Electrochemical impedance spectroscopy (EIS) has been acknowledged as a modern and ef®cient method in the evaluation of the anticorrosive behaviour of coatings. However, dif®culties in the interpretation of the complex experimental data present a signi®cant drawback in the use of the method in ®eld studies where quick results are required. The breakpoint frequency method is an extension of the basic EIS method, which allows rapid qualitative assessment of the condition of a coating. By the breakpoint frequency method, the behaviour of epoxy coatings containing various types of reinforcement and applied on steel specimens has been examined after long-term (up to 300 days) exposure to a corrosive environment. The parameter values obtained by the breakpoint frequency method, such as the delaminated area, have been compared with those obtained from ®tting the experimental EIS data to a suitable equivalent circuit. These results have also been compared with those of the water permeability of free membranes and the diffusion coef®cient determined by standard test methods (e.g. the cup test).
In this work pretreated steel specimens were coated by a spinning process with particulate polymeric composites consisting of an epoxy resin (DOW 33 1) and iron powder. Applied coatings were roughly 70 pm thick and the contained quantity of iron particles was varied (7.5, 15,30% wt./wt.). The effect of the presence of iron particles in the coatings as well as the influence of their concentration on the evaluation of the coatings' behaviour in a corrosive environment (3.5% NaCl) was studied. Electrochemical impedance spectroscopy, corrosion potential, corrosion current density (Tafel) and dielectric measurements were performed. Minor differences in the anticorrosive behaviour of the coatings were observed irrespective of the iron content in the coating. Effective resistance inhibition action of the composite coatings was diminished with the increase of exposure time to the corrosive environment being in all cases very close to that of the pure epoxy resin coatings.
The measurement of the dielectric spectra of PAnQR based ER fluids under shear and electric fields is discussed and results presented. Data in which either but not both shear or electric fields are present are submitted to analysis in terms of known theories. For flow alone, that analysis provides information on the attenuation of polarization by the uniform shear fields whilst the polarization of quiescent fluids by electric fields may lead to estimates of particles packing within the columns. Permittivity data when both fields are acting is presented, but in the absence of suitable theory, not modelled quantitatively. Empirical correlations are discussed and the conclusion drawn that fibrillation is readily suppressed by even moderate shear rates, although long range dipolar forces still persist to high shear rates.The dc conductance of these fluids have also been measured. This together with permittivity data under ER fluid working conditions has importance in establishing the electrical parameters for any ER fluid.
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