Chemistry:Lithium metaborate
| Names | |
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| Other names
boric acid, lithium salt
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| Identifiers | |
3D model (JSmol)
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PubChem CID
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| Properties | |
| LiBO2 | |
| Molar mass | 49.751 g/mol |
| Appearance | white hygroscopic monoclinic crystals |
| Density | 2.223 g/cm3 |
| Melting point | 849 °C (1,560 °F; 1,122 K) |
| 0.89 g/100 mL (0 °C) 2.57 g/100 mL (20 °C) 11.8 g/100 mL (80 °C) | |
| Solubility | soluble in ethanol |
| Thermochemistry | |
Heat capacity (C)
|
59.8 J/mol K |
Std molar
entropy (S |
51.3 J/mol K |
Std enthalpy of
formation (ΔfH⦵298) |
-1022 kJ/mol |
Std enthalpy of
combustion (ΔcH⦵298) |
33.9 kJ/mol |
| Hazards | |
| Safety data sheet | External MSDS |
| NFPA 704 (fire diamond) | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
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| Infobox references | |
Lithium metaborate is a chemical compound of lithium, boron, and oxygen with elemental formula LiBO
2. It is often encountered as a hydrate, LiBO
2 · nH
2O, 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 [BO
2O−
]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
Molten lithium metaborate, often mixed with lithium tetraborate Li
2B
4O
7, 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 Me
xO
y with x < y, such as SiO2 Al
2O
3, SO
3, P
2O
5, TiO
2, Sb
2O
3, V
2O
5, WO
3, 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
- ↑ David R. Lide (1998): Handbook of Chemistry and Physics, edition 87, pages 4–66. CRC Press. ISBN 0-8493-0594-2
- ↑ 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
- ↑ 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. https://pubs.aip.org/aip/apl/article/117/13/131901/567154/Consequences-of-sp2-sp3-boron-isomerization-in.
- ↑ 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. https://ceramics.onlinelibrary.wiley.com/doi/full/10.1111/ijag.16611.
- ↑ 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
- ↑ 6.0 6.1 6.2 Fernand Claisse (2003): "Fusion and fluxes". Comprehensive Analytical Chemistry: Sample Preparation for Trace Element Analysis, volume 41, pages 301-311.
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