Different organic groups affect anticorrosion

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Different organic groups affect anticorrosion properties of hybrid coatings. Three kinds of hybrid coatings modified by TEOS are prepared using precursors of vinyltrimeth- oxysilane (VMS), [3-(methacryloxy) propyl] trimethox- ysilane (MPMS) and (3-glycidoxyproyl) trimethoxysilane (GPS). The anticorrosion ability decreases in the order of VMS [ MPMS [ GPS coating [ 32 ]. 3.2 Ratio of inorganic and organic components The increase of polymer or organic component concen- tration tends to promote the formation of thicker films to restrict the diffusion of potentially corrosion species to the coating/metal interface [ 5 ]. However, a high concentration of polymer or organic component decreases the effect of adhesion and reinforcement of inorganic sol. There is an appropriate ratio of inorganic–organic components show- ing the maximum corrosion resistance of metals. Three different types of precursors including inorganic (pure boehmite), organic (hydrolyzed GPS) and hybrid sols Table 1 Performance of corrosion protection by different amino-silanes as crosslinking agents [ 31 ] Coating Potentiodynamic test Impedance modulus at low frequency (10 - 2 Hz) by EIS test I corro. (nA) E corro. (V) Immersion time | Z | ( X cm 2 ) Crosslinked with mono-amino-silane 211 - 0.581 Initial immersion 7.9 9 10 5 Crosslinked with di-amino-silane 20 - 0.569 14 days 2.8 9 10 5 Initial immersion 2.9 9 10 6 Crosslinked with tri-amino-silane 18 - 0.523 14 days 5.6 9 10 5 Initial immersion 1.4 9 10 6 Crosslinked with DETA 21 - 0.580 14 days 2.5 9 10 5 Initial immersion 1.3 9 10 4 Bare AA 2024-T3 1,460 - 0.591 Initial immersion 1.2 9 10 4 J Sol-Gel Sci Technol (2010) 54:174–187 177 123
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(boehmite-GPS) are prepared deposited on ultrasonically cleaned galvanized iron plates by dipping at room tem- perature. Only the coating cured at 150 ° C for 3 h with GPS to boehmite molar ratio = 0.7 exhibits the maximum cor- rosion resistance property, which attributes to the forma- tion of a dense microstructure by cross-linking of functionalized nano-particles [ 33 ]. We infer from the study that the hybrid coatings are more suitable for fighting corrosion than their inorganic or organic coatings, and an appropriate ratio of inorganic and organic components exhibits the maximum corrosion resistance. Zirconia-PMAA sol–gel hybrid coatings were deposited by dip-coating on stainless steel. The film prepared with 17 vol.% of PMAA has a maximum corrosion resistance, smaller roughness, is hermetic and adherent to the sub- strate, which increases the life time of the stainless steel by a factor 30 [ 34 ]. Hybrid sol–gel coatings have a maximum corrosion resistance with MTEOS/TEOS ratio 3 [ 35 ]. The hybrid coatings (VMS ? 20% TEOS) show the best anti- corrosion properties [ 32 ]. 3.3 Coatings thickness Thick hybrid coatings restrict the diffusion of potentially corrosion species such as water, oxygen and chloride ions to the coating/metal interface. An advantage of the organically modified sol–gel systems is the possibility to prepare thick, crack-free coatings [ 36 ].
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