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pl a tin gC L INIC n pfonline.com/experts PurPle on Platinum-Plated anodes Q. I run a captive Watts nickel plating shop and I recently discovered that our sulfuric acid activation pretreatment step was wired backwards. We use platinumplated titanium anodes for this step. The bath is made up at 7 percent sulfuric and is run at 30 amps/sq ft. By running this step incorrectly, a purple compound has appeared on the surface of the anodes. I believe it to be platinum oxide. We tried reversing the current in the correct direction, however no current is able to get through. I believe this is due to the purple compound on the anode. A replacement set of anodes were installed and the process now works properly. Is there any way to remove the purple compound off of the anodes so they can be reused? K.S. a. I am not an expert on platinum chemistry, but I believe your guess is correct about the purple compound being platinum oxide. One of the references I have indicates that one of the oxides formed by platinum is violet/black in color. If indeed the purple deposit is platinum oxide, there are ways to reduce it, but the information I found does not seem to be suitable for the plating environment. I suggest you contact the vendor of your platinized titanium anodes and see if they can offer you any help. n of articles on copper plating. One that I particularly recom-mend is found at pfonline.com/articles/choosing-andtroubleshooting-copper-electroplating-processes. In addition, if you search the site for the term ���copper plating��� you will fnd a number of other good articles. A good book on the subject is Electroplating and Electroless Plating of Copper and Its Alloys by N. Kanani, which is available at Amazon.com and well worth the price. n tin/ZinC eleCtroPlating Q. I am trying to find information on alloy plating, specifically tin/zinc. What can you tell me about this particular type of plating, and what kind of current density is necessary to get a consistent deposit on surfaces? P.R. a. Tin/zinc plating has been investigated and characterized by a number of different individuals. The most common plating bath is the sodium stannate/zinc cyanide bath. The details of this bath are: Q. Can you supply me with a few references for information about cyanide and non-cyanide copper plating baths? A.M. a. There are a number of very good articles and references available that discuss the various types of copper plating. As you are most likely aware, there are four main types of copper plating: the classic alkaline cyanide-based bath, the non-cyanide alkaline bath, the acid bath and the electroless bath. Since space does not enable adequate discussion of these four baths, check PFonline.com for a number Concentration Sodium stannate Na2Sn(OH)6 67 g/L (30 g/L tin) Zinc cyanide Zn(CN)2 4.5 g/L (2.5 g/L zinc) Sodium hydroxide CoPPer Plating BasiCs Component 5 g/L Sodium cyanide 28 g/L Operating Parameters Recommended Values Bath temperature 145��F ��5��F Cathode current density 10���30 ASF Anodic current density 7���15 ASF There are a few other things you must keep in mind when operating this plating bath. As in most alloy plating baths, control of the various components and parameters is very important. The composition of the plated alloy is governed by the ratio of the concentration of tin and zinc in the solution, the hydroxide ion concentration, and the cathode current density. Increased hydroxide concentration results in lowering of the current effciency for tin deposition and leads to increased zinc deposition. The alloy composition is most easily controlled by controlling sodium hydroxide concentration. Current effciency of this bath is also strongly temperature dependent. The temperature should be maintained at as high a temperature as practical, however at higher temperatures, decomposition of cyanide occurs more rapidly, and if this is not kept under control it will ARTHUR S. KUSHNER, Consultant, platingclinic@pfonline.com 50 JANUARY 2013