Vanadium

Vanadium (V, atomic number 23) is a Group 5 BCC transition metal with a melting point of 1,910 °C, density of 6.11 g/cm³, and an exceptional range of oxidation states (+2 through +5) that underpin its roles in both catalysis and electrochemistry. It does not occur as a free metal in nature; principal sources are vanadinite (Pb₅(VO₄)₃Cl), patronite (VS₄), and as a byproduct of petroleum refining (V concentrated in crude oil residues and fly ash) and steel slag from V-bearing titanomagnetite ores (the dominant production route, ~90% of global output, ~100,000 tonnes V₂O₅/year). V forms a stable, self-repairing V₂O₅ surface oxide that provides good corrosion resistance in oxidizing environments; unlike most refractory metals it is resistant to alkalis. V is a BCC superconductor below Tc = 5.4 K — the only elemental superconductor with a BCC structure at ambient pressure.

Steel microalloying is by far the dominant use of vanadium (~85% of consumption), where V additions of just 0.03–0.15 wt% refine austenite grain size and form V(C,N) precipitates that increase yield strength by 200–500 MPa through precipitation hardening — enabling high-strength low-alloy (HSLA) steels for rebar, structural sections, pipelines, and automotive components. V microalloying improves strength-to-weight ratio while maintaining weldability and toughness, critical for reducing steel mass in construction and automotive applications. Tool steels (e.g., H13, M2 high-speed steel with 1–5% V) use V to form very hard VC carbides (~2,800 HV) that resist abrasive wear at cutting temperatures. Ti-6Al-4V, the dominant structural titanium alloy, contains 4 wt% V as the primary β-stabilizer, making vanadium a major indirect contributor to aerospace material performance.

Vanadium redox flow batteries (VRFBs) exploit all four oxidation states of V (V²⁺/V³⁺ negative electrolyte, V⁴⁺/V⁵⁺ positive electrolyte) in a single-element electrolyte system that eliminates cross-contamination and gives indefinite electrolyte lifetime — making VRFBs a leading technology for multi-hour grid-scale energy storage. Installed VRFB capacity has grown rapidly, with systems from 1 MWh to >100 MWh deployed for renewable energy firming and grid frequency regulation; the ~20–30 kg V/kWh electrolyte requirement makes V supply and price a key cost driver. V₂O₅ is also the industrial catalyst for SO₂→SO₃ oxidation in the contact process for H₂SO₄ manufacture (~250 million tonnes/year) — one of the most important heterogeneous catalysts in the chemical industry. VO₂ undergoes a sharp insulator-to-metal transition at 68 °C (monoclinic→rutile) with a 3–4 order of magnitude change in resistivity, studied for thermochromic smart windows, Mott transistors, and neuromorphic computing.