Equilibrium metal phase

Electrodes such as Cu VCu which are reversible with respect to the ions of the metal phase, are referred to as electrodes of the first kind, whereas electrodes such as Ag/AgCl, Cl" that are based on a sparingly soluble salt in equilibrium with its saturated solution are referred to as electrodes of the second kind. All reference electrodes must have reproducible potentials that are defined by the activity of the species involved in the equilibrium and the potential must remain constant during, and subsequent to, the passage of small quantities of charge during the measurement of another potential. 

For a multi-stage counter-current extraction operated in true equilibrium without side reactions, the partitioning of a solute into the metal phase (fm) and the salt phase (fs) is defined as follows ... 

In the state of equilibrium between both phases, i.e. the solution phase eontaining the M" species and the solid metal phase, the sum of the chemical potentials in both phases are equal. Sinee charged speeies are involved, the usual chemical potential jUi has to be extended by a term representing the work neeessary to bring one mol of charged species with a charge of Zj e into a phase where an eleetrostatie potential E is present... 

The interfacial tension always depends on the potential of the ideal polarized electrode. In order to derive this dependence, consider a cell consisting of an ideal polarized electrode of metal M and a reference non-polarizable electrode of the second kind of the same metal covered with a sparingly soluble salt MA. Anion A is a component of the electrolyte in the cell. The quantities related to the first electrode will be denoted as m, the quantities related to the reference electrode as m and to the solution as 1. For equilibrium between the electrons and ions M+ in the metal phase, Eq. (4.2.17) can be written in the form (s = n — 2)... 

The metal ion level at the surface is equal to the metal ion level in the metal interior, if ionic equilibrium is established between the surface and the interior of the metal phase. However, the imitary metal ion level, a, at the surface differs in general from the unitary metal ion level, aj, in the interior of the solid. The metal ion in the interior is located at a lattice site or at an interstitial site ... 

Since the electrochemical potential of electrons in metals is a function of the inner potential of the metal (P ca) = p. - inner potential difference, Mmb, across the interface where electron transfer is in equilibrium is represented by the difference in the chemical potential of electrons between the two metal phases A and B is shown in Eqn. 4-8 ... 

Starting from point 1, a small amount of hydrogen goes into solution in the metal phase as the H2 pressure increases. At point 2, the hydriding reaction begins (Eq, l) and H2 is absorbed at nearly constant pressure. This pressure Pp is termed the "plateau pressure" and corresponds to a two-phase mixture of metal. Me, and metal hydride, MeHx. At point 3, the metal has been completely converted to the hydride phase. Further increases in H2 pressure (point h) result in only a small addition of hydrogen in solution in the hydride phase. In principle this curve is reversible. Extraction of H2 from the gas phase results in the dissociation of the hydride phase in an attempt to maintain the equilibrium plateau pressure. 

Due to the potential high-temperature application of nanocomposites, as well as the fact that metal-reinforced ceramic nanocomposites combine metal and non-metal phases in equilibrium, it is important to understand the oxidation resistance of such materials. Using the Ni-alumina system as an example, and following Sekino et al.,12 the partial pressure of oxygen required to prevent the formation of nickel spinel (NiAl204) from a two-phase mixture of Ni and A1203 can be described as 58,59... 

When the equilibrium mixture is permitted to cool rapidly, the heavier salt phase settles and solidifies, thus leaving the lighter metal phase on top as a liquid. Inasmuch as calcium metal starts to precipitate and settle before the solidification point of the salt phase is reached, some of the calcium is trapped in the salt phase and, together with the calcium which is dissolved by the molten salt, is not recovered in the following synthesis. Once the sodium chloride-calcium chloride layer has solidified, however, the precipitating calcium remains trapped in the metal layer. When the metal layer freezes, its composition consists of calcium crystals embedded in a sodium matrix which may be removed by preferential reaction with a lower alcohol.9... 

By combining the thermodynamic data with those on the structure of the equilibrium binary phase diagram, R. Pretorius et al 261,262 were able to improve the accuracy of predicting the sequence of compound-layer formation in the transition metal-aluminium systems. For this, they used the values of the standard enthalpies (heats) of formation of the compounds. 

By a reducing phase is meant hydrogen or any metal phase which is supposed to stand in a dynamic equilibrium with it, so that the action of the different cathode materials can be taken as equal, a condition which can be experimentally obtained by the choice of a cathode potential which remains always the same. 

Americium is separated from plutonium by a liquid-liquid extraction process involving immiscible molten salt and molten plutonium metal phases. The molten salt extraction process is based upon equilibrium partitioning (by oxidation-reduction reactions) of americium and plutonium between the molten chloride salt and molten plutonium metal phases. 

The salt-to-metal term (s/m) is the weight ratio of the liquid salt and metal phases present at equilibrium. The actual weights of the liquid salt and metal present at equilibrium may be estimated from the feed weights by factoring in the weight changes caused by (1) transfer of plutonium and americium from the metal to the salt, (2) transfer of magnesium from the salt to the metal, (3) salt take-up of plutonium insoluble impurities associated with the plutonium metal feed, (4) build-up and release of salt and metal on the crucible and stirrer, and (5) evaporation of volatiles, such as Mg, from the metal. 

Two unit operations are used in the equilibration of the salt and metal phases (1) intermixing of salt and metal, and (2) disengagement of salt and metal. Because this is a batch extraction, both operations (intermixing and disengagement of phases) occur sequentially in the same vessel. For practical operation of the molten salt extraction process, attainment of equilibrium or near-equilibrium conditions (when the value of F approaches 1) in a relatively short period of time is essential. 

There is no thermodynamic equilibrium between the ideally polarizable electrode (more exactly the metal phase) and the solution phase because there is no common component capable of changing its charge and being transferred between the phases, conditions necessary for equilibrium. The state of an ideally polarizable electrode is well defined only if an external source is used to maintain a constant polarization potential, i.e., the double-layer capacitor charged with a definite charge. The polarization potential is an independent parameter of the system. 

Wt of solute in salt phase Wt of solute in metal phase Kd = distribution coefficient (as defined above) s/m = salt to metal ratio by weight F = fraction of equilibrium attained 0 = effects of side reactions... 

The equilibrium metal concentrations in the aqueous and organic phases and the equilibrium acidity of the aqueous phase are presented along with the calculated values for the distribution coefficient in Table IV. 

The adsorbed atoms formed in step 1 are mobile on the surface and must be considered as belonging to the metallic phase although their bonding to the metal is considerably ionic in character. Pertinent results were obtained by investigating the dependence of the equilibrium concentrations of adsorbed atoms on the equilibrium potential in the case of a silver electrode (3). It was shown that the adsorbed atoms are partially... 

---