Electrochemical Noise of Electrophoretic Coatings with Nanoparticles TiO2 and ZnO
Authors: Estupiñan-Lopez Francisco , Gaona-Tiburcio Citlalli , Cabral-Miramontes Jose A. , Treviño-Morales Raul , Almeraya-Calderón Facundo 
Published: February 2020

INTRODUCTION

Organic coatings based on nanotechnology have been of great interest in recent years, thanks to the increase in performance with significantly optimized or improved properties in various aspects such as those that block UV rays, anti-scratch coatings, anti-abrasion, anticorrosive, superhydrophobic and coatings of barrier. Previous studies have found that there are nanoparticles that provide qualities to the coating such as the incorporation of nanoparticles such as Al2O3, SiO2, ZrO2 and TiO2 in a transparent layer matrix could significantly improve the scratch resistance as suggested by Bautista, et. al.
Despite the efforts that have been made by incorporating some type of nanoparticles in organic coatings as mentioned above, this type of systems are prone to suffer corrosion damage in various environments. This type of damage can be analyzed by laboratory-level electrochemical techniques, including Electrochemical Noise, which is a non-destructive technique, and which reflects the individual sum of the random events of the potential and / or current fluctuations of a material subject to corrosion conditions; and the value of the root mean square (RMS) of the amplitude of these events or standard deviation has been shown to provide the fingerprint of the amount of dissolved metal, depending on the metal-environment combination. Another technique used for this type of systems is Electrochemical Impedance Spectroscopy, which, like EN is a non-destructive technique that indicates changes in the system before they are visible. For the specific case of coatings, it is possible to study the deterioration of these by the action of an electrolyte and the increase of the corrosion rate in the substrate, either by the deterioration of the coating or by the attack of the electrolyte.
In recent years, the enormous potential of electrophoretic deposition (EPD) as a processing method for the realization of unique micro and nanostructures and combinations of novel materials has been recognized by the materials science community. Within this type of paintings is the so-called E-coat (cathodic)
In this work we will analyze the transients observed in the time series of potential and current corresponding to the Electrochemical Noise and graphics of Electrochemical Impedance Spectroscopy measurements, of EPD coatings with and without the addition of TiO2 nanoparticles.

EXPERIMENTAL METHODOLOGY

Cathode Electrophoretic Coating (e-coat)

The cathodic electrophoretic coating (e-coat) will be applied on steel sheets with a cathodic epoxy resin paint, previously preparing the surface with alkaline washing, pickling, phosphating and sealer. After the deposition of the paint, a curing will be carried out for the polymerization and evaporation of paint solvents.
Coatings will be made without and with the addition of TiO2 nanoparticles to evaluate the effect of these.
The bath temperature was set at 36 ° C and the deposition time was 2:50 min with an applied voltage of 140 V.

Electrochemical tests.

AC and DC techniques will be used, and corrosion monitoring will be carried out for various periods. The electrochemical parameters derived from each of the techniques will be obtained. The solutions used for the electrochemical tests will be prepared before carrying out these and will be 3.5% sodium chloride (NaCl) and distilled water. A cell will be used to evaluate paintings. The electrochemical techniques used will be: Electrochemical Noise (ASTM G199) and Electrochemical Impedance Spectroscopy (ASTM G106). using a potentiostat / galvanostat brand Solartron 1287A with 1285 interface.

RESULTS

The Bode diagrams obtained from the electrochemical impedance tests for the coatings, exposed in a 3.5%wt NaCl solution. It can be seen that the coating with the addition of TiO2 nanoparticles presents a higher impedance at high and low frequencies. In addition, in the system that does not have the addition of nanoparticles, noise is observed at frequencies between 102 and 103 Hz, which indicates, possibly, an activity between the electrolyte and the pigments contained in the paint. Impedance values between 105 and 106 Ω-cm2 are presented.

CONCLUSIONS

Laboratory coatings were prepared without and with the addition of TiO2 nanoparticles. The coatings with the addition of nanoparticles presented a visual finish with greater aesthetics.
The electrochemical impedance tests indicate that the coating with addition of TiO2 nanoparticles, provides a slight increase in the resistance against corrosion, presenting impedance values between 105 and 106 Ω-cm2.