Search Results (9)

In this study, we address the need for sustainable and scalable synthesis routes for hydrogen storage materials by developing a FeTi alloy in which vanadium (V) partially substitutes for titanium (Ti). The alloy was synthesized using mechanical alloying, compaction, and post-annealing, employing industrial-grade Fe and Ti powders and an alternative to pure vanadium, i.e., ferrovanadium (Fe–V). X-ray diffraction (XRD) analysis of the mechanically alloyed mixture revealed the partial formation of a Fe(V) solid solution, along with residual Ti. Subsequent compaction and annealing at 1000 °C led to the formation of the FeTi(V) phase, accompanied by two minor secondary phases, Fe₂Ti and Fe₂Ti₄O. A maximum phase yield of 90% for FeTi was achieved after 48 h of annealing. The novelty of this work lies in the demonstration of a sustainable and economical synthesis approach for V-substituted FeTi alloys using industrial-grade raw materials, offering a potential reduction in the carbon footprint compared with conventional melting techniques. Full article

A novel high-efficiency industrialized clean production technology based on multi-stage gradient batching and smelting was proposed for the production of high-quality ferrovanadium. The thermodynamic mechanism of aluminothermic reduction equilibrium, alloy settlement and raw material impurity distribution were confirmed, and a multi-stage double-gradient aluminum addition pattern (DG-ADP), the highly efficient separation of molten slag and alloy, and typical impurity control standards of raw materials were achieved on the basis of a self-propagating high-temperature synthesis with an electric auxiliary heating (SHS-EAH) process. The reduction efficiency, separation efficiency and the comprehensive utilization rate of the secondary resources were significantly improved, as the whole total vanadium (T.V) content in the industrially produced residue slag reduced from 2.34 wt.% to 0.60 wt.%, while the corresponding smelting yield increased from 93.7 wt.% to 98.7 wt.% and the aluminum consumption decreased from 510 kg·t⁻¹ to 400 kg·t⁻¹. The multi-stage DG-ADP process enabled the internal circulation of vanadium-bearing materials in the ferrovanadium smelting system, as well as the external circulation of iron and residue slag in the same system, and finally achieved the zero discharge of solid and liquid waste from the ferrovanadium production line, which provides a brand-new perspective for the cleaner production of ferrovanadium alloy. Full article

Ti-V-based metal hydrides have decent overall performance as hydrogen storage materials, but V is expensive and it is therefore tempting to replace it by less expensive ferrovanadium containing about 20% Fe. In the present work we have investigated how Fe influences the structure and hydrogen storage properties of (Ti_0.7V_0.3)_1−zFe_z alloys with $\begin{array}{c}\hfill errortypecez\end{array}\in \{0,$ 0.03, 0.06, 0.1, 0.2, 0.3} using synchrotron radiation powder X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry and manometric measurements performed in a Sieverts apparatus. The alloys form body-centered cubic (bcc) crystal structures for all considered values of z, and the addition of Fe causes the unit cell to contract. When exposed to hydrogen gas, the bcc alloys form face-centered cubic (fcc) hydrides if $\begin{array}{c}\hfill errortypecez\end{array}\le 0.1$ while other hydrogen-containing phases are formed for higher Fe-contents. The hydrogen capacities of the fcc hydrides at 20 bar are not significantly influenced by the addition of Fe and reach 3.2(3) wt% in (Ti_0.7V_0.3)_0.9Fe_0.1H_1.6(2). For higher Fe contents the hydrogen capacity is decreased. The absorption kinetics are fast and the reactions are complete within minutes when the alloys are exposed to 20 bar H₂ at room temperature. Increasing Fe content reduces the desorption enthalpy, onset temperature and activation energy. Full article

Ti-V-based body-centered cubic (BCC) alloys have potential for large-scale hydrogen storage if expensive vanadium is substituted with much cheaper Fe-containing ferrovanadium. Use of ferrovanadium reduces the alloys’ hydrogen storage capacity. This is puzzling since the amount of Fe is low and hydrogen atoms are accommodated in interstitial sites which are partly coordinated by Fe in many intermetallic compounds. The present work is aimed at finding a structural explanation for Fe-induced capacity loss in Ti-V alloys. Since such alloys and their hydrides are highly disordered without long-range occupational order of the different metal species, it was necessary to employ a technique which is sensitive to local structure. Neutron total scattering coupled with reverse Monte Carlo modelling was thus employed to elucidate short-range atomic correlations in Ti_0.63V_0.27Fe_0.10D_1.73 from the pair distribution function. It was found that Fe atoms form clusters and that the majority of the vacant interstitial sites are within these clusters. These clusters take the same face-centered cubic structure as the Ti-V matrix in the deuteride and thus they are not simply unreacted Fe which has a BCC structure. The presence of Fe clusters is confirmed by transmission electron microscopy. Density functional theory calculations indicate that the clustering is driven by thermodynamics. Full article

