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Potential (mV vs. AgiAgCI)

Fig. 5. Mean tunneling barrier height vs. substrate potential on DIN 1.4301 in 0.01 M sulfuric acid. The formation of an oxide layer leads to lower tunneling barrier height.

In Fig. 6 both the measurements on DIN 1.4301 and on DIN 1.4529 immersed in 0.01 M H2S04 at E = 0 mV are shown. It is obvious that the tunneling barrier on the more highly alloyed DIN 1.4529 is substantially higher than for DIN 1.4301 stainless steel. This is due to the fact that the passive layer on the less alloyed steel contains more Fe2+ ions and therefore introduces more localized states which lower the tunneling barrier. In case of the more highly alloyed steel the presence of Mo ions in the passive film may replace the Fe2+ and, due to their multivalent nature will not lead to electronic misfits.

A 1.4301 passivated (OmV) _ 1.4529 passivated (OmV)

A 1.4301 passivated (OmV) _ 1.4529 passivated (OmV)

01 .1 1 5 1 0 2 03 0 5 0 7 0 8 0 9 0 9 5 9 9 99.9 99.99 Percent

Fig. 6. Measured tunneling barrier height on DIN 1.4301 and 1.4529 in 0.01 M sulfuric acid at E = 0 mV, covered by an oxide film.

01 .1 1 5 1 0 2 03 0 5 0 7 0 8 0 9 0 9 5 9 9 99.9 99.99 Percent

Fig. 6. Measured tunneling barrier height on DIN 1.4301 and 1.4529 in 0.01 M sulfuric acid at E = 0 mV, covered by an oxide film.

0 0

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