films containing finely divided copper and copper oxide particles. A
copper oxide film is believed to cause inter-granular corrosion, which
promotes disintegration of surface layer into the copper particles.
Some, however, have attributed the films to copper particles formed by
the disproportionation of copper (I) ion to copper (II) ion and metal.
The films on the anodes in the sulfate bath also contain insoluble
impurities such as arsenic, selenium, tellurium, lead, and silver.
Anode film particles often become detached from the anodes. Air
agitation promotes the detachment, causing some particles to be
dissolved by the free acid. If the work is racked so that cathode
shelves lie in a horizontal plane, particles will settle out on these
areas and roughen the plate. In such cases, the anode sludge can
sometimes be decreased and the deposits made smoother by raising the
bath temperature or increasing the acid concentration. In on series of
test, less copper was found in anode films formed in flouborate baths
than in those form sulfate baths.
Fine copper particles can be prevented from reaching the cathode by
bagging anodes with woven Dynel or polypropylene. To allow good mixing
of the solution adjacent to the anodes placed edgewise to the
cathodes.
Rolled and cast bars and electrolytic copper sheets have been employed
as anodes in sulfate and fluoborate baths. Anode sludge is decreased
by using oxygen-free, high conductivity copper. On the other hand, the
tenacity of the anode film is improved and the number of particles
that become detached from anodes surface in air agitated baths is
decreased by adding 0.02 to 0.04% phosphorous to cast copper. The
films on phosphorized copper anodes are responsible for the slight
polarization of about 0.5 V. Boiled copper anodes containing at least
0.004% phosphorous are customarily recommended by the vendors of
brighteners for plating bright copper in copper sulfate solutions.
Chunks of phosporized copper are frequently used in titanium anode
baskets.
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