Electric Phenomena in Silanes Chlorination and Oxidation

Abstract

Chemiionization was revealed in the chlorination of dichlorosilane, the lower limit of the concentrations of charged particles was estimated as ~10⁷ charged units cm⁻³. The detected relationship between chemiionization and phase formation in low-temperature heterophaseous BC gives grounds to consider the chemical nature of a reaction zone of silanes oxidation over the region of flame propagation as weakly ionized plasma. The use of the properties of the plasma in an external electric field has allowed developing an essentially new technique of low-temperature deposition. Evolution of thermal ignition and induced ignition of dichlorosilane-oxygen mixtures over the pressure range from 4 to 500 Torr at initial temperatures from 300 to 400 K was studied by means of framing Schlieren cinematography. It was shown that the ignition is of non-thermal nature; the reaction originates on the reactor surface with the generation of adsorbed chain carriers, which subsequently escape into the volume; a visible flame velocity makes ~50 m/s. SF₆ additives to the combustible mixture suppress thermal ignition, in this case the concentration of SiO₂ aerosol decreases dramatically. SF₆ molecules presumably take part in a competing reaction of chain termination involving also charged species.

The influence of a constant electric field on kinetic regularities of dichlorosilane oxidation near the lower limit of thermal ignition was established. The features of this influence on both the lower limit and the delay period of thermal ignition, as well as on the period and quantity of chemical oscillations are determined by the material and a surface state of the reactor, as well as by the reactions of the long-lived intermediate. The new critical phenomenon is revealed: a sharp decrease of integrated intensity of chemiluminescence at thermal ignition of DCS + O₂ mixes over CuSO₄ coating over a small interval of electric field strength.