Stability Domains of NbC and Nb(CN) During Carbothermal Reduction of Niobium Oxide

Abstract

The Gibbs free energies of formation of Nb(CO) and Nb(CN) were calculated using ab initio simulation. Phase stability diagrams of the Nb 2 O 5 -NbO 2 -Nb(CO)-NbC/Nb(CN) system were constructed with respect to carbon activity, oxygen pressure, and the characteristics of solution formation. The constructed diagrams suggest that Nb 2 O 5 can be reduced without the formation of NbO owing to the formation of an Nb(CO) solid solution phase. The Nb(CO) phase might not be formed under a high partial pressure of nitrogen. This study demonstrates the absences of NbO and Nb(CO) during, respectively, the syntheses of NbC and Nb(CN) from Nb 2 O 5 . The constructed stability diagrams could also represent the conditions for syntheses of niobium carbide or stoichiometric niobium carbonitride by the carbothermal reduction of Nb 2 O 5 under argon or nitrogen. †

Low temperature synthesis of NbC/C nano-composites as visible light photoactive catalyst

“…The decarburization of NbC may be caused by a lower CO/CO 2 ratio (CO 2 rich reaction) beyond 10 h at 800 °C 56 , 57 . While the formation of NbO 2 as a result of decarburization at longer holding (11 h) instead of NbO (as observed in the case of lower temperature) may be attributed to the higher stability of NbO 2 than NbO 58 .…”

Thermal and structural studies of carbon coated Mo2C synthesized via in-situ single step reduction-carburization

“…Moreover, further increase in soaking time to 12 h in R-6 sample, the minor phase of MoO 2 appears because of decarburization and oxidation. At higher temperature, affinity of oxygen diffusion is more when the reaction time is sufficient enough for oxygen to diffuse into Mo 2 C to favor reversible reaction 29 , 32 . The carburizing atmosphere inside the autoclave is very different involving the interaction of numerous gases.…”

Applicability of special quasi-random structure models in thermodynamic calculations using semi-empirical Debye–Grüneisen theory

“…SC models (8,64,256, and 512 atoms) with random substitutions of C by N were employed to depict the intermediate compositions of ZrC 1Àx N x (x ¼ 0.25, 0.50, and 0.75). The random substitutions module which is implemented in MedeA-VASP package was employed to generate the randomly substituted SC models [17e20].…”

“…Shin et al calculated thermodynamic properties of several binary hcp random alloys using lowsymmetry SQS models [7]. In the author's previous work, SQS was employed to obtain the thermodynamic properties of random solid solutions with a B1 structure by using first principles phonon calculations [8,9]. However, despite the importance and utility of SQS models, they have not been used to calculate thermodynamic properties with semi-empirical DebyeeGrüneisen theory (DGT).…”