element47.5 said:
Pure metals melt faster than alloys and what is more, they do tend to stick together.
There is nothing about that sentence I agree with. Eutectic solder, for example, melts at 183 C, while tin melts at 232 C and lead at 327.5 C.
Most brasses melt in the 900-940 range. But "red" brass melts right around 1000 C. Copper melts at 1084 C and zinc at 419.5 C. Cupronickel melts between 1170 C and 1240 C. Nickel, at 1453 C. There are many alloys that form eutectic mixtures whose melting point is below that of the pure metals that comprise the alloy.
Sorry, my statement was misleading and confusing. Of course you are right. I did not mean in alloys general but the alloys that are usually used underneath the coatings in electronic contacts from IT hardware. It is just an observation, I cannot say what these alloys are made of exactly (mostly copper of course, then zinc but also some tiny traces of exotic metals)
I try to narrow it by saying that I have observed the coatings to melt before the core of the contacts does, whatever alloy is used there.
Of course you are right, not ANY alloy has a higher melting point than silver/900 °C but the ones I used to try it out (mainly from memory sockets, pci sockets) seem to have a melting point higher and/or they simply need more time to change phase, so the gold or silver coating melted first and dropped down.
What I observed as well is that the purer gold is, the faster it melts. If there are impurities after AP->HCl/Cl process it takes much longer to melt and form a button.
So that is why I came to the conclusion that the gold from the plating melts faster than the rest of the metal, maybe even if their melting point is lower(!).
I dont know enough about the physics behind that but gold is the best heatconducting metal we play with, so maybe that plays a role.
The melting points and the heat that is exposed to the material is given and cannot be influenced.
But maybe (and this is my personal speculation) the better conductivity of gold and also silver makes it react faster and change the aggregate phase faster than the rest of the metal.
It is only a matter of seconds I am talking about! I have no reference, no link that I can give you. Just try it out and maybe you will also observe that the coating usually melts first, then drops down and gathers at the bottom of the material. Take away the heat, let it cool and watch how it has seperated.
But its enough, if you take the heat away at the right moment, to make the gold drop down.
Edit: All this needs tin and lead free contacts!!!