Tungsten

Tungsten (W, atomic number 74) is a Group 6 refractory metal with the highest melting point of any metal (3,422 °C), the highest boiling point of any element (5,555 °C), the lowest vapor pressure of any metal above ~1,650 °C, and one of the highest densities of any element (19.25 g/cm³) — properties that make it irreplaceable in applications requiring dimensional stability at extreme temperatures. Tungsten has a BCC crystal structure stable from room temperature to its melting point; unlike most BCC refractory metals it can be drawn into fine wire, enabled by "AKS doping" (K₂O/Al₂O₃/SiO₂ additions at ~100 ppm each) which pins grain boundaries and suppresses recrystallization embrittlement during lamp operation. It is a moderately rare element (~1.3 ppm crustal abundance), sourced from wolframite ((Fe,Mn)WO₄) and scheelite (CaWO₄), with China producing ~85% of global supply (~90,000 tonnes/year WO₃ equivalent). Tungsten cannot be conventionally cast due to its extreme melting point and is instead produced by powder metallurgy — hydrogen reduction of ammonium paratungstate (APT) to W powder followed by sintering and thermomechanical processing.

Cemented tungsten carbide (WC-Co) is the dominant application of tungsten, consuming ~60% of global production, and is one of the most important engineering materials — used for virtually all metal cutting, drilling, mining, and wear-resistant tooling requiring hardness approaching diamond combined with adequate fracture toughness. WC-Co hardmetals (typically 3–25 wt% Co binder, WC grain size 0.2–10 µm) are produced by liquid-phase sintering at ~1,400 °C, with hardness ~700–2,200 HV and fracture toughness ~5–25 MPa·m½ depending on composition. Coated grades (TiN, TiCN, Al₂O₃, TiAlN by CVD/PVD) dominate modern metal cutting, providing oxidation resistance at cutting temperatures of 700–1,000 °C. W metal itself is used for rocket nozzle throats, X-ray anodes, TIG welding electrodes, kinetic energy penetrators (W-Ni-Fe alloy, ~18 g/cm³), and radiation shielding as a non-toxic Pb replacement.

Tungsten's role in advanced technology spans plasma-facing components for fusion reactors, W thin-film metallization in semiconductor back-end-of-line processing, W-Re thermocouple wire for temperatures to 2,760 °C, and emerging applications in WS₂ and WSe₂ transition metal dichalcogenide (TMD) 2D materials. ITER uses W monoblocks for the divertor — handling steady-state heat flux of ~10–20 MW/m² — exploiting W's low sputtering yield, high thermal conductivity, and negligible tritium retention compared to carbon. In semiconductor manufacturing, CVD W (from WF₆ + H₂/SiH₄ at ~400 °C) fills contact vias and local interconnects in CMOS devices from the 0.35 µm node to current production. Monolayer WS₂ and WSe₂ are direct-bandgap semiconductors with strong photoluminescence and valley polarization, of interest for atomically thin transistors and optoelectronics.