AMME1362 Chapter Notes - Chapter 3: Atomic Packing Factor, Metal, Coordination Number

• School: University of Sydney
• Department: Aeronautical Engineering (Mechanical)
• Course: AMME1362
• Professor: Xiaozhou Liao

Document Summary

As well as the highest level of geometrical symmetry. 3. 4 metallic crystal structures: metallic atomic bonding is nondirectional in nature. Consequently there are minimal restrictions as to the number and position of nearest-neighbor atoms: for metals, each atom has the same number of nearest-neighbor or touching atoms, which is the coordination number. Face-centered cubic (fcc) e. g. copper, aluminium, silver and gold a = 2r/ (cid:2779) Each corner in a fcc crystal structure is shared among eight unit cells. Metals typically have relatively large apf to maximize the shielding provided by the free electron cloud. Atomic packing factor (apf) = (cid:2204)(cid:2197)(cid:2194)(cid:2203)(cid:2195)(cid:2187) (cid:2197)(cid:2188) (cid:2202)(cid:2197)(cid:2195)(cid:2201) (cid:2196) (cid:2203)(cid:2196)(cid:2202) (cid:2187)(cid:2194)(cid:2194) (cid:2202)(cid:2197)(cid:2202)(cid:2194) (cid:2203)(cid:2196)(cid:2202) (cid:2187)(cid:2194)(cid:2194) (cid:2204)(cid:2197)(cid:2194)(cid:2203)(cid:2195)(cid:2187) a = (cid:2781) (cid:2780) There are only 2 atoms associated with each bcc unit cell. The c/a (long side/short side) ratio should be 1. 633, however, for hcp metals this ratio deviates from the ideal value. The coordination and apf is the same as a fcc; 12 and 0. 74 repsectively.