The Efficiency of Corrosion Inhibitors - Halox

Topics Basics of corrosion Corrosion control methods Features of corrosion inhibitors• Types of Ions, Solubility & Synergy Applying Synergy to Solve CorrosionProblems Meeting the demands of the future Concluding remarks & references

Standard Reduction PotentialsStandard Potential (V)Reduction half reaction1.23 O 2 + 4H + + 4e - 2H 2 O0.80 Ag + (aq) + e - Ag (s)0.34 Cu 2+ (aq) + 2e - Cu (s)0.0 2H + (aq) + 2e - H 2 (g)-0.44 Fe 2+ (aq) + 2e - Fe (s)Since E 0 red (Fe 2+ ) < E 0 red (O 2 )iron can be oxidized by oxygen

Basics of Corrosion Dissolved oxygen in water usuallycauses the oxidation of iron Fe 2+ initially formed can be furtheroxidized to Fe 3+ which forms rust,Fe 2 O 3 .xH 2 O Oxidation occurs at the site with thegreatest concentration of O 2

Galvanizing to Prevent Corrosion

Corrosion ControlMethods

Corrosion Control Methods Protective Coatings (92%)• Organic – Paint, Varnishes, Coal tar• Metallic – Galvanizing, Electroplating• Conversion – Phosphate, Chromate Corrosion Resistant Materials (6-7%)• Alloys, Plastics, Composites, Glass Corrosion Inhibitor Additives (1-2%)• Chemical – Inorganic, Organic, Mixtures

Features of CorrosionInhibitors

FeatureTypes of ions Solubility Purity / ModificationMorphologyPigment PolymerInteractionMoisture contentPVC of CIEnvironment(pH, Corrosive)Synergy What does it Influence?Protective film formedLeaching, blistering, protecting abilityProtective film, blistering, corrosionDispersion, film formation, water transmissionLong-term stability, accelerated cross-linking,catalytic effects on cureAccelerated cure, decreased corrosion resistanceGloss, film formation, blisteringSolubility, efficiency of pigmentProtective mechanisms

Ionic types: ComparisonRef # Trade Name Chemistry/IonsP1 Zinc Chromate Zinc ChromateP2 Butrol 23 Barium MetaborateP3 Shieldex Calcium Silica GelP4 Cotrol 18-8 Amino CarboxylateP5 HALOX BW-111 Barium PhosphosilicateP6 K-White 105 Aluminum TriphosphateP7 Heucophos ZPZ Modified Zinc Phosphate

Pigment Extracts Chosen to StudyPigments Protective Ability Leaching 1 g of each (sparinglysoluble) pigment in 500 ml of 0.5 MNaCl for a period of 24 hrs Mixture is filtered and pH &conductivity of the extracts ismeasured Substrates was submerged inelectrolyte for 16 hrs (steady-state) Polarization experiments conductedusing the extract solutions over CRSand zinc substrates Fresh electrolytes (0.5 M NaCl) areused each time for the anodic andcathodic polarization scansElectrolyteCounter electrodeCellSubstrateElectricContact

Corrosion Efficiency on CRSWhere:i 0= Corrosion rate inabsence of corrosion inhibitori I= Corrosion rate inpresence of corrosion inhibitor

Corrosion Efficiency on CRSRef #E corr(mV vs SCE)Rp(kΩ)i corr(µA/cm 2 )% InhibitionEfficiencyBlank -639 0.21 ± 0.07 76 ± 7-P1-5781.20 ± 0.1713 ± 383P2-5450.60 ± 0.0234 ± 155P3-5521.23 ± 0.0721 ± 172P4-5500.74 ± 0.0931 ± 159P5-5030.90 ± 0.1125 ± 367P6-5490.95 ± 0.0518 ± 276P7-5853.37 ± 0.424 ± 195DECREASING CORROSION EFFICIENCY:P7 > P1 > P6 > P3 > P2, P4, P5Best Performer = Modified Zinc Phosphate

Anodic & Cathodic Polarizations oncold rolled steel (CRS)more nobleLess currentmore nobleLess currentANODICCATHODICDECREASING CORROSION EFFICIENCY:P7 > P1 > P6 > P3 > P2, P4, P5Best Performer = Modified Zinc Phosphate

Anodic & Cathodic Polarizationson zinc substratesANODICCATHODICDECREASING CORROSION EFFICIENCY:P1 >> P7 > P3 > P6 >> P2, P4, P5Best Performer = Zinc Chromate

Applying Synergy toSolve a CorrosionProblem

Cut-Edge Corrosion Inhibition Cut edge corrosion is most commonfailure mechanism of organic coatedgalvanized steel (HDG) Strontium chromate is generally used insteel primers to mitigate this Synergy of non-toxic corrosion inhibitorshas been found to perform equal tochromate

Cut-Edge Corrosion InhibitionModel Cell for Measurement of galvanic corrosion current betweenZinc and Mild steel

Artificial Rain Water (pH 4.5)

Results of Galvanic CurrentMeasurements

Observations All inhibitive pigments decreased thegalvanic currents more than the blank Blank: Current dropped from 12 to 9 µA SrCrO 4 : Current dropped to 0.2 µA Other individual pigments were down to4.5 µA Synergistic pigments had better currentsuppression; down to 1.1 µA

Meeting the Demandsof the Future

The Future The future is “Green” Technology – No heavy metals! OSHA PEL Proposed 5 µg/m 3 for Cr 6+ in workplaces Feb27, 2006. OSHA ordered to promulgate new PEL.(aerospace PEL now 20 µg/m3) End-of-Life Vehicle (EU Directive 2000/53/EC): Cr 6+ , Pb,Cd, Hg banned from vehicles marketed after July 1, 2003 California Air Resources Board (CARB) approved anAirborne Toxic Control Measure (ATCM) for Emissions ofCr 6+ and Cd from Motor Vehicle and Mobile EquipmentCoatings (Automotive Coatings) September 21, 2001. Registration, Evaluation and Authorization of Chemicals(REACH) – Authorization of chemicals causing cancer,mutations, reproductive problems, or are bioaccumulativein humans & the environment

Demand for High PerformanceCorrosion InhibitorsThin FilmsClear CoatsTemporaryCoatingsGreenTechnologiesCoil coating5-10 µmWash Primer10-15 µmConversionCoatings1-3 µmWaterborneLacquers2-10 µmRustPreventative5-20 µmZero VOCLow VOCCorrosionPreventingCompoundsUVPowder100% solidsHigh solidEpoxyAcrylicUrethaneAlkyd

The Future Chromate-free Heavy metal-free Sub-micron anticorrosive pigments Smart coatings (e.g. corrosion sensing) Nanotechnology

Smart Coatings

NanotechnologyWATERBORNE ACRYLICGalvanized – 336 hrs Salt Spray – 2.0 – 4.0 µm thick

Concluding Remarks Electrochemical methods can be used tostudy the efficiency of corrosioninhibitors Many factors influence the behavior andefficiency of corrosion inhibitors The future is “Green” New technologies such as SmartCoatings and Nanotechnology will soonemerge

“Bust the Rust”Thank You All !!

ReferencesSlide #Source12-17 Thierry et al – Progress in Organic Chemistry(25) 339-355 (1995)21-23 Scantlebury et al - Journal of ElectrochemicalSociety 148 (8) 293-298 (2001)29 Calle et al – Corrosion Technology Lab NASAKennedy Space Center