NaK78

NaK78 is a sodium–potassium eutectic alloy with about 22% sodium and 78% potassium by weight. It melts at −12.6 °C, so it is liquid at room temperature and above. The alloy is known for its relatively low viscosity and high thermal conductivity, properties that have made it attractive as a liquid metal coolant and heat-transfer fluid in certain experimental and early reactor designs. The eutectic composition gives a convenient low melting point and a wide liquid range compared with other alkali metal mixtures.

Because NaK78 contains reactive alkali metals, it is highly reactive with water and air. Contact with water evolves hydrogen and heat, which can ignite; exposure to air can lead to vigorous reactions if the material is hot. Handling requires strict safety measures: operation in inert atmospheres or sealed systems, dry purging, and storage under mineral oil or in an inert environment. Materials intended to contact NaK78 must resist corrosion and embrittlement; many common metals and gaskets are unsuitable.

Applications and history: NaK78 has been studied and used in liquid metal cooling loops and heat-transfer experiments, notably in early or specialized nuclear reactor concepts. In modern practice its use is limited due to safety concerns and the availability of alternative coolants, but it remains a reference example in discussions of eutectic alkali metal systems.

See also: sodium–potassium alloy, eutectic, liquid metal cooling, alkali metal safety.