A novel in-situ technique of ultra purification of cadmium for electronic applications

A novel in-situ ultra purification technique incorporating both 'distillation' and 'zone refining' was devised using simple see-through quartz wares. The purification experiments, e.g. distillation followed by zone refining were carried out on 3N7 purity raw cadmium in a clean room environment of class 10,000. After a single run of purification employing one distillation and subsequent 25 passes of zone refining, cadmium of purity m6N (99.9999%) achieved w.r.t. metallic impurities (viz. Si, Ca, Fe, Ni, Cu, Zn, As, Se, Ag, Sb, Tl, Pb, Bi, etc.) as analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES). The trace oxygen as analyzed by O-N analyzer reduced from 230-350 ppm for raw Cd to 20-27 ppm for distilled and zone refined Cd. Carbon analyzed by glow discharge optical emission spectroscopy (GD-OES) reduced from 60-70 to 4-7 ppm on purification. The different process parameters such as soaking temperature for distillation, zoning temperature, speed of zone, etc., were optimized and the analysis results were discussed w.r.t. vapor pressures and segregation coefficients.