CIVE265 Chapter Notes - Chapter 3: Face Diagonal, Nanometre, Coordination Number
15 Nov 2016
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Document Summary
Simple structure for metals to complex ones displayed by ceramic & polymeric materials (chapter focuses on common metallic crystal structure) Lattice: crystal structure; three-dimensional array points coinciding w/ atom position. 3. 3 unit cells: parallelepipeds/ prisms having 3 sets of parallel faces; represent the symmetry of crystal structure. 3. 4 metallic crystal structure: atomic bonding in group is metallic & nondirectional; minimal restrictions on number & position of nearest- neighbour atoms; relatively large numbers of nearest neighbours & dense atomic packings for most metallic structures. Structure (hcp: hexagonal unit cell, cadmium, magnesium, titanium, zinc, n = 6 atoms/unit cell, Coordination # = 12, apf =0. 74 (same as fcc) c/a ratio 1. 633. Theoretical density for metals n = number of atoms associated with each unit cell. Na = avogadro"s number (6. 022 1023 atoms/mol) Difficult to grow in nature due to carefully controlled environment required. Used in modern technology, electronic microcircuits, single crystals of silicon & other semiconductors.
