Reduction and Nitridation of Iron/Vanadium Oxides by Ammonia Gas: Mechanism and Preparation of FeV45N Alloy

Abstract

The steel micro-alloyed with ferrovanadium nitride has extremely superior properties that make it widely utilized in structural components, construction and aircraft. The conventional methods for synthesizing ferrovanadium nitride include nitridation of pure ferrovanadium alloy or carbothermal nitridation of metallic oxides, using nitrogen or ammonia gas as nitrogen sources. In this study, ferrovanadium nitride (FeV45N) was prepared by direct reduction and nitridation of the corresponding metal oxides with ammonia as the reductant and nitrogen source. This method avoids the introduction of other impurity elements, except the negligible trace elements accompanied with the raw materials. The thermodynamics of the reduction and nitridation process were initially analyzed. During the subsequent ammonia reduction process, the FeV45N powders were successfully obtained at 1273 K for 6 h. The obtained powders were pressed into cylindrical briquettes by hot pressing (HP) at 1473 K for 1 h in vacuum. In the investigation, the X-ray diffraction and morphological analysis of the products was also carried out, and the reaction mechanisms were discussed in detail. The nitrogen content of the final product can reach 11.85 wt. %, and the residual oxygen content can be reduced to 0.25 wt. %. By sintering, the density of the alloy can reach 5.92 g/cm 3 .

Vanadium Sesquioxide/Nitride Nanostructures in Electrospun Carbon Fibers for High Energy Density Supercapacitors

“…The particulate V 2 O 3 was then partially converted to VN via a reaction with NH 3 produced by PAN as shown in eq . The multichannel in the carbon nanofibers becomes more obvious. , V 2 O 5 + 2C → V 2 O 3 + 2CO ( g ) V 2 O 3 + 2NH 3 ( g ) → 2VN + 3H 2 normalO ( g ) …”

Micro‐/nanostructure evolution of C/SiFeO(N,C) polymer‐derived ceramic papers pyrolyzed in a reactive ammonia atmosphere

“…42 Moreover, generating CO consumes available oxygen, thus lowering pO 2 and shifting the composition in the Fe-O system toward the α-iron + wüstite two-phase field at 700 • C. 41 Another possible reducing agent in the crucible atmosphere is molecular hydrogen originating in the thermal decomposition of ammonia. 43 2NH 3(𝑔) → 3H 2(𝑔) + N 2(𝑔) → ΔH = 46kJmol −1 (1) While this reaction is more favorable at a higher temperature, 44 the employment of a flowing ammonia atmosphere could considerably mitigate the effects of hydrogen accumulation in the atmosphere. Still, elevated H 2 concentrations may be present inside the macropores in between the fibers, potentially acting as a local reducing agent that, in addition, features comparably high diffusion rates in most materials.…”

“…At 1000 • C, the ε-Fe x N precipitates have not only withstood reduction but also undergone considerable growth compared to the sample prepared at 700 • C, while FeO enclosed in the ceramic layer has been reduced to α-iron by either CO or H 2 . According to Equation (1), ammonia decomposes due to both elevated temperature 43,44 and catalytic conversion at ε-Fe x N sites, 55 likely generating H 2 and N 2 inside the fiber. Hydrogen diffuses through the fiber, whereas N 2 is retained presumably resulting in a locally increased nitriding potential.…”