Characterization of Al–Cr and Al–Cr–Ni Alloys Produced via Cr- and Ni-Bearing Oxides
摘要
Al–Cr and Al–Cr–Ni alloys were synthesized via in-situ aluminothermic reduction of CrO3 and NiO in molten aluminum at 1000 °C using cryolite as a flux. XRD and SEM/EDX analyses confirmed the formation of Al–Cr intermetallics (Al7Cr, Al4Cr, Al8Cr5) in the binary alloys, while the ternary alloys additionally contained (Al3Ni) and complex Al–Cr–Ni phases (AlCrNi2, Al0.983Cr0.017, and Cr7Ni3). Differential thermal analysis (DTA) revealed sequential events corresponding to CrO3 decomposition, aluminum melting, and rapid aluminothermic reduction accompanied by intermetallic formation. Chromium recovery increased steadily with CrO3 content in the absence of NiO but was markedly reduced in its presence due to competitive reduction. Nickel recovery in the Al–Cr–Ni alloys was relatively consistent, ranging from 0.83 to 0.99 wt pct Ni, corresponding to 30 to 33 pct of the added NiO. Although NiO reduction is thermodynamically more favorable than Cr2O3 reduction, actual recoveries were influenced by kinetic factors including mixing efficiency, temperature, fluxing, and slag entrapment. Cryolite fluxing and mechanical stirring were identified as critical parameters governing both the rate and extent of metal recovery.
Graphical Abstract