Ok I’ve got a question.
What is it that produces the gold colour of Aus $1 and $2 coins?
Is it just a property of the composition, will any bog standard mix of 92% Copper, 6% Aluminium, 2% Nickel be this colour?
Or is there some specific process used during alloying to get this colour?
Or are there traces of something else in the coin?
interesting question.. no idea..
have you tried facebook?
What’s Facebook?
No, sorry to be a technoramus but I’ve never known where on FB this SSSF group thingy is. Never seen anything listed on mutual friends sites. (And never asked).
https://www.facebook.com/groups/55383347592/
Group name – Dr Karl’s Self Service Science Forum (SSSF)
I think I’ve sent an invitation, but the admins have to approve you.
S’funny. Is it closed? I did try searching for SSSF a few times but nothing comes up for me.
MartinB said:
S’funny. Is it closed? I did try searching for SSSF a few times but nothing comes up for me.
It’s an invite only group, as I understand it.
Anyway, I think the answer is – that’s the colour you get with that alloy.
Geoff D said:
Anyway, I think the answer is – that’s the colour you get with that alloy.
Couldn’t the alloy be coloured via electrolysis or similar?
poikilotherm said:
Geoff D said:
Anyway, I think the answer is – that’s the colour you get with that alloy.
Couldn’t the alloy be coloured via electrolysis or similar?
…
http://www.copper.org/applications/architecture/arch_dhb/copper_alloys/color_chart.html
I just added Martin but got a message saying that it requires admin approval.
I dunno who the admins are. Some bunch of wannabe Hitlers probably.
excellent, just the kind we need.
I’m touched to feel wanted.
Now can you answer the frickin Q?
Is Geoff right? Is it solely a property of the alloy’s composition?
Shit I don’t know, but It is certainly a modest claim.
The mint web page is no help at all.
Although I note that it doesn’t say that electrolytic methods were used …
but the ones and twos certainly look, well, platy.
It’s almost as though the mint wants to discourage counterfeiters.
Barstewards!
It’s probably just paint.
http://www.copperinfo.co.uk/alloys/bronze/
Aluminium Bronze
These are alloys of copper with 5 – 12% aluminium, some having additions of iron, nickel, manganese and silicon, available in cast and wrought form. They are stronger than the brasses or tin bronzes with better corrosion resistance due to a hard, adherent, protective alumina film (Al2O3) They have an attractive golden colour, with very little tarnishing with time. The major use for aluminium bronzes is in sea water applications, such as:
* Fasteners * Pumps and valve components * Pipe fittings * Heat exchangers * Bearings> Is it just a property of the composition, will any bog standard mix of 92% Copper, 6% Aluminium, 2% Nickel be this colour?
A similar colour.
I’ve searched the web without success for which two electron shells of copper are responsible for its colour. Electrons in one shell absorb photons in an energy band that pushes them up into a higher energy state, and this light absorption band accounts for the colour. In a covalent compound the energies of outer electron shells are changed greatly. This means that the surface copper oxide is what accounts for a lot of the colour we see when looking at copper, the pure un-oxidised copper has a more golden colour, (for example, search for pure+copper under Google images).
In an alloy the change in outer electron shell energies is small, but perhaps enough to change the wavelength of absorbed light a bit. I would guess that the 2% nickel is there for strength. At 2% and 6%, the nickel and aluminium are present in solid solution in the copper, not present in separated phases. This means that any heat treatment or variation in alloy preparation will have little effect on the microstructure (apart from crystal size). The thin aluminium oxide layer on the surface protects the copper underneath from oxidisation. The alloys also lighten the colour simply by their presence.