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Croda Performance Technologies Home Care
Corrosion on Metal Substrates and Chemical Methods
to Inhibit Oxidation
2014 SATA Conference John Hughes, Applications Scientist
Croda, Inc.
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Outline
Introduction to Corrosion
What is Corrosion?
Types of Corrosion
Prevention of Corrosion
Types of Corrosion Inhibitors
Old Technologies
New Technologies
Performance Data
Conclusions
Questions
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What is Corrosion?
Corrosion is the degradation of a metal through electrochemical
reactions with the environment
Ulick R. Evans “The Father of Corrosion Science” once said,
“Corrosion is largely an electrochemical phenomenon, [which]
may be defined as destruction by electrochemical or chemical
agencies.”
The type of corrosion we are concerned about takes place in
aqueous/humid environments with normal atmospheric
conditions.
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Corrosion
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Basics of Corrosion
Corrosion involves the reaction of the water in the environment
with the metal substrate.
Source: www.chemistryadda.blogspot.com
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Basics of Corrosion Iron will react by the following mechanism:
Source: Fundamentals of Metallic Corrosion in Fresh Water
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Basics of Corrosion Aluminum metal will react in roughly the same way, except the
oxide layer formed by aluminum is relatively inert and does not
react further except under specific circumstances.
Aluminum will pit quite readily and the pitting will weaken the
metal, allowing for catastrophic failure to occur.
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Types of Corrosion
There are many forms that corrosion can take:
Uniform corrosion
A direct chemical reaction on the metal surface that produces a uniform
pattern.
Galvanic corrosion
Electrochemical reaction of when two dissimilar metals are in the
presence of an electrolyte and a conductive path.
Concentration cell corrosion
When two or more areas of a metal surface are in contact with different
concentrations of the same solution.
Pitting corrosion
Localized corrosion that occurs on a metal surface.
Crevice corrosion
Corrosion that occurs at the joints or meeting place of metal on metal or
non-metals.
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Types of Corrosion Filiform corrosion
Corrosion occurs on metal that has been painted. The moisture
seeps through the coating, then reacts with the metal underneath,
causing delamination of the paint.
Stress corrosion cracking
Cracking of the metal that occurs through repeated stress applied
onto an area that has started corroding, thereby weakening the
metal.
Microbial corrosion
Corrosion caused by microbes that have affinity for certain metals.
Flash rust corrosion
Caused by reaction of liquid with the salts found on metal. Flash
rust occurs nearly instantaneous and migrates through a paint to the
surface.
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Prevention of Corrosion
There are many methods to prevent corrosion, but none of them are perfect. Some of the methods/treatments for corrosion protection are below:
Paints, coatings, sealers, waxes, oils.
This type of treatment forms a barrier between the metal and the atmosphere.
Anodizing, conversion coatings, pretreatments.
All of these treatments depends on a chemical reaction on the surface of the metal. This reaction allows for the formation of a very thin layer of a corrosion resistant chemical directly on top of the metal. The resulting chemical is inert with the atmosphere (hexavalent chromium, cadmium, lead).
Galvanizing, aluminum deposition.
This method allows for a more electrochemically reactive metal to sacrifice itself by corroding before the base metal does.
Use of Noble metals
The use of nobel metals in place of steel, iron or other reactive metals allows for an increase in corrosion resistance, however the cost is usually very high.
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Corrosion Inhibitors – Old Technologies
Corrosion inhibitors that were used before regulations restricted
their use:
Red lead
Hexavalent Chromium
Cadmium
Nickel
Corrosion inhibitors that are under consideration for further
regulations:
Vanadium
Sodium nitrite
Phosphates – in limited uses
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Corrosion Inhibitors – Old Technologies Two types of corrosion inhibitors based on older technologies
Inorganic anti-corrosive pigments
Zinc phosphates
Calcium carbonates
Strontium zinc phosphates
Organic liquid corrosion inhibitors
Heterocyclic corrosion inhibitors
Sulfonic acid corrosion inhibitors
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Corrosion Inhibitors – New Technologies
Borate esters
Sarcosinates
Water soluble Fatty acids
Organometallic esters
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Performance – Borate Esters
Features and benefits Water soluble
Non-foaming
Effective at low addition levels [0.5%]
Applications Corrosion inhibition
Tin plated steel, e.g. aerosol cans
Cast iron
Steel
Other ferrous metals
Flash rust inhibition
Low VOC formulations
Metalworking Fluids
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Performance – Borate Ester Methodology
Tin plated steel aerosol cans, both unlined and lined (double epoxy
phenolic coating)
Aerosol cans were cut in half and filled with various test solutions,
which included:
DI water
DI water with 250 ppm NaCl
DI water with 0.5% Borate Ester
DI water with 250 ppm NaCl and 0.5% Borate Ester
Aerosol cans containing the test solutions were then covered and
allowed to sit at ambient conditions for 36 days
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Performance – Borate Ester Unlined Aerosol Can corrosion results
DI water
250 ppm NaCl
DI water + 0.5% Borate Ester
