To avoid excessive polarization at any anode in the copper sulfate bath, the anode current density should not be more than about 5 A/dm2 in un-agitated baths. With vigorous air agitation, the limiting anode current density is more than 17 A/dm2. The anode current density in an agitated fluoborate bath can be as high as 40 A/dm, and with air agitation, it can be increased to 55 A/dm2
Small amount of silver, sulfur, lead, tin, nickel, and other elements are common impurities in rolled, cast and electrolytic copper. Silver as impurities in the anodes employed in sulfate and fluoborate baths is of much less consequence than it is cyanide bath. OFCHC and electrolytic copper were found to have lower impurity content than rolled or ordinary cast anodes. The metallic impurities in OFHC and electrolytic copper totaled about 0.006%.
Grain size is considered inconsequential. Two batches of high purity anodes with average grain sizes of 10 and 0.01 mm performed similarly. On the other hand, high density is a desirable characteristic, because it promotes uniform anode dissolution.
An instance is reported of a preference fro continuously using insoluble, conforming anodes in order to improve deposit thickness distribution. Copper was replenished by circulating the solution through an auxiliary electrolytic tank connected in series with the electroforming tanks. The electrolytic corrosion tank was equipped with soluble copper anodes and scrap. On each side of a rotating disk cathode efficiency low. The insoluble anodes in the electroforming tanks were made with silver lead alloy (1% silver).
Lead containing 3% tin and 3% antimony has been proposed as an insoluble anode for facilitating the plating of printing rolls.
An insoluble of copper, silicon, iron, and lead. Graphite is the only electrically conductive material known to be insoluble as an anode in the fluoborate bats. When used as an anode, graphite produces a sludge of finely divided carbon particles.