On the Roughening of Ceramic Surfaces
- PDF / 3,270,794 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 30 Downloads / 192 Views
individual facets are quite flat. In this study, different orientations of cx-A12 0 3 (alumina) were annealed and used to study the dynamic processes involved with the faceting of ceramic surfaces. In general, the surface of a single-crystal ceramic facets into either a terrace-and-step or a hill-and-valley surface structure.2,3 The type of surface structure that develops depends on the material and surface orientation. Surfaces other than those found on the equilibrium form are predicted to decomposed into two or more other surfaces in order to minimize total surface energy. 4 The final surface morphology, whether terrace-and-step or hill-and-valley, raises the question as to how the surfaces developed from the original polished surface. The present study works to answer this question by observing the faceting of several different orientations of single-crystal alumina as a function of annealing time. The (1010) surface orientation of alumina, which facets into the hill-and-valley structure, provides the most dramatic representation of the different stages by which a surface facets. A comparison between the facet formation on the 11010) surface with facet formation on different orientations of alumina and the (100) surface of LaA10 3 is presented. EXPERIMENTAL Alumina samples were prepared from polished single-crystals (Crystal Systems, Salem, MA). Samples with a nominal surface orientation of (0001), ( 1010), and ( 1120) were acid cleaned (HCl and HNO 3) and annealed at 1400TC for different times in air. Special precautions were taken to minimize the exposure of the surfaces to any contamination from the furnace environment by annealing the samples inside a high-purity alumina crucible. A sample of (100) LaA103 (Superconductive Components, Inc., Columbus, OH) was prepared in the same fashion as the 263 Mat. Res. Soc. Symp. Proc. Vol. 399 0 1996 Materials Research Society
alumina samples. This sample was annealed at 1400°C for 8 hours in air. Characterization of the surfaces was performed by atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). AFM studies were performed using a Nanoscope III (Digital Instruments, Santa Barbara, CA) with microfabricated Si 3N4 cantilevers (Ultralevers, Park Inst., Sunnyvale, CA). All images were recorded in air with a nominal applied force of 10-15 nN. SEM was performed in a Hitachi S-900 field-emission SEM operating at 5 kV, and TEM was performed in a Philips CM30 operating at 300 kV. RESULTS AND DISCUSSION Surface Structures of Annealed f 10101 and (0001) cc-alumina Annealing of the {1010) ct-alumina substrate produces a faceted hill-and-valley surface morphology. Figure 1 is a secondary-electron image of the {1010} surface which was annealed at 1400'C for 8 hours in air. Determined by cross-section TEM analysis, the two surface planes are
the (1012) and the { 10111 planes, which are low energy surfaces in alumina. 5 In comparison to the 11010) surface, the (0001) surface facets into a terrace-and-step morphology. Figure
Data Loading...
