Thermodynamic stability of solid phases in the system Cu–O–Al2O3 by means of the EMF and DSC-TGA techniques

Journal of Solid State Electrochemistry - Thermodynamic properties of solid phases in the Cu–O–Al2O3 system were measured by means of the EMF method with oxygen concentration galvanic...     

Structure and properties of glasses in the system Li2O–SnO–B2O3

Glasses in the system Li₂O–SnO–B₂O₃ system were prepared by a melt-quenching method. Thermal and viscous properties and local structure of these glasses were investigated. The SnO–B₂O₃ glasses exhibited relatively low glass-transition temperatures (T_g) around 350 °C and excellent thermal stability against crystallization. Viscosity measurements in the vicinity of T_g indicated that the glasses were considerably fragile compared to alkali borate glasses. Fraction of four-coordinated boron was maximized at the composition with 50 mol% SnO and that of nonbridging oxygen, which is not purely ionic in alkali borate systems but partially covalent, augmented with an increase in the SnO content. Correlation between glass properties and structure was discussed in the SnO–B₂O₃ binary system.     

Thermal stability of In2(MoO4)3 and phase equilibria in the MoO3–In2O3 system

Thermal stability of a compound forming in a binary system MoO₃?CIn₂O₃ was investigated by DTA/TG, XRD and SEM methods in this study. For the first time, the diagram of phase equilibria established in the whole range of concentrations of this system's components has been constructed. The temperature and concentration ranges of the components of MoO₃?CIn₂O₃ system in which the compound In₂(MoO₄)₃ co-exists in solid state with MoO₃ or In₂O₃ or with the liquid were determined. The composition and melting point of the eutectic mixture consisting of In₂(MoO₄)₃ and MoO₃ were found.     

Biaxial phase and coexistence of the two uniaxial nematic phases in the system sodium dodecyl sulphate–decanol–D2O

The system sodium dodecyl sulphate (SDS)/decanol (DeOH)/water presents, with temperature increase, an unusual phase transition between a stable biaxial phase and a coexistence region of the two uniaxial nematic phases (discotic N_D + cylindrical N_C). This has been detected previously by several methods for a sample with water/SDS molar ratio M_w = 36. Here, this system is investigated changing the ratio M_w to 32, where previously the coexistence region was reported after a discotic N_D phase, without the biaxial phase. We report now the existence of a biaxial N_B in the temperature range of ~2°C, defining for both values of M_w and the phase sequence as N_B – (N_D + N_C) – N_C. The change in temperature is followed by conoscopic and orthoscopic optical techniques and also analysed through the curve obtained by the technique of digital image processing of the textures, which reveals a continuous transition N_D – N_B – (N_D + N_C). While the biaxial phase is stable for at least 10 hours, in a reproducible way, the coexistence region evolves with time, and drops of the discotic phase grow immersed in a N_C matrix. Results are explained in terms of recent theories dealing with stabilisation of mixtures of cylinders and discs.     

Phases in the subsolidus area of the system CuO–V2O5–Fe2O3

The phase equilibria in the solid state in the system FeVO₄?CCu₃V₂O₈ and FeVO₄?CCuO have been determined. Based on the obtained DTA and XRD analysis results and some additional research, a phase diagram in the whole subsolidus area of the system CuO?CV₂O₅?CFe₂O₃ has been worked out. Eighteen subsidiary subsystems can be distinguished in this ternary system. Basic properties of the obtained phases with howardevansite- and lyonsite-type structure have been investigated by DTA, IR, and SEM methods.     

