| Abstract: | SUMMARIES. A simulated occluded cell was utilized to study the localized corrosion in seawatcr and desalination treatment in alkaline solution of simulated cast iron artifacts. After the simulated occluded cell galvanostatic test, high acidity and enrichment in chloride ions in the occluded cell were demonstrated as a result of an autocatalytic process. In addition, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) indicated the degree of the localized corrosion and the enrichment in chloride ions. An investigation was also made of the chemical changes within the occluded cell during the desalination treatment; the results showed that the pH values and the amount of chloride ion removed from the occluded cell increased with the treatment time. The decrease in chloride of the corroded surface of the specimen was confirmed by EDX. The research appeared to prove that the simulated occluded cell is capable of providing useful information on the localized corrosion and desalination treatment of simulated cast iron artifacts.
CONCLUSIONS. A simulated occluded cell was used to study the localized corrosion and the desalination treatment of simulated cast iron artifacts. It is a convenient method to reveal the chemical changes within an occluded cell, which can not only study the mechanism of the local¬ized corrosion of cast iron, but can also investigate chloride ion migration in and out of the occluded cell during localized corrosion and desalination treatment. In the present work, the changes of chemical state for localized corrosion of simulated cast iron artifacts in 3.5 wt% NaCl solution were studied. It was found that as an anodic current was passed through the cell, the pH value inside the cell initially fell quickly and then decreased gradually. Meanwhile, the chloride ions migrated into the occluded cell. The quantity of chloride ion migration increased with the time that the current was flowing. The results of the SEM analysis showed acceleration of dissolution of cast iron with the time of application of the anodic current, and EDX analysis indicated the enrichment in chloride ion. A study was made of the chemical changes within the simulated occluded cell after the 72-hour desalination treatment which was applied to samples that had first been corroded at 1 mA-cm-2 anodic current density for 48 hours. During chloride removal, the pH value in the occluded cell gradually increased over time. In addition, the amount ot chloride ions removed from the occluded cell increased with the treatment time. The chloride ion extraction rate initially decreased rapidly and then became almost stable with the washing time. Furthermore, the EDX analysis disclosed the change of composition ot chlonde after the treatment. It is evident that the simulated occluded cell could help in understanding the degree of localized corrosion and the progress of the treatment of cast iron artifacts, thereby enabling their safe and effective preservation. |
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