Emmanuel Gasana

Influence of changes of platinum electrode surface condition on the kinetics of the oxidation of sodium dithionite and sulfite in alkaline solution.

Abstract The influence of the surface condition of a platinum electrode on the kinetics of the electrochemical oxidation of sodium dithionite and sulfite was investigated. It was found that the oxidation of sulfite does only occur at platinum oxide while the oxidation of dithionite takes place at platinum oxide as well as at platinum hydroxide and bare platinum. However, dithionite cannot be oxidised at rearranged platinum hydroxide, which is formed during the reduction of platinum oxide, a process that is strongly dependent on the applied anodic vertex potential. For both substances a hysteresis effect was observed between forward and backward scan but in both cases the effects could be explained considering the platinum surface condition. As well in the absence as in the present of sulfite and/or dithionite reproducible current-potential curve were obtained after cycling three times between the applied vertex potentials. The observed difference between the first and subsequent scans again could be explained when the variation of the platinum surface condition as a function of potential and number of cycles was taken into consideration.

Electrochemical behaviour of sodium dithionite at a platinum electrode and determination of diffusion coefficient in alkaline solution

The electrochemical behaviour of sodium dithionite at a platinum electrode has been investigated in this paper. Two oxidation waves of sodium dithionite were observed with formation of sulfite as a stable intermediate species. It has been found that the oxidation of sodium dithionite to sulfite, according to the first wave, is controlled by the rate of mass transport, the oxidation of sulfite to sulfate, however, is not purely controlled by transport phenomena. Using the ratio of the limiting currents of both oxidation waves it was possible to determine the diffusion coefficient of sodium dithionite by extrapolation to the small rotation rate of the platinum electrode. From the obtained results it is also advisable to make use of the first oxidation reaction for analytical purposes.

Improving Quality and Reproducibility of the Indigo Dye Process by Measuring and Controlling Indigo and Sodium Dithionite Concentrations

This paper describes a sensor system for continuous on-line and in-line measurement of indigo and sodium dithionite concentrations during textile dyeing with indigo. The system is based on an electrochemical method, more specifically, multistep chronoamperometry. A repetitive sequence of potentials is applied at the surface of a platinum electrode, resulting in the oxidation of indigo and dithionite. The electrons released in these reactions are measured as an electrical current, and this signal is proportional with the concentra tions of indigo and dithionite. The platinum electrode is positioned in a so-called wall-jet electrode configuration in order to obtain time-independent electrode signals and a configuration that is relatively easy to implement in industrial dyeing lines. The system has potential industrial applications because of its fast response time (continuous mea surement), good reproducibility, acceptable precision and accuracy, and promising long- term stability.

Kinetics and mechanism of the oxidation of sodium dithionite at a platinum electrode in alkaline solution

Abstract In this paper the oxidation of sodium dithionite in alkaline solution was studied by cyclic voltammetry at a stationary and rotating platinum disk electrode. The reaction proceeds in two steps, with sulfite as a relatively stable intermediate and sulfate as final product. It was possible to quantitatively analyze the kinetics of the oxidation wave making use of the experimental evidence that the reaction rate is not dependent on pH, with a reaction order of 0.5 with respect to sodium dithionite and a charge transfer coefficient of 0.5. The proposed mechanism of the overall electron transfer reaction consists of five consecutive steps starting with the adsorption of dithionite, followed by decomposition into SO 2 − , which releases an electron in the rate determining step and finally two more chemical steps leading to the formation of sulfite. The predicted behavior by this mechanism is in agreement with the experimentally observed one.

Gold Coated Polyester Yarn

Textiles are increasingly studied to use them as sensing and measuring devices of body parameters. For this purpose they need to be modified to provide on the one hand reliable and stable electroconductive properties and on the other they should be biocompatible. This can be achieved by depositing electroconductive materials such as metals on the textile surface. Gold is an ideal material to use as it offers the aforementioned criteria and can be applied as a thin coating on the surface of a fibre, yarn or fabric. We developed gold coated yarns that are highly electrically conductive, skin-friendly and stable. In this presentation, we describe the gold coating method and show first results of the characterisation of the coated yarns. A commercially available polyester yarn was coated with a thin layer of gold by using an electroless plating method. The plating solution was optimised towards the concentration of each component, the working temperature and pH. The quantitative analysis of the surface coverage of gold with EDAX and cyclic voltammetry showed in both cases a surface coverage of more than 95%. For the future, research will be continued to characterise the longterm behaviour of the yarns.