Evaluation of a sulfursilane anticorrosive pretreatment on galvannealed steel compared to phosphate under a waterborne epoxy coating
By Francisco, J.S.; Capelossi, V.R. & Aoki, I.V.
Published in Electrochimica Acta
NULL
2014
Abstract
Galvannealed coatings are produced by annealing zinc hot dip coated steel where iron and zinc undergo interdiffusion to form iron–zinc alloys. They offer some attractive features like better weldability, paintability, corrosion resistance, ductibility and formability, depending on the morphology, composition and structure of the coating phases. Silane films are a good choice to replace phosphate pretreatment, and in the case of bis-sulfursilane films, the sulfur chains also help to increase the hydrophobicity of the film and its protection against corrosion. Epoxy coatings are reasonably corrosion resistant and generally applied as primers or direct-to-metal (DTM) coatings in coating systems for different metallic substrates. Using the optimum conditions previously determined for obtaining a 3% bis-1,2-[triethoxysilylpropyl] tetrasulfide (BTESPT) solution in a water/ethanol solvent at pH 4 hydrolyzed in the presence of 50 ppm Ce(IV) ions, the silane solution was applied on galvannealed steel samples by dip coating process with samples remaining immersed for 15 min before being withdrawn and cured for 40 min at 150 ÌŠC. The bare galvannealed samples were previously treated, first by sonication in acetone and then by a commercial alkaline degreasing solution. The phosphate samples were prepared in an industrial set using the tricationic bath containing Mn, Zn and Fe phosphates. The waterborne epoxy coating was applied with a brush to reach a 60 ± 6 μm dry film thickness layer. The evaluation was performed by electrochemical technique: EIS, electrochemical impedance spectroscopy, and also by accelerated tests in a salt spray cabinet (SSC). The silane, phosphate and non-treated samples were tested in 3.5wt% NaCl solution in a cell of 20 cm2 after 3 h, 24 h, 96 h, 264 h, 360 h, 528 h and 720 h of immersion in the electrolyte solution. The results indicated that the silane pre-treated samples have shown the highest impedance modulus value even after 530 h of immersion. Adherence and flexibility were also evaluated by tape test–X method–and conic mandrel test. The results have evidenced the superior adherence of the coating for the silane pre-treated samples. The SSC test revealed that the silane pretreated samples showed less blistered area around the scratch. In summary, the sulfursilane pretreated samples presented an overall better performance concerned to the corrosion resistance compared to phosphate and waterborne epoxy coated galvannealed steel samples.
Microsoft is Ending Support for Windows 7
Microsoft will discontinue support for Windows 7 on January 14, 2020 which means Gamry will also be discontinuing support for Windows 7. If you are upgrading to Windows 10, like many companies and institutions, you need to be running Version 7 of our s oftware . Please note that only USB and Ethernet-based instruments can run in Version 7. Eligible users can download the latest version of our software through our online Client Portal .
If you haven't already registered your instrument, you can do so through the Client Portal .
Please email Technical Support if you have any questions regarding this transition. Please be sure to include your instrument model and serial number when contacting us.