CBE30361 Lecture 24: Materials lecture 24
21 Mar 2016
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% ionic character increases with difference in electronegativity. Reflected in formula: amxp (m, p values to achieve charge neutrality) Stable structures require that the anions and cations touch Maximize the number of oppositely charged ion neighbors. Packing of ions: coordination number and ionic radii. Coordination number: a number of anions nearest neighbors for a cation coordination (cid:1755)(cid:1755)(cid:1755)(cid:1755)(cid:1755) number increases with: (cid:3045)(cid:3278)(cid:3276)(cid:3295)(cid:3284)(cid:3290)(cid:3289) (cid:3045)(cid:3276)(cid:3289)(cid:3284)(cid:3290)(cid:3289) : 8 (each cs+ has 8 neighbor cl atoms) It is not bcc structure because two different atoms are involved. 4 na+ and 4 cl- per unit cell. : 6 (each na+ has 6 neighbor cl atoms) The structure is formed from two interwoven fcc structures. Mgo, cao, feo, nio have this type of structure. Most common elements on earth are si and o. Silicates -- materials involved primarily silicon and oxygen. Silicates are the basis of traditional ceramics (glass, clays, rocks, sand, cements, quartz, etc. )
