Ceramics-Silikáty 68, (2) 174 - 180 (2024)

The presence of residual carbon in powder precursors prepared using the sol-gel method can pose significant challenges in producing ceramics and glasses of high quality. In the case of glass, carbon dioxide formation during the glass-melt heating process leads to bubble/pore formation, while in the case of ceramics, residual carbon can significantly impair its optical properties. The present study aims to identify the reasons for the persistence of residual carbon in YAG and YAG ⁺ Al₂O₃ (YAGA) precursor powders prepared by the sol-gel Pechini method, even under high-temperature conditions exceeding 1400 °C. The study seeks to provide insights to aid in the development of strategies that mitigate the impact of residual carbon on the quality of ceramics and glasses produced using sol-gel techniques. It was found that even after the annealing of the precursor at a temperature of 1200 °C for two hours, a small amount of carbon remains in the precursor powder. The X-ray diffraction (XRD) analysis of the YAGA precursor powders showed that the crystallisation of alumina was delayed and began at 1200 °C. The amount of α-alumina, which corresponds to its actual addition, was identified at a temperature of 1500 °C. Additionally, as the alumina crystallises, the carbon is released from the precursor which is the reason for microspheres blowing in the flame, even when the precursor was burnt out at a temperature of 1400 °C.