Floating-zone melting

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. 

Elements dissolved in boron influence its crystal structure. Dissolved impurities also influenee the physical and chemical properties of boron, especially the electrical properties, because boron is a semiconductor. Preparation of solid solutions in jS-rh boron requires a careful choice of crucible material. To avoid contamination, boron nitride or a cold, coinage-metal crucible should be used or the levitation or floating-zone melting techniques applied. 

Terbium metal is obtained from its anhydrous trifluoride, TbFs, or trichloride, TbCls, by thermal reduction with calcium, carried out in a tantalum crucible. Terbium produced by such methods may contain traces of calcium and tantalum. High purity metal can be prepared by various methods such as vacuum remelting, distillation, amalgam formation, floating zone melting, and various chemical processes. 

If further purification is desired, rods are produced by compacting and sintering and are subjected to electron beam floating zone melting. This procedure does not further reduce the concentrations of uranium and thorium, but does reduce the concentrations of many other elements as shown in Table 5.15. Moreover, residual impurity elements are distributed homogeneously. 

Chemical element B has two stable isotopes, B and "B, nuclei of which differ by one neutron. In the universe, "B/ B natural abundance ratio is estimated as 4.05 0.10 (Viola 1991). This value coincides with the natural isotopic composition of boron, 19.85% B+80.15% "B, determined in floating-zone-melted P-rhombohedral boron by the glow-discharge mass-spectrometry laboratory method (Nogi et al. 2000). Since boron and its compounds have found a variety of applications, the elemental and isotopic analyses of boron become important steps of an investigation with special challenges (Balaram 2011). 

Mer] Floating zone melting method Eutectic C-Fe alloys with 0.1-0.6 mass% Si... 

Bohm, J., A. Ludge and W. Schroder, 1994, Crystal growth by floating zone melting, in Handbook of Crystal Growth, Vol. 2b, ed. D.T.J. Hurle (North-HoUand, Amsterdam) ch. 4, pp. 215-250. 

Synthesis of intermetallic compounds 6 4.3.4. Float zone melting 27... 

Crucible-less techniques require no physical containment and rely on the surface tension of a free floating molten zone in contact with the corresponding solid. This method of crystal growth is concerned primarily with vertical float zone melting with RF, electron beam or infra-red heating and will be discussed in section 4.3.4. 

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