Letter 23057

How to avoid excessive gassing when conducting electropolishing  

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Hi there.

I'm interning for a research institute in Hsinchu, Taiwan for the summer. Our work here concerns many aspects of mechanical engineering and material science, but one of the topics I handle is electropolishing stainless steel samples. I'm supposed to find optimal conditions for electropolishing through trial and error along with stacks of reference books my boss gives me. However, this is still all really new to me.

One of the largest problems in this particular field of metal cleansing is the issue of pitting. We always have some sort of irregularity when we polish these samples. My boss is wondering what type of electrolyte should be used to avoid excessive gassing, which is one of the main causes that contributes towards pitting. What "ingredients" should be included in the electrolyte? What other techniques should we use to avoid this problem? (such as moving cathode/anode to evade bubbles, spinning, etc) Are there any other suggestions that can promote optimal electropolish for stainless steel?

Joseph Huang
- Illinois, USA

Electroplating Engineering Handbook --probably in your stack of reference books--gives about a dozen different formulations, each of which has its proponents. Straight sulfuric acid is a very common solution though. It's hard to summarize the wonderful information you'll find there, but some principal causes of etching are: excess water building up in the solution, inadequate current density, and insufficient air agitation.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

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