Thermodynamic Assessment of the System CoO-MnO

The thermodynamic properties of pure CoO and CoO-MnO solutions have been analyzed in terms of thermodynamic models applying various experimental data. Expressions for the Gibbs energy of the individual phases have been obtained and the phase diagram is calculated. It reveals a homogeneous solid solution at temperatures above room temperature but a miscibility gap at very low temperatures.     

Zirconia-Based Metastable Solid Solutions through Self-Propagating High-Temperature Synthesis: Synthesis, Characterization, and Mechanistic Investigations

Cubic Zr_{1− x} Me _x O _y (Me = Fe, Co, Ni, Cu) metastable solid solutions with metal content significantly higher than equilibrium levels have been synthesized by the self-propagating high-temperature synthesis method based on a thermite reaction between metallic zirconium and the transition-metal oxides CoO, Fe₂O₃, CuO, and NiO. Through in situ XRD analysis, it was determined that when heated to 1100°C, the cubic solid solution transformed to the tetragonal phase with the concomitant formation of iron oxide. When cooled to lower temperatures, the tetragonal phase transformed to the monoclinic phase at or below 500°C. Results of auxiliary experiments strongly suggest that the formation of the solid solution takes place behind the combustion front by a reaction between zirconia and the metal.     

Segregation and Near-Surface Diffusion for Undoped and Cr-Doped CoO

Work function measurements were used to monitor the re-equilibration kinetics for the system CoO-Cr₂O₃ involving undoped CoO, Cr-doped CoO, CoCr₂O₄ spinel phase, and undoped Cr₂O₃. The activation energy of chemical diffusion for the near-surface layer was determined for these materials. Combined work function, X-ray, and ESCA studies indicate that Cr segregates in CoO-Cr_zO₃ solid solutions, which leads to the formation of a new "surface phase" of spinel-like structure.     

CeO2−CoO Phase Diagram

Phase equilibria in the CeO₂−CoO system at temperatures above 1500°C were investigated. The microstructures and the phase compositions of the DTA (differential thermal analysis) samples and the quenched solid pellets were analyzed using SEM (scanning electron microscope), EDX (energy dispersive X-ray), and WDX (wavelength dispersive X-ray). A eutectic reaction was found at 1645 ± 5°C. The eutectic point was calculated to be at 82 ± 1.5 mol% CoO. The eutectic phases were the CeO₂-rich phase (containing <5 mol% CoO) and the CoO-rich phase (containing ∼0.5 mol% CeO₂). At 1580°C, the solubility of CoO in CeO₂ was ∼3 mol%.     

Activity–Composition Relations in MnCr2O4–CoCr2O4 Solid Solutions and Stabilities of MnCr2O4 and CoCr2O4 at 1300°C

Phase equilibria in the system MnO–CoO–Cr₂O₃ were investigated at 1300°C under controlled oxygen partial pressures by using the gas equilibration technique. The CoO activities in various phase assemblages of the system were measured by determining the partial pressures of oxygen in the gas phase for coexistence with metallic cobalt. The activity data revealed that at 1300°C, MnO–CoO and MnCr₂O₄–CoCr₂O₄ solid solutions exhibit mild positive departures from ideal behavior. The activities in the stoichiometric spinel solutions were found to be in good agreement with those predicted from a model based on cation distribution equilibria. The standard free energy of formation of the compound CoCr₂O₄ from its oxide components at 1300°C was determined as −37 636 J/mol, while that for MnCr₂O₄ was found as −44 316 J/mol.     

