Outside Vapor Deposition of High-Purity Silicon Dioxide

A study of the outside vapor deposition (OVD) process for the manufacture of fiber optic sleeve tubes is presented. High purity silicon dioxide (SiO₂) is deposited on the outside of a rotating substrate via flame hydrolysis of silicon tetrachloride (SiCl₄). Three double-flame burners hydrolyze the precursor forming streams of nominal 50 nm particulate, which are driven to the substrate surface via thermophoresis. The partial-premix burners utilize two concentric combustion chambers to provide fine control of the hydrolyzation process and heat flux to the preform surface. The bulk average deposition rate and efficiency to create a full-size sample are 4.93 gm/min/burner and 28%, respectively. The peak surface temperatures hover around 980 deg C at the bare quartz substrate surface, but then rapidly increase to 1200 deg C as the first four layers of SiO₂ are deposited. These peak surface temperatures then monotonically decrease as the circumference and surface area of the porous preform increase. Similarly, the SiO₂ layer density is 0.96 gm/cm³ at the substrate surface, but then decreases to 0.28 gm/cm³ as the porous preform grows to a diameter of 174 mm.