Controllable thermal expansion and phase transition in Yb2−xCrxMo3O12

The thermal expansion and phase transition of solid solutions Yb_2?xCr_xMo₃O₁₂ have been investigated by X-ray powder diffraction and differential thermal analysis. The XRD patterns and the results of Rietveld refinement of Yb_2?xCr_xMo₃O₁₂ indicate that the solid solution limit was in the composition range of 0.0 ≤ x ≤ 0.4 and 1.7 ≤ x ≤ 2.0. Yb_2?xCr_xMo₃O₁₂ (0.0 ≤ x ≤ 0.4) has an orthorhombic structure and exhibits negative thermal expansion between 200 °C and 800 °C. Yb_2?xCr_xMo₃O₁₂ (1.7 ≤ x ≤ 2.0) crystallizes in monoclinic below the phase transition and above, transforms to orthorhombic. Both monoclinic and orthorhombic compounds Yb_2?xCr_xMo₃O₁₂ (1.7 ≤ x ≤ 2.0) present positive thermal expansion. Orthorhombic Yb_2?xCr_xMo₃O₁₂ exhibit anisotropic thermal expansion with the contraction of a and c axes, and the linear thermal expansion coefficients range from negative to positive with increasing chromium content. Partial substitution of Yb³⁺ for Cr³⁺ exhibits depressed monoclinic to orthorhombic phase transition.     

Phase equilibria in the solid state and colour properties of the CuO–In2O3 system

Phase equilibria up to solidus line in CuO?CIn₂O₃ system have been investigated using XRD and DTA/TG methods. According to the results, only one compound of the formula Cu₂In₂O₅ formed in the system studied. Its thermal stability was determined in the air and argon proving that the compound did not melt but underwent decomposition. The decomposition of Cu₂In₂O₅ in the air atmosphere began at 1080?°C, while in argon at 835?°C. Additional studies were undertaken to determine the hitherto unknown colour properties of samples representing the CuO?CIn₂O₃ system in the equilibrium state.     

Influence of SrO content on microstructure and crystallization of glazes in the SiO2–Al2O3–CaO–MgO–K2O system

The effect of the SrO addition on the microstructure and structure of the glazes from the SiO₂–Al₂O₃–CaO–MgO–K₂O system was investigated in this study. The results were obtained by testing the ability of the frits crystallization, the stability of the crystallizing phases during the single-step fast-firing cycle depending on their chemical composition and the effect of addition of strontium oxide. Differential scanning calorimetry (DSC) curves showed that all glazes crystallized, and diopside and anorthite were mainly identified as dominant phases in the obtained glazes, while the size and amount of each depended on the amount of SrO introduced. The thermal characteristic of the frits was carried out using DSC, and crystalline phases were determined by X-ray diffractometry. The glaze microstructure was investigated by scanning electron microscopy and transmission electron microscopy. Additional information on the microstructure of frits was derived from spectroscopic studies in the mid-infrared range.

     

Investigation of phase equilibria in the Er2O3–Na2O–P2O5 system: the partial system ErPO4–NaPO3–Er(PO3)3

The partial system ErPO₄–NaPO₃–Er(PO₃)₃ of the Er₂O₃–Na₂O–P₂O₅ oxide system has been investigated by thermoanalytical methods and X-ray powder diffraction. On the basis of the obtained results the phase diagram of the partial system is proposed. The system is bounded by three subsystems: (i) ErPO₄–Er(PO₃)₃, (ii) Er(PO₃)₃–NaPO₃ and (iii) ErPO₄–NaPO₃. Their phase diagrams are proposed. In the Er(PO₃)₃–NaPO₃ subsystem an intermediate compound NaEr(PO₃)₄ occurs; it melts incongruently at 655 °C. It was found that ErPO₄ and NaEr(PO₃)₄ form a section which is a real system only in the subsolidus region (below 646 °C). Two ternary invariant points (one ternary peritectic and one ternary eutectic) occur in the investigated partial system ErPO₄–NaPO₃–Er(PO₃)₃.     

