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Rare-earth element
The rare-earth elements, or rare earths, are a group of 17 chemically similar metals: the 15 lanthanides plus scandium and yttrium, used in magnets, phosphors, and catalysts.
Rare-earth ion
A rare-earth ion (REI) is a charged lanthanide, scandium, or yttrium ion embedded in a host crystal, whose shielded 4f electrons give narrow, stable optical transitions used in quantum memories.
Refractory metals
Refractory metals, usually niobium, tantalum, molybdenum, tungsten, and rhenium, are metals with melting points above 2,000 °C and resistance to softening at high temperatures, though they oxidize poorly; tungsten melts at 3,422 °C.
Rhenium
Rhenium is a rare, dense transition metal with atomic number 75, discovered in Germany in 1925 and used mainly in jet engine superalloys and refining catalysts.
Rhodium
Rhodium is a chemical element with symbol Rh and atomic number 45, a rare, expensive silvery-white platinum-group metal best known for reducing nitrogen oxides in car catalytic converters.
Ruthenium
Ruthenium (Ru) is a hard, silvery transition metal, atomic number 44, and one of the six platinum-group metals, used mainly in chip resistors, electrical contacts, and catalysts.
Samarium
Samarium (symbol Sm, atomic number 62) is a silvery rare-earth metal isolated in 1879, best known for samarium-cobalt magnets and for dating the oldest rocks on Earth.
Scandium
Scandium, symbol Sc and atomic number 21, is a silvery lightweight transition metal discovered in 1879 by Lars Fredrik Nilson, confirming Mendeleev's prediction of ekaboron.
Silver
Silver (symbol Ag, from the Latin argentum) is a soft, lustrous white metallic element with atomic number 47, prized since prehistoric times for coinage, jewelry, and tableware.
Silver as an investment
Silver as an investment is the purchase of silver or silver-linked financial instruments to preserve or increase wealth, through bullion, trusts, futures, or mining shares.
Spectrochemical series
The spectrochemical series is an empirical ranking of ligands by the ligand field splitting they cause in transition-metal complexes, from iodide (weak field) to cyanide and carbon monoxide (strong field).
Sterling silver
Sterling silver is a silver alloy containing 92.5% pure silver, with copper usually making up the rest, and has been the standard for silverware since the 14th century.
Tanaka Kikinzoku Kogyo
Tanaka Kikinzoku Kogyo (田中貴金属工業) is a Japanese precious metals company founded as a Tokyo bullion dealer in 1885, refining and recycling gold, silver, and platinum group metals.
Tantalum
Tantalum, symbol Ta and atomic number 73, is a rare, dense transition metal valued for corrosion resistance; its dominant use is in capacitors for portable electronics.
Terbium
Terbium, element 65, is a silvery lanthanide metal isolated in 1843 by Carl Gustav Mosander and named after Ytterby, Sweden, best known for green phosphors and the Terfenol-D alloy.
Thorium
Thorium is a weakly radioactive silvery metallic element of the actinide series, atomic number 90, whose isotope thorium-232 can be bred into fissile uranium-233 for nuclear fuel.
Thulium
Thulium is a chemical element with symbol Tm and atomic number 69, the least abundant stable rare-earth metal, used mainly as a dopant in surgical lasers.
Titanium
Titanium is a chemical element with symbol Ti and atomic number 22, a transition metal as strong as steel but far less dense, best known for aerospace and medical uses.
Toxic heavy metal
Toxic heavy metal is a loose term for metals like lead, cadmium, mercury, and arsenic that harm health; IUPAC found in 2002 that the term has no authoritative definition.
Transition metal
Transition metals, also called transition elements, are elements with an incomplete d sub-shell, found in the center of the periodic table, with variable oxidation states and colored compounds.
Tungsten
Tungsten, also known as wolfram, is a hard, steel-gray transition metal with the highest melting point of any metal, 3414 °C, best known for tungsten carbide tools and light bulb filaments.
Uranium
Uranium is a naturally occurring, weakly radioactive silvery metal of the actinide series, atomic number 92, discovered in 1789 by Martin Heinrich Klaproth and used chiefly as nuclear reactor fuel.
Vanadium
Vanadium is a silvery transition metal with atomic number 23, named for the Norse goddess Vanadis; about 80% of production goes into steel, and it powers vanadium redox flow batteries.
Ytterbium
Ytterbium is a soft, silvery lanthanide element with symbol Yb and atomic number 70, used chiefly in high-power fiber lasers, optical atomic clocks, and medical brachytherapy.
Yttrium
Yttrium is a chemical element with symbol Y and atomic number 39, a silvery metal grouped with the rare earths and used in phosphors, lasers, and superconductors.
Zirconium
Zirconium, symbol Zr and atomic number 40, is a hard, silvery, corrosion-resistant metal extracted from the mineral zircon and used chiefly as cladding for nuclear fuel.