Lithium metaborate
Lithium metaborate is a chemical compound of lithium, boron, and oxygen with elemental formula Template:Chem2. It is often encountered as a hydrate, Template:Chem2, 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 Template:Chem2.
The γ form is stable at 15 kbar and 950 °C. It has a polymeric cation consisting of a tridimensional regular array of Template:Chem2 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.[1]
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.[2][3]
Applications
Laboratory
Molten lithium metaborate, often mixed with lithium tetraborate Template:Chem2, is used to dissolve oxide samples for analysis by XRF, AAS, ICP-OES, ICP-AES, and ICP-MS,[4] modern versions of classical bead test. The process may be used also to facilitate the dissolution of oxides in acids for wet analysis.[5] Small amounts of lithium bromide Template:Chem2 or lithium iodide Template:Chem2 may be added as mold and crucible release agents.[5]
Lithium metaborate dissolves acidic oxides Template:Chem2 with x < y, such as SiO2, [[alumina|Template:Chem2]], [[sulfur trioxide|Template:Chem2]], [[phosphorus pentoxide|Template:Chem2]], [[titanium dioxide|Template:Chem2]], [[antimony oxide|Template:Chem2]], [[vanadium(V) oxide|Template:Chem2]], [[tungsten trioxide|Template:Chem2]], 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.[5]
References
- ↑ 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-. Script error: No such module "doi".
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- ↑ 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. Script error: No such module "doi".
- ↑ a b c Fernand Claisse (2003): "Fusion and fluxes". Comprehensive Analytical Chemistry: Sample Preparation for Trace Element Analysis, volume 41, pages 301-311.
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