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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 firstname.lastname@example.org Dr T. J. Smith Biomedical Research Centre email@example.com Sheffield Hallam University.
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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 firstname.lastname@example.org Dr T. J. Smith Biomedical Research Centre email@example.com Sheffield Hallam University
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!
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
Existing antifouling/corrosion strategies • Use of inhibitors and biocides • – Expensive • – Often ineffective (location & concentration issues) • – Can be damaging to the environment
Outline • Sol-gel : Materials chemistry and anti-corrosion aspects (RA) • Sol-gel : Microbiology and Antifouling aspects (TJS) • Summary • Acknowledgements
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
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
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
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)
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
Bioactive coating for anti-fouling and anti-microbial induced corrosion applications.
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
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)
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
Do protective bacteria exist and work? High Corrosion Rate Low Note: the bacterial strain(s) are added as planktonic bacteria (i.e., freely suspended)
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
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
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
Colonisation of cells within sol-gel coating Immersion in nutrient broth for 1 hour Rods - Vegetative cells Solid discs - Endospores
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
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