• Indra Sanghi

      Articles written in Proceedings – Section A

    • Electro-deposition and dissolution of zinc in zincate solutions

      Indra Sanghi W F K Wynne-Jones

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    • Electrochemical behaviour of zinc in alkaline solutions - Part I. Constant current measurements

      Indra Sanghi W F K Wynne-Jones

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      The cathodic and anodic polarization of zinc in different concentrations of alkaline solutions has been studied under constant-current conditions. The changes of zinc electrode-potential with reference to a Hg/HgO/KOH system have been measured both in KOH and zincate solutions using a “Luggin” capillary and a specially designed cell, current being drawn from an electronic current stabilizer. Time-potential curves have been plotted and it is found that the anodic zinc passivates at a certain stage showing a sudden rise in potential by as much as 3–4 volts. Before the passivation, the main electrode reaction is the formation of Zn++, while after the passivation it changes to gas evolution. No definite relationship as previously suggested by Muller, between the current density and the passivation time was found, perhaps due to migration and non-linear diffusion effects and other reasons discussed in the paper. It has been found that the behaviour of zinc differs in concentrated alkaline solutions (i.e., 0·5 N to 5 N) from that in dilute solutions (0·2 N to 0·01 N), in which case the open circuit rest-potential of zinc is indefinite and may vary by as much as 500–600 mV., while the maximum passivation jump in potential is about 2 volts only. Also the passivation and the decay of current on breaking the circuit are found to be slower than in the case of concentrated solutions. Colour changes of the zinc electrode, during the polarization, are also briefly described and discussed.

    • Some polishing experiments on copper in a hyperbolic cell

      VR Ramanathan Indra Sanghi

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      Some polishing experiments have been carried out on copper anodes in a hyperbolic cell designed by Gilmont and Walton, using orthophosphoric acid as the electrolyte. The results obtained have been compared to those obtained in similar experiments in a Hull cell. It has been found that very similar bands of different reflectivity and polishes are found to form in both the cells. These bands shift with time and a study of such displacements has been made. The results are briefly discussed.

    • Electrochemical behaviour of zinc in alkaline solutions - Part II. Constant over-voltage measurements

      Indra Sanghi M Fleischmann

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      As the whole passivation phenomenon in the case of zinc is very quick and sudden and as it cannot be fully studied and followed by galvanostatic techniques alone, the constant over-potential technique has, for the first time, been applied to zinc and results reported. A special apparatus consisting of suitable oscillator, modulator, demodulator and a stable D.C. amplifier with a gain of 100,000 was used for the purposes and is described. Potential curves for equilibrium current rates, achieved on 0·1 V. and 25 mV. steps after 1 minute each, have been obtained in 6N, N, 0·1 N KOH and zincate solutions for the complete range of −1·3 to about −2·0 volts with reference to Hg/HgO/KOH reference electrode. It has been found that in the first truly active region, the main electrode reaction is the formation of zinc ions while after the passivation it changes to gas evolution. Potentiostatic techniques reveal intermediary stages, undisclosed by constant current methods, of pseudo-passivation and current-plateau regions in which the anodic layer thickens, controlled by the high field cation transport. These observations and explanations are further supported by plotting rate-time transients obtained by suddenly dropping the potentials from higher to lower values, when the rates were found to cut off. Some anomalies and sudden reversal of currents with increasing over-voltages, have also been fully discussed. The influence of other factors,e.g., concentration, stirring, sudden changes in over-voltages, presence of zincate, sulphate, etc., has also been considered. Studies such as these are found to throw considerable light on the electrochemical behaviour of zinc.

    • Influence of surface active agents on spectrophotometric determinations of pH

      Indra Sanghi N V Parthasarathy

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    • Polarisation and polishing studies on copper in a Hull cell

      Indra Sanghi VR Ramanathan

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      In continuation of our previous work,1–2 the effects of polishing time, sp. gr. of the electrolyte, addition of EDTA, electrolyte level, etc., on the position, size and shape of the variously polished bands obtained in a Hull cell have now been studied. I–V measurement when carried out showed that total cell voltage increases regularly with total cell current, thereby affording no explanation for the variously polished bands. However, with a specially designed probe electrode,3 it has been possible to study the current distribution as existing during polarisation at different points of the anode surface and thus offer some explanation for the appearance of variously polished bands which could not be interpreted earlier in terms of electrode potentials.

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