Kazimierz Darowicki

Theoretical description of the measuring method of instantaneous impedance spectra

Abstract Theoretical principles for determination of instantaneous impedance spectra were formulated. Coupling of the pseudo-white noise and short-time Fourier transformation methods allows determination of impedance spectra changes as the function of time. The theoretical principles of the new measurement method indicate the possibility of conducting impedance investigations of non-stationary processes. The frequency resolution and time selection of the total time–frequency analysis of impedance spectra depend on the choice of the size of the Gaussian window.

Dynamic electrochemical impedance spectroscopy of the first order electrode reaction

Abstract Continuous short time Fourier transformation transforms of the sinusoidal perturbation signal and current have been found for the first order electrode reaction. The electrode impedance has been determined in the joint time–frequency domain. Measurements of the Cd(II) reduction reaction have been performed on a hanging mercury electrode (HDME) as a function of potential. The possibility of instantaneous impedance spectra generation has been presented. The dependence of the charge transfer resistance, Warburg coefficient and double layer capacitance on potential has been described.

Instantaneous impedance spectra of a non-stationary model electrical system

Abstract Results of impedance measurements of a non-stationary model electric system are presented. Impedance measurements were realised by the pseudo-white noise technique. Simultaneous time–frequency analysis of the response signal was performed using the short-time Fourier transformation method. It is shown that the measurement method correctly reflects changes of the system investigated in the time and frequency domains.

The amplitude analysis of impedance spectra

Abstract The amplitude analysis of a non-linear model of an electric system has been carried out. The possibility of linear and non-linear electric element differentiation has been stated on the basis of impedance measurements. The simultaneous frequency and amplitude analysis of impedance spectra allowed the determination by extrapolation of electric element values corresponding to the zero value of the perturbation signal. The amplitude analysis of impedance spectra allows the determination of the effective amplitude value in an accurate way. The determination of the polarization resistance dependence on the function of the effective amplitude of the perturbation signal is the static characteristic of a tested system.

Investigation of pitting corrosion of stainless steel by means of acoustic emission and potentiodynamic methods

Abstract Measurements of pitting corrosion by potentiodynamic method and also by acoustic emission technique were carried out simultaneously. Cumulative distribution function of pitting corrosion (CDF P ) occurrence was determined based on the results of potentiodynamic measurements. Independently cumulative distribution function of acoustic events (CDF AE ) was found. The correlation analysis of both distributions was also performed. The occurrence of pitting corrosion was checked by metallographic observation. The measurements proved that observable acoustic activity is an effect of hydrogen evolution inside the pits. The random character of acoustic events during polarization, statistical analysis and existence of pits are good confirmation.

Corrosion rate measurements by non-linear electrochemical impedance spectroscopy

Abstract A theoretical analysis and non-linear impedance measurements of model non-linear electric systems have been carried out. The frequency and amplitude analysis of obtained impedance spectra enabled the complex and unequivocal determination of the parameters of the tested model of electric systems. Non-linear impedance measurements have been carried out of the process of carbon steel dissolution in a sulphuric acid environment. A possibility has been stated of using non-linear impedance measurements for the simultaneous evaluation of the corrosion current density and the Tafel coefficients. The theoretical discussion and non-linear impedance measurements have been limited to corrosion processes, the kinetics of which are described by the static, exponential Volmer-Buttler equation.

Accelerated ageing of organic coating systems by thermal treatment

Abstract The accelerated laboratory ageing of coated steel by multiple thermal shock has been proposed. Three polyvinyl coated steel panels exposed to natural weathering for different periods (0, 3 and 6 years) were thermally treated from temperatures of 20–65°C. A new epoxy coating for tank protection was treated by multiple thermal shock. Observed changes were interpreted as a protective system degradation and explained on the basis of analysis of stresses within the coating system. It was concluded that the proposed procedure allows to distinguish the performance of different coatings in a shorter time compared to traditional laboratory exposition.

Linearization in impedance measurements

A nonlinear description of a first order reaction proceeding in activation control conditions is presented. The effect of the amplitude of perturbation signal on the values of the effective potential and the direct current has been determined. A dependence between the effective potential, the direct current and the frequency of the generated sine perturbation signal is stated. Based on the derived dependencies current, potential and practical criteria referring to impedance measurements have been formulated.

Pitting corrosion in steel and electrochemical noise intensity

Electrochemical noise data in the presence of pitting corrosion were analyzed. A correlation between the intensity of the observed noise and mass loss of steel electrodes was recognized. The registered noise was decomposed into a set of band limited components using wavelet transform. It has been observed that the standard deviation of the chosen component was more strictly correlated with mass loss of electrodes than the standard deviation of the other components. The frequency band of the chosen component was adequate to the band where energy of transients, typical for pitting corrosion dominated. The measurement results were obtained only for the limited number of electrodes due to a very long time of noise observation.

Nonlinearity of electrochemical noise caused by pitting corrosion

Measurements of statistical quantities other than spectrum or amplitude distribution can provide additional information about mechanisms of electrochemical noise generation. The third-order cumulant and bispectrum are used to determine whether the nonlinear components exist in the observed noise. The electrochemical current noise, recorded under conditions when pitting corrosion dominated, is analyzed. Transients, characteristic for metastable pitting, are observed. The recognized nonlinear components in the recorded current fluctuations characterize processes of the electrode film repassivation during metastable pitting. It is suggested that the intensity and form of the nonlinear components are related to the intensity of metal dissolution into the electrolyte.