Thulium
Thulium is a chemical element that has the symbol Tm and atomic number 69. Thulium is the second least abundant of the lanthanides (promethium is only found in trace quantities on Earth). It is an easily workable metal with a bright silvery-gray luster. Despite its high price and rarity, thulium is used as the radiation source in portable X-ray devices and in solid-state lasers.
Occurrence and production
The element is never found in nature in pure form, but it is found in small quantities in minerals with other rare earths. Its abundance in the Earth crust is 0.5 mg/kg. 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. Thulium is principally extracted from monazite (~0.007% thulium) ores found in river sands, through ion-exchange. Newer ion-exchange and solvent-extraction techniques have led to easier separation of the rare earths, which has yielded much lower costs for thulium production. The principal sources today are the ion adsorption clays of southern China. In these, where about two-thirds of the total rare-earth content is yttrium, thulium is about 0.5% (or about tied with lutetium for rarity). The metal can be isolated through reduction of its oxide with lanthanum metal or by calcium reduction in a closed container. None of thulium's natural compounds are commercially important.
| Symbol | Tm | |
| Atomic Number | 69 | |
| Atomic Weight | 168.93421 | |
| Oxidation States | +3 | |
| Electronegativity, Sanderson | 0.96 | |
| State at RT | Solid, Metal | |
| Melting Point, K | 1818 | |
| Boiling Point, K | 2220 |
Harmful effects:
Thulium is considered to be non-toxic.
Characteristics:
- Thulium is a bright, soft, malleable, silvery-gray metal.
- It is a rare earth metal and is one of the least abundant.
- The metal tarnishes slowly in dry air to form the oxide and reacts with water to form the hydroxide and hydrogen gas.
- Tm3+ ions emit a strong blue luminescence when excited.
- When present in compounds, thulium exists usually in the trivalent state, Tm3+. It forms compounds – mostly green in color – with oxygen and the halogens.
Uses of Thulium
- Radioactive isotope 170Tm is produced by bombarding thulium in a nuclear reactor. It has a half-life of 128 days and is used as a portable source of x-rays.
- Thulium is used to dope yttrium aluminum garnets (YAG) used in lasers.
- Thulium is also used in alloys with other rare earth metals.
- Thulium is used in euro banknotes for its blue fluorescence under UV light to defeat counterfeiters.
