THERMOPHORESIS - MASS-TRANSFER MECHANISM IN MODIFIED CHEMICAL VAPOR-DEPOSITION

The mass transfer of particulates of silica and germania is characteristic of the MCVD process for preparing optical fiber preforms. Here, after considering a number of alternatives, it is suggested that the dominant mechanism of mass transfer is thermophoresis, i.e., diffusion due to a large temperature gradient. Analytical arguments are given which support this assertion and compare favorably with experiments carried out in a MCVD apparatus.