Thermal effects accompanying spontaneous ignitions in gases III. The explosive decomposition of diethyl peroxide

Abstract

An extensive quantitative test of the application of thermal theory of the spontaneous ignition of diethyl peroxide has been carried out, and both indirect aspects and direct temperature measurements in systems on the verge of ignition have been studied. The principal conclusions may be stated as follows. (i) Ignition is always preceded by self heating. Temperatures are greatest at the vessel centre and in accordance with the postulates of Frank–Kamenetskii there is no detectable excess at the walls. (ii) Temperature-position profiles differ significantly from parabolae being less steep at the walls and more curved at the centre. (iii) Stable decomposition is impossible once the centre temperature exceeds 20 °C (i. e. close to 1.61RT20/E) or the wall-gradient a value greater than 2RT20/Er0. (iv) The 'experimental ’ value forδaround the explosion boundary derived from fifteen sets of measurements ofpcr,Tcrtogether with new values for Q, λ and ‘ isothermal’ values fork, A, andEis 4.0. Agreement with theory is good and if a correction is made to allow for reactant consumption, the discrepancy is insignificant. (v) A graph ofRlnpcr/T3against 1/Tgives a straight line with slope (35 kcal (147 kJ) mol-1) in good agreement with expectations (34 kcal (143 kJ) mol-1), based on isothermal kinetics. (vi) Inert diluents exert their principal influence on critical conditions by their effect (here measured experimentally) on thermal conductivity, but because mixtures with diluents undergo more self-heating on admission to an evacuated vessel than does the pure peroxide there are deviations from simple proportionality betweenpcrand λ. (vii) The critical ignition temperature and the critical wall gradient are unaffected by dilution. The experiments carried out represent the fullest test to date of thermal theory. They have been made possible by the use of very fine (13μm) thermocouples as temperature measuring devices.