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This paper presents a numerical analysis of the chemical-electrochemical (CE) mechanism of a rotating disk electrode at steady-state. Two sets of kinetic constants (denominated "fast kinetics" and "slow kinetics") were used to evaluate how they alter the original concentration profiles and the current response. Comparing the results obtained with those in the literature allows concluding that the range of validity of the reaction layer hypothesis, although able to accurately predict the current density in some cases, is intrinsically limited, because it will always fail for sufficiently high rotation speeds. Hence, a system with "fast kinetics" is merely one in which the hypothesis is applicable for all the rotation speeds that were studied. It was also observed that the range of validity of the reaction layer hypothesis is independent of the equilibrium constant of the chemical process and is determined solely by the absolute values of the kinetic constants.

This paper addresses the hydrogen evolution reaction (HER) occurring on platinum in an aqueous solution containing dissolved CO2 at several pressures. A new setup that uses a low inertia rotating disk electrode (RDE) adapted in an autoclave is proposed. This setup allows obtaining polarizations curves and electro-hydrodynamic (EHD) impedance, the latter for the first time in pressured conditions. New equations to adjust the Levich plots are proposed and briefly discussed.

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Austenitic stainless steels, when exposed to welding conditions or aging for length of service, it's observed the formation of numerous deleterious phases, such as several kinds of carbides type MC, M 6 C, M 7 C 3 , M 23 C 6 , and intermetallic secondary phases (sigma, chi, laves), which cause the process of intergranular corrosion. The aim of this work was verifying the formation of the types of carbides and/or intermetallic phases existing in the stainless AISI 304 at 800 ºC, varying the timing of heat treatment between 30, 360 and 1,440 min. The optical microscopy analysis revealed the predominant formation of the carbide type M 23 C 6 . The results of DL-EPR (double loop electrochemical potentiokinetic reactivation) tests showed a gradual increase in the precipitation of this carbide with the increase of treatment time. The potentiodynamic polarization showed that the precipitation of this carbide reduce the formation of the Cr 2 O 3 passive layer, suggesting that the precipitate carbide to be predominantly of the Cr 23 C 6 type.