Probing Dynamic Interfacial Evolution in Al(OH)3-Coated CaCO3
Composite Materials via Multispectral Synergy
XU Yan1, BAO Wei-jun1*, WEI Fu-guang2, JIANG Zong-chen2
1. National Engineering Research Center of Green Recycling for Strategic Metal Resources, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China
2. Hezhou Inspection and Testing Center, Hezhou 542899, China
Abstract：Using ordinary ground calcium carbonate (D50≈38 μm) as the core phase, a CaCO3/Al(OH)3 core-shell composite material was constructed in a supersaturated sodium aluminate solution via heterogeneous nucleation. By multiple spectroscopic techniques, including X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), the dynamic evolution of phase composition, interfacial chemical states, and bonding structures during the coating process was systematically revealed. The coating pathway was regulated by reaction time gradients (2 h, 12 h, 36 h). Combined with SEM-EDS cross-sectional morphology analysis and XRD phase identification, a three-layer model of the core-shell structure was established: a calcite-type CaCO3 core (≈38 μm), a C3AH6 intermediate layer (300～500 nm), and a dense Al(OH)3outer shell, following a stepwise reaction path of “CaCO3→C3AH6→Al(OH)3”. FTIR and Raman spectra further corroborated the interfacechemical bonding path: FTIR detected the characteristic OH stretching vibration peak of C3AH6 at 3 664 cm-1, while Raman identified additional lattice vibration modes of C3AH6 in the 3 390～3 640 cm-1 range, collectively confirming chemical bonding (via Ca—O—Al bonds) rather than physical mixing between calcium and aluminum. XPS quantitative analysis demonstrated that the surface Ca/Al molar ratio decreased from 1.45 at 2 h (close to the theoretical value of 1.5 for C3AH6) to 0.08 at 36 h. Combined with the Ca(2p) binding energy shift and the Al(2p) chemical state transition (Al—O→Al—OH), this directly revealed the dynamic formation of the C3AH6 intermediate phase and the coverage mechanism of the Al(OH)3 shell. The innovation of the multispectral coupling strategy lies in: achieving phase-morphology collaborative characterization through XRD/SEM-EDS, analyzing bonding structure evolution with FTIR/Raman, and quantitatively tracking surface chemical state migration with XPS. This integrated approach overcomes the limitations of single-technique characterization and systematically elucidates the pivotal role of the C3AH6 intermediate phase in interfacial bonding. The study provides a theoretical foundation for the controllable synthesis of core-shell composites. For instance, optimizing the Al(OH)3 shell thickness (300～500 nm) and uniformity by adjusting the sodium aluminate concentration and reaction time can enhance the material's weathering resistance and interfacial compatibility. Through multidimensional synergy of spectroscopic techniques, this work establishes a critical theoretical basis for the interfacial chemical regulation and industrial applications of CaCO3/Al(OH)3 composites.
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