An Attempt to Calculate the Adiabatic Temperatures and the Composition for 1-12-02-SiCI4 Combustion Flames, and Its Application to t h e Formation of Fumed Silica

Abstract

In order to analyze H₂-O₂-SiCl₄ combustion flames, a simplified and widely appl icable calculation method was proposed to evaluate adiabatic temperatures and also to evaluate partial pressures of materials existing in the flames. Generally, it becomes very complicable to evaluate them when the more kinds of metarials exist in the combustion flames. In this study, starting values adopted on the calculations were giv en based on the main reaction in the H₂-O₂-SiCl₄ combustion flames. Succesively, multiple simultaneous equations to solve were separated into two groups of liner and non-liner ones and attempted to be solved. Thus, an iteration between these two groups was converged, and adiabatic temperatures and partical pressures of the materials were possible to be evaluated easily. Furthermore, the results of calculated adiabatic temperatures were applie d to an analysis of actual H₂-O₂-SiCl₄ combustion flames which generate fumed-silicas. Properties of fumedsilicas generated were examined in relation to adiabatic temperatures which were considerd to be almost the same as actual flame temperatures judging from few results of temperature measurements using CARS methods. As a result, specific surface areas, apparent refractive index and number of hydroxyl groups which characterize properties of fumed-silicas changed dynamically around temperatures corresponding to melting point of SiO₂ (1873-1986 K). We concluded that this resulted from a different formation process of silica primary particles dependent on temperatures. At a temperature lower than melting point, numerous pores exist inside and outside primary particles because particles have formed in a non-melted phase. On the other hand, at higher temperatures particles were assumed to have formed in a melted phase and thus they hardly include pores.