Improved ablation resistance of carbon–phenolic composites by introducing zirconium silicide particles

The effect of ZrSi 2 on the thermal degradation behavior of phenolic and the role of ZrSi 2 on the ablation resistance of carbon–phenolic (C–Ph) composites are investigated by introducing ZrSi 2 particles into phenolic, and then ZrSi 2 particles into C–Ph composites. Thermogravimetry (TG) analysis illustrates that the residue yield of phenolic at high temperatures is increased by the introduction of ZrSi 2 particles. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses reveal that the increased residue yield is attributed to the reactions between ZrSi 2 particles and pyrolysis volatiles. Therefore, partial carbon and oxygen elements in the volatiles remain in the thermal residue in the forms of amorphous carbon , ZrO 2 and SiO 2 , respectively. Moreover, the ablation resistance of C–Ph composites is significantly improved by the introduction of ZrSi 2 particles with formation ZrO 2 and SiO 2 during the oxygen–acetylene ablation process . The average linear and mass ablation rates of ZrSi 2 modified carbon–phenolic (Z/C–Ph) composites evidently reduce by comparison with those of C–Ph composites under similar conditions. As depicted in the microstructure, the ablation occurs in volume in C–Ph composites. The oxygen-containing molecules penetrate deeply inside the matrix, thus the ablation by oxidation is accelerated. However, the ablation occurs in surface in Z/C–Ph composites. ZrSi 2 reacts with the oxygen-containing molecules to form SiO 2 –ZrO 2 layer and molten SiO 2 cover on the ablated surface, thus the ablation by the oxidation of matrix and fibers in the interior has been inhibited.