Deciphering thermal-state structure and thermal strength structure-property relationships via "High-temperature quenching cross-state SEM analysis"

Abstract

This study investigates the structural drivers of high-temperature compressive strength degradation in metallurgical coke during pyrolysis (25–1200 °C) through an integrated approach combining in-situ mechanical testing and multi-scale characterization. A novel in-situ high-temperature compression system coupled with liquid nitrogen quenching enabled real-time strength measurements and thermal-state structure preservation. XRD, TEM, and BET revealed dual-regime behavior: Below 1000 °C, compressive strength remained stable (28.03 ± 0.77 MPa) due to C-O crosslinking networks, while exceeding this threshold triggered irreversible strength loss (21.54 MPa at 1200 °C). Graphitization dominated structural evolution, evidenced by decreased (002) interlayer spacing (0.3860→0.3774 nm) and increased graphitic stacking height (Lc: 0.67→0.77 nm). Specific surface area surged 149 % (4.23→10.51 m²·g⁻¹) above 1000 °C, with micropore volume growth indicating pore network reconstruction. XPS and FT-IR confirmed thermal cleavage of C-O bonds (25.36 %→9.84 %), destabilizing carbon matrices. Natural cooling leads to the collapse of the pore structure of coke and the fusion of pore walls, while the liquid nitrogen quenching process can clearly reveal the evolution law of pores. The deterioration mechanism links sp² domain growth (7.74 %→65.41 %) to weakened interlayer cohesion and microcrack propagation. These findings establish a pyrolysis-structure-strength correlation model, providing actionable insights for designing coke with enhanced thermal stability in blast furnace operations.