Preparation of high pure zinc for electronic applications using selective evaporation under vacuum

Abstract

m6N pure (99.9999%) zinc (Zn) was obtained through multiple vacuum distillations using 99.9% (m3N) pure Zn as input material at 2 kg batch-size. The soaking (distillation) temperature and the time of distillation at a dynamic vacuum level of 2.1 * 10 −3 Torr were optimized to achieve the desired purity, distillation rate and yield. The detailed analysis of input as well as purified Zn was carried out by inductively coupled optical emission spectroscopy (ICP-OES) technique for 14 major impurity elements. This confirmed the reduction of total impurity content from ∼983 to <1.53 μg/g (∼m6N) upon three consecutive distillations. The major impurities separated from the distilled zinc were Al, Cu, Fe, Sn, Pb, Si, Ca, As, Ag, Sb, Ni, Bi, Mg, Mn, etc. The trace oxygen as determined by O–N analyzer reduced from (230–350) μg/g for raw Zn to (20–27) μg/g for distilled Zn and the nitrogen impurity from (34–45) to (15–19) μg/g. Carbon determined by GD-OES reduced from (60–70) to (5–8) μg/g on purification. The overall yield of distillation was found to be 67.5%. Analysis results, i.e. yield and purity are discussed with respect to vapor pressure of impurities and mean free path. ( λ) of Zn vapor. Crystalline structure of distilled Zn was studied by XRD.