Thulium (Tm), chemical element, a rare-earth metal of the lanthanide series of the periodic table. Thulium is a moderately hard, silvery white metal that is stable in air but can easily be dissolved in diluted acids—except hydrofluoric acid (HF), in which an insoluble trifluoride (TmF3) layer forms on the surface of the metal, impeding further chemical reaction. Thulium is a strong paramagnet above 56 K (−217 °C, or −359 °F). Continue reading from Encyclopedia Britannica
Thulium was first isolated in 1879 as its oxide by Per Teodor Cleve at the University of Uppsala, Sweden. The discoveries of the many rare earth elements (aka lanthanoid) began with yttrium in 1794. This was contaminated with these chemically similar elements. Indeed the early chemists were unaware they were there. In 1843, erbium and terbium were extracted from yttrium, and then, in 1874, Cleve looked more closely at erbium and realised that it must contain yet other elements because he observed that its atomic weight varied slightly depending on the source from which it came. He extracted thulium from it in 1879.
In 1911, the American chemist Theodore William Richards performed 15,000 recrystallisations of thulium bromate in order to obtain an absolutley pure sample of the element and so determine exactly its atomic weight. Continue reading from Royal Society of Chemistry
Thulium is named for Thule, the earliest name for Scandinavia. While it is the least abundant of all the lanthanides, or rare earth elements, new sources have been recently discovered, putting it on par with cadmium, silver and gold in terms of supply. Because of the relatively high price of the metal, thulium has not yet found many practical applications, but it has potential use as an energy source. When bombarded in a nuclear reactor, thulium can be used as a radiation source in portable X-ray equipment. Continue reading from LiveScience
