The Dependence of N2 Carrier Gas Flow Rate on Deposition Rate and Density Changes of Porous Silica Preform Synthesized by Eco‐Friendly Octamethylcyclotetrasiloxane

A porous silica preform for the fabrication of optical fibers is generally synthesized by flame hydrolysis deposition (FHD). To synthesize the porous silica preform, SiCl 4 containing chlorine (Cl) is normally used. However, the Cl generated through the FHD process is highly reactive and generates toxic substances, which seriously affect the environment. In this study, the porous silica preform with a radius of more than 250 mm is synthesized using vaporized octamethylcyclotetrasiloxane (OMCTS), which does not contain the Cl. In addition, the effect of the N 2 carrier gas flow rate on the deposition rate of the silica soot and the density of the porous silica preform are investigated. As the carrier gas flow rate increases, the deposition rate decreases and the density of the porous silica preform tends to increase. This result may be due to the difference in the substrate and flame temperature gradients depending on the carrier gas flow rate. The characteristics of the porous silica preform are investigated at the top, middle, and bottom positions. Regardless of the position, the porous silica preform is composed of spherical silica particles with the size of 100–200 nm.