Before asking the question, I have to warn: I am no chemist and English is not my native language so the text can mean not what I want it to mean:)
I'd like to design a small power-free device that could measure a time of its being in an environment with 100% humidity. Say, you take some sensor and put it into water. After some time you take it out, attach it to some microcontroller or a computer and it says for how long it has been under water. The device should have no in-built power source.
I think about it as some chemical device that irreversibly changes any of its electrical characteristics (resistance, capacitance, inductance) while being in high humidity. As we know the time-dependence of this characteristic in advance, we can find out the time.
What I can imagine it to be is for example two small metallic plates that become covered with oxide film and the resistance (capacitance) between them changes with time.
I know that probably it is a known concept in chemistry and everyone knows how to do that. Thanks in advance for any answer everyone!