DI Water itself is not corrosive, but it is aggressive, if you get the
difference. Having been stripped of all it's ionic content, it's "hungry"
to replace those ions, and will draw them from wherever it can. That's what
makes it so effective at removing ionic contamination from boards. However,
it doesn't discriminate about where it draws ions from, and draws them just
as readily from seals and gaskets if it can. Domestic appliance seals are
not resistant to this sort of attack, and the loss of ionic content from
their composition degrades them to the point where they fall apart and dump
more dirt back onto boards than is ever removed. The machines then leak and
eventually become useless for anything.

Peter


Rudy Sedlak <[log in to unmask]> 10/07/2002 09:08 PM
Sent by: TechNet <[log in to unmask]>

Please respond to "TechNet E-Mail Forum."; Please respond to RSedlak

              To:  [log in to unmask]
              cc:  (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
              Subject: Re: [TN] Water soluble batch washers.../deionized water








The "hazards" of deionized water are somewhat blown out of proportion.

Deionized water is not really that corrosive, only marginally more than tap
water...
HOWEVER, deionized water lacks the buffering capacity of tap water.  (All
that water hardness serves to buffer the pH nicely)   So, if the "stuff"
you are rinsing is corrosive inherently, the deionized water also becomes
corrosive, especially to metals.

However, most of the aqueous cleaners are pretty mild and non-corrosive, so
rinsing them with deionized water should be safe, even for the common home
dishwasher.

This is assuming that the ratio of (acidic/corrosive) flux on the parts in
the washer to the amount of alkaline cleaner being used is not so bad that
the wash water becomes acidic...then you have BIG problem.

The answer is to clean just a few boards, OR use a lot of cleaner to keep
the pH above 9, and preferably higher than that...

Rudy Sedlak
RD Chemical Company



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