Eutectic Definition and Examples

What Is a Eutectic System?

This binary phase diagram indicates the eutectic composition, eutectic temperature, and the eutectic point.
This binary phase diagram indicates the eutectic composition, eutectic temperature, and the eutectic point. Wizard191

Eutectic System Definition

A eutectic system is a homogeneous solid mixture of two or more types of atoms or chemicals that forms a super-lattice. The phrase most commonly refers to a mixture of alloys. A eutectic system only forms when there is a specific ratio between the components. The word comes from the Green words "eu" meaning "good" or "well" and "tecsis" meaning "melting".

Related Terms

Eutectoid - Eutectoid (n) refers to a homogeneous solid mixture that forms from cooling a melt of two or more metals to a certain temperature.

Eutectic Temperature or Eutectic Point - The eutectic temperature is the lowest possible melting temperature for all of the mixing ratios of the components. At this temperature, the super-lattice will release all of its components and the eutectic system will melt into a liquid as a whole. Contrast this with a non-eutectic mixture, in which each component will solidify into a lattice at its own specific temperature, until eventually the whole material becomes solid.

Eutectic Alloy - A eutectic alloy is an alloy formed from two or more components which exhibits eutectic behavior. A eutectic alloy melts at a distinct temperature. Not all binary alloys form eutectic alloys. For example, gold-silver does not form a eutectoid, as the valence electrons are not compatible for super-lattice formation.

Eutectic Percentage Ratio - This is defined as the relative composition of components of a eutectic mixture.

The composition, particularly for binary mixtures, is often shown on a phase diagram.

Hypoeutectic and Hypereutectic - These terms apply to compositions which could form a eutectoid, but do not have the appropriate ratio of components. A hypoeutectic system has a smaller percentage of β and greater percentage of α than the eutectic composition, which a hypereutectic system has a greater percentage of α and lower percentage of β than the eutectic composition.

Examples of Eutectic Systems

Several examples of eutectic systems or eutectoids exist, both in metallurgy and involving nonmetallic components:

  • Sodium chloride and water form a eutectoid when the mixture is 23.3% salt by mass with a eutectic point at -21.2 °C. The system is used to make ice cream and to melt ice and snow.
  • The eutectic point of the mixture of ethanol and water is nearly pure ethanol. The value means there is a maximum proof or purity of alcohol that can be obtained using distillation.
  • Eutectic alloys are used for soldering. A typical composition is 63% tin and 37% lead, by mass.
  • Eutectoid glassy metals exhibit extreme corrosion resistance and strength.
  • Inkjet printer ink is a eutectic mixture, permitting printing at a relatively low temperature.