good bugs, bad bugs; sol-gel encapsulated bacteria in anti- fouling and anti-corrosion coatings...
TRANSCRIPT
Good bugs, Bad bugs; Sol-gel Encapsulated Bacteria in Anti-Fouling and Anti-Corrosion Coatings
Professor R. Akid & Dr H. WangCentre for Corrosion Technology
Dr T. J. SmithBiomedical Research Centre
Sheffield Hallam University
What are the benefits of these coatings?
For industrialised countries the cost of Corrosion is currently around 3-4% GDP. This is estimated this at a cost of $140Bn
Bridges, railroads Gas, Electricity distribution
Road, air , sea
Oil & gas, chemicals
DefenceNuclear waste
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
Gelation is the process of bond formation
Evaporation
Gelation
GelSolNanocompositedense material
Cure
at T & t
Formation of Sol-gel MaterialsFormation of Sol-gel MaterialsWhat 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?
Sol gel chemistrySol gel chemistry
Metal substrate
Precursor Si (OC2H5)3 = Si-O-R', where R' = C2H5
O
R'-O-Si-O-R'
Si-O-R'
Si
O
O
Hydrolysis
Condensation
Tetraalkoxysilanes – (Methoxy or Ethoxy)
Bond Formation of the Sol-gel CoatingBond Formation of the Sol-gel Coating
Metal
Sol-gel applied onInner layer
Outer layer
-O-Si-O-R'
Si-O-R'
Si
O
O
O
MO ─
Si
OR
M
Si O
O
Sol gel Al
interface
Si particles
Opportunities for organic-inorganic hybrid sol-gel Opportunities for organic-inorganic hybrid sol-gel basic network structuresbasic network structures
1. Modify the Si backbone
3. Modify silicon structure with functional organic groups (R)
2. Incorporate three-dimensional inorganic oxide network based on silicon or other metals ( M= Ti, Zr, or Al)
3. Encapsulated functional additives, e.g., bacteria, antibiotics, inhibitors
M
Sol gel Application MethodologySol gel Application Methodology
Cure at selected
temperature
Apply top coat directly to sol gelfor anti-corrosion coating
Use asfunctional/barrier coating
Colloid solution(s)Organic and
Inorganic components
Functional Additivese.g., corrosion inhibitors,bio-active molecules, etc.
Mix and Age*
*Ageing time dependant upon formulation chemistry
Apply to
metal;
Dip, Spray..
Bioactive coating for Bioactive coating for anti-fouling and anti-microbial anti-fouling and anti-microbial
induced corrosion applications.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)
}
Colonisation ofSulphateReducingBacteria(SRB)
H2S formation
Localised Corrosion(pitting)
Microorganisms, especially bacteria, colonise surfaces to form Biofilms
Biofilm formation; up to 48hrs depending upon temperature
Consequences of MICConsequences of MIC
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)
Antifouling/MIC approach at SHUAntifouling/MIC approach at SHU
• Combination of anti-corrosion sol-gel coating and protective bacteria.
• Uniform distribution of protective bacteria fixed on the surface
Substrate
'Biocoat'
Viable bacterial cells immobilised in coating
Paenibacillus polymyxa
• A bacterium that actually inhibits corrosion and biofouling
• often found in soil• non-pathogenic• Forms highly-resistant
endospores in response to environmental stress
• Endospores remain inert until nutrients/germinants available
Magnification x 1000
Paenibacillus polymyxa endospores
Viability of P. polymyxa endospores within sol-gel coating
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
Magnification x 1000
Abiotic
Biotic
Colonisation of cells within sol-gel coatingColonisation of cells within sol-gel coating
Rods - Vegetative cells
Solid discs - Endospores
Immersion in nutrient broth for 1 hour
Immersion in nutrient broth for Immersion in nutrient broth for 8 hours8 hours
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
Bio-active coating - field trialsBio-active coating - field trials