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Unformatted text preview: 材材材材材材
Fundamental of Materials
Prof: Tian Min Bo
Tel: 62795426 材 62772851
Department of Material Science and Engineering
Tsinghua University. Beijing 100084 Lesson seven §2.9 Some Additional Terminology in
Crystallography Ⅰ. Single crystal versus polycrystal
1.. For single crystals there is only one type of structure with
Single crystals is characterized by anisotropy.
2.. Polycrystal consists of a lot of grain, small single crystals,
with same structure but different orientations. These small
single crystals are called grains. The boundaries between
them are called grain boundaries. grain grain
boundary single crystal polycrystal Ⅱ. Allotropy
Same crystal has different crystallographic
structure at different condition.
Examples: C , graphite , diamond , CNT
Examples: α − Fe
BCC 910°C γ − Fe
FCC 1400°C δ − Fe
BCC 1540°C Liquid Graphite C60 molecule Carbon Nanotubes Ⅲ. Atomic radii Definition:
2 Examples and Discussions
Exercise Thank you !
Thank you !
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- Spring '11