Physicochemical Characterization of Passive Films and Corrosion Layers by Differential Admittance and Photocurrent Spectroscopy

Two different electrochemical techniques, differential admittance and photocurrent spectroscopy, for the characterization of electronic and solid state properties of passive films and corrosion layers are described and critically evaluated. In order to get information on the electronic properties of passive film and corrosion layers as well as the necessary information to locate the characteristic energy levels of the passive film/electrolyte junction like: flat band potential (Ufb), conduction band edge (EC) or valence band edge (EV), a wide use of Mott-Schottky plots is usually reported in corrosion science and passivity studies. It has been shown, in several papers, that the use of simple M-S theory to get information on the electronic properties and energy levels location at the film/electrolyte interface can be seriously misleading and/or conflicting with the physical basis underlying the M-S theory. A critical appraisal of this approach to the study of very thin and thick anodic passive film grown on base-metals (Cr, Ni, Fe, SS etc..) or on valve metals (Ta, Nb, W etc..) is reported in this work, together with possible alternative approach to overcome some of the mentioned inconsistencies. At this aim the theory of amorphous semiconductor Schottky barrier, introduced several years ago in the study of passive film/electrolyte junction, is reviewed by taking into account some of the more recent results obtained by the present authors. Future developments of the theory appears necessary to get more exact quantitative information on the electronic properties of passive films, specially in the case of very thin film like those formed on base metals and their alloys. The second technique described in this chapter, devoted to the physico-chemical characterization of passive film and corrosion layers, is a more recent technique based on the analysis of the photo-electrochemical answer of passive film/electrolyte junction under illumination with photons having suitable energy. Such a technique usually referred to as Photocurrent Spectroscopy (PCS) has been developed on the basis of the large research effort carried out by several groups in the 1970’s and aimed to investigate the possible conversion of solar energy by means of electrochemical cells. In this work the fundamentals of semiconductor/electrolyte junctions under illumination will be highlighted both for crystalline and amorphous materials. The role of amorphous nature and film thickness on the photo-electrochemical answer of passive film/solution interface is reviewed as well the use of PCS for quantitative analysis of the film composition based on a semi-empirical correlation between optical band gap and difference of electronegativity of film constituents previously suggested by the present authors. In this frame the results of PCS studies on valve metal oxides and valve metal mixed oxides will be discussed in order to show the validity of the proposed method. The results of PCS studies aimed to get information on passive film composition and carried out by different authors on base metals (Fe, Cr, Ni) and their alloys, including stainless steel, will be also compared with compositional analysis carried out by well-established surface analysis techniques

Random Excitation of Bistable Harvesters

This chapter considers nonlinear piezoelastic energy harvesters driven by stationary random noise. A range of devices that exhibit nonlinear dynamics have been proposed, and their response to sinusoidal excitation is often complex, with coexisting periodic solutions or even chaotic solutions. The response of nonlinear harvesters to random noise depends on the statistics of the excitation; the maximum response can occur at particular excitation variances, and this is called stochastic resonance. The stochastic linearisation method is proposed for the optimal design of bistable harvesters subjected to random excitation

Energy Harvesting in a Coupled System Using Nonlinear Impact

Energy harvesting from broadband excitation, such as aircraft noise, and low frequency excitation, such as human motion, has gained significant interest recently. Vibro-impact is one of the methods used to improve capability of the harvester by low to high frequency conversion. The present paper analyses the effect of vibro-impact within a coupled beam system. The system is base excited and a localised non-linearity is induced at the point of impact. Modal reduction techniques are applied to reduce the computational time. The localisation effect on the coupled beam system is performed by varying the system parameters, for example the amplitude of excitation, the clearance and stiffness between the beams

From functional analysis to energy harvesting system design: application to car suspension

International audienceIn the context of global energy demand increase, working on energy efficiency is essential. This paper deals with energy harvesting on car suspensions. In order to have a real added value, some criteria must be considered: the need to design a system that would be easily integrated into cars, the possibility to locally use the recovered energy to add new functionalities that can improve the security or the comfort of the car, and the necessity to not degrade and, if possible, to improve (semi-active or active dampers) the performances of the suspension. From the mechanical point of view, the functional analysis is used to define and to characterize the main suspension parts, to investigate the connexions and the energy flows and to identify the key elements for energy recovery. Then, quarter car and half car models implemented with Matlab/Simulink software are presented in order to evaluate the quantity of energy that could be recovered. Three locations are presented and evaluated. Simulations results will finally give an overview on the implementation opportunities