Effect of CaO/SiO2 ratio on phase transformation and properties of anorthite-based ceramics from coal fly ash and steel slag

摘要

Anorthite-based ceramics were produced entirely from coal fly ash and steel slag. The effect of the CaO/SiO2 ratio (0.12-0.8) on the phase transitions was examined by adding steel slag to coal fly ash in the range of 10-50 wt%, and a temperature range of 900-1200 degrees C. The influence of CaO/SiO2 and sintering temperatures on the technological properties were assessed by response surface methodology (RSM) and correlated with the phase changes. The results revealed that anorthite was the main phase for the CaO/SiO2 ratio ranging from 0.12 to 0.56, while at 1200 degrees C, a ratio of 0.8 involved a high content of gehlenite. RSM showed that the CaO/SiO2 ratio was the main influencing factor on the density, while the variation of apparent porosity and compressive strength were more affected by sintering temperature. The crystallisation of the anorthite phase significantly enhanced the properties of the obtained ceramics, whereas the appearance of gehlenite reduced the mechanical strength. The optimum conditions to fabricate anorthite-based ceramics with suitable properties were found to be a CaO/SiO2 ratio of 0.46 and a temperature of 1188 degrees C. The optimised anorthite-based ceramic exhibited a low thermal conductivity (0.39 W/m.K) and a dielectric constant of 6.03 at 1 MHz, along with a compressive strength of 41 MPa, which makes this sample a potential candidate for insulator applications.