Dichlorosilane Oxidation Research Articles

Kinetic regularities of solid-phase formation in the branching chain reaction of dichlorosilane oxidation in rf plasma at low pressures and 293 K

In studies of the initiated ignition of dichlorosilane−oxygen mixtures it has been shown that rf discharge applied before ignition leads to an increase in the lifetime of aerosol particles in the reactor volume, in contrast to direct current discharge which markedly decreases the amount of aerosol particles formed in ignition. Ordered structures of the type of ‘liquid dust crystal’ have been detected in rf plasma of branching-chain heterophaseous reaction.

Factors in Phase Formation in the Heterogeneous Chain Oxidation of Dichlorosilane at Low Pressures

Dichlorosilane oxidation, a heterogeneous branching-chain reaction, is considered in terms of unsteady-state nucleation theory taking into account the condensation growth of nuclei, and the following observations are interpreted: the crossover between the homogeneous and heterogeneous phase formation; the dependence of the amount of aerosol on the initial temperature, pressure, and admixture concentration; and the kinetics of phase formation and of the disappearance of the original substance. Introducing an inhibitor is found to reduce the mean size of aerosol particles. This result is in qualitative agreement with experimental data. It is found that it is because of the growing equilibrium vapor pressure of the new phase that the amount of aerosol formed decreases with increasing initial temperature, including when an active admixture is present. The reactivity of the silicon dioxide aerosol obtained in the presence of Freon-12 varies reversibly. The role of surface diffusion and surface nucleation in the deposition of thin films is discussed.

Transition of Flame Propagation from Isothermal to Thermal Regimes in Chain Processes with Nonlinear Chain Branching

The transition of an isothermal flame to a thermal combustion regime is considered experimentally and theoretically for the thermal decomposition of nitrogen trichloride. Experimental data on the transition of a thermal regime of flame propagation to a chain-thermal explosion are presented for dichlorosilane oxidation. One of the ways for the development of the chain-thermal explosion is shown to be the appearance of a local center of intense combustion in the thermal flame front.

Flame emission spectra in the region 400-600 nm during low-pressure silane and dichlorosilane oxidation

The flame emission in the region 400–600 nm during monosilane and dichlorosilane oxidation (initial pressures of 3–20 torr; T = 300 K) is caused by radical luminescence processes on the surface of aerosol microparticles of the SiO2 formed. The generation of energy by the interaction of gas-phase species with the SiO2 surface at the initial stages of the phase formation depends on the presence of the intrinsic structural defects Si+ and defects like Si+ implanted into SiO2. The addition of SF6 to the starting mixture results in the appearance of emission bands due to the Si+ defects in the radical luminescence spectrum.

Kinetic factors determining specific features of solid phase formation in dichlorosilane oxidation

Experimental data on the kinetic regularities of aerosol SiO2 formation in the course of dichlorosilane oxidation by oxygen at different initial pressures, compositions of the reaction mixture, and temperatures ranging from 380 to 578 K are presented. It is shown that the regularities of the process, including the specific feature of the transition from the regime of solid phase formation in the form of a film to the regime of aerosol formation can be explained on the basis of the Volmer–Weber–Frenkel–Zeldovich nucleation theory taking into account the branched chain nature of the reaction. The conditions for the transition of chain combustion into the regime of chain–thermal explosion almost coincide with the conditions of intensive formation of aerosol. The SF6 additives inhibit the process and thereby increase the dispersity of aerosol and the minimal pressure of its formation.

Kinetic Features of Aerosol Formation in the Branched Chain Process of Dichlorosilane Oxidation under Static Conditions: I. Initiated Ignition

It is found experimentally that the initial pressure of aerosol formation progressively decreases with an increase in the initial concentration of dichlorosilane in the initiated ignition of dichlorosilane mixtures with oxygen at 293 K. The dependence of the maximal aerosol concentration on the total pressure is S-shaped. A generalized kinetic scheme is proposed that qualitatively describes the regularities observed in the experiments. The most important calculated parameters are the heat evolved in the chain process and the dependence of the pressure of the saturated vapor of a new phase on temperature. It is shown that the specific features of branched-chain processes under nonisothermic conditions determine the kinetic regularities of new phase formation. The optimal range of pressures is recommended for obtaining particles with as low dispersivity as possible.

Kinetic Study of the Chemiluminescence Spectrum of Rarified Flame in Dichlorosilane Oxidation in the Near IR Region

Electronically excited HO2.radicals (A2A"–X2A""), OH.radicals (ν= 2 – 0), and HCl molecules (ν= 3 – 0) are identified using the emission spectra at 0.8–1.6 μm in the rarefied flame in dichlorosilane combustion at 293 K and low pressures. The spectrum also contains the composite bands of the H2O (0.823 μm) and H2O2(0.854 μm) molecule vibrations. The maximum intensity of emission of these species is attained behind the front of the active chemical transformation, and the equilibrium between the vibrational and translational degrees of freedom is established in the region of the regular thermal regime of cooling. SF6additives act as a reservoir that accumulates the vibrational energy in developed ignition. The processes responsible for the inhibition of dichlorosilane oxidation by SF6additives are considered.

The effect of the electric field on the kinetics of dichlorosilane oxidation in the absence of discharge

A constant electric field incapable of discharge generation affects the kinetics of the ignition and combustion of dichlorosilane-oxygen mixtures: near the lower self-ignition limit, the induction period decreases and the region of the oscillating combustion regimes is enlarged. These phenomena depend on the material and state of the reactor surface. The lower self-ignition limitP1 over the CuSO4 and ZnSO4 surfaces abruptly increases with an increase in the voltage of the constant electric field.

NIR investigation of the rarefied flame of dichlorosilane oxidation at low pressures and 293 K

Electronically excited radicals HO 2 (A 2 A’ – X 2 A” ), vibrationally excited OH ( v = 2–0 ), HCl ( v = 3–0), combined vibrational bands of H 2 O (0.823 μm) and H 2 O 2 (0.854 μm) have been detected in the emission spectra of rarefied flame of dichlorosilane oxidation at 293 K and low pressures over the range 0.8–1.6 μm.