. The potential between atomic sites A and B is:where f = 1.2. r AB is the intersite distance, and c AA and c BB are the on-site repulsion terms.

No abstract

The crystallization behavior of amorphous CdGe,As,, where thex values were varied from 0 to 1.2, was studied in order to document the effect of germanium on the amorphous structure. The glass-forming tendency of amorphous CdGe,As2 was evaluated by Hruby's criterion. The crystallization mechanism of each group was proposed, interpreting DSC, XRD, EDS, and TEM data, interactively. The crystallization behavior appeared as two distinct groups: those based on the CdAsz structure and those on the CdGeAsz structure (chalcopyrite), depending on Ge content. Ge atoms were found to suppress a glass-to-glass exothermic transformation to higher temperatures in the CdAs2 group, and crystallization in both groups. Proposed models of amorphous structure from previous investigators, measuring the radial distribution function, magnetic susceptibility, and macroscopic density, were correlated to the crystallization studies herein. A model of the transformation of glass structure with increasing Ge content from a CdAs, to a CdGeAsJike structure was established by extrapolation of experimental results indicating this behavior in crystalline CdGexAsz compounds with varyingx. [

The oxidation resistances of ZrB2 containing SiC, TaB2, and TaSi2 additions of various concentrations were studied using isothermal thermogravimetry at 1200, 1400, and 1500 °C, and specimens were further characterized using x-ray diffraction and electron microscopy. Increasing SiC concentration resulted in thinner glassy surface layers as well as thinner ZrO2-rich underlayers deficient in silica. This silica deficiency was argued to occur by a wicking process of interior-formed borosilicate liquid to the initially-formed borosilicate liquid at the surface. Small (3.32 mol%) concentrations of TaB2 additions were more effective at increasing oxidation resistance than equal additions of TaSi2. The benefit of these additives was related to the formation of a zirconium-tantalum boride solid solution during sintering, which during oxidation, fragmented into fine particles of ZrO2 and TaC. These particles resisted wicking of their liquid/glassy borosilicate encapsulation, which increased overall oxidation resistance. With increasing TaB2 or TaSi2 concentration, oxidation resistance degraded, most egregiously with TaB2 additions. In these cases, zirconia dendrites appeared to grow through the glassy layers, providing conduits for oxygen migration.