A detailed study of high-temperature solid-phase transformations occurring in dispersed microspheres smaller than 10 mm in size (dm = 3 mm and d99 = 10 mm) belonging to the suspended matter (PM10) of fly ash from the combustion of hard coal from the Ekibastuz and Kuznetsk coal basins has been carried out within the synthesis of glass-ceramic materials. It has been established for PM10 microspheres of macrocomponent composition SiO2-Al2O3-FeO isolated as narrow fractions from fly ash from the combustion of Ekibastuz coal that there is an increase in the content of mullite phase (from 17 to 31 wt%), cristobalite phase is formed (up to 29 wt%); the content of glass phase decreases from 65 to 25 wt%. In the samples of narrow fractions of PM10 microspheres from fly ashes from Kuznetsk coal combustion, crystallisation of the glass phase at 1100 °C leads to a noticeable increase in the concentration of mullite phase (from 3 to 17 wt%), the formation of cristobalite and anorthite phases (3 and 6 wt%, respectively); the amount of glass phase decreases from 93 to 70 wt%. A well-consolidated composite with low porosity (0.4 %), insignificant water absorption (0.2 %), and high strength (56 MPa) was obtained using the direct sintering method based on dispersed microspheres of PM10 fly ash from the combustion of Kuznetsk coal. On the basis of dispersed microspheres of PM10 fly ash from the combustion of Ekibastuz coal, high-porous (open porosity 44-52 %) composites with the homogeneous microporous structure, strength 20-36 MPa, liquid permeability up to 478 L/(m2•h•bar) and the dispersed microimpurities retention ratio of 0.98-0.99 were obtained. The acid resistance of the obtained glass-ceramic materials is 97-100 %.
Akimochkina et al. (Tue,) studied this question.