• T L Prakash

      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.

    • Purification of cadmium up to 5N+ by vacuum distillation

      S T Ali J V Rao K S Varma T L Prakash

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      Cadmium was refined by vacuum distillation, a technique suitable for low boiling and melting point materials, to remove the heavy and low vapour pressure impurities at ppm level. The detailed analysis of the purified Cd as well as raw Cd was done by ICP–OES techniques for 27 impurity elements. Purification was carried out in an efficient high-yield vacuum distillation system designed and fabricated for purifying 3N+ purity indigenous cadmium to 5N+ (99.999%). Analysis confirmed the reduction of total impurity content from 134 ppm (3N7) for raw Cd to 3 ppm (5N7) upon vacuum distilled Cd. The present study shows that the analysis of impurities such as Fe, Mg and Ca are contributed from environmental effect, whereas impurities such as Pb, Bi, Ag, Ni, Cu, Zn and Tl require adaptation of elemental analysing technique to counter dilution effect. The Hg trace analysis can however be carried out by hydride generation techniques.

    • 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.

    • Foreword

      S B Krupanidhi T L Prakash N R Munirathnam

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    • 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.

    • Purification of cadmium by selective volatilization in vacuum in presence of oxide phase on its melt

      N R Munirathnam K Srinivasa Rao T L Prakash

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      Purification of cadmium in the presence of a thin (∼0.001 mm) oxide layer on the surface of the molten metal was carried out using a simple system designed and fabricated locally. The analytical results revealed that the distillation through oxide layer gave better separation for Co, Ni, Cu, Zn, Ag, Sn, Hg and Tl, when compared to the distillation without oxide layer. This was attributed due to the impurity metal oxide phases formation on the surface of the molten metal. The influence of oxygen flow time on the distillation rate of cadmium was established. There was no excess oxygen (O) retained in the distillate after two consecutive vacuum distillations through oxide route. The experiments were conducted at the level of nearly 1.5 kg a batch to study the impurities behaviour due to upscaling. The detailed chemical analysis of 58 impurity elements in Cd in presence and absence of oxide layer was carried out by glow discharge mass spectrometry (GDMS).

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    • Dr Shanti Swarup Bhatnagar for Science and Technology

      Posted on October 12, 2020

      Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
      Chemical Sciences 2020

      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
      Physical Sciences 2020

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      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

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