Dissolving Titanium Anode Baskets
Q. Has anyone experienced titanium anode baskets dissolving in a nickel sulfamate plating bath with a pH of 2.5 and no current flowing? I am wondering if the baskets I have purchased are of inferior quality compared to the older baskets I am replacing. These new baskets tend to dissolve even in alkaline cyanide plating baths, although not as quickly as in the nickel bath. Do you have any ideas as to what is going on? B.J.
A. If you purchased the new titanium baskets from a reputable manufacturer, it is not likely that the titanium used in the baskets is inferior to that which was used in your previous set of baskets.
Corrosion of the titanium baskets in your alkaline cyanide plating bath should not occur if the baskets are completely filled with a good-quality copper. Oxygen-free high thermal conductivity (OFHC) copper is recommended. Corrosion of the baskets has been reported with other grades of copper anodes.
Titanium is attacked by fluorides and, to a lesser degree, by chlorides. High concentrations of sulfate (in excess of 20 percent), usually from sulfuric acid, will corrode titanium at a fairly high rate. Titanium forms an oxide layer on the surface that protects the underlying titanium from damage. If the titanium anodes are subject to a voltage higher than 25 V DC this oxide layer starts to dissolve. This might be your problem. Another possibility is that your titanium anode baskets are not completely filled, so that the entire basket makes contact with nickel and localized corrosion is taking place. Titanium baskets that are too close to the size of the plating tank also have been known to corrode. Inadequate agitation may lead to corrosion as well.
Some platers have solved this problem by switching to zirconium anode baskets, which are available commercially. Find vendors by searching PFOnline.com.
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