Hi Ashok! Just an fyi but chromate conversion coated aluminum surfaces
(e.g. such as heatsinks on pwbs) which are subjected to water temperatures
150F or greater and under a typical spray pressure (e.g. a water wash
system) will have the conversion coating removed by the process. The black
appearance you have observed may be a now "bare" aluminum surface reacting
to the pH of your saponified solution.

Dave Hillman
Rockwell Collins
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                      "Dhawan, Ashok"
                      <AshokDhawan@SOLE        To:       [log in to unmask]
                      CTRON.COM>               cc:
                      Sent by: TechNet         Subject:  [TN] Tarnished Surface
                      <[log in to unmask]>


                      12/17/2003 03:12
                      PM
                      Please respond to
                      "TechNet E-Mail
                      Forum."; Please
                      respond to
                      "Dhawan, Ashok"






Technetters

Anyone who has experienced and resolved tarnishing of Aluminium surface
upon
cleaning with DI water + saponifier. The aluminium surface is protected
with
conversion coating (clear) which is turning black when exposed to
saponifier
solution.



Ashok  Dhawan P.Eng
Manufacturing Engineer
Solectron
Snailmail:1455 Mountain Avenue
Winnipeg MB R2X 2Y9 CANADA
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