Beilby layer in Electropolishing of stainless steel
A discussion started in 1995 & continuing through 2011(1995)
Q. Don't know whether this question got through previously:
I have recently been asked whether it is true that austenitic stainless steel tubing intended for gas delivery in the semiconductor manufacturing industry cannot be be satisfactorily passivated after electro-polishing because of the absence of a 'Beilby layer', which prevents suitable formation of chromium oxides. Is this true? and What is a Beilby layer? I would appreciate it if anyone could shed a little light on these matters. Thanks,Wolf Penzel
Q. Found a reference in The Surface Treatment & Finishing of Aluminum and its Alloys by S. Wernick, R. Pinner, P.G. Sheasby where, on page 28, it is described as 'the much debated Beilby layer of amorphous or very finely crystalline metal' resulting from the last stages of polishing. Whether it is plastic deformation or viscous flow remains a matter of debate, according to further comments made. Whether this condition has the effects I asked about remains unanswered. Thanks,Wolf Penzel
March 27, 2011
A. Hi, Wolf.
I am not familiar with this Beilby layer you speak of, but I do know that electropolishing itself constitutes an efficient passivation procedure that requires no subsequent treatment to render the surface of stainless steel passive. I am confident that electropolished austenitic steel will outperform nitric acid passivated stainless steel. Lee Kremer asserts in letter 11762 that citric acid can be applied to an electropolished surface to provide even greater passivation, but I am quite confident that it isn't actually necessary.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
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