Trichlorides of Rare Earth Elements, Yttrium, and Scandium

Trichlorides of the Rare Earth Elements, Yttrium, and Scandium 39 

TRICHLORIDES OF THE RARE EARTH ELEMENTS, YTTRIUM, AND SCANDIUM 

Submitted by JOHN D. CORBETT Checked by SMITH L. HOLTt 

A convenient apparatus for the reaction is shown in Fig. 1. A molybdenum boat is folded from thin sheet or foil to contain the metal. The fused silica cylinder ( 30-mm o.d.) which holds this is not necessary but does make product removal easier. The outer fused silica tube ( 40-mm o.d.) is terminated on the outlet end through a standard taper joint to a (Pyrex) cap with stopcock and connection to an exit bubbler (H2S04, not H20) which prevents back diffusion of air. The inlet end (which is slightly elevated) is connected through a stopcock and joint to a (Pyrex) mixing manifold, the three inlets of which connect through bubblers filled with H2S04 for flow measurement to sources of HC1, H2, and Ar or He (not N2). 

The usual commercial grade of HC1 is a chlorination by-product, and the chlorinated hydrocarbons therein contribute a significant carbide impurity in the trichloride through their reaction with the heated metal. Subsequent removal of this appears to require one extra sublimation. However, high purity electronic-grade HC1 (available from several gas suppliers) greatly reduces contamination from traces of the chlorocarbons, 02, N2, and H20 which are present in the usual grade of HC1. 

Containment of this particular combination of metal, trichloride, and HO at reaction temperatures presents a problem of the same character as occurs in the preparation of the triiodides of these elements (this volume. Chapter 1, Sec. 6). These metals all dissolve in (reduce) the liquid trichlorides to some d ee, and this process greatly accelerates the spontaneous reduction of SiO by the metal to form silicide and oxide. The same problem pertains to all known ceramic materials. Container metals which are the most inert to both the rare earth elements and HQ are limited to tungsten and molybdenum and then only if reactions such as Mo(s) + 4HCl(g) - MoCl4(g) + 2H2(g) are suppressed by the addition of H2. The last is not a serious problem for example, with Phj/Pho 10 the pressures of all gaseous molybdenum chlorides are estimated to be 10 atm at 800°. Molybdenum is the material of choice because of its greater ease of fabrication.  

The Mo boat is loaded with the requisite metal (5-20 g), in the dry box if a light rare earth metal is involved and maximum purity is desired. If loaded in the air, the assembled apparatus is flushed for about IS min with a good flow of Ar (or He) (not H2). Once the air has been displaced, the furnace is heated and a moderate flow of Ar and H2 (SO 50) introduced at about 200 . During the subsequent heat-up, at least some of the metal will be converted to the hydride which probably enhances its reactivity. Once the temperature reaches 600-800, the H2 flow is greatly reduced and a good flow of HO Ar (1 1) is started. 

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