"Metallurgical Bonding" in electroplating

A. Hi Yan. I just googled this and there must be a couple of dozen sites which use generally similar but slightly different definitions.

I am guilty of using the term frequently on this site without defining it myself when we've noted the difference in adhesion values between electroplating onto a clean metallic surface as opposed to a dirty or oxidized one. I think one characteristic of a metallurgical bond as it relates to plating would be "perfect adhesion" -- attempting to mechanically separate the plating from the substrate results in tearing one or the other rather than separation at the junction of the two metals.
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Alright, time to go out into the weeds, I guess. I grabbed my old freshman chemistry book to make sure I have this right. Talking about the nature of crystalline solids, you have:

Ionic solids, where one type of atom gives up electrons to the other type entirely
Molecular solids, where the material has discreet covalently bonded molecules but they join together based on hydrogen bonds and such to form the crystal
Atomic solids, further subdivided into three categories:

Noble gases bonding together with London dispersion forces
Network solids with strong directional covalent bonds (e.g. carbon, silicon)
Metallic solids with delocalized nondirectional covalent bonds and an "election sea" of widely shared electrons

That's what I was remembering as being called a "metallic bond", though I had to grab a different textbook to see that exact term being used.

"Metallurgical Bond" might be one of those neologisms that arise when half-remembered technical terms are tossed around casually.

"Perfect adhesion" might be as good a layman's definition as any. I would say it's when the different metal layers have formed those electron-sharing bonds and have started to co-mingle the same as any alloy.

As a for-instance, we might recall that stainless steel is difficult to plate on due to the rapidly-forming passive chromium oxide layer, and the surface must be activated to create a surface free of covalently bonded oxygen and containing all zero-valence metal atoms that are ready to form bonds with the metal being deposited.