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Black coating on nickel and how to remove it

2007

Hello,

I have purchased several Nickel plated Stainless Steel bolts, and needed to clean them fairly well as my experiment requires very high cleanliness specifications. I immersed these bolts into a detergent solution (Micro 90 detergent, ~1.5%) heated to about 100 ° F in an ultrasonic cleaner. I checked back on them after about an hour and they had a black coating on them.

I took a few and tried a different detergent (Liquinox, 2% heated to 130 F in ultrasonic bath), and they turned even blacker. This coating seems to come off if I use a stainless steel welding brush, is this coating likely to be Nickel Nitride or Nickel Oxide, and do you have any suggestions on how to remove it chemically without removing the Nickel plating underneath?

Steve Hardy
Virginia Tech Physics Dept - Blacksburg, Virginia

As a follow-up, I purchased a bottle of Citranox cleaner, and have used a heated (60 C) 2% solution in an ultrasonic bath for several hours with minimal results.

Steve Hardy
- Blacksburg, Virginia
2007