Incorporation of insoluble heavy metal oxide in structure of Z phase during hydrothermal treatment

The incorporation of CdO and CuO in the crystal structure of calcium silicate hydrates (C–S–H) during hydrothermal treatment at 200°C was examined. The synthesis of C–S–H was carried out in unstirred suspensions for 4, 8, 12, 16, 24, 48 and 72 h at 200°C. The molar ratios of the primary mixture were CaO/(SiO2+X) = 0·55 and X/(SiO2+X) = 0 or 0·025 (where X indicates CdO or CuO). It was estimated that, at the beginning of the synthesis, additives were stable in the reacting solution and did not participate in the C–S–H crystallisation processes. Cadmium oxide became unstable within 24 h and fully penetrated into the structure of the synthesis products (gyrolite gel and Z phase). Meanwhile, with the use of copper oxide, the cation incorporation mechanism proceeded in a different way because these ions are unreactive and did not enter into the structure of products under all experimental conditions.