Heat release of carbon particle formation from hydrogen-free precursors behind shock waves

The process of heat release during carbon particle formation and growth after pyrolysis of carbon suboxide C3O2 behind shock waves was investigated. For this goal, temperature and optical density of gas-particle mixtures initially consisting of 3% C3O2 + 5% CO2 in Ar were measured as a function of time. The temperature was determined by two-channel emission–absorption spectroscopy at λ = 2.7 ± 0.4 μm, corresponding to the CO2 (1,0,1) vibrational band. In the range of initial temperatures behind the shock waves from 1600 up to 2200 K a significant heating of the mixture during particle formation and growth was observed that increased towards higher temperatures. The analysis of the obtained data in combination with previous results about the temperature dependence of the particle size shows a decrease of the heat release of condensation from ∼200 kJ/mol per atom for particles containing ∼1000 atoms to ∼50 kJ/mol per atom for particle containing ∼106 atoms.