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Lithium metaborate is a chemical compound of lithium, boron, and oxygen with elemental formula LiBO2. It is often encountered as a hydrate, LiBO2·nH2O, where n is usually 2 or 4. However, these formulas do not describe the actual structure of the solids.

Lithium metaborate is one of the borates, a large family of salts (ionic compounds) with anions consisting of boron, oxygen, and hydrogen.

Structure

Lithium metaborate has several crystal forms.

The α form consists of infinite chains of trigonal planar metaborate anions [BO2O−]n.

The γ form is stable at 15 kbar and 950 °C. It has a polymeric cation consisting of a tridimensional regular array of [B(O−)4]− tetrahedra sharing oxygen vertices, alernating with lithium cations, each also surrounded by four oxygen atoms. The B-O distances are 148.3 pm, the Li-O distances are 196 pm.[2]

Lithium metaborate forms glass relatively easily, and consists of approximately 40% tetrahedral borate anions, and 60% trigonal planar boron. The ratio of tetrahedral to trigonal boron has been shown to be strongly temperature dependent in the liquid and supercooled liquid state.[3][4]

Applications

Laboratory

Fusion flux consisting of lithium metaborate and lithium teraborate, with a small amount of lithium bromide.

Molten lithium metaborate, often mixed with lithium tetraborate Li2B4O7, is used to dissolve oxide samples for analysis by XRF, AAS, ICP-OES, ICP-AES, and ICP-MS,[5] modern versions of classical bead test. The process may be used also to facilitate the dissolution of oxides in acids for wet analysis.[6] Small amounts of lithium bromide] LiBr or lithium iodide LiI may be added as mold and crucible release agents.[6]

Lithium metaborate dissolves acidic oxides MexOy with x < y, such as SiO2 Al2O3, SO3, P2O5, TiO2, Sb2O3, V2O5, WO3, and Fe2O3. Lithium tetraborate, on the other hand, dissolves basic oxides with x > y, such as CaO, MgO and other oxides of the alkali metals and alkaline earth metals. Most oxides are best dissolved in a mixture of the two lithium borate salts, for spectrochemical analysis.[6]

References

  1. ^ David R. Lide (1998): Handbook of Chemistry and Physics, edition 87, pages 4–66. CRC Press. ISBN 0-8493-0594-2
  2. ^ M. Marezio and J. P. Remeika (1966): "Polymorphism of LiMO2 Compounds and High‐Pressure Single‐Crystal Synthesis of LiBO2". Journal of Chemical Physics, volume 44, issue 9, pages 3348-. doi:10.1063/1.1727236
  3. ^ Alderman, Oliver; Benmore, Chris; Weber, Rick. "Consequences of sp2–sp3 boron isomerization in supercooled liquid borates". Applied Physics Letters. 117: 131901. doi:10.1063/5.0024457.
  4. ^ Alderman, Oliver; Benmore, Chris; Reynolds, Bryce; Royle, Brock; Feller, Steve; Weber, Rick. "Liquid fragility maximum in lithium borate glass‐forming melts related to the local structure". International Journal of Applied Glass Science. 14: 52–68. doi:10.1111/ijag.16611.
  5. ^ Terrance D. Hettipathirana (2004): "Simultaneous determination of parts-per-million level Cr, As, Cd and Pb, and major elements in low level contaminated soils using borate fusion and energy dispersive X-ray fluorescence spectrometry with polarized excitation". Spectrochimica Acta Part B: Atomic Spectroscopy, volume 59, issue 2, pages 223-229. doi:10.1016/j.sab.2003.12.013
  6. ^ a b c Fernand Claisse (2003): "Fusion and fluxes". Comprehensive Analytical Chemistry: Sample Preparation for Trace Element Analysis, volume 41, pages 301-311.


source: https://en.wikipedia.org/wiki/Lithium_metaborate