Transcript Bob Akid and Tom Smith Anti-Corosion Coatings part 1.pps

Good bugs, Bad bugs;
Sol-gel Encapsulated Bacteria in AntiFouling and Anti-Corrosion Coatings
Professor R. Akid & Dr H. Wang
Centre for Corrosion Technology
[email protected]
Dr T. J. Smith
Biomedical Research Centre
[email protected]
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
Defence
Nuclear waste
Oil & gas,
chemicals
Road, air , sea
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
Sol
Nanocomposite
dense material
Gel
Evaporation
Cure
Gelation
at T & t
Sol gel chemistry
Precursor Si (OC2H5)3
= Si-O-R', where R' = C2H5
Tetraalkoxysilanes – (Methoxy or Ethoxy)
Si-O-R'
O
R'-O-Si-O-R'
O
Si
Hydrolysis
O
Condensation
Metal substrate
Bond Formation of the Sol-gel Coating
Sol-gel applied on
Outer layer
Inner layer
Metal
Si-O-R'
O
-O-Si-O-R' Al
Sol gel
Si particles R
O
O
Si
O Si O
Si O ─
M
interface
M O
Opportunities for organic-inorganic hybrid sol-gel
basic network structures
2. Incorporate threedimensional inorganic
oxide network based on
silicon or other metals (
M= Ti, Zr, or Al)
3. Encapsulated
functional additives,
e.g., bacteria,
antibiotics, inhibitors
3. Modify silicon structure
with functional organic
groups (R)
1. Modify the Si
backbone
M
Sol gel Application Methodology
Use as
functional/
barrier
coating
Colloid solution(s)
Organic and
Inorganic components
Mix and Age*
Functional Additives
e.g., corrosion inhibitors,
bio-active molecules, etc.
Apply to
metal;
Dip, Spray..
Cure at
selected
temperature
Apply top coat directly to sol gel
for anti-corrosion coating
*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
}
Colonisation
of
Sulphate
Reducing
Bacteria
(SRB)
H2S formation
Biofilm formation;
up to 48hrs depending
upon temperature
Localised
Corrosion
(pitting)
Consequences 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 SHU
• Combination of anti-corrosion sol-gel coating and protective
bacteria.
• Uniform distribution of protective bacteria fixed on the surface
Viable bacterial cells
immobilised in coating
'Biocoat'
Substrate
Paenibacillus polymyxa
Paenibacillus polymyxa endospores
• 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
Viability of P. polymyxa endospores within
sol-gel coating
Viability of P. polymyxa endospores
within sol-gel coating on AA 2024 T3
Biotic
•
Abiotic
• 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
Colonisation of cells within sol-gel coating
Immersion in
nutrient broth
for 1 hour
Rods - Vegetative cells
Solid discs - Endospores
Immersion in nutrient broth for
8 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 trials