Mónica L. Afonso

Evolução temporal da interfase açoinoxidável P558/solução de cloreto de sódio por espectroscopia de impedânciaeletroquímica

P558 stainless steel, nickel free, has been studied by this group with the purpose of verifying its viability for use in orthopedic implants. In previous works, it has been shown by stationary electrochemical techniques that this steel presents a similar behavior of that presented by ISO 5832-9 with a corrosion resistance significantly higher when compared to ISO 5832-1 stainless steel, usually known as F138 SS. In this work the temporal evolution of the interfase P558/NaCl 0.11 mol L-1 was studied by electrochemical impedance spectroscopy, at the open circuit potential. The time intervals observed were 10 min. 1 day, 2 days and 5 days. It was observed that the passive film became more protective with the increase of time. The experimental data was modeled using the equivalent electrical circuit approach. This approach suggested an initial existence of a slightly protective passive film, which then permitted the formation of a more compact secondary film upon stabilization of the conditions.

Inkjet printed organic electrochemical transistors with highly conducting polymer electrolytes

Organic Electrochemical Transistors (OECTs) were fabricated with two kinds of highly conducting polymer electrolytes, one with cations of small dimensions (Li+) and the other with cations of large dimensions (1-ethyl-3-methylimidazolium, EMI+). All OECTs exhibit transconductance values in the millisiemens range. Those with the larger EMI+ cations reach higher transconductance values and the saturated region of their I(V) characteristics extends to drain negative voltages of the order of −2 V without breakdown. These OECTs aim at potential applications for which it is relevant to use a solid polymer electrolyte instead of an aqueous electrolyte, namely, for integration in complex devices or in sensors and transducers where the electrolyte film may act as a membrane to prevent direct contact of the active material (PEDOT:PSS) with the biological media. The choice of electrolytes with cations of disparate sizes aims at assessing the nature (Faradaic or capacitive) of the processes occurring at the electrolyt...

Studies on the electrochemical growth of (Per)2[Au(mnt)2].

The first stages of the electrocrystallization of (Per)(2)[Au(mnt)(2)] salt from dichloromethane on gold, platinum, and highly orientated pyrolytic graphite (HOPG) were investigated by cyclic voltammetry, atomic force microscopy, and X-ray photoelectron spectroscopy in order to understand the determinant factors for nucleation and crystal growth. The crystal growth occurs from adsorbed films of dithiolate on gold or platinum and of perylene on HOPG, after homogeneous nucleation, and it is controlled by the low diffusion of the species toward the growing surface.

Estudo eletroquímico comparativo do aço ISO 5832-9 em diferentes meios de interesse biológico

The electrochemical behavior of ISO 5832-9 stainless steel at 37 oC in 0.9% NaCl, Ringer Lactate and minimum essential medium (MEM) has been studied, using linear voltammetry, and surface analysis by SEM and EDS. Mechanical and toxicity tests were made. ISO 5832-9 is passivated at corrosion potential (Ecorr) and it does not present pitting corrosion on the media studied from Ecorr to 50 mV above the transpassivation potential (Ei). SEM and EDS analysis have shown that the sample previously immersed in MEM presents a different behavior at 50 mV above Ei: the manganese oxide inclusions are absent in the surface. Ecorr values and passivation current density values jpass changed according to the following. Ecorr, RL < Ecorr,NaCl < Ecorr, MEM and jMEM << jRL ≅ jNaCl. The stainless steel was characterized as non toxic in the cytotoxicity assay.