Optimization of melting parameters and minimizing OH content in SiO₂‐B₂O₃‐Na₂O‐BaO glass system in microwave heating

Abstract

This study investigates the optimization of melting process for the glass comprising SiO2‐B2O3‐Na2O‐BaO under microwave (MW) heating. Batches were melted at different temperatures in the range of 900‐1250°C to optimize melting condition. X‐ray diffraction suggests amorphous nature of samples melted above 1150°C. Optimization of melting time was carried out by varying soaking time (8‐60 minutes) at 1250°C. UV‐Vis‐NIR spectra reveal ~90% transmission over 300‐2000 nm wavelength range for glass melted at 1250°C. Optical microscopic images suggest that the bubble‐free glass can be produced at 1250°C for 1 hour melting in MW heating. MW heating also helps in reducing OH content in glass. However, OH concentration is found to increase with melting time. OH content could be minimized to 68.56 ppm in glass employing oxygen atmosphere melting, which prevents OH diffusion from atmosphere into the melt. Residual stresses are estimated to be less in MW heating than conventional heating. Maximum MW power was observed to be 1 kW with a total electrical power consumption of around 5 kWh. Also, total time needed to prepare the glass is around 2 hours. Thus, MW heating could be an alternate efficient tool in producing low OH content glass.