Effect of the Additives on the Thermal Decomposition of 3CaO·SiO₂

Abstract

The effect of the minor components added to 3CaO·SiO₂ on the thermal decomposition of 3CaO·SiO₂ has been studied by the methods of X-ray diffraction, differential thermal analysis and thermogravimetric analysis. The tricalcium silicate is prepared by heating the mixture of guaranteed reagents of calcium carbonate and silica, and also the guaranteed reagents used for the additives.
The results obtained are summarized as follows;
(1) The minor components, i.e., B₂O₃, Cr₂O₃, CoO, CuO, BaO, NaCl and CaF₂ accelerate the thermal decomposition of 3CaO·SiO₂ in the mixture of 3CaO·SiO₂ 1mol+the minor component 0.05mol heated at 1200°C for 5 or 10hr, as shown in Table I.
(2) The mixtures of 3CaO₃·SiO₂+additives, i.e., Cr₂O₃, MnO₂, NiO, CoO, ZnO and CuO are influenced by the heating atmosphere.
(3) It seems that the ions of nearly the same size as Si⁴⁺ or having smaller size and larger ions than Ca²⁺ are possible to stabilize β or α' form of 2CaO·SiO₂ and accordingly these ions are effective for the thermal decomposition of 3CaO·SiO₂.