Nanoparticle Based Coatings for Corrosion Protection of Steel, Aluminium and Magnesium Alloys

Transcription

1 Research for Sustainable Technologies F. Depentori, S. K. Weidmann, B. Tigges, D. Tabatabai, W. Fürbeth Nanoparticle Based Coatings for Corrosion Protection of Steel, Aluminium and Magnesium Alloys METALKOKKOLA, Finnland, Materials Chemical Engineering Biotechnology

2 acknowledgements! Fraunhofer IKTS, Germany - Dr. Michael Schneider, Kerstin Kremmer Fraunhofer IFAM, Germany - Dr. Olga Yezerska University of RWTH Aachen, Germany - Prof. Dr. Wolfgang Bleck, Dr. Christian Klesen, Alexander Tenié University of Paderborn, Germany - Prof. Dr. Guido Grundmeier, University of Paderborn, Germany 2

3 Outline introduction oxidation protection by SiO 2 nanoparticle pore sealing nanoparticle stabilized Mg-oxide 3

4 why coatings for corrosion protection often cheapest available method typical applications: galvanized steel anodizing layer anodized aluminium base metal 4

5 advantages of nanoparticle based coatings unique properties surface to volume ratio lowered melting point lowered sintering T size dependent melting point of Au tunable IEP size dependent IEP of TiO 2 Suttiponparnit et al. Nanoscale Res Lett 2011, 6:27, p. 5 Ph. Buffat and J.P. Borel, Phys Rev. A13,2287 (1976) 5

6 Outline introduction oxidation protection by SiO 2 nanoparticle pore sealing nanoparticle stabilized Mg-oxide 6

7 High temperature corrosion of 22 MnB5 steel Steel alloy Formation of an austenitic microstructure (950 ⁰C, N 2 ) Steel alloy Steel alloy Formation of martensitic microstructure Fast cool-down to 200 ⁰C Steel alloy strong oxidation of 22 MnB5 in hot stamping oxide scale inhibits further processing 7

8 Severe oxidation of 22MnB5 steel! Scales formed during exposure to 950 C Further processing e. g. welding impossible 8

9 application of a mixed nanoparticulate Solution of 5 and 100 nm SiO 2 nanoparticles filling of voids Steel alloy 700 C low melting point low sintering point Steel alloy 9

10 cross section of coated sample Mixed dispersion coated on 22MnB5 C, 30 min, N C 10

11 coated sample after testing Mixed dispersion coated on 22MnB5 C, 30 min, N C 30 min, N 2 slight oxidation 700 C C 11

12 Outline introduction oxidation protection by SiO 2 nanoparticle pore sealing nanoparticle stabilized Mg-oxide 12

13 anodizing of aluminium alloys Idea: apply high voltage thick oxide layer pores Problem: anodizing layer is porous Solution: sealing of pores 13

14 the nanoparticle approach standard procedure: Chromic acid anodizing (CAA) toxic (Cr 6+, violates EU regulations) new approach: Phosphoric acid anodizing (PAA) pores seal pores with nanoparticles (impregnation) dip coating nanoparticle solution pore sealing 14

15 SiO 2 sealed pores on AA 1050 alloy Size of nanoparticles: 9 nm (aqeous dispersion) height of pore filling 30 % SiO 2 solution 20 % SiO 2 solution 10 % SiO 2 solution Different SiO 2 content different level of pore filling 15

16 phase / SiO 2 sealed pores on AA 1050 alloy impedance Z / cm 2 comparison to CAA process: 1G 100M 10M 1M 100k 10k 1k CAA modified PAA- impregnated log (f/hz) 0.1 M NaCl competitive! R P similar to CAA different phase response 16

17 Outline introduction oxidation protection by SiO 2 nanoparticle pore sealing nanoparticle stabilized Mg-oxide 17

18 Mg AZ 31, modified anodizing process Idea: anodizing solution contains nanoparticles anodized without particles SEM image: Nadine Buitkamp, Coating Materials & Polymers, University Paderborn δ - δ - δ - δ - δ - δ - δ - Mg alloy Mg alloy Mg alloy 18

19 particle stability of anodizing solution two concentrations of electrolyte: 0.1 M / 1 M KOH 1 M solution must be used within few days! conductivity vs. concentration 19

20 cross section of anodized layer Si well dispersed in anodizing layer embedding resin anodizing layer AZ 31 1 M KOH 10 ma/cm 2 20

21 Comparison of different surface modifications protective effect visible from anodizing best effect: modified anodizing but: no long term stability! layer is still porous! 21

22 Conclusions nanoparticle based coatings new possibilities each system has its difficulties more research in progress combination with other techniques: diffusion coatings, plasma electrolytic oxidation (PEO) 22

23 Outlook Corrosion inhibitor containing nanoparticles on Mg alloys: PEO + hydroxyapatite on Ti-alloys biocompatibility 23