Reply to Thread

Message:: [QUOTE="Pavlos, post: 7461229, member: 96635"]I do not fully agree with your definition, it is exactly what [USER=82322]@Ed Snible[/USER] mentions, it is intergranular corrosion, which doesn't necessarily only has to be on the impurities such as Cu. Also it is no crystallization at all, I do not know why we even use that term in Ancient coins in general, it is false. When cooling down the metal, the grain boundaries of the metal crystals are already set. What happens over the 2000 years in the ground, is that the conditions of the environment (heat, water, oxygen, UV, salts etc) reveal the grain structures by etching of the grain boundaries i.e. intergranular corrosion. Atoms at the boundaries of crystalline grains and bounderies will be in locally higher energy states and this is why metallic crystal grains can be revealed.It really is false to call structural failures "crystallization", just because we are seeing the surface of the grain boundaries.Due to the intergranular corrosion, the surface is just revealing what was already there, but people generally do not know that almost all metals are polycrystalline in the first place. I have done an extensive research project of Metallurgy regarding this topic at a university before I stepped in the commercial world. It was then intended for electrical properties (grain boundaries of the metals limit electrical conduction, and could be compared using impedance measurements).[/QUOTE]