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