Connect with us

Guy Macon's adventures with ultrapure water

Discussion in 'Electronic Basics' started by Guy Macon, Jan 5, 2005.

Scroll to continue with content
  1. Guy Macon

    Guy Macon Guest

    MIME-Version: 1.0
    Content-Type: Text/Plain; charset=US-ASCII


    (Keeping in mind that I am an electronics engineer with quite
    limited knowledge of chemistry and some experience in designing
    low-cost low-performance resistivity meters...)
    Water over 18.2Mohm/[email protected] doesn't exist. At room temperature
    it spontaneously forms H+ and OH- Ions (and H3O+ Ions?
    My memory fails me on that one).

    Also, at what temperature? Ultrapure changes resistivity
    4.5% per degree C @25C.
    It doesn't exist. You need to purify it on the spot. Ultrapure
    water will dissolve anything it possibly can, and you want to give
    it as little time leaching chloride from plastics and dissolving
    metals and glass as possible. Making pure water is difficult,
    and keeping it that way is impossible
    No. To stay even close to 18.2Mohm/[email protected] you must start with
    vacuum degassed ultrapure water and then never let it contact
    air.

    O2 dissolved in the water makes it better at attacking metals
    (and lowering the resistivity) and dissolved CO2 will make
    carbonic acid, which then attack the metal. You will get
    lots of CO2 in the water even though the air doesn't have
    much because CO2 dissolves so well, and ultrapure water has
    little or no buffering capacity.

    The pH of pure water is around 7 if I recall correctly, but
    after being exposed to the air for a while the dissolved CO2
    gives you a pH reading closer to 5. This will drop your
    resistivity to somewhere in the 7 to 12 Mohm/[email protected] range.
    Please note that measuring the pH of ultrapure water with
    a pH sensor will not work right. Too little conductivity.

    If this doesn't frighten you enough, do a Google search
    on [ oligotrophic ultrapure ]. Better get some superbright
    UV lamps!
    You are aware that distillation *concentrates* some impurities,
    aren't you? I don't know what the "Quartz" is all about, but
    it sounds like a great way to get dissolved silicon oxide in
    your ultrapure water.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-