Effect of Al2O3 on the molten slag microstructure information by molecular dynamics simulation and experimental analysis

The metallurgical properties of blast furnace slag changed when high alumina iron ore was used extensively due to the resulting changes of the molten slag microstructure. In the study, based on typical CaO-MgO-SiO2-Al2O3 slag systems with different w(Al2O3) content, molecular dynamics simulation was used to calculate the microstructural properties of particles in the high-temperature slag system, such as bond length, partial radial distribution function, coordination numbers, and diffusion coefficient. In addition, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and Al-27 solid-state magic angle spinning nuclear magnetic resonance (Al-27 SS MAS NMR) were used to detect and analyze the samples. The comprehensive calculations and experimental results show that increasing w(Al2O3) can enhance the structural stability of each ion pair, and the strength of the structural stability is such that Si-O > Al-O > Mg-O > Ca-O. The self-diffusion coefficients are as follows: Mg2+ > Ca2+ > Al3+ > Si4+, which leads to the transformation of the [SiO4](4-)(Q(0)), [Si2O7](6-) (Q(1)) and [Si2O6](4-) (Q(2)) structural units to [Si2O5](2-)(Q(3)). The degree of polymerization of slag increased as well as the stability of the structural units. Moreover, the coordination of Al will change from the [AlO6](9-) octahedral structure of six-coordinated Al to the [AlO5](7-) pentahedra) structure of five-coordinated Al and the [AlO4](5-) tetrahedral structure of four-coordinated Al. It was also found that the content of non-bridge oxygen in the whole slag system decreased continuously, leading to the increasing degree of polymerization of slag, and the experimental results were consistent with the molecular dynamics calculation.