Lithium hydride

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Lithium hydride
  Lithium cation, Li+
  Hydrogen anion, H
NaCl polyhedra.png
__H __Li+
Structure of lithium hydride.
Lithium hydride.png
3D model (JSmol)
ECHA InfoCard 100.028.623 OOjs UI icon edit-ltr-progressive.svg
PubChem CID
RTECS number
  • OJ6300000
  • InChI=1S/Li.Hssss X mark.svgN
  • InChI=1/Li.H/q+1;-1
  • [H-].[Li+]
Molar mass 7.95 g·mol−1
Appearancecolorless to gray solid [1]
Density 0.78 g/cm3 [1]
Melting point 688.7 °C (1,271.7 °F; 961.9 K) [1]
Boiling point 900–1,000 °C (1,650–1,830 °F; 1,170–1,270 K) (decomposes) [2]
Solubility slightly soluble in dimethylformamide
reacts with ammonia, diethyl ether, ethanol
4.6·10−6 cm3/mol
1.9847 [3] :43
fcc (NaCl-type)
a = 0.40834 nm [3] :56
6.0 D [3] :35
3.51 J/(g·K)
Std molar
170.8 J/(mol·K)
−90.65 kJ/mol
−68.48 kJ/mol
Occupational safety and health (OHS/OSH):
Main hazards
extremely strong irritant, highly toxic, highly corrosive
GHS labelling:
GHS-pictogram-flamme.svg GHS-pictogram-acid.svg GHS-pictogram-skull.svg
H260, H301, H314
P223, P231+P232, P260, P264, P270, P280, P301+P316, P301+P330+P331, P302+P335+P334, P302+P361+P354, P304+P340, P305+P354+P338, P316, P321, P330, P363, P370+P378, P402+P404, P405, P501
NFPA 704 (fire diamond)
NFPA 704.svgHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelInstability 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
200 °C (392 °F; 473 K)
Lethal dose or concentration (LD, LC):
77.5 mg/kg (oral, rat) [4]
22 mg/m3 (rat, 4 h) [5]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 0.025 mg/m3 [6]
REL (Recommended)
TWA 0.025 mg/m3 [6]
IDLH (Immediate danger)
0.5 mg/m3 [6]
Safety data sheet (SDS) ICSC 0813
Related compounds
Other cations
Sodium hydride
Potassium hydride
Rubidium hydride
Caesium hydride
Related compounds
Lithium borohydride
Lithium aluminium hydride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Lithium hydride is an inorganic compound with the formula Li H. This alkali metal hydride is a colorless solid, although commercial samples are grey. Characteristic of a salt-like (ionic) hydride, it has a high melting point, and it is not soluble but reactive with all protic organic solvents. It is soluble and nonreactive with certain molten salts such as lithium fluoride, lithium borohydride, and sodium hydride. With a molar mass of 7.95 g/mol, it is the lightest ionic compound.


Physical properties

LiH is a diamagnetic and an ionic conductor with a conductivity gradually increasing from 2×10−5 Ω−1cm−1 at 443 °C to 0.18 Ω−1cm−1 at 754 °C; there is no discontinuity in this increase through the melting point. [3] :36 The dielectric constant of LiH decreases from 13.0 (static, low frequencies) to 3.6 (visible-light frequencies). [3] :35 LiH is a soft material with a Mohs hardness of 3.5. [3] :42 Its compressive creep (per 100 hours) rapidly increases from < 1% at 350 °C to > 100% at 475 °C, meaning that LiH cannot provide mechanical support when heated. [3] :39

The thermal conductivity of LiH decreases with temperature and depends on morphology: the corresponding values are 0.125 W/(cm·K) for crystals and 0.0695 W/(cm·K) for compacts at 50 °C, and 0.036 W/(cm·K) for crystals and 0.0432 W/(cm·K) for compacts at 500 °C. [3] :60 The linear thermal expansion coefficient is 4.2×10−5/°C at room temperature. [3] :49

Synthesis and processing

LiH is produced by treating lithium metal with hydrogen gas:

2 Li + H2 → 2 LiH

This reaction is especially rapid at temperatures above 600 °C. Addition of 0.001–0.003% carbon, and/or increasing temperature and/or pressure, increases the yield up to 98% at 2-hour residence time. [3] :147 However, the reaction proceeds at temperatures as low as 29 °C. The yield is 60% at 99 °C and 85% at 125 °C, and the rate depends significantly on the surface condition of LiH. [3] :5

