scratchy wrote:
The corrosion happens when an oxidant (e.g water) comes into contact with the metal. When the outer layers corrode or oxidise the the water can then come into contact with the other metals forming an electrolytic cell as in a battery and a voltage passes between the different metals which accelerates what is now electrolytic corrosion.
The oxidant can be as something as simple as flood or rainwater, or even water vapour in air. I could go into more depth on this subject, however there are many articles on the web on electrolytic corrosion and the chemical series. The latter show the voltage differential between two metals in an electrolyte.
I must understand that if water / moisture penetrates the magnetic layer ( where the data is ), a chain reaction starts and it completely corrodes in a short space of time?