Tobermorite, crystal structure

Hamid, S. A. 1981. The crystal structure of 11-A natural tobermorite Ca225[Si307i5(0H15)] H20. Zeitschrift fiir Krista llographie, 154, 189-198. 

The crystal structure of the natural mineral tobermorite was partly worked out by Megaw and Kelsey (22). Taylor and coworkers (15, 17, 26, 27) have carried out detailed investigations of tobermorite prepared synthetically, and correlated their structural features with those of the natural mineral structure. However, little was known about the nature of the surface, except what may be deduced from the surface energy results, the surface energy being approximately the geometric mean of the surface energies of calcium hydroxide and hydrous amorphous silica. 

It was stated that weakly crystallized tobermorite was synthesized in a mixture of calcium hydroxide and silica gel. The reaction is most efficient at the reagent ratio CaO Si02=5/6 and water-to-solid ratio 4 1. At short activation time, the formation of poor crystallized calcium silicates of B type with tobermorite-like structure was observed, Mechanochemically obtained tobermorite is stable till 800°C. Above this temperature, it... 

Figure 2.53. The crystal structure of tobermorite, viewed along the be plane. The amorphous gel produced during cement formation likely contains defects such as missing/disordered silicate tetrahedra and/or water sites. Reprinted from Chem. Geol. 2000, 167,129, Copyright 2000, with permission from Elsevier.

The silicate group Si207, ordered along one direction, and having the possibility of wollastonite chains formation, is the basic element of the stracture of these silicates. The lack of some individual SiO in this chain does not change the basic structure. This is the source of variable C/S molar ratio not only in the amorphous calcium silicate hydrates but also in the relatively well crystallized tobermorite in which the tendency for increasing C/S ratio is observed [160],... 

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