Electrochemical study of the synergic effect of phosphorus and cerium additions on a sol-gel coating for Titanium manufactured by powder metallurgy

Abstract

The goal of this work was to combine the physical barrier properties provided by the sol-gel network with an active-chemistry protection against corrosion provided by corrosion inhibitors and cross-linking agents. Sol-gel coatings, organic-inorganic hybrid materials were prepared by hydrolysis and condensation of (3-glycidylox-ypropyl)trimethoxysilane (GPTMS) and tetraethylorthosilane (TEOS) in an ethanol/water solution. This coatings were satisfactorily modified by adding an inhibitor of the corrosion, namely hexahydrate cerium nitrate, and a cross-linking agent, namely tris(trimethylsilyl)phosphite (TMSP). The synergetic effect of these two compounds was evaluated by means of electrochemical characterization. The evolution rate of the hydrolysis-poly-condensation reaction was monitored by Fourier-transform infrared spectroscopy and viscosity. Once the hy-drolysis-polycondensation rate was reached, sols were deposited on titanium fabricated by powder metallurgy. The morphological characteristics and elemental distribution of the coatings were studied using scanning electrochemical microscopy (SEM). The solid-state of Si-NMR spectroscopy and thermogravimetric analysis (TGA) was employed in order to identify the cross-linking state of the coating by ensuring the creation of enough siloxane bonds. Impedance measurements were carried out to study the effect of cerium and TMSP on the corrosion resistance. It was observed that the coating with additions of cerium presented stable and good barrier features against 5 mM NaCl solution. The synergy between the cerium inhibitor and the TMSP cross-linking agent was found not to exert a positive effect because the electrochemical behaviour was dominated by the phosphorus compound over the cerium.

The effect of the organosilane content on the barrier features of sol-gel anticorrosive coatings applied on carbon steel

“…These chemical shifts correlate with the ones reported in the literature [22,23]. The absence of T0 and Q0 signals in the three xerogels corresponds to the non-condensable molecules of GPTMS and TEOS [21], which ensures a high cross-linkage of the sol-gel network. The good cross-linkage achieved in the three networks is confirmed with the identification of signals T3 and Q4.…”

“…The first step, at low temperatures from 30 to 300 °C, the second stage at middle temperaturas between 300 and 500 °C, and the final step from 500 to 850 °C. Peaks detected at low temperatures are assigned to the evaporation of residual, small molecules, such as water, ethanol, unreacted silanols, or molecules from scissions of the unstable head-to-head linkages [18][19][20][21]. The second stage is originated from the degradation of organic chains of siloxanes, therefore xerogels with more proportion of organic compound (GPTMS), TG12, has higher intensity on the first derivate peak and the maximum of these peaks is displaced to lower temperaturas (Table 3).…”

Influence of Addition of Antibiotics on Chemical and Surface Properties of Sol-Gel Coatings

“…Sols were dried at room temperature for 7 days and ground into powder in an agate mortar before the characterization by 29 Si-NMR and TGA [31].…”

Surface Modification of Biomedical Titanium Alloy: Micromorphology, Microstructure Evolution and Biomedical Applications

“…Sol-gel coating can not only act as a barrier layer to isolate the metallic substrates from the human body environment, but also achieve multi-functional coating by adding different components, such as corrosion inhibitors, growth factor and antibacterial factor [106]. Michelina et al [107] prepared organic-inorganic composite coatings on the surface of CP Ti grade 4 substrates by sol-gel method, and successfully improved the elastic-plastic coating without cracks by adding poly (ε-caprolactide).…”