Less common ways of LiH synthesis include thermal decomposition of lithium aluminium hydride (200 °C), lithium borohydride (300 °C), n-butyllithium (150 °C), or ethyllithium (120 °C), as well as several reactions involving lithium compounds of low stability and available hydrogen content. [3] :144–145

Chemical reactions yield LiH in the form of lumped powder, which can be compressed into pellets without a binder. More complex shapes can be produced by casting from the melt. [3] :160 ff. Large single crystals (about 80 mm long and 16 mm in diameter) can be then grown from molten LiH powder in hydrogen atmosphere by the Bridgman–Stockbarger technique. They often have bluish color owing to the presence of colloidal Li. This color can be removed by post-growth annealing at lower temperatures (~550 °C) and lower thermal gradients. [3] :154 Major impurities in these crystals are Na (20–200 ppm), O (10–100 ppm), Mg (0.5–6 ppm), Fe (0.5-2 ppm) and Cu (0.5-2 ppm). [3] :155

Cracking in cast LiH after machining with a fly cutter. Scale is in inches. LiHcrack.jpg
Cracking in cast LiH after machining with a fly cutter. Scale is in inches.

Bulk cold-pressed LiH parts can be easily machined using standard techniques and tools to micrometer precision. However, cast LiH is brittle and easily cracks during processing. [3] :171

A more energy efficient route to form lithium hydride powder is by ball milling lithium metal under high hydrogen pressure. A problem with this method is the cold welding of lithium metal due to the high ductility. By adding small amounts of lithium hydride powder the cold welding can be avoided. [7]


LiH powder reacts rapidly with air of low humidity, forming LiOH, Li2O and Li2CO3. In moist air the powder ignites spontaneously, forming a mixture of products including some nitrogenous compounds. The lump material reacts with humid air, forming a superficial coating, which is a viscous fluid. This inhibits further reaction, although the appearance of a film of "tarnish" is quite evident. Little or no nitride is formed on exposure to humid air. The lump material, contained in a metal dish, may be heated in air to slightly below 200 °C without igniting, although it ignites readily when touched by an open flame. The surface condition of LiH, presence of oxides on the metal dish, etc., have a considerable effect on the ignition temperature. Dry oxygen does not react with crystalline LiH unless heated strongly, when an almost explosive combustion occurs. [3] :6

LiH is highly reactive towards water and other protic reagents: [3] :7

LiH + H2O → Li+ + H2 + OH

LiH is less reactive with water than Li and thus is a much less powerful reducing agent for water, alcohols, and other media containing reducible solutes. This is true for all the binary saline hydrides. [3] :22

LiH pellets slowly expand in moist air, forming LiOH; however, the expansion rate is below 10% within 24 hours in a pressure of 2  Torr of water vapor. [3] :7 If moist air contains carbon dioxide, then the product is lithium carbonate. [3] :8 LiH reacts with ammonia, slowly at room temperature, but the reaction accelerates significantly above 300 °C. [3] :10 LiH reacts slowly with higher alcohols and phenols, but vigorously with lower alcohols. [3] :14

LiH reacts with sulfur dioxide to give the dithionite:

2 LiH + 2 SO2 → Li2S2O4 + H2

though above 50 °C the product is lithium sulfide instead. [3] :9

LiH reacts with acetylene to form lithium carbide and hydrogen. With anhydrous organic acids, phenols and acid anhydrides, LiH reacts slowly, producing hydrogen gas and the lithium salt of the acid. With water-containing acids, LiH reacts faster than with water. [3] :8 Many reactions of LiH with oxygen-containing species yield LiOH, which in turn irreversibly reacts with LiH at temperatures above 300 °C: [3] :10

LiH + LiOH → Li2O + H2

Lithium hydride is rather unreactive at moderate temperatures with O2 or Cl2 . It is, therefore, used in the synthesis of other useful hydrides, [8] e.g.,

