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Mixed Metal
Published: April 9, 2021

Q. We are interested in a cleaner that will perform well for mixed metal ultrasonic baths. We are cleaning titanium and cobalt chrome. What can you recommend?

A. As a general rule, mixed metal baths should be avoided. When metals are far enough apart on the galvanic potential scale, batteries can form and the plating out of metal oxides can result, manifesting in dark deposits. This occurs when you clean active metals in electrical and electrolyte solutions in contact with another metal at a different galvanic potential.

If you have a scratched, degraded, or a poorly passivated stainless steel sonication tank, and you clean an active metal, you run the risk of galvanic reactions with the exposed iron in the degraded stainless steel as well. This may occur with the cobalt chrome you are cleaning. Dirtier solutions/bath will contain more electrolytes and increase this likelihood.

It would be best to avoid this problem, by cleaning active metals in a fresh solution of detergent with no other dissolved metals, in a separate tank or sonication run. If that is not possible, use an electrically isolated “sub-tank” such as glass. Glass beakers with fresh cleaning solution can be used in ultrasonic tanks to clean aluminum very effectively as glass does a good job of transmitting the ultrasonic energy from the solution in the tank to the solution inside the glass. I would not recommend the use of plastic beakers or “sub-tanks” as it tends to absorb ultrasonic energy.  If a simple immersion soak (no sonication) is being performed, a plastic container is fine.

If oxidation does occur, using an acidic detergent such as Citranox® Liquid Acid Cleaner and Detergent can often help.  We would recommend an ultrasonic run with a 2% solution.

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