Abstract
The formation mechanism under hydrothermal conditions and the thermal stability of kilchoanite, when primary mixtures consisted of CaO and amorphous SiO2·nH2O, was examined in detail. The hydrothermal synthesis has been carried out in unstirred suspensions under saturated steam pressure in a 175–220 °C temperature range for 4, 8, 16, 24, 48 and 72 h by applying extra argon gas (10 bar). It was determined that under hydrothermal conditions, the formation of kilchoanite proceeded heavily because this compound was produced at 190 °C after 48 h, at 200 °C after 24 h and at 210–220 °C after 4–8 h. While synthesizing kilchoanite, the intermediary compounds, α-C2SH and semi-crystalline C–S–H-type phases are always formed. In addition to this, it was also proved that synthetic kilchoanite is stable till 1120 °C and at higher temperature recrystallized to rankinite. It was determined that both tribochemical and thermal activation have no influence on the stability of kilchoanite and quartz sample structure. Meanwhile, the amount of total cumulative heat after 60 h of hydration was equal only to 7.97 J g−1. The products of synthesis and calcination were characterized by STA, XRD, SEM, FT-IR analyses and BET method.
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