China Nonferrous Metallurgy

High purity tellurium is a key semiconductor material widely used in infrared detection, nuclear radiation detection, photovoltaic, refrigeration and other fields. Its application range is limited by the purity of tellurium. At present, the mainstream process for preparing 6N and 7N high-purity tellurium is vacuum distillation-hydrogen zone melting process, but for high-selenium raw materials, the products prepared by this process are difficult to meet the standards. In this paper, 4N grade tellurium was used as raw material (the main impurity elements were selenium and sodium, and the selenium content was 6.2×10-6), and the preparation experiment of high purity tellurium was carried out. By analyzing the difference of impurity content in the inner and outer layers at the same condensation position, it is found that there is a phenomenon of ‘slip in the condensation zone’, which causes the problem of low boiling impurity and product mixing. The experiment also shows that prolonging the preheating time of raw materials and adding high purity quartz also affect the purification of tellurium. In view of the above problems, the original process is improved. Under the conditions of prolonging the constant temperature preheating time of raw materials to 70min, pre-baking the condenser, and adding high-purity quartz fragments to the raw material, the selenium and sodium in tellurium can be efficiently separated before the hydrogen zone melting process. The improved process can prepare 6N grade high purity tellurium by one distillation without hydrogen in the vacuum distillation process, which greatly saves the manufacturing cost, and provides conditions for the preparation of 7N grade ultra-high purity tellurium with 4N grade high selenium tellurium.