A LANTHANIDE LANTHOLOGY (.pdf) - Davidson Physics

Metallothermic ProcessesMETALSThe metallothermic approach, widely used for pure element production, is suitable for mostof the Ln series (including mixed-Ln's) and uses as the precursor :• fluoride, chloride, or, for certain elements, oxide.The fluoride is the preferred salt because it can be prepared relatively oxygen-free, is nothygroscopic and a stable end-product slag results. Calcium metal is the reductant most usuallyemployed in industry. For example, Neodymium is produced commercially by mixing a slightexcess of Calcium particles with the fluoride in a Tantalum crucible and heating to initiate theexothermic reaction:• 3 Ca + 2 NdF 3 => 3 CaF 2 + 2 NdThe charge is then held at a high temperature, above the Ln m.pt., to ensure a good separation ofthe lighter immiscible calcium fluoride slag from the heavier Ln metal.Metallothermic reduction of anhydrous chloride precursors has limited applicability. It hasbeen explored as a route to some of the heavy non-volatile Ln's, using Lithium metal vapor as thereductant. The resulting Lithium chloride is distilled off.• LnCl 3 + 3 Li => Ln + 3 LiClOxide reduction is used for the metals, Sm, Eu, Tm and Yb, that have high vapor pressuresaround their melting points, with La metal ( essentially non-volatile at reaction temperatures) as thereductant. The volatile lanthanide is distilled off and collected on a cooled surface, e.g. an invertedTa crucible.• 2 La + Sm 2 O 3 => 2 Sm + La 2 O 3A extension of oxide-reduction is used for the commercial production [2] of thepermanent-magnet intermetallic compound SmCo 5 , a process that avoids the intermediate step ofSm metal production and goes directly to a powder form of the desired metal.• 3 Ca + 10 Co + Sm 2 O 3 => 2 SmCo 5 + 3 CaO[2] C.Herget and H.-G.Domazer, Methods for the Production of Rare Earth-3d Metal Alloys with ParticularEmphasis on the Cobalt Alloys, Goldschmidt Informiert, 1975, 35, 3 (publ. Th.Goldschmidt AG)4