Effect of multi-pass, zone length and translation rate on impurity segregation during zone refining of tellurium

The efficiency of zone refining as a function of number of zone passes; zone length and translation rate was studied. Multi-pass, depending on the initial concentration of impurity, leads to a significant segregation and major trace impurities in tellurium such as Fe, Ni, Bi, Sb, Sn and Zn were reduced effectively after quadruple zone refining. It was found that for a tellurium material of different distribution coefficient (K) values, the constant zone size of 3 to 6 cm is optimum for all of them. Good segregation behaviour was observed at a minimum translation rate of 30 mm/h and impurity concentration has increased at higher translation rate. Also, a detailed account on the reduction of selenium, which is a major impurity in tellurium, is discussed.