Abstract: A gas-tight aluminum oxide tube having an Al.sub.2 O.sub.3 content of 98.0 to 99.8 wt-%, wherein the interior of the tube has a coating of Al.sub.2 O.sub.3 with a thickness of from 0.03 to 0.30 mm and a mean roughness R.sub.a of 2 to 10 .mu.m, is provided. Preferably, the outer surface of the tube can have a mean roughness of 1.0 to 1.5 .mu.m. Also, the coating material can contain from 15 to 30 vol-% pores and the tube material can contain from 5 to 10 vol-% pores.

Abstract: A process is described for the manufacture of a gas-tight aluminum oxide tube which is suitable for performing catalytic high-temperature reactions. For this purpose water, a binder and a plasticizer are added to aluminum oxide powder, the mixture is extruded to give a tubular green body and the tube is dense-sintered at about 1740.degree. C.An aqueous suspension of aluminum oxide is obtained by grinding aluminum oxide, and a spray powder of a maximum particle size of 200 .mu.m is prepared therefrom. Presintering takes place at a temperature T between 1300.degree. and 1400.degree. C. and grinding takes place with water and a water-soluble stabilizing agent. The aqueous suspension is sprayed and the resultant spray powder is treated with water and a plasticizer, the mixture is kneaded to give a plastic mass and this mass is extruded to give a tubular green body which is also presintered at the temperature T.