Caustic treatment of silver plated parts

[armourian78]

Hello,

I need some advise. We have a rust reworking process which uses a caustic solution (20% sodium hydroxide with water) to kill the rust. In our experience this works very well to kill the rust on tool and chrome type steels we put through this process.

However on one particular component, we have areas of the naked base steel (which show signs of rust), together with areas of silver plating. If I put this component through the caustic solution, and completely drain off all caustic solution and protect with rust protective oil, will the silver plating be ok?

I know that if the caustic solution is left on the component for some time it will attack the silver plating (green/brown discolorations). However if the caustic solution is completely removed, and drained off, with the silver plating not showing any form of chemical attack, and stored in rust preventive oil - Will the silver plating continue to deteriorate over time (eventually showing green/brown discolourations)?

My assumption is the silver plating will be ok, so long as the as the chemical source for the plating attack has been removed.

Thanks
Ian

 

[CoryPad]

Silver is resistant to sodium hydroxide. Silver is reactive with sulfur, and silver corrosion products usually are dark brown to black. Your proposed cleaning should work, although you may have contaminants that you did not know you have.

 

[tomwalz]

What Corypad said plus attack under the silver layer.

NaOH solutions can be very hard to rinse completely. Sometimes a commercial preparation with rinsing agents can be a good choice.

I use a 15%, 150F NaOH solution to electro-clean before plating but then follow with rinsing and a 10%, 70F HCl bath.

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.