I.VDLIATRIAL .t.VD ENGIINEEIZING CNEMISTIZY
September, 1'327
.- . . .
i ? - -g~ a m~S ~U O ~ a~ ~i~~~~ 5, =fter 40
~
minuter.
100
x
~i~~~~
s-samc
1009
.. .
spot as pigure 5 , *iter BO 100 x
deerease until aft,or 100 minut,es.
minutes.
Conclusion
ring was photographed a t intervals of 20 minutes, as with the electrolytic iron. (Figures 5 to 8) Results
Arinco iron corroded much faster tlran electrolytic iron in the beginning. However, a corrosion spot appearing on Armco iron after a certain period of time enlarged much more slowly than a similar spot on electrolytic iron. The rate of corrosion of these two kinds of iron after a certain periodthat is, one hour in the case of electrolytic iron and a half hour in that of Anneo iron-is shown in Figure 9. The curve is similar to that obtained by a purely chemical process, such as the oxygen drop method of Speller and co-workers.3 On the
2
;/s +
These results show that the protective film produced hy corrosion after a certain time will reverse an original rate of corrosion of metals, thus bringing out a paradox that the more favorable the condition for corrosion the less would Ise the corrosion. Evidently, this contradicts the electrolytic t,heory, which claims that the pure mota1 corrodes less than the impiire metal. The foregoing statement, however, does not mean that. the total corrosioii of Armeo iron is less than that of electrolytic iron. Experiment proved that Armeo iron was protected by corrosion prodiict,s hctter than electrolytic iron after R certain period of time in rvlricli both had begun to corr