Subsolidus phase relationship in the Y2O3-Mn3O4-CoOx system in air

The subsolidus phase relations in the Y₂O₃-Mn₃O₄-CoO_x system in air were investigated by X-ray powder diffraction. All the samples were prepared by solid state reaction method. There are 8 single-phases, 9 two-phase regions and 8 three-phase regions in this system. Two solid solutions, namely o-YCo_xMn_1-xO_3-δ with a narrow range of 0.70 ≤ x ≤ 0.76 and m-YCo_xMn_1-xO_3-δ with a wider range of 0.28 ≤ x ≤ 0.60, were found to form. o-YCo_xMn_1-xO_3-δ crystallizes in an orthorhombic Pnma perovskite structure, while m-YCo_xMn_1-xO_3-δ exhibits diffraction features of either monoclinic P2₁/n or/and orthorhombic Pnma perovskite structure. The homogeneity ranges for hexagonal YMnO₃ (less than 3 at. % CoO), orthorhombic YMn₂O₅ (less than 4 at. % CoO) and the tetragonal spinel phase t-Co_xMn_3-xO₄ (0-31 at. % CoO), the cubic spinel phase c-Co_xMn_3-xO₄ (65-69 at. % CoO) were determined.     

复合氧化物La0.8Sr0.2CoO3的合成及其析氧电催化

通过有机酸辅助法在较低温度下合成了La0.8Sr0.2CoO3复合氧化物,XRD结果表明,用该方法合成的La0.8Sr0.2CoO3具有单相钙钛矿结构,从稳态物化曲线得出,在碱性溶液中,在La0.8Sr0.2CoO3表面的析氧Tafel斜率为65mV/dec,OH-的反应级数为1,在分析了反应机理后,得出了析氧反应的动力学方程,恒电流测试结果表明,用该方法制备的La0.8Sr0.2CoO3/Ni电极,在碱性溶液中具有良好的析氧催化活性.     

Thermodynamic Assessment of the ZrO2─YO1.5 System

An optimal set of thermodynamic functions for the ZrO₂─YO_1.5 system are obtained using phase diagram and thermodynamic data. The liquid is described by a subregular solution model. Both cubic ZrO₂ and YO_1.5 solid solutions are regarded as one cubic solution, which is also treated as a subregular solution. The ordered Zr₃Y₄O₁₂ phase is treated as a stoichiometric compound. A regular solution model is applied to the other solid solutions. Tentative equilibrium boundaries between monoclinic and tetragonal ZrO₂ solid solutions are evaluated from information about the T ₀ line. The calculated phase diagram and thermodynamic functions agree well with experimental data.     

Activity-Composition Relations in Co2SiO4-Fe2SiO4 Solid Solutions at 1180°C

Activity-composition relations of cobalt orthosilicate in cobalt-iron-orthosilicate solid solutions were determined at 1180°C by studying the equilibrium between these solid solutions, silica, metallic cobalt, and a gas phase of known oxygen pressures. The solution shows a slight positive deviation from ideality.     

氯化铵溶蚀下水泥基材料的固-液平衡方程

通过开展硬化水泥净浆与模拟孔溶液间的溶解平衡实验,获得了6 mol/L氯化铵溶液加速溶蚀条件下,硅酸盐水泥体系的固-液平衡曲线.实验得到的固-液平衡曲线与去离子水溶蚀条件下的平衡曲线相似,氯化铵溶液与去离子水溶液对水泥基材料具有相似的溶蚀机理.此外,氯化铵溶液溶蚀过程中还伴随着固相镁和固相硫的溶解流失,且其溶解流失规律...     

Eutectoid decomposition processes of solid solutions in the HfO2  PrO1.5 and HfO2  MgO systems and their influence on the physico-chemical properties of refractory materials

Microscopy and electron microprobe analysis were used to study the process of eutectoid decomposition of cubic solid solutions in the HfO₂  PrO_1.5 and HfO₂  MgO systems. In the first system this occurs by forming of a Pr-rich pyrochlore-type phase and monoclinic HfO₂ solid solution. In the HfO₂  MgO system, magnesium concentrates mainly at crystal boundaries yielding a MgO solid solution; the second, MgO-poor phase is a HfO₂-based monoclinic solid solution. As a result of decomposition the electrical conductivity of the cubic solid solutions is reduced by two orders of magnitude in the HfO₂  PrO_1.5 system and more than orders of magnitude in the HfO₂  MgO system.     

