Relationship between Structure and Thermodynamic Properties in the CaO-SiO_2-BO_(1.5) Slag System

摘要

To understand the relationship between thermodynamic properties and structures in the CaO-SiO_2-BO_(1.5) slag system, the thermodynamic properties of BO_(1.5) and SiO_2 were measured by a chemical equilibrium technique and the local structures of boron(B) and silicon(Si) were investigated by ~(11)B and ~(29)Si magic angle spinning-nuclear magnetic resonance (MAS-NMR) measurements. Activity coefficients of BO_(1.5) increased with an increase in the BO_(1.5) content of the slag system. Activity coefficients of SiO_2 increased with increasing BO_(1.5) content and decreased with increasing CaO/SiO_2 ratio. By using ~(11)B MAS-NMR, the existence of two types of B sites was confirmed-three- and four-coordinated B sites. The relative fraction of four-coordinated B increased with an increase in the BO_(1.5) content and decreased with an increase in the CaO/SiO_2 ratio. ~(29)Si MAS-NMR results revealed that bridging oxygen bonding to Si atoms increased with an increase in the BO_(1.5) content and decreased with decreasing CaO/SiO_2 ratio. The number of non-bridging oxygen atoms bonded to the tetrahedrally coordinated Si atom (NBO/T) was calculated using ~(29)Si and ~(11)B MAS-NMR under specific assumptions. By comparing NBO/Ts calculated from these two methods, the number of non-bridging oxygen atoms bonded to three-coordinated B in the studied composition region was estimated to be one. Finally, by comparing the thermodynamic properties with the results of MAS-NMR measurements, it was found that the composition dependences on BO_(1.5) and SiO_2 activity coefficients were dependent on changes in the local structure of B and Si with composition.