Iron artificial pits have been used in this work to investigate the effect of a carbon-based black layer that can form within a pit during iron dissolution in HCl solutions. Commercial purity iron (99.5%) and high purity iron (99.99+%) have been compared, and a black layer has been observed only in the 99.5% iron pit. It has been found that the formation of a black layer within an iron artificial pit is potential dependent: it can form at applied voltages below 0.2 V(SCE), but not at 0.6 V(SCE). The presence of a black layer can decrease the rate of mass transport inside a pit, which may help to maintain the aggressive acidic solution in an active pit. This effect has been characterised quantitatively via potentiostatic and potential step methods. In addition, the black layer has also been found to induce a small extra resistance in the solution.
FlisJZiomek-MorozMFlis-KabulskaI. Effect of carbon on corrosion and passivation of iron in hot concentrated NaOH solution in relation to caustic stress corrosion cracking. Corros Sci. 2009; 51: 1696–1701. doi: 10.1016/j.corsci.2009.04.020
2.
HaHTaxenCWilliamsK. Effects of selected water chemistry variables on copper pitting propagation in potable water. Electrochim Acta. 2011; 56: 6165–6183. doi: 10.1016/j.electacta.2011.04.008
3.
PoulsonB. The fractography of stress corrosion cracking in carbon steels. Corros Sci. 1975; 15: 469–477. doi: 10.1016/0010-938X(75)90013-X
4.
XuWYuFYangL. The inhibitive effect of carbon containing corrosion products inside corrosion pits on the repassivation of carbon steels. Int J Electrochem Sci. 2016; 11: 4323–4336. doi: 10.20964/2016.06.78
5.
KawaleyG. Localised corrosion of iron in food products. Birmingham, UK: University of Birmingham; 2008.
6.
XuWStreetSAmriM. In-situ synchrotron studies of the effect of nitrate on iron artificial pits in chloride solutions. (ii) On the solid corrosion products. J Electrochem Soc. 2015; 162: C243–C250. doi: 10.1149/2.0591506jes
7.
MiN. Synchrotron X-ray studies of atmospheric pitting corrosion of stainless steel. Birmingham, UK: University of Birmingham; 2013.
8.
SridharNDunnDS. In situ study of salt film stability in simulated pits of nickel by Raman and electrochemical impedance spectroscopies. J Electrochem Soc. 1997; 144: 4243–4253. doi: 10.1149/1.1838173
9.
HaischTMittemeijerEJSchultzeJW. On the influence of microstructure and carbide content of steels on the electrochemical dissolution process in aqueous NaCl electrolytes. Mater Corros. 2002; 53: 740–755. doi: 10.1002/1521-4176(200210)53:10<740::AID-MACO740>3.0.CO;2-J
10.
GreenJASParkinsRN. Electrochemical properties of ferrite and cementite in relation to stress corrosion of mild steels in nitrate solutions. Corrosion. 1968; 24: 66–69. doi: 10.5006/0010-9312-24.3.66
11.
HaischTMittemeijerESchultzeJW. Electrochemical machining of the steel 100Cr6 in aqueous NaCl and NaNO3 solutions: microstructure of surface films formed by carbides. Electrochim Acta. 2001; 47: 235–241. doi: 10.1016/S0013-4686(01)00561-8
12.
InghamBKoMKearG. In situ synchrotron X-ray diffraction study of surface scale formation during CO(2) corrosion of carbon steel at temperatures up to 90 degrees C. Corros Sci. 2010; 52: 3052–3061. doi: 10.1016/j.corsci.2010.05.025
13.
NesicSLundeL. Carbon-dioxide corrosion of carbon-steel in 2-phase flow. Corrosion. 1994; 50: 717–727. doi: 10.5006/1.3293548
14.
RaspiniIChungESaragoviC. Corrosion layers of low-alloy carbon steels in CO2(g)-saturated solutions by Mossbauer spectroscopy. Corrosion. 2000; 56: 832–838. doi: 10.5006/1.3280586
15.
GaudetGTMoWTHattonTA. Mass transfer and electrochemical kinetic interactions in localized pitting corrosion. AIChE J. 1986; 32: 949–958. doi: 10.1002/aic.690320605
16.
NovakovskiVMSorokinaAN. Model study of chloride pitting in 18-8 stainless steel. Corrosion Sci. 1966; 6: 227–233. doi: 10.1016/S0010-938X(66)80033-1
GrimmRDWestACLandoltD. AC impedance study of anodically formed salt films on iron in chloride solution. J Electrochem Soc. 1992; 139: 1622–1629. doi: 10.1149/1.2069467
19.
LaycockNJNewmanRC. Localised dissolution kinetics, salt films and pitting potentials. Corrosion Sci. 1997; 39: 1771–1790. doi: 10.1016/S0010-938X(97)00049-8
20.
DanielsonMJ. Transport properties of salt films on nickel in 0.5 N HCl. J Electrochem Soc. 1988; 135: 1326–1332. doi: 10.1149/1.2095974
21.
TangYCDavenportAJ. Magnetic field effects on the corrosion of artificial pit electrodes and pits in thin films. J Electrochem Soc. 2007; 154: C362–C70. doi: 10.1149/1.2736662
22.
SteinsmoUIsaacsHS. Dissolution and repassivation kinetics of Fe-Cr alloys in pit solutions. 1. Effect of the surface salt layer. J Electrochem Soc. 1993; 140: 643–653. doi: 10.1149/1.2056137
23.
ZhangQLWangRGKatoM. Observation by atomic force microscope of corrosion product during pitting corrosion on SUS304 stainless steel. Scr Mater. 2005; 52: 227–230. doi: 10.1016/j.scriptamat.2004.09.024
24.
GalveleJr. Transport processes and mechanism of pitting of metals. J Electrochem Soc. 1976; 123: 464–474. doi: 10.1149/1.2132857
25.
FrankelGS. Pitting corrosion of metals – a review of the critical factors. J Electrochem Soc. 1998; 145: 2186–2198. doi: 10.1149/1.1838615
26.
NewmanRCIsaacsHS. Diffusion-coupled active dissolution in the localized corrosion of stainless-steels. J Electrochem Soc. 1983; 130: 1621–1624. doi: 10.1149/1.2120048
