Rowland M Cannon | PubMed Health

PubMed2006

Grain boundary transitions in binary alloys.

A thermodynamic diffuse interface analysis predicts that grain boundary transitions in solute absorption are coupled to localized structural order-disorder transitions. An example calculation of a planar grain boundary using a symmetric binary alloy shows that first-order boundary transitions can be predicted as a function of the crystallographic grain boundary misorientation and empirical gradient coefficients. The predictions are compared to published experimental observations.

Journal Article↗

PubMed2005

Nanometer-thick surficial films in oxides as a case of prewetting.

Stable, nanometer-thick films are observed to form at the {1120} facets of Bi(2)O(3)-doped ZnO in several bulk-phase stability fields. Electron microscopy shows these surficial films to exhibit some degree of partial order in quenched samples. The equilibrium film thickness, corresponding to the Gibbs excess solute, decreases monotonically with decreasing temperature until vanishing at a dewetting temperature, well below the eutectic. Assuming that perfect wetting occurs at some higher temperature above the eutectic, as is observed on polycrystal surfaces and at grain boundaries in the same system, the adsorption and wetting events in this system illustrate temperature- and composition-dependent prewetting. The observation of a second class of thicker films coexisting with nanodroplets and a numerical evaluation of thickness versus temperature elucidate the critical role of volumetric thermodynamic terms in determining film stability and thickness. Analogous temperature-dependent surface films involving adsorbed MoO(3) on Al(2)O(3) were also observed.

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