The principal properties of metals

The high reflectivity of metals is also due to the free electrons. When light photons strike the metal surface, those electrons near to the Fermi surface can absorb the photons, as plenty of empty energy states lie nearby. However, the electrons can just as easily fall back to the lower levels originally occupied, and the photons are re-emitted. A detailed explanation of reflectivity of a metal requires knowledge of the exact shape of the Fermi surface and the number of energy levels (density of states) at the Fermi surface. 

When two dissimilar metals are joined, electrons will flow from the higher Fermi energy to the lower. This gives rise to thermoelectric effects and to the operation of thermocouples. Less directly, the Fermi energy is related to the extent to which metals corrode. 

In this short section, only the principal properties of metals and a simple appreciation of the origins of these properties are outlined. Far more detail will be found in Part 4, Chapters 10-15. 

Ceramics are inorganic materials fabricated by a high-temperature chemical reaction. Most ceramics are oxides, but the term is also used for silicides, nitrides and oxynitrides, hydrides and other inorganic materials. Ceramics are regarded as chemically inert materials that are hard, brittle thermal and electronic insulators. 

It is convenient to consider ceramics that are essentially silicates, called traditional ceramics, separately from all of the others. This latter group comprises engineering ceramics, with important mechanical properties, electroceramics, when 

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