Lithium hydride

Lithium hydride
Identifiers
CAS number	7580-67-8 Y
PubChem	62714
RTECS number	OJ6300000
Properties
Molecular formula	LiH
Molar mass	7.95 g/mol
Appearance	colorless to gray solid
Density	0.82 g/cm3,[1] solid
Melting point	692 °C[2]
Solubility in water	reacts
Thermochemistry
Std enthalpy of formation ΔfHo298	-11.39 kJ/g
Specific heat capacity, C	3.51 J/(g.K)
Hazards
MSDS	ICSC 0813
EU Index	Not listed
NFPA 704	2 3 2 W
Autoignition temperature	200 °C
Related compounds
Other cations	Sodium hydride Potassium hydride Rubidium hydride Cesium hydride
Related compounds	Lithium borohydride Lithium aluminium hydride
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Lithium hydride (LiH) is the compound of lithium and hydrogen. It is a colourless crystalline solid, although commercial samples appear gray. Characteristic of a salt-like, or ionic, hydride, it has a high melting point of 689 °C (1272 °F). Its density is 780 kilograms per cubic metre. It has a standard heat capacity of 29.73 J/mol.K with thermal conductivity that varies with composition and pressure (from at least 10 to 5 W/m.K at 400 K) and decreases with temperature.

It is a flammable solid and very reactive with water, producing the corrosive compound lithium hydroxide as well as hydrogen.

LiH + H₂O → LiOH + H₂

With a molecular mass of slightly less than 8, it is the lightest ionic compound.

Synthesis

It is produced by reacting lithium metal with hydrogen gas:^[3]

2 Li + H₂ 2 LiH

Uses

LiH has numerous uses:

• as a desiccant;
• as a precursor for the synthesis of lithium aluminium hydride (LAlH);
• in hydrogen generators;
• in hydrogen storage;
• as both a coolant and shielding in nuclear reactors;
• and in the manufacture of ceramics.
• reducing agent^[4]. (redox)

LiH has the highest hydrogen content (in mass percentage) of any saline hydride. The hydrogen content of LiH is three times that of NaH (though its stoichiometry is identical), because lithium is lighter than sodium, making LiH of interest for hydrogen storage. The compound was used in the LEX ONERA with a so called Lithergol hypergolic Hybrid rocket fuel grain in 1967[1][2] [3]

The corresponding lithium-6 deuteride, formula Li-6-D, is the fusion fuel in thermonuclear weapons. In warheads of the Teller-Ulam design, LiD is compressed and heated by the explosion of the fission primary to the point where fusion occurs. Lithium-6 deuteride, unlike tritium, is non-radioactive. It should be noted, as was discovered when the Castle Bravo nuclear test ran away, that the isotope lithium-7 which makes up the bulk of natural lithium is also subject to neutrons as is lithium-6, when bombarded by fast neutrons^[5]

Lithium-6 deuteride can also be used as a storage vessel for use in hydrogen vehicles. Li-6-D can be made by heating lithium-6 and deuterium gas (from electrolyzing heavy water) in a hermetically sealed container to 600-700 C.

Safety

LiH is flammable in air, and it reacts explosively with water to give corrosive LiOH together with hydrogen gas.

See also

• Hydride

In popular culture

In Larry Niven's science fiction book Protector, his character Brennan describes the by-products of a bussard ramjet as being an assortment of strange chemicals including "Lithium Hydride... a normally impossible chemical..." The book was published in 1973.

References

1. ^ Sigma-Aldrich website
2. ^ Greenwood, Norman N.; Earnshaw, A. (1997), Chemistry of the Elements (2nd ed.), Oxford: Butterworth-Heinemann, p. 65, ISBN 0-7506-3365-4 
3. ^ Dr. Floyd Beckford. "University of Lyon course online (powerpoint) slideshow". http://www.lyon.edu/webdata/users/fbeckford/CHM%20120/Lecture%20Notes/Chapter-14.ppt. Retrieved 2008-07-27. "definitions:Slides 8-10 (Chapter 14)" 
4. ^ Aufray M, Menuel S, Fort Y, Eschbach J, Rouxel D, Vincent B (2009). "New Synthesis of Nanosized Niobium Oxides and Lithium Niobate Particles and Their Characterization by XPS Analysis". JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 9 (8): 4780-4789. doi:10.1166/jnn.2009.1087. 
5. ^ Castle Bravo#Cause of high yield

External links

Look up lithium hydride in Wiktionary, the free dictionary.

• Compounds of lithium: Lithium (I) Hydride
• Emergency First Aid Treatment Guide – Lithium Hydride
• Computational Chemistry Wiki
• University of Southampton, Mountbatten Centre for International Studies, Nuclear History Working Paper No5.