Structure and viscosity of CaO–Al <sub>2</sub> O <sub>3</sub> –B <sub>2</sub> O <sub>3</sub> –BaO slags with varying mass ratio of BaO to CaO
Harishchandra Singh, Qifeng Shu, Graham King, Ziqing Liang, Zhifeng Wang, Wei Cao, Marko Huttula, Timo Fabritius
Abstract
Abstract The structure of CaO–Al 2 O 3 –B 2 O 3 –BaO glassy slags with varying mass ratio of BaO to CaO has been investigated by Raman spectroscopy, 11 B and 27 Al magic angle spinning nuclear magnetic resonance (MAS‐NMR) spectroscopy and atomic pair distribution function (PDF). 11 B MAS‐NMR spectra reveal the dominant coordination of boron as trigonal. Both simulations on 11 B 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. 27 Al MAS‐NMR and PDF show the Al coordination as tetrahedral. Raman spectral study shows that the transverse vibration of Al IV –O–Al IV and Al IV –O–B III , 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.