Cécile Vallières

Complexation Chemistry in Copper Plating from Citrate Baths

An experimental and theoretical study of the influence of solution chemistry on the electrodeposition of copper from complexing citrate baths is proposed and discussed. The behavior of the system is described in terms of the relative distribution of various copper-citrate complexes, combined with a model mechanism for electrodeposition kinetics involving an adsorbed blocking intermediate. Studies of partial-current polarization curves for copper deposition over a wide range of solution pH and free citrate concentration substantiate the mechanism and offer convincing evidence for the significant role of solution chemistry in the electroreduction process. In addition to the copper system, the mechanism proposed offers a framework that may be useful for the study of other metals and alloys electrodeposited from complexing baths containing citrate or citrate-like molecules.

A Multisectioned Porous Electrode for Synthesis of D‐Arabinose

A multisectioned flow-through porous electrode, consisting of alternating conducting and insulating sections, was designed, built, and tested for the electrosynthesis of D-arabinose in aqueous solution. The laboratory prototype, consisting of ten independent porous graphite slices each of 5 mm thickness, can be adapted by external electrical connection to allow both traditional and sectioned operations to be run in a single device. The experimental study in this work focuses on use of the multisectioned arrangement to improve current-distribution uniformity in the porous-electrode reactor. A model electrosynthesis system, consisting of oxidation of sodium gluconate to D-arabinose in competition with the parallel reaction of oxygen evolution, has been chosen for investigation. Measurements in the sectioned electrode show that the performance, expressed in terms of current efficiency for gluconate oxidation, increases significantly with an increase in the number of sections. A comparison of predicted theoretical performance with experimental measurements on the ten-section prototype has been used to extrapolate the performance of the sectioned electrode to configurations with larger numbers of sections. Extrapolation indicates that optimal performance in the 5 cm electrode can be achieved with fewer than 100 sections, a design that is feasible to construct with modern microfabrication technology

Separation of binary mixtures by dense membrane processes: influence of inert gas entrance under variable downstream pressure conditions

The influence of an inert gas on the separation performances of a dense polymeric membrane module working under partial vacuum on the downstream side, such as possibly encountered in gas permeation, vapor permeation or pervaporation, has been investigated through an experimental and theoretical study. A whole range of situations on the downstream side, covering ideal vacuum pumping (i.e. zero downstream pressure under leak free conditions) to inert gas sweeping under atmospheric pressure has been tested. A theoretical framework, previously developed for single permeant situation has been extended to the multicomponent case. The separation of methanol and 2-propanol by a dense silicone rubber membrane confirms the ability of this simple modelling strategy to offer quantitative predictions of the permeate composition under variable downstream pressure and inert gas flowrate conditions. Based on this observation, the implications of an inert gas contribution on pervaporation or gas separation operation are discussed, particularly in relationship to the global energy consumption of the system or to analytical devices making use of a gas sweep.

A Comparison of the Wheeler-Jonas Model and the Linear Driving Force at Constant-Pattern Model for the Prediction of the Service Time of Activated Carbon Cartridges

The linear driving force (LDF) model is applied to predict the service life of activated carbon cartridges. It is compared with the currently used Wheeler-Jonas equation, which results from a model of chemical reaction kinetics. The LDF model is based on a mass transfer model of adsorbate into the particle. The two models are studied in constant-pattern conditions. The properties of the two models are first clarified and then compared. It is shown that the Wheeler-Jonas equation leads to symmetrical breakthrough curves, whereas the constant-pattern LDF equation results in asymmetrical curves. Thus, the curvature of the isotherm has no influence on the shape of the Wheeler-Jonas curve. For the LDF breakthrough curve, it is shown that the asymmetry increases with the curvature of the isotherm. Wheeler-Jonas can be used with a Dubinin-Raduskevitch isotherm, whereas the LDF model analytical solution is valid for a Langmuir isotherm only. The LDF model can be used with the DR isotherm, but a numerical solution is required. At very low concentrations where the isotherm is linear, the constant pattern no longer exists and both models fail. The Dubinin-Raduskevitch isotherm must be fitted with a Langmuir isotherm to use the analytical solution of the LDF model.

Potentiometric Detection of Oxygen Based on the Mixed Potential of Zinc

A new potentiometric oxygen sensor is proposed, based on the mixed potential of zinc in a chloride electrolyte. Variations in the sensor potential with oxygen concentration are the direct result of changes in the corrosion rate of the zinc electrode due to diffusion-limited reduction of oxygen at its surface. For static concentration measurements, the performance of the new (potentiometric) sensor is essentially equivalent to that of a traditional (amperometric) Clark sensor. For transient measurements, however, the response of the potentiometric sensor can be considerably faster than the analogous amperometric sensor, due to the sensitivity of the potentiometric method to logarithmic (rather than linear) variations in oxygen concentration.