8 research outputs found
Zinc-cobalt alloy electrodeposition from chloride baths
Electrodeposition of Zn-Co alloys on iron substrate from chloride baths under galvanostatic and potentiostatic conditions were carried out. Current density, temperature and cobalt percentage in the bath were found to strongly influence the composition of the deposits and their morphology. Changes in potentials, current efficiency and partial current densities were studied. The results show that the shift in potential and in the cobalt percentage of the deposits, for a particular current density during galvanostatic electrodeposition, does not always correspond to the transition from normal to anomalous codeposition. This shift is attributed to zinc ion discharge, which passes from underpotential to thermodynamic conditions. In the range of potentials for the underpotential deposition of zinc, the electrodeposition of zinc-cobalt alloys is discussed, emphasizing the influence of the electrode potential on the composition and microstructure of the deposits.2791088109
New Sol-gel Formulations to Increase the Barrier Effect of a Protective Coating Against the Corrosion and Wear of Galvanized Steel
This study proposes a new pretreatment method that uses alkoxide precursors with a plasticizing agent; the purpose of this study is to improve the electrochemical and mechanical properties of a galvanized steel surface. Galvanized steel was covered with a hybrid film obtained from a sol that consisted of two alkoxide precursors, 3 - (trimethoxysilylpropyl) methacrylate (TMSM) and tetraethoxysilane (TEOS), with nitrate cerium in a concentration of 0.01 M and a polyethylene glycol (PEG) plasticizer. The hybrid coatings were obtained by dip-coating method with various concentrations of plasticizer (0, 20, 40 and 60 g.L-1). The hybrid films were analyzed by scanning electron microscopy (SEM), profilometry, contact angle measurements, a tribometer with the type-setting ball on the plate and electrochemical tests. The addition of the plasticizer into the hybrid films improves the corrosion resistance behavior compared to the sample without the plasticizer. The addition of 20 g.L-1 of plasticizer showed the best performance in the electrochemical tests. The mechanical behavior results indicated that higher PEG concentrations resulted in films with enhanced durability
Hybrid solâgel coatings for corrosion protection of galvanized steel in simulated concrete pore solution
The aim of this experimental research was to study the electrochemical behavior of organicâ
inorganic hybrid (OIH) coatings for corrosion protection of hot-dip galvanized steel (HDGS) in the first
instants of immersion in simulated concrete pore solution (SCPS) (pH > 12.5). The electrochemical
performance of the OIH coatings was assessed by electrochemical impedance spectroscopy, potentiodynamic
polarization curves, macrocell current density, and polarization resistance. The OIH coatings were
prepared via the solâgel method and were deposited on HDGS surfaces by dip-coating using one or three dip
steps. The electrochemical results obtained for HDGS samples coated with OIH matrices in SCPS showed
higher corrosion resistance than bare HDGS; as the molecular weight (MW) of Jeffamine increased the
barrier protection of the coating decreased. The lowest protection efficiency was found for HDGS samples
synthesized with oligopolymers with an MW of 2000.
Coatings produced with an oligopolymer of 230 MW
conferred the highest protection. The surface morphology
of the OIH coatings deposited on HDGS
surfaces was studied by atomic force microscopy. The
results show that the roughness of the OIH films
depends on the MW of Jeffamine and on the number
of dip-coating steps used. Thermogravimetry results
show that the Jeffamine MW affected the thermal
properties of the prepared OIH samples. The prepared
OIH materials are thermally stable within the range of
20â80 C.The authors would like to gratefully acknowledge the financial support from Fundacao para a Ciencia e Tecnologia (FCT) for the PhD grant SFRH/BD/62601/2009 and EU COST action MP1202: HINT-"Rational design of hybrid organic-inorganic interfaces: the next step towards functional materials.''info:eu-repo/semantics/publishedVersio