Thermal conversion of organosilicon cobalt precursors to mixed Si/Co/C/O ceramics

Abstract

Cobalt organosilicon ceramic precursors I, I(D), III and IV were prepared by reaction of dicobalt octacarbonyl with normal and Si-deuterated 2,5-disilahexane, 2,4-disilapentane and 1,4-disilabutane respectively. Precursor II is a dimeric silicon cobalt cluster [mu;-{(CH3)Si(CH2)}2][Co(CO)3]2. Thermal decomposition of the precursors was performed under argon. Evolution of H2 in the early stage of the pyrolysis (120C) shows that an initial cross-linking of the material is induced by the remaining SiH bonds. Between 120 and 300C, the thermal decomposition of the complexes results either in the elimination of the CO ligands or in their reaction with incorporation of oxygen and carbon. At higher temperature, the elimination of hydrogen and methane corresponds to the mineralisation step of the precursors. By 1000C, the material is formed of metal-rich nodules homogeneously dispersed in a matrix. Co2Si is detected by X-ray analysis. Between 1000 and 1400C, carbothermal reduction occurs with evolution of CO. Simultaneously SiO2, SiC and CoSi phases are formed.