Abstract: The invention relates to a recuperative heat exchanger comprising an elongate rotationally symmetric body of ceramic material having radially outwardly extending, flow channels of slot like cross-section extending along the axis of the body. Alternate flow channels extend further toward the surface of the body and further toward the axis of the body, respectively. Inlet and outlet openings are provided for the flow channels about at the ends of the body. The invention also comprises a process for making such a heat exchanger, including extruding ceramic material through an extrusion nozzle with a free cross-section in which core bodies are shaped and positioned for generating the flow channels and inner and outer cover walls defining the flow channels. The invention further comprises the extrusion nozzle in which the process is performed.

Abstract: In the production of shaped silicon-carbide bodies, especially tubes which onsist predominantly of silicon carbide throughout their thickness for use in nuclear-reactor technology, a carbon-containing preform (body of the desired shape) is contacted with elemental silicon powder at a temperature of 1400.degree. C. to 1500.degree. C. and the silicon-contacted carbon-containing body is thereafter treated at a temperature of 1800.degree. C. to 2000.degree. C. to transform at least the major part of the carbon into silicon carbide.