Effect of combustion gas mass flow rate on carbon/carbon composite nozzle ablation in a solid rocket motor

A 4-direction carbon/carbon composite was produced. The ablation of 4-direction carbon/carbon composite nozzles was investigated in the combustion environment of a solid rocket motor. The ablation surface and microstructure were examined by scanning electron microscopy and the ablation mechanism was also studied. The results show that the nozzle recession rate increases with the increasing mass flow rate of combustion gases. The ablation of the composite was attributed to the heterogeneous reactions between carbon and oxidizing species. This is consistent with the fact that the nozzle ablation was mainly diffusion-limited when the wall temperature was high. The ablation of the composite resulted in cone-shape fibers, ring-shaped grooves and a lamellar matrix with pits and craters on the surfaces. The deposition of spherical carbon particles on the surface was attributed to the formation of volatile hydrocarbons during the pyrolysis of the propellant inhibitor layer, which consisted of epoxy resin and silica and was used for inhibiting combustion of the solid-propellant in rocket motor, under a high mass flow rate.