Molecular Dynamics Analysis of the Microscopic Structural Behavior of K Ions in the CaO–Al₂O₃–K₂O System Slag

In order to further elucidate the structural behavior of K⁺ ions in CaO–Al₂O₃–K₂O system slag, molecular dynamics simulations were performed to analyze the influence of K ions on the microscopic structure of the slag under different K₂O contents. The results indicate that Al–O forms a tetrahedral structure, while Ca–O, K–O, O–O, Al–K, and Al–Ca structures are less stable compared to Al–O. In this slag, K⁺ primarily functions as a charge compensator, forming K–O bond (K–O_b) structures and elongating the K–O bond length, whereas Ca²⁺ mainly leads to network disruption, resulting in Ca–O bond (Ca–O_nb) structures with shortened Ca–O bond length. The charge compensating ability of K⁺ is superior to that of Ca²⁺. As the K/Ca ratio increases, [AlO₄]⁵⁻ tetrahedra achieve charge balance through K⁺ compensation, reducing the distortion of the Al–O structure. Furthermore, the substitution of K⁺ for Ca²⁺ narrows the distribution of bond angles, enhancing the stability of [AlO₄]⁵⁻ tetrahedral structures. It was also observed that K⁺ reduces the coordination of Al–O–Al by decreasing the proportion of tricoordinate oxygen in the shared tetrahedral structures, leading to the disappearance of minor peaks in Al–O–Al. As the K/Ca ratio increases, the proportion of non-bridging oxygen (O_nb) and free oxygen (O_f) decreases, promoting the formation of bridging oxygen (Al–O_b–Al) structures. Finally, the complex microstructure of the CaO–Al₂O₃–K₂O melt was verified through Raman spectroscopy, confirming the accuracy of the molecular dynamics simulation.