When iron rusts, the corrosion product flakes off exposing new areas to corrosion. Does a similar process occur with nickel, or does it form a "passive coating" as is seen with copper. (Hey, I'm a polymers guy, so if I'm misusing terminology here, feel free to correct me. The kindness of the correction will be returned if you ever post to sci.polymers)
Since corrosion is the reaction of a material with its environment, and you didn't specify an environment, you have actually asked half of a question. So, here is half of an answer.
Nickel is more noble than iron, and less noble than copper. It forms a passive film (of oxides or hydroxides) in some neutral or alkaline environments. Pure nickel is an excellent material for handling hot concentrated caustic soda (sodium hydroxide), as has been discussed previously on this newsgroup.
Even in air nickel may not stay bright, since it can form a "fog" (thin layer of nickel sulfate). In stagnant seawater nickel can pit. Artificial sweat (for tests) also will corrode it.
Nickel alloys containing combinations of chromium and molybdenum are quite resistant to a wide variety of corrosive environments. Loads of information may be found from the Nickel Development Institute (website
Nickel should do a good job of resisting DI water.
The following appears in the section on Fresh and Process Waters in the publication "High-Performance Alloys for Resistance to Aqueous Corrosion"
"The resistance of Nickel 200 to corrosion by distilled an natural waters is excellent. Analysis of distilled water from a nickel storage tank indicated a rate of corrosion of 0.001 mpy (mils per year). Similarly, tests in domestic hot water up to 200F normally show rates of less than 0.02 mpy."
Check the manual for your conductivity meter - the electrodes may be pure nickel (they are in some of the YSI meters).
For more details regarding purer water, why not contact the Nickel Development Institute and ask them if they have more data specific to DI water.
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