Characterization of supported palladium catalysts: II. PdSiO2☆

Metal-support interaction in the Pd/SiO2 system: Influence of the support pretreatment☆

Structures with atomic medium range order (MRO) extending as small as ∼2 nm in amorphous alloys can be observed under suitable defocus conditions as clear lattice fringe images by means of axial-beam high-resolution electron microscopy (HREM). In this article, our studies of local structure observation in some metal-metalloid amorphous alloys with the “selected-defocus method” are introduced. Also introduced are an HREM image simulation study of amorphous alloy structures and a nano-probe (1–1.5 nm) electron diffraction analysis of MRO structure. A multislice image simulation study for suitable structure models (1) with a random atomic distribution, (2) with MRO regions having different sizes, distributions, and specimen thicknesses, is a necessary step to verify the MRO observation in amorphous alloys. It was demonstrated that not only HREM information but also nano-diffraction information are necessary in order to understand local structures of amorphous alloys. Microsc. Res. Tech. 40:284–312, 1998. © 1998 Wiley-Liss, Inc.

Study of amorphous alloy structures with medium range atomic ordering.

High-resolution transmission electron microscopy (HRTEM), image simulation and image analysis were used to examine the atomic structure of the (211) solid-liquid interface between crystalline Pd3Si and amorphous Pd80Si20. Analysis of the intensities in HRTEM images provide direct experimental evidence of atomic order in the first several layers of the Liquid adjacent to the crystalline phase, as predicted by most theoretical analyses. The effect of imaging conditions on the interpretation of the HRTEM images is discussed.

Direct observation of order in the liquid at a solid-liquid interface by high-resolution transmission electron microscopy

The pdsi (palladiumsilicon) system

The Pd-Si system was examined in the 13 to 25 at. pct silicon range by X-ray diffraction, thermal analysis, and metallography. The existence of the compounds Pd5Si, Pd9Si2, and Pd3Si was confirmed. The three compounds form peritectically. Pd5Si is monoclinic, while Pd9Si2 and Pd3Si are orthorhombic. These compounds form defect structures having low symmetry and large unit cells. Electron concentrations per unit cell govern compound formation. However, there was no evidence of the existence of either Pd4Si or Pd9Si4.

J. A. Wysocki

Papers

Equilibrium Suicides of Palladium