WCO Explanatory Notes reproduced for reference. © World Customs Organization. Verify against official WCO publication.
28.10 - Oxides of boron; boric acids. (A) OXIDES OF BORON Diboron trioxide (Boron sesquioxide) (B,O,) 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. (l3) 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 lknps, 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 coeficient of expansion), vltrifiable compounds, Guignet's green (hydrated chromc oxide), artificial borates (borax), hydroxy- and amino-anthraquinones; for impregnating candle wicks; for fire-proofing cloth. Crude naturaI boric acid falls in heading 25.28 when containing not more than 85 % of H3BO3, calculated on the dry weight; when the H3BO3content exceeds 85 %, the acid is classified in this heading. Metaboric acid (HB02), is also classified here. The heading does not include : (a) Tetrafluoroboric acid (fluoroboric acid) (heading 28.11). (b) Glyceroboric acid (heading 29.20).
1.- Except where the context otherwise requires, the headings of this Chapter apply only to : (a) Separate chemical elements and separate chemically defined compounds, whether or not containing impurities; (b) The products mentioned in (a) above dissolved in water; (c) The products mentioned in (a) above dissolved in other solvents provided that the solution constitutes a normal and necessary method of putting up these products adopted solely for reasons of safety or for transport and that the solvent does not render the product particularly suitable for specific use rather than for general use; (d) The products mentioned in (a), (b) or (c) above with an added stabiliser (including an anti-caking agent) necessary for their preservation or transport; (e) The products mentioned in (a), (b), (c) or (d) above with an added anti-dusting agent or a colouring substance added to facilitate their identification or for safety reasons, provided that the additions do not render the product particularly suitable for specific use rather than for general use.