8 LiH + Al2Cl6 → 2 Li[AlH4] + 6 LiCl
2 LiH + B2H6 → 2 Li[BH4]


Hydrogen storage and fuel

With a hydrogen content in proportion to its mass three times that of NaH, LiH has the highest hydrogen content of any hydride. LiH is periodically of interest for hydrogen storage, but applications have been thwarted by its stability to decomposition. Thus removal of H2 requires temperatures above the 700 °C used for its synthesis, such temperatures are expensive to create and maintain. The compound was once tested as a fuel component in a model rocket. [9] [10]

Precursor to complex metal hydrides

LiH is not usually a hydride-reducing agent, except in the synthesis of hydrides of certain metalloids. For example, silane is produced in the reaction of lithium hydride and silicon tetrachloride by the Sundermeyer process:

4 LiH + SiCl4 → 4 LiCl + SiH4

Lithium hydride is used in the production of a variety of reagents for organic synthesis, such as lithium aluminium hydride (Li[AlH4]) and lithium borohydride (Li[BH4]). Triethylborane reacts to give superhydride (Li[BH(CH2CH3)3]). [11]

In nuclear chemistry and physics

Lithium hydride (LiH) is sometimes a desirable material for the shielding of nuclear reactors, with the isotope lithium-6 (Li-6), and it can be fabricated by casting. [12] [13]

Lithium deuteride

Lithium deuteride, in the form of lithium-7 deuteride (7Li2H or 7LiD), is a good moderator for nuclear reactors, because deuterium (2H or D) has a lower neutron absorption cross-section than ordinary hydrogen or protium (1H) does, and the cross-section for 7Li is also low, decreasing the absorption of neutrons in a reactor. 7Li is preferred for a moderator because it has a lower neutron capture cross-section, and it also forms less tritium (3H or T) under bombardment with neutrons. [14]

The corresponding lithium-6 deuteride (6Li2H or 6LiD) is the primary fusion fuel in thermonuclear weapons. In hydrogen warheads of the Teller–Ulam design, a nuclear fission trigger explodes to heat and compress the lithium-6 deuteride, and to bombard the 6LiD with neutrons to produce tritium in an exothermic reaction:

6LiD + n → 4He + T + D

The deuterium and tritium then fuse to produce helium, one neutron, and 17.59 MeV of free energy in the form of gamma rays, kinetic energy, etc. The helium is an inert byproduct.

Before the Castle Bravo nuclear weapons test in 1954, it was thought that only the less common isotope 6Li would breed tritium when struck with fast neutrons. The Castle Bravo test showed (accidentally) that the more plentiful 7Li also does so under extreme conditions, albeit by an endothermic reaction.


LiH reacts violently with water to give hydrogen gas and LiOH, which is caustic. Consequently, LiH dust can explode in humid air, or even in dry air due to static electricity. At concentrations of 5–55 mg/m3 in air the dust is extremely irritating to the mucous membranes and skin and may cause an allergic reaction. Because of the irritation, LiH is normally rejected rather than accumulated by the body. [3] :157,182

Some lithium salts, which can be produced in LiH reactions, are toxic. LiH fire should not be extinguished using carbon dioxide, carbon tetrachloride, or aqueous fire extinguishers; it should be smothered by covering with a metal object or graphite or dolomite powder. Sand is less suitable, as it can explode when mixed with burning LiH, especially if not dry. LiH is normally transported in oil, using containers made of ceramic, certain plastics or steel, and is handled in an atmosphere of dry argon or helium. [3] :156 Nitrogen can be used, but not at elevated temperatures, as it reacts with lithium. [3] :157 LiH normally contains some metallic lithium, which corrodes steel or silica containers at elevated temperatures. [3] :173–174,179

Related Research Articles

<span class="mw-page-title-main">Hydrogen</span> Chemical element, symbol H and atomic number 1

Hydrogen is a chemical element; it has symbol H and atomic number 1. It is the lightest element and, at standard conditions, is a gas of diatomic molecules with the formula H2, sometimes called dihydrogen, but more commonly called hydrogen gas, molecular hydrogen or simply hydrogen. It is colorless, odorless, tasteless, non-toxic, and highly combustible. Hydrogen is the most abundant chemical substance in the universe, constituting roughly 75% of all normal matter. Stars such as the Sun are mainly composed of hydrogen in the plasma state. Most of the hydrogen on Earth exists in molecular forms such as water and organic compounds. For the most common isotope of hydrogen each atom has one proton, one electron, and no neutrons.

