Eutectic Definition and Examples

A eutectic system is a homogeneous, solid mixture of two or more substances that form a super-lattice; the mixture either melts or solidifies at a lower temperature than the melting point of any of the individual substances. 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."

Examples of Eutectic Systems

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Several examples of eutectic systems or eutectoids exist, in metallurgy and in various other fields. These mixtures typically have useful properties that are not possessed by any single constituent substance:

• Sodium chloride and water form a eutectoid when the mixture is 23.3% salt by mass with a eutectic point at -21.2 degrees Celsius. 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 often 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.
• Galinstan is a liquid metal alloy (composed of gallium, indium, and tin) used as a low-toxicity replacement for mercury.

Related Terms

Concepts and terms related to eutectic systems include:

• Eutectoid: Eutectoid refers to a homogeneous solid mixture that forms from cooling two or more melted 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 component substances in a eutectoid. 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 the whole material eventually becomes solid.
• Eutectic Alloy: A eutectic alloy is an alloy formed from two or more components that 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 with super-lattice formation.
• Eutectic Percentage Ratio: This is defined as the relative composition of the 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 that could form a eutectoid, but do not have the appropriate ratio of component substances. A hypoeutectic system has a smaller percentage of β and a greater percentage of α than a eutectic composition, while a hypereutectic system has a greater percentage of α and a lower percentage of β than a eutectic composition.