Q&A: Hard-To-Buff Silver Deposit

By: Arthur S. Kushner 17. June 2013

 

 

Q. I work for a specialty silver plating company that restores silver-plated candelabras, silverware and other household items. Our silver plating bath has been well-maintained in terms of testing and maintaining proper chemical composition, but we have noticed over the last few months that the plated deposits are more difficult to polish and buff. Do you have any suggestions for resolving this problem? S.L.

 

A. Start by checking the current density in the bath. Low current density will enable you to deposit silver, but if it is at the very low end of the suggested range you can get harder-than-normal silver deposits. There are several types of impurities that will cause silver deposits to become hard and difficult to polish and buff, including the presence of iron and high chlorides. Lead, tin, nickel and organics also can cause this problem. To remove the unwanted organics, filter the plating solution through activated carbon. Keep in mind, however, that activated carbon treatment will also remove desirable organic additives, so you will most likely have to reconstitute the bath with the required additives. To remove most of the “tramp” metals mentioned above, dummy the bath at 2 asf for 12 to 24 hrs.  

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Plating Q&A: Black Finish on 430 Stainless Steel

By: Arthur S. Kushner 12. April 2013

 

Q. We supply parts to the OEM automotive market and include screws for fastening, some of which are 430 stainless steel. We have been asked to supply the screws with a matte black finish but are concerned about the cost of using a complicated system to plate screws that are inherently anti-corrosive simply to make them black. Do you know of a way to get a black surface finish on the parts that will stand up to the road blast under a car? M.J.

 

A. You make a very interesting point regarding stainless steel and corrosion. It does seem absurd to spend money to get a black finish on a component that will stand up well in a corrosive environment. The issue here is strictly cosmetic.

 

That being said, in situations where stainless steel requires a black finish, the method of choice is the hot black oxide process, which requires a hot chemical bath followed by a sealing step. This will give you corrosion protection and an attractive finish. The only problem is that the finish looks pretty and gives you some corrosion protection in an indoor environment, but it is less reliable in an outdoor environment. I do not think the black finish will last long on the underside of an automobile. 

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Q&A: Purple on Platinum-Plated Anodes

By: Arthur S. Kushner 23. January 2013

 

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 platinum-plated 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 in-formation 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. 

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Plating Q&A: Electroless Nickel on Tungsten

By: Arthur S. Kushner 9. November 2012

 

Q. Can one apply electroless nickel over a tungsten metal matrix? S.T.

 

A. There are a couple of different procedures for doing this that are found in the plating literature. One such procedure is outlined in the book Electroless Plating – Fundamentals and Applications (1990), edited by Glenn O. Mallory and Juan B. Hadju.

 

The general procedure is as follows:

  1. Alkaline potassium ferrocyanide soak, 215 g/L in 75 g/L potassium hydroxide, room temperature, for one min.
  2. Rinse.
  3. Boil in 10 percent potassium hydroxide for 10 min.
  4. Rinse.
  5. Dip in 10 percent hydrochloric acid for 30 sec.
  6. Rinse.
  7. Activate with palladium chloride (0.1–0.5 g/L in 1–3 mL/L hydrochloric acid).*
  8. Rinse.
  9. Electroless nickel plate.

*A Wood’s nickel strike may be substituted in some cases.

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Q&A: Green Sludge in Nickel Tank

By: Arthur S. Kushner 9. October 2012

 

Q. I have green sludge collecting on the filters in my nickel plating bath. What is it, and what can I do to prevent this from happening in the future? T.E.

 

A. The sludge that you observe is nickel salts that form over time. Usually the buildup of these green-colored salts is slow, but if the overall chemistry of your plating bath is off, the buildup rate may be more rapid. For example, nickel hydroxide has a greenish color and can form if there is a small amount of hydroxide ions in the bath. Probably the simplest solution is to drain your plating tank, clean it and than place the plating solution back in the tank. You must perform one more step before using the bath, however. Carefully check out the chemistry of the bath, and pay particular attention to the pH as well as the amount of boric acid present. Changes in pH and low boric acid can increase the amount of hydroxide present and will lead to a greater rate of nickel hydroxide formation.

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