ask aluminium Forum

Transparent aluminum does not exist.

Transparent aluminum oxide exists.

They are completely two different materials. Aluminum is a metal, aluminum oxide is a ceramic. Aluminum can react with oxygen in the atmosphere to form aluminum oxide. So you can convert a piece of thin aluminum to aluminum oxide to make it transparent, but you are also changing the material.

Rule of thumb: if something is transparent (e.g. glass), then it is non-conductive. If something is conductive (e.g. metals), then it is not transparent.  This is a fundamental struggle and limitation we have in the solar industry, if we can really make a material that is highly transparent and highly conductive, then you win the next Nobel price (someone did win the Nobel on something similar, the conductive polymer, but it's not a very viable material).

Actually, if we area going to allow the aluminum oxide passivation layer to count as transparent aluminum then we may as well go all in and include un-doped sapphire and aluminum oxy-nitride which also is transparent in bulk and used as armored glass in some military vehicles. It is pretty remarkable stuff but close to sapphire in properties and very hard to fabricate. Aluminium oxynitride.