Тулий: Химиялық элемент және қасиеттері

Chemical element with symbol Tm, atomic number 69

Thulium is a chemical element; it has symbol Tm and atomic number 69. It is the thirteenth element in the lanthanide series of metals. It is the second least abundant lanthanide in the Earth's crust, after radioactively unstable promethium. It is an easily workable metal with a bright silvery gray luster. It is fairly soft and slowly tarnishes in air. Despite its high price and rarity, thulium is used as a dopant in solid state lasers, and as the radiation source in some portable X ray devices. It has no significant biological role and is not particularly toxic. In 1879, the Swedish chemist Per Teodor Cleve separated two previously unknown components, which he called holmia and thulia, from the rare earth mineral erbia; these were the oxides of holmium and thulium, respectively. A relatively pure sample of thulium metal was first obtained in 1911. Like the other lanthanides, its most common oxidation state is +3, seen in its oxide, halides and other compounds. In aqueous solution, like compounds of other late lanthanides, soluble thulium compounds form coordination complexes with nine water molecules.

The isotopes of thulium range from |^{144}Tm to |^{183}Tm. The primary decay mode before the most abundant stable isotope, |^{169}Tm, is electron capture, and the primary mode after is beta emission. The primary decay products before |^{169}Tm are element 68 (erbium) isotopes, and the primary products after are element 70 (ytterbium) isotopes. Thulium 169 is thulium's only primordial isotope and is the only isotope of thulium that is thought to be stable; it is predicted to undergo alpha decay to holmium 165 with a very long half life. The longest lived radioisotopes are thulium 171, which has a half life of 1.92 years, and thulium 170, which has a half life of 128.6 days. Most other isotopes have half lives of a few minutes or less. In total, 40 isotopes and 26 nuclear isomers of thulium have been detected. Cleve started by removing all of the known contaminants of erbia (|Er2O3). Upon additional processing, he obtained two new substances; one brown and one green. The brown substance was the oxide of the element holmium and was named holmia by Cleve, and the green substance was the oxide of an unknown element. Cleve named the oxide thulia and its element thulium after Thule, an Ancient Greek place name associated with Scandinavia or Iceland. Thulium's atomic symbol was initially Tu, but later changed to Tm. Thulium was so rare that none of the early workers had enough of it to purify sufficiently to actually see the green color; they had to be content with spectroscopically observing the strengthening of the two characteristic absorption bands, as erbium was progressively removed. The first researcher to obtain nearly pure thulium was Charles James, a British expatriate working on a large scale at New Hampshire College in Durham, USA. In 1911 he reported his results, having used his discovered method of bromate fractional crystallization to do the purification. He famously needed 15,000 purification operations to establish that the material was homogeneous. High purity thulium oxide was first offered commercially in the late 1950s, as a result of the adoption of ion exchange separation technology. Lindsay Chemical Division of American Potash & Chemical Corporation offered it in grades of 99% and 99.9% purity. The price per kilogram oscillated between US$4,600 and $13,300 in the period from 1959 to 1998 for 99.9% purity, and it was the second highest for the lanthanides behind lutetium.

The element is never found in nature in pure form, but it is found in small quantities in minerals with other rare earths. Thulium is often found with minerals containing yttrium and gadolinium. In particular, thulium occurs in the mineral gadolinite. However, like many other lanthanides, thulium also occurs in the minerals monazite, xenotime, and euxenite. Thulium has not been found in prevalence over the other rare earths in any mineral yet. Its abundance in the Earth's crust is 0.5 mg/kg by weight. Thulium makes up approximately 0.5 parts per million of soil, although this value can range from 0.4 to 0.8 parts per million. Thulium makes up 250 parts per quadrillion of seawater. In the Solar System, thulium exists in concentrations of 200 parts per trillion by weight and 1 part per trillion by moles.

Holmium chromium thulium triple doped yttrium aluminium garnet (|Ho:Cr:Tm:YAG, or |Ho,Cr,Tm:YAG) is an active laser medium material with high efficiency. It lases at 2080 nm in the infrared and is widely used in military applications, medicine, and meteorology. Single element thulium doped YAG (Tm:YAG) lasers operate at 2010 nm. The wavelength of thulium based lasers is very efficient for superficial ablation of tissue, with minimal coagulation depth in air or in water. This makes thulium lasers attractive for laser based surgery.

Despite its high cost, portable X ray devices use thulium that has been bombarded with neutrons in a nuclear reactor to produce the isotope Thulium 170, having a half life of 128.6 days and five major emission lines of comparable intensity (at 7.4, 51.354, 52.389, 59.4 and 84.253 keV). These radioactive sources have a useful life of about one year, as tools in medical and dental diagnosis, as well as to detect defects in inaccessible mechanical and electronic components. Such sources do not need extensive radiation protectiononly a small cup of lead. They are among the most popular radiation sources for use in industrial radiography. Thulium 170 is gaining popularity as an X ray source for cancer treatment via brachytherapy (sealed source radiation therapy).

Thulium has been used in high temperature superconductors similarly to yttrium. Thulium potentially has use in ferrites, ceramic magnetic materials that are used in microwave equipment. Because thulium fluoresces with a blue color when exposed to ultraviolet light, thulium is put into euro banknotes as a measure against counterfeiting. The blue fluorescence of Tm doped calcium sulfate has been used in personal dosimeters for visual monitoring of radiation.

Soluble thulium salts are mildly toxic, but insoluble thulium salts are completely nontoxic. In humans, thulium occurs in the highest amounts in the liver, kidneys, and bones. Humans typically consume several micrograms of thulium per year. The roots of plants do not take up thulium, and the dry matter of vegetables usually contains one part per billion of thulium. Thulium dust and powder are toxic upon inhalation or ingestion and can cause explosions.