Design of Micro/Nano-Lamellar C₄AcH₁₁ and Hydrotalcite in Alumina-Spinel Castables: Enhanced High-Temperature Damage Resistance

ABSTRACT: In the present study, lamellar hydrates were designed via curing regimes and additives. Structural and high-temperature fracture behavior analyses were employed to elucidate the influence of initial lamellar hydrates on microstructural evolution and thermal stress resistance at elevated temperatures. Key findings reveal that: Pure CAC cured at 25 °C for 24 h predominantly forms metastable CAH₁₀ and C₂AH₈, whereas under the two-step curing regime, the hydration products are granular C₃AH₆ and lamellar AH₃. Incorporating CaCO₃ and MgO under two-step curing promotes the simultaneous generation of micro/nano-lamellar C₄AcH₁₁ and Mg-Al Hydrotalcite (M-A-H). The enhanced extent of hydration and pore-filling effect of M-A-H refines matrix porosity, increasing the volume fraction of 5–100 nm pores and elevating the fractal dimension (Ds). This microstructural optimization improves bonding strength, as evidenced by an 82% increase in demolding strength in the designed samples compared with the R samples. C₄AcH₁₁ and M-A-H serve as reactive CaO and MgO sources, respectively, facilitating the interlocking distribution of in-situ CA₆ and MgAl₂O₄ at 1600 °C and optimizing pore structure. The hierarchical pore structure and refined crystals synergistically enhance thermal stress resistance by increasing crack deflection, dissipating energy, and improving plastic deformation capacity.