CaO rapidly reacts with water, even with vapor phase. to control the hydration rate of CaO, several methods have been suggested. In the present work, the effect of carbonation on the hydration of CaO was studied.
Densified CaO powder between $44-88 \mu m$ particle size was prepared by sintering $Ca(OH)_2$ and subsquent grinding, sieving. Carbonation reaction was performed at 300, 500, and 700℃ for 30 min, 1 hr, and 4 hr.
Carbonation at 300℃ which had cracked surface because of anisotropic $Ca(OH)_3$ formation did not influence on the hydration of CaO.
As carbonation temperature was increased above 500℃, the external surface of CaO was covered with well developed $CaCO_3$ coating layer without crack formation. The protective $CaCo_3$ coating layer made induction period before CaO began to Hydrate. The thicker the depth of $CaCO_3$ layer, the longer the induction period. Namely, $1\mu m$ thickness of $CaCo_3$ coating later made about 110 min induction period.
It was found that the determining mechanism of induction period to be the diffusion of $H_2O$ through $CaCO_3$ layer.
The hydration procedure was investigated by methanol treatment, leading to the observation by SEM. Within induction period, the external shape of the carbonated surface had not changed. Beyond the induction period, the coating layer was broken like chapped shin and showed granular shape of $Ca(OH)_2$ crystal. These results were well coincident with the heat of hydration tests.
From the above results, the idealized hydration model of carbonated CaO was presented.
