Effect of Temperature on Segregation Coefficients of Impurities in Tellurium

Abstract

The lowest values of effective segregation coefficients Keff of impurities in tellurium are the main parameters required to obtain an optimal purification ( ≥ 6N). A series of (13 × 4) values of Keff were determined at the same starting concentration C0 and velocity of interface v. Four different temperatures of the molten zone were used. The effect of some of these values was investigated for the first time. The influence of temperature in zone refining was analyzed through the relation of ln Keff versus 1/T. Experimental study showed two kinds of impurities. The first one was easily removed despite the variation of T while the other was strongly affected by T and trapped in the molten zone. The activation energies of 13 impurities in tellurium were also determined. The values of Keff seems to be acceptable about 773°K. For the molten zone, we proposed an adequate temperature range which was about 50°K higher than the melting temperature of tellurium. This was necessary to achieve an electronic grade purification of tellurium with a good efficiency by zone melting process.

A New Theoretical Formulation of Temperature Effect on Impurities Diffusion Coefficients in Molten Tellurium

“…Indeed, the particular anomaly of liquid tellurium at high temperature, where the quasi-polymer chain structure is not destroyed, enhances the formation of complex tellurides. The interface is then quickly saturated leading to a weak segregation of impurities, thus some K eff values tend toward unity [10].…”

“…Using the expression LnK eff = A T + B, where the constants A and B are graphically determined for each impurity: A < 0, B > 0, and A B [10], we can write the lower part of relation ( 9) as:…”

“…Indeed, the particular anomaly of liquid tellurium at high temperature, where the quasi-polymer chain structure is not destroyed, enhances the formation of complex tellurides. The interface is then quickly saturated leading to a weak segregation of impurities, thus some K eff values tend toward unity[10].Equations (9) and (11) require the knowledge of the value of the concentration layer . However, in the case of (i) low concentration C 0 , (ii) vigorous stirring in liquid metal, and (iii) constant velocity of interface v, the concentration layer was estimated to be 10 −5 m[8].…”

Study of segregation process of impurities in molten tellurium after one pass of three conjoint zones in zone refining

“…One of the most convenient techniques of physical purification is the zone-melting process, which seems to be reliable to obtain electronic grade tellurium, many impurities are easily removed due to the suitable values of effective segregation coefficients K eff o1 [4]. The action of successive molten zones traveling in the same direction is to redistribute impurities.…”