In-flight melting method with an oxygen-excess gas burner for glass making

Abstract

This study investigated the in-flight melting method using an oxygen-excess gas burner with which glass powder with specific elemental components can be easily produced in one quick energy-saving-process (<1 s). First, granulated raw powder was formed from soda-lime-glass batch components by using a spray-drying machine and dropped directly into an oxygen–excess gas burner with a vertical downward converging flame. Partially or fully melted materials with powder-like shapes were formed in the flame and collected along the flight path through the flame. Granulated raw powder and powder-like sample materials collected at different positions in the flight path were observed by X-ray diffraction (XRD), optical microscopy, and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The granulated raw powder included only crystals. The XRD peaks of these crystals disappeared and the halo identifying them as glass materials became more pronounced in the powder-like materials collected in going from the upstream to downstream positions in the flight path. We calculated the vitrification ratios by using the main peak intensities of SiO₂ in the XRD data; the vitrification ratio for a ∼600-mm-long path was ∼85 %. We observed changes in the morphology and elemental distribution on the surfaces of the samples by using optical microscopy and SEM-EDS and in cross sections of the samples by SEM-EDS. Although the sodium and oxygen, the silicon and oxygen, and the calcium partial distributions differed from each other on the surfaces and in the cross sections of the granulated raw powder and sodium parts were often observed around the silicon part on the surfaces and in the cross sections of the granulated raw powder and samples collected at upstream positions, the elemental distributions of the collected materials became more homogenous as vitrification proceeded from up-to-downstream, and the materials eventually became glass.