高铝粉煤灰合成莫来石的SEM和XRD研究

Research on Mullite Synthesized from High-alumina Fly Ash by SEM and XRD

以Al2O3含量为52.72%的高铝粉煤灰和工业氧化铝为原料,在1300～1500℃保温2～4h合成了平均含量超过70%的M50、M60和M70莫来石。用SEM和XRD研究了合成莫来石的显微结构和物相组成。结果表明,未经盐酸处理的粉煤灰比用盐酸处理过的粉煤灰合成的莫来石的晶体和长径比大;随粉煤灰中Al2O3含量的增高,合成的莫来石的晶体尺寸和长径比变小,合成莫来石的温度需相应提高至1500℃;恒温时间长短对合成莫来石的影响远小于烧结温度的影响,高温下缩短恒温时间比低温下延长恒温时间有利于莫来石的生成。以高铝粉煤灰为原料合成M50和M60莫来石较为适宜,Al2O3与SiO2的质量比应控制在1.5～2.0。

M50, M60 and M70 mullite samples, with more than 70 % mullite content, were synthesized from high-alumina fly ash （Al2 O3 = 52.72% ） and high-alumina fly ash-industrial alumina mixtures by reaction sintering at 1300 -1500 ℃ for 2-4 h. The microstructure and phase constituents of sintered samples were studied by SEM and XRD. The results show that the size and aspect ratio of mullite crystals synthesized from as-received fly ash are bigger than that synthesized from beneficiated fly ash by 20% HCl at the same synthesis condition. With the increase of Al2 O3, the size and aspect ratio of mullite crystals become small, and the sintering temperature should be elevated to 1500℃. The effect of holding time on synthesis of mullite is less than that of sintering temperature. Decreasing the holding time at a higher temperature is preferred, compared with increasing the holding time at a lower temperature during the sintering mullite. MSO and M60 mullites synthesized from high-alumina fly ash are profitable, and the ratio of Al2 03 and SiO2 should be controlled within 1.5-2.0 in preparation of mullite.