Cerium compounds

28.46 - Compounds, inorganic or organic, of rare-earth metals, of yttrium or of scandium or of rmxtures of these metals. 2846.10 2846.90 - Cerium compounds - Other This heading covers the inorganic or organic compounds of yttrium, of scandium or of the rare-earth metals of heading 28.05 (lanthanum, cerium, praseodymiurfl,neodymium, samarium, euro ium, gadolinium, terbium, dysprosium, holmium, erbium, thul~um,ytterbium, lutetium). The eading also covers compounds derived directly by chemical treatment fiom mixtures of the elements. This means that the heading will include mixtures of oxides or h droxides of these elements or mixtures of salts havine the same anion (e. rare-earth metal c lorides), but not mixtures of salts having different aruons, whether or not cation is the same. The heading will not therefore, for example, cover a mixture of europium and samarium nitrates with the oxalates nor a mixture of cerium chloride and cerium sulphate since these examples are not compounds derived directly from mixtures of elements, but are mixtures of compounds which could be conceived as having been made intentionally for special purposes and which, accordingly, fall in heading 38.24. h 8; The heading also includes double or complex salts of these with other metals. The compounds of this heading include : (I) Cerium compounds. (a) Oxides and hydroxides. Ceric oxide, a white powder insoluble in water, is obtained fiom cerium nitrate; it is used as an opacifier m ceramics, for colouring glass, in the preparation of arc-lamp carbons and as a catalyst in the manufacture of nitric acid and ammonia. There is also a ceric hydroxide. Cerous oxide and cerous hydroxide are not very stable. (b) Cerium salts. Cerous nitrate (Ce(N03)3)is used in the manufacture of gas-mantles. Ammonium ceric nitrate appears in the form of red crystals. Cerium sulphates (cerous sulphate and its hydrates, h drated ceric sulphate, orange-yellow prisms soluble in water) are used in photograp y as reducers. There are also double sulphates of cerium. il In addition to cerous chloride (CeC13) there are various other colourless cerous salts and yellow or orange ceric salts. r Cerium oxalate appears as a powder or in ellowish-white hydrated crystals, practically insoluble in water; it is used in the iso ation of metals of the cerium group or in medicine. (2) Other rare-earth metal compounds. Yttrium oxide (yttria), terbium oxide (terbia), mixtures of ytterbium oxides (ytterbia) and of oxides of other rare-earth metals of commerce are reasonably pure. The heading includes mixtures of salts derived directly from such mixtures of oxides. The oxides of europium, samarium, etc. are used in nuclear reactors for the absorption of slow neutrons. This heading excludes : (a) Natural compounds of rare-earth metals, e. ., xenotime (com lex phosphates), gadolinite or ytterbite and eerite (complex silicates) (herding 25. 0)and monazite &hosphates of thorium and of ran-asnh metaIs) (heading 26.12). f (b) Salts and other compounds, inorganic or organic, of promethium (heading 28.44).