Spinodal Decomposition Structure Research Articles

Stability of critical fluid mixtures: Experimental simulation of microgravity conditions

We have closely matched the densities of the two components of a binary fluid by adding to one component a small amount of its deuterated derivative. The system Cyclohexane + deuterated Cyclohexane − Methanol thus becomes isopycnic. Measurements of the critical properties of this system show that the deuterated component does not act as a third component nor as an impurity with respect to the liquid-liquid phase transition. In such a system a phase transition in microgravity conditions can be experimentally simulated and new features found: macroscopic spinodal decomposition structures appear just after a thermal quench, and macroscopic wetting layers are observed at the final equilibrium state. Such phenomena should exist in a real microgravity environment.

Microstructure and phase solubility extension in rapidly solidified NiAl-Cr quasibinary eutectic

The microstructure of melt-spun ribbon of the NiAl-Cr quasibinary eutectic composition has been characterized by optical and transmission electron microscopies. The eutectic composition is Ni-33 at.%Al-34 at.%Cr and is of interest because of the similarity of crystal structures (CsCl for β-NiAl and b.c.c. for α-Cr) and lattice parameters of the two phases in the eutectic. The rapidly quenched microstructure consists of 0.5μm diameter columnar grains with a composition near that of the eutectic. These grains exhibit a fine spinodal decomposition structure. Based on the presence of coarse antiphase domains within the columnar grains it is concluded that they originally formed from the melt as supersaturated β-NiAl. Between the grains a fine rod-type eutectic structure of the β-NiAl and α-Cr phases is observed with eutectic spacings as fine as 12 nm. A solidification model for the appearance of a supersaturated β-NiAl phase near the eutectic composition, rather than a supersaturated α-Cr phase, is presented based on the T 0 curves for this alloy system.