Gold Pitting Problem
Q. How can we solve problems with pitting and haze on our hard gold deposit?—J.R.
A. Pitting can be caused by a number of different factors. Hydrogen gassing, particulate matter suspended in the plating solution and inadequate cleaning of the base material are three common causes.
Hydrogen gas formed during the plating process can stick to the surface of the parts being plated. If the bubbles that stick to the surface do not slide off rapidly, the plate will form pits. Typically, a pit due to hydrogen has a “small” tail. In most plating baths, this problem can be minimized by adding wetting agents/surfactants. The problem also can be minimized by increasing the agitation of the bath. Depending on the type of agitation, different wetting agents may be required.
Particulate matter and organic matter can also cause pits. For example, if your plating operation is set up in a dusty area, some of that dust will settle into your plating bath and must be removed by filtration. Also, organic impurities may be introduced into the plating bath by the decomposition of wetting agents or other organic additives in the bath. This is why filtration is a critical part of the plating process.
Lastly, cleaning of the parts prior to the plating step is critical. In my opinion, more than 60 percent of plating failures have to do with the cleanliness of the surface prior to plating. This means removing not only things you can see on the surface but also things that you cannot see, like oxides.
Hazy gold deposits can be due to insufficient brighteners in the plating bath or a pH that is too high. Carbon filtration is called for to remove breakdown products from brighteners and wetting agents, but you may be carbon treating your bath too frequently. I have no problems with this, but some operators believe that if a little is good, a lot has to be better. Just remember that, in many cases, after the plating bath is treated with carbon you must rebuild the organic portion of the bath, because carbon filtration will remove both good and bad products. I am not suggesting that you give up on carbon treatment, but that you use a polypropylene-type filter that is suitably sized for your plating bath.
You also might try reducing your pH by a couple of tenths and see if that makes a difference. If you are not using a Hull cell to monitor the day-to-day health of your plating bath, you should.
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