A study has been carried out to clarify the sintering behavior of silica filler sand. Sintering experiments were firstly conducted and the experimental data were compared with the thermodynamic calculations by FactSage and MELTS software.It was found that sintering of the silica sand proceeded through the evolution of liquid phases, which were originated from alkali feldspars. The liquid proportion was found to increase with an increase in temperature. It wan considered that the viscous liquid phases connecting silica particles contributed to the strength of the sintered sand. The thermodynamic calculations revealed that MELTS software could sufficiently simulate the phases in equilibrium with each other. The comparison of the experimental data with the thermodynamic simulations demonstrated that the whole system of the silica sand did not attain equilibrium. It was hence inferred that filler sands should be designed to prevent the state fully sintered by controlling the particle size.

Synopsis :A study was undertaken to understand dissolution behavior of solid CaO particles into molten slags. Experiments were carried out to determine the effects of the basicity (CaO (mass%) / SiO 2 (mass%)) and the kinds of additives (Al 2 O 3 , MgO or CaF 2 ) on the dissolution rate of the rotating cylindrical CaO sinter into the ternary calcium silicate based slags at 1823 K. (Contact materials: graphite, Atmosphere: Ar) The dissolution rate increased with increasing rotation velocity of the cylindrical CaO sinter. It was found that the dissolution rate was highest with the CaO-SiO 2 -CaF 2 slag so that CaF 2 was proved as a good flux material. The dissolution rate of CaO increased with lowering slag basicity for the all slag system. However, this tendency was found to be weaker with the CaO-SiO 2 -Al 2 O 3 system than the others due to the significant viscosity increase in the lower basicity region. The observation of the interface between CaO and each slag indicated that the dicalcium silicate (Ca 2 SiO 4 ) phase was formed for all the slag systems. Further, the additive elements of Al and Mg were condensed in the interlayer between the Ca 2 SiO 4 and the CaO phases as the calcium aluminates and the magnesia. On the other hand, in the case of fluorine containing system, solid phase precipitation was not observed in the interlayer. The results of CaO dissolution experiments indicated these interlayers also affected the dissolution rates. The CaO dissolution was retarded with the CaO-SiO 2 -MgO system, compared to the other two kinds of systems. It could be explained by the magnesia precipitation in the interlayer.

A study has been carried out to measure the solubility of oxygen in a molten Ni-Cr alloy contained in a MgO crucible in equilibrium with CaO-SiO 2-MgO-Cr 2 O 3 system slag. It was found that oxygen content increased with increasing Cr content in the range between 2 and 40 mass%. According to SEM observation along with EDS analysis, the oxide phases in the slag consisted of MgO•Cr 2 O 3 crystals and CaO-SiO 2-MgO slicate phases. In the crucible close to the surface in contact with the molten alloy and the slag, almost pure MgO phases were observed in addition to the above two phases. Therefore, it was confirmed that soluble oxygen in the molten Ni-Cr alloy was supplied by decomposition of the MgO•Cr 2 O 3 phase as MgO•Cr 2 O 3 (s) = MgO(s) + 2Cr + 3O. Consequently, thermodynamic analysis led to the interaction coefficient of e O(Ni) Cr = − 0.162 ± 0.012 (Cr: 2-5 mass% in reference to Ni) and − 0.044 ± 0.001 (Cr: 5-40 mass% in reference to Ni-5%Cr) available in molten Ni.