Stirlingengineforum.com

Had to scrap an old hot air gun (Clarke/Machinemart) and inside the nozzle is a very accurately formed ceramic cylinder, about 20mm diameter, 80mm long - thought this would make a useful power cylinder as very heat proof, albeit fairly fragile.

.........Even if it is a smooth bore it is not glazed and has a flat finish apperance. It would grind your power piston up into powder. A sleeve of copper or brass tubing within would let a piston live.