250 ppm NaCl + 0.5% Borate Ester
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Performance – Borate Ester Lined Aerosol Can corrosion results
DI water DI water + 0.5% Borate Ester
250 ppm NaCl 250 ppm NaCl + 0.5% Borate Ester
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Performance – Borate Ester Cold Rolled Steel testing
Methodology
CRS coupons were partially submerged in test solutions, which
included:
DI water
DI water with 250 ppm NaCl
DI water with 0.5% Borate Ester
DI water with 250 ppm NaCl and 0.5% Borate Ester
The coupons stayed submerged for 36 days at ambient
conditions
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Performance – Borate Ester Cold Rolled Steel results
DI water DI water + 0.5%
Borate Ester
250 ppm NaCl 250 ppm NaCl + 0.5%
Borate Ester
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Performance – Borate Ester Aerosol Can strip testing
Methodology
Strips of tin plated steel aerosol cans were cut and submerged
in test solutions, which included:
DI water
DI water with 250 ppm NaCl
DI water with 0.5% Borate Ester
DI water with 250 ppm NaCl and 0.5% Borate Ester
DI water with 0.5% sodium nitrite
DI water with 250 ppm NaCl and 0.5% sodium nitrite
The strips stayed submerged for 30 days at ambient conditions
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Performance – Borate Ester Can Strip Results
DI water 250 ppm NaCl DI water + 0.5%
Borate Ester
250 ppm NaCl + 0.5%
Borate Ester
DI water + 0.5%
Sodium Nitrate
250ppm NaCl + 0.5%
Sodium Nitrate
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Performance – Sarcosinates Key properties of N-acyl sarcosinates
N -acyl sarcosine Sodium N-acyl sarcosinate
- pH (acid)
+ pH (aq NaOH)
R = C12 – C18
Sarcosinates are ‘interrupted soaps
The amide group separates the carboxylic acid moiety from the alkyl
chain
Leads to performance differences when compared to fatty acids
Properties affected by pH
Acyl sarcosines are insoluble in water and soluble in oil (low HLB values)
Neutralised salts are water soluble and enhance detergency of
formulations (high HLB values)
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Performance – Sarcosinates Key properties of Sarcosinates: Substantivity (corrosion inhibition)
-
Strong adsorption (chelation) via
amino acid groups
Alkyl groups form hydrophobic
monolayer on the metal surface
Immersion of cold rolled steel plates in deionised water plus 0.25% active surfactant for 3.5 months @ ambient (including 1 month @ 50oC)
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Performance – Sarcosinates Key properties of Sarcosinates: Substantivity
1% LS 30 0.5% LS 30 + 0.5% SLS
When used in conjunction with wetting agents, improvements can
be seen in corrosion protection
Differing chemistries for sarcosinates allow for use in both
aqueous and non-aqueous systems
DI water 1% SLS
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Performance – Water-Soluble Fatty Acids Provides excellent ferrous corrosion inhibition performance in
water-based lubricants
Water-soluble fatty acids have an inherently low-foam profile
Water-soluble fatty acids are pre-neutralized liquid products
No blending or handling of solids required ease of use
No heating required lower energy costs
No handling of irritant solids (dust) or amines less phosphorous or
sulfur
Contain no nitrites, borates, secondary amines, metals,
phosphorus, or sulfur
Produced from 100% renewable raw materials
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Performance – Water-Soluble Fatty Acids
ASTM D 4627, cast iron chip test, 70:1 dilution in 100ppm water
Water Soluble Fatty
Acids Industry Standard
Package
No CI Package
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Performance – Water-Soluble Fatty Acids Galvanic Corrosion Inhibition
Modified chip test- 70:1 dilution in 100ppm water on mild steel Q-panel
Industry Standard
Package Water Soluble Fatty
Acids
No CI Package
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Performance – Organometallic Esters
New chemistry needed for waterborne paints to:
Increase barrier resistance
Improve corrosion resistance
Eliminate flash rusting
Development of organometallic esters:
For use in Direct-To-Metal paints
Provide maximum protection on mild steel
Eliminate flash rusting
Provide long-term corrosion protection
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Performance – Organometallic Esters Flash Rust
Flash Rust Results 1 Hour after 3 mil Drawdown
Control – DTM Paint DTM Paint + 2% OME
Corrosion Inhibitor
DTM Paint + 2%
Aromatic Sulfonic Acid
Corrosion Inhibitor
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Performance – Organometallic Esters Direct-To-Metal Latex Acrylic
Unscribed DTM Primer Spray-Applied Panels
after 500 Hours 5% Salt Fog Exposure
DTM primer with traditional
corrosion inhibitor
DTM primer with an
Organometallic Ester
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Performance – Organometallic Esters Direct-To-Metal Latex Acrylics
Scribed DTM Primer Spray-Applied Panels
after 500 Hours 5% Salt Fog Exposure
DTM primer with traditional
corrosion inhibitor
DTM primer with an
Organometallic Ester
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Performance – Organometallic Esters Alkyd Emulsion-based Paint
Alkyd Emulsion-based Paint
after 784 Hours of Continuous Salt Spray Exposure
Alkyd Emulsion Based Paint
without an Organometallic Ester
Alkyd Emulsion Based Paint
with an Organometallic Ester
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Conclusions
Corrosion takes different forms based on the metal substrate
Performance of corrosion inhibitors depend not only on solution
they are in, but also the substrate they are in contact with
Borate esters and Sarcosinates are excellent for in-can
corrosion
Water soluble fatty acids can be used at very low concentrations
in aqueous systems to inhibit galvanic corrosion
Organometallic esters are very effective for flash rust and long-
term corrosion resistance in very harsh environments