Walter Bogaerts

Electrochemical Frequency Modulation: A New Electrochemical Technique for Online Corrosion Monitoring

Abstract Since a corrosion process is a nonlinear electrochemical phenomenon, a potential perturbation signal by one or more sine waves will generate current responses at more frequencies than the ...

Materials for photothermal solar energy conversion

Commencally or potentially available selective and non-selective absorber surfaces for solar heat collectors are reviewed and the state-of-the-art of solar collector corrosion processes is outlined. The review of available published literature has indicated that a lack of quantitative information exists, relative to corrosion of collector surfaces. Available information (mostly qualitative) on durability aspects and corrosion of solar receiver surfaces is described to indicate potential corrosion problem areas and corrosion prevention possibilities. An outline of appropriate durability tests is presented.

The physical meaning of noise resistance

The noise resistance defined as the ratio of the standard deviations of the potential noise and the current noise has been empirically correlated to the polarization resistance in order to calculate the corrosion rate. The attitudes of investigators towards this correlation are still controversial because it is often said to lack theoretical background. Based on the principal electrochemical theory. a mathematical derivation of the noise resistance in electrochemical noise measurements is presented in this paper. It shows that the noise resistance is indeed equivalent to the polarization resistance.

Instantaneous Corrosion Rate Measurement with Small-Amplitude Potential Intermodulation Techniques

Abstract With the intermodulation technique, a potential distortion using two sine waves is applied to a corrosion system. The alternating current (AC) response consists of amplitudes measured at different frequencies. Simple relations are derived from the current-vs-potential relation for a corroding process under activation control, from which the corrosion rate and Tafel parameters can be calculated. These are valid when the amplitude of the applied potential distortion is sufficiently small. With the intermodulation technique, the corrosion rate and Tafel parameters can be obtained within one measurement, which makes this technique an ideal candidate for application as a corrosion monitoring tool. Results obtained with this technique were shown to be in agreement with other electrochemical methods for corrosion rate measurement, such as Tafel extrapolation, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS).

A theoretical study of AC-induced corrosion considering diffusion phenomena

The effect of AC-induced voltages on corrosion systems was investigated. Two cases were distinguished: the anodic and cathodic reactions were under activation control, the anodic reaction was under activation control and the cathodic reaction was under mixed control. For the first case simple relations could be derived that relate the AC-induced voltage with the corrosion potential and corrosion rate. For the second case numerical analysis was necessary to obtain these relations. It was shown that the influence of the AC-induced voltages on the corrosion behaviour strongly depended on the Tafel parameters. As the cathodic reaction was under mixed control the increase of the corrosion rate was limited to the diffusion-limited current density.

Concept-based retrieval of hypermedia information: from term indexing to semantic hyperindexing

Abstract The key to unlocking the information retrieval potential of hypertext and hypermedia systems lies in a more semantics-aware indexing of the information in the hypernetwork, and in the effective visualization and navigation of this hypermedia index structure. We briefly highlight the information retrieval issues specific to hypertext and hypermedia systems, and discuss our concept-based information retrieval model for hypertext. We then examine in detail two different approaches to the concept-based indexing of hypermedia information which we developed during the Active LibraryTM on Corrosion project: term indexing with three-dimensional index navigation and semantic hyperindexing with broad-button link navigation. Finally, we discuss how a conceptbased indexing technique could represent a significant step towards a more intelligent retrieval of hypermedia information.

Electrochemical Emission Spectroscopy for Monitoring Uniform and Localized Corrosion

Abstract A modified electrochemical noise (EN) technique (electrochemical emission spectroscopy [EES]) was developed for nondestructive, real-time corrosion rate measurements. Unlike conventional c...

Simple and Robust External Reference Electrodes for High-Temperature Electrochemical Measurements

Two simple and robust designs for an external high-temperature reference electrode are described. The first external reference electrode uses a movable polytetrafluoroethylene (PTFE) piston to maintain the pressure balance between the reference solution and test solution. The second external reference electrode uses the test solution as reference solution, and this is feasible if the test solution contains a minimum amount of chloride. For both electrodes it is necessary to determine the potential drop across the (cooled) salt bridge, which connects the reference electrode to the autoclave. It is shown that a simple correction algorithm can be used to calculate this potential drop and that the corrections are in agreement with literature values. It is also shown that this correction algorithm is independent of the solution composition for a wide range of neutral and alkaline solutions. The potential difference between two standard hydrogen electrodes (SHE) at different temperatures has been determined. This potential difference has been used to extend the correction algorithm to be able to calculate the potential against the SHE at 25°C.

Harmonic analysis of corroding systems considering diffusion phenomena

Due to the nonlinear nature of a corroding system, a sinusoidal potential distortion results in an ac current response, which contains higher harmonics. These harmonics can be measured and evaluated to obtain kinetic information, for example the corrosion rate and Tafel parameters. A model was developed for the case that the anodic reaction was charge transfer controlled and the cathodic reaction was under mixed control, i.e., both the charge-transfer and diffusion determine the reaction rate. This model was used to obtain the corrosion rate and Tafel parameters for the corrosion of mild steel in an aerated sodium sulfate solution.

Application of Electrochemical Impedance Spectroscopy for Monitoring Stress Corrosion Cracking

Abstract The present study investigated whether electrochemical impedance spectroscopy (EIS) could be used to monitor stress corrosion cracking (SCC). First, a model was developed that interpreted the impedance response of a cracked surface (i.e., the model could distinguish between a flat electrode surface and a surface with cracks). Experiments on stainless steel (SS) electrodes with artificial “crack” (electrically drilled small holes) in 0.1 M sodium sulfate (Na2SO4) showed that the influence of the artificial “cracks” on the impedance response was reflected mainly in the phase shift at frequencies between 100 Hz and 1 Hz. To generate real stress corrosion cracks, slow strain rate tests (SSRT) were performed with a sensitized Type 304 SS (UNS S30400) specimen in a 5-N sulfuric acid (H2SO4) + 0.1-M sodium chloride (NaCl) solution at room temperature. Analysis of the fracture surface clearly showed intergranular attack, suggesting that stress corrosion cracks were formed. Impedance measurements were per...