- Achieving highly cross-linked sol-gel coatings to provide effective corrosion protection of Mg alloys remains a challenging task. The aim of this work is to evaluate the effect boron trifluoride diethyl etherate (BF3·O(C2H5)2) as catalyst to epoxy group in a GPTMS/TEOS/SiO2 sol and assesses its effect on the structure and corrosion resistance properties of Flash-PEO coated pre-treated Mg alloy. 29Si MAS NMR and 13C CPMAS-NMR demonstrated that (BF3·O(C2H5)2) efficiently promotes the epoxy polymerization of the GPTMS and the formation of a hybrid silica network. However, the amount of (BF3·O(C2H5)2) should be optimized to minimize the formation of undesirable byproducts such as ethyl ether terminal units. Therefore, GPTMS/TEOS/SiO2 sols containing different amounts of (BF3·O(C2H5)2) were synthesized and deposited onto the Flash-PEO coated Mg alloy, leading to bilayer systems with a total thickness of ⁓8 μm. The corrosion behavior of the bilayer coatings in 3.5 wt% NaCl solution wasAchieving highly cross-linked sol-gel coatings to provide effective corrosion protection of Mg alloys remains a challenging task. The aim of this work is to evaluate the effect boron trifluoride diethyl etherate (BF3·O(C2H5)2) as catalyst to epoxy group in a GPTMS/TEOS/SiO2 sol and assesses its effect on the structure and corrosion resistance properties of Flash-PEO coated pre-treated Mg alloy. 29Si MAS NMR and 13C CPMAS-NMR demonstrated that (BF3·O(C2H5)2) efficiently promotes the epoxy polymerization of the GPTMS and the formation of a hybrid silica network. However, the amount of (BF3·O(C2H5)2) should be optimized to minimize the formation of undesirable byproducts such as ethyl ether terminal units. Therefore, GPTMS/TEOS/SiO2 sols containing different amounts of (BF3·O(C2H5)2) were synthesized and deposited onto the Flash-PEO coated Mg alloy, leading to bilayer systems with a total thickness of ⁓8 μm. The corrosion behavior of the bilayer coatings in 3.5 wt% NaCl solution was evaluated by electrochemical impedance spectroscopy (EIS) and Scanning Kelvin probe microscope (SKPFM). The results revealed that the barrier properties of the coatings with enhanced cross-linked structure showed impedance modulus (│Z│f:0.1 Hz) approximately four orders of magnitude higher than the bare magnesium alloy and two orders of magnitude higher than the F-PEO coated sample. A suitable compromise between (BF3·O(C2H5)2) amount and sol-gel film structure is required to obtain a more durable barrier coating capable to extend the protective lifespan of the magnesium alloy.…

