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Summary: Ammonia gas (NH3) is a clean energy, as well as an efficient reduction and nitridation agent. A novel process of reduction and nitridation with NH3 followed by magnetic separation and low‐temperature selective chlorination to deal with vanadium slag has been proposed. Vanadium spinel (V‐Fe spinel, FeV2O4) is the main V‐bearing phase in vanadium slag, and its reduction and nitridation behavior with NH3 were investigated in this study. Thermodynamic analysis indicated that the reaction was feasible. The experimental results demonstrated that NH3 gas was an excellent reagent for reduction and nitridation. DFT calculation proved that NH3 molecule was easier adsorbed on V atom. The phase component of the final product was Fe/Fe4N/VNxOy, whose relative mass fractions obtained by Rietveld refinement analysis were 23.5%, 1%, and 75.5%, respectively. The evolution of iron and vanadium was in the order FeV2O4 → Fe4N/Fe6N2−3 → Fe4N/Fe and FeV2O4 → V2O3 → VNxOy, respectively. VNxOy was a solid solution, whose O content decreased gradually as the temperature and duration time increased, whereas the N content increased correspondingly. The O content can be decreased to less than 0.10 wt.% after reduction and nitridation at 800°C to 850°C for 3 h. [ABSTRACT FROM AUTHOR]

Ammonia gas can be simultaneously used as a reductant and nitrogen source to prepare TiN from titania. In this work, the mechanisms on reduction and nitridation of micrometer‐sized anatase with ammonia gas have been investigated, using both thermodynamic and experimental studies. The thermodynamic analysis indicated that reduction and nitridation of TiO2 by NH3 was feasible. Anatase will undergo different paths to form TiN, depending on the reaction temperature. Upon heating, NH3 was seen to partially decompose into N2 and H2, although the actual NH3 decomposition ratio was less than the theoretical value. The experimental results indicated that the obtained titanium nitride was non‐stoichiometric (TiNxO1−x, x ≤ 1), as it contained a certain amount of oxygen. Based on the phase transformation and X‐ray photoelectron spectroscopy analysis, the reduction and nitridation routes were deduced: TiO2 reacted with NH3 to form TiNxO1−x directly, at lower temperatures, and followed the path TiO2 → TinO2n−1 → TiNxO1−x, at higher temperatures. TinO2n−1 was determined to be Ti4O7 and Ti3O5 at 1100°C and 1200°C, respectively. Reaction temperature and time significantly affected the oxygen and nitrogen contents in TiNxO1−x, with the lattice parameter of roasted products gradually increasing—approaching those of pure TiN—with an increase in reaction temperature and holding time. At the same time, the content of oxygen in TiNxO1−x decreased, and its nitrogen content correspondingly increased. [ABSTRACT FROM AUTHOR]

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/cm3. [ABSTRACT FROM AUTHOR]

Ferrochromium nitride is an important alloying additive for smelting nitrogen–containing steel. Preparing nitrides by using ammonia gas as reducing and nitriding agent is characterized by high–efficiency and carbon free. In this study, the reaction behavior between chromite spinel and ammonia gas was investigated. Thermodynamic analysis revealed that the reaction was feasible. The transformation of chromite spinel as well as the final products were dependent on reaction temperature, time and input fraction of ammonia gas. The experimental results proved the effect of reaction parameters on the reduction and nitridation process. Chromite spinel was reduced and nitrided to form metallic iron and CrN at temperatures below 950 °C, while metallic iron and Cr 2 N were the main products at 1000 °C. XPS analysis also proved the existence of CrN and Cr 2 N. Ferrochromium nitride with N content treater than 15 wt% was obtained when reducing above 950 °C for 3 h. [Display omitted] • Ammonia gas is a high-efficiency and carbon-free agent that is used for reducing and nitriding. • The transformation of chromite spinel is revealed in this study. • Ferrochromium nitride is prepared by using ammonia gas as reducing and nitriding agent. • Mechanism on reaction between chromite spinel and ammonia gas is revealed. [ABSTRACT FROM AUTHOR]

