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.     

Oxidation Behavior of Si-C-O Fibers (Nicalon) under Oxygen Partial Pressures from 102 to 105 Pa at 1773 k

Polycarbosilane-derived SiC fibers (Nicalon) were oxidized at 1773 K under oxygen partial pressures from 10² to 10⁵ Pa. The effect of oxygen partial pressure on the oxidation behavior of the Nicalon fibers was investigated by examining mass change, surface composition, crystal phase, morphology, and tensile strength. The Nicalon fibers were passively oxidized under oxygen partial pressures of >2.5 ×10² Pa and actively oxidized under an oxygen partial pressure of 10² Pa. Under oxygen partial pressures from 2.5 × 10² to 10³ Pa, active oxidation occurred at the earliest stage of oxidation, resulting in the formation of both a silica film and a carbon intermediate layer. Although the unoxidized core retained considerable levels of strength under the passive-oxidation condition, fiber strength was lost under the active-oxidation condition.     

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.     

The System MgO-MgCl2-H2O at 23°C

Solubilities of MgO in aqueous HC1 solutions at 23°±3°C were measured and combined with analyses of neat magnesium oxychloride cements, cured in sealed containers, to construct an equilibrium phase diagram for the system MgO-MgCl₂-H₂O. Specific gravities and acidities of solutions saturated with MgO and relative humidities of vapor phases over sealed samples were measured and combined with XRD data to define the compositions in equilibrium with two crystalline phases. Studies of relative reaction rates indicated that the 5–1–8 phase crystallizes more rapidly than the 3·1·8 phase and that cements near the 3·1·8 composition react rapidly with atmospheric CO₂ to form the chlorocarbonate phase.     

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.     

Deviation from Stoichiometry in Cr2O3 at High Oxygen Partial Pressures

The deviation from stoichiometry, δ, in Cr₂−δO₃ was measured by a tensivolumetric method in the high pO₂ range of ≊10⁴ to 10⁴ Pa at 1100°C. The value of δ, or chromium vacancy concentration, was≊9×10⁻⁵ mol/mol Cr₂O₃ in air for Cr₂O₃ with 99.999% purity. The chemical diffusion coefficient, DT, determined from equilibration data was ≊4.6× cm²·s⁻¹ at 1100°C for pO₂= 2.2 ×10¹ Pa. The self-diffusion coefficient of Cr ions was calculated from and δ and found to be≊1.6×10-17 cm²-s⁻¹, in good agreement with recently measured values.     

Phase Equilibria of the La2O3-SrO-CuO System at 950°C and 10 kbar

Phase equilibria of the La₂O₃-SrO-CuO system have been determined at 950°C and 10 kbar (1 GPa). Stable phases at the apices of the ternary phase diagram are CuO, La₂O₃, and SrO. Stable intermediate phases are La₂CuO₄ in the LaO_1.5-CuO binary and Sr₂CuO₃, SrCuO₂, and Sr₁₄Cu₂₄O₄₁ in the CuO-SrO binary. The La_2-xSr _x CuO_4-δ solid solution is stable where 0.0 ≤ x ≤ 1.3, the La_2-xSr_1+xCu₂O_6+δ solid solution is stable where 0.0 ≤ x ≤ 0.2, the La_8-xSr _x Cu₈O_20-δ solid solution is stable where 1.3 ≤ x ≤ 2.7, the La _x Sr_14-x-Cu₂₄O₄₁ solid solution is stable where 0 ≤ x ≤ 6, and the La_1+xSr_2-xCu₂O_5.5+δ phase is stable where 0.04 ≤ x ≤ 0.16. The La₂O₃-SrO-CuO phase diagram at 950°C and 10 kbar is almost identical to that determined by other authors at 950°C and 1 atm, in terms of phase stability and solid-solution ranges.     

