Experimental study of carbon particle charging at shock-wave pyrolysis of C3O2

Abstract

The temporal variation in electron and ion concentrations have been measured in shock-heated mixtures of Ar + (0–2)% C3O2 in the 2000–3600K temperature and 15–30bar pressure range. Experiments in pure argon proved that the observed free electrons and ions originate from inherent impurities of sodium. The equilibrium concentrations of free charges in argon were established during (1–3)×10−5s and varied from 4×1011cm−3 at T5=2500K to 5×1012cm−3 at 3500K. In the reactive mixtures, containing C3O2, the time profiles of electron and ion concentrations showed a more complicate behavior—a fast rise to a maximum followed by a gradual decay. The maximum ion concentrations were much higher and electron concentrations were much lower than in similar conditions in argon. The extent of the subsequent decay of electron concentration increased proportionally to the square of the C3O2 concentration. In the mixture with 2% C3O2 the final electron concentration was about 100 times less than in pure argon. The characteristic decay time of free charges varied from 400 to 40μs and decreased proportionally to the square root of the charge concentration. The data analysis is based on the assumption that the observed redistribution of electron and ion concentrations is caused by charging of the carbon particles formed during pyrolysis of C3O2. The kinetics of particle charging and the final distribution of charges were evaluated by the analysis of electron and ion fluxes to the particles in accordance with the electric potentials of charged particles and corresponding sodium ionization. A predominance of negatively charged particles, caused by the high electron mobility, resulted in their much higher concentration than the concentration of free electrons.