Poly(ether ether ketone) (PEEK) thermally sprayed coatings find more and more applications, and ensure often the protective effect of substrate metals when the coated material is exposed to an aggressive medium. This coating exhibits extremely high impedance, and the impedance measurements of coated specimen were impossible to perform several years ago. Therefore, it was unable to evaluate quantitatively the coating protective performance by an electrochemical impedance method. Such measurements were realized, in this paper, with a recent device, and the impedance behaviour observed was interpreted in terms of dielectric relaxation after extracting the frequency dependent capacitance from the impedance spectra. It was found that the water uptake in PEEK coating is particularly low, ca. 1% and no interaction with absorbed water molecules and polymer matrix was detected. This result verifies therefore exceptionally high performance behaviour of PEEK thermally sprayed coating in an aqueous medium. The impedance measurements may therefore be used to evaluate accurately the corrosion protective effect of such a coating during development for new applications, and also to optimize the deposition conditions.

In situ Raman analysis was applied to identify the corrosion products formed on iron coated with epoxy-amine varnish and exposed to sodium chloride solution saturated by hydrogen sulfide or carbon dioxide. The results showed the formation of iron sulfide or iron carbonate layer while electrochemical impedance spectrum predicted the polymer coating exhibiting an almost perfect protecting barrier property. It is concluded therefore, that the corrosion process involves the permeation of water and hydrogen sulfide at molecular state through polymer interstices whereas no ionic conduction is allowed to take place in the coating film. The corrosion process induces the complete delamination of the exposed coating area but as far as its integrity is respected (no macroscopic pores or crevices) the corrosion rate is very low, far from that expected from permeation measurements of H2S.

The fast Fourier transform and the maximum entropy method (MEM) provide algorithms for the estimation of the power spectral density (PSD) of fluctuations. Both have been employed for the analysis of electrochemical noise in corrosion studies, and claims have been made concerning the superiority of one method with respect to the other. in this paper, the two methods are compared to assess their relative advantages. A summary of the principles of the MEM is given and its main properties investigated. In particular, the effect on spectrum accuracy of varying the number of coefficients in computing the MEM and the validity of the low-frequency plateau in the PSD usually produced by this technique are examined. Also, the robustness of the two methods is compared when the random process is not completely stable, for instance, in the presence of signal drifts or slowly varying amplitude of the fluctuations. The results presented may be used as a guideline to choose the best computation method as a function of the measurement conditions.

The study of the kinetics of a nickel hydroxide electrode has been carried out by ac electrogravimetric measurements between 1kHz and 0.01Hz. The reaction involves an incorporation of hydrated alkaline cation and a slow deprotonation reaction. The effect of alkaline cations (Li+, Na+, K+, Cs+, Rb+) incorporation is also considered.

An electronic device has been devised in order to measure simultaneously the potential fluctuations and the electrolyte resistance fluctuations of an electrode. The separation of the ohmic and faradaic components of the potential fluctuations allows a more precise identification of the elementary events generating this voltage electrochemical noise (bubble detachment on a gas-evolving electrode, contact between particles in a fluidized electrode, etc.). Transients of the electrolyte resistance as fast as 1 ms can be measured by this device with a precision better than 0.1%.

Electrochemical impedance spectroscopy (EIS) is frequently reported to be used in mechanism analysis, state estimation, and fault diagnosis of lithium-ion batteries. For a long time, EIS has been measured in the laboratory using carefully designed equipment, which has the problem of long measurement time and is not convenient for field applications. How to obtain broadband electrochemical impedance spectroscopy quickly and accurately has become a key issue. Being different from the traditional impedance measurement method based on sinusoidal frequency sweep, in this paper, we obtain the EIS by using Fast Fourier Transform (FFT) for maximum length sequence (M-Sequence) excitation current and corresponding response voltage. M-sequence excitation can be generated by fast responding charging and discharging equipment, etc., with higher flexibility. To guide the engineering application, for the first time, the effect of M-Sequence parameters and sampling frequency on the impedance calculation results are investigated through experiments. A series of experimental results show that when given the frequency range to be measured, the parameters of M-Sequence and the sampling frequency can be determined to calculate the EIS quickly and accurately.