Microelectrochemical Studies of Pit Initiation on High Purity and Ultra High Purity Aluminum

Abstract

The onset of pitting on high purity and ultra high purity aluminum has been studied in the micrometer range by using a microelectrochemical cell in order to evaluate influences that induce localized corrosion. Microelectrochemical tests on polished samples of Al 99.999 and Al 99.9999 in 1 M NaCl showed that pitting at large areas occurred at several hundreds mV more negative than at small areas, suggesting that even very pure Al contains weak points. On rough surfaces weak points are more “activated” than on smooth surfaces. Locally measured pitting potentials of polished samples were shifted to more positive values than those measured on ground samples. Larger areas contain always small scratches, even on polished samples. Hence, the surface roughness showed a minor influence on the onset of pitting on larger areas. Microelectrochemical measurements performed on pure Al 99.99 with small amounts of copper showed that a copper content below 30 ppm is too small to have a beneficial or detrimental effect, whereas a copper content above 300 ppm probably leads to the formation of small inclusions or precipitations that acted as preferential corrosion initiation sites. A copper content around 100 ppm showed a beneficial effect on very small areas but not on larger ones.

Absorbable Metals for Biomedical Applications

“…The smoother surface of the polished sample and its related chlorine absorption capacity is given as a possible explanation. This behavior is distinct from reports that report that rougher surfaces on steel [75,76] and aluminum [77] lead to faster degradation and more pitting.…”

An electrochemical impedance spectroscopy and potentiodynamic polarization study of the effect of unidirectional roughness on the corrosion of nickel

“…These observations are in agreement with Lee et al's [15] fi nding that samples with deep grooves, i.e. those with higher reduced valley depth (R vk ) values, show poorer corrosion resistance and Suter et al's [9] observations that these deeper grooves trap the corrosive ions and corrosion products leading to more pitting.…”

The Effect of Surface Morphology on Corrosion Performance of SS 316 LVM Biomedical Devices

“…The observations are in agreement with the observations of Toloei and Suter that deeper grooves trap the corrosive ions and corrosion products and will result in more corrosion. The results also confirm corrosion results and in situ observations(Ref 17,24).…”