Tungsten is the metal with the highest melting point in nature, hard, dense and low in thermal expansion, a textbook material for extreme service conditions. Its most classic use is as the filament of incandescent and halogen lamps; though incandescent lamps are being phased out rapidly by LEDs, tungsten-filament lamps still find use in stage lighting, infrared heaters and special light sources. A larger modern use is in cemented carbide - pressing tungsten-carbide powder together with cobalt binder into cutting tools, dies, mine drill bits and tunnel-boring-machine cutter heads - which alone accounts for over half of tungsten consumption; modern metal cutting, oil drilling and stone working all but depend on it. In defense and armor-piercing, high-density tungsten-alloy long-rod penetrators are the main kinetic-energy weapon against armored targets, with density close to depleted uranium but none of the radioactivity concern. Tungsten is also used as the electrode in gas-tungsten arc welding, as grid electrodes and cathodes in vacuum tubes, as heating elements in glass-melting furnaces, as protection tubes for high-temperature thermocouples, and in golf club heads, fishing weights and rotating X-ray anodes. With top-tier melting point, density and hardness all at once, it has almost no rival wherever the rule is 'hotter means harder and heavier means more accurate'.
Tungsten trioxide (WO3) is an intermediate of tungsten smelting, a yellow powder used to prepare tungsten powder and cemented carbide, and also as an electrochromic film and gas-sensor material. Calcium tungstate (CaWO4), i.e. scheelite, is both one of the main tungsten ores and, in crystal form, a classic scintillator material, long used in X-ray fluorescent screens and scintillation counters and, when europium-doped, as a luminescent material. Ferrous tungstate (FeWO4), i.e. wolframite, is another traditional tungsten ore that, together with scheelite, makes up the bulk of the world's tungsten resources; its beneficiation and alkaline-leaching processes form the basis of modern tungsten metallurgy. Tungsten carbide (WC) is tungsten's most commercially valuable compound, with hardness close to diamond; cemented-carbide tools bonded with cobalt can cut steel at high speed and are widely used in machine tools, drilling and extraction, dies and wear parts, earning it the name 'the teeth of modern manufacturing'. In addition, tungsten disulfide (WS2) serves as a high-temperature solid lubricant for vacuum and extreme-pressure service.
