Spherical shape PbO-B₂O₃-SiO₂ glass powders prepared by flame spray pyrolysis

Micron-sized PbO-B₂O₃-SiO₂ glass powders were directly prepared by high temperature flame spray pyrolysis. The flow rates of fuel and carrier gas in the flame spray pyrolysis were critical to the control of morphologies of PbO-B₂O₃-SiO₂ glass powders. The optimum flow rate of fuel gas to prepare the PbO-B ₂O₃-SiO₂ glass powders with spherical shape and micron-size was 20 L/min. The powders prepared at low flow rates of carrier gas had bimodal size distributions with nanometer and micron sizes. The number of the nanometer size powders increased with decreasing the flow rate of carrier gas. When the flow rate of carrier gas was 30 L/min, the prepared powders had spherical shape and micron size. The transmittances of the dielectric layers were higher than 90% regardless of the flow rates of carrier gas when the dielectric layers were sintered at temperatures between 520 and 580° C.