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Abstract  

In this paper, examples are given of how calorimetric values can give greater certainty to phase equilibria calculated from thermodynamic data. Errors that may arise when phase diagram evaluations are carried out largely from the basis of Gibbs energy information only are illustrated by reference to recent evaluations of the Ti−Si system and the resulting calculated oxidation behaviour of titanium silicides. The importance of calorimetric values for calculation of metastable phase equilibria is demonstrated by results of work on the AlN−TiN hard-metal coating system. Finally, suggestions are made with regard to areas of work where calorimetric data are urgently needed.

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The phase diagrams of the binary systems of tetracyanoethylene (TCNE) with some methylbenzenes were determined by differential scanning calorimetry. In the durene-TCNE system a 1∶1 complex was observed. The other two pairs of components form both 1∶1 and 1∶2 complexes. In all the systems, the complexes melted incongruently. Solid — solid phase transitions were found in the complexes in the pentamethylbenzene-TCNE system. The excess free energy of mixing of the liquid phase was estimated by fitting the modified van Laar equation to the measured liquidus lines. The enthalpy and the entropy of complex formation were used as the fitting parameters.

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The correlation between morphological changes and DSC recordings gives valuable information on the mechanism of phase transformations. The present paper describes a new instrument for simultaneous DSC and thermomicroscopy in transmitted light, where a DSC device is placed in a commercially available hot-stage. The application of this DSC/thermomicroscopy is exemplified by study of the phase diagrams for KNO3-NaNO3, diphenylamine-benzophenone and a liquid crystal system.

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Phase equilibria in the V2O5-Ag2O system were investigated at a constant pressure of oxygen (0.2 atm) and the phase diagram found under these conditions was compared with the results of the authors who investigated the same system in vacuum and at an oxygen pressure of 1 atm. On the basis of all these results, an attempt was made to construct the hypothetical diagram of V2O5-Ag2O-O2.

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Abstract  

The phase diagrams of the binary system Ta2O5-K2TaF7 and the ternary system KF-Ta2O5-K2TaF7 were determined using the thermal analysis method. The system Ta2O5-K2TaF7 was measured up to 25 mol% of Ta2O5. Eutectic point is estimated to be at
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$x_{Ta_2 O_5 }$$ \end{document}
=0.14 and t=601°C. Crystallization of K2TaF7, K2Ta2O3F6 and a new phase was identified. The new phase shows isomorphism with K3Nb2F11O. In the ternary system four nonvariant equilibria points at 3 mol% of Ta2O5, 72 mol% of KF and 25 mol% of K2TaF7 at 715(1)°C; 6 mol% of Ta2O5, 44 mol% of KF and 50 mol% of K2TaF7 at 603(2)°C; 1 mol% of Ta2O5, 22 mol% of KF and 77 mol% of K2TaF7 at 704(1)°C and 8 mol% of Ta2O5, 8 mol% of KF and 84 mol% of K2TaF7 at 580(1)°C were proposed. Crystallization fields of KF, K2TaF7, K3TaF8, K3TaOF6, K4Ta2OF12 and K2Ta2O3F6 were considered.
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estimation. In addition, experimental data in literature are often contradictory. All of the lanthanide–alkali metal chloride binary systems have been successfully examined or reexamined at large by Seifert [ 1 ]. The phase diagrams of the homologous bromide

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Abstract  

The thermotropic phase solid–solid transitions compound (n-CnH2n+1NH3)2ZnCl4 (n = 14, 16, 18) were studied, and a series of their mixtures were prepared. These laminar materials contain bilayers sandwiched between metal halide layers. The low temperature crystal structures of the pure salts are characteristic of the piling of sandwiches in which a two-dimensional macro-anion ZnCl4 2− is sandwiched between two alkylammonium layers. These layers become conformationally disordered in the high temperature phases. The subsolidus binary phase diagrams of (n-C14H29NH3)2ZnCl4-(n-C18H37NH3)2ZnCl4 and (n-C16H33NH3)2ZnCl4-(n-C18H37NH3)2ZnCl4 were established by differential thermal analysis and X-ray diffraction. In each phase diagram, an intermediate compound and two eutectoid invariants were observed. There are three noticeable solid solution ranges (α, β, γ) at the left boundary, right boundary, and middle of the phase diagram.

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Abstract  

Differential thermal analysis, optical microscopy and ionic conductivity studies have been carried out on polymer electrolyte films prepared by deposition of solutions of neodymium trifluoromethanesulphonate and poly(ethylene oxide). A wide range of electrolyte concentrations were examined and a partial pseudo-equilibrium phase diagram of the system was determined. From the results obtained it is evident that the presence of relatively high concentrations of ionic guest species in the polymer host results in an inhibition of the growth of crystalline material (polymer spherulites or a polymer—salt coordination complex).

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Abstract  

The thermotropic phase transitions in the perovskite type layer compound (n-C10H21NH3)2MnCl4 and (n-C14H29NH3)2MnCl4 were synthesized and, at the same time, a series of their mixtures C10Mn-C14Mn were prepared. The experimental binary phase diagram of C10Mn-C14Mn was established by differential thermal analysis (DTA), IR and X-ray diffraction. In the phase diagram new material (n-C10H21NH3)(n-C14H29NH3)MnCl4 and two eutectoid invariants were observed, two eutectic points temperatures are about 29.8 and 27.9°C. Contrasting other similar system, there are three noticeable solid solution ranges (α, β, γ) at the left and right boundary and middle of the phase diagram.

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Abstract  

A set of phase diagrams for the systems CuX–AlkX (where Alk=Li, Na, K, Rb or Cs and X=Cl, Br or I) is given, basing on authors investigation and selected literature data. Sizes and valences of ions involved in Coulombic and polarization interactions were considered as main factors affecting phase equilibria. An increasing tendency for compound formation was noted in series Na→K→Rb→Cs, Na→Li and I→Br→Cl. The most strongly represented are compounds of the formulas AlkCu2X3 and Alk2CuX3.

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