Influence of an Applied Field on the Tarnishing of Silver and Copper in Iodine Vapour

Patnaik, R. N.; Bose, Saswata; Sircar, S. C.

doi:10.1179/000705977798319594

Cited by 10 publications

(7 citation statements)

References 22 publications

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“…It was further predicted that this phenomenon would prevail for the tarnishing reaction of any system with an ion-conducting reaction product. Enhancement in the rate of tarnishing under short circuiting was also observed by Patnaik et al [24] and Bose and Sircar [19,20] in Ag-I 2 system. They identified the migration of cations as the ratelimiting step during short-circuit conditions, which received further support from their study on the Ag-Cd system, where a further increase in the rate of iodination by short circuiting was observed.…”

Section: Introductionsupporting

confidence: 57%

“…The observed enhancement may be attributed to the presence of an external short-cir- cuit path for easy flow of electrons from the inner (Ag/AgI) to outer (AgI/I 2 ()) interface. Further, as pointed out by Patnaik et al, [24] these extra electrons available at the outer interface would naturally be expected to ionize more iodine. As a consequence, there will be an enhanced incorporation rate of iodine into the growing AgI lattice at the outer interface, with reduced injection of positive holes in the valence band and increased injection of cation vacancies at the outer surface of the ionic lattice.…”

Section: B Iodination Under Short-circuit Conditionsmentioning

confidence: 93%

“…Similar explanations have also been reported in previous publications. [14,15,19,20,24,25] Further, it was observed that the addition of a higher valent cation like Cd in Ag has reduced the rate of iodination considerably in comparison to that of pure Ag. This is expected because during iodination process, Cd ions are incorporated into the cation sites of AgI lattice to result in either a decreased concentration of electron holes or an increased concentration of cation vacancies, per the following reactions:…”

Section: A Normal Iodinationmentioning

confidence: 95%

“…The experimental details of the short-circuit attachment have been reported in previous publications. [24,[27][28][29] Mass gain due to the formation of metal iodide film was recorded with the help of an electronic microbalance (Sartorius MCl, (Weenderland Stra␤e 94-108, Germany) Model-RC210D, accuracy ‫01ע‬ g). All the experiments were carried out in a discontinuous mode, i.e., each specimen was taken out of the reactor intermittently to measure the mass gain and re-exposed inside the reactor for further iodination.…”

Section: B Iodination Reactor and Proceduresmentioning

confidence: 99%

“…The surfaces of each test specimen were prepared in the same manner as reported previously. [19,20,24] A platinum wire was spot welded at the center of one edge of each rectangular specimen. Then, the specimens were washed thoroughly, cleaned with a solution of 1: 10 dil nitric acid, rinsed in distilled water, and dried in acetone.…”

Section: A Materials and Specimen Preparationmentioning

confidence: 99%

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Influence of short circuiting on the kinetics and mechanism of iodide film growth on Ag and Cd-doped Ag

Kuiry¹,

Roy

Bose

1997

Metall Mater Trans B

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Results of iodination studies on pure Ag and Ag with 6000 ppm of Cd under normal and shortcircuit conditions in the temperature and iodine pressure ranges of 333 to 373 K and 0.067 to 6.078 kPa, respectively, are reported. Under all experimental conditions, the iodide film growth kinetics conform to parabolic rate law. The iodide films have been characterized by scanning electron microscopy (SEM), electron probe microanalysis (EPM), X-ray diffraction (XRD), and Auger electron spectroscopy (AES) analyses. The effect of a higher valent dopant like Cd in Ag is observed to decrease the rate of normal iodination, which suggests that the film growth process is controlled by migration of electron holes across the iodide layers. The presence of a short-circuit path enhances the rate of iodination for pure Ag. However, the iodination rate of Cd-doped Ag under short-circuit mode is found to be further enhanced compared to that for pure Ag. This has been explained on the basis of the ion migration mechanism. The pressure dependence of rate constants is found to follow a relation like k P ␣ for pure Ag and Cd-doped Ag under normal conditions. The corresponding 1/2 P I2 relations under short-circuit mode are observed to be k P ␣ and k P ␣ for Ag and Cd-doped 1/3 1/4 P P I I 2 2Ag, respectively. Arrhenius plots have yielded activation energy values of 25.8 and 15.2 kJ⅐mol Ϫ1 under normal and short-circuit conditions, respectively. The kinetic results of parabolic film growth have been explained with the help of defect equilibria, considering the predominance of Frenkel defects in pure and doped AgI lattices. The mechanism of film growth processes has been confirmed to be Wagner's electrochemical potential gradient-induced migration of defect species across the iodide layer.

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Section: Introductionsupporting

confidence: 57%

Section: B Iodination Under Short-circuit Conditionsmentioning

confidence: 93%