Heat of pyrolysis of resin in silica-phenolic ablator.

The heat of pyrolysis of resin in 70/30 silica-phenolic ablator, as used in the Apollo system, was determined directly from the relevant heats of formation. Average heats of formation of pyrolytic volatiles were obtained by performing the pyrolyses of resin at three temperatures (750°, 1110°, and 1620°F). The heats of formation of virgin resin and of resin chars (corresponding to each temperature of pyrolysis) were determined by combustion calorimetry. All the experiments were carried out on an actual ablative composite. The combined data yielded three different heats of pyrolysis for the respective temperatures of pyrolysis. The significance of this finding is discussed. If the temperature of 1000°F is taken as representing the pyrolysis of resin in the ablation process, the heat of pyrolysis (standard states, 298°K) is +477 Btu/lb resin, by interpolation. The applicability of this method to other crosslinked resins is indicated.