Thermodynamics of Ferroelectric Solid Solutions with Morphotropic Phase Boundaries

A thermodynamic analysis is presented for the diffusionless phase diagrams of ferroelectric solid solutions that display a morphotropic phase boundary (MPB) separating adjacent tetragonal and rhombohedral phases. Equations are developed for the shape of the MPB, the locations of triple and tricritical points, and for the line along which the anisotropy of polarization vanishes. The appearance of lower symmetry orthorhombic and monoclinic phases is considered and the topologies of energy surfaces in the region of the phase diagram where these phases may stabilize are illustrated. The theory is applied to the solid solution of lead zirconate with lead titanate (PZT) and relationships between polar anisotropy and the transformation strain, dielectric susceptibility and piezoelectric properties, are discussed. The analysis is used to reproduce phase boundary lines for solid solutions of lead titanate with lead magnesium niobate (PMN‐PT) and lead zinc niobate (PZN‐PT) and composition–temperature diagrams along isopleths in the ternary system PMN‐PZT are estimated. The anisotropies of polarization in solid solutions based on lead titanate and barium titanate are contrasted. The results provide a thermodynamic framework useful for guiding experimental investigations of ferroelectric solid solutions and for generating energy functions used in constitutive modeling and phase field simulations of microstructure and properties.     

Film‐surface diffusion during the adsorption of acid dyes onto activated carbon

A mass transport model has been developed and applied to the adsorption of three acid dyes onto activated carbon in three single component systems. The mass transfer model is based on two rate controlling mass transfer steps, namely external film mass transfer and homogeneous solid‐phase surface diffusion (HSD). Almost all previous film‐HSD models have been based on numerical solutions to the diffusion equation using orthogonal collocation or Crank–Nicolson finite difference solutions. However, in the present model a semi‐analytical solution to the solid surface diffusion equation is presented, yielding a sophisticated solution of the differential equations. The solutions provide a good correlation between the experimental concentration–time decay curves by incorporating the Langmuir equilibrium isotherm to describe the solid phase surface dye concentrations. However, the surface diffusivities show a dependence on the carbon particle surface coverage and these diffusivities have been correlated using a Darken relationship. Copyright © 2004 Society of Chemical Industry     

固溶体技术用于AlN-SiC微波衰减材料改性

结合AlN SiC二元系相图的理论分析 ,提出了利用固溶体技术实现AlN SiC微波衰减材料性能优化的研究思路 ;采用热压烧结工艺 ,通过合理的烧结温度及保温时间的控制 ,制备了性能优异的AlN SiC微波衰减材料。通过XRD、SEM、网络分析仪等测试手段 ,研究了材料的显微结构 (晶粒尺寸和晶粒形状等 )对材料微波衰减性能的影响 ,结果表明 ,AlN SiC局部固溶体具有广频衰减特性 ,而AlN SiC均质固溶体具有选频衰减特性 ;并初步探讨了AlN SiC固溶体陶瓷的微波衰减机理     

Characterization of Mixed Cobalt-Molybdenum Oxides Prepared by Evaporative Decomposition of Solutions

The synthesis of Co-Mo oxides by the evaporative decomposition of solutions method has been investigated. The oxides were prepared from atomized metal salt solution precursors decomposed in less than 3 s in air at 700°C. The materials obtained were primarily hollow spheres (1 to 6 μm) composed of fine (100 to 500 Å (10 to 50 nm)) crystallites. CoO, Co₂Mo₃O₈, and CoMoO₄ were the major crystalline phases identified. The Co-Mo oxides were depleted in Mo relative to the precursor solutions and could not be prepared with Co/Mo atom ratios less than unity. A schematic Co-Mo-O isothermal section was constructed to explain the compositions, morphologies, and phase distributions observed for materials having different Co/Mo ratios. The loss in Mo was explained by the high vapor pressure of MoO₃.     

