Mineral transition of high-temperature sintering confirmed in CaAl2O4-Ca2SiO4 non-equilibrium binary system

Abstract

The mineral transition mechanism, microstructure evolution and chemical reactivity of CaAl2O4-Ca2SiO4 samples during the high-temperature sintering process at 1300–1500 °C were systematically studied using the pre-synthesized CaAl2O4 and Ca2SiO4 as raw materials when the mass ratio of Al2O3 to SiO2 is 3.0. The results show that increasing calcination temperature from 1300–1500 °C could promote the process CaAl2O4 reacts with Ca2SiO4 to form Ca12Al14O33, Ca2Al2SiO7 and CaAl2Si2O8 during the sintering process. The transition process CaAl2O4 reacts with Ca2SiO4 to form Ca12Al14O33 and Ca2Al2SiO7 could be restrained by controlling calcination temperature lower than 1350 °C or higher than 1500 °C with cooling in the furnace. Ca12Al14O33 and Ca2Al2SiO7 also could transform into CaAl2O4 and Ca2SiO4 again easily during the slow cooling process. The amounts of phases Ca12Al14O33 and Ca2Al2SiO7 generated at high temperature could stay stably at room temperature by cooling in the air immediately after the sintering process. The crystal transformation process of Ca2SiO4 from γ to β starts at 1328 °C during the heating process. Furthermore, increasing calcination temperature higher than 1400 °C could restrain the crystal form transformation of Ca2SiO4 from β to γ again during the cooling process. The formation of Ca2Al2SiO7, decreasing of CaAl2O4 and γ-Ca2SiO4 also could deteriorate the pulverization property and alumina leaching property of CaAl2O4-Ca2SiO4 sample.