Silver, phase equilibria

Partial Miscibility in the Solid State So far, we have described (solid + liquid) phase equilibrium systems in which the solid phase that crystallizes is a pure compound, either as one of the original components or as a molecular addition compound. Sometimes solid solutions crystallize from solution instead of pure substances, and, depending on the system, the solubility can vary from small to complete miscibility over the entire range of concentration. Figure 14.26 shows the phase diagram for the (silver + copper) system.22 It is one in which limited solubility occurs in the solid state. Line AE is the (solid -I- liquid) equilibrium line for Ag, but the solid that crystallizes from solution is not pure Ag. Instead it is a solid solution with composition given by line AC. If a liquid with composition and temperature given by point a is... 

Also, in the case of more complex electrochemical processes, these conditions may hold. Consider, for instance, the electrochemical equilibrium between Ag and Ag+ (aq) (Eq. 80). The hydrated silver ion is, finally, outside the double layer its chemical potential does not depend on the electrode potential. Since a change of the electrode potential only affects the interfacial potential drop and (see Section 4.5), it is reasonable to assume that the chemical potential of the silver atoms in the silver phase is also independent of the electrode potential. Hence, also in the case of Eq. 80, the polarization V — leads to a change of only. In contrast, if products or reactants are chemisorbed on the electrode, their chemical potential depends on the electrode potential. If the conditions presented by Eqs. 106 are valid, it also holds that... 

Suh et demonstrated that SERS could be used to detect two-dimensional phase equilibrium between a gaslike phase and a solidlike phase, for p-aminobenzoic acid adsorbed on silver. 

The concentration of the test atmosphere must be reasonably uniform throughout the chamber and should increase and decrease at a rate close to theoretical at the start or end of the exposure. Silver (1946) showed that the time taken for a chamber to reach a point of equilibrium was proportional to the flow rate of atmosphere passing through the chamber and the chamber volume. From this, the concentration-time relationship dining the run-up and run-down phase could be expressed by the equation... 

The multiphase equilibrium technique using silver as the liquid phase was resorted to in Ref.153 but the details were not given. The 7S of stainless steel containing 0.001 —0.006% boron appeared to be near 880 erg/cm2 at 1050 °C, and the 71 again was unusually high, namely about 620 erg/cm2. 

The interface structure for non-blocking interfaces is similar to that for related blocking interfaces. Thus the distribution of charge at the C/ Ag4Rbl5 interface will be similar to that at the Ag/Ag4Rbl5 interface. The major difference is that there is one particular interfacial potential difference at which the silver electrode is in equilibrium with Ag ions in the bulk electrolyte phase. At this value of A, there is a particular charge on the electrolyte balanced by an equal and opposite charge — on the metal. At any potential different from value of q different... 

Other two-component systems may exhibit either limited solubility or complete insolubility in the solid state. An example with limited solubUity is the silver-copper system, of which the reduced-phase diagram is shown in Figure 13.5. Region L represents a liquid phase, with F = 2, and S and 5s represent solid-solution phases rich in Ag and Cu, respectively, so they are properly called one-phase areas. S2 is a two-phase region, with F= 1, and the curves AB and DF represent the compositions of the two solid-solution phases that are in equilibrium at any... 

We now come to internal metal contacts in ISEs without an internal solution. As discussed above, systems without internal electrolytes are used very often, with both solid and liquid membranes. Obviously, the condition of thermodynamic equilibrium requires that common electrically-charged particles (ions or electrons) be present in electrically-charged phases that are in contact (see chapter 2). ISEs with a silver halide membrane to which a silver contact is attached are relatively simple. In the system... 

The following table lists the standard electrode potentials (in V) of some electrodes of the second kind.13 These consist of three phases. The metal is covered by a layer of its sparingly soluble salt and is immersed in a solution of a soluble salt of the anion. Equilibrium is established between the metal atoms and the solution anions through two partial equilibria one between the metal and its cation in the sparingly soluble salt and the other between the anion in the solid phase of the sparingly soluble salt and the anion in solution. The silver chloride electrode is preferred for precise measurements. 

Point C The two curves AC and BC meet at a common point C. Therefore, C gives conditions of temperature and composition under which three phases, viz., solid silver, solid lead and solution co-exist in equilibrium. It is thus a non-variant point as,... 

Equilibrium between the solid and liquid phases of silver (freezing point of silver) 1,235.08 961.93... 

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... 

Since the silver ion is at equilibrium in the two phases (otherwise this electrode would not act as a reversible Ag/AgCl/Cl electrode), it follows from Eqs. 17H and 18H that... 

The first equation represents the equilibrium between hydrated Ag+ ions and Ag atoms in a single-crystal configuration. Alternatively, we may say that there is a heterogeneous thermodynamic equilibrium between Ag+ ions in the solid phase (where they are stabilized by the gas of free electrons) and Ag+ ions in the liquid phase (stabilized by interaction with water molecules). The forward reaction step corresponds to the anodic dissolution of a silver crystal. On an atomic level, one may say that a Ag" " core ion is transferred from the metallic phase to the liquid water phase. In an electrochemical cell, an electron flows from the Ag electrode (the working electrode) to the counter electrode each time that one Ag+ ion is transferred from the solid to the liquid phase across the electrochemical double layer. Although the electron flow is measured in the external circuit between the working... 

They concluded that exchange exceeding the equilibrium value is due to phase transition. During aging the total number of precipitate particles decreases strongly. Meehan and Chiu found that for colloidal silver bromide the number of particles decreased 80-fold during the aging that occurred after 2 min and up to 1 day. 

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