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In this study, voids commonly associated with tin particles in two aluminium alloys containing microalloying additions (0.01 at.%) of tin have been observed by transmission electron microscopy. The voids were generated by quenching the alloys at moderate rates (102-103 K s-1) from a temperature (718 K) in excess of the melting temperature (501 K) of elemental tin in tin-microalloyed aluminium. Estimates of the void volume as a function of the volume of the associated tin particle reveal a linear relationship consistent with the excess volume resulting from the solidification of the tin particle. The formation and stabilisation of shrinkage voids in metallic alloys are suggested to arise from a combination of high vacancy supersaturation, the large volumetric misfit strain of the solidifying tin particle and a reduction in void surface energy associated with segregation of alloying elements. [ABSTRACT FROM AUTHOR]

Abstract: Indium oxide (In2O3)-coated titanium dioxide (TiO2) core-shell nanostructures were produced via a sol–gel route. The presence of the thin In2O3 shell was established by X-ray photoelectron spectroscopy (XPS) and the morphology was investigated by high-resolution transmission electron microscopy (HRTEM). It was found that the In2O3 content increased with increased number of coatings on the TiO2 nanostructure. Lattice fringes were observed for the nanosized TiO2 particles, and the In2O3 shell showed an amorphous structure revealing a clear distinction between the core and shell materials. These morphologies were supported by energy dispersive X-ray analysis to further validate the presence of a core-shell structure. [Copyright &y& Elsevier]

The structure of carbon (C) and boron nitride (BN) columnar particles produced alongside by heat-treating a turbostratic B-C-N compound was investigated by analytical transmission electron microscopy. The particles were shown to be helical cones with a well-defined apex, and a helical pitch equal to usually one and at most two layers. The cone apex angle distribution was found to be centred on different values for C and BN. These results strongly suggested that BN and C cones nucleated from different ring defects in the hexagonal networks: square-like ring defects in BN and pentagon-like ring defects in C. These observations were consistent with the supposition that the creation of non B-N bonds and hence odd-membered rings is avoided in BN. Such restriction in BN could also allow one to understand the observed morphological differences between C and BN cones, and in particular the relative difficulty for BN cone edges to join via curved sheets. [ABSTRACT FROM AUTHOR]

Novel BN tassel-like and tree-like nanostructures were synthesized through a CVD method. The tassel-like morphology is made up of a BN bamboo-shaped nanotube and numerous polyhedral particles attached onto it. The tree consists of a BN main stem and many BN nanotube branches growing outward from it. The attachments, either particles or nanotube branches, maintain adhering to the primary stems even after 15 min sonication treatment, indicating the high stability of these nanostructures. The formation of these unusual structures is proposed to arise from a two-stage deposition process: firstly, primary BN stems were formed, followed by subsequent precipitation of amorphous clusters onto the rough outer surfaces. Secondly, polyhedral particles or BN nanotubes nucleated and grew on the outer surface as a result of further deposition from the vapor phase. [Copyright &y& Elsevier]