What Xe Nanocrystals in Al Can Teach us in Materials Science
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What Xe Nanocrystals in Al Can Teach Us in Materials Science C. W. Allen, R. C. Birtcher, U. Dahmen1, K. Furuya2, M. Song2 and S. E. Donnelly3 Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA. 1National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. 2National Institute for Materials Science, Tsukuba, Ibaraki 305-0003, Japan 3Joule Laboratory, University of Salford, Manchester, M5 4WT, UK. ABSTRACT Noble gases are generally very insoluble in solids. For example, Xe implanted into Al at 300 K forms a fine dispersion of crystalline precipitates and, at large enough fluence, fluid precipitates, both of which are stabilized, relative to the gas phase, by the Laplace pressure due to precipitate/matrix interface tensions. High resolution electron microscopy has been performed to determine the largest Xe nanocrystalline precipitate in local equilibrium with fluid Xe precipitates within the Al matrix. From the shape and size of the largest crystal and the Laplace pressure associated with its interface, we show that the interface tensions can be derived by setting the Laplace pressure equal to the pressure for solid/fluid Xe equilibrium derived from bulk Xe compression isotherms at the temperature of equilibration and observation. The Xe/Al interface tensions thus derived are in the range of accepted values of surface tensions for the Al matrix. Furthermore, it is suggested that this same technique may be employed to estimate unknown surface tensions of a solid matrix from the size and shape of maximal nanocrystals of a noble gas element, which have been equilibrated in that matrix at the temperature of observation.
INTRODUCTION The existence of nanometer-sized crystals of noble gas atoms was first recognized in 1984 in specimens of Al into which Kr had been implanted [1]. The phenomenon has now been studied for various noble gases including Ne, Ar, Kr and Xe in a number of metallic and non-metallic matrices, a good review of which is that by Templier [2]. More recently with the emergence of high resolution transmission electron microscopy (HREM) as an analytical tool during in situ experiments, we have studied the behavior of Xe nanoprecipitates in Al with emphasis on electron irradiation effects that result in dynamic shape changes, faulting, migration and coalescence of the Xe precipitates [3–6]. In this contribution, we will demonstrate that the upper limit in size of a Xe nanocrystal in Al at 300 K is consistent with the pressure for solid/fluid equilibrium determined from published bulk isothermal compression data for Xe. Generalizing this result, we then will suggest that the surface tensions of any host matrix can be estimated experimentally by locally establishing solid/fluid equilibrium at any temperature for which appropriate bulk isothermal compression data have been established and then measuring the size of the largest solid nanoprecipitate. From the dimensions of the largest solid particle an estimate V11.2.1
of the surface tensi
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