A hybrid method through faradaic rectification and a.c. impedance measurements for the corrosion rate determination of metal/oxide/electrolyte systems. I. Theory

The interference of the oxide film in corrosion rate measurements of oxide covered metals is confirmed, and is found to limit the accuracy of measurements in all d.c. and a.c. polarization methods including impedance techniques. A new method is proposed to measure the corrosion rate in metal/oxide/electrolyte systems. It involves the use of faradaic rectification measurements in the absence of concentration polarization. The contribution of the oxide film to the measured currents and potentials are appropriately compensated and this represents a unique feature of the proposed method. Alternating current impedance values of the oxide film measured at the same frequency as that of faradaic rectification are used for this purpose.     

Characterization of porous aluminium oxide films from a.c. impedance measurements

An equivalent circuit (EC) that reproduces the a.c. impedance of porous aluminium oxide films in a highly approximate manner is proposed. The results reveal that electrochemical impedance spectroscopy (EIS) is a powerful tool for obtaining detailed information on the electrochemical properties of both the porous and barrier layer on which the corrosion resistance of aluminium depends. The impedance at a given frequency can be used for accurate calculation of the electrochemical parameter for the oxide film represented by each element of the EC. In this way, the effects of any factor on sealing and ageing of anodized aluminium oxide films can be precisely analysed. The EIS technique provides an effective, advantageous alternative to existing seal quality control tests.     

Use of impedance measurements for the determination of the instant rate of metal corrosion

The various methods of evaluating corrosion rate and charge transfer resistance have been critically reviewed on the basis of the recent developments on the measurement and interpretation of faradaic impedances. It is demonstrated that the entity which is most accurately correlated with corrosion rate is the transfer resistance, the limit of the faradaic impedance at infinite frequency. In the case of iron, with and without inhibitor (propargylic alcohol), it has been ascertained, under various experimental conditions, that the measurement of this resistance constitutes nowadays the best electrochemical test for corrosion, and allows thea priori calculation of corrosion rate.This paper constitutes a chapter of H. Takenouti's University thesis, which was presented in Paris on June 25, 1971 [1]     

Alternating current impedance studies on oxide films in metal/oxide/electrolyte systems: a modified approach

The accurate determination of the impedance of oxide films in metal/oxide/electrolyte systems is shown to be possible through a modified procedure. The film impedance thus determined is found to be quite different from the measured cell impedance for anodic aluminium oxide formed on pure aluminium. The computed values of tan and conductivity are found to be in agreement with the values reported earlier for anodic and thermal oxides.     

Flux and Characteristic Parameters in Mediated Transport through Liquid Membranes. II. A Model for Co-transport and Experimental Study of Kl Transport through a Bulk Liquid Membrane

Abstract

In this article we establish a steady-state theoretical model for cotransport through liquid membranes. Integration of the flux equation gives the concentration in the receiving phase as a linear function of time under certain conditions. From this, an expression for the relative permeability of the carrier-permeant complex with respect to the carrier is obtained; this permeability depends on the equilibrium constant of the interphases reaction and on another parameter related to the initial concentration of permeant in extramembrane phases. An experimental study of the variation of permeant concentration in the receiving phase allows determination of several characteristic transport parameters.     

Ca3(PO4)2‐incorporated poly(ethylene oxide)‐based nanocomposite electrolytes for lithium batteries. Part II. Interfacial properties investigated by XPS and a.c. impedance studies

The surface layer and elemental composition of a lithium‐metal electrode before and after in contact with nanocomposite polymer electrolytes (NCPEs) comprising poly(ethylene oxide)/Ca₃(PO₄)₂/LiX (X = N(CF₃SO₂)₂, ClO₄) were analyzed by X‐ray photoelectron spectroscopy. The presence of Li₂CO₃/LiOH in the outer layer of the native film was identified. The formation of LiF was detected on lithium surface when in contact with NCPE containing LiN(CF₃SO₂)₂ and is attributed to the reaction between the native film and impurities. Li/NCPE/Li symmetric cells were assembled, and the thickness of the solid electrolyte interface as a function of time was analyzed at 60°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

De- and rehydration of Ca(OH)2 in a reactor with direct heat transfer for thermo-chemical heat storage. Part A: Experimental results

Heat storage technologies are used to improve energy efficiency of power plants and recovery of process heat. Storing thermal energy by reversible thermo-chemical reactions offers a promising option for high storage capacities especially at high temperatures. Due to its low material cost the use of the reversible reaction Ca(OH)₂ ? CaO + H₂O has been suggested. This paper reports on the thermal behavior of a reactor with direct heat transfer between the gaseous reactant and the solid material. Cycling stability is confirmed and the impact of the most significant parameters such as the maximum possible enthalpy difference of the heat transfer fluid between inlet and outlet, the heat transfer, the particle reaction rate and the mass transport is derived. In the test system the particle reaction rate could be identified as the main limiting parameter.