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High-alumina coal fly ash (HAFA) is a special solid waste due to the existence of more than 45% alumina and 35% silica, which can be applied to prepare Al-Si series ceramics if the impurities can be removed and the Al/Si mass ratio can exceed 2.55 (Mullite: 3Al 2 O 3 .2SiO 2 ). In this work, a new mechanical–chemical synergistic activation–desilication process is proposed, and the contents of different impurities can be lowered up to less than 1%, and the Al/Si mass ratio can be elevated from 1.26 to 2.71. Especially, the mechanism of this process is investigated in detail. The analysis of the mechanism shows that the decrease of Q 4 (3Al) and the increase of Q 4 (0Al), Q 4 (1Al), and Q 4 (2Al) improve amorphous silicate reactivity through synergistic activation, and the exposed amorphous Si-O-/Si-O-Si can be removed by OH- during the desilication process (desilicated ratio>55%), which help the fine mullite to exhibit excellent properties (bulk density > 2.85 g/cm 3 , apparent porosity < 0.5%) during the sintering process. Finally, this process not only decreases the pollution but also alleviates the shortage of Al/Si resources and promotes the clean development of coal-fired power generation. [ABSTRACT FROM AUTHOR]

Zirconia fiber, with its resistance to ultra-high temperature, is irreplaceable in many applications. Herein, a technique combining the sol-gel method and electrospinning was used to fabricate uniform 1D zirconia nanofibers from zirconium polyacetate. A suitable heat treatment process was established, and the effects of spinning parameters and additives on the fiber morphology were investigated using XRD, SEM, TGA, and FTIR. The results showed that addition of silica effectively inhibited grain growth and reduced the grain size to 30–60 nm. By optimizing the electrospinning parameters and the sintering process, fine-grained tetragonal zirconia fibers of 400–700 nm diameter could be produced. [ABSTRACT FROM AUTHOR]

High-alumina coal fly ash (HAFA) is a special solid waste because it contains more than 45% alumina and 35% silica. This material can be applied to prepare Al–Si series ceramics if the impurities can be removed and the Al/Si mass ratio can be elevated to a high level. In this work, a new mechanical–chemical synergistic activation–desilication process is proposed and optimized. During the synergistic activation, the morphology, ironic leaching ratios, efficient desilicated ratio (EDR), and mineral phases of different treatments are investigated. The reactivity of amorphous silica can be elevated to a high level (EDR>11%). After the desilication process, the contents of different impurities can be lowered up to less than 1%, and the Al/Si mass ratio can be elevated from 1.26 to 2.71. Mullite refractories are prepared from desilicated HAFA by forming and sintering process, and the bulk density and apparent porosity can reach to 2.85 g/cm 3 and 2.07%, respectively. [ABSTRACT FROM AUTHOR]