Liquid–liquid phase separation and crystallization of polydisperse isotactic polypropylene solutions

Phase diagrams were calculated based on Flory-Huggins solution thermodynamics to investigate the effects of polydispersity of polymer molecules and interaction parameter on the phase equilibria of crystallizable polymer solutions. The polydispersity was modeled with blends of two monodisperse polymers differing in chain lengths as a simplification. It was found that a longer chain length component could be separated easily to a polymer-rich phase by liquid demixing, but a shorter chain length component might exist at relatively constant concentration in each phase on fractionation. The influence of polydispersity on the liquid–solid phase equilibrium was small, and the phase boundary could be moved significantly in the region of low concentration of polymer by a small change of temperature. Liquid–liquid phase separation was more sensitive to the interaction between polymer and solvent than liquid–solid phase transition. Numerical calculations showed that the temperature at which liquid–liquid phase separation was coupled with liquid–solid phase equilibrium increased with a lower concentration of the polymer due to polydispersity of polymer chain lengths, and this phenomenon was observed at a lower temperature with more favorable interaction. The results were consistent with the experimental observations of isotactic polypropylene solutions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 849–857, 1998     

The effect of zirconia substitution on the high-temperature transformation of the monoclinic-prime phase in yttrium tantalate

Amorphous yttrium tantalate, as well as solid solutions containing zirconia, transform on heating to a monoclinic-prime phase and then, with further heating, to a crystalline tetragonal (T) solid solution phase at ～1450?°C. On subsequent cooling the tetragonal phase converts by a second-order displacive transformation to a different monoclinic phase not to the monoclinic-prime phase. On subsequent reheating and cooling, the phase transformation occurs between the monoclinic (M) and tetragonal phases, and the monoclinic-prime phase cannot be recovered. The limit of zirconia solubility in both the monoclinic-prime and monoclinic phases lies between 25 and 28?m/o ZrO₂, consistent with previous first-principles calculations. The monoclinic-prime phase is stable up to at least 1400?°C for 100?h for zirconia concentrations from 0 to ～60?m/o ZrO₂. This temperature exceeds the temperature of the equilibrium M-T phase transformation suggesting that the monoclinic-prime phase transforms directly to the tetragonal phase by a reconstructive transformation and is unaffected by the zirconia in solid solution.     

Defect Structure of NiO-CoO Solid Solutions

Measurements at high temperature of integrated intensities of Bragg peaks were used to examine the defect structure in two NiO-CoO solid solutions. The results indicate that the concentrations of vacant cation sites at 1100° to 1500°C are 4 to 10% and the tetrahedral occupations 2 to 5%. The concentration of these defects increases with temperature and partial pressure of O₂. The mean-square displacements of oxygen ions and cations increase with temperature and CoO concentration.     

Interdiffusion in CoO-NiO Solid Solutions

Interdiffusion coefficients were measured in CoO-NiO solid solutions over the range 1000° to 1600°C in air and at po₂=5×10⁻⁸ atm. Isothermal values of the interdiffusion coefficients in this system increased exponentially with the CoO concentration. Comparison of the present results with cation-tracer diffusion coefficients for this system measured under similar conditions by Chen and Peterson shows that a Darken-type equation relating the interdiffusion coefficient to the cation-tracer diffusivities is valid for these data.     

Activity-Composition Relations in Orthosilicate and Metasilicate Solid Solutions in the System MnO-CoO-SiO2

Activity-composition relations in Mn-Co orthosilicate and metasilicate solid solutions were determined at 1200° to 1250°C by equilibrating selected phase assemblages with metallic cobalt and a gas phase of known oxygen potentials at a total pressure of 1 atm. The orthosilicate solid solution shows a slight negative departure from ideality, whereas the metasilicate solid solution is ideal. The stability data derived for the Mn₂SiO₄ and MnSiO₃ end-members are in good agreement with those previously determined from the system MnO-"FeO"-SiO₂. The free-energy change for the reaction 2CoSiO₃= Co₂-SiO₄+ SiO₂ was determined to be -3.8 kcal at 1250°C.