Silica is one of the stable metal oxides. It has been used to
form a nanocapsule [16,17] and a template-shaped cavity [18].
Tetraethoxysilane, the starting material of SiO2, is stable in a neutral
condition against hydrolysis and hydrolyzes quickly in acid or
base conditions. It is liquid at room temperature and dissolves well
in ethyl acetate. Therefore, it was expected to be a suitable material
for covering CaO by the procedures described above.