Structure and viscosity of CaO–Al₂O₂–B₂O₂–BaO slags with varying mass ratio of BaO to CaO

Abstract The structure of CaO–Al₂O₃–B₂O₃–BaO glassy slags with varying mass ratio of BaO to CaO has been investigated by Raman spectroscopy, ¹¹B and ²⁷Al magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy and atomic pair distribution function (PDF). ¹¹B MAS-NMR spectra reveal the dominant coordination of boron as trigonal. Both simulations on ¹¹B MAS-NMR spectra and Raman spectroscopy indicate the presence of orthoborate as the primary borate group with a few borate groups with one bridging oxygen and minor four-coordinated boron sites. ²⁷Al MAS-NMR and PDF show the Al coordination as tetrahedral. Raman spectral study shows that the transverse vibration of AlIV–O–AlIV and AlIV–O–BIII, stretching vibration of aluminate structural units and vibration of orthoborate and pyroborate structural groups. A broader distribution of Al–O bond lengths in PDF also supports the enhanced network connectivity. Viscosity measurements show the increase in viscosity of molten slags with increasing mass ratio of BaO to CaO, which further attributes to the enhanced degree of polymerization of the aluminate network