Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
CHARACTERIZATION METHODS. 63 The atomic planes of the rutile structure are clearly seen, as are crystallographic and morphological relationships among the grains. The atomic structure of grain boundaries in nanophase Pd has been very recently studied by atomic-resolution electron microscopy (Thomas et al., 1989). Comparisons between observed and calculated images of these boundaries indicate structures that are rather similar to those found in conventional polycrystalline boundaries (see frontispiece). Figure 17 shows a rather typical grain-size distribution for such a nanophase material (in this case TiO2) in the as-compacted state determined from dark-field images. TEM measurements on both an oxide (Siegel et al., 1988) and a metal (Hort, 1986) indicate rather good grain-size stability (see sections on stability in Chapter 5) with increasing temperature and only modest grain growth taking place until about 700°C and 400°C in nanocrystalline TiO2 and Fe, respectively. Figure 17 Grain-size distribution for an as-compacted TiO2 (rutile) sample determined using TEM (Siegel et al., 1988). Analytical Electron Microscopy Analytical electron microscopy (AEM) is the only technique that can provide both structural and chemical information about individual catalyst particles at near-atomic-level spatial resolution. The companion technique of high-resolution electron microscopy (HREM) produces atomic-level images of metal particles and their supports (Smith et al., 1983). AEM is really a group of techniques, each of which can provide different information about
