Consolidation of Participate Layers in the Fabrication of Optical Fiber Preforms

Viscous sintering is experimentally identified through electron microscopy as the mechanism of consolidation of thin particulate layers in the fabrication of optical fibers. The rate of consolidation is primarily a function of the capillary number, C=νl₀(1 -ε₀)^1/3/(σ t _s)], where ν is the glass viscosity, l ₀ the size of the initial void regions, ε₀ the initial void fraction, σ the surface tension, and t_s the sintering time. Numerical results indicate a sensitivity of the sintering rate to temperature, chemical composition of the particles, and gas thermal properties, primarily through the strong dependence of glass viscosity on these variables. These results are fully supported by the available experimental evidence. Under the conditions of the experiments, gas bubbles were occasionally produced; the causes are discussed.