<span class="mw-page-title-main">Lithium</span> Chemical element, symbol Li and atomic number 3

Lithium is a chemical element; it has symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid element. Like all alkali metals, lithium is highly reactive and flammable, and must be stored in vacuum, inert atmosphere, or inert liquid such as purified kerosene or mineral oil. It exhibits a metallic luster. It corrodes quickly in air to a dull silvery gray, then black tarnish. It does not occur freely in nature, but occurs mainly as pegmatitic minerals, which were once the main source of lithium. Due to its solubility as an ion, it is present in ocean water and is commonly obtained from brines. Lithium metal is isolated electrolytically from a mixture of lithium chloride and potassium chloride.

<span class="mw-page-title-main">Hydride</span> Molecule with a hydrogen bound to a more electropositive element or group

In chemistry, a hydride is formally the anion of hydrogen (H), a hydrogen atom with two electrons. The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride of nitrogen, etc. For inorganic chemists, hydrides refer to compounds and ions in which hydrogen is covalently attached to a less electronegative element. In such cases, the H centre has nucleophilic character, which contrasts with the protic character of acids. The hydride anion is very rarely observed.

<span class="mw-page-title-main">Arsine</span> Chemical compound

Arsine (IUPAC name: arsane) is an inorganic compound with the formula AsH3. This flammable, pyrophoric, and highly toxic pnictogen hydride gas is one of the simplest compounds of arsenic. Despite its lethality, it finds some applications in the semiconductor industry and for the synthesis of organoarsenic compounds. The term arsine is commonly used to describe a class of organoarsenic compounds of the formula AsH3−xRx, where R = aryl or alkyl. For example, As(C6H5)3, called triphenylarsine, is referred to as "an arsine".

<span class="mw-page-title-main">Diborane</span> Chemical compound

Diborane(6), commonly known as diborane, is the chemical compound with the formula B2H6. It is a toxic, colorless, and pyrophoric gas with a repulsively sweet odor. Given its simple formula, borane is a fundamental boron compound. It has attracted wide attention for its electronic structure. Several of its derivatives are useful reagents.

<span class="mw-page-title-main">Lithium aluminium hydride</span> Chemical compound

Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula Li[AlH4] or LiAlH4. It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic synthesis, especially for the reduction of esters, carboxylic acids, and amides. The solid is dangerously reactive toward water, releasing gaseous hydrogen (H2). Some related derivatives have been discussed for hydrogen storage.

<span class="mw-page-title-main">Stibine</span> Chemical compound

Stibine (IUPAC name: stibane) is a chemical compound with the formula SbH3. A pnictogen hydride, this colourless, highly toxic gas is the principal covalent hydride of antimony, and a heavy analogue of ammonia. The molecule is pyramidal with H–Sb–H angles of 91.7° and Sb–H distances of 170.7 pm (1.707 Å). This gas has an offensive smell like hydrogen sulfide (rotten eggs).

<span class="mw-page-title-main">Zirconium hydride</span> Alloy of zirconium and hydrogen

Zirconium hydride describes an alloy made by combining zirconium and hydrogen. Hydrogen acts as a hardening agent, preventing dislocations in the zirconium atom crystal lattice from sliding past one another. Varying the amount of hydrogen and the form of its presence in the zirconium hydride controls qualities such as the hardness, ductility, and tensile strength of the resulting zirconium hydride. Zirconium hydride with increased hydrogen content can be made harder and stronger than zirconium, but such zirconium hydride is also less ductile than zirconium.

<span class="mw-page-title-main">Lithium aluminate</span> Chemical compound

Lithium aluminate, also called lithium aluminium oxide, is an inorganic chemical compound, an aluminate of lithium. In microelectronics, lithium aluminate is considered as a lattice matching substrate for gallium nitride. In nuclear technology, lithium aluminate is of interest as a solid tritium breeder material, for preparing tritium fuel for nuclear fusion. Lithium aluminate is a layered double hydroxide (LDH) with a crystal structure resembling that of hydrotalcite. Lithium aluminate solubility at high pH is much lower than that of aluminium oxides. In the conditioning of low- and intermediate level radioactive waste (LILW), lithium nitrate is sometimes used as additive to cement to minimise aluminium corrosion at high pH and subsequent hydrogen production. Indeed, upon addition of lithium nitrate to cement, a passive layer of LiH(AlO
· 5 H
is formed onto the surface of metallic aluminium waste immobilised in mortar. The lithium aluminate layer is insoluble in cement pore water and protects the underlying aluminium oxide covering the metallic aluminium from dissolution at high pH. It is also a pore filler. This hinders the aluminium oxidation by the protons of water and reduces the hydrogen evolution rate by a factor of 10.

