Eutectic System and Eutectic Point

Eutectic System

The term eutectic comes from the Greek word 'eutektos' meaning 'easily melted.'
Eutectic system is a system of a homogeneous mixture of substances that either melts or solidifies at a particularly given temperature that is lower than the melting point of any of the mixture of any of the components. This particular temperature is known as the eutectic point.
Example- A mixture of Pb and Ag comprises of such a system.

When a non-eutectic mixture is cooled, all the individual components are at different temperatures until all the components i.e. the entire material are solidified. Thus, a eutectic system is a homogenous and solid mixture of a few substances that form a different lattice that melts or solidifies at a temperature lower than any of the melting points of the individual components. A eutectic system forms only when two or more solid components are mixed at a particular ratio.

Characteristics of a Eutectic System

The eutectic system has the following characteristics-
1. The melting point of the mixture corresponding to the eutectic point is the lowest.
2. In this eutectic system, the solid-liquid phase transition that is all three phases are in equilibrium.
3. The eutectic system is invariant that is the degree of freedom is 0 and the system has a fixed temperature and composition.
F = C – p + 1 = 2 – 3 + 1 = 0
4. The eutectic temperature can be shown as the eutectic point on a phase diagram.
At above Eutectic temperature solid phase disappears and at below Eutectic temperature liquid phase disappear.

Application of Eutectic system

Eutectic mixtures are composed of alloys are used as fail safe devices in boilers, as plugs in automobiles and other safety devices.
Because of their low melting points, eutectics are also used in preparing solders, which are used in joining two metal pieces.
Example- Pb-Sn solders.
Also used in safety fuses, used in buildings to protect them against fire hazards.

Eutectic Point

Eutectic Point is the lowest freezing point that can be reached for a eutectic combination (lowest melting point).
This is the point in the solid-liquid system where all three phases, namely the liquid melt of the two metals and the solid phases of each of the components, are in equilibrium.
The melting point of the mixture corresponding to the eutectic point is the lowest.
At this stage, the system is invariant (i.e., the degrees of freedom or variance are zero) and has a fixed temperature and composition.