CaO-based slag is generally used to remove impurities in steel.For producing a CaO-based slag,various solid oxides such as lime and dolomite are added as flux.It is well known that the dissolution rate of these oxides in a molten slag has an important role in increasing the reaction rate between steel and slag.In a previous study,an experimental technique for measuring the dissolution rate of fragile oxides in a molten slag used in actual operation was developed by measuring the compositional changes in the molten slag after the addition of these oxides.The results obtained showed that the effect of solid oxide porosity on the dissolution rate was significant when no interfacial layer was observed between the molten slag and solid oxide.On the other hand,the dissolution rates of a dense and porous solid oxide in the molten slag when interfacial layer was observed were approximately same.For example,a dicalcium silicate ( Ca2 SiO4 or C2S) layer was observed when Cao was dissolved in a FeO-CaO-SiO2 slag system.In this study,the effect of the dissolution rates of various experimentally sintered C2S rods was measured to clarify the dissolution behavior of C2S in a FeO-CaO-SiO2 slag system compared with the dissolution rate of lime.The results showed that the dissolution rates of C2S rods were greater than that of lime,and were influenced by C2S density.Moreover,the density of C2S formed around lime was estimated as 3.0 - 3.1 g/cm3.