Effect of melting time on volatility, OH in glass in microwave processing

Glass comprising of SiO2-B2O3-Na2O-CaO-K2O is melted at 1523 K in the microwave (MW) and conventional heating. Evaporation loss was studied with varying melting time (30 min to 3 h). Assessment of B2O3, a more volatile component in the studied composition, is carried out by adopting wet chemical method like volumetric titrimetry. The rate of evaporation loss (of B2O3) is found similar to 20% less in MW heating. The density of glass increases slightly with increasing melting time. Chemical analysis for other volatile ingredient, K2O using ICP-AES suggests higher yield in glass signifying less loss of K2O in MW heating. A study adopting X-ray photoelectron spectroscopy (XPS) indicates that the ratio of nonbridging oxygen (NBO) to the total oxygen in glass increases with melting time. This signifies a higher loss of glass network former like B2O3. OH content in conventional glass decreases with increasing soaking time at melting temperature whereas it initially increases with time and reduces beyond 120 min of soaking at melting temperature in MW furnace. A significant reduction in energy consumption and time savings in MW heating has been recorded.