<span class="mw-page-title-main">Titanium hydride</span> Chemical compound

Titanium hydride normally refers to the inorganic compound TiH2 and related nonstoichiometric materials. It is commercially available as a stable grey/black powder, which is used as an additive in the production of Alnico sintered magnets, in the sintering of powdered metals, the production of metal foam, the production of powdered titanium metal and in pyrotechnics.

Lithium carbide, Li
, often known as dilithium acetylide, is a chemical compound of lithium and carbon, an acetylide. It is an intermediate compound produced during radiocarbon dating procedures. Li
is one of an extensive range of lithium-carbon compounds which include the lithium-rich Li
, Li
, Li
, Li
, Li
, Li
, and the graphite intercalation compounds LiC
, LiC
, and LiC
is the most thermodynamically-stable lithium-rich carbide and the only one that can be obtained directly from the elements. It was first produced by Moissan, in 1896 who reacted coal with lithium carbonate.

<span class="mw-page-title-main">Sodium aluminium hydride</span> Chemical compound

Sodium aluminium hydride or sodium alumanuide is an inorganic compound with the chemical formula NaAlH4. It is a white pyrophoric solid that dissolves in tetrahydrofuran (THF), but not in diethyl ether or hydrocarbons. It has been evaluated as an agent for the reversible storage of hydrogen and it is used as a reagent for the chemical synthesis of organic compounds. Similar to lithium aluminium hydride, it is a salt consisting of separated sodium cations and tetrahedral AlH

Transition metal hydrides are chemical compounds containing a transition metal bonded to hydrogen. Most transition metals form hydride complexes and some are significant in various catalytic and synthetic reactions. The term "hydride" is used loosely: some of them are acidic (e.g., H2Fe(CO)4), whereas some others are hydridic, having H-like character (e.g., ZnH2).

<span class="mw-page-title-main">Beryllium hydride</span> Chemical compound

Beryllium hydride is an inorganic compound with the chemical formula n. This alkaline earth hydride is a colourless solid that is insoluble in solvents that do not decompose it. Unlike the ionically bonded hydrides of the heavier Group 2 elements, beryllium hydride is covalently bonded.

<span class="mw-page-title-main">Magnesium hydride</span> Chemical compound

Magnesium hydride is the chemical compound with the molecular formula MgH2. It contains 7.66% by weight of hydrogen and has been studied as a potential hydrogen storage medium.

Zinc hydride is an inorganic compound with the chemical formula ZnH2. It is a white, odourless solid which slowly decomposes into its elements at room temperature; despite this it is the most stable of the binary first row transition metal hydrides. A variety of coordination compounds containing Zn–H bonds are used as reducing agents, however ZnH2 itself has no common applications.

<span class="mw-page-title-main">FLiBe</span> Chemical compound

FLiBe is the name of a molten salt made from a mixture of lithium fluoride (LiF) and beryllium fluoride. It is both a nuclear reactor coolant and solvent for fertile or fissile material. It served both purposes in the Molten-Salt Reactor Experiment (MSRE) at the Oak Ridge National Laboratory.

Uranium hydride, also called uranium trihydride (UH3), is an inorganic compound and a hydride of uranium.

Cadmium hydride is an inorganic compound with the chemical formula (CdH
. It is a solid, known only as a thermally unstable, insoluble white powder.

<span class="mw-page-title-main">1,2-Dimethyldiborane</span> Chemical compound

1,2-Dimethyldiborane is an organoboron compound with the formula [(CH3)BH2]2. Structurally, it is related to diborane, but with methyl groups replacing terminal hydrides on each boron. It is the dimer of methylborane, CH3BH2, the simplest alkylborane. 1,2-Dimethyldiborane can exist in a cis- and a trans arrangement. 1,2-Dimethyldiborane is an easily condensed, colorless gas that ignites spontaneously in air.


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