Eutectic Definition and Examples

What Is a Eutectic System?

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

A eutectic system is a homogeneous solid mixture of two or more types of atoms or chemicals that form 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 Greek 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 a greater percentage of α than the eutectic composition, which a hypereutectic system has a greater percentage of α and a 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.