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. Full article

Chromium carbide, vanadium carbide, and chromium–vanadium mixture coatings were deposited on AISI D2 steel via the thermo-reactive deposition/diffusion (TRD) technique. The carbides were obtained from a salt bath composed of molten borax, ferro-chrome, ferro-vanadium, and aluminum at 1020 °C for 4 h. Analysis of the morphology and microstructure of the coatings was done via scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The hardness of the coatings was evaluated using nano-indentation, and the friction coefficient was determined via pin-on-disk (POD) testing. The electrochemical behavior was studied through potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS). The XRD results show evidence of the presence of V8C7 in the vanadium carbide coating and Cr23C6 and Cr7C3 in the chromium carbide coating. The hardness value for the vanadium–chromium carbide coating was 23 GPa, which was higher than the 6.70 ± 0.28 GPa for the uncoated steel. The wear and corrosion resistance obtained was higher for the niobium–chromium carbide coating, due to the nature of the ceramic carbide produced. Full article

The main objective of this paper is to present results of the research in the development of a specialized self-propagating high-temperature synthesis (SHS) technology for ferroalloy composites, as applied to steelmaking. The problem of creating such a production cycle has been solved by developing a new approach to the practical implementation of self-propagating high-temperature synthesis, as applied to metallurgy. The metallurgical variation of SHS is based on the use of different metallurgic alloys (including waste in the form of dust from ferroalloy production) as basic raw materials in the new process. Here, the process of synthesis by combustion is realized through exothermic exchange reactions. The process produces a composite, based on inorganic compositions with a bond of iron and/or alloy based on iron. It has been shown that in terms of the aggregate state of initial reagents, metallurgical SHS processes are either gasless or gas-absorbing. Combustion regimes significantly differ when realized in practice. To organize the metallurgical SHS process in weakly exothermic systems, different variations of the thermal trimming principle are used. In the present study, self-propagating high-temperature synthesis of ferrovanadium nitride, which is widely used in steel alloying, was investigated. It has been shown that the phase composition of the initial alloy has a profound impact on the regular patterns in ferrovanadium combustion in nitrogen and on the mechanism itself. During the nitriding of σ-(Fe-V), process activation is taking place. The activation is due to the transformation of the intermetallide into an α-solid solution, when the temperature of phase transition is reached (~1200 °C). The composite structure of the products of ferrovanadium is nitriding by the fusion of particles-droplets composed of molten Fe and solid VN. Full article

This paper examines possible industrial applications of high manganese steel and the feasibility of its inoculation with a new ferroalloy, vanadium nitride. The abrasive and impact-abrasion surface wear experienced by castings has a classical pattern: microcutting—i.e., the deformation twinning of surface layers. Ferrovanadium nitride enhances the surface resistance of castings both as a cast and as thermally treated. A fine grain structure is formed in the surface layers, specifically layers in direct contact with abrasive particles. The deformation twins that are present at the solid solution grain boundaries tend to change their orientation and characteristics. The impact-abrasion wear also leads to hardened layer formation at the working surface due to deformation twinning. The carbides (nitrides) present in the surface wear do not produce any significant impact on the process of deformation twinning. As the wear line extends deeper into the casting surface, the carbides and nitrides are ripped out and cavities occur in the wearing zone. The wear is controlled by the solidification rate. Thus, at lower rates a hardened layer is formed, which accommodates adjacent areas with differing twin characteristics, such as orientation and spacing. Full article

We report here the effect on hydrogen sorption behavior of replacing vanadium by ferrovanadium (FeV) in Ti-V-Cr Body Centred Cubic (BCC) solid solution alloys. The compositions studied were Ti_1.56V_0.36Cr_1.08 and Ti_1.26V_0.63Cr_1.11. Both of the alloys were synthesized by melting with 4 wt % of Zr₇Ni₁₀ in order to enhance the first hydrogenation (i.e., activation) kinetics. The ferrovanadium substitution leads to the same microstructure as the vanadium pristine alloys and no significant change in the lattice parameters was found. However, a longer incubation time was observed in the activation process for the FeV substituted alloy. Finally, the replacement of vanadium by ferrovanadium did not have a noticeable impact on the hydrogen capacities, heat of formation, and entropy. Full article