Phase Equilibria in Synthetic Coal–Petcoke Slags (Al2O3–CaO–FeO–SiO2–V2O3) under Simulated Gasification Conditions

Phase equilibria of the Al 2 O 3 –CaO–FeO–SiO 2 –V 2 O 3 system in synthetic slag mixtures simulating coal–petcoke slag chemistry at 1500 °C in an oxygen partial pressure of 10 –8 atm were investigated by a series of quench experiments. Quenched samples were analyzed by inductively coupled plasma optical emission spectrometry (ICP), X-ray diffractometry (XRD), transmission electron microscopy (TEM), and wavelength dispersive X-ray (WDX). Two precipitated crystal phases were identified in molten slags: mullite (3Al 2 O 3 ·2SiO 2 ) in Al 2 O 3 -rich slags and karelianite (V 2 O 3 ) in V 2 O 3 -rich slags. Scanning electron microscopy and TEM diffraction patterns confirmed the presence of the mullite and karelianite phases. On the basis of experimental results, an isothermal phase diagram of the Al 2 O 3 –CaO–FeO–SiO 2 –V 2 O 3 system at 1500 °C and P O 2 = 10 –8 atm is proposed while keeping CaO = 7.0 wt % and FeO = 13.5 wt %.