Phase separating systems present a unique opportunity for designing composites with hierarchical microstructure at different length scales. We report here our success in synthesizing phase separating metallic glasses exhibiting the entire spectrum of microstructural possibilities expected from a phase separating system. In particular, we report novel core shell and hierarchical structures of spherical glassy droplets, resulting from critical wetting behavior and limited diffusion. We also report synthesis of a bulk phase separating glass in a metallic glass system. The combination of unique core shell and hierarchical structures in metallic glass systems opens a new avenue for the microstructure design of metallic glasses.

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We have studied diffusion controlled growth of an isolated, misfitting precipitate in a supersaturated matrix using a phase field model. Treating our simulations as computer experiments, we have critically compared our simulation results with those from Zener-Frank and Laraia-Johnson theories for the growth of non-misfitting and misfitting precipitates, respectively. The agreement between simulations and the ZF theory is very good for 1D systems. In 2D systems with interfacial curvature, we still get good agreement between simulations and both ZF and LJ theories, but only for large supersaturations. At small supersaturations, the growth coefficient from our simulations does converge towards that from theory, but a large gap does remain when the simulations end due to overlap of diffusion fields. An interesting finding from the simulations is the less complete realization of the Gibbs-Thomson effect during growth, particularly in more supersaturated alloys. Thus, even at the same precipitate size, the curvature effects are less severe in more supersaturated alloys.

Using a lattice model for adsorption in microporous materials, pure component adsorption isotherms are obtained within a mean field approximation for methane at 300 K and xenon at 300 and 360 K in zeolite NaA. It is argued that the increased repulsive adsorbate–adsorbate interactions at high coverages must play an important role in determining the adsorption behavior. Therefore, this feature is incorporated through a “coverage-dependent interaction” model, which introduces a free, adjustable parameter. Another important feature, the site volume reduction, has been treated in two ways: a van der Waal model and a 1D hard-rod theory [van Tassel et al., AIChE J. 40, 925 (1994)]; we have also generalized the latter to include all possible adsorbate overlap scenarios. In particular, the 1D hard-rod model, with our coverage-dependent interaction model, is shown to be in best quantitative agreement with the previous grand canonical Monte Carlo isotherms. The expressions for the isosteric heats of adsorption indicate that attractive and repulsive adsorbate–adsorbate interactions increase and decrease the heats of adsorption, respectively. It is concluded that within the mean field approximation, our simple model for repulsive interactions and the 1D hard-rod model for site volume reduction are able to capture most of the important features of adsorption in confined regions.

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