2000 Volume 7 Issue 288 Pages 413-419
Highly crystallized Al-substituted 11 Å tobermorites were hydrothermally prepared from lime-quartz and amorphous silica. The starting mixtures were carried out in stirred suspensions with Ca/ (Al + Si) = 0.80 and Al/ (Al + Si) = 0.00-0.15. The cell parameters of the prepared specimens were determined by XRD, the atomic ratios of Ca/Si and Al/Si for each crystal by ATEM, and the silicate anion structures by 29Si NMR. It was found that with an increase of the substitution of Si by Al there was almost no change in the cell dimensions in the a-and b-axis, but a large increase in the c-axis. The ATEM results showed the maximum substitution of Al/ (Al + Si) = 0.13-0.14 in 11 Å tobermorite, which coexisted with a trace of hydrogarnet as shown under electron microscopy for the specimens prepared using 0.15 starting ratios. The NMR results showed that the 11 Å. tobermorites had a double chain silicate anion structure, and Al was selectively concentrated at the Q3 sites. The crystal chemistry of synthetic 11 Å tobermorite was discussed in comparison with the natural crystal.
