Melting zone

What can be done With a of 0.1 (defined later), the ultimate purification is about 10 of the original value after 20 passes and a charge to zone length of 10. Three passes purified 99.91 % benzoic acid to 99.997 mole %. This is equivalent to 11 recrystallizations from benzene or 25 from water. 

Zone refining was developed originally to produce very pure germanium for the semiconductor industry. It Was successful in that Bell Laboratories produced 99.99999999 % pure germanium Since then, many elements have been prepared in high purity, as well as many organic compounds. 

The least expensive way to do zone refining it to plaee the sample in a quartz, eeramic, or graphite tube, and place the tube in a metal lathe. Move the heater with the lathe. 

A circle of 1/4 plywood acts as a float which moves upward at a constant rate as water fills the desiccator. A coat of paint keeps it from becoming water logged. The overflow tube acts the same as that in a Soxhlet extractor (Chapter 

Experiment No. 3 in Appendix A can be used to show what happens when a small amount of methyl red is added 

2 Ulrich, J. (2003) Melt Crystallization -Fundamentals, Equipment and Applications (eds J. Ulrich and H. Glade), Shaker, Aachen, pp. 1-6. 

3 Neumann, M. (1996) Vergleich statischer und dynamischer Schichtkristallisation und das Reinigungspotential der Diffusionswiische. Ph.D. thesis, Universitat Bremen, Papierflieger, Clausthal-Zellerfeld. 

5 Ulrich, J. (2002) Kirk-Othmer Encyclopedia of Chemical Technology, vol. 8 (eds R.E. Kirk and D.F. Olhmer), Wiley-VCH Verlag GmbH, Weinheim, pp. 95-147. 

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Zone electrophoresis Zone melting Zone refining... 

Plutonium trichloride, PUCI3, is the only known binary chloride of plutonium. No higher chloride in the soHd state has been prepared so far. The trichloride is a blue-green soHd and can be prepared from the reaction of Pu metal or PUO2, and HCl gas at elevated temperatures, and can be purified by sublimation and zone melting. The yellow complex chloride, CS2PUCI3, is stoichiometric, stable, and can be used as a primary analytical standard for plutonium (156). 

W. G. Pfann, Zone Melting, 2nd ed., John Wiley Sons, Inc., New York, 1966. 

Zone Melting. A similar material balance may be made for a zone of mass moving a short distance in such a manner that the mass dm of sohd is frozen out and an identical mass melts into the zone (Fig. 4). For the first zone pass, it is assumed that the rod is initially at uniform composition i to obtain the following (1,4,8) ... 

Containers. The ideal container for zone melting should not contaminate the melt nor be damaged by the melt or subsequent contraction of the sohd. For organic materials, borosiUcate glasses are especially suitable, although metals and fluorocarbon and other polymers have also been successfliUy employed. 

It is pmdent to perform zone melting in a dry inert atmosphere. Oxygen causes most organic melts to oxidize slowly. Oxygen and moisture not only oxidize metals and semiconductors, but often enhance sticking to the container. Molten salts attack sUica more rapidly in the presence of moisture. Oxygen and water are considered impurities in some inorganic compounds. 

The primary application for floating-zone melting is crystal growth rather than purification. Semiconductor-grade siUcon is not purified by zone refining siUcon chlorides are distilled and then reduced with hydrogen. 

With vertical zone melting and horizontal zone melting without a gas bubble, simple tube rotation at a constant moderate velocity does not significantly influence 5. In those cases, accelerated cmcible rotation or spin up—spin down could be used (72—75). The tube is spun more rapidly than described above, but not at constant velocity. It may, for example, be spun rapidly, suddenly stopped, spun rapidly, etc, resulting in very vigorous stirring. 

Semiconductor and Solar Cells. High purity (up to 99.9%) antimony has a limited but important appHcation in the manufacture of semiconductor devices (see Semiconductors). It may be obtained by reduction of a chemically purified antimony compound with a high purity gaseous or soHd reductant, or by thermal decomposition of stibine. The reduced metal may be further purified by pyrometaHurgical and zone melting techniques. 

FIG. 22-4 Cl irves for progressive freezing, showing solute concentration C in the solid versus fraction-solidified X (Pfann, Zone Melting, 2d ed., Wileij, New York, 1966, p. 12. )... 

Some materials are so reactive that they cannot be zone-melted to a high degree of purity in a container. Floating-zone techniques in which the molten zone is held in place by its own surface tension have been developed by Keck et al. [Phys. Rev., 89, 1297 (1953)]. 

Continuous-zone-melting apparatus has been described by Pfann (op. cit., p. 171). This technique offers the advantage of a close approach to the ultimate distribution, which is usually impractical for batch operation. 

Powers, Symposium on Zone Melting and Column Crystallization, Karls-nilie, 1963. 

Benzopbenone [119-61-9] M 182.2, m 48.5-49°, pK -6.0 (aq H2SO4). Crystd from MeOH, EtOH, cyclohexane, benzene or pet ether, then dried in a current of warm air and stored over BaO or P2O5. Also purified by zone melting and by sublimation [Itoh J Phys Chem 89 3949 1985 Naguib et al. J Am Chem Soc 108 128 1986 Gorman and Rodgers J Am Chem Soc 108 5074 1986 Ohamoto and Teranishi J Am Chem Soc 108 6378 1986 Naguib et al. J Phys Chem 91 3033 1987],... 

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