Silver ion migration

Because of the high values of conductivity which in individual cases are found at room temperature, such compounds are often called superionic conductors or ionic superconductors but these designations are unfounded, and a more correct designation is solid ionic conductors. Strictly unipolar conduction is typical for all solid ionic conductors in the silver double salts, conduction is due to silver ion migration, whereas in the sodium polyaluminates, conduction is due to sodium ion migration. 

Many oxidation/reduction reactions can be carried out in either of two ways that are physically quite different. In one, the reaction is performed by bringing the oxidant and the reductant into direct contact in a suitable container. In the second, the reaction is carried out in an electrochemical cell in which the reactants do not come in direct contact with one another. A marvelous example of direct contact is the famous silver tree experiment, in which a piece of copper is immersed in a silver nitrate. solution (Figure 18-1). Silver ions migrate to the metal and are reduced ... 

Strictly unipolar conduction is typical for all solid ionic conductors in the silver double salts, conduction is because of silver ion migration, while in the sodium polyaluminates, conduction is because of sodium ion migration. 

When high-conductivity electrolytes, in particular RbAg4l5, were discovered they opened the way for the development of batteries for higher discharge current. A battery with such an electrolyte can have a silver anode and an iodine cathode. In the course of the operation of batteries, silver is dissolved and the silver ions migrate through the solid electrolyte and react with the iodine ions produced in the cathodic reaction the final reaction product is silver iodide, Agl. 

Herewith we can calculate a maximum possible partial conductivity for a substance, for example, silver iodide. Assuming that the silver ions migrate with thermal velocity V from one lattice site to another without oscillating at each lattice site, we get a jump frequency v = vla = 3.4 X 10 s at a temperature of 300°C, a diffusion coefficient of Dkj =5.6 X 10 cm /s, and the maximum conductivity is (T(max) =2. Q cm for a jump distance of 1 A. The measured conductivity is a = 1.97 cm which is not much less than the calculated value. 

Silver ion migration and antimicrobial activity of PLA/silver zeolite composites were investigated. Films prepared by solution-casting/solvent evaporation presented an extended release of silver ions into food simulants and TSB (tryptone soy broth). Antimicrobial activity against Staphylococcus aureus and E. coli was significant, although the concentration of silver in simulants exceeded the legal limit. ... 

Figure 9-8. Left Under the influence of an electric field applied across silver conductors, positively charged silver ions migrate from the anode to the cathode where they plate out, forming a dendritic structure that eventually grows back towards the anode and causes an electrical short. Right Micrograph of a silver dendrite.

An instructive use has been made of the solid electrolyte, Agl, which conducts by the migration of silver ions. If this material is used as an electrolyte in the cell... 

The pressed disc (or pellet) type of crystalline membrane electrode is illustrated by silver sulphide, in which substance silver ions can migrate. The pellet is sealed into the base of a plastic container as in the case of the lanthanum fluoride electrode, and contact is made by means of a silver wire with its lower end embedded in the pellet this wire establishes equilibrium with silver ions in the pellet and thus functions as an internal reference electrode. Placed in a solution containing silver ions the electrode acquires a potential which is dictated by the activity of the silver ions in the test solution. Placed in a solution containing sulphide ions, the electrode acquires a potential which is governed by the silver ion activity in the solution, and this is itself dictated by the activity of the sulphide ions in the test solution and the solubility product of silver sulphide — i.e. it is an electrode of the second kind (Section 15.1). 

Selectivity to primary metathesis products is usually less than 100%, as a consequence of side reactions, such as double-bond migration, dimerization, oligomerization, and polymerization. The selectivity can be improved by adding small amounts of alkali or alkaline earth metal ions, or, as has recently been shown, thallium 40), copper, or silver ions (41)-... 

Since, in both these reactions (i.e. KI or Rbl and Agl), product formation occurs on both sides of the original contact interface, it is believed that there is migration of both alkali metal and silver ions across the barrier layer. Alkali metal movement is identified as rate limiting and the relatively slower reaction of the rubidium salt is ascribed to the larger size and correspondingly slower movement of Rb+. The measured values of E are not those for cation diffusion alone, but include a contribution from... 

Auother uauostructuriug techuique shares some commou features with that described above and is shown in Fig. 36.3. A polymer-coated Pt ultramicroelectrode is used as the tip of a STM, and graphite is used as substrate. Ag atoms are deposited on the tip at underpotentials, so that approximately one atomic monolayer is deposited on the tip. After this, a first bias pulse is applied to the tip, causing the formation of a shallow pit. Then a second bias pulse with a smaller amplitude is applied to cause the desorption of silver from the tip. The silver ions desorbed diffuse aud migrate across the tip-sample gap aud deposit ou the high coordiuatiou sites preseut... 

Salts such as silver chloride or lead sulfate which are ordinarily called insoluble do have a definite value of solubility in water. This value can be determined from conductance measurements of their saturated solutions. Since a very small amount of solute is present it must be completely dissociated into ions even in a saturated solution so that the equivalent conductivity, KV, is equal to the equivalent conductivity at infinite dilution which according to Kohlrausch s law is the sum of ionic conductances or ionic mobilities (ionic conductances are often referred to as ionic mobilities on account of the dependence of ionic conductances on the velocities at which ions migrate under the influence of an applied emf) ... 

The liberated electron is free to move in the structure and migrates to an interstitial silver ion, Ag, which is part of a Frenkel defect, to form a neutral silver atom Ag ... 

Adding copper(l) chloride to the molten glass makes the process reversible. When light intensity diminishes, copper ions remove electrons from silver atoms, converting the silver atoms into silver ions. The silver ions then migrate back to the silver chloride crystals. The glass becomes transparent again. 

Other electrolytes, such as sodium sulfate or potassium nitrate, could be chosen for the salt bridge. Neither of these electrolytes interferes in the cell reaction. Silver nitrate, AgN03(aq), would be a poor choice for the salt bridge, however. Positive silver ions would migrate into the half-cell that contains the cathode. Zinc displaces both copper and silver from solution, so both copper(n) ions and silver ions would be reduced at the cathode. The copper produced would be contaminated with silver. 

The separator used in silver—zinc cells should be permeable to water and hydroxyl ions, stable in strong alkaline solutions, and not oxidized by the solid silver oxide or dissolved silver ions and should retard the migration of dissolved ions to the anode. 

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