1.Corrosion study: Selection of frequency range depends upon type of the system that you want study, for coatings or thicker/stable passive film surfaces you would need few microHz to 100MHz.

Reasonable limit are from 0.01 to 50000 HZ for systems that "are changing". For steady state systems you can extend the range taking in account the kind of material studied. Let me say that 1 microHz means 1000000 seconds (about 278 hours) to acquire only one point. If you want to perform 10 cycles per point you need 2780 hours (about 116 days) to obtain one point on your curve. For corroding systems (but I think for all kind of systems) is too long time. On the other hand for frequency higher 50000Hz very good shielded apparatus are needed. For frequency higher that 1 megaHz you are in the radio frequency domain so the signal is transmitted via “skin effect”

Thanks for your answers.

Thanks.