Lesson_2 Behaviour of metals (10)

Lesson_2 Behaviour of metals (10) - 3-8 Covalent Structures...

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and the aluminum cations occupy some of the available octahedral positions (Fig- ure 3-27). Alumina is probably the most widely used ceramic material. Applications include, but are not limited to, spark plugs, refractories, electronic packaging sub- strates, and abrasives. 3-8 Covalent Structures Covalently bonded materials frequently have complex structures in order to satisfy the directional restraints imposed by the bonding. Diamond Cubic Structure Elements such as silicon, germanium (Ge), a -Sn, and carbon (in its diamond form) are bonded by four covalent bonds and produce a tetrahedron. The coordination number for each silicon atom is only four, because of the nature of the covalent bonding. (See Figure 3-28.) Figure 3-26 The perovskite unit cell showing the arrangement of different ions. Note : Ion sizes not to scale. Figure 3-27 Corundum structure of alpha-alumina ( a -Al 2 O 3 ). Note : Ion sizes not to scale. Figure 3-28 The diamond cubic (DC) unit cell. This open structure is produced because of the require- ments of covalent bonding.
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  • Spring '14
  • Colombo
  • Physics, Atom, Electron, Material Science, Plastics, Manufacturing, Metals, Crystal, Packing Factor, William Henry Bragg, covalent structures

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