WCO Explanatory Notes reproduced for reference. © World Customs Organization. Verify against official WCO publication.
28.17 - Zinc oxide; zinc peroxide. (A) ZINC OXIDE Zinc oxide (zinc white, flowers of zinc) (ZnO), is prepared by passin a current of air over zinc brought to red heat; the zinc may be replaced by a mixture of oxidise zinc ores (roasted blende, calamine - heading 26.08) and carbon. The gases pass through chambers forming deposits of increasing1 pure oxides, the purest of which consbtute flowers of zinc. Zinc oxide is a flaky white pow er which turns yellow on heating. f ‘l Its uses include in paints instead of white lead, for the preparation of cosmetics, matches, oil-cloth or ceramic glazes, as an o acifier and vulcanising accelerator in the rubber industry, as a catalyst, in the manufacture of g ass, in the preparation of gas-masks, or in medicine for the treatment of skin diseases. P The zincates of heading 28.41 correspond to this arnphoteric oxide. (B) ZINC PEROXIDE Zinc peroxide (ZnOz) White powder, insoluble in water. Used in medicine, either pure or with zinc oxide as impurity, and also for preparing cosmetics. This heading does not include : (a) Natural zinc oxide or zincite (heading 26.08). @) Residues of zinc metallurgy known as zinc scurf, skimmings or dross, which also consist of impure oxides (heading 26.20). (c) Zinc hydroxide (Zn(OH)2) or gelatinous white, or the hydroperoxide (heading 28.25). (d) The impure zinc oxide, sometimes known as zinc grey (heading 32.06). 28.18- Artificial corundum, whether or not chemically defmed; aluminium oxide; aluminium hydroxide. 28 18.20 - Artificial corundum, whether or not chemically defined - Aluminium oxide, other than artificial corundum 28 18.30 - 28 18.10 Aluminium hydroxide (A) ARTIFICIAL CORUNDUM, WHETHER OR NOT CHEMICALLY DEFINED Artificial corundum is formed by fusing duminiurn oxide in an electric furnace. The aluminium oxide may contain small proporhons of other oxides (e.g., titanium oxide, chromium oxide) either deriving fkom the natural starting material (bauxites) or added to improve, for example, the hardness of the fused ain or to modify the colour. However, mechamcal mixtures of artificial corundum and other su stances, such as zirconium dioxide, are excluded (heading 38.24). f Artificial corundum is put up in small pieces or masses, crushed or in grains; it is more resistant than ordinary aluminium oxide to the action of air and acids, and is very hard. It is used, e.g., as an abrasive, in the manufacture of refractory conglomerates (such as mullite and sillimanite, mixtures of corundum with pure refractory clay and with anhydrous aluminium silicates, respectively) or of laboratory utensils and in the electrical industry. (B) ALUMINIUM OXIDE, OTHER THAN ARTIFICIAL CORUNDUM Aluminium oxide (anhydrous or calcined alumina) (A1203) is obtained by calcining the aluminium hydroxide described below, or from ammonium alum. It is a light white powder, insoluble in water, specific gravity about 3.7. Uses include, e-g., in aluminium metallurgy, as a filler for paints, in the manufacture of abrasives and synthetic precious or semi-precious stones (rubies, sa phires, emeralds, amethysts, aquamarines, etc.), as a dehydrahng agent (for dqmg or as a catalyst (manufacture of acetone and acetic acid, cracking operations, etc.). (C) ALUMINIUM RYDROXIDE Aluminium hydroxide (hydrated alumina) (A1203.3H20) is obtained from bauxite (a mixture containin aluminium hydroxide) during aluminium metallurgy (see the General Explanatory Note to C apter 76). 8, The dry hydroxide is an amorphous, friable white powder, insoluble in water; when damp it is in gelatinous masses (alumina gel, gelatinous alumina). Aluminium hydroxide is used for the manufacture of ceramic glazes, rinting inks, medicinal products, alums, the artificial corundum described above and for clari&ing liquids; it is mixed with carbon for the manufacture of anti-rust paints and is also used, due to its affinity for organic colouring matter, for preparing the colour lakes of heading 32.05 and textile mordants. The aluminates of heading 28.41 correspond to this arnphoteric hydroxide. This heading also covers activated alumina, obtained by controlled heat treatment of hydrated alumina, in which process the latter loses most of its constitutional water; activated alumina is used primarily as an adsorption agent or as a catalyst. This heading does not include : Natural corundum (native aluminium oxide) and emery (aluminium oxide containing iron oxide) (heading 25.13). (b) Bauxite, whether or not washed and calcined, but not chemically purified (e.g., by treatment with soda) for use as an electrolyte (heading 26.06). (c) Activated bauxite (heading 38.02). (d) Colloidal solutions of aluminium hydroxide (soluble alumina) (heading 38.24). (e) Artificial corundum on a backing of paper, paperboard or other materials (heading 68.05) or agglomerated as grinding wheels, whetstones, hones or other goods of heading 68.04. (f) Natural precious or semi-precious stones with a basis of aluminium oxide (heading 71.03 or 71.05). (g) Synthetic recious or semi-precious stones with a basis of aluminium oxide (e.g., artificial rubies) (hading f1.04 or ,i.oq.
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.