The Rate of Corrosion of Silver in Solutions of Ferric Sulfate

360

180

Rates of ionic mass transfer at nickel electrodes rotating about their axes in the center of stationary electrodes were studied using the ferri-ferrocyanide couple in alkaline solutions. A general mass transfer correlation was found to apply equally well to dissolution rates of rotating solids and to rates of ionic mass transfer at rotating electrodes. This correlation takes into account physical properties of the system as well as geometric and hydrodynamic factors. The correlation allows prediction of limiting currents and concentration polarization at rotating electrodes under a wide range of conditions. The nature of polarization involved in reduction of Fe(CN)6-a and oxidation of Fe(CN)~-4 was also investigated. Polarization was found to depend strongly on the presence of electrode poisons. With freshly prepared solutions, under exclusion of light, and with cathodically treated nickel electrodes, relatively small chemical polarizations were determined. For rotational speeds not exceeding Reynolds number 11,000, chemical polarization was found to be negligible in comparison with concentration polarization. Under such conditions, the ferro-ferricyanidc couple can be conveniently used to obtain mass transfer rates for various hydrodynamic conditions, or conversely, to verify the validity of mass transfer equations by a comparison of experimental and calculated values of limiting currents and concentration polarization. The rotating electrode model was found to be most suitable for studying the nature of electrolytic polarization phenomena beeause of uniformity of the current distribution and the hydrodynamic diffusion layer at the electrode surface.

mentioning

confidence: 99%

Ionic Mass Transfer and Concentration Polarization at Rotating Electrodes

Eisenberg

Tobias

Wilke

1954

360

180

“…The reversible potentials of Ag-Ag + and Fe++-Fe+++ electrodes are of similar magnitudes and rates might be correlated with potential differences. It was actually found in ferric-ferrous-silver sulfate solutions that adsorption of the various ions is the principal rate-controlling factor (2). The rate was found to be much higher in ferric sulfate than in ferric nitrate or perchlorate solutions; the present study in perchlorate solutions was made to find the reasons for this difference.…”

Section: Introductionmentioning

confidence: 66%

“…The rate was found to be much higher in ferric sulfate than in ferric nitrate or perchlorate solutions; the present study in perchlorate solutions was made to find the reasons for this difference. EXPERIMENTAL Pure silver (99.97%) cylinders were rotated in 500 ml of solution, at controlled temperatures and speeds as described before (2). Stock solutions of the best commercial reagents were standardized and diIuted to prepare mixtures.…”

Section: Introductionmentioning

confidence: 99%

The Rate of Corrosion of Silver in Ferric Perchlorate Solutions

King¹,

Lang²

1952

Silver dissolves much more slowly in ferric perchlorate and nitrate than in ferric sulfate solutions. A detailed study of the rate in perchlorate solutions has been made, with the effect of concentration of ferric, ferrous, and silver ions, of other salts including sulfates, and of stirring speed, temperature, and electrical polarization. Two factors are responsible for the difference in rates: (a) silver perchlorate is more strongly adsorbed on silver than silver sulfate is, and (b) a sulfato‐ferric complex ion reacts more rapidly than the normal hydrated ferric ion. Spectrophotometric evidence is given for the existence of the sulfato‐ferric ion.

“…Formation of purple ion from green automatically slows down the conversion, since it increases the acidity. EXPERIMENTAL Cylinders of Special Purity zinc, 2 about 2.5 cm long and 2.0 to 1.6 cm in diameter (decreasing with use), were rotated in the solutions as in previous work (1)(2)(3). A few experiments with analytical grade zinc showed no significant difference except in hydrochloric acid alone.…”

Section: November 1953mentioning

confidence: 99%

“…It was desired to compare the reaction kinetically with reactions of similar type, for example, the oxidation of copper and silver by ferric and eerie ions (1)(2)(3). Finally, it was hoped to compare the reaction of zinc with that of iron and cadmium, where the driving potentials are smaller; this aim has been only partly realized.…”

Section: Introductionmentioning

confidence: 99%

The Rate of Dissolution of Zinc and Cadmium in Chromic Chloride Solutions

King

Mayer

1953

Self Cite

The relative potentials of the zinc-zinc ion, chromous-chromic ion systems might lead one to expect smooth progress of the reaction Zn + 2Cr +++ ~ Zn + § + 2Cr ++. However, various other reactions are possible, and the dissolution or corrosion process is complicated; it is electrochemical in nature, and, in some solutions, rapid enough to permit transport control of the rates. The dissolution rate is highly dependent on the form of chromic ion present, on pretreatment of the metal surface, in some solutions on the acidity, and, under some conditions, the main reaction is hydrogen evolution with little reduction of chromic ion.