J. Stafiej

A double layer study of the (210) and (111) faces of gold in aqueous NaBF4 SOLUTIONS

Abstract Au(111) and Au(21O) faces of gold in aqueous NaBF4 solutions have been investigated using cyclic voltammetry and admittance measurements. On Au(21O) no specific adsorption of B F 4 − has been found. The results were first analysed accepting the Gouy-Chapman-Stern model for the double layer; like Ag(11O) and Ag(100) the inner layer capacity versus charge density curve has a broad maximum. For Au(111) it was not possible to draw clear conclusions and the variation of the inner layer capacity versus charge density seems to correspond to the accepted model only for the more negative densities of charge investigated. Models for the inner layer were discussed for the (210) face.

Field theoretical approach to inhomogeneous ionic systems: thermodynamic consistency with the contact theorem, Gibbs adsorption and surface tension

Using a statistical field approach we investigate the structure of an electrolyte solution in contact with a neutral impenetrable wall. The Hamiltonian contains the Coulomb interaction and the ideal entropy. At the level of the quadratic approximation, the Hamiltonian yields the Debye-Hückel theory in the bulk. Analytic expressions of the charge-charge and potential-potential inhomogeneous correlation functions are obtained. Exact asymptotic results for point ion charge correlation functions are obtained and the profile for the fluctuation of the electric potential is calculated. We also consider the term beyond the quadratic expansion of the ideal entropy in the Hamiltonian. With this term a higher order coupling between charge density and number density produces a non-trivial profile for the total ion density. This density profile is consistent with the contact theorem and the related surface tension calculated from the Gibbs adsorption isotherm.

A FIELD THEORY STUDY OF THE EFFECT OF SPECIFIC INTERACTIONS IN IONIC SYSTEMS : A SIMPLE MODEL

The effect of specific ionic interactions on the Debye length has been studied using a simple model Hamiltonian for a binary mixture of anions and cations in the framework of the field theory. The Hamiltonian contains the Coulombic interaction and an independent non-Coulombic part describing a binary mixture of equivalent uncharged particles. We use a local and quadratic approximation to calculate the partition function via a functional integral. The Debye limiting law is obtained with a renormalized screening length. The screening is enhanced when the specific interactions favor demixion. This is illustrated on the example of an asymmetric hard sphere mixture.

Model for the mixed ion-exclusion—adsorption retention mechanism in ion-exclusion chromatography☆

The model elaborated in a previous paper for the retention mechanism in ion-exclusion chromatography was generalized to include adsorption of the solute. The computer modelling of the column performance by the Craig method was used in the case of an unbuffered mobile phase. The retention process in the case of a sufficiently buffered mobile phase turned out to be governed by a linear partition isotherm and can be described globally by simple equations. The adsorption constants of several compounds were calculated from the data available in the literature.

Numerical simulation of column performance in ion-exclusion chromatography

Abstract The separation mechanism of acidic compounds in ion-exclusion chromatography has been described using two approaches. The first one is based on the global thermodynamic and chromatographic relationships, the other on a computer simulation of the column performance. Strong acids leave the column unseparated, within its dead volume, and weak acids appear at the end of the chromatogram also unseparated. It was found that the addition of an acidic compound eliminates the dependence of the retention volume on the sample concentration. By use of the computer simulations, the evolution of the chromatographic peaks with time and the peak shape for the sample analyzed have been studied. The results compare favourably with the experimental data available in the literature.

The Cooper-Harrison catastrophe in the case of the multistate models for unassociated solvent structure at polarizable interfaces

The possibility of occurrence of the so-called Cooper—Harrison catastrophe has been discussed in the case of a multistate model for unassociated solvent structure at a polarizable interface by Fawcett and de Nobriga. The catastrophe is avoided when the effective coordination number, Cc, is greater than 14.5. The case when Cc < 14.5 has been discussed.

Corrosion-passivation processes in a cellular automata based simulation study

A short survey of cellular automata based models for corrosion and passivation phenomena is given. Results of simulations based on the model of spatially separated anodic and cathodic reactions are presented for a cavity development from a point-like damage of a protective layer and from an initially flat unprotected surface. We show some new peculiar examples of the symmetry breaking in the cavity development. The results for the initially flat surface show roughening of the surface at the beginning of the corrosion process. After that, pit merging causes a resmoothing of the surface. An oscillatory behavior of the surface roughness is observed caused by a peninsula formation with subsequent island detachment. These results are obtained in 2D because of computational limitations. We plan simulations in 3D and point out the problems we encounter in their realization.

Field theory for ionic systems. From fluctuations and structure at a hard wall to thermodynamics

Abstract We use a field theoretical approach to study ionic systems. In this paper we illustrate this formalism in a grand canonical ensemble for the long range Coulomb potential. For the inhomogeneous system near a hard neutral plane wall we go beyond the well known Debye–Huckel electrolyte results and predict the existence of a desorption profile. The results are compared with well established sum rules for ionic systems and thermodynamic relations are verified. We also calculate the differential capacitance in a slab using the linear response theory. The capacitance is calculated from the charge–charge correlations for the neutral system using the fluctuation–dissipation theorem.

Solvent structure at the mercury/solution interface in dimethylsulphoxide

The entropy of formation of the Hg/DMSO interface, ΔSi, has been evaluated from the temperature dependences of the double-layer capacity, zero charge potential and electrocapillary maximum. At the pzc, ΔSm-s0 is negative, implying that the solvent is more structured at the Hg/solution interface than in the bulk. ΔSi,σ has a maximum at negative charge densities. The charge dependence of the potential drop in the inner layer is discussed in terms of the dipole potential and dipole orientation.

Cellular automata approach to corrosion and passivity phenomena

Our research on employing the cellular automata methodology to corrosion and passivation phenomena is reviewed. Examples of a peculiar pit development are found and presented. The diffusion rate in the corroding medium is argued and shown in the simulation results to affect mainly the characteristic length scale for the corrosion process. New data for the pitting corrosion development on a planar interface are presented and discussed.