Ion dissolution

The first assumption of this treatment is metal ion dissolution through the protective film, as shown in Fig. 34, where the potential difference between both sides of the film is defined as y, t). The potential... 

Fig. 9-4. Anodic and cathodic polarization curves measured for transfer of divalent cadmium ions (dissolution-deposition) at a metallic cadmium electrode in a sulfate solution (0.005MCd + 0.4MS04 ) i (i )= anodic (cathodic) reaction current a = Tafel constant (transfer coefficient). [From Lorenz, 1954.]...

Fig. 9-5. Anodic and cathodic polarization curves observed for transfer of divalent iron ions (dissolution-deposition) at a metallic iron electrode in a sulfuric add solution at pH 4 (0.5MFesS04-)-0.5MKaS04) = anodic iron dissolution (cathodic iron...

In the stationary state of anodic dissolution of metals in the passive and transpassive states, the anodic transfer of metallic ions metal ion dissolution) takes place across the film/solution interface, but the anodic transfer of o Q en ions across the Qm/solution interface is in the equilibrium state. In other words, the rate of film formation (the anodic transfer oS metal ions across the metal lm interface combined with anodic transfer of osygen ions across the film/solution interface) equals the rate of film dissolution (the anodic transfer of metal ions across the film/solution interface combined with cathodic transfer of oitygen ions across the film/solution interface). 

Ion dissolution, such as in the salt type minerals when, for example, Ag+ and I- dissolve unequally when Agl is placed in water. 

The origin of the electrostatic force is the surface charge that solid particles acquire when they are immersed in a liquid that contains a sufficient amount of ions. Possible charging mechanisms are ionisation, ion adsorption and ion dissolution, which are now discussed. 

Upon conlacl wilh an aqueous medium, most materials acquire a surface electric charge. A variety of processes have charging mechanisms, including ion adsorption, ionization, and ion dissolution. 

Ion dissolution This is less common for pharmaceutical cases. Ionic charges are acquired by the unequal dissolution of the oppositely charged ions due to the excessive presence of ions in a solution. The concentrations of the excessive ions determine the electrical potential at the surface (i.e., potential determining ions). 

However, information is still rare regarding the effects of ultraviolet fight on the zero-valent iron system. In the case of nitrate reduction by Fe(0), a detrimental effect of 254-nm irradiation on ferrous ion dissolution and ni-... 

Initially, crystallite growth occurs rapidly either by ion dissolution/reprecipitation (Ostwald ripening) or by surface atom diffusion, due to the requirement for lowering the surface energy of any individual crystallite. This thermodynamic driving force will tend to eliminate the incomplete faces but with the drive to lower the surface energy, the crystallites also will strive towards sphericity. This means, that to all intents and purposes, the ratios ofthe (111) and (100) faces should be approximately the same. Bett et al.1 noted that as the platinum crystallite sizes grew, the size distribution increased. If this is so, then... 

The mechanisms for electrocatalyst surface area loss are by a) crystallite migration or b) atom or ion dissolution and reprecipitation, either to the electrolyte or over the carbon surface. It is well known that surface diffusion of atoms on the individual crystallites can provide for mobility (much like the treads on a military tank). In either case, small crystallite become annihilated and fewer but larger crystallites are produced.18 In either event, these processes lead to demetallization of the less noble components in the alloy. 

As mentioned above, the dispersion stability of the slurry is directly related with CMP performance, removal rate, within-wafer nonuniformity (WIWNU), which is defined as the standard deviation divided by the average of remaining thickness after CMP, microscratching, and the remaining particle on the wafer. To avoid poor CMP performance, the dispersion stability of the slurry must be controlled by preventing silicon ion dissolution. Surface modification of the silica particle was produced by addition of an organic additive. Without surface modification, the amount of silicon dissolution was 1.370 0.002 mol/L, while surfaces modified with poly(vinylpyrrolidone) (PVP) polymer yielded a dissolution of 0.070 0.001 mol/L, almost 20 times less than the unmodified surface. 

CaC03(s) Calcium carbonate (limestone) - Precipitation- Ca2+ Calcium ion dissolution reactions + CO - Carbonate ion -8.3b 11.6... 

In some cases a compound contains more than two kinds of ions. Dissolution of the slightly soluble compound magnesium ammonium phosphate, MgNH PO, in water and its solubility product expression are represented as... 

In the opposite case, hv > g, photons produce electron-hole pairs. Accumulation of holes at the oxide surface increases the local potential drop which may cause a fast photocorrosion. Ion migration is enhanced in the thin film, corrosion is enhanced, and altogether a fast dissolution of metal takes place by a photoelectro-chemical process in the passive film. An example is given for Ti [160]. This technique can be used for microstructuring of Ti- or Al surfaces [104]. On the other hand, anodic metal ion dissolution competes with the opposite anodic film forming ITR of oxygen ions. Therefore, in dependence on the special conditions, laser induced oxide growth may overcome pit formation [160]. 

If the release of ions (dissolution) is the only reaction, and the metal is not connected to an external circuit, a surplus of electrons is produced in the metal. It becomes more negative, and the dissolution rate is reduced. At the same time the concentration of positive metal ions in the liquid increases, causing an increasing... 

Ni Sorption on Clay Minerals A Case Study. Initial research with Co/clay mineral systems demonstrated the formation of nucleation products using XAFS spectroscopy, but the stmcture was not strictly identified and was referred to as a Co hydroxide-like stmcture (11,12). Thus, the exact mechanism for surface precipitate formation remained unknown. Recent research in our laboratory and elsewhere suggests that during sorption of Ni and Co metal ions, dissolution of the clay mineral or aluminum oxide surface can lead to precipitation of mixed Ni/Al and Co/Al hydroxide phases at the mineral/water interface (14,16,17,67,71). This process could act as a significant sink for metals in soils. The following discussion focuses on some of the recent research of our group on the formation kinetics of mixed cation hydroxide phases, using a combination of macroscopic and molecular approaches (14-17). 

This process describes the reaction of metal atoms with ligands L forming metal ions (dissolution, corrosion) or the deposition of metal atoms by reduction of metal ions. The solvent molecules are a special example of ligands that reacts with the metal ions. A partial step of the total process, ad-atom deposition and dissolution, was aheady discussed in Chapter 4. The rate equations are similar to Eqs. (6.2) and (6.3). 

Ion dissolution Unequal dissolution of ions in the case of ionic substances can lead to a net charge on the substrate. A classical example of this mechanism is the silver iodide surface. When silver iodide is immersed in an aqueous environment, dissolution occurs as Agl Ag "-h 1 . Since the solubility product for this equilibrium is relatively small (K p = ciAg cir 10 ), the concentrations of Ag " and I" in solution are small. The surface of the crystal consists of an array of Ag " and 1 ions in cubic close packing, and no net charge develops when the number of each ion is the same. However, an equal number of each ion on the surface does not occur at the concentration where there are equal numbers of Ag" " and I ions in the solution. Instead, due to their higher affinity for the surface, the iodide ions tend to... 

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