What is Thulium
Thulium (pronounced as Thoo-lee-em)  is a soft, silver-gray rare earth metal  belonging to the Lanthanides group and represented by the symbol Tm . While its most abundant, naturally occurring isotope is 169Tm, it has 34 radioactive isotopes, out of which the most stable one is 171Tm with a half-life period of 1.92 years .
Where is it Found
Thulium is found in small quantities in monazite, a mineral that has approximately 20 parts per million (ppm) of the metal in the earth’s crust . It is then commercially extracted through ion-exchange and solvent-extraction processes . The element can as well be isolated through calcium reduction of anhydrous fluoride or by reduction of oxide with lanthanum . While the top 3 thulium producing nations are China, Russia, and Malaysia, the top 3 thulium reserve holders are China, CIS Countries, and Russia .
Origin of its Name: It is named after Thule, the ancient name that stood for the present-day Scandinavia [1, 2].
Who discovered it: The Swedish chemist Per Teodor Cleve is credited for the discovery of thulium .
When and How was it discovered
Men started finding the lanthanoids or rare earth elements in 1794 when yttrium was found by Johan Gadolin . Later, the chemists analyzed the composition of yttrium and observed that it was contaminated with chemically similar elements . As a result, two new elements terbium and erbium were isolated in 1843 .
Per Teodor Cleve started working on erbium in 1874 and was able to successfully isolate thulium in its oxide form in 1879 at the Uppsala University, Sweden [1, 5]. In 1911, the exact atomic weight of thulium was determined by Theodore William Richards, an American chemist who carried out 15,000 thulium bromate-recrystallizations to produce the pure form of thulium .
|Atomic number||69 |
|CAS number||7440-30-4 |
|Position in the periodic table||Group||Period||Block|
|Lanthanides ||6 ||f |
Properties and Characteristics of Thulium
|Relative atomic mass||168.934 |
|Color||Bright silvery-gray [1, 5]|
|Melting point/freezing point||1545 °C, 2813 °F |
|Boiling point||1950 °C, 3542 °F |
|Density||9.32 g cm-3 |
|State of matter at room temperature (solid/liquid/gas)||Solid [1, 5]|
|– Brinell||471 MPa |
|– Mohs||1.77 |
|– Vickers||520 MPa |
|Electrical conductivity||1.4X106 S/m |
|Thermal (heat) conductivity||17 W/(m K) |
|Specific heat||160 J kg-1 K-1 |
|Bulk modulus||44.5 GPa |
|Shear modulus||30.5 GPa |
|Young’s modulus||74 GPa |
|– Temperature (K)||400||600||800||1000||1200||1400||1600||1800||2000||2200||2400|
|– Pressure (Pa)||–||6.03X 10-10||5.94X 10-5||5.61X 10-2||5.22||130||–||–||–||–||–|
|Oxidation state/Oxidation number||+2, +3, (+4) |
|Isotopes||Isotope||Mass||Abundance||Half-life||Mode of decay|
Atomic Data of Thulium (Element 69)
|Valence electrons||3 |
|Quantum numbers||2F7/2 |
|Electron configuration (noble gas configuration)||[Xe] 4f136s2 |
|– Number of electrons||69 |
|– Number of neutrons||100 |
|– Number of protons||69 |
|Radius of Atom|
|– Atomic radius||2.27 Å |
|– Covalent radius||1.77 Å |
|Electronegativity (Pauling-scale)||1.25 |
|Electron affinity||99.283 kJ mol-1 |
|Ionization energy (kJ mol-1)||1st||2nd||3rd||4th||5th||6th||7th||8th|
What is Thulium used for
- Thulium-170 (170Tm), a radioactive isotope formed by bombarding thulium in a nuclear reactor, can be used as a portable source of radiation in medical x-ray machines [1, 7].
- The element 69 is used as a dopant in fiber lasers for surgical applications [1, 3].
- Since it emits a bluish glow when exposed to ultra-violet light, thulium is used in Euro banknotes for detecting counterfeit currency .
- It can also be used with other lanthanides for producing alloys .
Possible Harmful Effects or Toxicity
Being a non-toxic element, it does not cause any health hazards .
- Because of its softness and malleability, thulium can be easily cut with a knife .
- The element is sometimes represented by an image of a snow-covered mountain to indicate the origin of its name, suggesting a region far off to the north .
Cost of Thulium
While one gram of thulium costs about $50 , a hundred gram of the element approximately costs $500-$700 [5, 8].