Thulium (Tm)

Tm is a bright, silvery metal with atomic number 69 and belongs to the lanthanide series. It was first discovered in 1879 by Swedish chemist Per Teodor Cleve in oxide form and derives its name from Thule, the ancient name for Scandinavia. It is particularly used in portable X-ray devices and laser technologies.

Classification and Basic Properties

Tm (thulium) is an element located in the sixth period of the periodic table within the lanthanide group. Its electron configuration is [Xe] 4f¹³6s². It is considered one of the rarest lanthanides, excluding promethium which does not occur naturally. At room temperature it exists as a solid. It is a soft, malleable and ductile metal with a density of approximately 9.32 g/cm³.

Discovery

Thulium oxide (tulia) was first discovered in 1879 by Swedish chemist Per Teodor Cleve while separating other rare earth element oxides from a mineral sample then known as erbium oxide and containing a high proportion of yttrium. Cleve separated two new substances from erbium oxide: one was holmium oxide and the other was thulium oxide. Pure metallic thulium, however, was not obtained until much later, in 1911, by Charles James using electrolysis and reduction methods.

Thulium (Generated by Artificial Intelligence.)

Etimology

Per Teodor Cleve named the newly discovered element "thulium" after Thule, a term from mythology and ancient geography referring to the northernmost part of Scandinavia or a legendary northern landmass.

Natural Occurrence

Thulium occurs in very low concentrations in minerals such as monazite, xenotime, gadolinite and euxenite, alongside other lanthanide elements. Its abundance in the Earth's crust is very low and it is among the rarest lanthanides. Commercially, it is obtained as a byproduct during the processing of other rare earth elements using complex methods such as ion exchange and solvent extraction.

Physical and Chemical Properties

Thulium is a bright silvery metal. It is relatively stable in air but slowly oxidizes; this oxidation accelerates in moist air and at elevated temperatures. Its melting point is 1545 °C and its boiling point is 1950 °C. Its atomic radius is approximately 227 pm and its electronegativity value is 1.25. Its electron affinity is reported as 99.283 kJ/mol. It reacts slowly with water and more rapidly with acids, releasing hydrogen gas. In its compounds, it typically exhibits a +3 oxidation state, although a +2 oxidation state is also known.

Isotopes

The only naturally occurring stable isotope of thulium is thulium-169 (¹⁶⁹Tm). Therefore, thulium is considered a monoisotopic element. The important isotope is ¹⁶⁹Tm. Numerous radioactive isotopes have been artificially produced.

• ¹⁶⁹Tm: Constitutes 100% of natural thulium. When irradiated in a nuclear reactor, it transforms into the gamma-ray-emitting isotope thulium-170 (¹⁷⁰Tm).
• ¹⁷⁰Tm: Has a half-life of approximately 128.6 days. It decays via beta emission to ytterbium-170 while emitting X-rays and gamma rays. Due to this property, it is used in portable X-ray sources.

Thulium (Generated by Artificial Intelligence.)

Applications

Due to its rarity and high cost, thulium has limited applications, but several specialized uses exist:

• Portable X-ray Sources: The radioactive isotope thulium-170, produced by irradiation in nuclear reactors, is used in lightweight, portable X-ray devices that require no electrical power. These devices are useful in medical imaging, especially in remote locations or emergency situations, and in certain industrial radiography applications.
• Laser Technology: Thulium-doped crystals, such as Tm:YAG (thulium-doped yttrium aluminum garnet), are used in the production of solid-state lasers, particularly for surgical applications. These lasers emit light at specific wavelengths (typically around 2 micrometers) that are well absorbed by biological tissues.
• Ceramic Magnetic Materials (Ferrites): Thulium oxide may be used in the production of certain ceramic magnetic materials (ferrites) employed in microwave equipment.
• Superconductors: It may be present in the composition of some high-temperature superconductors.
• Currency Security: Thulium compounds that emit blue fluorescent light under ultraviolet light are used in euro banknotes as an anti-counterfeiting measure.

Biological Role and Precautions

Thulium has no known biological role and is generally considered non-toxic. Soluble thulium salts are thought to have low toxicity. However, as with all rare earth elements, harmful effects may occur if ingested in large quantities or in certain compound forms. Like other fine metal powders, thulium powder can pose fire and explosion hazards. Standard safety precautions are recommended when handling the element.