Sodium silicide
In-game article clicks load inline without leaving the challenge.
Sodium silicide (NaSi, Na4Si4) is a binary inorganic compound consisting of sodium and silicon. It is a solid black or grey crystalline material. It can be synthesized by melting sodium or a sodium-potassium alloy with finely powdered silica gel. Temperature control of the reaction determine the final product's reactivity; heating above 400 °C creates an air-stable and less reducing product, while the product produced at room temperature is a pyrophoric and highly moisture-sensitive powder.
Sodium silicide's empirical formula (NaSi) is deceptive, as it is a Zintl phase: instead of containing discrete Si− anions, it contains Si4−4 tetrahedra, which leads to the more descriptive formula Na4Si4. These silicon tetrahedra condense into various crosslinked silicon polymers at high pressure.
Sodium silicide reacts readily with water yielding gaseous hydrogen and aqueous sodium silicate in an exothermic reaction (~175 kJ·mol−1):
2 NaSi + 5 H2O → 5 H2 + Na2Si2O5
This is used in hydrogen technologies to generate hydrogen as a fuel. It is also used as high energy dense storage for hydrogen under low pressure.