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Good bugs, Bad bugs; Sol-gel Encapsulated Bacteria in Anti-Fouling and Anti-Corrosion Coatings PowerPoint Presentation
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Good bugs, Bad bugs; Sol-gel Encapsulated Bacteria in Anti-Fouling and Anti-Corrosion Coatings

Good bugs, Bad bugs; Sol-gel Encapsulated Bacteria in Anti-Fouling and Anti-Corrosion Coatings

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Good bugs, Bad bugs; Sol-gel Encapsulated Bacteria in Anti-Fouling and Anti-Corrosion Coatings

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  1. Good bugs, Bad bugs; Sol-gel Encapsulated Bacteria in Anti-Fouling and Anti-Corrosion Coatings Professor R. Akid & Dr H. Wang Centre for Corrosion Technology Dr T. J. Smith Biomedical Research Centre Sheffield Hallam University

  2. What are the benefits of these coatings?

  3. Bridges, railroads Gas, Electricity distribution Defence Nuclear waste Oil & gas, chemicals Road, air , sea For industrialised countries the cost of Corrosion is currently around 3-4% GDP. This is estimated this at a cost of $140Bn 1 Hurricane Katrina every year!

  4. Costs of fouling 1994 – world shipping fleet burnt 184 Million tonnes of fuel oil. If no antifouling paints are used this fuel consumption is increased by 40% (= 72M tonnes of FO) Note in that year the North Sea oil platforms produced 100M tonnes of FO

  5. Existing antifouling/corrosion strategies • Use of inhibitors and biocides • – Expensive • – Often ineffective (location & concentration issues) • – Can be damaging to the environment

  6. Outline • Sol-gel : Materials chemistry and anti-corrosion aspects (RA) • Sol-gel : Microbiology and Antifouling aspects (TJS) • Summary • Acknowledgements

  7. Formation of Sol-gel Materials What is sol-gel? A sol is a colloidal suspension of solid particles (1-1000nm size) in a liquid What is a gel? A gel is a substance that contains a continuous liquid phase What is gelation? Gelation is the process of bond formation Nanocomposite dense material Sol Gel Cure Evaporation Gelation at T & t

  8. Si-O-R' Si O R'-O-Si-O-R' O Metal substrate Sol gel chemistry Precursor Si (OC2H5)3 = Si-O-R', where R' = C2H5 Tetraalkoxysilanes – (Methoxy or Ethoxy) Hydrolysis O Condensation

  9. Bond Formation of the Sol-gel Coating Si-O-R' Si Sol-gel applied on Outer layer O -O-Si-O-R' Inner layer Metal O R O O M Si O Al Sol gel O Si M O ─ Si particles interface

  10. Opportunities for organic-inorganic hybrid sol-gel basic network structures 1. Modify the Si backbone 2. Incorporate three-dimensional inorganic oxide network based on silicon or other metals ( M= Ti, Zr, or Al) M 3. Encapsulated functional additives, e.g., bacteria, antibiotics, inhibitors 3. Modify silicon structure with functional organic groups (R)

  11. Use as functional/ barrier coating Apply to metal; Dip, Spray.. Cure at selected temperature Mix and Age* Apply top coat directly to sol gel for anti-corrosion coating Sol gel Application Methodology Colloid solution(s) Organic and Inorganic components Functional Additives e.g., corrosion inhibitors, bio-active molecules, etc. *Ageing time dependant upon formulation chemistry

  12. Bioactive coating for anti-fouling and anti-microbial induced corrosion applications.

  13. Background • Fouling & Microbially-induced corrosion • Marine corrosion is exacerbated by the formation of destructive biofilms on metal surfaces • For example, sulfate-reducing bacteria (SRB) such as Desulfovibrio desulficurans forms H2S as a metabolic by product

  14. Microbiologically Influenced Corrosion (MIC)(Bacteria & Biofilms) Microorganisms, especially bacteria, colonise surfaces to form Biofilms } Biofilm formation; up to 48hrs depending upon temperature Colonisation of Sulphate Reducing Bacteria (SRB) H2S formation Localised Corrosion (pitting)

  15. Consequences of MIC

  16. Current Approaches to mitigate Fouling & MIC • Application of synthetic polymers/paints: some bacteria can use the coating as a hydrocarbon food source • Controlled dosing with biocides: impacts upon the environment • Changes in environmental conditions, e.g., remove water from fuels, oils etc. not often feasible Biocoat approach • Bacteria can reduce corrosion • Coating designed upon fundamental knowledge of corrosion and microbial ecology

  17. Do protective bacteria exist and work? High Corrosion Rate Low Note: the bacterial strain(s) are added as planktonic bacteria (i.e., freely suspended)

  18. Viable bacterial cells immobilised in coating 'Biocoat' Substrate Antifouling/MIC approach at SHU • Combination of anti-corrosion sol-gel coating and protective bacteria. • Uniform distribution of protective bacteria fixed on the surface

  19. Paenibacillus polymyxa A bacterium that actually inhibits corrosion and biofouling often found in soil non-pathogenic Forms highly-resistantendospores in response to environmental stress Endospores remain inert until nutrients/germinants available Paenibacillus polymyxa endospores Magnification x 1000

  20. Viability of P. polymyxa endospores within sol-gel coating

  21. Viability of P. polymyxa endospores within sol-gel coating on AA 2024 T3 Following immersion in artificial sea-water, germination occurs, forming microcolonies within the sol-gel microstructure Coating thickness ~10µm Akid R, Wang H, Smith T. J, Greenfield D, and Earthman, J. C, 2008, Advanced Functional Materials 18, 203-211 Abiotic Biotic Magnification x 1000

  22. Colonisation of cells within sol-gel coating Immersion in nutrient broth for 1 hour Rods - Vegetative cells Solid discs - Endospores

  23. Immersion in nutrient broth for 8 hours

  24. Spores in the coating remain viable • There is an increase in the number of vegetative cells visible under fluorescence microscopy the longer the Al 2024 coupons are immersed in the nutrient broth • This suggests a sustained ability of the spores to germinate under these conditions, and that enough nutrition is able to reach the spores in order to induce germination

  25. Propagation of corrosion/biofouling bacteria from the coating • It was possible to recover vegetative cells from the nutrient broth, following removal of the metal substrate • This indicates the release of vegetative cells from the sol-gel coating that are the result of the germination of encapsulated spores

  26. Bio-active coating - field trials