The mechanism and kinetics of the reaction between CaO and 2CaO⋅SiO2 to form 3CaO⋅SiO2 in the presence of the melt were investigated for an example of the solid state reaction in the presence of a liquid phase.
1) When the specimen is heat-treated, the glassy phase melts with increasing temperature, and the starting materials (CaO and 2CaO⋅SiO2) are dissolved into the melt, in which counter diffusion takes place. After the melt is supersaturated on these components, 3CaO⋅SiO2 is crystallized out from the melt.
2) The reaction rate is found to be expressed by the Jander type equation with better accordance even in the later stage. The reaction of this type seems to be controlled by diffusion in the melt.
3) In the sintering of the specimen consisted of CaO and 2CaO⋅SiO2 in the presence of the melt, the shrinkage is proportional to the n powre of time, and the slope representing this relation is divided into two parts. These parts seem to be due to reaction and sintering of reactants and product, and the sintering of product alone. The slope of the latter has the n value of about 1/3, which coincides with the case derived by Kingery of diffusion contolled sintering in the presence of a liquid phase.