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P.O. Box 1606, Palmer Lake, CO 80133
Tel: (719) 488-9640, Fax: (866) 453-8473
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||Precipitating Excess Copper
in a Peroxide-Sulfuric Etchant
If the test indicates that too much copper is present, it will
be necessary to change the acid content of the bath to force the
copper to precipitate out as copper sulfate pentahydrate. The
procedure presented here is straightforward, but requires care
when handling the extremely corrosive etchant.
If you have not done so, review the safety procedures
for handling corrosive materials and follow them explicitly!
- Use the sulfuric acid analysis
procedure to determine the sulfuric acid content.
- If necessary, add enough acid to bring the total
concentration up to a minimum of 10% (by volume). The
level of acid will bring bring the pH of the bath down to
a point where the excess copper will spontaneously
precipitate out as the bath cools.
BE VERY CAREFUL WHEN ADDING THE ACID TO THE BATH.
READ THE ACID ANALYSIS PROCEDURE AND FOLLOW IT EXPLICITLY.
- One half of the etchant should now be drained into the
carboy supplied with the system (marked ETCHANT) and
allowed to sit in a cool place until it's temperature
drops below 20 degrees C. At that point the copper will
precipitate out as copper sulfate pentahydrate, a bright
blue crystal that will settle to the bottom of the
carboy. Precipitation will commence as soon as the
etchant has cooled, but the carboys should be allowed to
sit for at least a couple of days to ensure that adequate
separation occurs. Note: precipitation can be
accelerated by using a lower temperature, the lower the
better, as long as the electrolyte does not freeze.
Instead of precipitating the entire bath at one time, many
users have found it preferable to drain about 1/2 of the bath
every Friday to let this smaller volume precipitate over the
- Once precipitation is complete, the etchant should be
pumped back into the etcher with care being exercised to
avoid picking up any of the sediment. After the etcher is
refilled, it should be re-analyzed for both hydrogen
peroxide and acid content.
- Decant the copper sulfate pentahydrate crystals into a
holding container (plastic) and allow it to air dry.
These crystals can be used to make a concentrated
solution of copper sulfate which, after carbon treating, can be added to
the acid copper plating bath to reduce erosion of the
To insure adequate precipitation of
excess copper, the acid content of the bath MUST be adjusted to
(digital titrator count = 178).
HANDLE WITH CARE
Always use the proper equipment as outlined
above in the SAFETY section when handling concentrated sulfuric
acid. If contact should occur, flush affected area with cool tap
water for 15 minutes. CONTACT A PHYSICIAN IMMEDIATELY.
Always wear protective clothing, acid
resistant gloves, and a full coverage face shield
when handling this or any other corrosive material.
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