Surface Exchange Reactions of Silver and Its Ions

Sandor, J. E.

doi:10.1139/v61-251

Cited by 3 publications

(7 citation statements)

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“…If we use the equation (9) D = 0.724 exp (--45,500/RT) cm2/sec [3] the value of D for lattice diffusion extrapolated to 25~ is 3.6 x 10 -34 cm2/sec, in sharp contrast to our value of about 10 -21 cm~/sec. Further, combination of our values at room temperature and at 60 ~ gives an activation energy of about 20,000 cal/g at.…”

Section: Discussioncontrasting

confidence: 97%

“…Extrapolation of equations similar to [3] to 25 ~ gives: D (parallel to symmetry axis) ~ 1.3 x 10 -I~ cm2/sec D (perpendicular to symmetry axis) ----9.1 x 10 -19 cm2/sec Our results of 8.8, 9.1 x 10 -is are intermediate. Two zinc crystals were used in our work, and accidental fractures, which occur along the basal (perpendicular) planes, showed that the surfaces used were inclined at 10 o_ 15 o to the parallel planes.…”

Section: Discussionmentioning

confidence: 55%

“…The self-diffusion coefficient of zinc has been measured in the temperature range 240~176 (10). Extrapolation of equations similar to [3] In attempting to avoid corrosion of zinc specimens, solutions of Zn(C104)2 in methanol and ethanol were tried. It is doubtful if the anhydrous salt can be prepared, and alcohol solutions of the hydrate led to as much corrosion as aqueous solutions.…”

Section: Discussionmentioning

confidence: 99%

“…In most previous studies of exchange between silver and zinc and their ions in solution, polycrystalline specimens have been used (1)(2)(3). This has the disadvantage that both grain-boundary and 1at-rice diffusion occur within the metal.…”

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Ion Exchange on Single-Crystal Silver and Zinc

King¹,

Simmons²,

Berlin³

1963

J. Electrochem. Soc.

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Exchange studies have been made with electropolished singIe-crystal specimens of silver and zinc immersed in dilute solutions of their salts, using Ag110 and Zn 65 ions as tracers. In 0.02M solutions of the salts, exchange in the surface layer of the metals is rapid and complete, and continued tracer pickup is due to diffusion within the crystals. At lower salt concentrations the tracer pickup is slower, apparently because complete exchange is not maintained in the surface layer of atoms.In most previous studies of exchange between silver and zinc and their ions in solution, polycrystalline specimens have been used (1-3). This has the disadvantage that both grain-boundary and 1at-rice diffusion occur within the metal. The rate of radiotracer pickup depends on the grain size and grain-boundary area, and only the ratio of the two diffusion coefficients is significant. One run with a silver single crystal was carried out by Gerischer and Tischer (4), who concluded that the behavior was not essentially different from that of polycrystalline specimens. Zinc single crystals were used by Bushmanov and Vozdvizhenskii (5), who found somewhat different exchange rates on base and prism facets. Zinc bicrystals were investigated by Sandor (3), who found that the metal specimens corroded promptly even in well-deaerated solutions.The purpose of the present investigation was to find whether single-crystal specimens, prepared with minimum surface roughness, would show a consistent and understandable pattern of exchange with their ions in aqueous solution. We find that silver specimens do so, with no complication from corrosion or surface films. On the other hand, zinc is subject to corrosion by water in the absence of oxygen Zn ~-H20-~ ZnO -P Hf; AG ~ : --19 kcal A similar free energy value applies if Zn(OH)2 is the product. A polished specimen does not acquire a visible film for a long time in deaerated water; in salt solutions the initiation of visible film formation appears to be accidental and in general occurs sooner, the more concentrated the salt. ExperimentalSingle-crystal rods of silver and zinc 2 about 2 cm in diameter were cut into disks 2 mm thick, and a 1 mm hole was drilled near the edge for suspending. After smoothing the surfaces the disks were annealed (silver at 400 ~ zinc at 120~ and cooled slowly. Before use each disk was electropolished to remove distorted material and to give a smooth, bright surface (silver in AgCN-NaCN, zinc in phosphoric acid-ethanol).active solutions the disks were electropolished to remove the active material.In electropolishing, the disks were suspended on a Pt wire, midway between 2 stainless steel cathodes. Disks were suspended in the radioactive solutions either on glass hooks or on wire hooks coated with insulating lacquer. Solutions of AgNO8 were not deaerated except in a few tests; Zn (C104)2 solutions were deaerated with nitrogen or hydrogen which was passed over hot copper, then through two wash bottles containing solution of the same concentration as the test solution. Immersi...

