Zone melting applications

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. 

Applications Zone melting has been used to purify hundreds of inorganic and organic materials. Many classes of inorganic compounds including semiconductors, intermet lic compounds, ionic salts, and... 

If an actinide metal is available in sufficient quantity to form a rod or an electrode, very efficient methods of purification are applicable electrorefining, zone melting, and electrotransport. Thorium, uranium, neptunium, and plutonium metals have been refined by electrolysis in molten salts (84). An electrode of impure metal is dissolved anodically in a molten salt bath (e.g., in LiCl/KCl eutectic) the metal is deposited electrochemically on the cathode as a solid or a liquid (19, 24). To date, the purest Np and Pu metals have been produced by this technique. 

Fractional solidification and its applications to obtaining ultrapure chemical substances, has been treated in detail in Fractional Solidification by M.Zief and W.R.Wilcox eds, Edward Arnold Inc, London 1967, and Purification of Inorganic and Organic Materials by M.Zief, Marcel Dekker Inc, New York 1969. These monographs should be consulted for discussion of the basic principles of solid-liquid processes such as zone melting, progressive freezing and column crystallisation, laboratory apparatus and industrial scale equipment, and examples of applications. These include the removal of cyclohexane from benzene, and the purification of aromatic amines, dienes and naphthalene. 

Gradient Zone Melting (TGZM) method (34 35), which is well known in many related applications, but does not appear to have been applied to the production of composites, particularly for electrooptic applications. 

Radiant tube burners are made by using CMC. These are used for indirect-fired, high-temperature zones, controlled atmosphere heating and melting applications. 

Recently, Mg and Be compounds have been used in alloys with ZnSe to make blue and green semiconductor lasers. Bulk growth by zone melting and molecular beam epitaxy (MBE) ° has been used. In these cases, good semiconductor material has been obtained dilution with group IIB compounds may be responsible. However, growth of pure MgS in very thin films on ZnSe has been achieved the epitaxial orientation effect of the substrate results in a tetrahedral cubic (sphalerite or zinc-blende) structure. It is likely that improvements in these materials will take place at a rapid rate, driven in part by applications and in part by newer, cleaner synthetic methods. 

Semiconductor and Solar Cells. High purity (up to 99.9%) antimony has a limited but important application 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 solid reductant, or by thermal decomposition of stibine. The reduced metal may be further purified by pyrometalluigical and zone melting techniques. 

A detailed review of zone melting and its applications has been given recently by Shaw (2). In the present paper we shall confine our attention primarily to the convective-diffusive characteristics of such systems, and we shall strive primarily to obtain a sound qualitative understanding of their behavior. 

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). 

The application of zone melting to the purification of semiconductor materials has been well established. In this technique a molten zone is passed along the length of a solid rod in one direction several times. Impurities more soluble in the molten metal i ill move in the direction in which the molten zone is moved while impurities less soluble in the liquid metal will be deposited in the solid metal and will tend to move in the opposite direction. Since the degree of purification depends on the solubility of the impurities in the solid metal, those impurities which are soluble in the solid cannot be removed to below the equilibrium concentration. Thus the interstitial impurities which are quite soluble in the solid rare earths just below their melting point cannot be completely removed. 

Compared with the three other semi-finished materials, the tapes are fully consolidated (Fig. 7.16), that is, the micro and macro impregnation are completely done. FuUy consolidated tapes are available on the market with fiber volume contents of up to 60% and even higher. Due to the not applicable impregnation process the winding speed can be higher in comparison to the other winding patterns. The heating zone melts the polymer and the tension (Fig. 7.6) or compaction roller (Rg. 7.7) presses the filaments on the mandrel. 

Some of the early crystal growth experiments on the rare earth elements employed arc zone melting. Carlson et al. (1975) grew a Lu crystal (7.8 cc) and subsequently Schmidt and Carlson (1976) an Er crystal (13 cc) by this method. Verhoeven et al. (1976) describe the application of arc zone melting to LaB, producing rods —20 x 6 mm at rates 50p,ms , and this approach has been adopted by other workers for rare earth hexaborides (Gruhl and Winzer 1986). 

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