Synthesis and hydration behaviour of calcium zirconium aluminate powders by modifying co-precipitation method

摘要

Calcium zirconium aluminate, Ca7ZrAl6O18, is only the ternary compound of CaO, Al2O3 and ZrO2 with hydration reactivity. Calcium zirconium aluminate is conventionally synthesized by a solid-state reaction processing using CaCO3, Al2O3 and ZrO2, as starting materials at temperatures exceeding 1400 degrees C. In the present study, Ca7ZrAl6O18 along with some admixture phases was prepared by modifying co-precipitation method using ammonia solution, NH3(aq) or saturated oxalate ammonium solution in concentrated ammonia solution, (NH4)(2)C2O4-NH3(aq) as a precipitation agent. Crystalline Ca7ZrAl6O18 phase was detected at relatively low temperature (similar to 900 degrees C) together with other intermediate crystalline products. Formation of the final product of Ca7ZrAl6O18 powders, with CaZrO3 and Ca12Al14O33 as accessory phases, requires heat treatment at 1200 degrees C for 5 h. Two novel approaches for the synthesis of Ca7ZrAl16O18 affect its further hydration behaviour. Ca-3[Al(OH)(6)](2) or C(3)AH(6) with a hitherto unknown rounded crystal habit was formed within the cement pastes made of Ca7ZrAl6O18, which was synthesized by the modifying co-precipitation method using (NH4)(2)C2O4-NH3(aq) as a precipitation agent.