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28.10 ‑ Oxides of boron; boric acids.
(A) OXIDES OF BORON
Diboron trioxide (Boron sesquioxide) (B2O3) exists as transparent vitreous masses, crystals or white flakes.
It has been used for making synthetic precious or semi‑precious stones (corundum, sapphire, etc.) by action on volatile metal fluorides.
The heading also includes all other oxides of boron. (B) BORIC ACIDS
Boric acid (orthoboric acid) (H3BO3) is obtained either by acid decomposition of natural borates, or by physico‑chemical treatment of crude boric acid.
It exists in the form of powder or small scales, micaceous flakes or vitrified lumps, with transparent edges, ash‑grey or bluish (crystallised acid). It is odourless, greasy to the touch.
Its uses include : as an antiseptic (boracic water); for the manufacture of borosilicate glass (low coefficient of expansion), vitrifiable compounds, Guignet's green (hydrated chromic oxide), artificial borates (borax), hydroxy‑ and amino‑anthraquinones; for impregnating candle wicks; for fire‑proofing cloth.
Crude natural boric acid falls in heading 25.28 when containing not more than 85 % of H3BO3, calculated on the dry weight; when the H3BO3 content exceeds 85 %, the acid is classified in this heading. Metaboric acid (HBO2)n is also classified here.
The heading does not include :(a) Tetrafluoroboric acid (fluoroboric acid) (heading 28.11). (b) Glyceroboric acid (heading 29.20).
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