Synthesis and characterization of calcium aluminate compounds from gehlenite by high-temperature solid-state reaction

The mineral transition mechanism and self-pulverization property of the sintered products in the Ca2Al2SiO7-CaO system were systematically studied using pre-synthesized gehlenite determined by XRD, SEM, FTIR and particle size analyses. The minerals of Ca12Al14O33, CaAl2O4, Ca3SiO5 and Ca2SiO4 are formed by the direct reactions of Ca2Al2SiO7 with CaO. CaAl2O4 reacts with CaO to form Ca12Al14O33 or Ca3Al2O6, while Ca3SiO5 reacts with Ca2Al2SiO7 to form Ca2SiO4 and calcium aluminate compounds. The sintered products mainly contain CaAl2O4, Ca12Al14O33 and Ca2SiO4 at 1350 °C or above 1500 °C when the molar ratio of CaO to Al2O3 is 1.0. Increasing the sintering duration or the CaO consumption promotes the transition of Ca2Al2SiO7 to Ca2SiO4 and calcium aluminate compounds when sintered at 1350 °C, which accordingly improves the self-pulverization property of the sintered products. The formed minerals of Ca12Al14O33, CaAl2O4 and Ca2SiO4 transform into Ca2Al2SiO7 again when the sintering temperature is between 1400 °C and 1450 °C, and the corresponding self-pulverization property of the sintered products deteriorates sharply.