Decomposition and Oxidation of C2F4 Behind Shock Waves

Abstract

Ultraviolet absorption and mass-spectrometric observations of shocked C2F4–Ar gas mixtures have indicated that the C2F4 monomer exists in thermal equilibrium with CF2 radicals and that the initial C2F4 oxidation mechanism involves two steps C2F4→ lim Ar2CF2CF2+O2→CO+2F+O.Dissociation and oxidation rates were determined from uv absorption measurements of CF2 at 2536 Å behind incident shock waves. The C2F4 dissociation reaction appeared to be second order, 12d[CF2]/dt=kAr[C2F4][Ar], with kAr=7.82×1015T12 exp(−55 690/RT) cc/mole·secover the temperature interval from 1200° to 1800°K at total concentrations between 0.9×10−5 and 1.7×10−5. A least-squares fit to the experimental equilibrium constants for the reaction C2F4=2CF2, using the integrated form of the van't Hoff equation, yielded logKc=−69 432/2.303RT+4.62 (Kc in mole/cc).From the measured heat of reaction, the heat of formation of CF2 at 298°K was calculated to be −39.7±3.0 kcal/mole. Mixtures of C2F4 and O2 in varying mole ratios were allowed to react at temperatures between 1500° to 2500°K with molar concentrations of reactants ranging from 4×10−8 to 6×10−7 mole/cc. The oxidation reaction was observed to be first order in both CF2 and O2, d[CF2]/dt=−kox[CF2][O2], with kox=2.92×1010T12 exp(−13 280/RT) cc/mole·sec.