Lithium nitride explained

Lithium nitride is an inorganic compound with the chemical formula . It is the only stable alkali metal nitride. It is a reddish-pink solid with a high melting point.

Preparation and handling

Lithium nitride is prepared by direct reaction of elemental lithium with nitrogen gas:^[1]

Instead of burning lithium metal in an atmosphere of nitrogen, a solution of lithium in liquid sodium metal can be treated with .

Lithium nitride must be protected from moisture as it reacts violently with water to produce ammonia:

Structure and properties

• alpha- (stable at room temperature and pressure) has an unusual crystal structure that consists of two types of layers: one layer has the composition contains 6-coordinate N centers and the other layer consists only of lithium cations.^[2]

Two other forms are known:

• beta-, formed from the alpha phase at 0.42 GPa has the sodium arsenide structure;
• gamma- (same structure as lithium bismuthide) forms from the beta form at 35 to 45 GPa.^[3]

Lithium nitride shows ionic conductivity for, 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.^{[4] [5]} The activation energy for lithium transfer across lithium nitride crystals (intercrystalline) has been determined to be higher, at c. 68.5 kJ/mol.^[6] The alpha form is a semiconductor with band gap of c. 2.1 eV.^[3]

Reactions

Reacting lithium nitride with carbon dioxide results in amorphous carbon nitride, a semiconductor, and lithium cyanamide, a precursor to fertilizers, in an exothermic reaction.^{[7] [8]}

Under hydrogen at around 200°C, Li₃N will react to form lithium amide.^[9]

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.^[10]

References

1. 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.
2. Barker M. G. . Blake A. J. . Edwards P. P. . Gregory D. H. . Hamor T. A. . Siddons D. J. . Smith S. E. . . 1999 . 1187–1188 . 10.1039/a902962a . Novel layered lithium nitridonickelates; effect of Li vacancy concentration on N co-ordination geometry and Ni oxidation state . 13.
3. Book: Solid-State Hydrogen Storage: Materials and Chemistry. G. Walker. §16.2.1 Lithium nitride and hydrogen:a historical perspective. 2008.
4. Solid State Ionics. 11. 2. October 1983. 97–103. Ionic conductivity of pure and doped Li₃N. Torben . Lapp . Steen. Skaarup. Alan. Hooper. 10.1016/0167-2738(83)90045-0.
5. Lithium ion conductivity in lithium nitride. B. A. . Boukamp. R. A. . Huggins. 10.1016/0375-9601(76)90082-7 . Physics Letters A. 58. 4. 6 September 1976. 231–233. 1976PhLA...58..231B.
6. Materials Research Bulletin. 13. 1. January 1978. 23–32. Fast ionic conductivity in lithium nitride. B. A. . Boukamp. R. A.. Huggins. 10.1016/0025-5408(78)90023-5.
7. Fast and Exothermic Reaction of CO₂ and Li₃N into C–N-Containing Solid Materials . The Journal of Physical Chemistry A . 115 . 42 . 11678–11681 . The Journal of Physical Chemistry A 115 (42), 11678-11681 . Yun Hang Hu, Yan Huo . 12 September 2011 . 10.1021/jp205499e . 21910502 . 2011JPCA..11511678H.
8. Web site: Chemical reaction eats up CO₂ to produce energy...and other useful stuff . NewAtlas.com . Darren Quick . 21 May 2012 . 17 April 2019.
9. Goshome . Kiyotaka . Miyaoka . Hiroki . Yamamoto . Hikaru . Ichikawa . Tomoyuki . Ichikawa . Takayuki . Kojima . Yoshitsugu . 2015 . Ammonia Synthesis via Non-Equilibrium Reaction of Lithium Nitride in Hydrogen Flow Condition . Materials Transactions . 56 . 410–414 . 10.2320/matertrans.M2014382 . free . 3.
10. Ping Chen . Zhitao Xiong . Jizhong Luo . Jianyi Lin . Kuang Lee Tan . 2002 . Interaction of hydrogen with metal nitrides and amides . . 420 . 6913 . 302–304 . 2002Natur.420..302C . 10.1038/nature01210 . 12447436 . 95588150.

See also

• WebElements