High pressure study of low compressibility tetracalcium aluminum carbonate hydrates 3CaO ? Al_2O_3 ? CaCO_3 ? 11H_2O

摘要

Synchrotron X-ray diffraction data was collected from a sample of monocarboaluminate 3CaO ? Al_2O_3 ? CaCO_3 ? 11H_2O from ambient pressure to 4.3 GPa. The refined crystal structure at ambient pressure is tridinic with parameters a = 5.77(2) A, b = 8.47(5) A, c = 9.93(4) A, a = 64.6(2)°, p = 82.8(3)°, 7 = 81.4(4)°, and space group of PI or P 1. It showed some degree of perfectly reversible pressure-induced dehydration with a non-hygroscopic pressure-transmitting medium. However the dehydration effect does not critically affect a bulk modulus due to its strong framework. The isothermal bulk modulus of monocarboaluminate was found to be 53(5) GPa and 54(4) GPa with 3rd order and 2nd order Birch-Murnaghan Equation of state, respectively. That value is higher than for any other reported AFm or AFt phase. The pressure-volume behavior of the monocarboaluminate was compared with that of previous studied hemicarboaluminate.