Underpinning energetics of lithium bonding and stability in the Li–Pt–Sn system

Within the Li–Pt–Sn system, we examine the electronic structures and Li-binding of LiPtSn₂, Li₂PtSn and Li₃Pt₂Sn₃ with fluorite-related crystal structures. The structures with totally de-intercalated lithium keep the characteristics of the pristine ternary compound with a reduction of the volume. In Li₃Pt₂Sn₃ the binding energies of lithium belonging to three crystallographically inequivalent Wyckoff sites are different and point to distinct activities of de-intercalation concomitant with site-selective bonding magnitudes. The derived potentials are within the range of non-oxide binary and ternary lithium based compounds and indicate the possibility of at least partial delithiation.     

ZrO2–Sc2O3 Solid Electrolytes Doped with Yb2O3 or Y2O3

Russian Journal of Electrochemistry - The effects of the Y2O3 and Yb2O3 co-doping impurities on the transport characteristics and stabilization of the cubic phase in solid solutions based on...     

Synthesis of quasi-crystalline phases in the Al–Cu–Fe–Cr system

Phase equilibria in the Al–Cu–Fe system alloyed with 5% Cr were studied. Based on the data of X-ray powder diffraction analysis, electron microscopy, and differential thermal analysis, the effect of temperature on i ? d phase transitions in alloys Al₆₅Cu₂₅Fe₅Cr₅ and Al₇₀Cu₂₀Fe₅Cr₅. In the Al–Cu–Fe–Cr system, multiphase structures were detected; these structures are mixtures of quasi-crystalline and approximant phases, the contents and morphologies of which depend on the composition of the initial mixture and the crystallization rate.     

Phase equilibria in the oxide system Nd2O3–K2O–P2O5

A phase equilibria diagram of the partial system NdPO₄–K₃PO₄–KPO₃ has been developed as part of the research aimed at determining the phase equilibrium relationships in the oxide system Nd₂O₃–K₂O–P₂O₅. The investigations were conducted using thermoanalytical techniques, X-ray powder diffraction analysis and reflected-light microscopy. Three isopleths existing between: K₃Nd(PO₄)₂–K₄P₂O₇, NdPO₄–K₅P₃O₁₀ and NdPO₄–K₄P₂O₇ have been identified in the partial NdPO₄–K₃PO₄–KPO₃ system. Previously unknown potassium-neodymium phosphate “K₄Nd₂P₄O₁₅” has been discovered in the latter isopleth section. This phosphate exists in the solid phase up to a temperature of 890 °C at which it decomposes into the parent phosphates NdPO₄ and K₄P₂O₇. Four invariant points: two quasi-ternary eutectics, E₁ (1057 °C) and E₂ (580 °C) and two quasi-ternary peritectics, P₁ (1078 °C) and P₂ (610 °C), occur in the NdPO₄–K₃PO₄–KPO₃ region.     

Study of ceramic pigments based on cobalt doped Y2O3–Al2O3 system

Ceramic pigments based on Y₂O₃–Al₂O₃ system doped by cobalt as a colourant agent were synthesized by solid-state reaction at temperatures up to 1,400 °C. The reactivity of initial mixtures of components was improved by the mineralizer LiF and the mechanical activation in a planetary ball mill. The temperature region of the product formation was followed by the method of thermal analysis. The effect of the synthetic method on the phase composition of the products was studied by X-ray diffraction analysis. Studied pigment-application properties of the product include the measurement of optical properties in the visible region of light and particle size distribution. The simple solid-state reaction led to the formation of turquoise samples that contain mainly blue CoAl₂O₄ spinel and next to it also YAlO₃ perovskite and Y₃Al₅O₁₂ garnet phases. The mineralizer LiF promotes the formation of yttrium aluminium double oxides of sandy-yellow to grey–brown colour hue, although the samples also contain small amount of blue CoAl spinel phase. Intensive milling process did not results in CoAl spinel phase and the samples contain yttrium aluminium perovskite and cobalt oxide. Evaluation of Kubelka–Munk absorption as a function of the pigment concentration was found that hiding is complete by adding of 5 mass% of pigment to the ceramic glaze. Resulting colour hue of all pigment applications into ceramic glaze is blue. The size of particles lies in the range of 7–26 μm.