Phase Formation in the System Na2O · Al2O3-CaO · A12O3-Al2O3 at 1200°C in Air

Phase relations in the system Na₂O_· Al₂O₃-CaO· Al₂O₃-Al₂O₃ at 1200°C in air were determined using the quenching method and high-temperature X-ray diffraction. The compound 2Na₂O · 3CaO · 5Al₂O₃, known from the literature, was reformulated as Na₂O · CaO · 2Al₂O₃. A new compound with the probable composition Na₂O · 3CaO · 8Al₂O₃ was found. Cell parameters of both compounds were determined. The compound Na₂O · CaO-2Al₂O₃ is tetragonal with a = 1.04348(24) and c = 0.72539(31) nm; it forms solid solutions with Na₂O · Al₂O₃ up to 38 mol% Na₂O at 1200°C. The compound Na₂O · 3CaO · 8Al₂O₃ is hexagonal with) a = 0.98436(4) and c = 0.69415(4) nm. The compound CaO · 6Al₂O₃ is not initially formed from oxide components at 1200°C but behaves as an equilibrium phase when it is formed separately at higher temperatures. The very slow transformation kinetics between β and β "-Al₂O₃ make it very difficult to determine equilibrium phase relations in the high-Al₂O₃ part of the diagram. Conclusions as to lifetime processes in high-pressure sodium discharge lamps can be drawn from the phase diagram.     

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.     

The System MgO─P2O5─H2O at 25°C

The phase diagram for the ternary system MgO─P₂O₅─H₂O at 25°C has been constructed. The magnesium phosphates represented are Mg(H₂PO₄)₂· n H₂O ( n = 4, 2, 0), MgHPO₄·3H₂O, and Mg₃(PO₄)₂· m H₂O ( m = 8, 22). Because of the large differences in the solubilities of these compounds, the technique which involves plotting the mole fractions of MgO and P₂O₅ as their 10th roots has been employed. With the exception of MgHPO₄·3H₂O, the magnesium phosphates are incongruently soluble. Because incongruency is associated with a peritectic-like reaction, the phase Mg₂(PO₄)₃· 8H₂O persists metastably for an extended period.     

The System CaO-Al2O3-P2O5-H2O at 200°C

The phase relations were established experimentally for the system CaO-Al₂O₃-P₂O₅-H₂O at 200°C and 1710 kPa. The quaternary compound, crandallite, CaAl₃(PO₄)₂(OH)₅· H₂O, was found to be stable. Compatibility joins in the system were determined. The phase relations are presented on the isothermal-isobaric 90 wt% water plane and by projecting the primary fields of the liquidus surface onto the same plane.     

Phase Relations in Crystalline Ceramic Nuclear Waste Forms: The System UO2+x-CeO2-ZrO2-ThO2 at 1200°C in Air

Steady-state phase relations in the system UO_2+x-CeO_z-ZrO₂-ThO₂ were determined for application to phase relations in high-level crystalline ceramic nuclear waste forms. Samples were treated at 1200°C at an oxygen partial pressure of 21.3 kPa and a total pressure of 101.3 kPa. Phase assemblages were found to be comprised of cubic solid solutions of the fluorite-structure type, solid solutions based on ZrO₂, and orthorhombic solid solutions based on U₃O₈.     

Phase Equilibria in the System MgO—FeO—Fe2O2, in Temperature Range 1400° to 1800°C

Equilibrium relations in isothermal sections through the system MgO-FeO-Fe₂O₃ have been determined in the temperature range 1400° to 1800°C. Oxide mixtures prepared from reagent-grade chemicals were equilibrated and subsequently quenched to room temperature while sealed in 80Pt20Rh tubes. The data obtained for the isothermal sections are used to infer equilibrium relations existing along the liquidus surface of the system.     

Phase Compatibilities in the System Y2O3-BaO-CuO at 950°C

We report the compatibility relationships between compounds, including the newly discovered superconducting Y₁Ba₂Cu₃O_x phase, in the Y₂O₃-BaO-CuO system at 950°C. In addition to the previously reported ternary compounds, there is a new compound with a composition Y_lBa₃Cu₂O_x. The new compound is a perovskite 'space group P4mm) with lattice parameters a =4.078 Å (0.4078 nm) and c =4.01 Å (0.401 nm). There are also at least two structurally distinguishable binary phases between barium oxide and the known BaCuO₂, but they appear to be hygroscopic and are beyond our current capabilities of analysis.     

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.