WCO Explanatory Notes reproduced for reference. © World Customs Organization. Verify against official WCO publication.
28.40 Borates; peroxoborates (perborates). - Disodium tetraborate (refined borax) : 2840.1 1 - - Anhydrous 2840.19 - - Other 2840.20 2840.30 - Other borates - Peroxoborates (perborates) (A) BORATES Subject to the exclusions mentioned in the introduction to this sub-chapter, this headin covers borates, metal salts of the various boric acids, principally normal or orthoboric acid fk3E303) (heading 28.10). Borates obtained by crystallisation or by a chemical process are covered by this heading, as are also natural borates obtained by evaporating complex brines from certain salt lakes. (1) Sodium borates. The most important is the tetraborate disodium tetraborate, refined borax) (Na2B407).Obtained by crystallisation of solutions o natural borates, or by treating natural calcium borates or boric acid with sodium carbonate. Anhydrous or h drated with 5 H20or 10 H20. Heated and then cooled down, it gives a vitreous mass borax, borax glass, borax bead . Used for stiffening linen or pa er; in soldering metals (flux for hard solder); as a flux or enamels; in the manufacture o vitrifiable colours, specla1 glass (optical glass, lass for electric bulbs), glue or polish; for refining gold; and for preparing borates and an aquinone dyes. & f' belted F There are other sodium borates (metaborates, hydrogen diborate) for laboratory uses. (2) Ammonium borates. The most important of these is metaborate (NH4B02.2H20). Colourless c stals, very soluble in water, efflorescent. Decomposed by heat to give a fusible varnis of boric anhydride; hence its use as a fire-proofin material. Also used as a fixative in hair-lotions; as a component of electrolytes for electro ytic capacitors and in the coating of paper. ? f (3) Precipitated calcium borates. Obtained by treating natural borates with calcium chloride; white powder used in fire retardant compositions, in anti-freezing preparations and in ceramic insulators. It can also be used as an antiseptic. (4) Manganese borates. Mainly tetraborate (MnB407), pinkish powder, sparingly soluble. Used as a drier in paints or varnishes. (5) Nickel borate. Pale green crystals, used as a catalyst. (6) Copper borate. Blue crystals, very hard, insoluble in water. Used as a pigment (ceramic colours) and as an antiseptic and insecticide. (7) Lead borate. Greyish powder, insoluble in water. It is used to prepare driers, in glass-making, as a pigment for porcelain and in electroplating. (8) Other borates. Cadmium borate is used as a coating for fluorescent tubes. Cobalt borate is used as a drier; zinc borate as an antiseptic, in fire-proofing textiIes or as a flux in ceramics, zirconium borate as an opacifier. Natural sodium borates (kernite, tincal), used to prepare the borates of this headin ,and natural calcium borates, (pandermite, priceite), used in the manufacture of boric acid, are excluded heading 25.28). (B)PEROXOBORATES (PERBORATES) Subject to the exclusions mentioned in the introduction to this sub-Cha ter, this heading covers metal peroxoborates, which are more oxygenated than borates and readi y release their oxygen. I' The are enerally complex products the formula of which corresponds to several acids such as HB& or h o 4 . The main peroxoborates are : (1) Sodium peroxoborate (perborax). Obtained by the action of sodium peroxide on an aqueous solution of boric acid, or by treatin an aqueous solution of soQum borate with h drogen eroxide. White amorphous pow er or c stals (with 1 or 4 H20). Used for breaching inen, textiles and straw; for preserving hi es; in the manufacture of household washing preparations, detergents and antiseptics. f (2) Magnesium peroxoborate. White powder, insoluble in water, used in medicine or in the manufacture of toothpastes. (3) Potassium peroxoborate. Similar characteristics and uses to sodium peroxoborate. (4) Other peroxoborates. Ammonium, aluminium, calcium or zinc peroxoborates, which occur as white powders, are used in medicine and in the manufacture of tooth-pastes.
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.