WCO Explanatory Notes reproduced for reference. © World Customs Organization. Verify against official WCO publication.
28.26 Fluorides; fluorosilicates, fluoroaluminates and other complex fluorine salts. - Fluorides : 2826.12 2826.19 2826.30 2826.90 - - Of aluminium - - Other - Sodium hexafluoroaluminate (synthetic cryolite) - Other (A) F'LUORIDES Subject to the exclusions s ecified in the introduction to this Sub-chapter, this heading covers the fluorides (i-e.,the meta salts of hydrofluoric acid of heading 28.1 1). The most important fluorides are : f (1) Ammonium fluorides : the neutral fluoride (NKF) and the -acid fluoride (NH4F.HF). These occur in deliquescent, colourless, toxic crystals, soluble in water. Uses rnclude : as antiseptics (for preserving hides or wood); to control fermentations, (in lieu of hydrofluoric acid); in dyeing (mordants); for etching glass (mainly acid fluoride); for scourlng copper; in metallurgy (to disintegrate ores, to prepare platinum), etc. r (2) Sodium fluorides : the neutral fluoride (NaF) and the acid fluoride aF.HF). Obtained by calcinin natural calcium fluoride of heading 25.29 (fluorspar or uorite) with a sodium salt. Co ourless crystals, not very soluble in water, toxic. Llke ammonium fluorides, they are used as antiseptics (for reserving hides, wood, eggs), to control fermentations, and for etching or frosting glass. d e y are also used in the manufacture of vitrifiable enamels or of parasiticides. f (3) Aluminium fluoride (AlF3 . Prepared from bauxite and hydrofluoric acid. Colourless crystals, insoluble in water. t is used as a flux in the enamel or ceramic industries and for purifying hydrogen peroxide. I (4) Potassium fluorides. Neutral potassium fluoride (KF.2H20) occurs in colourless, deliquescent, toxic crystals, very soluble in water. Also an acid fluoride (KF.HF). Same uses as sodium fluorides. In addition, the acid fluoride is used in the metallurgy of zirconium or of tantalum. A (5) Calcium fluoride CaF2). Prepared from the natural calcium fluoride fluorite, fluorspar) of headin 25.29. olourless crystals, insoluble in water; or may be in tLe gelatinous state. Used as a ux in metallurgy (particularly in the electrolytic preparation of magnesium from carnallite), and in the manufacture of glass or of ceramics. % (6) Chromium tritluoride (CrF3.4H20).Dark green powder, soluble in water. In aqueous solution it attacks glass. Used as a mordant in dyeing. a (7) Zinc fluoride (ZnF2). White owder, insoluble in water. Used for impregnating wood, in the preparation of enamels an in galvanising. of h dmfluoric acid on antimony oxides gives antimony in &liquescent white needles, soluble in water, and a viscous liquid which dissolves in water with a hissing H20). These salts are used in ceramics, as mordants in (9) Barium fluoride (BaF2). Prepared fiom hydrofluoric acid and barium oxide, sulphide or carbonate. A white powder, sparingly soluble in water; toxic. Used as a pigment in ceramics or enamels, as an antiseptic In embalming, as an insecticide, etc. This heading excludes nonmetal fluorides (heading 28.12). (B) FL,UOROSILICATES Fluorosilicates are the salts of the hexafluorosilicic acid (H2SiFs)of heading 28.1 1. (1) Diodium hexafluorosilicate (sodium fluorosilicate) WSiF6). Pr ared fiom silicon fluoride, a b product of the manufacture of superphosphates. 8 i t e powder, only sparingly solu le in cold water. Uses include the manufacture of opaque glass and enamels, synthetic stones, anti-acid cements, rat poisons, insecticides; the extraction of beryllium metal (electrolytic); the refining of tin by electrolysis; coagulating latex; as an antiseptic. r, I (2) Dipotassium hexafluorosilicate (potassium fluorosilicate) K2SiF6). White, odourless, crystalline powder, slightly soluble m water, soluble in hydroc oric acid. Uses include the manufacture of vitreous enamel fiits, ceramics, insecticides, synthetic mica; in metallurgy of aluminium and magnesium. (3) Calcium hexafluorosilicate (calcium fluorosilicate) (CaSiF6). White, crystalline powder; very slightly soluble in water; used as white pigment in cerarmcs. icUsiF (4) Cop er hexafluorosilicate (copper fluorosilicate) 6.6H20). Blue, crystalline ow er, soluble in water and toxlc. Used for the pro uchon of mottled effects or as a %ngicide. B (5) Zinc hexafluorosilicate (zinc fluorosilicate) (ZnSiF6.6H20).Crystalline owder, soluble in water; reacts with calcium compounds to give a coating of calcium uorides. Used for hardening concrete, for zinc electroplating, as an antiseptic or fimgicide (wood infections). K (6) Barium hexafluorosilicate (barium fluorosilicate) (BaSiF6). White powder used against the Colorado beetle and other insects, and to exterminate noxious animals. Other fluorosilicates. Magnesium fluorosilicate and aluminium fluorosilicate; like zinc fluorosilicate, these are used for hardening concrete. Chromium fluorosilicate and iron fluorosilicateare used in the dyestuff industry. The heading does not include topaz, a natural aluminium fluorosilicate (Chapter 71). (C) FLUOROALUMINATES AND OTHER COMPLEX FLUORINE SALTS (1) Trisodium hexafluoroalurninate (sodium hexafluoroalurninate) (Na3ALF6 synthetic cryolite, obtained as a precipitate on mixing aluminium oxide dissolved in ydrofluoric acid with sodium chloride, or b fusion of aluminium sulphate together with sodium fluoride. Occurs in whitish crysta& masses. It is used as a substitute for natural c olite (headin 25.30) in the metallurgy of aluminium, in pyrotechnics, in ename s, in glass-ma ng or as an insecticide. b. b (2) Fluoroborates. Sodium fluoroborate disinfectant), potassium fluoroborate (used in enamels), chromium fluoroborate and nic el fluoroborate (used in electro-plating), etc. I, (3) Fluorosulphates. In articular ammonium antimony fluorosulphate ((NH4)2S04SbF3) or " Haen salt "; solub e crystals which corrode glass and metal. Used as a mordant in dyeing. P (4) Fluorophosphates, for example, those obtained from natural ma wagnerite (heading 25.30) or aluminium lithium fluorop [heading 25.30). (5) Fluorotantalates (obtained in the metallurgy of tantalum); fluorotitanates, fluorogermanates, fluoroniobates, fluorozirconates (obtained in the metallurgy of zircomum), fluorostannates, etc. This headin includes metal fluoride oxides (of beryllium, etc.) and complex fluoride oxide salts but it exclu es fluoride oxides of non-metals (heading 28.12). di Fluorofonnates, fluoroacetates or other organic complex fluorine salts are excluded (Chapter 29).
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.