Lithium aluminate
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Lithium aluminate (), also called lithium aluminium oxide, is an inorganic
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
, an
aluminate In chemistry, an aluminate is a compound containing an oxyanion of aluminium, such as sodium aluminate. In the naming of inorganic compounds, it is a suffix that indicates a polyatomic ion, polyatomic anion with a central aluminum atom. Aluminate ...
of
lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the 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 el ...
. In
microelectronics Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture (or microfabrication) of very small electronic designs and components. Usually, but not always, this means micrometre-sc ...
, lithium aluminate is considered as a lattice matching substrate for gallium nitride. In
nuclear technology Nuclear technology is technology that involves the nuclear reactions of atomic nuclei. Among the notable nuclear technologies are nuclear reactors, nuclear medicine and nuclear weapons. It is also used, among other things, in smoke detectors an ...
, 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 Layered double hydroxides (LDH) are a class of ionic solids characterized by a layered structure with the generic layer sequence cB Z AcBsub>''n'', where c represents layers of metal cations, A and B are layers of hydroxide () anions, and Z are l ...
(LDH) with a crystal structure resembling that of
hydrotalcite Hydrotalcite or formerly also Völknerite is a layered double hydroxide (LDH) of general formula ·4, whose name is derived from its resemblance with talc and its high water content. Multiple structures containing loosely bound carbonate ions ex ...
. Lithium aluminate solubility at high pH (12.5 – 13.5) 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 A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mix ...
to minimise aluminium
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
at high pH and subsequent
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
production. Indeed, upon addition of lithium nitrate to cement, a passive layer of · 5 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 Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
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. Lithium aluminate also finds its use as an inert
electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...
support material in molten
carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...
fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requ ...
s, where the electrolyte may be a mixture of
lithium carbonate Lithium carbonate is an inorganic compound, the lithium salt (chemistry), salt of carbonate with the chemical formula, formula . This white Salt (chemistry), salt is widely used in the processing of metal oxides. It is listed on the World Health O ...
, potassium carbonate, and
sodium carbonate Sodium carbonate, , (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield moderately alkaline solutions ...
.


History

In 1906 Weyberg described his newly synthesized compound, lithium hydrogen aluminate. This was the first known synthesis of this unique compound. He asserted that this new compound had the corresponding chemical formula: : In 1915 Allen and Rogers asserted that an insoluble aluminate of lithium is formed when aluminum is dissolved in a solution of lithium hydroxide. This air-dried substance had an atomic ratio of 2Li:5Al and the chemical formula:The Formation and Composition of Lithium Aluminate Harold A. Horan and John B. Damiano Journal of the American Chemical Society 1935 57 (12), 2434-2436 : In 1929 Prociv recreated Allen and Rogers experiment and through a series of conductometric measurements on the saturated solution of the substance concluded that lithium and aluminum were present in the ratio of 0.8Li:2Al, which, he says, is an atomic ratio of approximately 1Li:2Al. According to him lithium aluminate may also be precipitated by the addition of a solution of lithium hydroxide to a solution of aluminum salt or by adding a solution of lithium salt to a solution of an alkali aluminate. Thus there was disagreement between Allen/Rogers and Prociv as to the composition of lithium aluminate. This may have been attributed to variations between their precipitation conditions. In 1932 Dobbins and Sanders described the formation of lithium aluminate by the addition of dilute ammonia to a solution containing lithium and aluminum salt, in the presence of phelphtalein as an indicator. In their preparation of acid lithium aluminate they dissolved strips of amalgamated aluminum in normal and tenth normal solutions of lithium hydroxide. The lithium aluminate was precipitated by the addition of a solution of lithium hydroxide to a solution of aluminum salts, or by adding a solution of lithium salt to a solution of alkaline aluminate. In all cases the composition of the compound of lithium aluminate was expressed by the formula: : They claimed that the formed compound contained lithium and aluminum in the atomic ratio of 2Li:5Al. Their chemical formula was simplified into the modern formulation for lithium aluminate: :


Fields of interest

The fundamental compound of lithium aluminate has found attention in two different fields: nuclear physics and solid-state chemistry. At least five different phases of lithium aluminate have been found.Reactivity and acidity of Li in lithium aluminum oxide (LiAlO2) phases Richard Dronskowski Inorganic Chemistry 1993 32 (1), 1-9 The lithium aluminate crystal structure may be found in either α, β, or γ phases.Synthesis of lithium aluminate by thermal decomposition of a lithium dawsonite-type precursor J. Jimenez-Becerril & I. Garcia-Sosa, Journal of Ceramic Processing Research. Vol. 12, No. 1, pp. 52-56 (2011) Nuclear physicists are interested in the modification of lithium aluminate, because of its good performance under high neutron and electron radiation. This modification also exhibits the essential chemical, thermo physical and mechanical stability at high temperature along with the required irradiation behavior. This phase appears to be a promising lithium ceramic, suitable as an in site tritium breeding material in future fusion reactors. Solid-state chemists investigating preparational routes to lithium aluminate discovered its interesting acid-base chemistry. The modification (but neither or ) reacts with molten benzoic acid leading to nearly total proton exchange thus forming There is a lot of interest in the chemical reactivity among the three modifications of . The reasons for the modification being highly reactive and the or modifications being totally unreactive is currently a mystery.


Formation


Early methods

Lithium aluminate powder preparation was based on the solid-state reactions between and lithium-containing compounds like , LiOH, , LiAc, and reactions occurred at temperatures between 400Deg C to 1000 Deg C. Due to the evaporation of lithium at high temperatures and contamination from grinding operations, pure lithium aluminate with controlled particle size has been difficult to synthesize.Chatterjee & Naskar “Novel technique for the synthesis of lithium aluminate (LiAlO2) powders from water-based sols” Journal of Materials Science Letters, Vol 22, Issue 24, pp 1747-1749


Current methods

Synthesis of lithium aluminate has been essentially performed by several methods: in the solid state, by wet chemical, sol-gel, with the use of templates, various precursors, and combustion processes. The main product in a solid state reaction is the phase; in a wet chemical reaction, the main product is a solid solution of and phases. The α-LiAlO2 modification (low temperature phase), with a hexagonal structure, undergoes transformation to the γ-modification (High temperature phase), with a tetragonal structure, at about 900 °C. The metastable β-modification, with a monoclinic structure, is assumed to transform to the γ-modification at about 900 °C.


Natural occurrence

The compound is unknown in the natural environment. However, a related compound, LiAl5O8, is known as the very recently discovered (as of 2020) and very rare mineral chukochenite.


References

{{Lithium compounds Aluminates Lithium compounds