OLIGOMERS WITH SILICON AND TRANSITION-METAL GROUPS - THERMOLYSIS OF POLY[1,1'-BIS( DIORGANOSILYLETHYNYL)FERROCENES] AND POLY[((DIORGANOSILYLENE) DIACETYLENE) DICOBALTHEXACARBONYLS] TO GIVE IRON SILICIDE-BASED AND COBALT SILICIDE-BASED CERAMICS

The pyrolysis of transition-metal-containing organosilicon-diacetylene oligomers was performed in order to prepare multiphase ceramics. Poly [1,1'-bis(diorganosilylethynyl)ferrocenes] (2) were pyrolysed, under a rgon, up to 1350 degrees C to give FexSiyCz phases with good yields, o wing to the incorporation of the cyclopentadiene groups in the carbon matrix and the participation of nearly all silicon and iron in the cer amic residue. The pyrolysis of poly[{(diorganosilylene) diacetylene} d icobalt hexacarbonyls] (3) at 1350 degrees C gave Co2Si and graphite-l ike carbon. Evolution of part of the carbon monoxide of 3 in the early stage of the pyrolysis (100 degrees C) showed that the cross-linking of the diacetylene units was induced by reactive cobalt species. Furth ermore, at higher temperatures (200-500 degrees C), cobalt clusters ca talysed the ceramic formation. Co2Si was shown to result from the reac tion of SiC with Co above 1000 degrees C, both formed during the pyrol ysis process. Finally, at 1100 degrees C, a carboreduction reaction le d to the elimination of the oxygen incorporated in the carbon matrix d uring the cross-linking process.