One of the characteristics of calcium oxide（CaO）is that it can be easily hydrated. The water resistance capacity of CaO can be improved by increasing its crystallite size. In this study, we examined the relationship between the ignition temperature and crystallite size of CaO and that between the crystallite size and dissolution rate of CaO to improve its water resistance capacity. The crystallite size of the sintered CaO body increased from 55 nm to 120 nm on increasing the ignition temperature. Furthermore, it was found that the sintered CaO body obtained at 1500 ℃ did not dissolve in water and the dissolution rate also decreased to 0.28 × 10－6 g･dm－3･s－1. Thus, we conclude that the dissolution rate of a sintered CaO body depends on its crystallite size.

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