Lithium nitride
Lithium nitride is an inorganic compound with the chemical formula Template:Chem2. It is the only stable alkali metal nitride. It is a reddish-pink solid with a high melting point.[1]
Preparation and handling
Lithium nitride is prepared by direct reaction of elemental lithium with nitrogen gas:[2]
Instead of burning lithium metal in an atmosphere of nitrogen, a solution of lithium in liquid sodium metal can be treated with Template:Chem2.
Lithium nitride is an extremely strong base, so it must be protected from moisture as it reacts violently with water to produce ammonia:
Structure and properties
- alpha-Template:Chem2 (stable at room temperature and pressure) has an unusual crystal structure that consists of two types of layers: one layer has the composition Template:Chem2 contains 6-coordinate N centers and the other layer consists only of lithium cations.[3]
Two other forms are known:
- beta-Template:Chem2, formed from the alpha phase at 0.42 GPa has the sodium arsenide (Template:Chem2) structure;
- gamma-Template:Chem2 (same structure as lithium bismuthide Template:Chem2) forms from the beta form at 35 to 45 GPa.[4]
Lithium nitride shows ionic conductivity for Template:Chem2, with a value of c. 2×10−4 Ω−1cm−1, and an (intracrystal) activation energy of c. 0.26 eV (c. 24 kJ/mol). Hydrogen doping increases conductivity, whilst doping with metal ions (Al, Cu, Mg) reduces it.[5][6] The activation energy for lithium transfer across lithium nitride crystals (intercrystalline) has been determined to be higher, at c. 68.5 kJ/mol.[7] The alpha form is a semiconductor with band gap of c. 2.1 eV.[4]
Reactions
Reacting lithium nitride with carbon dioxide results in amorphous carbon nitride (Template:Chem2), a semiconductor, and lithium cyanamide (Template:Chem2), a precursor to fertilizers, in an exothermic reaction.[8][9]
Under hydrogen at around 200°C, Li3N will react to form lithium amide.[10]
At higher temperatures it will react further to form ammonia and lithium hydride.
Lithium imide can also be formed under certain conditions. Some research has explored this as a possible industrial process to produce ammonia since lithium hydride can be thermally decomposed back to lithium metal.
Lithium nitride has been investigated as a storage medium for hydrogen gas, as the reaction is reversible at 270 °C. Up to 11.5% by weight absorption of hydrogen has been achieved.[11]
References
- ↑ Template:Greenwood&Earnshaw
- ↑ E. Döneges "Lithium Nitride" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, New York. Vol. 1. p. 984.
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