Abstract
The hardening reaction between water glass and dicalcium silicate (abbreviated as C2S) is utilized in the self-hardening mold. However, the mechanism involved in the hardening reaction and the strengthening of the mold by the above reaction have not yet been elucidated. In order to find them out, the main products of the hardening reaction was analyzed from observations with a polarized microscope together with values from X-ray diffraction and refraction index measurement. The main product was found to be an amorphous material which is very similar to silica gel. This is considered to produced by the coagulation of Ca++ ion liberated from C2S in the water glass and the ion exchange reaction between Ca++ ion and Na++ ion contained in the water glass. Subsequently, the reason for the strengthening of this mold was studied by measureing the strength of the test piece placed in a vapor saturated atomosphere. From this experiment, it was surmised that the strengthening of the mold was due to the formation of a silica-like gel and the removal of the water from the water glass which retains the C2S unreacted.
