Tantalum is a gray-blue, highly corrosion-resistant refractory metal with excellent ductility, and its largest consumer outlet is tantalum capacitors in the electronics industry. Tantalum capacitors are small, high-capacitance, highly reliable and extremely low in leakage current, appearing almost everywhere from mobile phones, laptops and automotive electronics to spacecraft and medical implants; a single smartphone often contains dozens of them - tantalum's most irreplaceable use to this day. In medicine, tantalum is non-toxic to human tissue and causes no rejection, and is made into surgical implants, cranioplasty plates, bone screws and surgical instruments, as well as surface coatings on artificial joints. In chemical engineering, its outstanding acid resistance is exploited to make heat exchangers, reactors, valves and pipe linings, which are almost untouched when handling corrosive media such as hydrochloric and nitric acids. Tantalum is also used in superconducting wire, high-temperature components of aero-engines, sputtering targets and vacuum-furnace heating elements. Tantalum is expensive and irreplaceable precisely because, in small-volume, high-reliability capacitors and in extreme-corrosion service, no cost-comparable substitute has yet appeared.
Tantalum pentoxide (Ta2O5) is tantalum's main oxide, with a very high refractive index and good insulation; it is used to make optical lenses, anti-reflection coatings and specialty high-refractive-index glass, and is also a key dielectric material for high-capacitance capacitors and certain solid electrolytes. Tantalum pentachloride (TaCl5) is an important intermediate in tantalum metallurgy and chemical vapor deposition, used to prepare high-purity tantalum powder, tantalum wire and certain homogeneous catalysts. Tantalum nitride (TaN) films are hard, dimensionally stable in resistance and strong diffusion barriers; in integrated circuits they serve as barrier layers for copper interconnects and as precision resistor films, as well as wear-resistant coatings on cutting tools. Tantalum carbide (TaC) is an extremely hard refractory compound that, together with tungsten carbide and titanium carbide, is added to cemented-carbide cutting tools to markedly raise red hardness and wear resistance, widely used in metal cutting, mine drill bits and wear parts. Beyond these, crystals such as potassium tantalate are also used in nonlinear optics and surface-acoustic-wave devices.
