Thulium is one of the lesser-known rare earth elements, yet it plays a fascinating role in the world of chemistry and material science. As a member of the lanthanide series, thulium exhibits properties typical of rare earth metals, including high reactivity in certain conditions. While it is relatively stable in dry air, it reacts more readily when exposed to moisture, heat, or certain chemicals. Understanding what thulium reacts with helps researchers and manufacturers handle it safely and use it effectively in technological applications.
Basic Characteristics of Thulium
Elemental Identity
Thulium is a chemical element with the symbolTmand atomic number 69. It belongs to the lanthanide group and is classified as a rare earth metal. Thulium is soft, malleable, and silvery-gray in appearance. It is the thirteenth element in the lanthanide series and has only one naturally occurring isotope,169Tm, which is stable.
Reactivity Overview
Thulium, like most lanthanides, is electropositive and reactive, particularly at elevated temperatures or when exposed to moisture. It readily forms compounds with halogens, oxygen, sulfur, and various acids. Thulium’s reactivity is of great interest for its use in electronics, lasers, and medical devices.
Reactions with Common Elements
Reaction with Oxygen
Thulium reacts slowly with oxygen in the air to form an oxide layer on its surface. The reaction becomes more pronounced when thulium is heated.
- Chemical reaction: 4Tm + 3O2→ 2Tm2O3
This reaction results in thulium(III) oxide (Tm2O3), a green compound that is often used in ceramics and high-temperature materials. The oxide layer also provides a certain level of protection against further oxidation, similar to the passivation effect seen in aluminum.
Reaction with Water and Moisture
Thulium is fairly stable in dry air, but when exposed to water or humid environments, it reacts slowly to form thulium hydroxide:
- Reaction: 2Tm + 6H2O → 2Tm(OH)3+ 3H2
This reaction produces hydrogen gas and thulium(III) hydroxide, a white solid. The reaction is more significant at higher temperatures. Because of this, thulium should be stored in moisture-free environments to prevent gradual degradation.
Reaction with Acids
Thulium reacts readily with dilute acids to release hydrogen gas and form thulium salts. One common example is its reaction with hydrochloric acid:
- Reaction: 2Tm + 6HCl → 2TmCl3+ 3H2
This produces thulium(III) chloride and hydrogen gas. Similar reactions occur with sulfuric acid and nitric acid, forming thulium sulfate and thulium nitrate, respectively. These salts are often used in research settings and in making phosphors or laser materials.
Reaction with Halogens
Thulium combines directly with halogens (fluorine, chlorine, bromine, and iodine) to form halide compounds. These reactions are typically exothermic and can occur at room temperature or with gentle heating.
- With fluorine: 2Tm + 3F2→ 2TmF3
- With chlorine: 2Tm + 3Cl2→ 2TmCl3
These halides are usually white or light-colored crystalline solids and are used in specialty optical and electronic applications.
Reactions with Other Nonmetals
Reaction with Sulfur
When heated with sulfur, thulium forms thulium sulfide (Tm2S3):
- 2Tm + 3S → Tm2S3
This compound is often used in semiconductor research. The reaction generally requires elevated temperatures and controlled conditions to ensure the desired stoichiometry.
Reaction with Nitrogen
Thulium reacts with nitrogen at high temperatures to form thulium nitride (TmN):
- 2Tm + N2→ 2TmN
Thulium nitride is a hard ceramic material with applications in electronic devices and possibly in advanced materials research. The reaction is typically carried out in an inert atmosphere with nitrogen gas introduced under controlled heating.
Reaction with Carbon
Under high-temperature conditions, thulium can form carbides when combined with carbon. These compounds are generally used in research contexts rather than industrial applications, as they are difficult to produce and handle.
Industrial and Laboratory Considerations
Handling and Storage
Because of its reactivity, especially with moisture and acids, thulium must be stored in sealed containers under inert gases like argon. In laboratory settings, glove boxes and desiccators are used to limit its exposure to air and humidity. Safety protocols are essential when reacting thulium with acids or water due to the generation of flammable hydrogen gas.
Uses of Reactive Thulium Compounds
Many of the compounds formed through thulium’s reactions are valuable in specific applications:
- Thulium oxideis used in ceramics and lasers.
- Thulium halideshave applications in lighting and optical devices.
- Thulium nitrate and sulfateare used in chemical research.
- Thulium-activated materialsare used in X-ray machines and portable medical lasers.
Understanding how thulium reacts with other elements is crucial for developing these technologies and ensuring safe handling during synthesis and application.
Comparing Thulium to Other Lanthanides
Thulium’s reactivity profile is similar to other middle lanthanides like erbium and holmium. It is neither the most reactive nor the most inert among them. However, it stands out for its ability to form highly efficient laser materials and for its usefulness in neutron-activated applications. These properties make it unique and valuable despite its relatively low abundance in Earth’s crust.
Thulium reacts with a variety of elements and compounds, including oxygen, water, acids, halogens, sulfur, and nitrogen. These reactions often result in the formation of useful compounds such as thulium oxide, thulium halides, and thulium salts. Due to its reactivity, thulium must be handled with care, especially when exposed to air, moisture, or reactive chemicals. The diverse reactions of thulium contribute to its use in specialized industries like electronics, optics, and medicine. As interest in rare earth elements continues to grow, thulium’s chemical behavior will remain an important subject of study for materials science and advanced engineering.