Yttrium

From Wikipedia, the free encyclopedia

Yttrium (IPA: /ɪˈtriəm/), is a chemical element that has the symbol Y and atomic number 39. A silvery metallic transition metal, yttrium is common in rare-earth minerals and two of its compounds are used to make the red color phosphors in cathode ray tube displays, such as those used for televisions.

[edit] Notable characteristics

Yttrium is a silver-metallic, lustrous rare earth metal that is relatively stable in air, strongly resembles scandium in appearance, and chemically resembles the lanthanides, and can appear to gain a slight pink lustre on exposure to light. Shavings or turnings of the metal can ignite in air when they exceed 400 °C. When yttrium is finely divided, it is very unstable in air. The metal has a low neutron cross-section for nuclear capture. The common oxidation state of yttrium is +3.

[edit] Applications

Yttrium(III) oxide is the most important yttrium compound and is widely used to make YVO₄:Eu and Y₂O₃:Eu phosphors that give the red color in color television picture tubes. Other uses:

• Yttrium oxide is also used to make yttrium iron garnets which are very effective microwave filters.
• Yttrium iron, aluminium, and gadolinium garnets (e.g. Y₃Fe₅O₁₂ and Y₃Al₅O₁₂) have interesting magnetic properties. Yttrium iron garnet is very efficient as an acoustic energy transmitter and transducer. Yttrium aluminium garnet has a hardness of 8.5 and is also used as a gemstone (simulated diamond).
• Small amounts of the element (0.1 to 0.2%) have been used to reduce grain size of chromium, molybdenum, titanium, and zirconium. It is also used to increase the strength of aluminium and magnesium alloys.
• Used as a catalyst for ethylene polymerization.
• Yttrium aluminium garnet, yttrium lithium fluoride, and yttrium vanadate are used in combination with dopants such as neodymium or erbium in infrared lasers.
• It is used on the electrodes of some high-performance spark plugs.
• This metal can be used to deoxidize vanadium and other non-ferrous metals.
• Yttrium is also used in the manufacture of gas mantles for propane lanterns, as a replacement for thorium, which is slightly radioactive.
• Cerium-doped yttrium aluminium garnet (YAG:Ce) crystals are used as phosphors to make white LEDs.
• Yttrium-90 microspheres have shown promise as a treatment for unresectable hepatocellular carcinoma.
• Yttrium was used as a "secret" element in a superconductor developed at the University of Houston, YBaCuO. This superconductor operated above 90K, an amazing feat because it can operate at above liquid nitrogen's boiling point (-195.9 C). (Y_1.2Ba_0.8CuO₄). The matter created was a multi-crystal multi-phase mineral, which was black and green.

Yttrium has been studied for possible use as a nodulizer in the making of nodular cast iron which has increased ductility (the graphite forms compact nodules instead of flakes to form nodular cast iron). Potentially, yttrium can be used in ceramic and glass formulas, since yttrium oxide has a high melting point and imparts shock resistance and low thermal expansion characteristics to glass.

• Yttrium oxide is used to stabilize the cubic form of zirconia, for use in jewelry, etc.
• Yttria (yttrium(III) oxide) is used as a sintering additive in the production of porous silicon nitride.
• Yttrium is a key element in YBCO superconductors.

[edit] History

Yttrium (named for Ytterby, a Swedish village near Vaxholm) was discovered by Finnish chemist, physicist, and mineralogist Johan Gadolin in 1794 and isolated by Friedrich Wöhler in 1828 as an impure extract of yttria through the reduction of yttrium anhydrous chloride (YCl₃) with potassium. Yttria (Y₂O₃) is the oxide of yttrium and was discovered by Johan Gadolin in 1794 in a gadolinite mineral from Ytterby.

In 1843, the Swedish chemist Carl Mosander was able to show that yttria could be divided into the oxides (or earths) of three different elements. "Yttria" was the name which was retained for the most basic one, which also happened to comprise the bulk of the crude mixture (typically about two-thirds) and the others were re-named erbia and terbia. (Later in the 19th century, both of these would also be shown to be complex, although the names would be retained for the most characteristic component of each.)

A quarry is located near the village of Ytterby that yielded many unusual minerals that contained rare earths and other elements. The elements erbium, terbium, ytterbium, and yttrium have all been named after this same small village.

[edit] Occurrence

This element is found in almost all rare-earth minerals and in uranium ores but is never found in nature as a free element. Yttrium is commercially recovered from monazite sand (3% content, [(Ce, La, etc.)PO₄]) and from bastnäsite (0.2% content, [(Ce, La, etc.)(CO₃)F]). It is commercially produced by reducing yttrium fluoride with calcium metal but it can also be produced using other techniques. It is difficult to separate from other rare earths and when extracted, is a dark gray powder. The original "rare earths" ceria (1803) and yttria (1794) reflect the great geochemical divide that occurs between the light and heavy lanthanides due to "lanthanide contraction". The lighter lanthanides, with a larger radius, partition into minerals in sites with a higher coordination number (e.g. monazite), whereas the smaller heavy lanthanides prefer a slightly lower coordination number (as in xenotime). The lighter lanthanides are also more relatively abundant in the earth's outer crust than the heavies, relative to the abundance in chondritic meteorites, due to size fractionation. Yttrium falls into the middle of the heavy group in size, and thus inevitably occurs with these in minerals, where it comprises about two-thirds of the mixed oxides by weight. This composition is typical of gadolinite, xenotime, and certain ion adsorption clays currently mined in the south of China.

Lunar Rock samples from the Apollo program have a relatively high yttrium content.

See also yttrium minerals.

[edit] Isotopes

Main article: isotopes of strontium

Natural yttrium is composed of only one isotope (Y-89). The most stable radioisotopes are Y-88 which has a half life of 106.65 days and Y-91 with a half life of 58.51 days. All the other isotopes have half lives of less than a day except Y-87 which has a half life of 79.8 hours. The dominant decay mode below the stable Y-89 is electron capture and the dominant mode after it is beta emission. Twenty six unstable isotopes have been characterized.

Y-90 exists in equilibrium with its parent isotope strontium-90, which is a product of nuclear explosions.

[edit] Precautions

Compounds that contain this element are rarely encountered by most people but should be considered to be highly toxic even though many compounds pose little risk^{[citation needed]}. Yttrium salts may be carcinogenic^{[citation needed]}. This element is not normally found in human tissue and plays no known biological role.