on a conventional triaxial diagram as a function of P _O2.     

Diffusion Studies of Na2O-SiO2-Fe2O3 Melts at 1200°C

The interdiffusion of ferric oxide and silica between Na₂O-SiO₂ and Na₂O-SiO₂-Fe₂O₃ melts containing the same mole % Na₂O was studied at 1200°C in air. Values in the range lO⁻⁵ to lO⁻⁸ cm² sec⁻¹ were obtained depending on the composition of the binary melt. The results were rationalized on the basis of the changing ionic nature of the iron with the soda-silica ratio of the ternary melt. It is concluded that significant concentrations of iron cations are present in the melt only if the mole fraction of soda is less than 0.3. A cursory examination of the relative electrical conductivity of a binary and a ternary melt tends to confirm this thesis.     

Subsolidus Phase Equilibria in the System Na2O-Bi2O3-TiO2 at 1000°C

Subsolidus phase relations in the system Na₂O-Bi₂O₃-TiO₂ at 1000°C were investigated by solid-state reaction techniques and X-ray diffraction methods. Five ternary compounds were observed in the system: Na_0.5Bi_4.5Ti₄O₁₅; Na_0.5Bi_0.5TiO₃; a cubic pyrochlore solid solution composed of xNa₂O.25Bi₂O₃.(75−;x) TiO₂ where x is 2.5 to 3.75; a new compound Na_0.5Bi_8.5Ti₇O₂₇ indexed with the orthorhombic cell of a = 5.45, b = 5.42, and c = 36.8 Å; and an unidentified phase with the probable composition NaBiTi₆O₁₄.     

Solubility Limit of MgO in Al2O3 at 1600°C

The solubility of Mg in alumina was measured using wavelength-dispersive spectroscopy mounted on a scanning electron microscope. Careful calibration of the microscope's working conditions was performed in order to optimize the detection limit and accuracy. Measurements were conducted on water-quenched and furnace-cooled samples, without any thermal or chemical etching to avoid alteration of the bulk concentration. The results indicate the solubility limit of Mg in alumina to be 132±11 ppm at 1600°C.     

Phase Diagram of the System Na2O·Ga2O3-Ga2O3 and its Relation to the System Na2O·Al2O3-Al2O3

A new phase diagram for the system Na₂O-Ga₂O₃ (>50 mol% Ga₂O₃) is presented. It is based on information from differential thermal analysis, X-ray examination of quenched samples, and a radiochemical technique for determining the compositions of a primary phase and a liquid in equilibrium with it. The diagram provides a guide for the growth of primary crystals of the two ionically conducting sodium gallates that are analogs of the technologically important β- and β"-aluminas.     

Phase-Diagram Studies in the La2O3–SrO–CaO–Mn3O4 System at 1200°C in Air

The phase equilibria of the La₂O₃–SrO–CaO–Mn₃O₄ system in air at 1200°C has been studied. Under these conditions, eight univariant four-phase equilbria were observed. Quaternary phases, as well as liquid phases, were not observed. Perovskite-structure phases LaMnO₃, SrMnO₃, and CaMnO₃ did not form complete solid solutions within the system.     

Compatibility Relations of A1203 in the System Zr02-Al203-Si02-CaO

Compatibility relations of Al₂0₃ in the quaternary system Zr02-Al₂0₃-Si0₂-CaO were studied by firing and quenching followed by microscopy and energy-dispersive X-ray examination. A projection of the boundary surface of the primary crystallization volume of Al₂0₃ was constructed in terms of the CaO, Si0₂, and Zr0₂ contents of the mixtures recalculated to 100 wt%. Two invariant points, where four solids coexist with a liquid phase, are defined, and the positions of the isotherms were established.     

Phase Equilibria in the System CaO-MgO-B2O3 at 900°C

Phase equilibria in the system CaO-MgO-B₂O₃ were investigated at 900°C using X-ray powder diffraction techniques. With the exception of MgO-B₂O₃, 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 patterns, whereas for CaO and MgO, accurate lattice parameters were compared. No solid solutions were detected. As a result, the isothermal equilibrium diagram at 900°C reduces to three phase triangles. X-ray powder diffraction data for the calcium berates are included.     

Subsolidus Phase Relationships in the System Fe2O3–Al2O3–TiO2 between 1000° and 1300°C

Subsolidus phase equilibria in the system Fe₂O₃–Al₂O₃–TiO₂ were investigated between 1000° and 1300°C. Quenched samples were examined using powder X-ray diffraction and electron probe microanalytical methods. The main features of the phase relations were: (a) the presence of an M₃O₅ solid solution series between end members Fe₂TiO₅ and Al₂TiO₅, (b) a miscibility gap along the Fe₂O₃–Al₂O₃ binary, (c) an α-M₂O₃( ss ) ternary solid-solution region based on mutual solubility between Fe₂O₃, Al₂O₃, and TiO₂, and (d) an extensive three-phase region characterized by the assemblage M₃O₅+α-M₂O₃( ss ) + Cor( ss ). A comparison of results with previously established phase relations for the Fe₂O₃–Al₂O₃–TiO₂ system shows considerable discrepancy.     

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.     

