Walter Alfredo Egli

Tin Coatings Electrodeposited from Sulfonic Acid-Based Electrolytes: Tribological Behavior

Abstract A high efficiency methane sulfonic acid electrolyte used for tin electrodeposition was studied, and the properties of the resulting deposits were compared to those of tin coatings obtained from an industrial phenol sulfonic acid electrolyte. Cyclic voltammetry was used to study the effect of organic additives on the reduction process to define the composition of the electrolytic bath. Thick tin electrodeposits were obtained on rotating cylinder steel electrodes, and their surface morphology, preferred crystal orientation, surface roughness, micro hardness, and tribological behavior were measured. Smooth, adherent, and bright tin coatings were obtained from the methane sulfonic acid electrolyte, which differed in morphology and texture from tin electrodeposited from the industrial bath. Influence of organic additives on preferred crystal orientation of the coatings was found to be stronger than changing the supporting sulfonic acid type. Tribological tests showed that the two types of deposits have a similar coefficient of friction. However, tin coatings obtained from methane sulfonic electrolytes presented a lower wear resistance and underwent galling at lower loads.

Protection of galvanized steel with silanes: its comparison with Chromium(VI)

The corrosion behavior of hot dip galvanized steel (HDGS) pre-treated with mercaptopropyltrimethoxysilane and a commercial sulfur-bearing silane was studied. Electrochemical polarization, electrochemical impedance spectroscopy, and electrochemical noise tests showed that silane coatings have a corrosion protection performance similar to the usual hexavalent chromium HDGS passivation treatments. It is also evident that the silane films protect the zinc surface through the formation of an isolating barrier. Through voltamperometric studies it was possible to define an electrochemical porosity of the protective coatings. Based on copper sulfate tests and electrochemical porosity results the films protection capability was evaluated, showing that silane treatments have similar or even better protection performance than standard chromium passivation.

Study of dendritic growth of zinc crystals on the edges of steel sheet

Abstract In this paper, the formation of zinc dendrites at the strip edge of an industrial electrogalvanizing line was studied. For that purpose, a rotating washer electrode was designed to reproduce the hydrodynamic conditions and the current density distribution found in the industrial process. Polarization curves were recorded at different rotation speeds in order to investigate the electrokinetic behavior of the cathodic process. The induction time for dendritic growth was estimated for different overpotential values and the existence of a minimum overpotential below which dendrites do not grow was confirmed. Dendrite precursors on the edge of the washers were well characterized and its birth and precise location were studied. The general model of disperse and dendritic metal electrodeposit formation derived by Popov et al. was used to explain the effect of electrolyte zinc concentration, rotation speed of the cathode, electrolyte temperature and edge roughness on the size and morphology of dendrites. The results showed that this theory provides an accurate description of the phenomenon even for non-stationary electrodes, which have not been extensively studied so far. The experimental setup proved to be a powerful means to study the formation of dendritic growth of zinc crystals on the edges of steel strip and is well suited to characterize other metals that produce this type of defect.

Influence of organic additives on the behaviour of zinc electroplating from alkaline cyanide-free electrolyte

Two similar polymeric organic compounds from the polyquaternium family were studied as levelling additives in an alkaline cyanide-free zinc plating electrolyte. One additive (LA) has amide bonds between its monomers and the other (LU) has urea unions in its chemical structure. Copper cementation on zinc and gas evolution during aging of the zinc coatings were used to evaluate the effect of the chemical structure of the organic additives on the characteristic deleterious aging process of the coatings when electrodeposited with LA. Scanning electron microscopy and X-ray diffraction were used to follow surface morphology and crystallographic modifications of the coatings during aging. Faster copper cementation kinetics, zinc whiskers growth, blistering of the coating and N2, CH4, CO2 and H2 evolution were observed during accelerated aging of the coatings when LA was used. The coatings produced with LU did not show any aging effect. These studies show the strong influence that subtle changes in the chemical structure of the organic additive may have on the performance of zinc coating during storage.

Morphology and Texture of Zinc Deposits Formed at the Edge of a Rotating Washer Electrode

In this paper, a rotating washer electrode was used to simulate the industrial conditions of strip edges during electrogalvanizing. Using this experimental setup, morphology and texture of the zinc deposits and dendrites formed at the edge of the electrode were studied. Dendrite precursors in the corner of the washer edge were well characterized and their nucleation and growth were also studied. The results indicated that the rotation speed has little effect on texture while, in contrast, current density modifies dendrite’s texture. It was found that dendrites are formed by platelets which are stacked on one another, which grow up in a series of steps oriented in the direction of growth of the dendrite’s stem yielding highly oriented structure. The presence of sodium ions in the electrolyte changes the morphology and shape of dendrites leading to rounded, ‘cabbage’-shaped crystals, while thiourea changes the morphology of both the deposit in the flat portion of the washer and the dendrites through adsorption on the zinc surface.

Preparation and Characterization of Silanes Films to Protect Electrogalvanized Steel

Silanes are an interesting alternative to chromate-based surface treatments for temporary protection of electrogalvanized steel. In this work, the protective behavior of 3-mercaptopropyltrimethoxysilane (MTMO), 3-aminopropyltriethoxysilane (AMEO), or 3-glycidoxypropyltrimethoxysilane (GLYMO) films applied on electrogalvanized automotive quality steel sheets has been studied. The silane coating morphology, composition, and porosity were characterized by scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), x-ray fluorescence, immersion in copper sulfate, and cyclic voltammetry. The corrosion protection was evaluated by polarization curves, electrochemical noise measurements, electrochemical impedance spectrometry, and accelerated humidity chamber tests. The results showed that the silanes protect temporarily electrogalvanized steel from corrosion. MTMO forms a relatively thick and cracked film. AMEO and GLYMO films were so thin that they could not be observed by SEM but silicon was detected by EDS. MTMO provided good temporary protection, being an alternative to replace Cr(VI) as protector of electrogalvanized steel.