Mixed Si/C/M/O ceramics from 2,5-disilahexane metal carbonyl (M = Fe and Co)

Reactions of 2,5-disilahexane with cobalt or iron carbonyl were performed in order to prepare cobalt or iron organosilicon ceramic precursors. Characterization of their structure by NMR and-IR spectroscopies indicates the presence of mixed oligomeric and molecular species. Pyrolysis under argon at 1000 degrees C gives multiphase ceramics in high yields. Part of the CO ligands were incorporated during the thermal decomposition. Materials were characterized by X-ray, Raman, TEM and magnetic susceptibility analyses. For cobalt and iron, formation of metal-rich nodules included in a homogeneous matrix is' observed for the sample pyrolyzed at 1000 degrees C. Crystalline Fe3Si or Co2Si are detected and the presence of amorphous oxide or oxycarbide phases is consistent with-the high oxygen level. Between 1200 degrees C and 1400 degrees C, a carbothermal reduction process occurs at different temperatures for the iron and the cobalt precursors. Elimination of CO and SiO occurs with modification of the ceramic phases. Formation of SiC and silicides (FeSi for I and CoSi for II) is observed. Melting of the Fe,Si phase leads to the formation of spherical metallic particles.