Session BB3.8

11:45 AM BB3.8
MICROSTRUCTURE AND PROPERTIES OF PLASMA-SPRAY FORMED CERAMICS. Ekkehard H. Lutz, LWK-Plasmakeramik GmbH, D-51617 Gummersbach, GERMANY; Udo Steinhauser, Wolfgang Braue, German Aerospace Research Establishment (DLR), Materials Research Institute, D-51147 Koln, GERMANY.

Plasma spraying, originally a surfacing technology used for ceramic coating of metal substrates, is meanwhile an established technology suitable for producing bulk ceramic bodies such as plates and tubes of almost any size with characteristic anisotropic physical, mechanical and thermomechanical properties. By plasma-spray forming, components can be produced in situ and directly with the desired dimensions, posing an interesting alternative to conventional methods of shaping green bodies by molding and casting followed by sintering These preferentially oxide and silicate ``plasma ceramics'' exhibit a porous laminar grain structure with porosities of 10 to 20 %, low structural hardness (200 to 600 HV), low thermal conductivity (1 W/mK and less) and heat capacity (1 J/gK and less), extremely low E-moduli of 4 to 20 GPa, low MOR with 20 to 40 MPa, but R-curve behavior and outstanding thermal shock properties. For example, mullite tubes of 3 mm wall thickness survive a $\Delta$T quench of 1200$^{\circ}$C in 20$^{\circ}$C water without fracture. Subsequent firing at 1000 - 1800$^{\circ}$C results in a slight density increase of I to 5 % and may cause a significant increase in MOR and a much greater increase in E-modulus. Accordingly, thermal shock resistance may be reduced considerably. The applications of plasma ceramics are manifold. They are used in hot corrosive environments of rapidly changing temperatures and where severe thermal gradients occur.

SESSION BB4: EMERGING TECHNOLOGIES AND APPLICATIONS - B
Chairs: Joachim V.R. Heberlein and Jan Ilavsky
Wednesday Afternoon, December 3, 1997
Essex North/Center (W)