COATING OF SILICA FIBERS BY ULTRAFINE PARTICLES IN A FLAME REACTOR

Formation of high surface area fibers by in situ coating of silica fibers with nanosize silica particles in a flame reactor was studied, High surface area fibers have potential for use in fabrication of fiber reinforced ceramics, in high-efficiency filters and in chromatographic bioseparations. Silica (quartz) fibers, about 1 mum in diameter and 100 mum long were suspended in air using a Timbrell-type fiber generator and introduced into a flame reactor. High-temperature oxidation and hydrolysis of silicon tetrachloride vapor resulted in the formation of silica aggregates that deposited onto the suspended fibers in the flame. Complete coverage of the fibers by the aggregates resulted in dendritic structures on the fibers as was evidenced by scanning electron microscopy. The effect of SiCl4 concentration on the enhancement of the specific surface area of the fibers was investigated. The specific surface area of the fibers was increased by more than 20 times compared to that of the bare fibers. A theoretical model for particle deposition and dendrite growth by coagulation and sintering in the free-molecule regime was proposed and compared with the experimental data.