Electrochemical Microcell Research Articles

A new electrochemical technique to study tribocorrosion at the micrometric scale

A new method to investigate the tribocorrosion properties of metals and alloys has been developed with which the current density of a metal probe in an electrolyte under rubbing conditions can be measured. The electrochemical microcell consists of a microcapillary (inner diameter 0.84 mm); the rubbing partner is an Al2O3 tube which rotates inside the microcapillary. Rotational speed, load and applied electrical potential can be varied, so that it is possible to analyse the corrosion rate during rubbing under various controlled conditions. With conventional tribocorrosion machines (e.g., pin-on-disc, ball-on-plate rig) and also with single-scratch test machines, the current measured also derives from surface areas which are not undergoing mechanical wear. In the present method, the activation of specific surface areas under rubbing conditions, and subsequent repassivation, can be studied separately.

On-line preconcentration of lead and cadmium for flame atomic absorption spectrometry using a flow-through electrochemical microcell

A method was developed for the trace determination of lead and cadmium by flame atomic absorption spectrometry (FAAS) with electrochemical preconcentration. Both metals were deposited on the glassy-carbon electrode in a flow-through microcell of volume 3 μl. At a consumption of a 3 μl sample volume, the procedure resulted in an enhancement factor of more than 20 and yielded a detection limit of 1 μg l −1 for Pb and 0.08 μg l −1 for Cd. The relative standard deviation ( n=12) was 2.1% at the 100 μg l −1 level for Pb and 3.2% at the 8 μg l −1 level for Cd. Results obtained for the standard reference material, water SRM 1643c, were in good agreement with the certified values.

Design of catalysts based on electrochemical microcell models

The concept and the strategy for designing catalytic systems on the basis of electrochemical microcell models have been proposed and demonstrated for Wacker-type oxidation of ethylene, selective hydrogenation of nitric oxide into hydroxylamine and partial oxidation of alkenes and alkanes. For designing active and selective catalysts, at least four fundamental catalytic elements are required. These are (1) the oxidation sites (anode), (2) the reduction sites (cathode), (3) proton conducting medium, and (4) electron conducting medium. The catalytic elements (3) and (4) would electrochemically connect the oxidation (anode reaction) on site (1) and the reduction (cathode reaction) on site (2). A mixture of these four catalytic elements generates an unlimited number of microcells which work as catalysts for desired synthetic reactions.

Microscale Electrolytic Fluorinations of 4-Nitrotoluene - Cell Construction, Computer Monitor and Control, and Chemistry

An electrochemical microcell that can utilize a 70:30 mixture of HF and pyridine as both the solvent and the supporting electrolyte was constructed and interfaced with a computer for monitoring and control. 4-Nitrotoluene was selectively fluorinated in the cell in good yield and good conversion to give an 83:17 mixture of two monofluoro products, α-fluoro-4-nitrotoluene and 2-fluoro-5-nitrotoluene (a product of rearrangement).

On-line electrochemical preconcentration of manganese for graphite furnace atomic absorption spectrometry using a flow-through electrochemical cell

A flow system incorporating a 2-electrode electrochemical microcell with a working electrode made from crushed reticulated vitreous carbon and a graphite furnace AAS instrument was used for the preconcentration and determination of trace amounts of Mn. The sample, rinsing and elution solutions were pneumatically transported through the system. Mn2+ ions can be quantitatively deposited both anodically and cathodically at a voltage of +1.5 to + 3 V and −2.5 to −4V, respectively applied to the cell. Samples of 0.1 to 1 ml volume were analyzed within 5–10 min. The limits of detection and determination were 8.7 and 29 pg, respectively. The reproducibility was 1.5 to 5%. The electrochemical behaviour of Mn in the flow system was studied by using a 3-electrode flow-through cell coupled on-line to a flame AAS instrument.

Surface modification of a planar electrochemical microcell

The fabrication of a three-electrode electrochemical microcell in which the working electrode is selectively modified with poly (vinylferrocene) (PVFer) is described for use as a chemical sensor. The microcell was characterized by cyclic voltammetric and differential-pulse voltammetric techniques and the behaviour of the PVFer-modified platinum electrode in contact with 0.1 M KCl is reported. The mediating properties of the PVFer film are demonstrated for this cell by using the oxidation of ascorbic acid, a process which is shown to be slow at the corresponding bare platinum microelectrode.

Amperometric flow injection technique for determination of hydrogen peroxide and sulfur(IV) in atmospheric liquid water

A sensitive, selective and fast method for the determination of hydrogen peroxide and sulfur(IV) present in atmospheric liquid phase is described and discussed. The flow injection system used contains a specially designed electrochemical micro-cell. The necessary selectivity is achieved using an alkaline carrier flow for the oxidative determination of H2O2 and an acidic one for the bisulfite oxidation, and employing differential measurements before and after addition of catalase or sulfite oxidase, respectively. Samples of 200 μl volume can be injected at a rate of 30 per hour and the electroactive species be determined in the range from millimolar level down to the detection limit of 2 · 10−8mol/l. The S(IV) present as hydroxymethanesulfonate or in form of other carbonyl adducts is determined after a previous alkalinization of the sample to liberate the sulfite. The method has been tested with rain, snow, fog and cryo-sampled atmospheric water vapor. The time resolution is adequate to follow precipitation events.

Synthesis and properties of C 28 polycyclic hydrocarbons

Electrochemical micro-cell systems based on the use of glass micro-capillaries enable to perform standard electrochemical measurements on areas with dimension in the micro- or submicrometer range. The base principle is the miniaturization of the working electrode, which is obtained using a micro-capillary to position the electrolyte on the sample surface. This technique has been extensively employed for the investigation of localized corrosion in passive surfaces like steels and aluminium alloys.This paper presents examples of the study of localized corrosion and its inhibition in aluminium alloys by means of the electrochemical micro-cell. These are discussed trying to highlight the major advantages and the critical aspects related to the use of the technique. Moreover, the combined use of the electrochemical micro-cell with other electrochemical and surface analysis techniques highlights that the micro-cell technique is a very powerful method for the investigation of corrosion phenomena.