If I were to build a Rocket Stove for the long run, then I would go for a mineral. Not just a mineral, but a fire resistant composition such as Grog, also known as fire sand and chamotte1. The reason for me to choose so, stems from the experience the following two YouTube pages had.
Bigelow Brook Farm
The following screenshot is taken from the last post of Bigelow Brook Farms2 YouTube page, which covers the build (and re-build) of a Rocket Stove in detail and shows a totally corroded iron heat riser:
This has happened over a course of a winter and intensive usage. Nonetheless it shows that intense heat can even corrode the toughest material. Bigelow Brook Farm has re-build the heat riser with fire bricks and will post an update on that in due time.
Zero Fossil Fuel
Has made as a very detailed series on how to build a Rocket Stove. At 1'18" in the video3, he makes reference to the fact that he was strongly advised against the use of steel.
- Grog (clay)
- Bigelow Brook Farm
- Zero Fossil Fuel
I'm not affiliated to either of the YouTube pages mentioned in this post.