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High temperature oxidation of Ni–19Fe–19Cr–5Nb alloys (based on the chemical composition of Alloy718) with different Al contents were investigated to elucidate the effect of Al on oxidation kinetics and scale formation during exposure at 800 °C in air. The experimental results indicated that the oxidation kinetics decreased with increasing Al content. The beneficial effect of Al could be attributed to be a result of the formation of γ′-Ni3Al, which stabilizes γ′′-Ni3(Nb,Al) and kinetically prohibits the coarsening of γ′′-Ni3(Nb,Al) phases. Faster dissolution of finer γ′′-Ni3(Nb,Al) precipitates due to greater γ-matrix / γ′′-Ni3(Nb,Al) interface region in as-received Al-containing alloys could supply greater Nb flux for the formation of CrNbO4, which promotes the formation of an exclusive Cr2O3 scale at the initial stage of oxidation. [ABSTRACT FROM AUTHOR]

In order to investigate whether adding a small amount of Al in a low oxygen pressure and high temperature environment has a synergistic effect ontheformationof aprotective Cr2O3oxidefilm on Co-Rebased hightemperature alloys，the isothermaloxidation behaviorofthe Co-20Re-25Cr-7Al alloy was studied under 3.0×10-5Pa O2at 1100～1 300 ℃for24h.Resultsshowed thattheoxidation kinetics curve of the alloy conformed to parabolic law quite well，with the value of oxidation activation energy of 242.3 kJ/mol.The oxidation film formed at 1 100～1 300 ℃were very similar and mainly composed of continuous and dense Cr2O3 layer，covered by a small amount of CoO and CoCr2O4 spinelle.The protective Cr2O3 layer could prevent the evaporation of Re element of alloy in the form of ReO3during the oxidation process，and thus provided better protection for the Co-20Re-25Cr-7Al quaternary alloy，as compared with the corresponding Co-20Re-25Cr ternary alloy，thus providing better protection for the alloy.The addition of 7% Al was not enough to result in the selective external oxidation of Al in Co-20Re-25Cr-7Al alloy，thus forming an internal oxidation zone of Al below the outer oxidation film.However，the addition of Al promoted the formation of continuous and dense Cr2O3 layer，and improved the high temperature oxidation resistance of the alloy greatly.The addition of Al and low oxygen pressure showed a synergistic effect on the formation of a protective Cr2O3 layer.

In this study, the effect of Al on the high temperature oxidation of Al-containing refractory high entropy alloys (RHEAs) Ta-Mo-Cr-Ti-xAl (x = 5; 10; 15; 20 at%) was examined. Oxidation experiments were performed in air for 24 h at 1200 °C. The oxidation kinetics of the alloy with 5 at% Al is notably affected by the formation of gaseous MoO3 and CrO3, while continuous mass gain was detected for alloys with the higher Al concentrations. The alloys with 15 and 20 at% Al form relatively thin oxide scales and a zone of internal corrosion due to the formation of dense CrTaO4 scales at the interface oxide/substrate. The alloys with 5 and 10 at% Al exhibit, on the contrary, thick and porous oxide scales because of fast growing Ta2O5. The positive influence of Al on the formation of Cr2O3 followed by the growth of CrTaO4 to yield a compact scale is explained by getter and nucleation effects. [ABSTRACT FROM AUTHOR]

In the typical hydrometallurgy-based recycling process of spent Li-ion batteries (LIBs), excessive amounts of Na ions are inevitably incorporated in leachate through a discharging process with salt solutions and a purification step for impurity removal. In this study, a facile Al3+ doping strategy is realized ranging from impurity level to usual doping levels for improving the LIB performance of Na-incorporated Li[Ni 0.8 Co 0.1 Mn 0.1 ]O 2 (N-NCM). We synthesize Na-incorporated hydroxide precursor via a coprecipitation reaction using a metal solution containing excess amounts of Na (12.6 mol%), simulating the resynthesis of NCM from purified leachate. The Na and Al co-doped NCM811 (NA-NCM) cathode materials are successfully synthesized by subsequent solid-state reactions with various concentrations of Al. The physicochemical and electrochemical properties of NA-NCM are systematically investigated, with N-NCM as a control sample. Notably, the trace amount of Al (0.05 mol%)-doped cathode material reveals the highest cyclability of 93.9% after 80 cycles at 1 C and more than six times higher discharge capacity (115 mAh g−1) at 20 C than N-NCM. Overall, the small amount of Al doping (0.05 mol%) makes the host structures stable and more favorable for Li+ diffusion, whereas the excessive Al (4 mol%) doping lead to the sluggish kinetics on rate capability due to thick A 2 O 3 film layers formed on the particle surface. This work suggests the rational design for upgrading the resynthesized Ni-rich NCM cathode materials for the sustainable recycling of spent LIBs. [Display omitted] • Na can be introduced in leachate during Li-ion battery recycling using salt water. • Strong bond strength of Al-O retards rapid structural degradation during cycling. • Na+ and Al3+ ions in bulk structure have a synergistic effect on rate performance. • Excessive Al doping forms A 2 O 3 layers on the surface of layered cathode materials. • Na and Al co-doping can shed light on upgrading the resynthesized cathode materials. [ABSTRACT FROM AUTHOR]