Grain-Boundary Orientations

The principal applications of REELS are thin-film growth studies and gas-surface reactions in the few-monolayer regime when chemical state information is required. In its high spatial resolution mode it has been used to detect submicron metal hydride phases and to characterize surface segregation and difRision as a function of grain boundary orientation. REELS is not nearly as commonly used as AES orXPS. 

It is known from experiment that the boundary energy and diffusivity are a function of the grain boundary orientation angle and often show minima at certain specific orientations [Q. Ma, R.W. Balluffi (1993) A.N. Aleshin, etal. (1977)]. This... 

Figure 3.40 Wedge fringes at a grain boundary (a) bright-held image and (b) schematic illustration of grain boundary orientation in a specimen that generates the fringes in the bright-held image. (Reproduced with permission from M. von Heimandahl, Electron Microscopy of Materials, Academic Press, New York. 1980 Elsevier B. V.)...

Most corrosion costs are due to corrosion in electrolytes, or wet corrosion. Local differences in a given metal can be chemical or mechanical in nature, for example, impurities such as oxides and other inclusions, grain boundaries, orientation of grains, differences in composition of the microstructure, localized stresses, and scratches and nicks. Highly polished surfaces are used in special cases. Pure and smooth zinc will only corrode slowly in pure hydrochloric add, but pure metals are not often used because they are expensive and have relatively low strength. 

The volume change associated with the annihilation of vacancies located at grain boundaries oriented normally to the plane of a thin film was discussed in Section 1.8.6. Although a volume change occurs at any site in a thin film where a vacancy is annihilated, this process need not always result in the generation of an internal stress. Provide a simple mechanistic justification for each of the following statements. 

Where K = a is defined as the grain-boundary orientation. Following from this, two cases emerge. 

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