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Section: Discussioncontrasting

confidence: 97%

Section: Discussionmentioning

confidence: 55%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Ion Exchange on Single-Crystal Silver and Zinc

King¹,

Simmons²,

Berlin³

1963

J. Electrochem. Soc.

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“…The exchange of silver ions between polycrystalline silver metal surfaces and aqueous solutions of silver salts has been investigated by a number of workers using radioactive silver isotopes as tracers (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11). In general, all agree that a rapid exchange involving only a few atom layers takes place in the first few seconds, followed by a slower process which is affected by the concentration of the solution, the state of the surface, and the temperature.…”

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Exchange of Silver Ions at Single Crystal/Solution Interfaces

Tingley

1965

J. Electrochem. Soc.

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The exchange of silver ions between the (111), (100), (110), and (311) surfaces of single-crystal silver and silver nitrate solutions has been studied, using Ag 110 as tracer. The initial step is very rapid and is probably largely adsorption, since much of the radioactivity acquired during the first few seconds can be removed by soaking in distilled water. After about 15 rain the ratecontrolling process appears to be diffusion in the solid. In 0.01M AgNO~ solution the radioactivity uptake continues steadily if the surfaces are frequently desorbed with distilled water, but if the adsorbed ions are allowed to remain, the rate of uptake is reduced. In 0.1M AgNO8 solution the radioactivity on the surfaces reaches constant values after 4 days, whether or not desorption is carried out. The penetration profile and diffusion coefficient in the metal were obtained by "chemical sectioning." It was found that diffusion occurred by means of "dislocation pipes," and resembled grain boundary diffusion rather than lattice diffusion by a vacancy mechanism which occurs at high temperatures.The exchange of silver ions between polycrystalline silver metal surfaces and aqueous solutions of silver salts has been investigated by a number of workers using radioactive silver isotopes as tracers (1-11). In general, all agree that a rapid exchange involving only a few atom layers takes place in the first few seconds, followed by a slower process which is affected by the concentration of the solution, the state of the surface, and the temperature. This slower uptake of ions from the solution is held to be controlled by diffusion in the solid. King and Levy (2) found that surfaces that were removed from the solution, and washed frequently, underwent more exchange than surfaces that were left undisturbed; they attributed this to the removal of adsorbed salt that slowed down the exchange. However, King and McKinney (3) concluded that the increased exchange was due, more likely, to increased diffusion caused by a rise in temperature due to the hot water used in the washing. They calculated a grain boundary diffusion coefficient of the order of 10 -21 cm2/sec. Sandor (8), who removed the radioactivity by electroetching, obtained a value of 1.37 x 10 -20 cm2/sec for the grain boundary diffusion coefficient.The present work was undertaken to ascertain the behavior of specific single-crystal surfaces with respect to the exchange of silver ions with aqueous silver nitrate solutions, and to obtain a value for the room temperature volume diffusion coefficient. Experimental DetailsThe single crystals of silver were grown in a horizontal furnace by the method of Chalmers (12), using 99.999% pure silver obtained from Johnson, Matthey and Mallory Limited, Toronto. The crystals were then sectioned and oriented along the desired direction, and the resulting surfaces were electroetched and/or chemically etched and polished, as described below. Most cuts were made using a spark cutter, but two specimens were cut by means of an "acid saw." The orientation of ...

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