We continue to review some of the most important materials in heat treatment and metallurgy.
Erbium (chemical symbol: Er)
Erbium (Fig. 1) is a bright, soft, silvery-white rare-earth metal that is malleable and considered to be moderately toxic. It tarnishes slowly in air and will react with water and dissolve in acids. In nature, it is always found in combination with other elements in minerals such as gadolinite and euxenite. Erbium salts have a rose-colored appearance due to the pink fluorescence of the trivalent erbium (III) ions, which makes it particularly useful in some laser applications. Erbium was one of the three elements found in “yttria” that were separated from the mineral gadolinite (Fig. 2), along with yttria and terbia.
Erbium was first discovered by the Swedish chemist Carl Gustaf Mosander in 1843, who had previously discovered the element lanthanum four years prior. While studying the yttria (yttrium oxide) within the mineral gadolinite, he used ammonium hydroxide to precipitate fractions of different elements within what he thought was a single metal oxide. He named these two new substances erbia (Er2O3) and terbia (Tb2O3) and later the elements erbium and terbium. He named both elements after the Ytterby mine in Sweden, the source of the location of gadolinite from which both elements were discovered. Similarly, the names of yttrium and ytterbium are also named from the same mine. Pure erbium was not produced until almost 100 years later in 1934.
Applications for erbium vary greatly across multiple industries. In the metallurgical industry it can be added as an alloying element to vanadium, which lowers its hardness but will improve workability. In the optics industry it can be used in photographic filters in order to absorb infrared light. In the medical industry, a yttrium-aluminum garnet (YAG) medical laser (Fig. 3) can be used for procedures involving skin resurfacing for tattoo removal as well as removing acne scars and blemishes such as moles or warts. Within the nuclear industry, erbium is used in neutron-absorbing control rods for nuclear reactors.
Here are a few important facts about erbium.[2,5]
- Atomic number: 68
- Atomic weight: 167.259
- Melting point: 1802 K (1529°C or 2784°F)
- Boiling point: 3141 K (2868°C or 5194°F)
- Density: 9.07 grams per cubic centimeter
- Phase at room temperature: Solid
- Element classification: Metal
- Period number: 6
- Group number: none
- Group name: Lanthanide
- Electron configuration: [Xe] 4f126s2