Modification of the Structure of Ti-Bearing Mold Flux by the Simultaneous Addition of B2O3 and Na2O

The present paper mainly focused on how B2O3 and Na2O additions influenced the structure of the Ti-bearing fluoride-free mold flux and investigated how the boron-related units were affected by Na2O. Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, B-11 magic angle spinning-nuclear magnetic resonance (MAS-NMR), and X-ray photoelectron spectroscopy (XPS) were utilized to identify different structural units and to analyze the overall modification of the network by additives. It was found that BO3 was more abundant than BO4 in the flux. In addition, the addition of B2O3 and Na2O was proved to promote conversion from non-ring BO3 to tetrahedral BO4, and this was confirmed by FTIR and B-11 MAS NMR analysis. BO3 was a two-dimensional structure unit and contributed to construct a less stable network. With increasing B2O3 content, degree of polymerization of the flux was increased as confirmed by increased fraction of Q(3) in Raman spectra and non-bridging oxygen in XPS. By contrast, the addition of Na2O, which is a strong network breaker, brought about more non-bridging oxygen by breaking the Si-O-Si linkage which was verified by XPS results. Consequently, a less polymerized network was observed by decreasing content of Q(3) from Raman spectra. (C) ASM International (ASM) and The Minerals, Metals & Materials Society (TMS) 2016