| Popis: |
The hydration of tricalcium silicate, Ca 3 SiO 5 , in a small steel ball mill at room temperature was investigated. The stoichiometry of the reaction is represented by 2Ca 3 SiO 5 + 6H 2 O = Ca 3 Si 2 O 7 ·3H 2 O + 3Ca(OH) 2 The initial products of the reaction are calcium hydroxide (both crystalline and amorphous) and a calcium silicate hydrate, designated as “hydrate III.” The latter shows marked similarities to the calcium silicate hydrate, tobermorite, produced by other methods of hydration of Ca 3 SiO 5 . The similarities include CaO/SiO 2 ratio, specific surface area, water content, heat of solution, heat of hydration, and surface energy (enthalpy). Hydrate III differs from tobermorite in that it is unstable; it slowly converts to another calcium silicate hydrate, afwillite. The chemical formula of afwillite is Ca 3 Si 2 O 7 ·3H 2 O, the same as that of hydrate III and tobermorite, but afwillite has a different crystal structure, and it is a well-crystallized substance. Hydrate III appears to be a form of tobermorite with a structure so disordered that it exhibits only a single X-ray diffraction line, that corresponding to the strongest line of tobermorite. The kinetics of the hydration reaction and of the conversion of hydrate III to afwillite were examined. A possible mechanism for the former was proposed. |
