Scandium oxides

The element was discovered by Nilson in 1878 in the minerals euxenite and gadolinite, which had not yet been found anywhere except in Scandinavia. By processing 10 kg of euxenite and other residues of rare-earth minerals, Nilson was able to prepare about 2g of highly pure scandium oxide. Later scientists pointed out that Nilson s scandium was idenhcal with Mendeleev s ekaboron. 

Goldschmidt has classed also with the ionic crystals the C-modification of the sesqui-oxides, cubic crystals with 16 M2O3 in the unit of structure. The inter-atomic distances reported by him are 2.16-2.20 A. for scandium oxide and 2.34-2.38 A. for yttrium oxide, in good agreement with the radius sums 2.21 A. for Sc+3-0= and 2.33 A. for Y+3-0". 

Scandium oxide, 32 43-44 Scanning electron micrography, copper, 31 255... 

Scandium oxide TSc " + 30 —> Sc O. Scandium oxide is used to prepare scan-... 

The ore thortveitite is crushed and powdered. It is mixed with a large excess of ammonium hydrogen fluoride and heated at about 400°C for several hours in a platinum container under a stream of dry air. Silica is converted to volatile silicon tetrafluoride and swept out with dry air. Scandium oxide is converted to scandium trifluoride, SCF3 ... 

In most recovery processes, scandium oxide is converted to its fluoride salt. The fluoride salt is the end product. The fluoride is converted to metallic scandium by heating with calcium in a tantalum crucible at elevated temperatures. A similar reduction is carried out with most rare earths. The metal is purified by distillation at 1,650 to 1,700°C under high vacuum in a tantalum crucible. 

Scandium oxide, ScsOo, has a specific gravity of 3 80, is more basic than alumina, less basic than yttria or magnesia. It is not soluble in alkalies and does not decompose ammonium chloride... 

Like the hydroxides of the Rare earth, scandium hydroxide, Sc(OH)3, is precipitated by addition of alkalies to solutions of scandium salts however, the latter is precipitated at pH 4.9, while the former require pH 6.3 or more, a property which is utilized in one method of separation. Upon heating the hydroxide (or certain oxyatid salts), scandium oxide. Sc>C>3 is produced. Scandium hydroxide is less acidic than aluminum hydroxide, requiring boiling KOH solution to form the complex potassium compound, K2[Sc(OH)5 H 0] 3H 0. 

Question 7.1 (a) Write equations for the (i) reduction of ScFs by calcium, (ii) scandium oxide dissolving in potassium hydroxide solution, (iii) the thermal decomposition of (NH4)3ScCl6. (b) Why is the thermal decomposition of (NH4)3ScCl6 a good way of making pure ScCls ... 

In 1869, Mendeleev predicted the existence and certain properties of an element with atomic mass 45, terming it ekaboron within a decade, the Swede L. F. Nilsson and Frenchman P. T. Cleve independently isolated scandium oxide, subsequently preparing various other compounds. There are few ores where scandium is the main element (e.g. thortveitite, a silicate, Sc2Si207, and sterrite, SCPO4 2H2O) so that it is mainly obtained as a by-product from uranium extraction. 

Scandium oxide is a refractory white solid (mp 3100 °C) formed on ignition of either the metal or appropriate compounds such as the nitrate, sulfate, and hydroxide. It has amphoteric tendencies denoted by its solubihty in excess alkali from which compounds like K3[Sc(OH)6], containing octahedrally coordinated scandium, have been isolated. In the solid state it has six-coordinate scandium in the Mu203 structure. 

It was only in 1995 that the first structure of a hydrated salt of scandium containing only water molecules in its coordination sphere was reported. Refluxing scandium oxide with triflic acid leads to the isolation of hydrated scandium triflate Sc(03SCF3)3 9H20. It is isomorphous with the hydrated lanthanide triflates, containing tricapped trigonally prismatic coordinate scandium in the [Sc(H20)g] ions, with Sc—O (vertices) = 2.171(9) A and Sc—O (face capped) 2.47(2) A. 

The substance discovered by Nilson was not pure scandium metal, but a compound of scandium and oxygen—scandium oxide (SC2O3). It is quite difficult to produce pure scandium metal from scandium oxide. In fact, it was not until 1937 that the metal was isolated. Then, it was another 20 years before a large sample (weighing one pound) was produced. Today, companies that use scandium often buy the oxide rather than the pure metal. In 2008, scandium oxide of 99.9995 percent purity cost about 3,260 per kilogram. 

Derivation Reaction of scandium oxide with ammonium hydrogen fluoride. 

Table VII. Impurity Content of Recovered Scandium Oxide...

The major impurities are those whose complexation characteristics are similar to scandium s and would be existed to be earned along in the process. The total of the unlisted impurities is 0.62 wt %, with none of them exceeding 0.1 wt %. The selectivity of the process is demonstrated by the fact that the scandium oxide contains only 0.07 and 0.044 wt % of Fe and Mn, respectively, whereas the starting material had 22 wt % Fe, 20 wt % Mn, and only 0.05 wt % of Sc. 

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