Solution-metal oxide interface

Adsorption-Desorption Kinetics at the Metal-Oxide-Solution Interface Studied by Relaxation Methods... 

A more complicated model situation is demanded if one thinks of the equivalent circuit for an electrode covered with an oxide film. One might think of A1 and the protective oxide film that grows upon it during anodic polarization. One has to allow for the resistance of the solution, as before. Then there is an equivalent circuit element to model the metal oxide/solution interface, a capacitance and interfacial resistance in parallel. The electrons that enter the oxide by passing across the interfacial region can be shown to go to certain surface states (Section 6.10.1.8) on the oxide surface, and they must be represented. Finally, on the way to the underlying metal, the electron... 

Yasunaga, T., and Ikeda, T. (1986). Adsorption-desorption kinetics at the metal-oxide-solution interface studied by relaxation methods. ACS Symp. Ser. 323, 230-253. 

See especially Chaps. 2 and 3 in D. L. Sparks and D. L. Suarez, op. cit.10 A summary review of chemical relaxation methods is given by T. Yasunaga and T. Ikeda, Adsorption-desorption kinetics at the metal-oxide-solution interface studied by relaxation methods, Chap. 12 in J. A. Davis and K. F. Hays, op. cit.2... 

To describe in detail such a specific system as the metal oxide/solution interface, it is necessary to prepare a model describing dependences between potential and surface charge and draw up reactions, the occurrence of which leads to the changes of surface charge o-The reaction equations describing an equilibrium state between the surface and solution as well as values of equilibrium constants of these reactions provide detailed information... 

Yasunaga, T., and T. Ikeda. 1986. Adsorption-desorption kinetics of the metal-oxide-solution interface studied by relaxation methods, p. 230-253. In J.A. Davis and K.F. Hayes (ed.) Geochemical processes at mineral surfaces. Proc. Am. Chem. Soc. Symp. Ser. 323, Chicago, IL. 8-13 Sept. 1985. ACS, Washington, DC. 

Yasunaga, T. and T. Ikeda (1986), Adsorption-Desorption Kinetics at the Metal-oxide-Solution Interface studied by Relaxation Methods, in J. A. Davies and K. F. Hayes, Eds., Geochemical Processes at Mineral Surfaces, American Chemical Society, Washington, DC, pp. 230-253. 

The first step in ATR-related studies involves the formation of a suitable solid-liquid interface. To obtain a metal oxide / solution interface which can be probed by ATR, several methods have been described in literature. 

A mechanism such as that given above provides explanations for the known effects of many process variables ". The reductive dissolution and undermining processes require access of the acid to the metal surface, hence the benefits obtained by the deliberate introduction of cracks in the oxide by cold-working prior to pickling. Also the increase in pickling rate with agitation or strip velocity can be explained in terms of the avoidance of acid depletion at the oxide-solution interface. 

The corrosion current due to diffusion of metal ions through the passivating film, and dissolution of metal ions at the oxide-solution interface. Clearly, the smaller this current, the more protective is the oxide layer. 

With regard to the assignment of ions to the mean planes in the interface, the oxide-solution interface can be compared to two ideal interfaces which are more thoroughly characterized the metal-solution interface and the silver iodide-solution interface. 

Chemical relaxation methods can be used to determine mechanisms of reactions of ions at the mineral/water interface. In this paper, a review of chemical relaxation studies of adsorption/desorption kinetics of inorganic ions at the metal oxide/aqueous interface is presented. Plausible mechanisms based on the triple layer surface complexation model are discussed. Relaxation kinetic studies of the intercalation/ deintercalation of organic and inorganic ions in layered, cage-structured, and channel-structured minerals are also reviewed. In the intercalation studies, plausible mechanisms based on ion-exchange and adsorption/desorption reactions are presented steric and chemical properties of the solute and interlayered compounds are shown to influence the reaction rates. We also discuss the elementary reaction steps which are important in the stereoselective and reactive properties of interlayered compounds. 

The basic idea of resonance tunneling relies on the reasonable assumption that there are impurity states in the oxide film (regarded as a semiconductor), the energy of which is in resonance with that of electrons in the metal on which the film has been formed. One considers the situation in terms of two coordinated tunnel transfers, one from the metal to the impurity state and then from the impurity state to an ion adsotbed at the oxide/solution interface. 

Electron transfer processes are at the heart of electrochemistry, and often the focus is on events at electrode surfaces. While the theory for electron-transfer in solution [94], and at metal surfaces [95] is rather extensive, a comprehensive theory for electron transfer at metal oxide-organic interfaces [96, 97] is still under development. This section is devoted to a discussion of some of the key elements of the surface electron transfer in dye-sensitized solar cells, illustrated by results from recent calculations. 

Fig. 13.54. Morphology of a thick oxide layer, showing crystallites, grain boundaries, and pores. The oxide/solution interface area is very large when the layer is impregnated with electrolyte solution. (Reprinted from S. Trasatti and K. Weil, Electrochemical Supercapacitors as Versatile Energy Stores, Platinum Metals Rev., 38 (2) 53, Fig. 8,1994, with permission from Johnson, Matthey Co.)...

At the beginning, the electric double layer at the solid-aqueous electrolyte solution interface was characterized by the measurements of the electrokinetic potential and stability of dispersed systems. Later, the investigations were supported by potentiometric titration of the suspension, adsorption and calorimetric measurements [2]. Now, much valuable information on the mechanism of the ion adsorption can be obtained by advanced spectroscopic methods (especially infrared ATR and diffuse spectroscopy) [3], Mosbauer spectroscopy [4] and X-ray spectroscopy [5]. Some data concerning the interface potential were obtained with MOSFET [6], and AFM [7]. An enthalpy of the reaction of the metal oxide-solution systems can be obtained by... 

The occurrence of neutral and charged ( ) surfaces at the oxide-solution interface has been attributed to the formation of metal aquo complexes as shown schematically in Fig. 12.9. 

Pivovarov, S., Acid-base properties and heavy and alkaline earth metal adsorption on the oxide-solution interface Non-electrostatic model, J. Colloid Interf. Sci., 206, 122, 1998. 

Compound semiconductors may be subject to both anodic oxidative dissolution and cathodic reductive dissolution. Let us now consider a metal oxide, MO, in aqueous solution. The anodic dissolution will occur with the oxidation of oxide ions at the metal oxide surface producing gaseous oxygen. Concurrently, the metal ions transfer from the metal oxide across the oxide-solution interface forming hydrated metal ions in the aqueous solution ... 

Interfacial phenomena at metal oxide/water interfaces are fundamental to various phenomena in ceramic suspensions, such as dispersion, coagulation, coating, and viscous flow. The behavior of suspensions depends in large part on the electrical forces acting between particles, which in turn are affected directly by surface electrochemical reactions. Therefore, this chapter first reviews fundamental concepts and knowledge pertaining to electrochemical processes at metal oxide powder (ceramic powder)/aqueous solution interfaces. Colloidal stability and powder dispersion and packing are then discussed in terms of surface electrochemical properties and the particle-particle interaction in a ceramic suspension. Finally, several recent examples of colloid interfacial methods applied to the fabrication of advanced ceramic composites are introduced. 

While it appears that no totally satisfactory model for the oxide-solution interface has emerged to date, progress is obviously being made in this area. Dispersion, hydration, hydroxylation, and acid-base properties (and, in particular, the variation of the latter with change in the oxidation state of the central metal ion) are all factors which must be combined before a model of general validity is obtained. 

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