High-temperature induced dehydration, phase transition and exsolution in amicite: A single-crystal X-ray study

摘要: Temperature dependent single-crystal X-ray data were collected on amicite K4Na4(Al8Si8O32)·11H2O from Kola Peninsula (Russia) in steps of 25 °C room temperature to 175 and 50 up 425 °C. At has space group I2 with a = 10.2112(1), b 10.4154(1), c 9.8802(1) A, β 88.458(1)°, V 1050.416(18) A3. Its crystal structure is based Si–Al ordered tetrahedral framework the GIS type two systems eight-membered channels running along axes. Extraframework K Na cations are at fully occupied sites. Above 75 was found partly dehydrate into separate but coherently intergrown phases, both I2/a, one K-rich ∼K8(Al8Si8O32) ·4H2O (at °C: 10.038(2), 9.6805(19), 9.843(2) 89.93(3)°, 956.5(3) A3) other Na-rich ∼Na8(Al8Si8O32)·2H2O 9.759(2), 8.9078(18), 9.5270(19) 89.98(3)°, 828.2(3) A3). Upon further heating above Na- K-phases lost remaining H2O only minor influence became anhydrous 375 °C, respectively. The phases persisted °C. Backscattered electron images heated displayed lamellar intergrowth K- phases. Exposed ambient humid conditions rehydrated conjoined original phase structure.