Preparation and Characterization of Silanes Films to Protect Electrogalvanized Steel
- PDF / 1,532,407 Bytes
- 9 Pages / 593.972 x 792 pts Page_size
- 25 Downloads / 257 Views
JMEPEG (2018) 27:1194–1202 https://doi.org/10.1007/s11665-018-3178-0
Preparation and Characterization of Silanes Films to Protect Electrogalvanized Steel Pablo R. Sere´, Walter Egli, Alejandro R. Di Sarli, and Cecilia Deya´ (Submitted August 11, 2016; in revised form November 6, 2017; published online February 8, 2018) 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), energydispersive 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. Keywords
protective films electrogalvanized, silane, surface treatment
1. Introduction Conversion coatings based on Cr(VI) have been used for many years to protect galvanized steel against corrosion during storage and use. Despite being very efficient, the Cr(VI) presents high toxicity and carcinogenicity (Ref 1), and therefore, it is necessary to find new alternatives, friendly with the environment and public health. As a result, in recent years, there have been numerous investigations on Cr(III), Ce(III), La(III)-based pretreatments with promising results (Ref 2-5). However, pretreatment solutions based on functionalized silanes appear to be one of the best alternatives (Ref 6, 7). Although the silanes do not provide the self-repair (‘‘selfhealing’’) effect offered by coatings containing Cr(VI), they are neither toxic nor pollutant, have good thermal stability and are resistant to erosion (Ref 8, 9). The protective mechanism provided to the substrate by silane coatings is only by barrier effect (Ref 10-14). Therefore, the protection ability not only depends on the film porosity and thickness, but also on the silane nature. The presence of hydrophilic or hydrophobic chains in its structure can control the rate of water diffusion through the coating film (Ref 15). In addition, substrate characteristics such as roughness, metal structure, and impurity Pablo R. Sere´, and Cecilia Deya´, CIDEPINT, Centro de Investigacio´n y Desarrollo en Tecnologı´a de Pinturas (CICPBA-CONICET), Av. 52 entre 121 y 122 S/N, CP 1900 La Plata, Argentina; and Facultad de Ingenierı´a, UNLP, 1 y
Data Loading...
