Iron continued

A comprehensive table of corrosion rates in sea water has been compiled by LaQue . This appears to show no obvious dependence of corrosion rates on the geographical location of the testing site, and few of the rates depart widely from an average of 0-11 mm/y. It is suggested that a figure of 0-13 mm/y may be taken as a reasonable estimate of the expected rate of corrosion of steel or iron continuously immersed in sea water under natural conditions, in any part of the world. 

Metal type Electrical furnace better placed for nodular or alloyed cast iron Continuous production Cupola is better placed... 

Why does iron continue to corrode even after a layer of rust forms on the surface, whereas aluminum stops corroding after a corrosion layer forms ... 

This reaction proceeds rapidly in acids, but only slowly in alkaline or neutral aqueous media. The corrosion rate of iron in deaerated neutral water at room temperature, for example, is less than 5 p,m/year. The rate of hydrogen evolution at a specific pH depends on the presence or absence of low-hydrogen overvoltage impurities in the metal. For pure iron, the metal surface itself provides sites for H2 evolution hence, high-purity iron continues to corrode in acids, but at a measurably lower rate than does commercial iron. 

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