Тербий: Свойства, применение и история открытия

Terbium is a chemical element; it has the symbol Tb and atomic number 65. It is a silvery white, rare earth metal that is malleable, and ductile. The ninth member of the lanthanide series, terbium is a fairly electropositive metal that reacts with water, evolving hydrogen gas. Terbium is never found in nature as a free element, but it is contained in many minerals, including cerite, gadolinite, monazite, xenotime and euxenite. Swedish chemist Carl Gustaf Mosander discovered terbium as a chemical element in 1843. He detected it as an impurity in yttrium oxide, |Y2O3. Yttrium and terbium, as well as erbium and ytterbium, are named after the village of Ytterby in Sweden. Terbium was not isolated in pure form until the advent of ion exchange techniques. Terbium is used to dope calcium fluoride, calcium tungstate and strontium molybdate in solid state devices, and as a crystal stabilizer of fuel cells that operate at elevated temperatures. As a component of Terfenol D (an alloy that expands and contracts when exposed to magnetic fields more than any other alloy), terbium is of use in actuators, in naval sonar systems and in sensors. Most of the world's terbium supply is used in green phosphors. Terbium oxide is used in fluorescent lamps and television and monitor cathode ray tubes (CRTs). Terbium green phosphors are combined with divalent europium blue phosphors and trivalent europium red phosphors to provide trichromatic lighting technology, a high efficiency white light used for standard illumination in indoor lighting.

Terbium is a silvery white rare earth metal that is malleable, ductile and soft enough to be cut with a knife. Terbium exists in two crystal allotropes with a transformation temperature of 1289 °C between them. Terbium has a simple ferromagnetic ordering at temperatures below 219 K. Above 219 K, it turns into a helical antiferromagnetic state in which all of the atomic moments in a particular basal plane layer are parallel, and oriented at a fixed angle to the moments of adjacent layers. This unusual antiferromagnetism transforms into a disordered paramagnetic state at 230 K.

Like most rare earth elements and lanthanides, terbium is usually found in the +3 oxidation state. Like cerium and praseodymium, terbium can also form a +4 oxidation state, although it is unstable in water. However, it is possible for terbium to also be found in the 0, +1 and +2 oxidation states.

Naturally occurring terbium is composed of its only stable isotope, terbium 159; the element is thus mononuclidic and monoisotopic. Thirty six radioisotopes have been characterized, with the heaviest being terbium 171 (with an atomic mass of 170.95330(86) u) and lightest being terbium 135 (exact mass unknown). The most stable synthetic radioisotopes of terbium are terbium 158, with a half life of 180 years, and terbium 157, with a half life of 71 years. All of the remaining radioactive isotopes have half lives that are much less than a quarter of a year, and the majority of these have half lives that are less than half a minute. The primary decay mode before the most abundant stable isotope, 159Tb, is electron capture, which results in production of gadolinium isotopes, and the primary mode after is beta minus decay, resulting in dysprosium isotopes. The element also has 27 nuclear isomers, with masses of 141–154, 156, and 158 (not every mass number corresponds to only one isomer). The most stable of them are terbium 156m, with a half life of 24.4 hours, and terbium 156m2, with a half life of 22.7 hours; this is longer than half lives of most ground states of radioactive terbium isotopes, except those with mass numbers 155–161. Terbium 149, with a half life of 4.1 hours, is a promising candidate in targeted alpha therapy and positron emission tomography.

Swedish chemist Carl Gustaf Mosander discovered terbium in 1843. He detected it as an impurity in yttrium oxide, |Y2O3. Yttrium is named after the village of Ytterby in Sweden. Terbium was not isolated in pure form until the advent of ion exchange techniques. Mosander first separated yttria into three fractions, all named for the ore: yttria, erbia, and terbia. "Terbia" was originally the fraction that contained the pink color, due to the element now known as erbium. "Erbia" (containing what is now known as terbium) originally was the fraction that was essentially colorless in solution. The insoluble oxide of this element was noted to be tinged brown. Later workers had difficulty in observing the minor colorless "erbia", but the soluble pink fraction was impossible to miss. Arguments went back and forth as to whether erbia even existed. In the confusion, the original names got reversed, and the exchange of names stuck, so that the pink fraction referred eventually to the solution containing erbium (which in solution, is pink). It is now thought that workers using double sodium or potassium sulfates to remove ceria from yttria inadvertently lost the terbium into the ceria containing precipitate. What is now known as terbium was only about 1% of the original yttria, but that was sufficient to impart a yellowish color to the yttrium oxide. Thus, terbium was a minor component in the original fraction containing it, where it was dominated by its immediate neighbors, gadolinium and dysprosium. Thereafter, whenever other rare earths were teased apart from this mixture, whichever fraction gave the brown oxide retained the terbium name, until at last, the brown oxide of terbium was obtained in pure form. The 19th century investigators did not have the benefit of the UV fluorescence technology to observe the brilliant yellow or green Tb(III) fluorescence that would have made terbium easier to identify in solid mixtures or solutions.

Terbium is contained along with other rare earth elements in many minerals, including monazite (|(Ce,La,Th,Nd,Y)PO4 with up to 0.03% terbium), xenotime (|YPO4) and euxenite (|(Y,Ca,Er,La,Ce,U,Th)(Nb,Ta,Ti)2O6 with 1% or more terbium). The crust abundance of terbium is estimated as 1.2 mg/kg. No terbium dominant mineral has yet been found. Currently, the richest commercial sources of terbium are the ion adsorption clays of southern China; the concentrates with about two thirds yttrium oxide by weight have about 1% terbia. Small amounts of terbium occur in bastnäsite and monazite; when these are processed by solvent extraction to recover the valuable heavy lanthanides as samarium europium gadolinium concentrate, terbium is recovered therein. Due to the large volumes of bastnäsite processed relative to the ion adsorption clays, a significant proportion of the world's terbium supply comes from bastnäsite.

Crushed terbium containing minerals are treated with hot concentrated sulfuric acid to produce water soluble sulfates of rare earths. The acidic filtrates are partially neutralized with caustic soda to pH 3–4. Thorium precipitates out of solution as hydroxide and is removed. After that the solution is treated with ammonium oxalate to convert rare earths into their insoluble oxalates. The oxalates are decomposed to oxides by heating. The oxides are dissolved in nitric acid that excludes one of the main components, cerium, whose oxide is insoluble in |HNO3. Terbium is separated as a double salt with ammonium nitrate by crystallization. Terbium is also used in alloys and in the production of electronic devices. As a component of Terfenol D, terbium is used in actuators, in naval sonar systems, sensors, in the SoundBug device (its first commercial application), and other magnetomechanical devices. Terfenol D is a terbium alloy that expands or contracts in the presence of a magnetic field. It has the highest magnetostriction of any alloy. Terbium oxide is used in green phosphors in fluorescent lamps and color TV tubes. Sodium terbium borate is used in solid state devices. The brilliant fluorescence allows terbium to be used as a probe in biochemistry, where it somewhat resembles calcium in its behavior. Terbium "green" phosphors (which fluoresce a brilliant lemon yellow) are combined with divalent europium blue phosphors and trivalent europium red phosphors to provide the trichromatic lighting technology which is by far the largest consumer of the world's terbium supply. Trichromatic lighting provides much higher light output for a given amount of electrical energy than does incandescent lighting. In 2023, terbium compounds were used to create a lattice with one iron (Fe) atom, that was then examined by synchrotron x ray beam, to examine one atom at sub atomic levels for the first time.

Little is known about the toxicity of Terbium. Handling of terbium, like other lanthanides, should be done with care.