carbon dioxide resistent material for high pressure application

[Syphex]

Hi folks,
I am kinda new to this forum, but I hope you will help me anyway ;-)
I am looking for a material, that can cope with a overcritical carbon dioxide atmosphere, for pressures up to 300 bars and up to 200 °C (~400°F).
The most important thing ist, that the material is long-lasting and not co2 solubly (not all all).
I was thinking of some Hastelloy alloys, or other noble metal alloy.
I hope you can give me a hint, or a source, where I can get the information I need.

p.s.: I need a sphere of that material, with a ~5cm diameter.

sorry for my bad english ;-)

thanks in advance