Thermal behaviour of the nitrated AFm phase Ca4Al2(OH)(12)(NO3)(2)center dot 4H(2)O and structure determination of the intermediate hydrate Ca4Al2(OH)(12)(NO3)(2)center dot 2H(2)O
G. Renaudin et al., Thermal behaviour of the nitrated AFm phase Ca4Al2(OH)(12)(NO3)(2)center dot 4H(2)O and structure determination of the intermediate hydrate Ca4Al2(OH)(12)(NO3)(2)center dot 2H(2)O, CEM CONCR R, 30(2), 2000, pp. 307-314
The nitrated AFm phase Ca4Al2(OH)(12)(NO3)(2). 4H(2)O, which belongs to the
layered double hydroxide family, is studied by thermogravimetric measureme
nts and Raman microspectrometry as a function of temperature. Its structure
at room temperature was determined previously. The existence of an interme
diate hydrate around 70 degrees C with composition Ca4Al2(OH)(12)(NO3)(2).
2H(2)O was detected and its structure resolved by single crystal X-ray diff
raction at that temperature. The structure at 70 degrees C is described and
has the rhombohedral space group R (3) over bar c with cell parameters a =
5.731(2) Angstrom and c = 48.32(1) Angstrom and Z = 3. It can be considere
d as a pillared layer structure, be cause adjacent main layers [Ca2Al(OH)(6
)](+) are bridged by nitrate groups. The remaining two water molecules are
space filling only, and are not connected to the main layers. The structure
exhibits dynamic disorder due to free rotation of nitrate groups around tr
igonal axes, in agreement with the Raman spectra. (C) 2000 Elsevier Science
Ltd. All rights reserved.