We investigate the isothermal kinetics of the reduction and nitridation of V 2 O 3 using NH 3. The reaction mechanism is also discussed based on the thermodynamic and experimental results. The reaction procedure between V 2 O 3 and NH 3 can be divided into two stages. The first stage is mainly the deoxygenation process, whereas the second is the nitridation process. The deoxygenation process follows a two-dimensional phase boundary reaction model, and a modified integrated model (IM + diffusion) was proved to be the best function at temperatures above 1023 K. For the second stage, the three-dimensional diffusion model is determined as the mechanism function. Thermodynamic analysis predicts the feasibility between V 2 O 3 and NH 3 to form VN. The VN product is a solid solution (VN x O y) (0 < x,y < 1, x + y = 1), which can be formed at 873 K. The Rietveld refinement analysis indicates the N content of VN x O y gradually increases with increasing temperature. The highest N content is approximately 15.83% at 1073 K for 2 h. [Display omitted] • Ammonia (NH 3) gas is a high-efficiency and carbon-free agent that is used for reducing and nitriding. • Vanadium nitride is synthesized by gas-based reduction and nitridation. • The chemical reaction kinetics between V 2 O 3 and NH 3 is firstly investigated. • The reduction and nitridation mechanism of preparing VN is also discussed. [ABSTRACT FROM AUTHOR]

Fe-based cermets are of considerable research interest owing to their excellent physical and mechanical properties. In this study, a new process for the reduction and nitridation of Panzhihua ilmenite using NH 3 was proposed to prepare Fe-TiN composites, and the process was deemed feasible by thermodynamic calculations. The final products, Fe and TiN, could be formed based on the reaction conditions. The experimental results validated that metallic Fe could be easily formed, while MgTiO 3 was more difficult to reduce than FeTiO 3. The final products of Fe/TiN/MgO obtained at 1373–1473 K were consistent with those from the thermodynamic analysis. By increasing the reduction temperature or duration, the Fe particles increased in size and mixed with the TiN particles. The elemental content of Mg, Al, and Ca in the magnetic product was 5.85 wt% after magnetic separation. A Fe-TiN cermet was prepared from the magnetic product by hot-pressing (HP) sintering. Fe and TiN were uniformly distributed in the cermet, and the hardness of the obtained cermet reached 18.2 GPa. This work could offer a new approach to the preparation of Fe-based cermets from low-grade ilmenite. [Display omitted] • A novel method for synthesizing Fe–TiN composites from low–grade ilmenite is proposed. • Clean ammonia gas is used as reduction and nitridation agent. • The phase transformation and microstructure evolution of ilmenite during the reduction roasting process are studied. • The Fe–TiN cermet with a hardness of 18.2GPa is prepared by hot pressing (HP) sintering. [ABSTRACT FROM AUTHOR]

[Display omitted] • Reduction and nitridation of V 2 O 3 with clean ammonia gas is investigated. • The phase and microstructure evolution are revealed. • A DFT study systematically reveals the adsorption of NH x and H on the V 2 O 3 (0001) surface. • The reaction route is as follows: V 2 O 3 → VN x O 1– x → VN. Vanadium nitride (VN) has a wide range of application because of its excellent properties, which include high hardness, outstanding wear resistance, and good electrical conductivity. This study investigated the mechanism for the reduction and nitridation of V 2 O 3 with clean ammonia gas, using both experimental and density functional theory (DFT) studies. The experimental results indicated that V 2 O 3 could easily be converted to VN in an ammonia atmosphere at 500–800 °C. The reaction pathway to form VN was V 2 O 3 → VN x O 1– x → VN. Increasing the reaction temperature was conducive to an increase in the N content of VN x O 1– x. A DFT study systematically revealed the adsorption of NH x and H on the V 2 O 3 (0001) surface. The results showed that with the dissociation of NH 3 , its adsorption energy on the surface of vanadium oxide became higher. The whole reaction process could be divided into NH 3 decomposition on the surface and the formation of H 2 O(g). Both of these were endothermic reactions, and the reaction step of generating H 2 O(g) needed a higher temperature. The bonding of V 3c –N facilitated the desorption of O 3c atoms to form H 2 O(g), which explained why VN can be prepared by the reaction of NH 3 and V 2 O 3. [ABSTRACT FROM AUTHOR]