Inhibition of the H2+ O2 reaction by alkyl silanes

Abstract

The inhibiting action of SiEt₄ and SiMe₄ on the second limit of the H₂+ O₂ reaction has been examined in KCl-coated vessels. The inhibition characteristics observed with SiEt₄ are essentially similar to those reported for C₂H₆, C₄H₈ and C₄H₁₀. The main inhibition process is the reaction of H atoms with SiEt₄, but a significant contribution arises from the reaction of OH or O (or both) with the silance. The resultant triethylsilylethyl radicals appear to undergo multi-stage reactions to form C₂H₄, CH₃CHO and presumably (SiO₂)_n, but at no time do they regenerate an active chain center. The experimental data are interpreted quantitatively and the velocity constant for the reaction H+SiEt₄ has been evaluated as 2.18 × 10⁹ 1. mole^–1 sec^–1 at 520°C.

The inhibition features of SiMe₄ are similar to those observed with CH₄ and CMe₄. Thus SiMe₄ does not inhibit directly, since the Me₃SiCH₂ radical, formed in the primary inhibition processes, reacts to regenerate an active centre and to form a “degenerate” inhibitor which has not reached a stationary concentration when the explosion boundary is reached. The consequent thermal nature of the explosion boundary has been confirmed by the effects of different inert gases on the ease of explosion.