Mechanisms of Incipient Chemical Reaction between Ca(OH)₂and SiO₂under Moderate Mechanical Stressing

The structure of mechanically induced precursor in an amorphous state between Ca(OH)₂and SiO₂was determined by solid state MAS and CP/MAS²⁹SiNMR spectroscopies, and the changes in the behavior of crystallization by linear heating were studied by X-ray diffractometry. A large broad Q₀peak due to the short-range order of hydrated calcium silicates appeared in the²⁹SiNMR spectra of mechanically induced precursors. The formation of the new ordering is confined in the near-surface region of SiO₂particles, as confirmed by comparing MAS and CP/MASNMR spectra. When the amorphous precursor obtained above was subsequently heated, a rapid solid state reaction led to single phasedα-CaSiO₃as the final product.