Pourbaix diagrams; Nernst potential; passivation; cathodic protection; pitting; galvanic; stress-corrosion; microbiologically-influenced; inhibitors; erosion; hydrogen-embrittlement; Tafel kinetics.
Corrosion Chemistry
Pourbaix diagram
Pourbaix 1945 E-pH diagram defines immunity / passivation / corrosion regions for each metal-water system at 25 C; basis for selecting…
Nernst corrosion potential
E = E0 + (RT/nF) ln([ox]/[red]); free-corrosion potential E_corr where anodic and cathodic partial currents balance; mixed-potential…
Passivation (stainless steel)
Cr 10.5 percent or more in Fe alloy forms self-healing Cr2O3 layer ~2 nm; 18-8 (304), 17-12-2 (316L) standard; passivation breaks down at…
Cathodic protection
Sacrificial anodes (Mg, Zn, Al) for ships and pipelines; impressed-current systems for buried structures; Davy 1824 first ship-protection…
Pitting corrosion
Local breakdown of passive film initiates pit; autocatalytic Cl- accumulation acidifies pit; Galvele 1976 critical-pitting-potential;…
Galvanic corrosion
Two-metal couple in electrolyte: more-active metal corrodes preferentially; galvanic series in seawater (Mg most active to Pt most noble);…
Stress-corrosion cracking
Specific environment-alloy combinations crack under static tensile-stress: Cl-SCC of austenitic stainless, NH3-SCC of brass,…
Microbiologically influenced corrosion
SRB (sulfate-reducing bacteria) and IRB (iron-reducing) accelerate corrosion of buried pipelines and ship-hulls; tubercule formation; oil…
Corrosion inhibitors
Anodic (chromate, molybdate), cathodic (Zn salts, polyphosphate), mixed (amines, imidazolines); REACH and OSHA restrict Cr(VI);…
Erosion-corrosion
Combined mechanical wear and electrochemical attack in flowing media; impingement attack on Cu pipes (above 1.5 m/s); cavitation-corrosion…
Hydrogen embrittlement
Atomic H from corrosion or cathodic-charge enters metal lattice and reduces toughness; high-strength steels (above 1000 MPa) and Ti alloys…
Tafel kinetics
eta = a + b log(i) Tafel slope b ~RT/(alpha F ln 10); from Butler-Volmer; polarization curves measure corrosion-current via Tafel…
Faraday law + electrolytic corrosion
Faraday 1834 first + second laws: m = (Q M)/(n F); applied to corrosion: weight-loss rate from corrosion-current via mol-eq weight; basis…
Galvanic series (extended; ASTM G82)
ASTM G82 standard galvanic-series in flowing seawater: Mg most-active (-1.6 V) -> graphite/Pt most-noble (+0.3 V); table of 50+ alloys;…
Mott-Cabrera thin-oxide growth
Mott-Cabrera 1948-1949: thin-oxide-film growth limited by tunneling-current of electrons through oxide; rate eq d/dt = A exp(-t/tau);…
Stern-Geary LPR (detailed)
Stern-Geary 1957: i_corr = B / R_p where B = b_a b_c / (2.303 (b_a + b_c)) and R_p = polarization-resistance from low-overpotential…
Impressed-current cathodic protection (detail)
Modern ICCP: silicon-iron / mixed-metal-oxide anodes + DC rectifier; ON/OFF criterion ~-850 mV vs Cu/CuSO4; instant-off potential…
ALARP corrosion allowance (design)
ALARP As-Low-As-Reasonably-Practicable principle in corrosion-engineering: design wall-thickness = nominal + corrosion-allowance +…