Y-Ba-Cu-O melt processed samples were prepared from mixtures of powders (starting average particle size ranging from to ) with and 1 wt% or 1 wt% . The resulting microstructure of the samples was composed of network and low concentration regions with size and morphology correlating with the starting powder size independently of the holding time in the melted state. The 211 particle size was smaller for Ce doped samples than for Pt doped samples. The differences in porosity of Pt and Ce doped samples were related to the changes in the interfacial energy of the constituent phases.
We present an analytic study to support the understanding of collapsing of glass tubes released by local heating and driven by the surface tension only. Our results provide a reliable analytic base for data evaluation if viscosity and surface tension of molten glasses are measured through collapsing. We complete existing 1D approaches to arrive at a consistent 2D description for axial symmetrical arrangements. We focus on advancing, steady-state collapsing profiles for heat sources moving with a constant axial velocity. The glass is considered an incompressible Stokes fluid with temperature-dependent viscosity of Arrhenius type that is ad hoc modeled by an axial, steady-state viscosity course comoving with the heat source. The analysis is carried out in comoving coordinates. Stringent scaling properties of collapsing are derived. We assume two distinct governing length scales L andh in axial and radial directions, respectively, as the base of a joint asymptotic multiscale analysis (AMSA) of the Stokes equation, boundary conditions, and kinematics for smallh/L. Numerical studies of collapsingrelevant parameters in comparison with finite element reference calculations are outlined for axial courses of the reciprocal viscosity idealized as Gaussian. For arbitrary axial viscosity courses, AMSA results in a consistent analytical description of collapsing for smallh/L. Forh/L < 1, precise formulae for collapsing-relevant geometry parameters are outlined.
A completely new crystal-growth device has been developed that permits charting a course across the phase diagram to produce crystalline samples optimized for diffraction experiments. The utility of the device is demonstrated for the production of crystals for the traditional X-ray diffraction data-collection experiment, of microcrystals optimal for data-collection experiments at a modern microbeam insertion-device synchrotron beamline and of nanocrystals required for data collection on an X-ray laser beamline.
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