Atomization of Borosilicate Glass Melts for the Fabrication of Hollow Glass Microspheres

Direct atomization of a free-flowing glass melt was carried out using a high-speed flame with the aim of producing tiny, self-expanding glass melt droplets to form hollow glass microspheres. Atomization experiments were carried out using a specially adapted free-fall atomizer in combination with a high-power gas burner to achieve sufficient temperatures to atomize the melt droplets and to directly expand them into hollow glass spheres. In addition, numerical simulations were carried out to investigate non-measurable parameters such as hot gas velocities and temperatures in the flame region by the finite volume-based software Star CCM+& REG; (v. 2022.1.1), using the Reynolds-Averaged Navier-Stokes (RANS) turbulence and the segregated flow model. To calculate the combustion process, the laminar flamelet method was used. The experiments and simulations indicated that a maximum gas velocity of about 170 m/s was achieved at the point of atomization in the flame. The particle size distribution of the atomized glass droplets, either solid or hollow, ranged from 2 & mu;m to 4 mm. Mean particle sizes in the range of 370 & mu;m to 650 & mu;m were highly dependent on process parameters such as gas velocity. They were in good agreement with theoretically calculated median diameters. The formation of hollow glass microspheres with the proposed concept could be demonstrated. However, only a small fraction of hollow glass spheres was found to be formed. These hollow spheres had diameters up to 50 & mu;m and, as expected, a thin wall thickness.

Automated summary

Direct atomization of free-flowing glass melt using a high-speed flame was conducted to produce tiny hollow glass microspheres. Numerical simulations showed that the maximum gas velocity achieved at the point of atomization in the flame was approximately 170 m/s. The particle size distribution of the atomized glass droplets ranged from 2μm to 4mm, with mean particle sizes varying from 370μm to 650μm depending on process parameters such as gas velocity.