Metal finishing Q&As since 1989

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Re-ionizing De-ionized water, necessary to prevent metal erosion?

Q. I am operating in an area of electronics that causes me to use ultra pure, 18 Megohm, DI water. I understand that in some areas of electronics (ALL?) a piece of equipment called a RE-ionizer (e.g: ultrat.com/h2oreionizers.htm) are used to reduce or even neutralize the corrosive / eroding effects of such pure water on metals and other materials to prevent the re-introduction of contaminants into a clean environment. The idea being that making semi-conductors is a tricky business and UN wanted metals, etc. can effect the yield and performance of some very expensive wafers in the many, many step process . . . So, as I understand RE-ionizing the water takes the place of the original minerals to keep the water from 1) having minerals neutralize the water and then contaminating wafers and 2) to use CO2 instead (dissociated into ions) to take their place as an inert way to bring the water back to a non-corrosive state.
Questions: 1) Is there another way to do this same thing. 2) how necessary is this to prevent corrosion and / or contamination of ultra clean products?

Brian Schreiber
mech engineer developing process - Maplewood, Minnesota, USA
2007

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A. If you really want lower quality water, why not make that way, or since 18 meg Ohm water is difficult to produce in quantity (that is a practical limit). Plan B might be to make up another storage tank with lower quality water before you recharge you DI system and then feed it into the original system as required. James Watts - Navarre, Florida 2007 A. Re-ionizers are used to prevent electrostatic discharge. High speed DI water jets can strip electrons from the surrounding air and create a harmful corona discharge to parts being rinsed. Adding CO2 to DI water increases the conductivity but also lowers the pH. Figure X1.1 in ASTM D5128 shows the effects of CO2 & NH3 on conductivity and pH of high purity DI water. It only takes 11 ppm CO2 to drop the pH to 5.0, making it more corrosive. Where re-ionizing is necessary, it is best done at the point-of-use; see US Patent 4,673,443 (1987). Ken Vlach [deceased] - Goleta, California Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015. Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from. 2007