# Properties of powdered metals

I have seen certain metals such as Aluminium used in a situation where it is in a powdered form and "compacted" into a shape under intense pressure (in a mould), and it ends up looking mostly like solid metal. It is also heated afterwards, I assume to form a complete metallic bond.
I have a few questions on this:

1. How are oxide layers on the powder affected when it is compacted? Eg. Can the $Al_2O_3$ layer, or at least the O atoms from them, be "inside" the moulded object when it is compacted?
2. Metals in a powdery form aren't as reflective as in their "solid" form (also please let me know the right word for that). Why is this?
3. Are most metals in their powdered form pure, eg. Not like a salt, but a single element?
4. I know gold powder, obtained from chloroauric acid, becomes gold in its metal form when melted down. It looks brownish and takes up far more volume than the gold it contains. Is this pure Au or a compound/salt?
5. Also, in 4. with the gold powder, it actually forms rather large clumps from the chloroauric acid. How is this possible assuming it's a pure element?

Thought I better get all the questions done in one go. Thanks in advance

• Start with a search for powder metallurgy- note its not limited to metals- it also combines metals and ceramics such as AL2O3. "solid" form- the usual term is dense where powder metallurgy has porousity. – user2617804 Jun 17 '14 at 13:52
• Hi baharini, I think you should split your question in this form really require too much information to be answered.... – G M Jun 18 '14 at 7:12