Phase Equilibria in the Ti-AI-O System at 945°C and Analysis of Ti/Al2O3 Reactions

Phase relations in the Ti-Al-O system were evaluated experimentally at 945°C. The tie lines were established using equilibrated samples with phase compositions determined by electron probe microanalysis. The phase relations were in agreement with previous estimates but the phase fields of α-Ti[O,Al] and Ti₃Al[O] were significantly different. The Ti₃Al[O] phase has a maximum solubility of 22 at. % O, corresponding to a nominal stoichiometry of Ti₃AlO, whereas the α-Ti[O,Al] phase, at a maximum O solubility of 33.33 at. %, has a negligible amount of Al in solution. The disagreement between these results and previous studies was attributed to the differences in experimental techniques for sample preparation and analysis. The reported layer sequences at the Ti/Al₂O₃ interface were evaluated based on the ternary section and the corresponding O activity diagram. The layered interfaces were found to be stable, with the evolution of the reaction products governed by the thickness of the initial Ti layer and the O partial pressure in the ambient.     

The Al2O3-Nd2O3 Phase Diagram

A tentative phase diagram for the system Al₂0₃-Nd₂O₃ is presented. Three compounds were obtained: a β -A1₂O₃-type compound, the perovskite NdAlO₃, and Nd₄Al₂O₉. The perovskite melts congruently (mp 2090°C), and the two other compounds exhibit incongruent melting behavior: β -Nd/Al₂O₃, mp 1900°C; Nd₄Al₂O₉, mp 1905°C. Two eutectics exist with the following compositions and melting points: 80 mol% Al₂O₃, 1750°C; 23 mol% Al₂O₃,1800°C. Nd₄Al₂O9 decomposes in the solid state at 1780°C.     

Volume Relations in Na2O·B2O3 and Na2O·SiO2 B2O3, Melts at 1300·C

Density (and some viscosity) data are presented for binary sodium borate melts containing as much as 60 mole % Na₂O and for ternary sodium silicoborate melts with B/Si <2.0 between 1000°C and 1300°C. The high-temperature partial molar volume analysis of the binary sodium borate melts reveals about 50% BO₄ tetrahedra at the 40 mole % Na₂O composition, in agreement with recent NMR estimates for the binary glasses. No "boron anomaly" was found near 18 mole % Na₂O at high temperature. The synthetic partial molar volume model that agrees best with experiment for all ternary melts studied involves the presence of some BO₄ tetrahedra, the percentage of which varies with composition. This ternary model involves a high degree of internal consistency. No tendency toward extensive micro-immiscibility was observed for ternary melts near the SiO₂·B₂O₃ binary.     

Leaching of Glasses with Molar Composition 20Na2O · 10RO ·x Al2O3· (70-x)SiO2

Sodium depth profiles were determined in water-leached glass samples with molar composition 20Na₂O · 10RO · x Al₂O₃· (70 - x)SiO₂ (RO = CaO, MgO, and ZnO) using secondary ion mass spectrometry. The leaching of sodium ions decreases with increasing Al₂O₃ content in all three glass systems. For x = 0 the leaching is hardly affected by the nature of the divalent cation. For x = 5 and 10 the corrosion resistance is highest for the glass containing ZnO, and for the glasses containing ZnO and MgO, respectively. These glasses correspond to those with the smallest fraction of NBOs. From all these results it is concluded that the nonbridging oxygen atoms play an important role in promoting the leaching of a glass.     

Growth of β-Alumina (Na2O · 11Al2O3) Single Crystals by the Flux Method

The crystal-growth process and growth conditions of β-alumina (Na₂O · Al₂O₃) were investigated using the Na₂B₄O₇-Na₃AlF₆ flux method. β-Alumina (electric fusion brick) was used as both nutrient and seed. Weight loss of the flux varied widely for various runs: ≅ 10 wt% of flux evaporated at 100 h, ≅ 17 wt% at 150 h, and 43 wt% at 600 h. When β-alumina crystal was grown, only 20 wt% Na₂B₄O₇ was added to the Na₃AlF₆ flux. The linear growth rates of the β-alumina single crystal grown by an Na₃AlF₆-20 wt% Na₂B₄O₇ flux method at 1040°C and Δ t = 18°C were ≅ 1.0 × 10⁻³ mm/h ( a face) and ≅0.3 × 10⁻³ mm/h ( c face). The β-alumina single crystals grown were bounded by only c [001] and a [100] and were colorless and transparent.     

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.     

Vaporization Kinetics of Na2SO4 from 900° to 1200°C

Continuous weight-change measurements were used to determine the vaporization kinetics of Na₂SO₄ from 900° to 1200°C in 150 torr O₂. Simple evaporation of the sulfate was indicated. An activation energy for vaporization of 71 kcal/mol was calculated. Vaporization results obtained for Na₂SO₄ on oxide substrates indicated an Na₂SO₄-Cr₂O₃ reaction; however, no Na₂SO₄-ZrO₂ reaction was observed.     

Studies in Lithium Oxide Systems: II, Li2O Al2O3–Al2 O 3

Solid-state reactions between Li₂O and Al₂ O₃ were studied in the region between Li₂O.Al₂ O ₃ and Al₂ O ₃. The compound Li₂ O Al₂ O ₃ melts at 1610°± 15°C. and undergoes a rapid reversible inversion between 1200° and 1300°C. Vaporization of Li₂ O from compositions in the system proceeds at an appreciable rate at 1400°C, as shown by fluorescence. Lithium spinel, Li₂ O -5Al₂O₃, was the only other compound observed. The effect of Li₂ O on the sintering of alumina was investigated.