Phase transformation mechanism in activation of high-alumina fly ash with Na₂CO₃

In this study, the phase transformation mechanism of a high-alumina fly ash (HAFA)-Na₂CO₃ mixture was investigated by temperature- and time-programmed heating in a muffle furnace. The temperature range was 600 °C-1000 °C, and the time interval was 20-120 min. The mass loss behaviour of the HAFA-Na₂CO₃ mixture was investigated by a thermogravimetric analysis method using argon at a heating rate of 10 °C min^-1. It was found that HAFA without any added flux showed no loss or gain of any element or material under the experimental conditions. The results also showed that HAFA hardly contained any volatile water, carbon, sulphur, or other components. The decomposition of Na₂CO₃ occurred at 844 °C, and the HAFA-Na₂CO₃ mixture began to react at 600 °C, indicating that the reaction of HAFA with Na₂CO₃ started before the decomposition of Na₂CO₃. The phase transformation of the HAFA-Na₂CO₃ mixture at different temperatures for 60 min or at 900 °C for different times was investigated by x-ray diffraction. Each reaction required different temperature conditions, and at a specific temperature, the length of the heating time affected the progress of the reaction.