Surface evaluation and electrochemical behavior of cerium conversion coating modified with silane on magnesium alloy

Abstract

A new cerium conversion coating modified with the hydrolysis silane is designed for AZ31 magnesium alloy, which aims at assessing the surface characterizations and electrochemical behaviors between the cerium conversion coating with and without the silane modified. The effect of the silane addictive is studied by scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS). The adhesion of the coatings is undertaken according to the American Society for Testing and Materials (ASTM) standard D3359‐08 cross tape test. The electrochemical behavior is evacuated by polarization experiment and electrochemical impedance spectroscopy (EIS) in NaCl electrolyte. The results show that the addition of bis‐[triethoxysilylpropyl] tetrasulfide (BTESPT) to loosen and porous cerium conversion coating leads to the formation of a more compact and homogenous film, higher resistance to water uptake and better adhesion to substrate. Electrochemical measurements show that, compared with the non‐modified cerium conversion coating, the coating modified with the silane exhibits better anticorrosion properties. Copyright © 2014 John Wiley & Sons, Ltd.

Chromate-Free Corrosion Protection Strategies for Magnesium Alloys—A Review: PART I—Pre-Treatment and Conversion Coating

“…Conversion coatings based on other rare earth elements have also been reported: La 3+ , Y 3+ , Nd 3+ , Pr 3+ , Sm 3+ and Gd 3+ [ 217 , 218 , 219 , 220 , 221 , 222 , 223 , 224 ]. Their combinations have been studied with each other, other inorganic ions (Zn 2+ , Mg 2+ , Ca 2+ , Al 3+ , MoO 4 2− , VO 3 − , MnO 4 − , PO 4 3− , P 2 O 7 4− ) [ 215 , 218 , 225 , 226 , 227 , 228 , 229 , 230 , 231 ], and organic compounds including silanes [ 232 ], gelatin [ 233 , 234 , 235 , 236 ], chitosan [ 233 , 234 ], sodium dodecyl benzene sulfonate [ 220 ], phytic acid [ 237 , 238 ], ascorbic acid [ 221 ], citric, and other carboxylic acids [ 215 , 220 , 221 , 233 , 239 ].…”

“…Figure 13 a shows the result of a cross-cut test after depositing a cerium conversion layer from a CeCl 3 solution containing H 2 O 2 on an AZ31 alloy (dry adhesion). Clearly, a significant part of the conversion layer was removed by the 3M 600 tape [ 232 ]. Modification of the conversion bath with silane (bis-[triethoxysilylpropyl] tetrasulfide (BTESPT)) significantly improved the adhesion ( Figure 13 ) [ 232 ].…”

Silane coatings of metallic biomaterials for biomedical implants: A preliminary review

“…79 Clearly, further work should be done on the in vitro corrosion of silane-epoxy composites. Silane-cerium composites Given the recent surge in studies on cerium-silane composites as corrosion-protective films in non-physiological environments, [80][81][82][83][84][85][86][87] it is interesting to note that silane-cerium films do not appear to have been tested in a physiologicalbased solution. Cerium ions in the coating can significantly reduce corrosion rates, provide self-healing to adjacent defect or uncoated sites and expedite crosslinking of the silane network.…”

Fabrication and properties of the superhydrophobic ceria‐based composite coating on magnesium alloy

“…[9] Many research results show that the cerium-based conversion coating can improve the corrosion resistance to a certain extent, but it is difficult to avoid the formation of surface cracks. [10][11][12][13] These cracks allow the electrolyte to easily penetrate and contact the substrate matrix, thereby accelerating corrosion. Many studies focus on optimizing the morphology and structure of the conversion coating, and some achievement have been obtained.…”