Thulium (Tm) is a rare-earth metal in the lanthanide series of the periodic table. It was discovered in 1879 by a Swedish chemist named Per Teodor Cleve. The element is named after "Thule," an ancient name for Scandinavia. Thulium is one of the least abundant rare-earth elements, making it rare and valuable. It has unique properties that make it useful in specific high-tech applications.
Thulium is a moderately hard, silvery-white metal. It is stable in air, which means it does not react quickly with oxygen. However, it can dissolve in diluted acids like hydrochloric acid (HCl) or sulfuric acid (H₂SO₄). Thulium does not react with hydrofluoric acid (HF) because an insoluble trifluoride (TmF₃) layer forms on its surface, which stops further reactions.
Thulium is magnetic. Above 56 K (-217 °C), it is a paramagnet, which means it is weakly attracted to a magnet. Between 56 and 32 K (-241 °C), thulium becomes antiferromagnetic, where its magnetic moments are aligned in opposite directions. Below 32 K, it turns ferrimagnetic, with magnetic moments pointing in opposite directions but not canceling out.
Thulium is very rare. It is found in tiny amounts in minerals like monazite, xenotime, and euxenite. These minerals are found in some types of clay and as by-products of nuclear reactions. The amount of thulium in the Earth's crust is about the same as that of antimony and iodine. This makes thulium one of the rarest of the rare-earth elements.
Ra'ike (see also: de:Benutzer:Ra'ike), CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
The main source of thulium is monazite, a rare-earth mineral that can contain up to 0.007% thulium. To extract thulium, scientists use a process called solvent extraction or ion exchange. In this process, thulium is separated from other elements using special chemicals. After that, thulium metal is made by reducing its oxide (Tm₂O₃) with another metal, such as lanthanum. This method is expensive and complex, which makes thulium costly and difficult to produce.
Thulium has several interesting physical and chemical properties:
Thulium is not widely used because it is rare and expensive. However, it has some specialized applications:
Medical Imaging: Thulium-170, a radioactive isotope, is used in small, portable X-ray machines. These machines are useful in medical imaging to look inside the body without needing large equipment. Thulium-170 is also used in testing materials, like checking for cracks in pipes or metal parts without damaging them.
Laser Technology: Thulium is used to make lasers. It is added as a dopant to yttrium aluminum garnet (YAG) crystals to produce lasers that emit infrared light. These lasers are used in medicine, such as in surgery and dentistry, to cut or remove tissues precisely. Thulium-doped lasers are also used in industrial settings to cut metals and other materials with high accuracy.
High-Temperature Superconductors: Thulium is part of some high-temperature superconducting materials, combined with elements like yttrium. These materials can conduct electricity without resistance at low temperatures. Superconductors are crucial for technologies like MRI machines, quantum computers, and power grids that require highly efficient electrical systems.
Anti-Counterfeiting Measures: Thulium is used to prevent counterfeiting. When exposed to ultraviolet (UV) light, thulium ions (Tm³⁺) emit a strong blue light. This property is used in euro banknotes to help detect fake currency. Thulium's fluorescence makes it a good tool for protecting against fraud.
Thulium forms various compounds, although none are very common in commercial use. Some of these compounds include:
Thulium compounds are mostly stable in the +3 oxidation state. They are studied for their unique magnetic and electronic properties, but they have limited use outside of research.
Thulium has 35 known isotopes, ranging from mass numbers 144 to 179. The only stable isotope is thulium-169. Thulium-170, a radioactive isotope, is produced by bombarding thulium with neutrons in a nuclear reactor. It has a half-life of about 128 days and is the most useful isotope for practical applications, like in portable X-ray devices.
Thulium is a rare, valuable metal with unique properties that make it useful in specialized applications, such as medical imaging, laser technology, and anti-counterfeiting. Though not widely used due to its high cost and limited availability, thulium plays a crucial role in specific fields where its properties offer distinct advantages. As technology evolves, new applications for thulium may emerge. Stanford Materials Corporation (SMC) is committed to supporting the advancement of materials like thulium and continues to provide high-quality rare-earth metals for research and industrial use. Explore our offerings to discover more about how thulium and other rare-earth elements can meet your needs.
Eric Loewen
Eric Loewen graduated from the University of Illinois studying applied chemistry. His educational background gives him a broad base from which to approach many topics. He has been working with topics about advanced materials for over 5 years at Stanford Materials Corporation (SMC). His main purpose in writing these articles is to provide a free, yet quality resource for readers. He welcomes feedback on typos, errors, or differences in opinion that readers come across.
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