Seventeen phases of the Ni-Al-O system at high temperatures were analyzed using thermodynamic calculations. An Ni-Al-O isothermal stability diagram was obtained from the thermochemical data. The diagram describes the interface equations for Ni/Al intermetallic compounds, Al/Al2O3, and Al2O3/AlXNiY compounds, and their corresponding regions. Four univariant equilibria points and ten bivariant equilibria lines below 1126 K were obtained. The equations for the coexistence points and interface lines were also obtained. A three-domain diagram of Ni-Al-O phase arrangement at temperatures between 900 and 1191 K is shown. Thermodynamic calculations confirmed that the formation of nickel aluminate spinel (NiAl2O4) requires a threshold NiO activity (log aNiO = -205.3/T - 0.347) and the partial pressure of oxygen (log PO2 = - 24622 / T + 8 atm) . In the Ni-Al-O system, aNiO < 0.266 at 900 K, the compounds in the Ni/Al interface are formed in the order Al3Ni(s) → Al3Ni2(s) → AlNi(s) → AlNi3(s) → Al2O3(α). When aNiO < 0.351 at 1911 K, the compounds in the Ni/Al interface are formed in the order AlNi(s) → Al2O3(α).
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