2019-01

Journal of The Electrochemical Society (القضية : 11) (الحجم : 166)

Pit location during atmospheric corrosion of Type 304L stainless steel under MgCl2 droplets depends on initial droplet concentration. Pits formed predominantly in the center of the droplet for concentrations ≥4 M, closer to the perimeter for 1.5 M to 3 M, and were randomly distributed for concentrations ≤1 M. Pits initiated only after the droplets had evaporated to a critical concentration >3 M, where droplets deposited with lower initial concentrations were thinner. The results can be explained in terms of “differential aeration” and IR drop effects, showing that corrosion in “splash zones” may differ from that under aerosol salt deposit layers that deliquesce forming initially saturated solutions.

2019-01

Corrosion Science (الحجم : 150)

Atmospheric pitting corrosion of stainless steel was examined with synchrotron X-ray microtomography, laboratory based tests and electrochemical measurements in order to provide a mechanistic basis for the development of corrosion prediction models. It was found that the morphology of corrosion pits was affected by the presence of residual ferrite, and some pits showed dense covers that may affect pit stability. Fluctuations in relative humidity may lead to partial or complete repassivation of pits, sometimes leading to the formation of new pits. Electrochemical measurements in artificial pits containing concentrated salt solutions show a strong dependence of the diffusion limited current density on chloride concentration.

2018-09

CORROSION (القضية : 12) (الحجم : 74)

Atmospheric corrosion of stainless steel is of concern for intermediate level nuclear waste (ILW) containers. The effect of microstructure on the morphology of atmospheric corrosion pits in Type 304L stainless steel plate was investigated on three orthogonal planes under MgCl2 droplets. Pits on the top surface of the plate show ring-like structures, whereas pits on the plate sides show a striped morphology. Synchrotron x-ray tomography of Type 304L stainless steel pins shows the presence of similar striped attack. Scanning electron microscopy on plate samples revealed the presence of parallel bands along the rolling direction. Energy dispersive spectroscopy maps and line scans across these bands indicated a local increase in the Cr/Ni ratio consistent with a ferrite phase, likely residual delta-ferrite formed during solidification. Vibrating sample magnetometer (VSM) detected the presence of ferrite on the base alloy. X-ray diffraction and electron backscatter diffraction quantified the volume fractions of ferrite and austenite phases. Ferrite phases affect the morphology of pits and promote pit propagation along the rolling direction.

2018-05

CORROSION (القضية : 5) (الحجم : 74)

Pit location during atmospheric corrosion of Type 304L stainless steel under MgCl2 droplets depends on initial droplet concentration. Pits formed predominantly in the center of the droplet for concentrations ≥4 M, closer to the perimeter for 1.5 M to 3 M, and were randomly distributed for concentrations ≤1 M. Pits initiated only after the droplets had evaporated to a critical concentration >3 M, where droplets deposited with lower initial concentrations were thinner. The results can be explained in terms of “differential aeration” and IR drop effects, showing that corrosion in “splash zones” may differ from that under aerosol salt deposit layers that deliquesce forming initially saturated solutions.

2015-01

Faraday Discussions (الحجم : 180)

The morphology of atmospheric pitting corrosion in 304L stainless steel plate was analysed using MgCl2 droplets in relation to changes in relative humidity (RH) and chloride deposition density (CDD). It was found that highly reproducible morphologies occur that are distinct at different RH. Pitting at higher concentrations, i.e. lower RH, resulted in satellite pits forming around the perimeter of wide shallow dish regions. At higher RH, these satellite pits did not form and instead spiral attack into the shallow region was observed. Increasing CDD at saturation resulted in a very broad-mouthed pitting attack within the shallow dish region. Large data sets were used to find trends in pit size and morphology in what is essentially a heterogeneous alloy. Electrochemical experiments on 304 stainless steel wires in highly saturated solutions showed that the passive current density increased significantly above 3 M MgCl2 and the breakdown pitting potential dropped as the concentration increased. It is proposed that the shallow dish regions grow via enhanced dissolution of the passive film, whereas satellite pits and a spiral attack take place with active dissolution of bare metal surfaces.

2014-09

Corrosion Engineering, Science and Technology (القضية : 6) (الحجم : 49)

Atmospheric pitting corrosion of stainless steel was examined with synchrotron X-ray microtomography, laboratory based tests and electrochemical measurements in order to provide a mechanistic basis for the development of corrosion prediction models. It was found that the morphology of corrosion pits was affected by the presence of residual ferrite, and some pits showed dense covers that may affect pit stability. Fluctuations in relative humidity may lead to partial or complete repassivation of pits, sometimes leading to the formation of new pits. Electrochemical measurements in artificial pits containing concentrated salt solutions show a strong dependence of the diffusion limited current density on chloride concentration.