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Forwarded message:
Subj:    Re: FAB: Etchback & NaMnO4 bath life
Date:    97-04-23 03:08:43 EDT
From:    RSedlak
To:      [log in to unmask]

Thinking about your problem, initially, there seems to be no problem about
buildup, or other reason for drop off in performance of the bath, but then on
reflection, I suddenly realized that you could easily get carbonate buildup,
and this bug has bit me on the A--
more than once.

So, the key to this is what is the mechanism by which you determine NaOH
concentration.  Give us the exact procedure please.  Could be, if you are
using the common procedure, which uses phenolphthalein as indicator, or pH
8.2 as endpoint, which is the same as using phenolphthalein as indicator,
that you have little if any NaOH present, and in fact all, or most of the
alkalinity that you are titrating is Carbonate.  If so, this is an easy fix.

Give us  the details, and if you need a better procedure, there is help
coming over the hill...

Rudy Sedlak
RD Chemical Company

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