Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Periodic Report Summary 1 - SISET (Enhancing Scanning Ion-Selective Electrode Technique)


Project Context and Objectives:

Scientific component of the joint exchange program SISET aimed at extending the capacity of Scanning Ion-selective Electrode Technique (SIET) and enhancing the value of data collected by several localized electrochemical techniques. The main focus of the consortium was on scanning microelectrode techniques for in-situ electrochemical measurements which provided valuable analytical information on actively changing interfaces. The experimental tools and procedures for simultaneous SVET-SIET and SVET-SIET-SPET measurements have been developed and tested (SVET-Scanning Vibrating Electrode Technique and SPET-Scanning Polarographic Electrode Technique). These techniques used simultaneously proved to bring very important added value by becoming every-day methods used in Partners’ institutions, namely at IST, VUB, UAVR and IMR. Vibration of either SVET or SIET microelectrodes was shown to have little influence on local mixing and thus does not affect local ion distribution to any significant extent.

A working modeling software tool has been made available in which fluid flow, induced by the mechanically vibrating SVET is simulated in time (this means fluid structure interaction was achieved). This flow is linked with a full multi-ion and reaction model such that concentration variations are simulated in time and space. Today the tool is limited to two-dimensional and axi-symmetrical geometries. The software tool has been used for studying the role of SVET and SVET-SIET in relevant situations encountered in practice. In performing corrosion simulations two main problems were encountered when comparing them with measurements. First there is always the influence of micro-convection in the measurements. This problem was not expected but has been solved now by introducing in the simulations an additional turbulent diffusion that is function of the distance to the walls. The second problem is related to reproducing in simulations distributions of measured species in space or time. Although qualitative match is achieved, numerical comparison still suffers from lack on mechanistic knowledge.

Plasticizer free pH-selective solid-contact microelectrodes were developed and fully characterized. The developed microelectrodes demonstrated better short- and long term stability even with longer periods of exposure to a solution compared to traditional glass-capillary and PVC-based membranes presented earlier. Owing to their advanced characteristics, the developed microelectrodes are expected to bring high quality, reliable data characterizing localized processes occurring at actively corroding sites. Developed solid-contact electrodes were used to approach the potentiometric measurements in vibrating mode. Although solid-contact microelectrodes indeed allowed for faster rastering of sample of interest (compared to direct potentiometry), micro-potentiometric measurements with vibrating ion-selective micro-electrode provide limited information for corrosion research. This is mostly due the fact that the measurements in vibrating mode yield the values of fluxes of specific ion rather than distribution of its concentration.

Membrane compositions of the most important for corrosion research sensors, namely for hydrogen-, sodium- and chloride-selective microelectrodes were described and all analytical characteristics established at the beginning of SISET project were successfully achieved. As for zinc-selective microelectrode, membrane composition was proposed fitting well all desirable criteria except for selectivity. Said sensor can be used in laboratory practice at low concentrations of interfering ions which is feasible. Although a big joint effort of several teams was made, acceptable aluminum-selective microelectrode has not been developed. Eleven unique ionophores were synthesized and systematically studied in order to develop aluminum-selective membrane cocktail. The influence of plasticizer and ion-exchanger nature and ion-exchanger-to-ionophore ratio on the characteristics of aluminum-selective electrodes was investigated. Nevertheless, among over 31 prepared membrane compositions none was found to be satisfactory for the development of a microelectrode suitable for corrosion studies.

The experimental measurements and theoretical simulations of corrosion process for industrially important AA2024-T3 was accomplished on the example of the most active intermetallic phase Al2CuMg. Quantitative current densities and distribution of H+ and Cl- for the model coupling Al-Cu-Mg and specifically synthesized intermetallic phase Al2CuMg were recorded using simultaneous SVET-SIET. The corrosion prediction of the model couplings was successfully achieved by artificial neural network modeling.

Summarizing, most of the scientific tasks of SISET project were achieved bringing new and improved methods, tools and modeling strategies to use of project Partners and wide scientific community through publications and conference presentations. Project partners estimate that all milestones have been reached and are convinced that SISET project was very successful.

Reported by

INSTITUTO SUPERIOR TECNICO
Portugal
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