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Poroese Siliciumcarbidkeramik und Verfahren zu ihrer Herstellung

Porous silicon carbide ceramic production - from sized powder mixture containing aluminium- and rare earth-containing sintering additive mixture.
: Adler, J.; Klose, T.; Stoever, H.; Teichgräber, M.

Frontpage ()

DE 1996-19626307 A1: 19960701
DE 1997-19727115 A: 19970626
DE 19727115 C2: 20010802
Patent, Elektronische Publikation
Fraunhofer IKTS ()

A novel porous silicon carbide ceramic has a SiC content of more than 90 (preferably more than 95)%, consists of SiC particles with an aspect ratio of much less than 3 bonded together by SiC and small amounts of thin Al-containing and rare earth element-containing grain boundary phases, has an open porosity of 20-65 (preferably 35-45)%, and has a narrow pore size distribution with a mean pore size in the range 0.5 microns to 1 mm, preferably 1-200 microns. The ceramic may consist of two or more layers of different mean pore sizes and porosities. Also claimed is a process for producing porous silicon carbide ceramics of more than 90% SiC content, in which SiC powder with a d50 value of less than 10 microns is mixed with 1-10 wt.% sintering additive of less than 5 microns particle size, such that (a) SiC powder with a d50 value of 1 micron to 3 mm is mixed with a mixture of rare earth element-containing sintering additive and 20-95 mol% Al-containing sintering additive; and (b) the mixtu re is moulded, freed from binder and then sintered in an inert atmosphere or vacuum at 1600-2300 deg. C or in air or an oxygen-containing atmosphere at 1200-1500 deg. C. Preferably, the SiC powder has a d50 value of 2-500 microns or 20 microns to 1 mm and may be in the alpha and/or beta modification, the powder especially having a grinding powder particle size distribution. The rare earth element-containing sintering additive is preferably selected from compounds of Sc, La, Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Nd, Lu and preferably Y, especially yttrium oxide. The sintering additive mixture preferably contains 50-90 mol% Al-containing sintering additive, especially aluminium nitride or aluminium oxide. The sintering additive particle size is preferably less than 1 micron. Preferably, sintering is carried out in air or an oxygen-containing atmosphere at 1300-1450 deg. C. USE - E.g. for filters, filter material supports, aerators for aggressive media, catalyst supports, cooling e l ements or reactor substrates or as moulding material especially for wet pressing of roof tiles. ADVANTAGE - The high SiC content ceramic has high strength, high pore volume and adjustable pore size, and can be produced by a simple, low temperature process.