Grain boundary structure in alumina
In liquid phase sintered aluminas, basal twins and glass phase at boundary regions are very common. The microstructures of a very glassy alumina show that coarse ledges (up to several hundred angstroms in height) are usually present at the Al/sub 2/O/sub 3//glass interface and the preferred ledge plane is (0001). This result suggests that the basal plane is the most stable plane at Al/sub 2/O/sub 3//glass interfaces while ((1 bar)012) plane is the most stable surface in Al/sub 2/O/sub 3/. The hot-pressed high purity material contains a small number of basal twins, rhombohedral twins, ((1 bar)011) twins and (10(1 bar)1) twins. This material also shows no detectable glass film at boundary regions. Both basal and rhombohedral twins have been shown to occur in alumina ceramics while the ((1 bar)011) and (10(1 bar)1) twins have never been reported in Al/sub 2/O/sub 3/. The four are well described by the conventional CSL/DSCL models as ..sigma.. = 3, 7, 11 and 11 boundaries, respectively. Basal twins sometimes, and rhombohedral twins always, contain SGBDs whose Burgers vectors lie on the relevant DSCL. The ((1 bar)011) and (10(1 bar)1) twins show stacking-fault like fringes at the (1(2 bar)10) common reflections. It is concluded that these boundaries contain rigid body displacement vectors to relieve atomic overcrowding at boundary regions. The magnitudes of displacement vectors at the ((1 bar)011) twin boundary can be measured indirectly by comparing the experimental image contrast with image simulation in computer.
- Research Organization:
- Illinois Univ., Urbana (USA)
- DOE Contract Number:
- AC02-76ER01198
- OSTI ID:
- 5315165
- Report Number(s):
- DOE/ER/01198-2055; ON: DE85016726
- Resource Relation:
- Other Information: Portions of this document are illegible in microfiche products. Thesis
- Country of Publication:
- United States
- Language:
- English
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