A study has been made on properties of fumed silica prepared from silicon tetrachloride in hydrogen combustion flames ranging from 1000 to 2200°C, while flame temperature in this study is determined by adiabatic calculation based on equilibrium conditions.
A marked change in properties occurred at temperatures around 1500-1700°C as evidenced by surface area, apparent refractive index, number of hydroxyl groups, and size of the primary particles.
The particular temperature of 1500-1700°C is considered to correspond to the melting point of silicon dioxide materials. At flame temperatures lower than 1500-1700°C numerous various size pores existed in the silica produced, then these silica particles were assumed to have grown in a non-melted phase. On the other hand, at higher temperature few pores existed and silica particles were assumed to have been grown in a melted phase.
