The Al-Rich Part of the Fe-Al Phase Diagram

The Al-rich part of the Fe-Al phase diagram between 50 and 80 at.% Al including the complex intermetallic phases Fe$_{5}$Al$_{8}$ (ε), FeAl$_{2}$, Fe$_{2}$Al$_{5}$, and Fe4Al$_{13}$ was re-investigated in detail. A series of 19 alloys was produced and heat-treated at temperatures in the range from 600 to 1100 °C for up to 5000 h. The obtained data were further complemented by results from a number of diffusion couples, which helped to determine the homogeneity ranges of the phases FeAl$_{2}$, Fe$_{2}$Al$_{5}$, and Fe$_{4}$Al$_{13}$. All microstructures were inspected by scanning electron microscopy (SEM), and chemical compositions of the equilibrium phases as well as of the alloys were obtained by electron probe microanalysis (EPMA). Crystal structures and the variation of the lattice parameters were studied by x-ray diffraction (XRD) and differential thermal analysis (DTA) was applied to measure all types of transition temperatures. From these results, a revised version of the Al-rich part of the phase diagram was constructed

Phase Behavior of Aqueous Na-K-Mg-Ca-CI-NO3 Mixtures: Isopiestic Measurements and Thermodynamic Modeling

A comprehensive model has been established for calculating thermodynamic properties of multicomponent aqueous systems containing the Na{sup +}, K{sup +}, Mg{sup 2+}, Ca{sup 2+}, Cl{sup -}, and NO{sub 3}{sup -} ions. The thermodynamic framework is based on a previously developed model for mixed-solvent electrolyte solutions. The framework has been designed to reproduce the properties of salt solutions at temperatures ranging from the freezing point to 300 C and concentrations ranging from infinite dilution to the fused salt limit. The model has been parameterized using a combination of an extensive literature database and new isopiestic measurements for thirteen salt mixtures at 140 C. The measurements have been performed using Oak Ridge National Laboratory's (ORNL) previously designed gravimetric isopiestic apparatus, which makes it possible to detect solid phase precipitation. Water activities are reported for mixtures with a fixed ratio of salts as a function of the total apparent salt mole fraction. The isopiestic measurements reported here simultaneously reflect two fundamental properties of the system, i.e., the activity of water as a function of solution concentration and the occurrence of solid-liquid transitions. The thermodynamic model accurately reproduces the new isopiestic data as well as literature data for binary, ternary and higher-order subsystems. Because of its high accuracy in calculating vapor-liquid and solid-liquid equilibria, the model is suitable for studying deliquescence behavior of multicomponent salt systems