Sublimation apparatus for purification

For purification the crude product is boiled with glacial acetic acid (preferably in the extraction apparatus shown in Fig. 27). Fine red needles melting point 289°. Sublimation in a vacuum from a sausage flask is also to be recommended the sausage should be fixed low down and the bulb completely immersed in a nitrate bath (equal parts of potassium and sodium nitrates). Much poorer yields of alizarin are obtained by using an open round-bottomed flask at 189°-190°. 

At the end of the reaction period, chamber B is evacuated and sealed off at C. The vessel is then sealed through D to the sublimation apparatus shown in Fig. 4. This amounts to a collection vessel J, which is separated from the initial sample by a coarse glass frit or plug of Fig. 4. Apparatus for the purification glass wool G. For amounts Of beryllium chloride. of beryllium up to 2.5 g., the... 

Sublimation.—This is a valuable means for the purification of many organic substances and is admirably adapted for small scale work since losses are generally small. Sublimation may be carried out either at atmospheric pressure or under reduced pressure. The apparatus shown in Fig. XII, 2, 20 is simple and effective the sublimate is collected on the cold finger condenser. 

At the present time, when gram to kilogram amounts of either Am isotope are available, the method of choice for the preparation of Am metal is the metallothermic reduction of Am02 with La (or Th) using a pressed pellet of the oxide and the reductant metal. An oxide reduction-metal distillation still system is shown schematically in Fig. 11. Yields of Am metal are typically >90% and purity levels equal or exceed 99.5 at %. Further purification of the product Am metal can be achieved by repeated sublimations under bigh vacuum in a Ta apparatus (Section III,B Fig. 4). A photograph of 2 g of Am metal distilled in a Ta apparatus is given in Fig. 12. 

One of the most useful and convenient techniques for the purification of solids is sublimation. In this process, the solid is warmed (often under reduced pressure) until its vapor pressure becomes high enough for it to collect on a cooled surface placed above the solid. Sublimation is limited to compounds which have reasonably high vapor pressures and which pass directly from the solid state to the vapor. However, the process involving initial melting followed by vaporization and deposition on the condenser may be carried out in the same apparatus and is often loosely called sublimation. 

Typically, La turnings and M2O3 are evacuated in a Ta crucible and heated slowly to 1400 C (Eu, Yb) or 1600°C (Sm, Tm). The sublimed metal is collected on a Ta condenser above the crucible in the vacuum apparatus. As with all reduction processes, purification of the reduced metal is necessary for researcher-quality products. In the case of Sm, Eu, Tm, and Yb, vacuum resublimation is a suitable purification method. 

Sublimations can be carried out under pressure or vacuum with equal ease. The technique is useful only if impurities associated with the component being sublimed have a substantially different vapor pressure at the sublimation temperature. It is often used as a final purification step in the preparation of an analytical sample. A simple but effective apparatus is shown in Fig. 2-6 the sample is placed in the bottom of the outside tube, it is heated, and crystals of sublimate collect on the large cold-finger condenser. A simple tube such as that illustrated in Fig. 2-7 can be used for... 

The conditions of sublimation must be chosen according to the requirements of the application. For simple purification the sample temperature is raised slowly, under reduced pressure if necessary, until the sublimate is observed on the condensing surface. These established conditions should then be maintained until no further sublimation appears to be occurring, at which point the sample temperature can be raised again if other components of the sample can be further removed. At any point in this cycle the apparatus can be dismantled and the sublimate removed. This process allows selective separation or fractional sublimation to be carried out. 

---