• D S Prasad

      Articles written in Bulletin of Materials Science

    • Preparation of high purity tellurium by zone refining

      N R Munirathnam D S Prasad Ch Sudheer A J Singh T L Prakash

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      This paper describes purification process of tellurium metal using zone refining technique under high purity hydrogen gas ambient in normal room environment. Process automation by newly designed stepper motor drive and allied process control instruments circumvent the complexity of electrical motors. It is observed that overall impurities have gone down substantially from 4N+ to 5N5 purity with reference to Fe, Mg, Al, Cr, Zn, Bi and Cu. Removal of selenium is effected by hydrogen, which also serves as carrier gas during zone refining. The selenium in tellurium matrix is found to be below detection limits. The zone temperature, zone length and tilt angle maintained in the experiment are adequate to go down to high purity levels.

    • Tellurium purification: various techniques and limitations

      D S Prasad Ch Sudheer N R Munirathnam T L Prakash

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      Limitations and techniques to purify tellurium metal especially using non-chemical techniques such as vacuum distillation and zone refining are discussed. It was found that the clean environments, design, handling and cleaning of quartz ware are equally important in achieving the desired purity levels.

    • Zone refining of cadmium and related characterization

      N R Munirathnam D S Prasad Ch Sudheer J V Rao T L Prakash

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      We present the zone refining results of cadmium using horizontal resistive zone refiner under constant flow of moisture free hydrogen gas. The boron impurity in cadmium can be avoided using quartz (GE 214 grade) boat in lieu of high pure graphite boat. The analytical results using inductively coupled plasma optical emission spectrometry (ICPOES) show that majority of the impurities are less than the detection limits. Comparatively, zinc is the most difficult impurity element to remove in cadmium matrix by zone refining.

    • High purity tellurium production using dry refining processes

      N R Munirathnam D S Prasad J V Rao T L Prakash

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      Tellurium (99.95 at.% purity) is purified using dry processes such as selective vapourization and zone melting in a thoroughly etched and cleaned quartz boat, under continuous flow of hydrogen (H2) gas. The tellurium ingot was quadruple zone refined (QZR) under continuous flow of H2 gas. Thus, the purified tellurium of ultra high purity (UHP) grade is analysed for 60 impurity elements in the periodic table using glow discharge mass spectrometer (GDMS). The sum of all elemental impurities indicate that the purity of tellurium as 7N (99.99999 at.%). The total content of gas and gas forming impurities like O, N and C are found to be within acceptable limits for opto-electronic applications.

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