ABSTRACT

The Earth's atmosphere is oxidising. Nearly all of the Earth's crust consists of oxides, which indicates that this is the preferred minimum energy state for most materials. Gold and silver are the only two metals that are found in their native, unoxidised state. With some materials, when loaded or stressed in a corrosive environment, cracks can grow steadily under a stress intensity factor (K), which is much less than the critical stress intensity factor Kc. At ambient temperatures, significant corrosion occurs only if moisture is present. If a metal in a corroding environment is connected to another metal that is more reactive, that is higher up the electromotive series, then the second metal will form the anode of the corrosion cell and hence will preferentially oxidise, thus protecting the first metal from corrosion. The management and control of corrosion is one of the most difficult problems facing the design engineer.