The Combustion of SiCl₄ in Hot O₂/H₂ Flames

Abstract

A simple kinetic model describing the molecular gas phase reactions during the formation of fumed silica (AEROSIL ) was developed. The focus was on the formation of molecular SiO 2 , starting from SiCl 4 , hydrogen and oxygen. Wherever available, kinetic and thermodynamic parameters were taken from the literature. All other parameters are based on quantum chemical calculations. From these data, an adiabatic model for the combustion reaction has been developed. It was found that a significant amount of molecular SiO 2 forms after about 0.1 and 0.6 ms at Die Verbrennung von SiCl 4 in heissen O 2 /H 2-Flammen Inhaltsübersicht. Zur Beschreibung der molekularen Reaktionen in der Gasphase während der Herstellung von pyrogenem Siliciumoxid (AEROSIL ) wird ein einfaches kinetisches Modell entwikkelt. Gegenstand der Arbeiten ist die Bildung von molekularem SiO 2 , ausgehend von SiCl 4. Kinetische und thermodynamische Parameter, die in der Literatur nicht zur Verfügung stehen, werden mit Hilfe von quantenmechanischen Methoden berechnet. Im Rah

Formation and optimization of deposition surface shape during fused silica glass synthesis by chemical vapor deposition

“…Figure shows the contours of temperature and SiO 2 concentrations in the x‐z plane (at y = 0) for the cases that SiCl 4 is injected from the first layer nozzle, secondary layer nozzle and fourth layer nozzle, respectively. It is found that the effects of SiCl 4 injection position on flame temperature are small (see Figure A‐C) due to the small heat release from SiCl 4 combustion . However, great differences are found in the distributions of SiO 2 concentrations when particle formation is not considered.…”

“…It is found that the effects of SiCl 4 injection position on flame temperature are small (see Figure 4A-C) due to the small heat release from SiCl 4 combustion. 12 However, great differences are found in the distributions of SiO 2 concentrations when particle formation is not considered. For the case that SiCl 4 is injected from the central nozzle (first layer nozzle), the generated SiO 2 monomers are primarily concentrated in the centerline near the burner inlet and a relatively large concentration gradient exists along the radial direction (see Figure 4D).…”

Modeling analysis on the silica glass synthesis in a hydrogen diffusion flame

“…Detailed twenty-step oxy-hydrogen reaction mechanism from CHEMKIN model [13] plus reduced four-step SiCl 4 hydrolysis mechanism [10] is included in the volumetric reaction model, as listed in The radiative heat transfer, mainly contributed by gas-phase H 2 O, is solved by a Discrete Ordinate (DO) model [14], which solves the radiative transfer equation (RTE) for a finite number of discrete solid angles in the global Cartesian system. Each octant of the angular space is sectioned into two uniform extents in the polar and azimuthal angles respectively, and thus RTE in a total of 8 Â 2 Â 2 directions are solved in the whole angular space 4p.…”

“…Table 2 shows that the peak temperature is the highest under the condition of unity equivalence ratio, while the peak temperature is 300 K lower under fuel lean condition and 200 K lower under fuel rich condition. Note that the reduced fourstep SiCl 4 hydrolysis mechanism [10] somewhat overestimated the peak temperatures compared with the values experienced in industrial furnace, therefore more detailed mechanisms needs to be developed to accurately reproduce the temperature field in the future study. A broader yet uniform high-temperature region is of benefit for the synthesis of high purity silica since the temperature gradient is smaller in the top part of furnace, which is the main silica-formation region.…”

“…Equilibrium analysis [9] also suggested that the flame temperature rise at SiCl 4 addition is mainly attributed to the condensation of silicon oxides since the heat release in the combustion of SiCl 4 is much small compared to that in the reaction between H 2 and O 2 . A simple kinetic mechanism describing the formation of silica starting from the SiCl 4 combustion in high-temperature oxy-hydrogen flames were developed to reveal the impact of reaction channels on the overall reaction, where the reactivity of SiCl 4 towards H 2 O is highly favored over its dissociation [10]. The deposition rate of synthetic silica glass in CVD processes is influenced by the available O 2 or H 2 O amounts for oxidation or hydrolysis to completely covert SiCl 4 to spherical silica particles, however, whose size and microscopic morphology are observed independent of the carrier gas [11].…”