Melting

From Encyclopedia Jr, free information reference for Kids

Mechanical failure modes
Buckling
Corrosion
Creep
Fatigue
Fracture
Melting
Thermal shock
Wear

In physics, melting is the process of heating a solid substance to a point (called the melting point) where it turns liquid. An object that has melted is molten.

[edit] Explanatory

Not only is heat required to raise the temperature of the solid to the melting point, but the melting itself requires heat; see also latent heat and heat of fusion.

From a thermodynamics point of view, at the melting point the change in Gibbs free energy ( $Δ G$ ) of the Material is zero, because the enthalpy ( $H$ ) and the entropy ( $S$ ) of the material are increasing ( $Δ H,Δ S > 0$ ). Melting phenomenon happens when the Gibbs free energy of the liquid becomes lower than the solid for that material. At various pressures this happens at a specific temperature. It can also be shown that:

$\Delta S = \frac {\Delta H} {T}$

The " $T$ "," $Δ S$ ", and " $Δ H$ " in the above are respectively the temperature at the melting point, change of entropy of melting, and the change of enthalpy of melting.

Freezing, the process of turning a liquid to a solid, is the opposite of melting. The melting point and freezing point are usually the same temperature. See the phase article for more detail.

[edit] Books

Kleinert, Hagen, Gauge Fields in Condensed Matter, Vol. II, "STRESSES AND DEFECTS; Differential Geometry, Crystal Melting", pp. 743-1456, World Scientific (Singapore, 1989); Paperback ISBN 9971-50-210-0 (readable online here)

[edit] Other meanings

In genetics, melting DNA means to separate the double-stranded DNA into two single strands by heating or the use of chemicals.

See also : Polymerase chain reaction

Categories: Materials science | Phase changes