Crystallization of two rare-earth aluminosilicate glass-ceramics using conventional and microwave heat-treatments

Crystallization of two (2)rare-earth glasses using 30 GHz high frequency microwave energy were investigated. Y₂O₃–Al₂O₃–SiO₂ and Nd₂O₃–Al₂O₃–SiO₂ glasses of eutectic compositions were prepared using the regular melt-quench method. Structural analyses of both glasses were done using X-ray diffraction, Fourier-transform infrared spectroscopy and Raman spectroscopy. Prepared glasses samples were thermally analyzed to determine their specific heats, thermal diffusivity and thermal conductivity. Some glasses samples were heat-treated using a conventional furnace up to 1200 °C for 50 h. Similar samples were heat-treated using 30 GHz microwave processing at 1200 °C for different and relatively shorter times (no holding time, 15 min and 30 min, respectively). Treated samples from both used methods were characterized using XRD, IR, Raman spectroscopy and scanning electron microscopy. Microwave heat-treated Y₂O₃–Al₂O₃–SiO₂ samples were fully crystallized in much shorter time and its nucleation and crystal growth were more homogeneous as compared to the conventionally furnace heat-treated samples. Despite, the low crystallization tendency of Nd₂O₃–Al₂O₃–SiO₂ glass system, the microwave heat-treated Nd₂O₃–Al₂O₃–SiO₂ samples were partly/semi-crystallized at relatively shorter time compared to its similar conventionally heat-treated samples. In both glasses, microwave processing is believed to enhance its crystallization kinetics and to induce more homogenous crystals distribution as compared to conventional heating.