eutectic mixture

Sometimes mixing two solids makes a blend that melts more easily than either one alone. A eutectic mixture is the special composition of two components that melts at the single lowest temperature of all their possible mixtures sometimes turning two powders that are each solid at room temperature into a liquid simply by grinding them together.

This happens because each component interferes with the other's ability to form an orderly crystal, so less heat is needed to break the structure apart. At the exact eutectic composition the blend melts sharply at one temperature, called the eutectic point, behaving almost like a pure substance rather than a mixture.

Pharmacy uses eutectics both deliberately and watchfully. A well-known designed example is a topical anaesthetic cream that combines lidocaine and prilocaine, two solids that form a liquid oil at room temperature, allowing a higher concentration of active drug at the skin. Conversely, an unintended eutectic between an active and an excipient can cause a powder blend to soften, cake or liquefy during manufacture or storage, so compatibility testing screens for it.