Phase transformation during the decomposition of hydrated calcium zirconium aluminate (Ca7ZrAl6O18) paste subjected to various dehydration temperatures

In this paper, the results of experimental study concerning the characterization of dehydration behavior of the hydrated Ca7ZrAl6O18 phase are presented. The hydrated and dehydrated Ca7ZrAl6O18 pastes were investigated by DTA-TG-EGA, LT-XRD, HT-XRD, FT-IR, and SEM/EDS techniques. The original Ca7ZrAl6O18 changed to the calcium-aluminate-hydrates (C-A-H; C CaO, A Al2O3, H H2O) and CaZrO3 due to the hydration reaction after mixing with water. C3AH6 was formed in the conversion reaction of metastable hexagonal hydrated phases, i.e., CAH10 and C2AH8 due to higher temperature. Calcium aluminates, Ca3Al2O6, Ca12Al14O33, and Ca5Al6O14 were formed as dehydration products of C-A-H phases. The results of IR spectroscopic measurements revealed that pentacalcium trialuminate, Ca5Al6O14 has appeared as a preliminary amorphous calcium aluminate phase. The unknown ternary compound in the system CaO-Al2O3-ZrO2 forming the dehydrated ring on the surface of the internal core of the unhydrated Ca7ZrAl6O18 grains has been identified by SEM-EDS.