Lithium metaborate is a chemical compound of lithium, boron, and oxygen with elemental formula . It is often encountered as a hydrate,, 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.
Lithium metaborate has several crystal forms.
The α form consists of infinite chains of trigonal planar metaborate anions .
The γ form is stable at 15 kbar and 950 °C. It has a polymeric cation consisting of a tridimensional regular array of 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.
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.[1] [2]
Molten lithium metaborate, often mixed with lithium tetraborate, is used to dissolve oxide samples for analysis by XRF, AAS, ICP-OES, ICP-AES, and ICP-MS, modern versions of classical bead test. The process may be used also to facilitate the dissolution of oxides in acids for wet analysis. Small amounts of lithium bromide] or lithium iodide may be added as mold and crucible release agents.
Lithium metaborate dissolves acidic oxides with x < y, such as SiO2 , , , , , , , 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.