aluminium barrel?

anyone considered using an anodised aluminium barrel? anodisation provides a sponge-like layer of aluminium oxide mere microns thick, which is electrically insulating, thermally conducting and should be fairly unaffected by 300 degree heat. At those temperatures, it would effectively be self-repairing against the heater scratching it since it would almost immediately re-oxidise.

Another idea I had was using a large SS washer with 3 holes drilled into it, and 3 SS screws holding the barrel away from the plastic, so it would vaguely resemble this, instead of the ptfe thermal break.

any ideas on how to best implement these?

Are you talking about pushing the filament through open air right before entering the aluminum barrel? I don't think this will work. There has to be a constrained phase transition zone so that the mechanical force of the solid filament can transition into a pressurized liquid. Since aluminum has such good thermal conductivity, the phase transition zone will drift toward the intake end and the pressurized liquid will leak out.

You might be able to get it to work with a thin walled steel barrel, which has much worse thermal conductivity, allowing you to have better control of the phase transition zone. A few people have tried steel barrels. [builders.reprap.org]