EXPLOSIVE DECOMPOSITION OF GASEOUS CHLORINE DIOXIDE

The slow thermal decomposition of gaseous OCIO has been investigated between 318 and 333 K and at initial pressures between 4 and 120 Torr in vitreous containers. A slow reaction proceeds while the OCIO partial pressure remains higher than a given critical pressure p(e)(OCIO), then an explosion occurs. p(e)(OCIO) depends on the total effective pressure, p(o)(OCIO), and follows the equation p(e)(OCIO) = a + b p(o)(OCIO). The system is in the explosive regime at temperatures > 336 K and with p(OCIO) ranging between 1 and 70 Torr. Prior to explosion, practically no OCIO decomposition is observed. The induction period, tau, of the explosion has been determined between 336 and 387 K, and follows the equation, tau = A + B/p(OCIO). A quadratic chain-branching reaction mechanism with initiation and termination reactions on the wall is operating. A bimolecular reaction between adsorbed OCIO leading to formation of the chain carrier, CIO, is proposed as the initiation. The chain-branching coefficient depends on the difference between the rate constants of the reactions: 2 ClO --> Cl + ClO2 and 2 ClO --> Cl2 + O2. The first-order diffusion-controlled reaction: Cl2O3/-->wall products, leads to chain termination.