Al-substituted tobermorite 11 Å:: Synthesis, analytical electron microscopy, NMR spectroscopy and cell parameters

Highly crystallized Al-substituted tobermorites 11 Angstrom 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 Al / Si and Ca / Si for each crystal by ATEM, and the silicate anion structures by Si-29 NMR. It was found that with an increase of the substitution of Si by Al there is almost no change in the cell dimensions in the a- or b-axis, but a large increase in the c-axis. The ATEM results show the maximum substitution of Al / (Al + Si) = 0.13-0.14 in tobermorite 11 Angstrom, which coexists with a trace of hydrogarnet as shown under electron microscopy for the specimens prepared using 0.15 starting ratios. The NMR results show that the tobermorites 11 Angstrom have a double chain silicate anion structure, and Al is selectively concentrated at the Q(3) sites. The crystal chemistry of synthetic tobermorite 11 Angstrom is discussed in comparison with the natural crystal.