Production of high purity granular metals: cadmium, zinc, lead

Abstract

Cadmium, zinc and lead are constituent components of many semiconductor compounds. The obtained high purity distillates and ingots are large-size elements, which is not always convenient to use, and thus require additional grinding, which does not always allow maintaining the purity of the original materials. For the growth of semiconductor and scintillation single crystals it is advisable to use «friable» granular high-purity distillates, which can be processed without the risk of contamination. For example, the European low-background experiment LUCIFER required more than 20 kg of high-purity granulated zinc, which was agreed to be supplied by NSC KIPT. This task was then extended to cadmium and lead. Motivated by these tasks, the authors of this paper propose complex processes of deep refining of cadmium, zinc and lead by vacuum distillation. A device producing granules has been developed. The process of granulation of high-purity metals is explored. The purity of produced granules for cadmium and zinc is >99,9999, and >99,9995% for lead granules. To prevent oxidation of metal granules during exposition to air, chemical methods of surface passivation were used. Organic solvent based on dimethylformamide used as a coolant improves the resistance of granules to atmospheric corrosion during the granulation of high purity Cd, Zn and Pb.

High-Purity Zinc for Low-Background Experiments

“…For zinc ultrapurification, a new, integrated zinc refining process and a specially designed apparatus for practical implementation of the process (Fig. 1) were developed at the Kharkiv Institute of Physics and Technology National Scientific Center [4][5][6]. The thermal and temporal conditions of the zinc ultrapurification process were reported previously [6].…”

“…1) were developed at the Kharkiv Institute of Physics and Technology National Scientific Center [4][5][6]. The thermal and temporal conditions of the zinc ultrapurification process were reported previously [6]. The concentrations of impurity elements in the starting zinc are listed in Table 1.…”

“…The distilled zinc was then granulated in a specially designed device by dripping molten purified zinc into cooled double-distilled water [6]. The final product was zinc granules ranging in diameter from 3 to 5 mm.…”

Enriched Crystal Scintillators for 2β Experiments

“…106 CdWO 4 crystal enriched in 106 Cd up to 66.4% have been developed for the highsensitivity experiments to search for 2β decay of 106 Cd [71]. Cadmium samples (including enriched ones) were deeply purified by a vacuum distillation technique with filtering on getter filters and cadmium tungstate compounds were synthesized from solutions [72,73]. The isotopic composition was precisely measured by thermal ionization mass-spectrometry (TIMS).…”