Protective coatings with self-healing ability based on nanocontainers of corrosion inhibitor

Transcription

1 Protective coatings with self-healing ability based on nanocontainers of corrosion inhibitor M.L. Zheludkevich, M.G.S. Ferreira University of Aveiro, CICECO, Dep. Ceramics and Glass Eng., Portugal

2 Corrosion protection of metallic substrates Passive corrosion protection Use of coatings +Good barrier against corrosive species +Tailored surface properties -Lack of self-healing Active corrosion protection Employment of inhibiting species +Decrease of corrosion rate +Self-healing of defects -Should be added to corrosive medium Passive + active Coating + Corrosion Inhibitor +Combination of barrier and self-healing -Negative effect of inhibitor on coating stability -Deactivation of inhibitor in coating -Uncontrollable release of inhibitor 2

3 Effect of inhibitor on stability of coating b) Lower hydrolytical stability Osmotic blistering 3

4 To nano-encapsulate corrosion inhibitors before addition to the coating Possible Advantages Prevention of inhibitor deactivation due to interaction with coating components Reduction of negative effect of the inhibitor on coating Controllable release of inhibitor on demand 4

5 Experimental Substrate: aluminium alloy 2024-T3 Cleaning: acetone, alkaline cleaning for 20 minutes at 65ºC with Metaclean T200r (aqueous solution 48g/L), alkaline etch for less than 1 minute at 60ºC with Turco Liquid Aluminetch nº2 (aqueous solution 43ml/L), acid desmutting for 5-10 minutes at 30ºC with Turco Liquid Smutgo NC (aqueous solution 180ml/L), rinsing with deionised water, drying with absorbent paper and forced warm air. Coating: epoxy-functionalized hybrid sol-gel film Inhibitor: n-benzotriazole, mercaptobenzothiazole, Ce (III) Nanoreservoirs: Oxide nanoparticles Porous nanostructured layers LbL constructed nanocontainers Halloysites 5

6 In-situ formed oxide nanopartcles as reservoirs of corrosion inhibitors GPTMS + 2-propanol+H 2 O TPOZ + H 2 O + Ce 3+ 6

7 Corrosion protection performance of nanocomposite films without inhibitor with inhibitor 1 month immersion in 3% NaCl solution 7

8 Porous layer as nanostructured reservoir of corrosion inhibitor nm 200nm 0.00 nm The micelle-template approach can be used to obtain porous nanostructured titania tania pre-layer before hybrid film deposition 8

9 Porous layer as nanostructured reservoir of corrosion inhibitor Evolution of pore resistance for different hybrid films R coat, Ohm cm doped TiO x + sol-gel sol-gel+0.13% benzotriazole undoped sol-gel time, hours Use of nanostructured porous reservoir prevents degradation of sol-gel film due to introduction of inhibitor Z mod, ohm.cm 2 Bode diagrams for two-layer system after long immersion in 0.05 M NaCl Frequency, Hz Frequency, Hz hours hours hours hours Increase of low frequency impedance is originated from defect passivation Phase angle, deg Two-layer system demonstrates promising results with signs of self-healing effect 9

10 LbL polyelectrolyte nanocontainers for inhibitor encapsulation Layer by Layer assembling process av. particle size, nm SiO 2 SiO 2 /PEI/PSS/BT/PSS/BT SiO 2 /PEI/PSS/BT/PSS SiO 2 /PEI/PSS/BT SiO 2 /PEI/PSS SiO 2 /PEI Layer number

11 Self-healing of an artificial defect 5 hours 24 hours 48 hours nanocontainers +benzotriazole undoped Suppression of the active corrosion processes demonstrates self-healing of artificial defect in sol-gel film doped with nanocontainers loaded with benzotriazole 11

12 Mechanism of smart self-healing Cl - Cl - Cl - Induced defect opens pathway for chloride ions Corrosion processes start on the alloy surface Cathodic reactions generate hydroxyls leading to local increase of ph: 2H O + 2e OH + H 2 2 O H O + e 2 4 OH 2 Raise of ph increases permeability of polyelectrolyte shell leading to release of inhibitor Released benzotriazole hinders corrosion activity healing the defect 12

13 Halloysite as nanocontainers of corrosion inhibitor Halloysite is defined as a two-layered aluminosilicate,, which has a hollow tubular structure in the submicrometer range. The halloysite tubules are very small with a typical size of less than 3.0 µm long 0.3 µm m outer diameter and have an inner diameter of nm depending on the deposits. SEM (A) and TEM (B) images of the halloysite nanotubes 13

14 Halloysite as nanocontainers of corrosion inhibitor Fabrication of 2-mercaptobenzothiazole-loaded halloysite/polyelectrolyte nanocontainers 14

15 Conclusions Several new approaches of corrosion inhibitor delivery on demand are proposed conferring intelligent self-healing ability to the protective films. Controllable delivery is achieved incorporating nanocontainers of corrosion inhibitor in the hybrid pretreatment systems. Cl -Cl- Cl - The sol-gel films doped with nanoreservoirs of corrosion inhibitors demonstrate very important selfhealing ability conferring active corrosion protection to the hybrid film. Introduction of the inhibitor in the form of nanocontainers instead of the direct addition to the sol-gel matrix prevents the interaction of an inhibitor with components of the coating, which can negatively influence the barrier properties of the hybrid film and lead to the deactivation of the corrosion inhibitor.

16 Acknowledgements This work is supported by IP "MULTIPROTECT" MULTIPROTECT" " Sixth Framework Programme Contract N Financial support from the FCT project (contract # POCI/CTM/59234/2004) ) is gratefully acknowledged. 16

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