Threshold Gas Flow Rate of Halide Materials for the Formation of Oxide Particles in the VAD Process for Optical Fiber Fabrication

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Abstract
The state of oxides produced by the flame hydrolysis reaction of halide materials, in particular whether the oxides exist as vapor or as solid particles in the oxy-hydrogen flame, is investigated because of its connection with the VAD process for optical fiber fabrication. Each halide gas is found to have a threshold flowrate below which the oxide product does not form solid particles in the flame but remains in the vapor state. The threshold flowrate of halide materials examined in this work is in the order TiCl4, SiCl44, BBr343. This peculiar order is dominated by the saturated vapor pressure values of the oxides produced at high temperatures in the flame. The relation between the experimental results and the refractive-index formation mechanism in the VAD process is discussed.