To understand the relationship between thermodynamic properties and structures in the CaO-SiO2-BO1.5 slag system, the thermodynamic properties of BO1.5 and SiO2 were measured by a chemical equilibrium technique and the local structures of boron(B) and silicon(Si) were investigated by 11 B and
29Si magic angle spinning-nuclear magnetic resonance (MAS-NMR) measurements.Activity coefficients of BO1.5 increased with an increase in the BO1.5 content of the slag system. Activity coefficients of SiO2 increased with increasing BO1.5 content and decreased with increasing CaO/SiO2 ratio.By using 11 B MAS-NMR, the existence of two types of B sites was confirmed-three-and fourcoordinated B sites. The relative fraction of four-coordinated B increased with an increase in the BO1.5 content and decreased with an increase in the CaO/SiO2 ratio.29 Si MAS-NMR results revealed that bridging oxygen bonding to Si atoms increased with an increase in the BO1.5 content and decreased with decreasing CaO/SiO2 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 BO1.5 and SiO2 activity coefficients were dependent on changes in the local structure of B and Si with composition.KEY WORDS: local structure; thermodynamic properties; MAS-NMR; CaO-SiO2-BO1.5 slag system.
A -Fe ð1ÀxÞ Co x Si 2 film was prepared by a cation-exchange reaction between molten NaCl-KCl-FeCl 2 -CoCl 2 salts and a Si substrate at 1173 K. At low CoCl 2 concentrations of molten salts, the -FeSi 2 phase was formed. However, when the CoCl 2 concentration was higher than 0.015 mol%, -FeSi 2 and FeSi phases were formed in addition to the -FeSi 2 phase. The -FeSi 2 and FeSi phases changed to -FeSi 2 when the sample was annealed at 1123 K for 24 h. The Co content of the reaction layer increased with the CoCl 2 concentration of molten salts. The electrical resistivity of -FeSi 2 was measured by the four-probe method, and the band gap (E g ) of the sample was roughly determined from the temperature dependence of electrical resistivity by using the equation ¼ 0 expðE g =2kTÞ. The electrical resistivity decreased and the band gap slightly decreased with the increase in the Co content of -FeSi 2 .
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