Ablative phenolic composites

The first materials used in solid rocket nozzles were refractory metals such as tungsten and polycrystalline graphite. The high density of the former and the low resistance to thermal shock with random fracture of the latter led to their gradual replacement by composite materials. In this application, the materials withstand temperatures close to 3,000 ˚C for durations of a few seconds to a few minutes. Moreover, given that in most nozzles chemical reactions take place in a rather reducing environment, it was natural to consider carbon as the material of choice to develop in the early sixties a family of composites called rigidimers or phenolic ablative composites, as they are made up of a refractory reinforcement such as carbon or silica and a phenolic resin-based ablative matrix. This resin decomposes under the effect of heat, leaving a large residue of carbon, which enables the thermal energy of the nozzle gases to be partially dissipated and the reinforcement to be held in place.