The application of mercury hemispherical ultramicroelectrodes to the study of very concentrated amalgams. Diffusion coefficients of thallium

Potential step chronoamperometry at hemispherical mercury electrodes: The formation of thallium amalgams and the measurement of the diffusion coefficient of thallium in mercury

“…The electrode was placed in a solution of 0.02 M TlNO 3 (99.999%, Aldrich), with 1 M KF (99%, Aldrich) supporting electrolyte [9] and two potential steps were applied. The first step to effect thallium deposition, was carried out at À0.75 V (vs. SCE), varying the time (from 0.05 s to 0.5 s) in each experiment (see Table 1), and a second potential step to eliminate (strip) thallium at À0.40 V (vs. SCE) for 0.4 s. The length of time in the Tl stripping step exceeds the time that is required for the full elimination of Tl in the amalgam by at least a factor of 5 (see experimental results).…”

“…Since then various studies have been carried out in order to obtain the diffusivities of thallium in both of these phases [5,6] using polarographic [5][6][7][8], chronoamperometric [9][10][11][12] and radiochemical methods [13,14]. The amalgam has been studied by several authors in order to study diverse physical and chemical properties such as adsorption effects [15,16], amalgam solidification [17], and bioelectrochemical applications [18].…”

Determination of the Diffusion Coefficient of Hydrogen in Aqueous Solution Using Single and Double Potential Step Chronoamperometry at a Disk Ultramicroelectrode

“…Through the use of single potential step chronoamperometry (SPSC) at an ultramicroelectrode (UME), it is possible to determine the value of the diffusion coefficient, D , of an electroactive species which undergoes a simple electron transfer process, independent of a knowledge of the concentration. − This technique was pioneered by Winlove et al7a to measure the concentration and diffusion coefficient of oxygen in phosphate-buffered sucrose and albumin solutions. The current ( i )−time ( t ) behavior for the electrolysis of the electroactive species following a potential step at a disk UME, of known radius a , from a value where no electrode reactions occur to one where electrolysis occurs at a diffusion-controlled rate, can be described analytically with an expression in which D is the only remaining unknown: In eq 1, i (∞) is the limiting, steady-state current which flows at the disk UME.…”

Voltammetry Involving Amalgam Formation and Anodic Stripping in Weakly Supported Media: Theory and Experiment

“…27,28 The Tl + /Tl(Hg) couple is a reversible model system that has been widely investigated at mercury drop electrodes, [29][30][31][32] mercury thin-film electrodes, 33,34 and mercury microelectrodes. 35,36 In a previous paper 8 dealing with the chronoamperometric response of this system, it was shown that even in the presence of fairly large amounts of supporting electrolyte, the potentiostatic stripping of Tl + in solution leads to unusual current-time transients. When the NPP equations in conjunction with the zero-field approximation were used, it was demonstrated that, in such conditions, the system is only partially supported.…”

“…In the present study, we focus on the voltammetric behavior of thallium at mercury microelectrodes. The accumulation (preconcentration) of reduced metals in mercury, followed by their subsequent anodic stripping, is a very popular analytical method of trace analysis. , The Tl + /Tl(Hg) couple is a reversible model system that has been widely investigated at mercury drop electrodes, – mercury thin-film electrodes, , and mercury microelectrodes. , In a previous paper dealing with the chronoamperometric response of this system, it was shown that even in the presence of fairly large amounts of supporting electrolyte, the potentiostatic stripping of Tl + in solution leads to unusual current−time transients. When the NPP equations in conjunction with the zero-field approximation were used, it was demonstrated that, in such conditions, the system is only partially supported.…”