Application of the in-flight melting (IFM) technology to an alkaline free borosilicate glass was investigated. Granules for the glass composition of 50SiO_2-15B_2O_3-10Al_2O_3-25BaO (wt %) were prepared by the spray drying method and fed into the radio-frequency (RF) induction thermal plasma or oxy/gas combustion flame. Although the granules were successfully melted and converted into the vitreous state, volatilization of B_2O_3 occurred severely. The results suggested that the vitrification degree was in a tradeoff relation with the residual amount of B_2O_3. RF plasma was more suitable than oxy/gas combustion for IFM of borosilicate glass in order to avoid the tradeoff relation. The use of granules with high mechanical strength, made from very fine raw materials, was found to be effective to achieve little volatilization of B_2O_3 and high vitrification degree simultaneously.
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